A laterally extensive geochemical discontinuity in the subcontinental Gondwana Lithosphere
- Erlank, Anthony J, Duncan, Andrew R, Marsh, Julian S, Sweeney, R J, Hawkesworth, C J, Milner, Simon C, Miller, R McG, Rogers, N W
- Authors: Erlank, Anthony J , Duncan, Andrew R , Marsh, Julian S , Sweeney, R J , Hawkesworth, C J , Milner, Simon C , Miller, R McG , Rogers, N W
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131678 , vital:36710
- Description: Cox et al. (1967) first delineated the existence of two major geochemical provinces in the Karoo basalts of southern Africa. Tholeiitic basalts in Zimbabwe are highly enriched in incompatible trace elements and constitute the "northern province". In contrast, basalts from Lesotho and from the southern segment of the Lebombo monocline have lower or “normal” abundances of these elements and were regarded as a "southern province'. Recent work has established that this change in composition takes place relatively rapidly in the Central Lebombo.
- Full Text:
- Date Issued: 1988
- Authors: Erlank, Anthony J , Duncan, Andrew R , Marsh, Julian S , Sweeney, R J , Hawkesworth, C J , Milner, Simon C , Miller, R McG , Rogers, N W
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131678 , vital:36710
- Description: Cox et al. (1967) first delineated the existence of two major geochemical provinces in the Karoo basalts of southern Africa. Tholeiitic basalts in Zimbabwe are highly enriched in incompatible trace elements and constitute the "northern province". In contrast, basalts from Lesotho and from the southern segment of the Lebombo monocline have lower or “normal” abundances of these elements and were regarded as a "southern province'. Recent work has established that this change in composition takes place relatively rapidly in the Central Lebombo.
- Full Text:
- Date Issued: 1988
Distribution and petrogenesis of the basic rocks of the Etendeka Formation of northwestern Namibia
- Marsh, Julian S, Duncan, Andrew R, Milner, Simon C, Erlank, Anthony J
- Authors: Marsh, Julian S , Duncan, Andrew R , Milner, Simon C , Erlank, Anthony J
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131667 , vital:36709
- Description: The igneous rocks which comprise the Etendeka Formation in northwestern Namibia cover an area of 78 000 km² and consist dominantly of interbedded basalts and quartz latites, with minor latites. They are spatially associated with, and intruded by, two suites of dolerites. The rocks of the Etendeka Formation are included in the Karoo Igneous Province but differ from most other Karoo volcanics with respect to their younger age (Cretaceous) and aspects of their mineralogy and geochemistry.
- Full Text:
- Date Issued: 1988
- Authors: Marsh, Julian S , Duncan, Andrew R , Milner, Simon C , Erlank, Anthony J
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131667 , vital:36709
- Description: The igneous rocks which comprise the Etendeka Formation in northwestern Namibia cover an area of 78 000 km² and consist dominantly of interbedded basalts and quartz latites, with minor latites. They are spatially associated with, and intruded by, two suites of dolerites. The rocks of the Etendeka Formation are included in the Karoo Igneous Province but differ from most other Karoo volcanics with respect to their younger age (Cretaceous) and aspects of their mineralogy and geochemistry.
- Full Text:
- Date Issued: 1988
Geochemistry and petrogenesis of the Etendeka volcanic rocks from SWA Namibia
- Erlank, Anthony J, Marsh, Julian S, Duncan, Andrew R, Miller, R M, Hawkesworth, C J, Betton, P J, Rex, D C
- Authors: Erlank, Anthony J , Marsh, Julian S , Duncan, Andrew R , Miller, R M , Hawkesworth, C J , Betton, P J , Rex, D C
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133923 , vital:37041 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6519919
- Description: The volcanic rocks of the Etendeka Formation from north-west SWA/Namibia have a present-day coverage of 70,000 km² and comprise a series of interbedded basalts, latites and quartz latites, together with four varieties of intrusive dolerite. Apart from one group of dolerites (regional dolerites) which have mineralogical and geochemical similarities to the Lesotho Formation lavas from the Central area, the Etendeka volcanics differ from all other Karoo volcanics by virtue of their Cretaceous age, stratigraphy, mineralogy, geochemistry, and range in mineralogical, elemental and isotopic compositions for the basaltic rocks.
