Click on the link to download (or contact us for) a pdf of the publications listed below.
Data reduction Geochronology Isotope analysis Radiometric age Secondary ion mass spectrometry SHRIMP SIMS Visual Basic
2014 |
D.R. Nelson, H.N. Bhattacharya, E.R. Thern, W. Altermann Geochemical and ion-microprobe constraints on the Archaean evolution of Singhbhum Craton, eastern India. (Journal Article) Precambrian Research, 255 , pp. 412–432, 2014. (Abstract | Links | BibTeX | Tags: Geochronology, Radiometric age) @article{nelson_geochemical_2014, title = {Geochemical and ion-microprobe constraints on the Archaean evolution of Singhbhum Craton, eastern India.}, author = {D.R. Nelson and H.N. Bhattacharya and E.R. Thern and W. Altermann}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/191.-Nelson-et-al-2014.pdf}, year = {2014}, date = {2014-01-01}, journal = {Precambrian Research}, volume = {255}, pages = {412--432}, abstract = {Geochemical and SHRIMP U-Pb zircon analyses were obtained for nine samples of the Singhbhum Craton to investigate major regional granite intrusion, volcanism, sedimentary deposition, metamorphism and deformation episodes. Detrital zircons within a recrystallized sandstone enclave within tonalitic gneiss provided a maximum time for deposition of 3375. ±. 3. Ma (all uncertainties are at 95% confidence unless otherwise specified) for the host sandstone. Igneous crystallization dates between 3380 and 3299. Ma were obtained for tonalite gneiss and foliated trondhjemite samples from widely dispersed sites, whereas unfoliated granitic samples provided igneous crystallization dates <3.3. Ga, thus constraining the time of regional deformation and amphibolite grade metamorphism to the interval c. 3325-3300. Ma. Volcanic, clastic sedimentary and banded iron-formation rocks assigned to the Iron Ore Group (IOG) are preserved around the margins of the Singhbhum Granite Complex. An igneous crystallization date of 3285. ±. 7. Ma, obtained for a biotite granodiorite that is overlain by conglomerate of the IOG, provides a maximum deposition age for components within the western (Jamda-Koira) IOG basin. A dacite tuff from the Malayagiri IOG basin south of Palalahara yielded an igneous crystallization date of 2806. ±. 6. Ma, confirming that the IOG as currently defined, includes unrelated sedimentary rocks that were deposited within different basins over an 800 Myr interval. Evolution of the Singhbhum Craton may be summarized as follows: (1) between 3530 and 3300. Ma, tonalites were emplaced, with volcanic, clastic and carbonate rocks and banded iron-formation (cycle 1) deposited onto tonalitic basement until 3375. Ma; (2) between 3325 and 3300. Ma, burial, deformation and uplift transformed the central part of the Singhbhum basement to tonalite gneisses, with cycle 1 sedimentary rocks incorporated into the gneisses as enclaves but preserved within synforms around the basement margins; post-3.3. Ga regional metamorphism granodiorite intrusions were emplaced until c. 3285. Ma; (3) BIF and clastic sedimentary rocks (cycle 2) were deposited around the margins of the craton onto the older (cycle 1) sedimentary rocks and adjacent gneissic basement until c. 3.1. Ga; (4) a further episode of granite intrusion at 3090. Ma was followed by uplift and erosion of the central part of the craton prior to 2806. Ma; (5) volcano-sedimentary and banded iron-formation rocks were deposited during a third sedimentary cycle at c. 2.8. Ga.}, keywords = {Geochronology, Radiometric age}, pubstate = {published}, tppubtype = {article} } Geochemical and SHRIMP U-Pb zircon analyses were obtained for nine samples of the Singhbhum Craton to investigate major regional granite intrusion, volcanism, sedimentary deposition, metamorphism and deformation episodes. Detrital zircons within a recrystallized sandstone enclave within tonalitic gneiss provided a maximum time for deposition of 3375. ±. 3. Ma (all uncertainties are at 95% confidence unless otherwise specified) for the host sandstone. Igneous crystallization dates between 3380 and 3299. Ma were obtained for tonalite gneiss and foliated trondhjemite samples from widely dispersed sites, whereas unfoliated granitic samples provided igneous crystallization dates <3.3. Ga, thus constraining the time of regional deformation and amphibolite grade metamorphism to the interval c. 3325-3300. Ma. Volcanic, clastic sedimentary and banded iron-formation rocks assigned to the Iron Ore Group (IOG) are preserved around the margins of the Singhbhum Granite Complex. An igneous crystallization date of 3285. ±. 7. Ma, obtained for a biotite granodiorite that is overlain by conglomerate of the IOG, provides a maximum deposition age for components within the western (Jamda-Koira) IOG basin. A dacite tuff from the Malayagiri IOG basin south of Palalahara yielded an igneous crystallization date of 2806. ±. 6. Ma, confirming that the IOG as currently defined, includes unrelated sedimentary rocks that were deposited within different basins over an 800 Myr interval. Evolution of the Singhbhum Craton may be summarized as follows: (1) between 3530 and 3300. Ma, tonalites were emplaced, with volcanic, clastic and carbonate rocks and banded iron-formation (cycle 1) deposited onto tonalitic basement until 3375. Ma; (2) between 3325 and 3300. Ma, burial, deformation and uplift transformed the central part of the Singhbhum basement to tonalite gneisses, with cycle 1 sedimentary rocks incorporated into the gneisses as enclaves but preserved within synforms around the basement margins; post-3.3. Ga regional metamorphism granodiorite intrusions were emplaced until c. 3285. Ma; (3) BIF and clastic sedimentary rocks (cycle 2) were deposited around the margins of the craton onto the older (cycle 1) sedimentary rocks and adjacent gneissic basement until c. 3.1. Ga; (4) a further episode of granite intrusion at 3090. Ma was followed by uplift and erosion of the central part of the craton prior to 2806. Ma; (5) volcano-sedimentary and banded iron-formation rocks were deposited during a third sedimentary cycle at c. 2.8. Ga. |
H.N. Bhattacharya, D.R. Nelson, E.R. Thern, W. Altermann Geological Magazine, 2014. (Abstract | Links | BibTeX | Tags: ) @article{bhattacharya_petrogenesis_2014, title = {Petrogenesis and geochronology of the Arkasani Granophyre and felsic Dalma volcanic rocks: implications for the evolution of the Proterozoic North Singhbhum Mobile Belt, east India.}, author = {H.N. Bhattacharya and D.R. Nelson and E.R. Thern and W. Altermann}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/190.-Bhattacharya-et-el-2014.pdf}, year = {2014}, date = {2014-01-01}, journal = {Geological Magazine}, abstract = {The North Singhbhum Mobile Belt (NSMB) is a 200 km long, curved Proterozoic fold-thrust belt that skirts the northern margin of the Archean Singhbhum Craton of NE India. The Singhbhum Shear Zone (SSZ) developed between the Dhanjori and Chaibasa formations near the southern margin of the NSMB and represents an important Cu-U-P metallotect. A SHRIMP U-Pb zircon date of 1861±6 Ma, obtained for the syn- to post-kinematic Arkasani Granophyre that has intruded the SSZ, provides a minimum age for the prolonged tectonic activity and mineralization along the SSZ and for the time of closure of the Chaibasa and Dhanjori sub-basins. The Dalma Volcanic Belt, a submarine rift-related bimodal mafic-felsic volcanic suite, forms the spine of the NSMB. A SHRIMP U-Pb zircon igneous crystallization date of 1631±6 Ma was obtained for an unfoliated felsic volcanic rock from the base of the Dalma volcanic sequence. These new findings suggest that the different sub-basins in the NSMB evolved diachronously under contrasting tectonic environments and were juxtaposed during a later orogenic movement.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The North Singhbhum Mobile Belt (NSMB) is a 200 km long, curved Proterozoic fold-thrust belt that skirts the northern margin of the Archean Singhbhum Craton of NE India. The Singhbhum Shear Zone (SSZ) developed between the Dhanjori and Chaibasa formations near the southern margin of the NSMB and represents an important Cu-U-P metallotect. A SHRIMP U-Pb zircon date of 1861±6 Ma, obtained for the syn- to post-kinematic Arkasani Granophyre that has intruded the SSZ, provides a minimum age for the prolonged tectonic activity and mineralization along the SSZ and for the time of closure of the Chaibasa and Dhanjori sub-basins. The Dalma Volcanic Belt, a submarine rift-related bimodal mafic-felsic volcanic suite, forms the spine of the NSMB. A SHRIMP U-Pb zircon igneous crystallization date of 1631±6 Ma was obtained for an unfoliated felsic volcanic rock from the base of the Dalma volcanic sequence. These new findings suggest that the different sub-basins in the NSMB evolved diachronously under contrasting tectonic environments and were juxtaposed during a later orogenic movement. |
S. Misra, D.R. Nelson, R.B.M. Mapeo Supracrustal-granite cyclic growth of Precambrian cratonic nucleus: examples from Singhbhum-Orissa craton (SOC), India, Kaapvaal craton (KC), South Africa, and Eastern Pilbara craton (EPC), Australia. (Journal Article) 25th Colloquium of African Geology (14-16, August 2014) and 3rd Young Earth Scientists Congress (11-13, August 2014), Mwalimu Julius Nyerere International Convention Centre, Dar es Salaam, Tanzania., 2014. (BibTeX | Tags: ) @article{misra_supracrustal-granite_2014, title = {Supracrustal-granite cyclic growth of Precambrian cratonic nucleus: examples from Singhbhum-Orissa craton (SOC), India, Kaapvaal craton (KC), South Africa, and Eastern Pilbara craton (EPC), Australia.}, author = {S. Misra and D.R. Nelson and R.B.M. Mapeo}, year = {2014}, date = {2014-01-01}, journal = {25th Colloquium of African Geology (14-16, August 2014) and 3rd Young Earth Scientists Congress (11-13, August 2014), Mwalimu Julius Nyerere International Convention Centre, Dar es Salaam, Tanzania.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2012 |
E.R. Thern, D.R. Nelson Provenance of ca. 4372-3000 Ma detrital zircons within Early Archean siliciclastic metasedimentary rocks from the Illaara and Maynard Hills Greenstone Belts, Western Australia (Unpublished) 2012. (BibTeX | Tags: ) @unpublished{Thern2012a, title = {Provenance of ca. 4372-3000 Ma detrital zircons within Early Archean siliciclastic metasedimentary rocks from the Illaara and Maynard Hills Greenstone Belts, Western Australia}, author = {E.R. Thern and D.R. Nelson}, year = {2012}, date = {2012-01-01}, journal = {Manuscript Submitted for Publication}, keywords = {}, pubstate = {published}, tppubtype = {unpublished} } |
E.R. Thern, D.R. Nelson Detrital zircon age structure within ca. 3 Ga metasedimentary rocks, Yilgarn Craton: elucidation of Hadean source terranes by principal component analysis (Journal Article) Precambrian Research, 214-215 , pp. 28-43, 2012. (Abstract | Links | BibTeX | Tags: ) @article{Thern2012, title = {Detrital zircon age structure within ca. 3 Ga metasedimentary rocks, Yilgarn Craton: elucidation of Hadean source terranes by principal component analysis}, author = {E.R. Thern and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/178.-Thern-and-Nelson-2012.pdf}, year = {2012}, date = {2012-01-01}, journal = {Precambrian Research}, volume = {214-215}, pages = {28-43}, abstract = {A multivariate approach using a similarity matrix derived from >5500 U-Pb zircon analyses was used to investigate the complex and overlapping detrital zircon age structure within ca. 3Ga metasedimentary rocks from the Yilgarn Craton, Western Australia. Detrital zircon analyses were grouped by their 207Pb/ 206Pb dates using a robust Chi-square grouping method which produced 74 Yilgarn-wide age groups from a pool of >3500 analyses and that were correlated between different metasedimentary rocks. Principal component analysis (PCA) was then used on a calculated similarity matrix of >65 samples which contained these age groups. PCA indicates that the main age populations of the detrital zircons in the ca. 3Ga metasedimentary rocks were derived in varying portions from the Narryer and Yarlarweelor Gneiss Complexes. Differences between the age structure of >3.9Ga zircon populations within the Mt. Alfred metasedimentary rocks with those from Mt. Narryer, Jack Hills and Maynard Hills localities is best explained by their derivation from two Hadean terranes which were joined by ca. 3.7Ga.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A multivariate approach using a similarity matrix derived from >5500 U-Pb zircon analyses was used to investigate the complex and overlapping detrital zircon age structure within ca. 3Ga metasedimentary rocks from the Yilgarn Craton, Western Australia. Detrital zircon analyses were grouped by their 207Pb/ 206Pb dates using a robust Chi-square grouping method which produced 74 Yilgarn-wide age groups from a pool of >3500 analyses and that were correlated between different metasedimentary rocks. Principal component analysis (PCA) was then used on a calculated similarity matrix of >65 samples which contained these age groups. PCA indicates that the main age populations of the detrital zircons in the ca. 3Ga metasedimentary rocks were derived in varying portions from the Narryer and Yarlarweelor Gneiss Complexes. Differences between the age structure of >3.9Ga zircon populations within the Mt. Alfred metasedimentary rocks with those from Mt. Narryer, Jack Hills and Maynard Hills localities is best explained by their derivation from two Hadean terranes which were joined by ca. 3.7Ga. |
