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
Petrogenesis of Karoo magmas from Namibia and the nature of their source areas
- Authors: Marsh, Julian S , Miller, R
- Date: 1982
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/71299 , vital:29831
- Full Text:
- Date Issued: 1982
- Authors: Marsh, Julian S , Miller, R
- Date: 1982
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/71299 , vital:29831
- Full Text:
- Date Issued: 1982
Significance of 87Sr/86Sr ratios in the Merensky cyclic unit of the Bushveld Complex
- Kruger, Floris J, Marsh, Julian S
- Authors: Kruger, Floris J , Marsh, Julian S
- Date: 1982
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133524 , vital:36986 , https://doi.org/10.1038/298053a0
- Description: In a number of mafic layered intrusions, layers with platinum group element (PGE) mineralization coincide with breaks in cumulus mineral composition and isotopic variation trends through the layered sequence1,2. For example, in the Bushveld Complex in South Africa, abrupt increases in initial 87Sr/86Sr ratios occur at the UG-2 and Merensky pegmatoid (or ‘reef’) horizons, both of which are exploited for PGEs. We report here the results of a detailed Sr-isotope study across the Merensky unit and its immediate foot- and hangingwall-rocks which, when considered together with new ideas on processes operating in magma chambers3–5, suggest that magma mixing and post-cumulus infiltration of liquids displaced from below were important during crystallization of the Merensky pegmatoid.
- Full Text: false
- Date Issued: 1982
- Authors: Kruger, Floris J , Marsh, Julian S
- Date: 1982
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133524 , vital:36986 , https://doi.org/10.1038/298053a0
- Description: In a number of mafic layered intrusions, layers with platinum group element (PGE) mineralization coincide with breaks in cumulus mineral composition and isotopic variation trends through the layered sequence1,2. For example, in the Bushveld Complex in South Africa, abrupt increases in initial 87Sr/86Sr ratios occur at the UG-2 and Merensky pegmatoid (or ‘reef’) horizons, both of which are exploited for PGEs. We report here the results of a detailed Sr-isotope study across the Merensky unit and its immediate foot- and hangingwall-rocks which, when considered together with new ideas on processes operating in magma chambers3–5, suggest that magma mixing and post-cumulus infiltration of liquids displaced from below were important during crystallization of the Merensky pegmatoid.
- Full Text: false
- Date Issued: 1982
Tertiary phonolite volcanism in the Klinghardt Mountains of South West Africa/Namibia
- Authors: Marsh, Julian S , Lock, B E
- Date: 1981
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133242 , vital:36953 , https://hdl.handle.net/10520/AJA10120750_2789
- Description: The Klinghardt Mountains in South West Africa (Namibia) were the site of an important volcanic outburst late in the Eocene or early in the Oligocene. Over a hundred endogenous domes and several lava flows of the coulee type were emplaced: all analysed samples (more than 60) comprise varieties of phonolite. A sequence of ash-flow tuffs of limited areal extent is present on Glasrucken.
- Full Text:
- Date Issued: 1981
- Authors: Marsh, Julian S , Lock, B E
- Date: 1981
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133242 , vital:36953 , https://hdl.handle.net/10520/AJA10120750_2789
- Description: The Klinghardt Mountains in South West Africa (Namibia) were the site of an important volcanic outburst late in the Eocene or early in the Oligocene. Over a hundred endogenous domes and several lava flows of the coulee type were emplaced: all analysed samples (more than 60) comprise varieties of phonolite. A sequence of ash-flow tuffs of limited areal extent is present on Glasrucken.
- Full Text:
- Date Issued: 1981
Base-metal mineralization in alkaline pyroclastics: the Regenstein Vent, South West Africa
- Ferreira, C A M, Jacob, Roger E, Marsh, Julian S
- Authors: Ferreira, C A M , Jacob, Roger E , Marsh, Julian S
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133220 , vital:36950 , https://hdl.handle.net/10520/AJA10120750_1123
- Description: Geochemical analysis of soil samples taken from the area underlain by the Regenstein alkaline diatreme indicated potential areas for Pb-Zn-Ag mineralization, and these were subsequently proved by drilling. The pipelike body, emplaced into quartzites of the Damara Supergroup, consists of lithic and volcanic breccias. The breccias have been intruded, first by phonolite dykes, and then by numerous bodies of alkaline mafic and ultramafic rocks.
