Volcanic rocks of the Witwatersrand Triad, South Africa. II: petrogenesis of mafic and felsic rocks of the Dominion Group
- Authors: Marsh, Julian S , Bowen, M P , Rogers, N W , Bowen, T B
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140443 , vital:37889 , https://doi.org/10.1016/0301-9268(89)90075-2
- Description: A bimodal suite of volcanic rocks builds the bulk of the Dominion Group which, with an age of ∼ 2.72 Ga, is the oldest cover sequence overlying the granite-greenstone Archaean basement of the Kaapvaal craton in the western Transvaal, South Africa. The basic lavas are relatively rich in SiO2 (50–58%) and aphyric and exhibit a large compositional range. This variation is typically tholeiitic in that it is characterized by strong enrichment of Ti, Fe, and V in differentiated lavas.
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- Date Issued: 2003
Volcanic rocks of the Witwatersrand triad, South Africa I: description, classification and geochemical stratigraphy
- 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
Tying up the continents
- Authors: Marsh, Julian S
- Date: 1989
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143282 , vital:38220
- Full Text:
- Date Issued: 1989
The role of continental lithosphere in the generation of the Karoo volcanic rocks: evidence from combined Nd-and Sr-isotope studies
- Authors: Hawkesworth, C J , Marsh, Julian S , Duncan, Andrew R , Erlank, Anthony J , Norry, M J
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/134165 , vital:37080 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6453596
- Description: 143Nd/144Nd, 87Sr/86Sr, Sm and Nd analyses are reported on suites of Karoo volcanic rocks from the four sub-areas of Nuanetsi-north Lebombo, south Lebombo, the Central area, and north-west SWA/Namibia. Only seven (12%) of the samples analysed have positive ENd values similar to those found in the majority of recent mantle-derived rocks. Most of the rest have negative ENd (-1.0 to -17.1) and positive ESr, (+3.0 to +240) and thus must contain at least a contribution from source areas which were both old, and had lower Sm/Nd and higher Rh/Sr ratios than the bulk earth.
- Full Text:
- Date Issued: 1984
The petrology and significance of a stratiform mafic segregation pegmatite in a Karoo-aged dolerite sheet
- Authors: Mitchell, Andrew A , Naicker, S B , Marsh, Julian S , Dunlevey, J N
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149496 , vital:38858 , https://hdl.handle.net/10520/EJC-9293fd659
- Description: A sub-horizontal stratiform mafic segregation pegmatite, of the order of 30 cm thick, occurs within 25 m of the top contact of a Karoo-aged dolerite sheet at Pietermaritzburg, South Africa. The host rock is an orthopyroxene-rich dolerite containing 5 - 8% interstitial granophyre. The pegmatite is similar to the host dolerite in many respects, except that the granophyre content is higher, and acicular augite is the only pyroxene. At its upper contact, a laterally continuous sub-horizontal joint forms a sharp boundary to the pegmatite, whilst the lower contact is gradational over a few millimetres. Low MgO and chalcophiles, and elevated incompatible element contents, are the main geochemical attributes of the pegmatite.
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- Date Issued: 1997
The petrogenesis of the Kirwan Basalts of Dronning Maud Land, Antarctica
- Authors: Harris, Chris , Marsh, Julian S , Duncan, Andrew R , Erlank, Anthony J
- Date: 1990
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145472 , vital:38441 , https://doi.org/10.1093/petrology/31.2.341
- Description: The 420 m thick sequence of Kirwan basalt crops out along the southernmost 50 km of the Kirwanveggen Escarpment (74°S, 6°W). There is little variation in major element chemistry of these basalts (SiO2 49·3–51·6 wt.%; MgO 5·1–6·6 wt.%), but the concentrations of certain incompatible elements (e.g., Zr) vary by factors of approximately two or more.
- Full Text: false
- Date Issued: 1990
The petrogenesis of the Kirwan Basalts of Dronning Maud Land, Antarctica
- Authors: Harris, Chris , Marsh, Julian S , Duncan, Andrew R , Erlank, Anthony J
- Date: 1990
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145492 , vital:38443 , https://doi.org/10.1093/petrology/31.2.341
- Description: The 420 m thick sequence of Kirwan basalt crops out along the southernmost 50 km of the Kirwanveggen Escarpment (74°S, 6°W). There is little variation in major element chemistry of these basalts (SiO2 49·3–51·6 wt.%; MgO 5·1–6·6 wt.%), but the concentrations of certain incompatible elements (e.g., Zr) vary by factors of approximately two or more.