- Full Text:
- Date Issued: 1984
- Authors: Erlank, Anthony J , Marsh, Julian S , Duncan, Andrew R , Miller, R M , Hawkesworth, C J , Betton, P J , Rex, D C
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133923 , vital:37041 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6519919
- Description: The volcanic rocks of the Etendeka Formation from north-west SWA/Namibia have a present-day coverage of 70,000 km² and comprise a series of interbedded basalts, latites and quartz latites, together with four varieties of intrusive dolerite. Apart from one group of dolerites (regional dolerites) which have mineralogical and geochemical similarities to the Lesotho Formation lavas from the Central area, the Etendeka volcanics differ from all other Karoo volcanics by virtue of their Cretaceous age, stratigraphy, mineralogy, geochemistry, and range in mineralogical, elemental and isotopic compositions for the basaltic rocks.
- Full Text:
- Date Issued: 1984
MORB-related dolerites associated with the final phases of Karoo flood basalt volcanism in southern Africa.
- Duncan, Andrew R, Armstrong, R A, Erlank, Anthony J, Marsh, Julian S, Watkins, R T
- Authors: Duncan, Andrew R , Armstrong, R A , Erlank, Anthony J , Marsh, Julian S , Watkins, R T
- Date: 1990
- Language: English
- Type: text , conference paper
- Identifier: http://hdl.handle.net/10962/143299 , vital:38222 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailampidt=6938249
- Description: The Rooi Rand dyke swarm is approximately 200km long and up to 20km wide. It crops out in the southern portion of the Lebombo monocline where the dykes intrude basalts of the Sabie River Basalt Formation which is the major basaltic unit in the eastern portion of the Karoo volcanic succession. The Horingbaai dolerites form thin dykes and sills which intrude the base of the Etendeka lava pile (considered part of the Karoo Volcanics, but correlated with the Serra Geral Formation of Brazil) along the coast of Namibia. Both the Rooi Rand and Horingbaai magma types are similar in composition to enriched MORB and are compositionally distinct from most of the Karoo-basalts they intrude.
- Full Text:
- Date Issued: 1990
- Authors: Duncan, Andrew R , Armstrong, R A , Erlank, Anthony J , Marsh, Julian S , Watkins, R T
- Date: 1990
- Language: English
- Type: text , conference paper
- Identifier: http://hdl.handle.net/10962/143299 , vital:38222 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailampidt=6938249
- Description: The Rooi Rand dyke swarm is approximately 200km long and up to 20km wide. It crops out in the southern portion of the Lebombo monocline where the dykes intrude basalts of the Sabie River Basalt Formation which is the major basaltic unit in the eastern portion of the Karoo volcanic succession. The Horingbaai dolerites form thin dykes and sills which intrude the base of the Etendeka lava pile (considered part of the Karoo Volcanics, but correlated with the Serra Geral Formation of Brazil) along the coast of Namibia. Both the Rooi Rand and Horingbaai magma types are similar in composition to enriched MORB and are compositionally distinct from most of the Karoo-basalts they intrude.
- Full Text:
- Date Issued: 1990
Oxygen isotope geochemistry of the Mesozoic volcanics of the Etendeka Formation, Namibia
- Harris, Chris, Smith, H Stuart, Milner, Simon C, Erlank, Anthony J, Duncan, Andrew R, Marsh, Julian S, Ikin, Nicholas P
- Authors: Harris, Chris , Smith, H Stuart , Milner, Simon C , Erlank, Anthony J , Duncan, Andrew R , Marsh, Julian S , Ikin, Nicholas P
- Date: 1989
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143272 , vital:38219 , https://doi.org/10.1007/BF00371087
- Description: The Etendeka Formation volcanics consist of a bimodal association of basalts and quartz latites. Forty three new whole rock oxygen isotope analyses are reported for all the major magma types. All the rocks except a minor suite of dolerites have higher δ18O values than normal mantle. The basic rocks (average of 29=8.8‰) have significantly different δ18O to the acid rocks (average of 10=14.4‰). These data are apparently consistent with previously published petrogenetic models, which propose that the basalts were affected by crustal contamination and that the quartz latites are crustally derived.