- Full Text:
- Date Issued: 1979
- Authors: Ferreira, C A M , Jacob, Roger E , Marsh, Julian S
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133220 , vital:36950 , https://hdl.handle.net/10520/AJA10120750_1123
- Description: Geochemical analysis of soil samples taken from the area underlain by the Regenstein alkaline diatreme indicated potential areas for Pb-Zn-Ag mineralization, and these were subsequently proved by drilling. The pipelike body, emplaced into quartzites of the Damara Supergroup, consists of lithic and volcanic breccias. The breccias have been intruded, first by phonolite dykes, and then by numerous bodies of alkaline mafic and ultramafic rocks.
- Full Text:
- Date Issued: 1979
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
New chemical analyses of the Suurberg volcanic rocks and their significance in relation to Mesozoic volcanism in Southern Africa
- Marsh, Julian S, Lock, B E, Fuchter, W H
- Authors: Marsh, Julian S , Lock, B E , Fuchter, W H
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133231 , vital:36951
- Description: Volcanic rocks are found associated with several of the late Mesozoic basins of southern South Africa. Bentonites are known from Plettenberg Bay and, according to an unconfirmed report, they are also found in the Worcester Basin, while vitric tuffs have been recorded from east of Oudtshoorn. The most extensive occurrences, however, are those of the Suurberg Group, which crops out sporadically around the margins of the Algoa Basin.
- Full Text:
- Date Issued: 1979
- Authors: Marsh, Julian S , Lock, B E , Fuchter, W H
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133231 , vital:36951
- Description: Volcanic rocks are found associated with several of the late Mesozoic basins of southern South Africa. Bentonites are known from Plettenberg Bay and, according to an unconfirmed report, they are also found in the Worcester Basin, while vitric tuffs have been recorded from east of Oudtshoorn. The most extensive occurrences, however, are those of the Suurberg Group, which crops out sporadically around the margins of the Algoa Basin.
- Full Text:
- Date Issued: 1979
Distribution of Ca in highly fractionated peralkaline magmas
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132974 , vital:36914 , https://doi.org/10.1016/0012-821X(76)90106-0
- Description: Many peralkaline rhyolites and granites contain less than 0.15 wt.% CaO. In contrast, strongly fractionated peralkaline nepheline syenites and phonolites usually contain greater than 0.5 wt.% CaO. Consideration of known distributions of Ca between crystals and liquid in conjunction with crystal fractionation does not provide an adequate explanation of the contrasting levels of Ca depletion observed. Examination of the suites of late-crystallizing accessory phases in peralkaline rocks suggests that Ca is more soluble in undersaturated magmas than in over-saturated magmas. Activities for CaO in silicic and phonolitic rocks are calculated and the latter have higher CaO activities than the former and this may manifest itself in the different suites of accessory phases and levels of Ca depletion noted in natural rocks.
- Full Text: false
- Date Issued: 1976
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132974 , vital:36914 , https://doi.org/10.1016/0012-821X(76)90106-0
- Description: Many peralkaline rhyolites and granites contain less than 0.15 wt.% CaO. In contrast, strongly fractionated peralkaline nepheline syenites and phonolites usually contain greater than 0.5 wt.% CaO. Consideration of known distributions of Ca between crystals and liquid in conjunction with crystal fractionation does not provide an adequate explanation of the contrasting levels of Ca depletion observed. Examination of the suites of late-crystallizing accessory phases in peralkaline rocks suggests that Ca is more soluble in undersaturated magmas than in over-saturated magmas. Activities for CaO in silicic and phonolitic rocks are calculated and the latter have higher CaO activities than the former and this may manifest itself in the different suites of accessory phases and levels of Ca depletion noted in natural rocks.
- Full Text: false
- Date Issued: 1976
The Lüderitz alkaline province, South West Africa, III: the Pomona and Drachenberg Syenite Complexes
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132984 , vital:36915 , https://hdl.handle.net/10520/AJA10120750_2853
- Description: The Pomona ring complex consists of several intrusive masses of syenitic magma that define a differentiation trend towards silica oversaturation. Volume relations, sequence of intrusion, and broad chemical characteristics are consistent with the syenites being derived by feldspar fractionation from an immediate syenitic parent. A plug of nepheline syenite and tinguaite dykes indicate the availability of silica-undersaturated magma generally in the Luderitz Province.
- Full Text:
- Date Issued: 1976
The Lüderitz alkaline province, South West Africa, III: the Pomona and Drachenberg Syenite Complexes
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132984 , vital:36915 , https://hdl.handle.net/10520/AJA10120750_2853
- Description: The Pomona ring complex consists of several intrusive masses of syenitic magma that define a differentiation trend towards silica oversaturation. Volume relations, sequence of intrusion, and broad chemical characteristics are consistent with the syenites being derived by feldspar fractionation from an immediate syenitic parent. A plug of nepheline syenite and tinguaite dykes indicate the availability of silica-undersaturated magma generally in the Luderitz Province.