P.G. Eriksson, O. Catuneanu, D.R. Nelson, M.J. Rigby, P.C. Bandopadhyay, W. Altermann Events in the Precambrian history of the Earth: Challenges in discriminating their global signifcance. (Journal Article) Marine and Petroleum Geology, 33 , pp. 8–25, 2012. (Abstract | Links | BibTeX | Tags: ) @article{eriksson_events_2012, title = {Events in the Precambrian history of the Earth: Challenges in discriminating their global signifcance.}, author = {P.G. Eriksson and O. Catuneanu and D.R. Nelson and M.J. Rigby and P.C. Bandopadhyay and W. Altermann}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/183.-Eriksson-et-al-2012.pdf}, year = {2012}, date = {2012-01-01}, journal = {Marine and Petroleum Geology}, volume = {33}, pages = {8--25}, abstract = {This paper discusses geological events with an approximately global preservational scale which can aid inter-cratonic correlations and contribute to postulates of supercontinents for a set of chosen Precambrian cratons. The chronological scale of such events is highly variable, and most event types detailed (supercontinent-, mantle plume-, orogenic-, chemostratigraphic-, glacial events and major unconformities) have durations concomitant with the large-scale interaction of mantle thermal and plate tectonic processes that were largely responsible for their genesis, i.e. 10s to 100s of millions of years. Geologically instantaneous events of global compass (e.g., impact or major eruptive events) provide important chronological markers for interpreting the longer term events. The same interplay of tectono-thermal geodynamic processes that drives the evolution of the Earth and the operation of its supercontinent cycles is also, ultimately, responsible for and of comparable duration to first- and second-order sequence stratigraphic cyclicity. This paper thus serves to introduce these concepts and discuss the problems in their application to specific Precambrian cratons, in relation to the aim of this special issue, of providing a set of accommodation curves for many of these ancient crustal terranes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper discusses geological events with an approximately global preservational scale which can aid inter-cratonic correlations and contribute to postulates of supercontinents for a set of chosen Precambrian cratons. The chronological scale of such events is highly variable, and most event types detailed (supercontinent-, mantle plume-, orogenic-, chemostratigraphic-, glacial events and major unconformities) have durations concomitant with the large-scale interaction of mantle thermal and plate tectonic processes that were largely responsible for their genesis, i.e. 10s to 100s of millions of years. Geologically instantaneous events of global compass (e.g., impact or major eruptive events) provide important chronological markers for interpreting the longer term events. The same interplay of tectono-thermal geodynamic processes that drives the evolution of the Earth and the operation of its supercontinent cycles is also, ultimately, responsible for and of comparable duration to first- and second-order sequence stratigraphic cyclicity. This paper thus serves to introduce these concepts and discuss the problems in their application to specific Precambrian cratons, in relation to the aim of this special issue, of providing a set of accommodation curves for many of these ancient crustal terranes. |
A. Moller, R. Bousquet, J. Oalmann, S. Schmitz, M. Wilke, D.R. Nelson, S. Schefer In-situ monazite geochronology of UHT granulites from the Gruf Complex, Central Alps. (Journal Article) International Geological Congress (IGC), Brisbane, August 2012., 2012. @article{moller_-situ_2012, title = {In-situ monazite geochronology of UHT granulites from the Gruf Complex, Central Alps.}, author = {A. Moller and R. Bousquet and J. Oalmann and S. Schmitz and M. Wilke and D.R. Nelson and S. Schefer}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/186.-MonaziteGruf_IGC2012.doc}, year = {2012}, date = {2012-01-01}, journal = {International Geological Congress (IGC), Brisbane, August 2012.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Y. Sabri, S. Ippolito, S.M. Al Kobaisi, M. Griffin, D.R. Nelson, S.K. Bhargava Investigation of Hg Sorption and Diffusion Behavior on Ultra thin Films of Gold Using QCM response analysis and SIMS Depth Profiling. (Journal Article) Journal of Materials Chemistry, 22 , pp. 20929–20935, 2012. (Abstract | Links | BibTeX | Tags: ) @article{sabri_investigation_2012, title = {Investigation of Hg Sorption and Diffusion Behavior on Ultra thin Films of Gold Using QCM response analysis and SIMS Depth Profiling.}, author = {Y. Sabri and S. Ippolito and S.M. Al Kobaisi and M. Griffin and D.R. Nelson and S.K. Bhargava}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/184.-Sabri-et-al-2012.pdf}, year = {2012}, date = {2012-01-01}, journal = {Journal of Materials Chemistry}, volume = {22}, pages = {20929--20935}, abstract = {Using the quartz crystal microbalance (QCM) technique, we demonstrate that the contribution of Hg adsorption and absorption on the sensor response profile can be distinguished by studying the dynamic response curve of QCM based Hg vapor sensors that employ an ultra-thin film of Au in the range of 10 to 40 nm thickness as the sensitive layer. The response magnitudes of the QCMs were extrapolated to zero thickness (ETZT) in an attempt to determine the contribution of adsorbed Hg on the sensor response magnitude and response profile. In general, the ratio of adsorbed to absorbed Hg on Au films is found to decrease with increased Hg vapor concentration. Furthermore, the same ratio was observed to decrease with increasing Au film thickness. The 10 nm and 40 nm Au films for example were found to contain adsorbed Hg content of 43.8% and 16.4%, respectively, with the balance attributed to absorption/amalgamation, when exposed to Hg vapor concentration of 10.55 mg m-3 for a period of 14 hours and an operating temperature of 28 °C. In addition, the QCMs were characterized using secondary ion mass spectroscopy depth profiling in order to study the diffusion behaviour of Hg in the Au surfaces. It is deduced that in order to reduce Hg accumulation in Au thin films, a non-continuous type film (similar to the 10 nm ultra-thin Au sensitive layer morphology) would be more functional as a Hg sensitive layer where quick absorption and desorption processes are required.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using the quartz crystal microbalance (QCM) technique, we demonstrate that the contribution of Hg adsorption and absorption on the sensor response profile can be distinguished by studying the dynamic response curve of QCM based Hg vapor sensors that employ an ultra-thin film of Au in the range of 10 to 40 nm thickness as the sensitive layer. The response magnitudes of the QCMs were extrapolated to zero thickness (ETZT) in an attempt to determine the contribution of adsorbed Hg on the sensor response magnitude and response profile. In general, the ratio of adsorbed to absorbed Hg on Au films is found to decrease with increased Hg vapor concentration. Furthermore, the same ratio was observed to decrease with increasing Au film thickness. The 10 nm and 40 nm Au films for example were found to contain adsorbed Hg content of 43.8% and 16.4%, respectively, with the balance attributed to absorption/amalgamation, when exposed to Hg vapor concentration of 10.55 mg m-3 for a period of 14 hours and an operating temperature of 28 °C. In addition, the QCMs were characterized using secondary ion mass spectroscopy depth profiling in order to study the diffusion behaviour of Hg in the Au surfaces. It is deduced that in order to reduce Hg accumulation in Au thin films, a non-continuous type film (similar to the 10 nm ultra-thin Au sensitive layer morphology) would be more functional as a Hg sensitive layer where quick absorption and desorption processes are required. |
A.J. Bumby, P.G. Eriksson, O. Catuneanu, D.R. Nelson, M.J. Rigby Meso-Archaean and Palaeo-Proterozoic sedimentary sequence stratigraphy of the Kaapvaal Craton. (Journal Article) Marine and Petroleum Geology, 33 , pp. 92–116, 2012. (Abstract | Links | BibTeX | Tags: ) @article{bumby_meso-archaean_2012, title = {Meso-Archaean and Palaeo-Proterozoic sedimentary sequence stratigraphy of the Kaapvaal Craton.}, author = {A.J. Bumby and P.G. Eriksson and O. Catuneanu and D.R. Nelson and M.J. Rigby}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/182.-Bumby-et-al-2012.pdf}, year = {2012}, date = {2012-01-01}, journal = {Marine and Petroleum Geology}, volume = {33}, pages = {92--116}, abstract = {The Kaapvaal Craton hosts a number of Precambrian sedimentary successions which were deposited between 3105 Ma (Dominion Group) and 1700 Ma (Waterberg Group) Although younger Precambrian sedimentary sequences outcrop within southern Africa, they are restricted either to the margins of the Kaapvaal Craton, or are underlain by orogenic belts off the edge of the craton. The basins considered in this work are those which host the Witwatersrand and Pongola, Ventersdorp, Transvaal and Waterberg strata. Many of these basins can be considered to have formed as a response to reactivation along lineaments, which had initially formed by accretion processes during the amalgamation of the craton during the Mid-Archaean. Faulting along these lineaments controlled sedimentation either directly by controlling the basin margins, or indirectly by controlling the sediment source areas. Other basins are likely to be more controlled by thermal affects associated with mantle plumes. Accommodation in all these basins may have been generated primarily by flexural tectonics, in the case of the Witwatersrand, or by a combination of extensional and thermal subsidence in the case of the Ventersdorp, Transvaal and Waterberg. Wheeler diagrams are constructed to demonstrate stratigraphic relationships within these basins at the first- and second-order levels of cyclicity, and can be used to demonstrate the development of accommodation space on the craton through the Precambrian.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Kaapvaal Craton hosts a number of Precambrian sedimentary successions which were deposited between 3105 Ma (Dominion Group) and 1700 Ma (Waterberg Group) Although younger Precambrian sedimentary sequences outcrop within southern Africa, they are restricted either to the margins of the Kaapvaal Craton, or are underlain by orogenic belts off the edge of the craton. The basins considered in this work are those which host the Witwatersrand and Pongola, Ventersdorp, Transvaal and Waterberg strata. Many of these basins can be considered to have formed as a response to reactivation along lineaments, which had initially formed by accretion processes during the amalgamation of the craton during the Mid-Archaean. Faulting along these lineaments controlled sedimentation either directly by controlling the basin margins, or indirectly by controlling the sediment source areas. Other basins are likely to be more controlled by thermal affects associated with mantle plumes. Accommodation in all these basins may have been generated primarily by flexural tectonics, in the case of the Witwatersrand, or by a combination of extensional and thermal subsidence in the case of the Ventersdorp, Transvaal and Waterberg. Wheeler diagrams are constructed to demonstrate stratigraphic relationships within these basins at the first- and second-order levels of cyclicity, and can be used to demonstrate the development of accommodation space on the craton through the Precambrian. |
A.A. Rahman Othman, B.F. Usher, A. Loykaew, D.R. Nelson Oxygen uptake during the MBE growth of AlxGa(1-x)As epitaxial layers. (Journal Article) 10th IEEE International Conference on Semiconductor Electronics 2012 (ICSE2012), Grand Millenium Hotel, Kuala Lumpur, Malaysia, 19?21 September 2012, pp. 694-698., 2012. @article{rahman_othman_oxygen_2012, title = {Oxygen uptake during the MBE growth of AlxGa(1-x)As epitaxial layers.}, author = {A.A. Rahman Othman and B.F. Usher and A. Loykaew and D.R. Nelson}, year = {2012}, date = {2012-01-01}, journal = {10th IEEE International Conference on Semiconductor Electronics 2012 (ICSE2012), Grand Millenium Hotel, Kuala Lumpur, Malaysia, 19?21 September 2012, pp. 694-698.}, abstract = {This paper presents the results of a study of oxygen incorporation in AlxGa1-xAs epitaxial layers during MBE growth. Controlled, low levels of high purity oxygen have been introduced during growth and the structural properties of the layers measured by high resolution x-ray diffraction (HRXRD), while Secondary Ion Mass Spectrometry (SIMS) has been used to measure the oxygen content in the layers. The observations are interpreted by comparing these lattice parameter measurements with AlxGa 1-xAs layers grown without admitting oxygen to the growth chamber. In the presence of oxygen, the AlxGa1-xAs lattice parameter exhibits contraction for Al fractions x up to 0.65 while layers with x fractions greater than 0.65 show an expansion in the AlxGa1-xAs lattice parameter. The x- fraction oxygen incorporation dependence, as well as the lattice parameter behavior, are accounted for by a model which discriminates between the propensities for O2 to incorporate at As sites by (i) bonding to pairs of Ga atoms in the layer below, (ii) to pairs of Al atoms in the layer below or (iii) a combination of one Ga and one Al atom in the layer below.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper presents the results of a study of oxygen incorporation in AlxGa1-xAs epitaxial layers during MBE growth. Controlled, low levels of high purity oxygen have been introduced during growth and the structural properties of the layers measured by high resolution x-ray diffraction (HRXRD), while Secondary Ion Mass Spectrometry (SIMS) has been used to measure the oxygen content in the layers. The observations are interpreted by comparing these lattice parameter measurements with AlxGa 1-xAs layers grown without admitting oxygen to the growth chamber. In the presence of oxygen, the AlxGa1-xAs lattice parameter exhibits contraction for Al fractions x up to 0.65 while layers with x fractions greater than 0.65 show an expansion in the AlxGa1-xAs lattice parameter. The x- fraction oxygen incorporation dependence, as well as the lattice parameter behavior, are accounted for by a model which discriminates between the propensities for O2 to incorporate at As sites by (i) bonding to pairs of Ga atoms in the layer below, (ii) to pairs of Al atoms in the layer below or (iii) a combination of one Ga and one Al atom in the layer below. |