- Full Text: false
- Date Issued: 1989
- Authors: Harris, Chris , Smith, H Stuart , Milner, Simon C , Erlank, Anthony J , Duncan, Andrew R , Marsh, Julian S , Ikin, Nicholas P
- Date: 1989
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143272 , vital:38219 , https://doi.org/10.1007/BF00371087
- Description: The Etendeka Formation volcanics consist of a bimodal association of basalts and quartz latites. Forty three new whole rock oxygen isotope analyses are reported for all the major magma types. All the rocks except a minor suite of dolerites have higher δ18O values than normal mantle. The basic rocks (average of 29=8.8‰) have significantly different δ18O to the acid rocks (average of 10=14.4‰). These data are apparently consistent with previously published petrogenetic models, which propose that the basalts were affected by crustal contamination and that the quartz latites are crustally derived.
- Full Text: false
- Date Issued: 1989
Petrology and geochemistry of Early Cretaceous bimodal continental flood volcanism of the NW Etendeka, Namibia Part 1: introduction, mafic lavas and re-evaluation of mantle source components
- Ewart, A, Marsh, Julian S, Milner, Simon C, Duncan, Andrew R, Kamber, B S, Armstrong, R A
- 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/10962/150583 , vital:38986 , https://doi.org/10.1093/petrology/egg083
- Description: The bimodal NW Etendeka province is located at the continental end of the Tristan plume trace in coastal Namibia. It comprises a high-Ti (Khumib type) and three low-Ti basalt (Tafelberg, Kuidas and Esmeralda types) suites, with, at stratigraphically higher level, interstratified high-Ti latites (three units) and quartz latites (five units), and one low-Ti quartz latite. Khumib basalts are enriched in high field strength elements and light rare earth elements relative to low-Ti types and exhibit trace element affinities with Tristan da Cunha lavas.
- Full Text: false
- Date Issued: 2004
- 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/10962/150583 , vital:38986 , https://doi.org/10.1093/petrology/egg083
- Description: The bimodal NW Etendeka province is located at the continental end of the Tristan plume trace in coastal Namibia. It comprises a high-Ti (Khumib type) and three low-Ti basalt (Tafelberg, Kuidas and Esmeralda types) suites, with, at stratigraphically higher level, interstratified high-Ti latites (three units) and quartz latites (five units), and one low-Ti quartz latite. Khumib basalts are enriched in high field strength elements and light rare earth elements relative to low-Ti types and exhibit trace element affinities with Tristan da Cunha lavas.
- Full Text: false
- Date Issued: 2004
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
- Ewart, A, Marsh, Julian S, Milner, Simon C, Duncan, Andrew R, Kamber, B S, Armstrong, R A
- 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
- 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
Preliminary geochemical data for dolerite dykes and sills of the southern part of the Etendeka Igneous Province
- Marsh, Julian S, Erlank, Anthony J, Duncan, Andrew R
- Authors: Marsh, Julian S , Erlank, Anthony J , Duncan, Andrew R
- Date: 1991
- Language: English
- Type: text , report
- Identifier: http://hdl.handle.net/10962/132133 , vital:36803
- Description: Over the last 15 years systematic geochemical and petrological investigation of the igneous rocks of the Early Cretaceous - Late Jurassic Etendeka Igneous Province of northwestern Namibia have focused on the tholeiitic basaltic lavas and interbedded silicic volcanic rocks and the large central subvolcanic complexes of Brandberg, Erongo, Okenyenya, Messum, Doros and Cape Cross. Previously these rocks were grouped into the Karoo Volcanic Province of South Africa, but in view of the distinct age difference between the igneous rocks of the Etendeka region and Karoo rocks occurring elsewhere in southern Africa , we propose to regard them as constituting a separate Etendeka Igneous Province which exhibits a close lithological, geochemical and temporal correlation with the Parana Flood Basalt Province of South America.
