Regional geochemistry of the Karoo igneous province
- Authors: Duncan, Andrew R , Erlank, Anthony J , Marsh, Julian S
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/134154 , vital:37079 , https://inis.iaea.org/search/searchsinglerecord.aspx?recordsFor=SingleRecordamp;RN=15001076
- Description: The extrusive and intrusive rocks of the Karoo Igneous Province are dominantly of basaltic or rhyolitic (sensu lato) composition. There are, however, a considerable variety of other rock types within the province including picritic basalts, nephelinites, shoshonites, latites, andesites and dacites. This paper deals with the geochemistry of the Karoo igneous province.
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- Date Issued: 1984
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.
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- Date Issued: 1975
New views on the Jurassic Clarens Formation: volcano-sedimentary interaction
- Authors: Holzforster, Frank , Holzforster, Heike W , Marsh, Julian S
- Date: 2002
- Language: English
- Type: text , abstract
- Identifier: http://hdl.handle.net/10962/132716 , vital:36874
- Description: The Lower Jurassic Clarens Formation of the Great Karoo Basin is usually viewed in the literature as a aeolian and, in places, fluvio-aeolian deposit of tremendous thickness variation form 0-250 m thickness. Interaction with the overlying Karoo Flood Basalts, particularly in the Eastern Cape area and in Lesotho, has been noted but was never a major topic. Relatively widespread pyroclastic deposits sandwiched between the Clarens Formation and the Karoo Flood Basalts have been interpreted as flood-lahars.
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- Date Issued: 2002
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.
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- Date Issued: 1984
Base-metal mineralization in alkaline pyroclastics: the Regenstein Vent, South West Africa
- 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.
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- Date Issued: 1979
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
Geochemical variations in a long Karoo dyke, Eastern Cape
- Authors: Marsh, Julian S , Mndaweni, M J
- Date: 1998
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149715 , vital:38877 , https://hdl.handle.net/10520/EJC-1abee09c1f
- Description: A prominent vertical dolerite dyke, up to 30 m wide and which can be traced for over 100 km, is compositionally homogeneous along much of its length and shows no evidence of flow differentiation. Associated parallel dykes are compositionally distinct and are unrelated by closed-system processes. The main dyke has geochemical characteristics of the Maloti or Senqu Units in the upper part of the main Lesotho basalt sequence, whereas the parallel dykes are geochemically similar to the lower Mafika Lisiu Unit. On the basis of size and composition the main dyke may well represent a fissure which once fed effusions of Karoo basalt.
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- Date Issued: 1998
Petrology and geochemistry of early cretaceous bimodal continental flood volcanism of the NW Etendeka, Namibia Part 2: characteristics and petrogenesis of the high-Ti latite and high-Ti and low-Ti voluminous quartz latite eruptives
- Authors: Ewart, A , Marsh, Julian S , Milner, Simon C , Duncan, Andrew R , Kamber, B S , Armstrong, R A
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150593 , vital:38987 , https://doi.org/10.1093/petrology/egg082
- Description: As a result of their relative concentration towards the respective Atlantic margins, the silicic eruptives of the Paraná (Brazil)–Etendeka large igneous province are disproportionately abundant in the Etendeka of Namibia. The NW Etendeka silicic units, dated at ∼132 Ma, occupy the upper stratigraphic levels of the volcanic sequences, restricted to the coastal zone, and comprise three latites and five quartz latites (QL).
- Full Text: false
- Date Issued: 2004
Sub-volcanic intrusions and the link to global climatic and environmental changes:
- Authors: Svensen, Henrik H , Planke, Sverre , Neumann, Else-Ragnhild , Aarnes, Ingrid , Marsh, Julian S , Polteau, Stéphane , Harstad, Camilla H , Chevallier, Luc
- Date: 2018
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/145166 , vital:38414 , ISBN 9783319140841 , https://link.springer.com/chapter/10.1007/11157_2015_10
- Description: Most of the Large Igneous Provinces (LIPs) formed during the last 260 million years are associated with climatic changes, oceanic anoxia, or extinctions in marine and terrestrial environments. Current hypotheses involve (1) degassing of carbon from either oceans or shallow sea-bed reservoirs, (2) degassing from flood basalts, or from (3) sedimentary basins heavily intruded by LIP-related sills. These hypotheses are based on detailed geological and geochemical studies from LIPSs or relevant proxy data sequences. Here we present new data on gas generation and degassing from a LIP, based on the LA1/68 borehole north of the Ladybrand area in the Karoo Basin, South Africa.
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- Date Issued: 2018
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.