E.R. Thern, D.R. Nelson Goldschmidt Conference Abstracts 2012., 2012. @article{thern_provenance_2012, title = {Provenance of Hadean to mid-Archaean detrital zircons from siliciclastic metasedimentary rocks of the Illaara and Maynard Hills greenstone belts, Western Australia. 22nd Goldschmidt Conference, Montreal, Canada, June 24-29, 2012.}, author = {E.R. Thern and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/187.-Thern-and-Nelson-Goldschmidt2012-Abstract-2012.pdf}, year = {2012}, date = {2012-01-01}, journal = {Goldschmidt Conference Abstracts 2012.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
L.R. Sheppard, M. Bello Lamo, J. Holik, K.J. Mayfield, D.R. Nelson Solute Diffusion of Platinum in Rutile Titanium Dioxide (Journal Article) Journal of the American Ceramic Society, 96(2) , pp. 407–411, 2012. @article{sheppard_solute_2012, title = {Solute Diffusion of Platinum in Rutile Titanium Dioxide}, author = {L.R. Sheppard and M. Bello Lamo and J. Holik and K.J. Mayfield and D.R. Nelson}, year = {2012}, date = {2012-01-01}, journal = {Journal of the American Ceramic Society}, volume = {96(2)}, pages = {407--411}, abstract = {195Pt solute diffusion coefficients in undoped single-crystal rutile TiO2 have been determined parallel to the c-axis over the temperature range of 1073–1523 K and oxygen partial pressure of 101 kPa. This has yielded the following temperature dependence: D195Pt = 1.3 ± 3.2 x 10-13m2s-1exp(-122.0 ± 13.6kJmol-1 / RT). On the basis of this result, it has been concluded that 195Pt diffuses via an interstitial mechanism involving rapid transport parallel to the c-axis through open interstitial diffusion channels. While other divalent cations have also displayed diffusion via the same mechanism, and report diffusion rates that greatly exceed that for cation self-diffusion, the overall rate of 195Pt diffusion is slow. This has been attributed to the size of Pt2+ (0.80 Å) which is comparative to the dimension of interstitial channels (0.77 Å) through which transport is believed to be taking place.}, keywords = {}, pubstate = {published}, tppubtype = {article} } 195Pt solute diffusion coefficients in undoped single-crystal rutile TiO2 have been determined parallel to the c-axis over the temperature range of 1073–1523 K and oxygen partial pressure of 101 kPa. This has yielded the following temperature dependence: D195Pt = 1.3 ± 3.2 x 10-13m2s-1exp(-122.0 ± 13.6kJmol-1 / RT). On the basis of this result, it has been concluded that 195Pt diffuses via an interstitial mechanism involving rapid transport parallel to the c-axis through open interstitial diffusion channels. While other divalent cations have also displayed diffusion via the same mechanism, and report diffusion rates that greatly exceed that for cation self-diffusion, the overall rate of 195Pt diffusion is slow. This has been attributed to the size of Pt2+ (0.80 Å) which is comparative to the dimension of interstitial channels (0.77 Å) through which transport is believed to be taking place. |
A.A. Rahman Othman, B.F. Usher, D.R. Nelson The impact of oxygen incorporation during MBE growth of AlGaAs. (Journal Article) Proceedings of the IEEE 3rd International Conference on Photonics 2012 (ICP), pp. 1–5, 2012. @article{rahman_othman_impact_2012, title = {The impact of oxygen incorporation during MBE growth of AlGaAs.}, author = {A.A. Rahman Othman and B.F. Usher and D.R. Nelson}, year = {2012}, date = {2012-01-01}, journal = {Proceedings of the IEEE 3rd International Conference on Photonics 2012 (ICP)}, pages = {1--5}, abstract = {This paper presents the results of a study of the effects of oxygen and nitrogen incorporation in AlxGa1-xAs epitaxial layers during MBE growth. Low level controlled air leaks were introduced during growth and the structural properties of the layers measured by HRXRD, while SIMS was used to measure the oxygen and nitrogen content in the layers. The Al xGa1-xAs lattice parameter exhibits contraction for Al fractions x up to 0.6 while layers with x fractions greater than 0.6 show an expansion in the AlxGa1-xAs lattice parameter. The observations are interpreted by comparing these lattice parameter measurements with AlxGa1-xAs layers grown without admitting air to the growth chamber. The x-fraction incorporation dependence, as well as the lattice parameter behavior, is accounted for by a model which discriminates between the propensities for O2 to incorporate at As sites by bonding to pairs of Ga atoms in the layer beneath, to one Al and one Ga in the layer beneath or to two Al atoms in the layer beneath. There is also evidence that the O2 and N2 molecules compete for these bonding sites. }, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper presents the results of a study of the effects of oxygen and nitrogen incorporation in AlxGa1-xAs epitaxial layers during MBE growth. Low level controlled air leaks were introduced during growth and the structural properties of the layers measured by HRXRD, while SIMS was used to measure the oxygen and nitrogen content in the layers. The Al xGa1-xAs lattice parameter exhibits contraction for Al fractions x up to 0.6 while layers with x fractions greater than 0.6 show an expansion in the AlxGa1-xAs lattice parameter. The observations are interpreted by comparing these lattice parameter measurements with AlxGa1-xAs layers grown without admitting air to the growth chamber. The x-fraction incorporation dependence, as well as the lattice parameter behavior, is accounted for by a model which discriminates between the propensities for O2 to incorporate at As sites by bonding to pairs of Ga atoms in the layer beneath, to one Al and one Ga in the layer beneath or to two Al atoms in the layer beneath. There is also evidence that the O2 and N2 molecules compete for these bonding sites. |
2011 |
E.R. Thern, F. Jourdan, N.J. Evans, B.J. McDonald, M. Danisik, R.A. Frew, D.R. Nelson Goldschmidt Conference Abstracts 2011., 2011. @article{thern_post-depositional_2011, title = {Post-depositional thermal history of the 4364-3060 Ma zircon-bearing metasandstones of the Illaara and Maynard Hills granite greenstone belts, Western Australia. Goldschmidt Conference, Prague, Czech Republic, August 14-19, 2011.}, author = {E.R. Thern and F. Jourdan and N.J. Evans and B.J. McDonald and M. Danisik and R.A. Frew and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/179.-Goldschmidt2011Abstract-ERT.pdf}, year = {2011}, date = {2011-01-01}, journal = {Goldschmidt Conference Abstracts 2011.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
E.R. Thern, D.R. Nelson Principal component analysis applied to 3.0-4.35 Ga detrital zircon populations within ca. 3.0 Ga metasediments of the Yilgarn Craton. Goldschmidt Conference, Prague, Czech Republic, August 14-19, 2011. (Journal Article) Goldschmidt Conference Abstracts 2011., 2011. (BibTeX | Tags: ) @article{thern_principal_2011, title = {Principal component analysis applied to 3.0-4.35 Ga detrital zircon populations within ca. 3.0 Ga metasediments of the Yilgarn Craton. Goldschmidt Conference, Prague, Czech Republic, August 14-19, 2011.}, author = {E.R. Thern and D.R. Nelson}, year = {2011}, date = {2011-01-01}, journal = {Goldschmidt Conference Abstracts 2011.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
R.T. Pidgeon, M.T.D. Wingate, S. Bodorkos, D.R. Nelson American Journal of Science, 310 , pp. 1115–1135, 2011. (Abstract | Links | BibTeX | Tags: ) @article{pidgeon_age_2011, title = {The age distribution of detrital zircons in quartzites from the Toodyay-Lake Grace Domain, Western Australia: implications for the early evolution of the Yilgarn Craton.}, author = {R.T. Pidgeon and M.T.D. Wingate and S. Bodorkos and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/177.-Pidgeon-et-al-2010.pdf}, year = {2011}, date = {2011-01-01}, journal = {American Journal of Science}, volume = {310}, pages = {1115--1135}, abstract = {Evidence for the early history of the Archean Yilgarn Craton has been largely obliterated by the craton-wide emplacement of granitic rocks at ca. 2650 Ma. However, detrital zircons from rare, ca. 3.1 Ga quartz-rich metasediments preserved in the Yilgarn Craton provide an opportunity to investigate the age structure and composition of the pre-existing basement and therefore provide a valuable record of the early history of crustal components that combined to form the Yilgarn Craton. In this report we present the results of an ion microprobe (SHRIMP) U-Pb geochronological study of detrital zircons from six samples of quartzites from the Toodyay-Lake Grace Domain (TLGD) in the South West Terrane of the Yilgarn Craton. Consistent features in the detrital zircon age spectra in all samples demonstrate a basic uniformity in the composition of the source rocks. The results suggest a provenance dominated by ca. 3350 to 3200 Ma granitic rocks with an age peak at ca. 3265 Ma. No granites of this age have so far been identified in the south-western part of the Yilgarn Craton, although ca. 3280 Ma granites occur in the Narryer Terrane in the northwestern corner of the craton. A second consistent zircon age component suggests an earlier episode of granite emplacement at ca. 3500 to 3400 Ma. A minor component of material contributed zircons as old as 3850 Ma to the pre-2650 Ma basement of the proto- Yilgarn Craton. Our zircon age results suggest that the provenance of the TLGD was different from that of the ca. 3.1 Ga quartzites and metaconglomerates from Mt Narryer and the Jack Hills in the Narryer Terrane and from the Maynard Hills greenstone belt in the Southern Cross Domain. Although the zircon age spectra are not consistent with an origin from presently exposed gneisses from the Narryer Terrane, the presence of granite and pegmatite in the Narryer Terrane close in age to the main zircon age peak in the TLGD sediments suggests a possible connection. Some detrital zircons in the TLGD have been altered hydrothermally or overgrown by zircon rims during the ca. 2650 Ma sillimanite-grade metamorphism that affected the southern part of the TLGD.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Evidence for the early history of the Archean Yilgarn Craton has been largely obliterated by the craton-wide emplacement of granitic rocks at ca. 2650 Ma. However, detrital zircons from rare, ca. 3.1 Ga quartz-rich metasediments preserved in the Yilgarn Craton provide an opportunity to investigate the age structure and composition of the pre-existing basement and therefore provide a valuable record of the early history of crustal components that combined to form the Yilgarn Craton. In this report we present the results of an ion microprobe (SHRIMP) U-Pb geochronological study of detrital zircons from six samples of quartzites from the Toodyay-Lake Grace Domain (TLGD) in the South West Terrane of the Yilgarn Craton. Consistent features in the detrital zircon age spectra in all samples demonstrate a basic uniformity in the composition of the source rocks. The results suggest a provenance dominated by ca. 3350 to 3200 Ma granitic rocks with an age peak at ca. 3265 Ma. No granites of this age have so far been identified in the south-western part of the Yilgarn Craton, although ca. 3280 Ma granites occur in the Narryer Terrane in the northwestern corner of the craton. A second consistent zircon age component suggests an earlier episode of granite emplacement at ca. 3500 to 3400 Ma. A minor component of material contributed zircons as old as 3850 Ma to the pre-2650 Ma basement of the proto- Yilgarn Craton. Our zircon age results suggest that the provenance of the TLGD was different from that of the ca. 3.1 Ga quartzites and metaconglomerates from Mt Narryer and the Jack Hills in the Narryer Terrane and from the Maynard Hills greenstone belt in the Southern Cross Domain. Although the zircon age spectra are not consistent with an origin from presently exposed gneisses from the Narryer Terrane, the presence of granite and pegmatite in the Narryer Terrane close in age to the main zircon age peak in the TLGD sediments suggests a possible connection. Some detrital zircons in the TLGD have been altered hydrothermally or overgrown by zircon rims during the ca. 2650 Ma sillimanite-grade metamorphism that affected the southern part of the TLGD. |
D.R. Nelson Zircon 206Pb-238U geochronology by low mass-resolution ion microprobe. (Journal Article) 17th AINSE Conference on Nuclear and Complementary Techniques of Analysis & 10th Vacuum Society of Australia Congress, Australian National University, 5–7 December 2011., 2011. @article{nelson_zircon_2011, title = {Zircon 206Pb-238U geochronology by low mass-resolution ion microprobe.}, author = {D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/181.-Nelson-AINSE-Conf-abstract-2011.pdf}, year = {2011}, date = {2011-01-01}, journal = {17th AINSE Conference on Nuclear and Complementary Techniques of Analysis & 10th Vacuum Society of Australia Congress, Australian National University, 5–7 December 2011.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2010 |