- Full Text: false
- Date Issued: 1990
The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?
- Authors: Harris, Chris , Le Roux, Petrus , Cochrane, Ryan , Martin, Laure , Duncan, Andrew R , Marsh, Julian S , Le Roex, A P
- Date: 2015
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/60774 , vital:27829 , https://link.springer.com/article/10.1007/s00410-015-1164-1
- Description: Olivine and orthopyroxene phenocrysts from picrite and picrate basalt lavas and dykes (Mg# 64-80) from the Tuli and Mwanezi (Nuanetsi) regions of the ~180 Ma Karoo Large Igneous province (LIP) have δ18O values that range from 6.0 to 6.7 ‰ (Fig. 1), suggesting that they crystallized from magmas having δ18O values about 1 to 1.5 ‰ higher than expected in an entirely mantle-derived magma. Olivines from picrite and picrite basalt dykes from the 135 Ma Etendeka LIP of Namibia and Karoo-age picrite dykes from Dronning Maud Land, Antarctica do not have such elevated δ18O values. The Etendeka picrites show good correlations between δ18O value and Sr-, Nd- and Pb-isotope ratios that are consistent with previously proposed models of crustal contamination (e.g. Thompson et al., 2007). Explanations for the high δ18O values in Tuli/Mwenezi picrites are limited to (i) alteration, (ii) crustal contamination, and (iii) derivation from mantle with an abnormally high δ18O. The lack of variation in olivine and orthopyroxene δ18O values, together with the lack of correlation between mineral and whole-rock δ18O values are not consistent with alteration being the cause of high δ18O values. The high δ18O values in selected olivine cores have been confirmed by SIMS, and aggressive cleaning of crystals with HF makes no difference to the δ18O value obtained. Average εNd and εSr values of -8 and +16, and high concentrations of incompatible elements such as K are typical of picrites from the Mwanezi (Nuanetsi) region, which have been explained by a variety of models that range from crustal contamination to derivation from the ‘enriched’ mantle lithosphere. The primitive character of the magmas combined with the lack of correlation between δ18O values and radiogenic isotope composition and MgO content or Mg# are inconsistent with crustal contamination, and lend weight to arguments in favour of an 18O-enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition. Although elevated initial Sr isotope ratios, εNd values of -8, and δ18O values about 1 ‰ higher than expected for mantle-derived magma are also a feature of the Bushveld mafic and ultramafic magmas, it is unlikely that a long-lived 18O-enriched mantle source would have survived for nearly 2 Ga. Incorporation of crustal material into the mantle by subduction or delamination of the lower crust are the most likely mechanisms for enriching the mantle in 18O.
- Full Text:
- Date Issued: 2015
The mineralogy, petrology, and origin of the Merensky cyclic unit in the western Bushveld Complex
- Authors: Kruger, Floris J , Marsh, Julian S
- Date: 1985
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136024 , vital:37329 , https://doi.org/10.2113/gsecongeo.80.4.958
- Description: The Merensky cyclic unit of the Bushveld Complex represents the first products to crystallize after the influx and mixing of a large new batch of magma in the chamber. Excluding the Merensky pegmatoid, the Merensky cyclic unit grades upward from an orthopyroxenite at the base, through norite to anorthosite at the top of the sequence. It is followed by the very similar Bastard cyclic unit.
- Full Text: false
- Date Issued: 1985
The Marinkas Quellen Carbonatite Complex, southern Namibia: carbonatite magmatism with an uncontaminated depleted mantle signature in a continental setting
- Authors: Smithies, Robert H , Marsh, Julian S
- Date: 1998
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149736 , vital:38879 , https://doi.org/10.1016/S0009-2541(98)00029-1
- Description: The Marinkas Quellen Carbonatite Complex, in southern Namibia, forms part of the ca. 490–550 Ma Kuboos-Bremen Igneous Province, a zone of alkaline igneous rocks that intrude the Mesoproterzoic to Paleoproterozoic Namaqualand Metamorphic Province and Neoproterozoic platform sediments. The carbonatite complex includes Ca-rich, Mg-rich and Fe-rich carbonatites as well as late ferrocarbonatite dykes that show extreme enrichments in Mn, REE and Th. Compared to most carbonatites, those at Marinkas Quellen are generally depleted in most trace elements, particularly Ba and the LREE.