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- Date Issued: 1975
Rock magnetic stratigraphy of a mafic layered sill: a key to the Karoo volcanics plumbing system
- Authors: Maes, S M , Ferré, E E , Tikoff, B , Brown, P E , Marsh, Julian S
- Date: 2008
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144901 , vital:38389 , https://doi.org/10.1016/j.jvolgeores.2005.07.038
- Description: The Insizwa sill is an 1 km-thick subhorizontal layered mafic intrusion and part of the Karoo Large Igneous Province in South Africa. This well-exposed intrusion consists of several superimposed petrologically and geochemically distinct units. Magnetic methods were used to study the intrusion in order to constrain the physical processes active in these types of bodies during crystallization. Rock magnetism studies indicate that within different petrologic units bulk susceptibility is controlled by primary magnetite (with minor pyrrhotite) and/or paramagnetic minerals (olivine, pyroxene). New magnetic data based on 659 specimens obtained from 3 vertical borehole cores, each spaced 5 km apart, confirm the prominent vertical zonation in low field magnetic susceptibility (Klf), degree of anisotropy (Pj) and orientation of the anisotropy of magnetic susceptibility (AMS) axes.
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- Date Issued: 2008
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
Stratigraphy and age of Karoo basalts of Lesotho and implications for correlations within the Karoo igneous province
- Authors: Marsh, Julian S , Hooper, P R , Rehacek, J , Duncan, R A , Duncan, A R
- Date: 2013
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/149507 , vital:38859 , https://doi.org/10.1029/GM100p0247
- Description: Remnants of the erupted and intrusive products of the Karoo igneous province, one of the classic Mesozoic continental flood basalt provinces, are found throughout southern Africa. Such large continental igneous events are frequently ascribed to the rise of deep-seated mantle plumes and, in some instances, are thought to be related to continental breakup.
- Full Text: false
- Date Issued: 2013
An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt: Naude's Nek section (South Africa)
- Authors: Moulin, Maud , Fluteau, Frédéric , Courtillot, Vincent , Marsh, Julian S , Delpech, Guillaume , Quidelleur, Xavier , Gérard, Martine , Jay, Anne E
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145022 , vital:38401 , https://doi.org/10.1029/2011JB008210
- Description: We have carried out paleomagnetic sampling of a ∼750 m sequence of the Karoo large igneous province (Naude's Nek Pass, South Africa). K‐Ar dating (Cassignol‐Gillot) has been performed on four samples from the 650 m upper unit (mean age 179.2 ± 1.8 Ma) and a sample from the lower unit (184.8 ± 2.6 Ma). A succession of two phases of volcanism is suggested. The lower 25 flows (115 m thick) have recorded a reversed polarity; the next 23 flows (135 m thick) are transitional and contribute a detailed record of the “Van Zijl” (1962) Jurassic reversal.
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- Date Issued: 2011
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 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.
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- Date Issued: 1988
The distribution of platinum group elements in the Insizwa lobe, Mount Ayliff Complex, South Africa: implications for Ni-Cu-PGE sulfide exploration in the Karoo igneous province
- Authors: Maier, W D , Marsh, Julian S , Barnes, Sarah-Jane , Dodd, D C
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150353 , vital:38969 , https://0-doi.org.wam.seals.ac.za/10.2113/gsecongeo.97.6.1293
- Description: The Mount Ayliff Complex of the Eastern Cape province of South Africa is a layered intrusion of some 800 km2 surface area and up to 1,200 m thickness. On the basis of compositional similarities and spatial association, it is generally interpreted to form part of the Karoo igneous province. Similarities between the Mount Ayliff Complex and the staging chambers and feeder conduits to flood basalts that host magmatic sulfide ores elsewhere in the world suggest that the Mount Ayliff Complex may have an enhanced potential for Noril’sk-Talnakh–type massive Ni-Cu sulfide ores, an idea that is supported by the well-known sulfide occurrence at Waterfall Gorge.
- Full Text: false
- Date Issued: 2002
Dyke swarms and associated lava formations in the northern Lebombo monocline, Karoo Large Igneous Province, South Africa
- Authors: Klausen, Martin B , Marsh, Julian S , Watkeys, M K
- Date: 2006
- Language: English
- Type: text , Abstracts
- Identifier: http://hdl.handle.net/10962/132751 , vital:36880
- Description: As one of the early classical examples of plume-generated Large Igneous Provinces (LIPs), the Karoo is characterized by a bulls-eye distribution of High-Ti basalts, picrites, and earliest nephelinites onto a conspicuous triple rift junction (i.e., Okavango dyke swarm and the two Mwenezi and Lebombo monoclines), surrounded by Low-Ti basalts. It is noted that this regional distribution between high-and low-Ti basalts within the Jurassic Karoo LIP differs from that of the Permian Emeishan LIP; thereby undermining the use of this particular feature as evidence for mantle plume involvement.
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- Date Issued: 2006