D.R. Nelson, G. Kay Pilbara iron ore venture may hit second tier. (Journal Article) The Australian Mining Review (www.miningoilgas.com.au), Finance Resource Intelligence, February 2010, p17., 2010. @article{nelson_pilbara_2010, title = {Pilbara iron ore venture may hit second tier.}, author = {D.R. Nelson and G. Kay}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/175.-Finance-Resources-Intelligence-Feb-2010.pdf}, year = {2010}, date = {2010-01-01}, journal = {The Australian Mining Review (www.miningoilgas.com.au), Finance Resource Intelligence, February 2010, p17.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Y. Nebel-Jacobsen, C. Monker, O. Nebel, A. Gerdes, K. Mezger, D.R. Nelson Reworking of Earth's first crust: constraints from Hf isotopes in Archean zircons from Mt. Narryer, Australia. (Journal Article) Precambrian Research, 182 , pp. 175–186, 2010. (Abstract | Links | BibTeX | Tags: ) @article{nebel-jacobsen_reworking_2010, title = {Reworking of Earth's first crust: constraints from Hf isotopes in Archean zircons from Mt. Narryer, Australia.}, author = {Y. Nebel-Jacobsen and C. Monker and O. Nebel and A. Gerdes and K. Mezger and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/176.-Nebel-jacobsen-et-al-PRECAM_3268.pdf}, year = {2010}, date = {2010-01-01}, journal = {Precambrian Research}, volume = {182}, pages = {175--186}, abstract = {Discoveries of >4. Ga old zircon grains in the northwest Yilgarn of Western Australia led to the conclusion that evolved crust formed on the Earth within the first few 100. Ma after accretion. Little is known, however, about the fate of the first crust that shaped early Earth's surface. Here we report combined solution and laser-ablation Lu-Hf-U-Pb isotope analyses of early Archean and Hadean detrital zircon grains from different rocks of the Narryer Gneiss Complex (NGC), Yilgarn Craton, Western Australia. The zircons show two distinct groups with separate evolutionary trends in their Hf isotopes. The majority of the zircon grains point to separation from a depleted mantle reservoir at ~3.8-3.9. Ga. The second Hf isotope trend implies reworking of older Hadean zircon grains. The major trend starting at 3.8-3.9. Ga defined by the Hf isotopes corresponds to a Lu/Hf that is characteristic for felsic crust and consequently, the primary sources for these zircons presumably had a chemical composition characteristic of continental crust. Reworked Hadean crust appears to have evolved with a similar low Lu/Hf, such that the early crust was probably evolved with respect to Lu-Hf distributions. The co-variation of Hf isotopes vs. age in zircon grains from Mt. Narryer and Jack Hills zircon grains implies a similar crustal source for both sediments in a single, major crustal domain. Age spectra and associated Hf isotopes in the zircon grains strongly argue for ongoing magmatic reworking over hundreds of millions of years of the felsic crustal domain in which the zircon grains formed. Late-stage metamorphic zircon grains from the Meeberrie Gneiss unit yield a mean U-Pb age of 3294.5 ± 3.2. Ma with initial Hf isotopes that correspond to the evolutionary trend defined by older NGC zircon grains and overlap with other detrital zircon grains, proving their genetic relationship. This 'Meeberrie event' is interpret here as the last reworking event in the precursor domain before final deposition. The continuous magmatic activity in one crustal domain during the Archean is recorded by the U-Pb ages and Hf isotope systematics of zircon grains and implies reworking of existing crust. We suspect that the most likely driving force for such reworking of crustal material is ongoing crustal collision and subduction. A comparison of Hf isotope signatures of zircon grains from other Archean terranes shows that similar trends are recognised within all sampled Archean domains. This implies either a global trend in crustal growth and reworking, or a genetic connection of Archean terranes in close paleo-proximity to each other. Notably, the Archean Acasta gneiss (Canada) shows a similar reworking patterns to the Yilgarn Craton of Hadean samples implying either a common Hadean source or amalgamation at the Hadean-Archean transition.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Discoveries of >4. Ga old zircon grains in the northwest Yilgarn of Western Australia led to the conclusion that evolved crust formed on the Earth within the first few 100. Ma after accretion. Little is known, however, about the fate of the first crust that shaped early Earth's surface. Here we report combined solution and laser-ablation Lu-Hf-U-Pb isotope analyses of early Archean and Hadean detrital zircon grains from different rocks of the Narryer Gneiss Complex (NGC), Yilgarn Craton, Western Australia. The zircons show two distinct groups with separate evolutionary trends in their Hf isotopes. The majority of the zircon grains point to separation from a depleted mantle reservoir at ~3.8-3.9. Ga. The second Hf isotope trend implies reworking of older Hadean zircon grains. The major trend starting at 3.8-3.9. Ga defined by the Hf isotopes corresponds to a Lu/Hf that is characteristic for felsic crust and consequently, the primary sources for these zircons presumably had a chemical composition characteristic of continental crust. Reworked Hadean crust appears to have evolved with a similar low Lu/Hf, such that the early crust was probably evolved with respect to Lu-Hf distributions. The co-variation of Hf isotopes vs. age in zircon grains from Mt. Narryer and Jack Hills zircon grains implies a similar crustal source for both sediments in a single, major crustal domain. Age spectra and associated Hf isotopes in the zircon grains strongly argue for ongoing magmatic reworking over hundreds of millions of years of the felsic crustal domain in which the zircon grains formed. Late-stage metamorphic zircon grains from the Meeberrie Gneiss unit yield a mean U-Pb age of 3294.5 ± 3.2. Ma with initial Hf isotopes that correspond to the evolutionary trend defined by older NGC zircon grains and overlap with other detrital zircon grains, proving their genetic relationship. This 'Meeberrie event' is interpret here as the last reworking event in the precursor domain before final deposition. The continuous magmatic activity in one crustal domain during the Archean is recorded by the U-Pb ages and Hf isotope systematics of zircon grains and implies reworking of existing crust. We suspect that the most likely driving force for such reworking of crustal material is ongoing crustal collision and subduction. A comparison of Hf isotope signatures of zircon grains from other Archean terranes shows that similar trends are recognised within all sampled Archean domains. This implies either a global trend in crustal growth and reworking, or a genetic connection of Archean terranes in close paleo-proximity to each other. Notably, the Archean Acasta gneiss (Canada) shows a similar reworking patterns to the Yilgarn Craton of Hadean samples implying either a common Hadean source or amalgamation at the Hadean-Archean transition. |
2009 |
P.G. Eriksson, S. Banerjee, D.R. Nelson, M.J. Rigby, O. Catuneanu, S. Sarkar, R.J. Roberts, D. Ruban, M.N. Mtimkulu, P.V. Sunder Raju A Kaapvaal craton debate: nucleus of an early small supercontinent or affected by an enhanced accretion event? (Invited contribution). (Journal Article) Gondwana Research, 15 , pp. 354–372, 2009. (Abstract | Links | BibTeX | Tags: ) @article{eriksson_kaapvaal_2009, title = {A Kaapvaal craton debate: nucleus of an early small supercontinent or affected by an enhanced accretion event? (Invited contribution).}, author = {P.G. Eriksson and S. Banerjee and D.R. Nelson and M.J. Rigby and O. Catuneanu and S. Sarkar and R.J. Roberts and D. Ruban and M.N. Mtimkulu and P.V. Sunder Raju}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/173.-Eriksson-et-al-2009.pdf}, year = {2009}, date = {2009-01-01}, journal = {Gondwana Research}, volume = {15}, pages = {354--372}, abstract = {Incorporation of the Kaapvaal craton within a speculative Neoarchaean-Palaeoproterozoic supercontinent has long been debated, and this idea provides a potential solution to solving the apparently enigmatic provenance of the huge quantities of gold within the famous Witwatersrand auriferous deposits of Kaapvaal. Within a framework of a postulated Neoarchaean "Kenorland" ("northern"; present-day reference) supercontinent, we examine possible "southern" cratons that may have been contiguous with Kaapvaal: Pilbara, Zimbabwe, Dharwar, São Francisco, Amazon, Congo. Brief reviews of their basic geology and inferred evolution in syn-Witwatersrand basin times (c. 3.1-2.8 Ga) show no obvious support for any such supercontinental amalgamations. An alternative idea to explain a measure of gross similarity amongst several Neoarchaean cratons is through global events, such as a c. 3125-3000 Ma cratonic-scale erosive event interpreted for both Pilbara and Kaapvaal, and a much more widespread magmatic event at c. 2760-2680 Ma. We postulate that a global superplume event at c. 3.0 Ga included a plume beneath the Kaapvaal cratonic nucleus, thus halting any subduction around that terrane due to the thermal anomaly. Such a speculative global magmatic event is assumed to have enhanced production of juvenile oceanic crust at mid-ocean ridges, including those "offshore" of the thermally elevated Kaapvaal nucleus. Intra-oceanic obduction complexes may have built up fairly rapidly under such conditions, globally, and once the plume event had abated, "normal" plate tectonics would have resulted in composite (greenstone-tonalite, possibly also including granite) terranes accreting with nuclei such as Kaapvaal. This enhanced plume-related cratonic growth can be seen as a rapid accretion event. Formation of the envisaged ophiolite complexes possibly encompassed deformation-related first-order concentration of gold, and once accretion occurred around Kaapvaal's nucleus, from north and west (present-day frame of reference), a second-order (deformation-related) gold concentration may have resulted. The third order of gold concentration would logically have occurred once placer systems reworked detritus derived from the orogens along the N and W margins of Kaapvaal. Such conditions and placer gold deposits are known from many Neoarchaean cratons. The initial source of gold was presumably from the much hotter Mesoarchaean mantle and may have been related to major changes in Earth's tectonic regime at c. 3.0 Ga. The unique nature of Kaapvaal is probably its early stabilization, enabling formation of a complex flexural foreland basin system, in which vast quantities of placer sediments and heavy minerals could be deposited, and preserved from younger denudation through a unique post-Witwatersrand history.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Incorporation of the Kaapvaal craton within a speculative Neoarchaean-Palaeoproterozoic supercontinent has long been debated, and this idea provides a potential solution to solving the apparently enigmatic provenance of the huge quantities of gold within the famous Witwatersrand auriferous deposits of Kaapvaal. Within a framework of a postulated Neoarchaean "Kenorland" ("northern"; present-day reference) supercontinent, we examine possible "southern" cratons that may have been contiguous with Kaapvaal: Pilbara, Zimbabwe, Dharwar, São Francisco, Amazon, Congo. Brief reviews of their basic geology and inferred evolution in syn-Witwatersrand basin times (c. 3.1-2.8 Ga) show no obvious support for any such supercontinental amalgamations. An alternative idea to explain a measure of gross similarity amongst several Neoarchaean cratons is through global events, such as a c. 3125-3000 Ma cratonic-scale erosive event interpreted for both Pilbara and Kaapvaal, and a much more widespread magmatic event at c. 2760-2680 Ma. We postulate that a global superplume event at c. 3.0 Ga included a plume beneath the Kaapvaal cratonic nucleus, thus halting any subduction around that terrane due to the thermal anomaly. Such a speculative global magmatic event is assumed to have enhanced production of juvenile oceanic crust at mid-ocean ridges, including those "offshore" of the thermally elevated Kaapvaal nucleus. Intra-oceanic obduction complexes may have built up fairly rapidly under such conditions, globally, and once the plume event had abated, "normal" plate tectonics would have resulted in composite (greenstone-tonalite, possibly also including granite) terranes accreting with nuclei such as Kaapvaal. This enhanced plume-related cratonic growth can be seen as a rapid accretion event. Formation of the envisaged ophiolite complexes possibly encompassed deformation-related first-order concentration of gold, and once accretion occurred around Kaapvaal's nucleus, from north and west (present-day frame of reference), a second-order (deformation-related) gold concentration may have resulted. The third order of gold concentration would logically have occurred once placer systems reworked detritus derived from the orogens along the N and W margins of Kaapvaal. Such conditions and placer gold deposits are known from many Neoarchaean cratons. The initial source of gold was presumably from the much hotter Mesoarchaean mantle and may have been related to major changes in Earth's tectonic regime at c. 3.0 Ga. The unique nature of Kaapvaal is probably its early stabilization, enabling formation of a complex flexural foreland basin system, in which vast quantities of placer sediments and heavy minerals could be deposited, and preserved from younger denudation through a unique post-Witwatersrand history. |
