Volcanic rocks of the Witwatersrand triad, South Africa I: description, classification and geochemical stratigraphy
- Bowen, Teral B, Marsh, Julian S, Bowen, Michael P, Eales, Hugh V
- Authors: Bowen, Teral B , Marsh, Julian S , Bowen, Michael P , Eales, Hugh V
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/138682 , vital:37663 , https://doi.org/10.1016/0301-9268(86)90038-0
- Description: The Witwatersrand triad contains thick volcanic sequences confined largely to the Dominion Group at the base and the Ventersdorp Supergroup at the top. These volcanic sequences are of late-Archaean to early-Proterozoic age and are amongst the oldest supracrustal volcanic sequences erupted onto the Archaean Kaapvaal craton. The volcanic rocks have suffered low-grade greenschist facies metamorphism but primary textures and, in some samples, primary mineralogies are well preserved.
- Full Text: false
- Date Issued: 2003
- Authors: Bowen, Teral B , Marsh, Julian S , Bowen, Michael P , Eales, Hugh V
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/138682 , vital:37663 , https://doi.org/10.1016/0301-9268(86)90038-0
- Description: The Witwatersrand triad contains thick volcanic sequences confined largely to the Dominion Group at the base and the Ventersdorp Supergroup at the top. These volcanic sequences are of late-Archaean to early-Proterozoic age and are amongst the oldest supracrustal volcanic sequences erupted onto the Archaean Kaapvaal craton. The volcanic rocks have suffered low-grade greenschist facies metamorphism but primary textures and, in some samples, primary mineralogies are well preserved.
- Full Text: false
- Date Issued: 2003
Some geochemical constraints upon models for the crystallization of the upper critical zone-main zone interval, northwestern Bushveld complex
- Eales, Hugh V, Marsh, Julian S, Mitchell, Andrew A, de Klerk, William J, Kruger, Floris J, Field, Matthew
- Authors: Eales, Hugh V , Marsh, Julian S , Mitchell, Andrew A , de Klerk, William J , Kruger, Floris J , Field, Matthew
- Date: 1986
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136044 , vital:37331 , https://doi.org/10.1180/minmag.1986.050.358.03
- Description: Ratios between elements Mg, Fe, Co, Cr, Ni, V, and Sc are consistently different in mafic rocks of the upper critical zone, and those above the Bastard unit. Within the 300 m section above the Merensky Reef, 87Sr/86Sr ratios increase from c.0.7063 to c.0.7087, irrespective of rock type. Decoupling of Mg/(Mg + Fe2+) ratios and the Ca contents of plagioclase, and wide variations in the proportions of anorthosite within the Bastard, Merensky, and Merensky Footwall units, are inconsistent with anorthosite formation by simple fractional crystallization of magma batches of limited volume.
- Full Text:
- Date Issued: 1986
- Authors: Eales, Hugh V , Marsh, Julian S , Mitchell, Andrew A , de Klerk, William J , Kruger, Floris J , Field, Matthew
- Date: 1986
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136044 , vital:37331 , https://doi.org/10.1180/minmag.1986.050.358.03
- Description: Ratios between elements Mg, Fe, Co, Cr, Ni, V, and Sc are consistently different in mafic rocks of the upper critical zone, and those above the Bastard unit. Within the 300 m section above the Merensky Reef, 87Sr/86Sr ratios increase from c.0.7063 to c.0.7087, irrespective of rock type. Decoupling of Mg/(Mg + Fe2+) ratios and the Ca contents of plagioclase, and wide variations in the proportions of anorthosite within the Bastard, Merensky, and Merensky Footwall units, are inconsistent with anorthosite formation by simple fractional crystallization of magma batches of limited volume.
- Full Text:
- Date Issued: 1986
The chemistry and petrogenesis of igneous rocks of the Karoo central area, southern Africa
- Eales, Hugh V, Marsh, Julian S
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133934 , vital:37042 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6519911
- Description: Outcrops of the Jurassic Karoo basalts and dolerites in central South Africa are remnants of an intracratonic continental igneous suite whose volume probably once exceeded 1.5 x 106 km³. Basic rocks with 6-8% MgO, 50-55% Si02 and Mg-number = 53-67 are overwhelmingly dominant in the Central area suite. Application of discriminant analysis to a data set of major and trace element analyses of the basic rocks confirms field and petrographic evidence that a number of compositionally distinct basalt magma types exist in the Central area.
- Full Text:
- Date Issued: 1984
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133934 , vital:37042 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6519911
- Description: Outcrops of the Jurassic Karoo basalts and dolerites in central South Africa are remnants of an intracratonic continental igneous suite whose volume probably once exceeded 1.5 x 106 km³. Basic rocks with 6-8% MgO, 50-55% Si02 and Mg-number = 53-67 are overwhelmingly dominant in the Central area suite. Application of discriminant analysis to a data set of major and trace element analyses of the basic rocks confirms field and petrographic evidence that a number of compositionally distinct basalt magma types exist in the Central area.