- Full Text:
- Date Issued: 1991
- Authors: Marsh, Julian S , Erlank, Anthony J , Duncan, Andrew R
- Date: 1991
- Language: English
- Type: text , report
- Identifier: http://hdl.handle.net/10962/132133 , vital:36803
- Description: Over the last 15 years systematic geochemical and petrological investigation of the igneous rocks of the Early Cretaceous - Late Jurassic Etendeka Igneous Province of northwestern Namibia have focused on the tholeiitic basaltic lavas and interbedded silicic volcanic rocks and the large central subvolcanic complexes of Brandberg, Erongo, Okenyenya, Messum, Doros and Cape Cross. Previously these rocks were grouped into the Karoo Volcanic Province of South Africa, but in view of the distinct age difference between the igneous rocks of the Etendeka region and Karoo rocks occurring elsewhere in southern Africa , we propose to regard them as constituting a separate Etendeka Igneous Province which exhibits a close lithological, geochemical and temporal correlation with the Parana Flood Basalt Province of South America.
- Full Text:
- Date Issued: 1991
Promotion of the Etendeka Formation to Group status: a new integrated stratigraphy
- Milner, Simon C, Duncan, Andrew R, Ewart, A, Marsh, Julian S
- Authors: Milner, Simon C , Duncan, Andrew R , Ewart, A , Marsh, Julian S
- Date: 1994
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145482 , vital:38442
- Description: The Etendeka volcanic rocks of northwestem Namibia are currently defined as the upper part of the Karoo Sequence in Namibia and have thus been represented as stratigraphically equivalent to the volcanic rocks of the Karoo Sequence in South Africa, Botswana, Lesotho, Swaziland and Zimbabwe. However, the Etendeka volcanic rocks (130-135 Ma) are considerably younger than those of the Karoo Sequence (180-190 Ma) in the areas mentioned above. They are compositionally distinct from Karoo volcanic rocks, and constitute an eastern portion of the Parana Igneous Province of Brazil. Stratigraphic studies have shown the Etendeka Formation to be made up of several definable volcanic successions and it is suggested that these successions now be formally recognized as Formations within an Etendeka Group which itself should no longer be part of the Karoo Sequence. Prominent quartz latite units and sequences of basalt flows are defined as Members within the new Formations.
- Full Text:
- Date Issued: 1994
- Authors: Milner, Simon C , Duncan, Andrew R , Ewart, A , Marsh, Julian S
- Date: 1994
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145482 , vital:38442
- Description: The Etendeka volcanic rocks of northwestem Namibia are currently defined as the upper part of the Karoo Sequence in Namibia and have thus been represented as stratigraphically equivalent to the volcanic rocks of the Karoo Sequence in South Africa, Botswana, Lesotho, Swaziland and Zimbabwe. However, the Etendeka volcanic rocks (130-135 Ma) are considerably younger than those of the Karoo Sequence (180-190 Ma) in the areas mentioned above. They are compositionally distinct from Karoo volcanic rocks, and constitute an eastern portion of the Parana Igneous Province of Brazil. Stratigraphic studies have shown the Etendeka Formation to be made up of several definable volcanic successions and it is suggested that these successions now be formally recognized as Formations within an Etendeka Group which itself should no longer be part of the Karoo Sequence. Prominent quartz latite units and sequences of basalt flows are defined as Members within the new Formations.
- Full Text:
- Date Issued: 1994
Regional geochemistry of the Karoo igneous province
- Duncan, Andrew R, Erlank, Anthony J, Marsh, Julian S
- 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.
- Full Text:
- Date Issued: 1984
- 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.