M. Norman, V.C. Bennett, G. Caprarelli, B. Carter, J. Clarke, D.R. Nelson, D. Stegman, S.R. Taylor, S. Vladimirov, M. Walter Planetary Science in Australia. (Book) 2009. @book{norman_planetary_2009, title = {Planetary Science in Australia.}, author = {M. Norman and V.C. Bennett and G. Caprarelli and B. Carter and J. Clarke and D.R. Nelson and D. Stegman and S.R. Taylor and S. Vladimirov and M. Walter}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/166.-Norman-et-al-2008.pdf}, year = {2009}, date = {2009-01-01}, keywords = {}, pubstate = {published}, tppubtype = {book} } |
2008 |
D.R. Nelson Geochronology of the Archaean of Australia. Special Issue on Geochronology in Australia. (Invited contribution). (Journal Article) Australian Journal of Earth Sciences, 55 , pp. 1–15, 2008. (Abstract | Links | BibTeX | Tags: ) @article{nelson_geochronology_2008, title = {Geochronology of the Archaean of Australia. Special Issue on Geochronology in Australia. (Invited contribution).}, author = {D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/164.-Nelson-2008.pdf}, year = {2008}, date = {2008-01-01}, journal = {Australian Journal of Earth Sciences}, volume = {55}, pages = {1--15}, abstract = {The Archean eon is a chronometrically defined subdivision of the Precambrian that extends from 3800 to 2500 Ma. In the Australian continent, Archean rocks (i.e. those with sedimentary deposition or igneous crystallisation ages confidently interpreted to be older than 2500 Ma) occur in the Pilbara and Yilgarn Cratons of Western Australia, the Mulgathing and Sleaford Complexes in the Gawler Craton of South Australia and as minor inliers in the Pine Creek Orogen of the Northern Territory. Metamorphosed lithological components with igneous or sedimentary precursors inferred to be of Archean age also occur in the Browns Range Dome and Billabong Complexes of the Tanami Inlier, Northern Territory, and possibly also in the Broken Hill Inlier. This contribution outlines aspects of the historical development of geochronological methods applied to the Archean of Australia, the respective strengths and weaknesses of these methods and how our understanding of the continent's Archean geology and tectonics was related to this development. The geological formation of the Yilgarn and Pilbara Cratons is investigated using a new statistical approach based on the distribution of SHRIMP U-Pb zircon and monazite dates obtained from rock samples that may have complex mineral age populations. Spatial and temporal characteristics of the magmatic episodes identified in the Yilgarn and Pilbara granite- greenstone terranes are atypical of rift/ collision processes attributable to tectonic-plate interactions, but are consistent with their interpretation as a response to major mantle convection events. The strengths of this geochronology-based approach are demonstrated by its application to the Narryer Gneiss Complex of the northwestern part of the Yilgarn Craton. It is shown that this approach offers unique insights into geological events that may be under-represented at the outcrop scale due to later crustal re-working.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Archean eon is a chronometrically defined subdivision of the Precambrian that extends from 3800 to 2500 Ma. In the Australian continent, Archean rocks (i.e. those with sedimentary deposition or igneous crystallisation ages confidently interpreted to be older than 2500 Ma) occur in the Pilbara and Yilgarn Cratons of Western Australia, the Mulgathing and Sleaford Complexes in the Gawler Craton of South Australia and as minor inliers in the Pine Creek Orogen of the Northern Territory. Metamorphosed lithological components with igneous or sedimentary precursors inferred to be of Archean age also occur in the Browns Range Dome and Billabong Complexes of the Tanami Inlier, Northern Territory, and possibly also in the Broken Hill Inlier. This contribution outlines aspects of the historical development of geochronological methods applied to the Archean of Australia, the respective strengths and weaknesses of these methods and how our understanding of the continent's Archean geology and tectonics was related to this development. The geological formation of the Yilgarn and Pilbara Cratons is investigated using a new statistical approach based on the distribution of SHRIMP U-Pb zircon and monazite dates obtained from rock samples that may have complex mineral age populations. Spatial and temporal characteristics of the magmatic episodes identified in the Yilgarn and Pilbara granite- greenstone terranes are atypical of rift/ collision processes attributable to tectonic-plate interactions, but are consistent with their interpretation as a response to major mantle convection events. The strengths of this geochronology-based approach are demonstrated by its application to the Narryer Gneiss Complex of the northwestern part of the Yilgarn Craton. It is shown that this approach offers unique insights into geological events that may be under-represented at the outcrop scale due to later crustal re-working. |
M. Lupulescue, J. Chiarenzelli, B. Cousens, E.R. Thern, D.R. Nelson GSA Abstracts with Programs, 40, No. 2. , 2008. @article{lupulescue_mineralogy_2008, title = {Mineralogy and geochemistry of a mafic-ultramafic intrusion from Pyrites, Adirondack Lowlands, New York. Geological Society of America, Northeastern Section - 43rd Annual Meeting, 27?29 March 2008, Hyatt Regency Buffalo, New York. (http://gsa.confex.com/gsa/2008NE/finalprogram/abstract_134822.htm)}, author = {M. Lupulescue and J. Chiarenzelli and B. Cousens and E.R. Thern and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/170.-Lupulescu-et-al-2008.pdf}, year = {2008}, date = {2008-01-01}, journal = {GSA Abstracts with Programs}, volume = {40, No. 2.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
C.V. Ly, A. Biondo, D.R. Nelson QEMSCAN chemical imaging of textures and structures within carbonaceous chondrites and iron meteorites. (Journal Article) Australian Earth Sciences Convention, Perth, 2008., 2008. @article{ly_qemscan_2008, title = {QEMSCAN chemical imaging of textures and structures within carbonaceous chondrites and iron meteorites.}, author = {C.V. Ly and A. Biondo and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/171.-Ly-et-al-2008.pdf}, year = {2008}, date = {2008-01-01}, journal = {Australian Earth Sciences Convention, Perth, 2008.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
A. Moller, S. Schmitz, M. Wilke, D.R. Nelson, W. Malzer, B. Kannigfsser, S. Schefer, R. Bousquet Sapphirine granulites of the Gruf Complex (Central Alps, N-Italy): in-situ monazite dating by SHRIMP and confocal synchrotron-XRF. (Journal Article) Goldschmidt Conference Abstracts 2008., 2008. (BibTeX | Tags: ) @article{mller_sapphirine_2008, title = {Sapphirine granulites of the Gruf Complex (Central Alps, N-Italy): in-situ monazite dating by SHRIMP and confocal synchrotron-XRF.}, author = {A. Moller and S. Schmitz and M. Wilke and D.R. Nelson and W. Malzer and B. Kannigfsser and S. Schefer and R. Bousquet}, year = {2008}, date = {2008-01-01}, journal = {Goldschmidt Conference Abstracts 2008.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
A.F. Trendall, J.R. de Laeter, D.R. Nelson SHRIMP and the Cloud Hypothesis. (Journal Article) 4th SHRIMP Workshop, 29 June – 4 July 2008, St Petersburg, Russia., 2008. @article{trendall_shrimp_2008, title = {SHRIMP and the Cloud Hypothesis.}, author = {A.F. Trendall and J.R. de Laeter and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/173.-Trendall-et-al-2008.pdf}, year = {2008}, date = {2008-01-01}, journal = {4th SHRIMP Workshop, 29 June – 4 July 2008, St Petersburg, Russia.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2007 |
C.V. Ly, D.R. Nelson, K. Mason Application of QEMSCAN for the interpretation of textures and minerals in extra terrestrial materials. (Journal Article) Automated Mineralogy 07, Brisbane, Australia, 1–2 September 2007., 2007. @article{ly_application_2007, title = {Application of QEMSCAN for the interpretation of textures and minerals in extra terrestrial materials.}, author = {C.V. Ly and D.R. Nelson and K. Mason}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/158.-Chi-Ly-et-al.-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {Automated Mineralogy 07, Brisbane, Australia, 1–2 September 2007.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
D.R. Nelson Fractal geochronology- dating of the past, planning for the future. (Invited contribution). (Journal Article) Gondwana Research, 12 , pp. 576–578, 2007. (Abstract | Links | BibTeX | Tags: ) @article{nelson_fractal_2007, title = {Fractal geochronology- dating of the past, planning for the future. (Invited contribution).}, author = {D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/162.-Nelson-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {Gondwana Research}, volume = {12}, pages = {576--578}, abstract = {Dates for regional-scale geological events are typically determined by analysis of radioactive decay processes within micron-scale closed systems, demonstrating that geochronology information is "fractal" - that is, largely independent of the scale of magnification. This has important implications for the way geochronology data should be stored, retrieved and processed in order to maximize extraction of useful geological information.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dates for regional-scale geological events are typically determined by analysis of radioactive decay processes within micron-scale closed systems, demonstrating that geochronology information is "fractal" - that is, largely independent of the scale of magnification. This has important implications for the way geochronology data should be stored, retrieved and processed in order to maximize extraction of useful geological information. |
E.R. Thern, D.R. Nelson Geochronology and microstructural studies of zircons from Mt. Alfred and the Maynard Hills, Western Australia. (Journal Article) International Conference on Precambrian Sedimentation and Tectonics and Second GPSS Meeting, Department of Earth Sciences, Indian Institute of Technology Powai, Mumbai-400076, 10-12 December, 2007., 2007. @article{thern_geochronology_2007, title = {Geochronology and microstructural studies of zircons from Mt. Alfred and the Maynard Hills, Western Australia.}, author = {E.R. Thern and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/169.-Thern-and-Nelson-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {International Conference on Precambrian Sedimentation and Tectonics and Second GPSS Meeting, Department of Earth Sciences, Indian Institute of Technology Powai, Mumbai-400076, 10-12 December, 2007.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
D.R. Nelson, A. Moller Goldschmidt Conference Abstracts, 2007 , pp. A710–A710, 2007. @article{nelson_improved_2007, title = {Improved U-(Th)-Pb dating of monazite by ion microprobe: correcting for an isobaric interference of PrP04 on 204Pb. Goldschmidt Conference, 19?24 August 2007, Cologne, Germany.}, author = {D.R. Nelson and A. Moller}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/159.-Nelson-and-Moller-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {Goldschmidt Conference Abstracts}, volume = {2007}, pages = {A710--A710}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
D.R. Nelson, H.N. Bhattacharya, S. Misra, N. Desgupta, W. Altermann New SHRIMP U-Pb zircon dates from the Singhbhum Craton, Jharkhand-Orissa region, India. (Journal Article) International Conference on Precambrian Sedimentation and Tectonics and Second GPSS Meeting, Department of Earth Sciences, Indian Institute of Technology Powai, Mumbai-400076, 10?12 December 2007., 2007. @article{nelson_new_2007, title = {New SHRIMP U-Pb zircon dates from the Singhbhum Craton, Jharkhand-Orissa region, India.}, author = {D.R. Nelson and H.N. Bhattacharya and S. Misra and N. Desgupta and W. Altermann}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/168.-Nelson-et-al-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {International Conference on Precambrian Sedimentation and Tectonics and Second GPSS Meeting, Department of Earth Sciences, Indian Institute of Technology Powai, Mumbai-400076, 10?12 December 2007.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
L. Bagas, D.R. Nelson Provenance for Neoproterozoic rocks in the northwest Paterson Orogen, Western Australia. (Journal Article) Publication volume, Central Australian Basins Symposium (CABS; see http://conferences.minerals.nt.gov.au/cabsproceedings/), 2007. @article{bagas_provenance_2007, title = {Provenance for Neoproterozoic rocks in the northwest Paterson Orogen, Western Australia.}, author = {L. Bagas and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/157.-Bagas-and-Nelson-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {Publication volume, Central Australian Basins Symposium (CABS; see http://conferences.minerals.nt.gov.au/cabsproceedings/)}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
J. Chiarenzelli, M. Lupulescue, B. Cousens, D.R. Nelson, E.R. Thern Recognition of oceanic crust in the Adirondack Highlands. (Journal Article) Geological Society of America, Denver Meeting, Colorado Convention Center, 2007., 2007. (BibTeX | Tags: ) @article{chiarenzelli_recognition_2007, title = {Recognition of oceanic crust in the Adirondack Highlands.}, author = {J. Chiarenzelli and M. Lupulescue and B. Cousens and D.R. Nelson and E.R. Thern}, year = {2007}, date = {2007-01-01}, journal = {Geological Society of America, Denver Meeting, Colorado Convention Center, 2007.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