- Full Text:
- Date Issued: 1976
Aenigmatite stability in silica-undersaturated rocks
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132942 , vital:36911 , https://doi.org/10.1007/BF00373333
- Description: Aenigmatite is common in many trachytes, phonolites and agpaitic nepheline syenites. Petrographic evidence suggests that the aenigmatite in these rocks arises by the reaction of Ti-magnetite with a peralkaline silica-undersaturated liquid, and it is postulated that a no-oxide field, where aenigmatite is stable, exists in alkaline undersaturated magmas.
- Full Text: false
- Date Issued: 1975
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132942 , vital:36911 , https://doi.org/10.1007/BF00373333
- Description: Aenigmatite is common in many trachytes, phonolites and agpaitic nepheline syenites. Petrographic evidence suggests that the aenigmatite in these rocks arises by the reaction of Ti-magnetite with a peralkaline silica-undersaturated liquid, and it is postulated that a no-oxide field, where aenigmatite is stable, exists in alkaline undersaturated magmas.
- Full Text: false
- Date Issued: 1975
The Klinghardt phonolites, South West Africa: Tertiary volcanism in western southern Africa
- Authors: Marsh, Julian S , Lock, B E
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70164 , vital:29627
- Description: Over 1OO phonolite bodies of mid-Tertiary age occur in the Klinghardt Mountains, 1OO km SE of Luderitz in Southern South West Africa the only published account of these rocks is that of Kaiser (1926) who gives a generalized map and describes briefly the mode of occurrence and petrography of the phonolites. The phonolite bodies are concentrated in an area roughly 8OO km2 and constitute an excellent example of an areal volcanic field (Rittmann, 1962), i.e. the activity occurred at a number of vents spread over a wide area and in most cases only a single eruptive episode took place at each vent.
- Full Text:
- Date Issued: 1975
- Authors: Marsh, Julian S , Lock, B E
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70164 , vital:29627
- Description: Over 1OO phonolite bodies of mid-Tertiary age occur in the Klinghardt Mountains, 1OO km SE of Luderitz in Southern South West Africa the only published account of these rocks is that of Kaiser (1926) who gives a generalized map and describes briefly the mode of occurrence and petrography of the phonolites. The phonolite bodies are concentrated in an area roughly 8OO km2 and constitute an excellent example of an areal volcanic field (Rittmann, 1962), i.e. the activity occurred at a number of vents spread over a wide area and in most cases only a single eruptive episode took place at each vent.
- Full Text:
- Date Issued: 1975
The Luderitz Alkaline Province, South West Africa I: descriptive petrology of the Granitberg Foyaite Complex
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132951 , vital:36912
- Description: The Granitberg foyaite complex is one of three known alkaline igneous complexes, which, together with a dyke swarm, constitute the Liüderitz Alkaline Province of Lower Cretaceous age. The near-circular complex is emplaced into dolomites and sandstones of the Bogenfels Formation. A large fragment of these sedimentary rocks, originally forming the roof of the intrusion, is preserved in the centre of the complex.
- Full Text:
- Date Issued: 1975
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132951 , vital:36912
- Description: The Granitberg foyaite complex is one of three known alkaline igneous complexes, which, together with a dyke swarm, constitute the Liüderitz Alkaline Province of Lower Cretaceous age. The near-circular complex is emplaced into dolomites and sandstones of the Bogenfels Formation. A large fragment of these sedimentary rocks, originally forming the roof of the intrusion, is preserved in the centre of the complex.
- Full Text:
- Date Issued: 1975
The Luderitz Alkaline Province, South West Africa II: metasomatism and assimilation in the contact aureole of the Granitberg Foyaite Complex
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132963 , vital:36913
- Description: Reactions between the Outer Foyaite magma of the Granitberg Complex and the sedimentary country rocks are striking. At sandstone contacts the magma has assimilated quartz-rich sedimentary material and a suite of pulaskites, peralkaline nordmarkites, and peralkaline granites have been generated by a complex process involving both assimilation and crystal fractionation.
- Full Text:
- Date Issued: 1975
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132963 , vital:36913
- Description: Reactions between the Outer Foyaite magma of the Granitberg Complex and the sedimentary country rocks are striking. At sandstone contacts the magma has assimilated quartz-rich sedimentary material and a suite of pulaskites, peralkaline nordmarkites, and peralkaline granites have been generated by a complex process involving both assimilation and crystal fractionation.
- Full Text:
- Date Issued: 1975