Papers by Michael W Knoper
Ar isotope data from all samples and summary of ages
New <sup>40</sup>Ar/<sup>39</sup>Ar data from dykes intruded into Sverdru... more New <sup>40</sup>Ar/<sup>39</sup>Ar data from dykes intruded into Sverdrupfjella and Ahlmanryggen, Dronning Maud Land, Antarctica, indicate that dyke emplacement commenced at <i>c</i>. 207 Ma and lasted until <i>c</i>. 178 Ma. Whereas the ages ascribed to the Karoo-age magmatism contributing to Gondwana breakup are typically inferred as being <i>c</i>. 182 Ma, the data indicate that ages older than <i>c</i>. 192 Ma in the broader Karoo Province are restricted to western Dronning Maud Land, Antarctica, indicating the locality where breakup was initiated. Limited palaeomagnetic data from <i>c</i>. 178–185 Ma dykes combined with published palaeomagnetic data from similar-aged dykes in Vestfjella and the Ferrar Province, suggest that Antarctica had already drifted/rifted significantly away from southern Africa from <i>c</i>. 207 Ma to <i>c</i>. 180 Ma, earlier than previously thou...
Journal of Petrology, 2021
The Bushmanland Subprovince of the Mesoproterozoic Namaqua-Natal orogenic belt in southern Africa... more The Bushmanland Subprovince of the Mesoproterozoic Namaqua-Natal orogenic belt in southern Africa hosts numerous occurrences of monazite-magnetite-(biotite-apatite-sulfide)-bearing veins and granitoid dykes, including the Steenkampskraal vein system, which is one of the highest-grade REE-Th ore deposits in the world. Here, we provide whole-rock geochemical data along with zircon and monazite U-Pb dates and monazite Sm-Nd isotope analyses of these REE-Th-rich veins and granitoid dykes. The U-Pb geochronology indicates that the monazite-rich veins and granitoid dykes formed between 1050 and 1010 Ma, contemporaneously with late-Namaqua granulite-facies metamorphism. They are also coeval with the Koperberg Suite mafic magmas at 1060–1020 Ma and the late stage of a major event of A-type granitoid magmatism that occurred from 1100 to 1030 Ma (i.e. the Spektakel Suite). Similar to the mafic intrusive rocks from the Koperberg Suite, monazite-rich veins and granitoid dykes, located in the so...
Amphibolites are a major component of an early Proterozoic supracrustal succession in West-Centra... more Amphibolites are a major component of an early Proterozoic supracrustal succession in West-Central Colorado extending from the Black Canyon area on the west to the Tincup area on the east. Preserved primary textures and structures indicate the amphibolites represent subaqueous basalt flows and hypabassyl dikes and sills. Published U-Pb zircon dates from associated felsic volcanics indicate two ages of supracrustal rocks: an older terrane (1770-1760 m.y.) extending from the Gateview area to the Quartz Creek area, and a younger terrane (1740-1730 m.y.) extending from Black Canyon to the Tincup area. Amphibolites from both terranes define two geochemical populations, tholeiites (TH) and calc-alkaline basalts (CAB). TH, which dominate in the older terrane, exhibit depleted light to flat REE patterns and have low HFSE concentrations. They are also slightly LILE enriched relative to MORB. Tectonic geochemical discrimination diagrams indicate an island-arc basin setting for the older amphibolites and either an island-arc or back-arc basin setting for the younger amphibolites. Mg numbers of both groups of amphibolites are generally low (40-55) indicating substantial olivine fractional crystallization. They may both be produced from the same parent magma, derived from a depleted mantle source, by open-system fractional crystallization in replenished and tapped magma chambers. Alternatively,more » they may reflect different mantle sources: TH from a depleted descending plate, and CAB from a metasomatized mantle wedge.« less
Precambrian Research, 2014
ASEG Extended Abstracts, 2001
Analysis of susceptibility and density data from a borehole in the Bushveld igneous complex in So... more Analysis of susceptibility and density data from a borehole in the Bushveld igneous complex in South Africa was performed using statistical tools such as power spectra, wavelet analysis, and windowed histogram plots. This analysis has revealed significant patterns and cycles that correlate both with rock type and subtle layering within and between units. These results can now be used to test models of layering processes.
Proceedings of the 10th International Congress for Applied Mineralogy (ICAM), 2012
Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is d... more Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is difficult, as petrologists are faced with issues of representative sampling, together with laborious and time-consuming microscopic examination. Although automated mineralogy ...
The Canadian Mineralogist, 2011
Mineralogy and Petrology, 2012
Proceedings of the 10th International Congress for Applied Mineralogy (ICAM), 2012
Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is d... more Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is difficult, as petrologists are faced with issues of representative sampling, together with laborious and time-consuming microscopic examination. Although automated mineralogy ...
Amphibolites are a major component of an early Proterozoic supracrustal succession in West-Centra... more Amphibolites are a major component of an early Proterozoic supracrustal succession in West-Central Colorado extending from the Black Canyon area on the west to the Tincup area on the east. Preserved primary textures and structures indicate the amphibolites represent subaqueous basalt flows and hypabassyl dikes and sills. Published U-Pb zircon dates from associated felsic volcanics indicate two ages of supracrustal rocks: an older terrane (1770-1760 m.y.) extending from the Gateview area to the Quartz Creek area, and a younger terrane (1740-1730 m.y.) extending from Black Canyon to the Tincup area. Amphibolites from both terranes define two geochemical populations, tholeiites (TH) and calc-alkaline basalts (CAB). TH, which dominate in the older terrane, exhibit depleted light to flat REE patterns and have low HFSE concentrations. They are also slightly LILE enriched relative to MORB. Tectonic geochemical discrimination diagrams indicate an island-arc basin setting for the older amphibolites and either an island-arc or back-arc basin setting for the younger amphibolites. Mg numbers of both groups of amphibolites are generally low (40-55) indicating substantial olivine fractional crystallization. They may both be produced from the same parent magma, derived from a depleted mantle source, by open-system fractional crystallization in replenished and tapped magma chambers. Alternatively,more » they may reflect different mantle sources: TH from a depleted descending plate, and CAB from a metasomatized mantle wedge.« less
Proceedings of the 10th …, Jan 1, 2012
Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is d... more Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is difficult, as petrologists are faced with issues of representative sampling, together with laborious and time-consuming microscopic examination. Although automated mineralogy ...
The Canadian …, Jan 1, 2011
Abstract The minerals of the platinum-group elements (PGM) and their associated host minerals fro... more Abstract The minerals of the platinum-group elements (PGM) and their associated host minerals from the Merensky Reef at the Two Rivers platinum mine, South Africa, were investigated using an FEI 600F field emission Mineral Liberation Analyzer. Polished ...
ASEG Extended Abstracts, 2001
Mineralogy and Petrology, 2012
Proceedings of the 10th International Congress for Applied Mineralogy (ICAM), 2012
Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is d... more Quantifying spatial relationships of minerals of the platinum-group elements in ores in situ is difficult, as petrologists are faced with issues of representative sampling, together with laborious and time-consuming microscopic examination. Although automated mineralogy ...
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Papers by Michael W Knoper