D.R. Nelson Short-lived radioactivity in the early Solar System. (Conference) 2007. @conference{nelson_short-lived_2007, title = {Short-lived radioactivity in the early Solar System.}, author = {D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/Nelsons-SINS-talk-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {Stellar Interiors and Nucleosynthesis (SINS) Workshop, 8–19 January 2007, Monash University, Melbourne}, keywords = {}, pubstate = {published}, tppubtype = {conference} } |
L. Bagas, F.P. Bierlein, S. Bodorkos, D.R. Nelson Tectonic setting, evolution and orogenic gold potential of the Late Mesoarchaean Mosquito Creek Basin, North Pilbara Craton, Western Australia. (Journal Article) Precambrian Research, 160 , pp. 227–244, 2007. (Abstract | Links | BibTeX | Tags: ) @article{bagas_tectonic_2007, title = {Tectonic setting, evolution and orogenic gold potential of the Late Mesoarchaean Mosquito Creek Basin, North Pilbara Craton, Western Australia.}, author = {L. Bagas and F.P. Bierlein and S. Bodorkos and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/163.-Bagas-et-al-2008.pdf}, year = {2007}, date = {2007-01-01}, journal = {Precambrian Research}, volume = {160}, pages = {227--244}, abstract = {The geology, evolution, and metallogenic potential of the Mesoarchaean Mosquito Creek Basin remains poorly understood, despite the presence of several orogenic gold deposits. The basin is dominated by medium- to coarse-grained, poorly sorted and chemically immature sandstone and conglomerates, characterised by very high Cr/Th, high Th/Sc, and low Zr/Sc relative to average continental crust. These features are consistent with the presence of significant mafic rocks in the source terrain(s), a limited role for sediment recycling, and deposition in an increasingly distal passive margin setting on the southeastern edge of the Palaeo- to Mesoarchaean East Pilbara Terrane. New U-Pb SHRIMP data on 358 detrital zircons indicate a conservative maximum depositional age of 2972 + 14/-37 Ma (robust median; 96.1% confidence). Zircon provenance spectra from conglomeratic rocks near the base of the unit are consistent with substantial derivation from the East Pilbara Terrane, but finer-grained sandstones higher in the stratigraphy appear to have been sourced elsewhere, as their zircon age spectra are not well matched by any of the exposed Pilbara terranes. The Mosquito Creek Basin was deformed before and during collision with the northern edge of the Mesoarchaean Kurrana Terrane, which resulted in the development of macroscopic north-verging folds, thrust faulting, and widespread sub-greenschist to greenschist facies metamorphism. This collisional event probably took place at ca. 2900 Ma, based on two identical Pb-Pb model ages of 2905 ± 9 Ma from epigenetic galena associated with vein-hosted gold-antimony mineralization. The metallogenic potential of the Mosquito Creek Basin remains largely unevaluated; however, the possibility of a passive margin setting and continental basement points to relatively limited potential for the formation of major orogenic gold deposits.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The geology, evolution, and metallogenic potential of the Mesoarchaean Mosquito Creek Basin remains poorly understood, despite the presence of several orogenic gold deposits. The basin is dominated by medium- to coarse-grained, poorly sorted and chemically immature sandstone and conglomerates, characterised by very high Cr/Th, high Th/Sc, and low Zr/Sc relative to average continental crust. These features are consistent with the presence of significant mafic rocks in the source terrain(s), a limited role for sediment recycling, and deposition in an increasingly distal passive margin setting on the southeastern edge of the Palaeo- to Mesoarchaean East Pilbara Terrane. New U-Pb SHRIMP data on 358 detrital zircons indicate a conservative maximum depositional age of 2972 + 14/-37 Ma (robust median; 96.1% confidence). Zircon provenance spectra from conglomeratic rocks near the base of the unit are consistent with substantial derivation from the East Pilbara Terrane, but finer-grained sandstones higher in the stratigraphy appear to have been sourced elsewhere, as their zircon age spectra are not well matched by any of the exposed Pilbara terranes. The Mosquito Creek Basin was deformed before and during collision with the northern edge of the Mesoarchaean Kurrana Terrane, which resulted in the development of macroscopic north-verging folds, thrust faulting, and widespread sub-greenschist to greenschist facies metamorphism. This collisional event probably took place at ca. 2900 Ma, based on two identical Pb-Pb model ages of 2905 ± 9 Ma from epigenetic galena associated with vein-hosted gold-antimony mineralization. The metallogenic potential of the Mosquito Creek Basin remains largely unevaluated; however, the possibility of a passive margin setting and continental basement points to relatively limited potential for the formation of major orogenic gold deposits. |
H. Zwingmann, D.R. Nelson Timing of illite authigenesis in well Empress 1A, Officer basin, Western Australia. (Journal Article) Publication volume, Central Australian Basins Symposium (CABS; see http://conferences.minerals.nt.gov.au/cabsproceedings/), 2007. @article{zwingmann_timing_2007, title = {Timing of illite authigenesis in well Empress 1A, Officer basin, Western Australia.}, author = {H. Zwingmann and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/156.-Zwingmann-Nelson-2007.pdf}, year = {2007}, date = {2007-01-01}, journal = {Publication volume, Central Australian Basins Symposium (CABS; see http://conferences.minerals.nt.gov.au/cabsproceedings/)}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Y. Nebel-Jacobsen, C. Munker, K. Mezger, O. Nebel, A. Gerdes, D.R. Nelson Tracing Earth's first crust with Hf isotopes in zircons from the Narryer Gneiss Complex, Australia. (Journal Article) Goldschmidt Conference, 19?24 August 2007, Cologne, Germany. Goldschmidt Conference Abstracts 2007 A709., 2007. @article{neble-jacobsen_tracing_2007, title = {Tracing Earth's first crust with Hf isotopes in zircons from the Narryer Gneiss Complex, Australia.}, author = {Y. Nebel-Jacobsen and C. Munker and K. Mezger and O. Nebel and A. Gerdes and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/155.-Nebel-Jacobsen-et-al-2007-A709.pdf}, year = {2007}, date = {2007-01-01}, journal = {Goldschmidt Conference, 19?24 August 2007, Cologne, Germany. Goldschmidt Conference Abstracts 2007 A709.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
L. Chrapowitzky, J. Chiarenzelli, D. Valentino, D.R. Nelson, E.R. Thern, R. Adams Zircon chronology of the Chimney Mountain metasedimentary sequence, Adirondack Highlands. (Journal Article) Geological Society of America, Denver Meeting, Colorado Convention Center, 2007., 2007. (BibTeX | Tags: ) @article{chrapowitzky_zircon_2007, title = {Zircon chronology of the Chimney Mountain metasedimentary sequence, Adirondack Highlands.}, author = {L. Chrapowitzky and J. Chiarenzelli and D. Valentino and D.R. Nelson and E.R. Thern and R. Adams}, year = {2007}, date = {2007-01-01}, journal = {Geological Society of America, Denver Meeting, Colorado Convention Center, 2007.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2006 |
D.R. Nelson CONCH: A Visual Basic program for interactive processing of ion-microprobe analytical data (Journal Article) Computers & Geosciences, 32 (9), pp. 1479–1498, 2006, ISSN: 0098-3004. (Abstract | Links | BibTeX | Tags: Data reduction, Geochronology, Isotope analysis, Radiometric age, Secondary ion mass spectrometry, SHRIMP, SIMS, Visual Basic) @article{Nelson2006, title = {CONCH: A Visual Basic program for interactive processing of ion-microprobe analytical data}, author = {D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/148.-Nelson-2006.pdf}, issn = {0098-3004}, year = {2006}, date = {2006-01-01}, journal = {Computers & Geosciences}, volume = {32}, number = {9}, pages = {1479--1498}, abstract = {A Visual Basic program for flexible, interactive processing of ion-microprobe data acquired for quantitative trace element, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni and U-Ŧh-Pb geochronology applications is described. Đefault but editable run-tables enable software identification of secondary ion species analyzed and for characterization of the standard used. Counts obtained for each species may be displayed in plots against analysis time and edited interactively. Count outliers can be automatically identified via a set of editable count-rejection criteria and displayed for assessment. Standard analyses are distinguished from Unknowns by matching of the analysis label with a string specified in the Set-up dialog, and processed separately. A generalized routine writes background-corrected count rates, ratios and uncertainties, plus weighted means and uncertainties for Standards and Unknowns, to a spreadsheet that may be saved as a text-delimited file. Specialized routines process trace-element concentration, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni, and Ŧh-U disequilibrium analysis types, and U-Ŧh-Pb isotopic data obtained for zircon, titanite, perovskite, monazite, xenotime and baddeleyite. Correction to measured Pb-isotopic, Pb/U and Pb/Ŧh ratios for the presence of common Pb may be made using measured 204Pb counts, or the 207Pb or 208Pb counts following subtraction from these of the radiogenic component. Common-Pb corrections may be made automatically, using a (user-specified) common-Pb isotopic composition appropriate for that on the sample surface, or for that incorporated within the mineral at the time of its crystallization, depending on whether the 204Pb count rate determined for the Unknown is substantially higher than the average 204Pb count rate for all session standards. Pb/U inter-element fractionation corrections are determined using an interactive loge-loge plot of common-Pb corrected 206Pb/238U ratios against any nominated fractionation-sensitive species pair (commonly 238U16O+/238U+) for session standards. Also displayed with this plot are calculated Pb/U and Pb/Ŧh calibration line regression slopes, y-intercepts, calibration uncertainties, standard 204Pb- and 208Pb-corrected 207Pb/206Pb dates and other parameters useful for assessment of the calibration-line data. Calibrated data for Unknowns may be automatically grouped according to calculated date and displayed in color on interactive Wetherill Concordia, Ŧera-Wasserburg Concordia, Linearized Gaussian ("Probability Paper") and Gaussian-summation probability density diagrams.}, keywords = {Data reduction, Geochronology, Isotope analysis, Radiometric age, Secondary ion mass spectrometry, SHRIMP, SIMS, Visual Basic}, pubstate = {published}, tppubtype = {article} } A Visual Basic program for flexible, interactive processing of ion-microprobe data acquired for quantitative trace element, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni and U-Ŧh-Pb geochronology applications is described. Đefault but editable run-tables enable software identification of secondary ion species analyzed and for characterization of the standard used. Counts obtained for each species may be displayed in plots against analysis time and edited interactively. Count outliers can be automatically identified via a set of editable count-rejection criteria and displayed for assessment. Standard analyses are distinguished from Unknowns by matching of the analysis label with a string specified in the Set-up dialog, and processed separately. A generalized routine writes background-corrected count rates, ratios and uncertainties, plus weighted means and uncertainties for Standards and Unknowns, to a spreadsheet that may be saved as a text-delimited file. Specialized routines process trace-element concentration, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni, and Ŧh-U disequilibrium analysis types, and U-Ŧh-Pb isotopic data obtained for zircon, titanite, perovskite, monazite, xenotime and baddeleyite. Correction to measured Pb-isotopic, Pb/U and Pb/Ŧh ratios for the presence of common Pb may be made using measured 204Pb counts, or the 207Pb or 208Pb counts following subtraction from these of the radiogenic component. Common-Pb corrections may be made automatically, using a (user-specified) common-Pb isotopic composition appropriate for that on the sample surface, or for that incorporated within the mineral at the time of its crystallization, depending on whether the 204Pb count rate determined for the Unknown is substantially higher than the average 204Pb count rate for all session standards. Pb/U inter-element fractionation corrections are determined using an interactive loge-loge plot of common-Pb corrected 206Pb/238U ratios against any nominated fractionation-sensitive species pair (commonly 238U16O+/238U+) for session standards. Also displayed with this plot are calculated Pb/U and Pb/Ŧh calibration line regression slopes, y-intercepts, calibration uncertainties, standard 204Pb- and 208Pb-corrected 207Pb/206Pb dates and other parameters useful for assessment of the calibration-line data. Calibrated data for Unknowns may be automatically grouped according to calculated date and displayed in color on interactive Wetherill Concordia, Ŧera-Wasserburg Concordia, Linearized Gaussian ("Probability Paper") and Gaussian-summation probability density diagrams. |