- Full Text:
- Date Issued: 1984
The Karoo igneous province: an introduction
- Eales, Hugh V, Marsh, Julian S, Cox, K G
- Authors: Eales, Hugh V , Marsh, Julian S , Cox, K G
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133945 , vital:37043 , http://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6519910
- Description: The Karoo rocks are amongst the earliest manifestations of igneous activity accompanying the break-up of Gondwanaland during the early Mesozoic. Remnants of the once extensive lava sequence and the associated dolerite sills are found throughout southern Africa south of latitude 150S, the present outcrop being ca. 140,000 km². The main peak of volcanic activity is dated at about 190 m.y. and is probably coincident with the earliest stages of the opening of the Indian Ocean by the separation of Antarctica from southern Africa.
- Full Text:
- Date Issued: 1984
- Authors: Eales, Hugh V , Marsh, Julian S , Cox, K G
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133945 , vital:37043 , http://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6519910
- Description: The Karoo rocks are amongst the earliest manifestations of igneous activity accompanying the break-up of Gondwanaland during the early Mesozoic. Remnants of the once extensive lava sequence and the associated dolerite sills are found throughout southern Africa south of latitude 150S, the present outcrop being ca. 140,000 km². The main peak of volcanic activity is dated at about 190 m.y. and is probably coincident with the earliest stages of the opening of the Indian Ocean by the separation of Antarctica from southern Africa.
- Full Text:
- Date Issued: 1984
Al/Cr ratios of coexisting pyroxenes and spinellids in some ultramafic rocks
- Eales, Hugh V, Marsh, Julian S
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1983
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133534 , vital:36987 , https://doi.org/10.1016/0009-2541(83)90045-1
- Description: Al/Cr atomic ratios of coexisting spinellids and ortho- and clinopyroxenes show a pattern of sympathetic variation that persists through ultramafic rocks of layered mafic complexes of upper-crustal type, Alpine complexes, and the nodules found in kimberlites and alkaline basalts. Simple expressions are empirically derived to link (Al/Cr) orthopyroxene and (Al/Cr)spinel ratios in putatively equilibrated rocks. Equivalence of spinel compositions in shallow layered complexes and kimberlite nodules of deep-seated origin negates direct crystallochemical control of Al/Cr ratios of spinels by pressure.
- Full Text: false
- Date Issued: 1983
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1983
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133534 , vital:36987 , https://doi.org/10.1016/0009-2541(83)90045-1
- Description: Al/Cr atomic ratios of coexisting spinellids and ortho- and clinopyroxenes show a pattern of sympathetic variation that persists through ultramafic rocks of layered mafic complexes of upper-crustal type, Alpine complexes, and the nodules found in kimberlites and alkaline basalts. Simple expressions are empirically derived to link (Al/Cr) orthopyroxene and (Al/Cr)spinel ratios in putatively equilibrated rocks. Equivalence of spinel compositions in shallow layered complexes and kimberlite nodules of deep-seated origin negates direct crystallochemical control of Al/Cr ratios of spinels by pressure.
- Full Text: false
- Date Issued: 1983
Karoo basalts, South Africa: Petrogenesis and the nature of their mantle rocks
- Marsh, Julian S, Eales, Hugh V
- Authors: Marsh, Julian S , Eales, Hugh V
- Date: 1982
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70141 , vital:29625
- Description: Outcrops of the Jurassic Karoo basalts and dolerites in central South Africa are remnants of a intracratonic continental igneous suite whose volume probably once exceeded 10 6km3.
- Full Text:
- Date Issued: 1982
- Authors: Marsh, Julian S , Eales, Hugh V
- Date: 1982
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70141 , vital:29625
- Description: Outcrops of the Jurassic Karoo basalts and dolerites in central South Africa are remnants of a intracratonic continental igneous suite whose volume probably once exceeded 10 6km3.
- Full Text:
- Date Issued: 1982
High-Mg tholeiitic rocks and their significance in the Karroo Central Province
- Eales, Hugh V, Marsh, Julian S
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/${Handle} , vital:36916 , https://hdl.handle.net/10520/AJA00382353_5039
- Description: Averages for the composition of dolerites from the Southern and Eastern Cape, and the correlative basaltic lavas of the Stormberg, are presented for major elements and 8 of the more significant trace elements. The remarkable correspondence between these averages is indicative of the uniformity in composition of the magma emplaced over a very large area.
- Full Text:
- Date Issued: 1979
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/${Handle} , vital:36916 , https://hdl.handle.net/10520/AJA00382353_5039
- Description: Averages for the composition of dolerites from the Southern and Eastern Cape, and the correlative basaltic lavas of the Stormberg, are presented for major elements and 8 of the more significant trace elements. The remarkable correspondence between these averages is indicative of the uniformity in composition of the magma emplaced over a very large area.
- Full Text:
- Date Issued: 1979
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