- Full Text: false
- Date Issued: 1998
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 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
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
The late Archaean Dominion Group, South Africa: petrogenesis of flood-type basalts and their mantle sources
- Authors: Marsh, Julian S , Rogers, N W , Bowen, M P , Bowen, T B
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131690 , vital:36721
- Description: The Dominion group has an age of 2.7 - 2.8 Ga and is the earliest of the cover sequences overlying the granite greenstone terrane in the western part of the Archaean Kaapvaal Craton, southern Africa. The Dominion group is largely built of volcanic rocks and is preserved over an area of 15,000 km² with a maximum thickness of 2.7 km.
- Full Text:
- Date Issued: 1988
The largest volcanic eruptions on Earth
- Authors: Bryan, Scott E , Peate, Ingrid Ukstins , Peate, David W , Self, Stephen , Jerram, Dougal A , Mawby, Michael R , Marsh, Julian S , Miller, Jodie A
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132887 , vital:36902 , https://doi.org/10.1016/j.earscirev.2010.07.001
- Description: Large igneous provinces (LIPs) are sites of the most frequently recurring, largest volume basaltic and silicic eruptions in Earth history. These large-volume (> 1000 km3 dense rock equivalent) and large-magnitude (> M8) eruptions produce really extensive (104–105 km2) basaltic lava flow fields and silicic ignimbrites that are the main building blocks of LIPs.
- Full Text: false
- Date Issued: 2010
The Karoo igneous province: an introduction
- 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
The Karoo igneous province:
- Authors: Duncan, Andrew R , Marsh, Julian S
- Date: 2006
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/145156 , vital:38413 , ISBN 9781919908779
- Description: The Karoo igneous province.
- Full Text:
- Date Issued: 2006
The geochemistry of potassic lavas from Vulsini, central Italy and implications for mantle enrichment processes beneath the Roman region
- Authors: Rogers, N W , Hawkesworth, C J , Parker, R J , Marsh, Julian S
- Date: 1985
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136034 , vital:37330 , https://doi.org/10.1007/BF00378265
- Description: Major and trace element and 143Nd/144Nd (0.51209–0.51216) and 87Sr/86Sr (0.70879–0.71105) isotope analyses are presented on a representative group of lavas from the Vulsini district of the Roman magmatic province. Three distinct series are identified; the high-K and low-K series are similar to those described from other Italian volcanoes, while the third is represented by a group of relatively undifferentiated leucite basanites which are thought to be near-primary mantle melts.
- Full Text: false
- Date Issued: 1985
The geochemistry and evolution of Palaeogene phonolites, central Namibia:
- Authors: Marsh, Julian S
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145000 , vital:38399 , https://doi.org/10.1016/j.lithos.2010.02.012
- Description: Phonolites of Palaeogene age occur at two different localities in central Namibia, occurring as clusters of eroded monogenetic lava domes. Six phonolites at Aris collectively exhibit a narrow compositional range and represent a single magma system of highly evolved phonolite with high concentrations of Na2O, Rb, Th, Zr, Zn, Pb, and REE and very low abundances of MgO, P2O5, Sr and Ba. No mafic rocks are associated with the Aris phonolites and their ultimate petrogenetic origin remains obscure. The more abundant Staalhart phonolites exhibit more variable but scattered compositional variation consistent with fractional crystallization dominated by sanidine (and nepheline) and pyroxene. The behaviour of REE is decoupled from Zr, Nb, and Th in this suite indicating a controlling role for minor phases in their evolution. The least evolved phonolites have initial 87Sr/86Sr 0.7043, which is identical to a small occurrence of associated plagioclase-bearing nephelinite indicating a possible petrogenetic link.
- Full Text:
- Date Issued: 2010
The geochemical structure of the Insizwa lobe of the Mount Ayliff complex with implications for the emplacement and evolution of the complex and its Ni-sulphide potential
- Authors: Marsh, Julian S , Allen, P , Fenner, N
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150556 , vital:38984 , https://doi.org/10.2113/106.4.409
- Description: Detailed petrographic, modal and geochemical studies on a number of deep boreholes (exceeding 1.2 km in some instances) along the southeastern margin of the Insizwa lobe of the Mount Ayliff Complex reveal the existence of a geochemical stratigraphy in the mafic intrusive rocks.
- Full Text: false
- Date Issued: 2003