G.R. Burton, L.J. Burn, K.J.R. Rosman, R.D. Loss, J.R. Moody, J-P. Candelone, P. Vallelonga, N. Bukilic, D.R. Nelson Advanced ultraClean Environment (ACE) for Processing Extraterrestrial Materials at Ultra-trace Levels. (Journal Article) 6th Australian Space Science Conference, 19?21 July 2006, Hyatt Hotel, Yarralumla, Canberra, Australia., 2006. (BibTeX | Tags: ) @article{burton_advanced_2006, title = {Advanced ultraClean Environment (ACE) for Processing Extraterrestrial Materials at Ultra-trace Levels.}, author = {G.R. Burton and L.J. Burn and K.J.R. Rosman and R.D. Loss and J.R. Moody and J-P. Candelone and P. Vallelonga and N. Bukilic and D.R. Nelson}, year = {2006}, date = {2006-01-01}, journal = {6th Australian Space Science Conference, 19?21 July 2006, Hyatt Hotel, Yarralumla, Canberra, Australia.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
T. Moxon, D.R. Nelson, M. Zhang Agate recrystallization: evidence from samples found in Archaean and Proterozoic host rocks, Western Australia. (Journal Article) Australian Journal of Earth Sciences, 53 , pp. 235–248, 2006. (Abstract | Links | BibTeX | Tags: ) @article{moxon_agate_2006, title = {Agate recrystallization: evidence from samples found in Archaean and Proterozoic host rocks, Western Australia.}, author = {T. Moxon and D.R. Nelson and M. Zhang}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/146.-Moxon-et-al-2006.pdf}, year = {2006}, date = {2006-01-01}, journal = {Australian Journal of Earth Sciences}, volume = {53}, pages = {235--248}, abstract = {The crystallite size and density of agates from three Western Australian host rocks aged 1.84, 2.72 and 3.48 Ga have been determined. Infrared and Raman spectra from these ancient agates have respectively shown minimal water and zero moganite content. Data comparison of agates from Western Australian and younger hosts showed an advanced crystallisation in the Western Australian samples with, in some instances, the crystallite size comparable to macrocrystalline quartz. Low-grade metamorphism is present in the host rocks and localised heating is one possible cause of the increased crystallite growth. Micrographs of one agate sample from the Warrawoona Group (3.48 Ga) show a breakdown in the fibrous chalcedony; regional variations within the agate were supported by data from infrared and X-ray diffraction. It has been shown that part of the sample had undergone a transformation of the fibrous chalcedony to granular microcrystalline quartz. The Crystallinity Index for microcrystalline quartz, based upon the degree of resolution of the (212) quartz reflection, offers a rapid method to identify abnormal crystallite growth that could serve as a palaeoindicator of host-rock metamorphism.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The crystallite size and density of agates from three Western Australian host rocks aged 1.84, 2.72 and 3.48 Ga have been determined. Infrared and Raman spectra from these ancient agates have respectively shown minimal water and zero moganite content. Data comparison of agates from Western Australian and younger hosts showed an advanced crystallisation in the Western Australian samples with, in some instances, the crystallite size comparable to macrocrystalline quartz. Low-grade metamorphism is present in the host rocks and localised heating is one possible cause of the increased crystallite growth. Micrographs of one agate sample from the Warrawoona Group (3.48 Ga) show a breakdown in the fibrous chalcedony; regional variations within the agate were supported by data from infrared and X-ray diffraction. It has been shown that part of the sample had undergone a transformation of the fibrous chalcedony to granular microcrystalline quartz. The Crystallinity Index for microcrystalline quartz, based upon the degree of resolution of the (212) quartz reflection, offers a rapid method to identify abnormal crystallite growth that could serve as a palaeoindicator of host-rock metamorphism. |
D.R. Nelson A new approach to the investigation of crustal evolution in complex terranes using statistical analysis of geochronology data. (Journal Article) SHRIMP Workshop 2006, 3-7 September 2006, Rottnest Island, Australia., 2006. @article{nelson_new_2006, title = {A new approach to the investigation of crustal evolution in complex terranes using statistical analysis of geochronology data.}, author = {D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/152.-Nelson-2006.pdf}, year = {2006}, date = {2006-01-01}, journal = {SHRIMP Workshop 2006, 3-7 September 2006, Rottnest Island, Australia.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
D.R. Nelson CONCH: a versatile Visual Basic program for the interactive processing of ion-microprobe data. (Journal Article) Computers and Geosciences, 32 , pp. 1479–1498, 2006. (Abstract | Links | BibTeX | Tags: ) @article{nelson_conch:_2006, title = {CONCH: a versatile Visual Basic program for the interactive processing of ion-microprobe data.}, author = {D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/148.-Nelson-2006.pdf}, year = {2006}, date = {2006-01-01}, journal = {Computers and Geosciences}, volume = {32}, pages = {1479--1498}, abstract = {A Visual Basic program for flexible, interactive processing of ion-microprobe data acquired for quantitative trace element, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni and U-Th-Pb geochronology applications is described. Default but editable run-tables enable software identification of secondary ion species analyzed and for characterization of the standard used. Counts obtained for each species may be displayed in plots against analysis time and edited interactively. Count outliers can be automatically identified via a set of editable count-rejection criteria and displayed for assessment. Standard analyses are distinguished from Unknowns by matching of the analysis label with a string specified in the Set-up dialog, and processed separately. A generalized routine writes background-corrected count rates, ratios and uncertainties, plus weighted means and uncertainties for Standards and Unknowns, to a spreadsheet that may be saved as a text-delimited file. Specialized routines process trace-element concentration, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni, and Th-U disequilibrium analysis types, and U-Th-Pb isotopic data obtained for zircon, titanite, perovskite, monazite, xenotime and baddeleyite. Correction to measured Pb-isotopic, Pb/U and Pb/Th ratios for the presence of common Pb may be made using measured 204Pb counts, or the 207Pb or 208Pb counts following subtraction from these of the radiogenic component. Common-Pb corrections may be made automatically, using a (user-specified) common-Pb isotopic composition appropriate for that on the sample surface, or for that incorporated within the mineral at the time of its crystallization, depending on whether the 204Pb count rate determined for the Unknown is substantially higher than the average 204Pb count rate for all session standards. Pb/U inter-element fractionation corrections are determined using an interactive loge-loge plot of common-Pb corrected 206Pb/238U ratios against any nominated fractionation-sensitive species pair (commonly 238U16O+/238U+) for session standards. Also displayed with this plot are calculated Pb/U and Pb/Th calibration line regression slopes, y-intercepts, calibration uncertainties, standard 204Pb- and 208Pb-corrected 207Pb/206Pb dates and other parameters useful for assessment of the calibration-line data. Calibrated data for Unknowns may be automatically grouped according to calculated date and displayed in color on interactive Wetherill Concordia, Tera- Wasserburg Concordia, Linearized Gaussian ("Probability Paper") and Gaussian-summation probability density diagrams.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A Visual Basic program for flexible, interactive processing of ion-microprobe data acquired for quantitative trace element, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni and U-Th-Pb geochronology applications is described. Default but editable run-tables enable software identification of secondary ion species analyzed and for characterization of the standard used. Counts obtained for each species may be displayed in plots against analysis time and edited interactively. Count outliers can be automatically identified via a set of editable count-rejection criteria and displayed for assessment. Standard analyses are distinguished from Unknowns by matching of the analysis label with a string specified in the Set-up dialog, and processed separately. A generalized routine writes background-corrected count rates, ratios and uncertainties, plus weighted means and uncertainties for Standards and Unknowns, to a spreadsheet that may be saved as a text-delimited file. Specialized routines process trace-element concentration, 26Al-26Mg, 53Mn-53Cr, 60Fe-60Ni, and Th-U disequilibrium analysis types, and U-Th-Pb isotopic data obtained for zircon, titanite, perovskite, monazite, xenotime and baddeleyite. Correction to measured Pb-isotopic, Pb/U and Pb/Th ratios for the presence of common Pb may be made using measured 204Pb counts, or the 207Pb or 208Pb counts following subtraction from these of the radiogenic component. Common-Pb corrections may be made automatically, using a (user-specified) common-Pb isotopic composition appropriate for that on the sample surface, or for that incorporated within the mineral at the time of its crystallization, depending on whether the 204Pb count rate determined for the Unknown is substantially higher than the average 204Pb count rate for all session standards. Pb/U inter-element fractionation corrections are determined using an interactive loge-loge plot of common-Pb corrected 206Pb/238U ratios against any nominated fractionation-sensitive species pair (commonly 238U16O+/238U+) for session standards. Also displayed with this plot are calculated Pb/U and Pb/Th calibration line regression slopes, y-intercepts, calibration uncertainties, standard 204Pb- and 208Pb-corrected 207Pb/206Pb dates and other parameters useful for assessment of the calibration-line data. Calibrated data for Unknowns may be automatically grouped according to calculated date and displayed in color on interactive Wetherill Concordia, Tera- Wasserburg Concordia, Linearized Gaussian ("Probability Paper") and Gaussian-summation probability density diagrams. |
M. Norman, M. Walter, B. Carter, S.R. Taylor, D.R. Nelson, V.C. Bennett, G. Caprarelli, J. Clarke, D. Stegman, S. Vladimirov National Committee for Space Science Decadal Plan- draft report of the Planetary Science Working Group. (Book) 2006. (BibTeX | Tags: ) @book{norman_national_2006, title = {National Committee for Space Science Decadal Plan- draft report of the Planetary Science Working Group.}, author = {M. Norman and M. Walter and B. Carter and S.R. Taylor and D.R. Nelson and V.C. Bennett and G. Caprarelli and J. Clarke and D. Stegman and S. Vladimirov}, year = {2006}, date = {2006-01-01}, keywords = {}, pubstate = {published}, tppubtype = {book} } |
U.D. Weber, B.P. Kohn, A.J.W. Gleadow, D.R. Nelson Tectonophysics, 419 (1-4) , pp. 107–109, 2006. @article{weber_reply_2006, title = {Reply to comment by Guedes et al. on: Low temperature Phanerozoic history of the Northern Yilgarn Craton, Western Australia. by Weber et al. [Tectonophysics 400 (2005), 127-151].}, author = {U.D. Weber and B.P. Kohn and A.J.W. Gleadow and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/149.-Weber-et-al-reply-2006.pdf}, year = {2006}, date = {2006-01-01}, journal = {Tectonophysics}, volume = {419 (1-4)}, pages = {107--109}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
D.R. Nelson Short-lived radionuclides: stellar sources and early solar system chronology. (Journal Article) 6th Australian Space Science Conference, 19?21 July 2006, Hyatt Hotel, Yarralumla, Canberra, Australia., 2006. (BibTeX | Tags: ) @article{nelson_short-lived_2006, title = {Short-lived radionuclides: stellar sources and early solar system chronology.}, author = {D.R. Nelson}, year = {2006}, date = {2006-01-01}, journal = {6th Australian Space Science Conference, 19?21 July 2006, Hyatt Hotel, Yarralumla, Canberra, Australia.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