- Full Text:
- Date Issued: 1984
Stratigraphy and age of Karoo basalts of Lesotho and implications for correlations within the Karoo igneous province
- Marsh, Julian S, Hooper, P R, Rehacek, J, Duncan, R A, Duncan, Andrew R
- Authors: Marsh, Julian S , Hooper, P R , Rehacek, J , Duncan, R A , Duncan, Andrew 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
- Authors: Marsh, Julian S , Hooper, P R , Rehacek, J , Duncan, R A , Duncan, Andrew 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
The Etendeka Igneous Province: magma types and their stratigraphic distribution with implications for the evolution of the Paraná-Etendeka flood basalt province
- Marsh, Julian S, Ewart, A, Milner, Simon C, Duncan, Andrew R, Miller, R McG
- Authors: Marsh, Julian S , Ewart, A , Milner, Simon C , Duncan, Andrew R , Miller, R McG
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149762 , vital:38882 , https://doi.org/10.1007/s004450000115
- Description: Detailed geochemical and field data for the volcanic sequence and intrusions of the Etendeka Igneous Province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the Etendeka-Paraná continental flood volcanic event. Geochemical and petrographic characterization of over 1,000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized.
- Full Text: false
- Date Issued: 2017
- Authors: Marsh, Julian S , Ewart, A , Milner, Simon C , Duncan, Andrew R , Miller, R McG
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149762 , vital:38882 , https://doi.org/10.1007/s004450000115
- Description: Detailed geochemical and field data for the volcanic sequence and intrusions of the Etendeka Igneous Province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the Etendeka-Paraná continental flood volcanic event. Geochemical and petrographic characterization of over 1,000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized.
- Full Text: false
- Date Issued: 2017
The Karoo igneous province:
- Duncan, Andrew R, Marsh, Julian S
- 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
- 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 oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?
- Harris, Chris, Le Roux, Petrus, Cochrane, Ryan, Martin, Laure, Duncan, Andrew R, Marsh, Julian S, Le Roex, A P
- 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
- 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 petrogenesis of the Kirwan Basalts of Dronning Maud Land, Antarctica
- Harris, Chris, Marsh, Julian S, Duncan, Andrew R, Erlank, Anthony J
- 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
- 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 petrogenesis of the Kirwan Basalts of Dronning Maud Land, Antarctica
- Harris, Chris, Marsh, Julian S, Duncan, Andrew R, Erlank, Anthony J
- 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
- 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 role of continental lithosphere in the generation of the Karoo volcanic rocks: evidence from combined Nd-and Sr-isotope studies
- Hawkesworth, C J, Marsh, Julian S, Duncan, Andrew R, Erlank, Anthony J, Norry, M J
- 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
- 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 timing and duration of the Karoo igneous event, southern Gondwana
- Duncan, R A, Hooper, P R, Rehacek, J, Marsh, Julian S, Duncan, Andrew R
- Authors: Duncan, R A , Hooper, P R , Rehacek, J , Marsh, Julian S , Duncan, Andrew R
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149485 , vital:38857 , https://doi.org/10.1029/97JB00972
- Description: A volcanic event of immense scale occurred within a relatively short period in early Jurassic time over large regions of the contiguous Gondwana supercontinent. In southern Africa, associated remnants of thick volcanic successions of lava flows and extensive dike and sill complexes of similar composition have been grouped together as the Karoo Igneous Province. Correlative volcanic and plutonic rocks occur in Antarctica and Australia as the Ferrar Province.
- Full Text:
- Date Issued: 1997
- Authors: Duncan, R A , Hooper, P R , Rehacek, J , Marsh, Julian S , Duncan, Andrew R
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149485 , vital:38857 , https://doi.org/10.1029/97JB00972
- Description: A volcanic event of immense scale occurred within a relatively short period in early Jurassic time over large regions of the contiguous Gondwana supercontinent. In southern Africa, associated remnants of thick volcanic successions of lava flows and extensive dike and sill complexes of similar composition have been grouped together as the Karoo Igneous Province. Correlative volcanic and plutonic rocks occur in Antarctica and Australia as the Ferrar Province.
- Full Text:
- Date Issued: 1997
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