S.T. de Vries, W. Nijman, J.R. Wijbrans, D.R. Nelson Stratigraphic continuity and early deformation of the central part of the Coppin Gap Greenstone Belt, Pilbara, Western Australia. (Journal Article) Precambrian Research, 147 , pp. 1–27, 2006. (Abstract | Links | BibTeX | Tags: ) @article{de_vries_stratigraphic_2006, title = {Stratigraphic continuity and early deformation of the central part of the Coppin Gap Greenstone Belt, Pilbara, Western Australia.}, author = {S.T. de Vries and W. Nijman and J.R. Wijbrans and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/147.-de-Vries-et-al-2006.pdf}, year = {2006}, date = {2006-01-01}, journal = {Precambrian Research}, volume = {147}, pages = {1--27}, abstract = {This article focuses on the discrepancy between the often advocated stratigraphic continuity of greenstone belts in the Pilbara Craton (Australia) on the one hand, and the observations of syndepositional deformation and other tectonic disturbance on the other hand. The Coppin Gap Greenstone Belt of the East Pilbara consists predominantly of mafic, intermediate and felsic rocks, with minor amounts of silicified sedimentary rocks of the early Archaean Warrawoona Group. Several well-defined zones subparallel to the bedding show intense brittle to ductile deformation, testifying to differential movements of the tectono- stratigraphic slices they delimit. These deformation zones were at least partly related to west-block-down normal faults and accommodated upper block to the west transport. However, new U-Pb zircon dates, geochemical analyses and detailed field observations show that the overall stratigraphic succession in the Coppin Gap Greenstone Belt has not been fundamentally disturbed. The normal faults occur in several irregularly superposed arrays of km-spaced faults, part of which were active during deposition. Normal faults also occur throughout the entire belt. Combined, the early deformation structures indicate east-west extension over a minimum period of 20 Ma, from ∼3469 Ma onwards. Likely, the extension took place over an even longer period of time, during much of the time of deposition of the Warrawoona Group, from ∼3490 Ma onwards. Syndepositional extension of the Warrawoona Group was geometrically unrelated to the doming of granitoid batholiths. Surficial (i.e. uppermost crustal) gravitational collapse during or shortly after deposition may have caused the apparent contradictory co-existence of deformation zones and stratigraphic continuity. Although the deformation has not caused major disruptions of the stratigraphic succession, the precision of the U-Pb SHRIMP ages is insufficient to rule out excisions or duplications of stratigraphy on the order of a few million years.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This article focuses on the discrepancy between the often advocated stratigraphic continuity of greenstone belts in the Pilbara Craton (Australia) on the one hand, and the observations of syndepositional deformation and other tectonic disturbance on the other hand. The Coppin Gap Greenstone Belt of the East Pilbara consists predominantly of mafic, intermediate and felsic rocks, with minor amounts of silicified sedimentary rocks of the early Archaean Warrawoona Group. Several well-defined zones subparallel to the bedding show intense brittle to ductile deformation, testifying to differential movements of the tectono- stratigraphic slices they delimit. These deformation zones were at least partly related to west-block-down normal faults and accommodated upper block to the west transport. However, new U-Pb zircon dates, geochemical analyses and detailed field observations show that the overall stratigraphic succession in the Coppin Gap Greenstone Belt has not been fundamentally disturbed. The normal faults occur in several irregularly superposed arrays of km-spaced faults, part of which were active during deposition. Normal faults also occur throughout the entire belt. Combined, the early deformation structures indicate east-west extension over a minimum period of 20 Ma, from ∼3469 Ma onwards. Likely, the extension took place over an even longer period of time, during much of the time of deposition of the Warrawoona Group, from ∼3490 Ma onwards. Syndepositional extension of the Warrawoona Group was geometrically unrelated to the doming of granitoid batholiths. Surficial (i.e. uppermost crustal) gravitational collapse during or shortly after deposition may have caused the apparent contradictory co-existence of deformation zones and stratigraphic continuity. Although the deformation has not caused major disruptions of the stratigraphic succession, the precision of the U-Pb SHRIMP ages is insufficient to rule out excisions or duplications of stratigraphy on the order of a few million years. |
2005 |
P.G. Eriksson, O. Catuneanu, D.R. Nelson, M. Popa Controls on Precambrian sea level change and sediment cyclicity. (Journal Article) Sedimentary Geology, 176 , pp. 43–65, 2005. (Abstract | Links | BibTeX | Tags: ) @article{eriksson_controls_2005, title = {Controls on Precambrian sea level change and sediment cyclicity.}, author = {P.G. Eriksson and O. Catuneanu and D.R. Nelson and M. Popa}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/140.-Eriksson-et-al-2005.pdf}, year = {2005}, date = {2005-01-01}, journal = {Sedimentary Geology}, volume = {176}, pages = {43--65}, abstract = {Although uniformitarianism applies in a general sense to the controls on relative and global sea level change, some influences thereon were more prominent in the Precambrian. Short-term base level change due to waves and tides may have been enhanced due to possibly more uniform circulation systems on wide, low gradient Precambrian shelves. The lack of evidence for global glacial events in the Precambrian record implies that intraplate stresses and cyclic changes to Earth's geoid were more likely explanations for third-order sea level change than glacio-eustasy. Higher heat flow in the earlier Precambrian may have led to more rapid tectonic plate formation, transport and destruction, along with an increased role for hot spots, aseismic ridges and mantle plumes (superplumes), all of which may have influenced cyclic sedimentation within the ocean basins. A weak cyclicity in the occurrence of plume events has an approximate duration comparable to that of first-order (supercontinental cycle) sea level change. Second-order cyclicity in the Precambrian largely reflects the influences of thermal epeirogeny, changes to mid-ocean ridge volume as well as to ridge growth and decay rates, and cratonic marginal downwarping concomitant with either sediment loading or extensional tectonism. Third-order cycles of sea level change in the Precambrian also reflected cyclic loading/unloading within flexural foreland basin settings, and filling/deflation of magma chambers associated with island arc evolution. The relatively limited number of studies of Precambrian sequence stratigraphy allows some preliminary conclusions to be drawn on duration of the first three orders of cyclicity. Archaean greenstone basins appear to have had first- and second-order cycle durations analogous to Phanerozoic equivalents, supporting steady state tectonics throughout Earth history. In direct contrast, however, preserved basin-fills from Neoarchaean-Palaeoproterozoic cratonic terranes have first- and second-order cycles of considerably longer duration than Phanerozoic examples, supporting less evolved tectonism affecting cratonic plates. It is possible that oceanic tectonic realms underwent more rapid and dynamic plate movements and arc generation, whereas early continental cratonic plates offered more stable platforms and may have been subject to slower migration rates. The wide range of controls on Precambrian sea level change, allied to their apparent variability (in rates and periodicity) through Precambrian time supports the conclusion that each order of cyclicity is relative and must be defined within the stratigraphic context of each individual case study. This underlines the importance of establishing a hierarchical order of cyclicity in sequence stratigraphic interpretations of Precambrian basins based on the relative importance of sequences rather than their temporal duration.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Although uniformitarianism applies in a general sense to the controls on relative and global sea level change, some influences thereon were more prominent in the Precambrian. Short-term base level change due to waves and tides may have been enhanced due to possibly more uniform circulation systems on wide, low gradient Precambrian shelves. The lack of evidence for global glacial events in the Precambrian record implies that intraplate stresses and cyclic changes to Earth's geoid were more likely explanations for third-order sea level change than glacio-eustasy. Higher heat flow in the earlier Precambrian may have led to more rapid tectonic plate formation, transport and destruction, along with an increased role for hot spots, aseismic ridges and mantle plumes (superplumes), all of which may have influenced cyclic sedimentation within the ocean basins. A weak cyclicity in the occurrence of plume events has an approximate duration comparable to that of first-order (supercontinental cycle) sea level change. Second-order cyclicity in the Precambrian largely reflects the influences of thermal epeirogeny, changes to mid-ocean ridge volume as well as to ridge growth and decay rates, and cratonic marginal downwarping concomitant with either sediment loading or extensional tectonism. Third-order cycles of sea level change in the Precambrian also reflected cyclic loading/unloading within flexural foreland basin settings, and filling/deflation of magma chambers associated with island arc evolution. The relatively limited number of studies of Precambrian sequence stratigraphy allows some preliminary conclusions to be drawn on duration of the first three orders of cyclicity. Archaean greenstone basins appear to have had first- and second-order cycle durations analogous to Phanerozoic equivalents, supporting steady state tectonics throughout Earth history. In direct contrast, however, preserved basin-fills from Neoarchaean-Palaeoproterozoic cratonic terranes have first- and second-order cycles of considerably longer duration than Phanerozoic examples, supporting less evolved tectonism affecting cratonic plates. It is possible that oceanic tectonic realms underwent more rapid and dynamic plate movements and arc generation, whereas early continental cratonic plates offered more stable platforms and may have been subject to slower migration rates. The wide range of controls on Precambrian sea level change, allied to their apparent variability (in rates and periodicity) through Precambrian time supports the conclusion that each order of cyclicity is relative and must be defined within the stratigraphic context of each individual case study. This underlines the importance of establishing a hierarchical order of cyclicity in sequence stratigraphic interpretations of Precambrian basins based on the relative importance of sequences rather than their temporal duration. |
A. Moller, D.R. Nelson Influence of matrix effects on U-Th-Pb dating of monazite by ion microprobe. (Journal Article) Goldschmidt Conference, Moscow, USA., 2005. @article{mller_influence_2005, title = {Influence of matrix effects on U-Th-Pb dating of monazite by ion microprobe.}, author = {A. Moller and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/143.-Moller-and-Nelson-2005.zip}, year = {2005}, date = {2005-01-01}, journal = {Goldschmidt Conference, Moscow, USA.}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
S. Sheppard, S.A. Occhipinti, D.R. Nelson Intercontinental reworking in the Capricorn Orogen, Western Australia: the 1680-1620 Ma Mangaroon Orogeny. (Journal Article) Australian Journal of Earth Sciences, 52 , pp. 443–460, 2005. (Abstract | Links | BibTeX | Tags: ) @article{sheppard_intercontinental_2005, title = {Intercontinental reworking in the Capricorn Orogen, Western Australia: the 1680-1620 Ma Mangaroon Orogeny.}, author = {S. Sheppard and S.A. Occhipinti and D.R. Nelson}, url = {http://www.geochron.com.au/wp-content/uploads/2016/11/142.-Sheppard-et-al-2005.pdf}, year = {2005}, date = {2005-01-01}, journal = {Australian Journal of Earth Sciences}, volume = {52}, pages = {443--460}, abstract = {Structures and metamorphic mineral assemblages throughout much of the Proterozoic Capricorn Orogen have been attributed to the 1830-1780 Ma Capricorn Orogeny. However, in the northern part of the Gascoyne Complex at the exposed western end of the orogen, precursor sediments to pelitic gneiss and metamorphosed feldspathic sandstone were deposited after 1680 ± 13 Ma. The sediments were first deformed and intruded by voluminous granites during intracontinental reworking (the Mangaroon Orogeny) between 1680 Ma and 1620 Ma. The Mangaroon Orogeny comprises a subhorizontal gneissic layering and peak metamorphic conditions of upper amphibolite facies (D 1m/M 1m) followed by upright, macroscopic southeast-trending folds and an associated subvertical foliation formed at greenschist facies (D 2m/M 2m). Schlieric biotite-muscovite granodiorite dated at 1677 ± 5 Ma represents an anatectic melt that intruded during D 2m. Cross-cutting biotite and biotite-muscovite monzogranites mainly crystallised at ca 1680-1660 Ma, but granite plutons were emplaced across the Gascoyne Complex until 1620 Ma. Our findings invalidate correlation of these metasedimentary rocks with lower grade rocks of the upper Wyloo Group along the northern margin of the orogen, and necessitate a reassessment of tectonic activity in the orogen attributed to the Capricorn Orogeny. © Geological Society of Australia.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Structures and metamorphic mineral assemblages throughout much of the Proterozoic Capricorn Orogen have been attributed to the 1830-1780 Ma Capricorn Orogeny. However, in the northern part of the Gascoyne Complex at the exposed western end of the orogen, precursor sediments to pelitic gneiss and metamorphosed feldspathic sandstone were deposited after 1680 ± 13 Ma. The sediments were first deformed and intruded by voluminous granites during intracontinental reworking (the Mangaroon Orogeny) between 1680 Ma and 1620 Ma. The Mangaroon Orogeny comprises a subhorizontal gneissic layering and peak metamorphic conditions of upper amphibolite facies (D 1m/M 1m) followed by upright, macroscopic southeast-trending folds and an associated subvertical foliation formed at greenschist facies (D 2m/M 2m). Schlieric biotite-muscovite granodiorite dated at 1677 ± 5 Ma represents an anatectic melt that intruded during D 2m. Cross-cutting biotite and biotite-muscovite monzogranites mainly crystallised at ca 1680-1660 Ma, but granite plutons were emplaced across the Gascoyne Complex until 1620 Ma. Our findings invalidate correlation of these metasedimentary rocks with lower grade rocks of the upper Wyloo Group along the northern margin of the orogen, and necessitate a reassessment of tectonic activity in the orogen attributed to the Capricorn Orogeny. © Geological Society of Australia. |