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
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
Al/Cr ratios of coexisting pyroxenes and spinellids in some ultramafic rocks
- Eales, Hugh V, Marsh, Julian S
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1983
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133534 , vital:36987 , https://doi.org/10.1016/0009-2541(83)90045-1
- Description: Al/Cr atomic ratios of coexisting spinellids and ortho- and clinopyroxenes show a pattern of sympathetic variation that persists through ultramafic rocks of layered mafic complexes of upper-crustal type, Alpine complexes, and the nodules found in kimberlites and alkaline basalts. Simple expressions are empirically derived to link (Al/Cr) orthopyroxene and (Al/Cr)spinel ratios in putatively equilibrated rocks. Equivalence of spinel compositions in shallow layered complexes and kimberlite nodules of deep-seated origin negates direct crystallochemical control of Al/Cr ratios of spinels by pressure.
- Full Text: false
- Date Issued: 1983
- Authors: Eales, Hugh V , Marsh, Julian S
- Date: 1983
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133534 , vital:36987 , https://doi.org/10.1016/0009-2541(83)90045-1
- Description: Al/Cr atomic ratios of coexisting spinellids and ortho- and clinopyroxenes show a pattern of sympathetic variation that persists through ultramafic rocks of layered mafic complexes of upper-crustal type, Alpine complexes, and the nodules found in kimberlites and alkaline basalts. Simple expressions are empirically derived to link (Al/Cr) orthopyroxene and (Al/Cr)spinel ratios in putatively equilibrated rocks. Equivalence of spinel compositions in shallow layered complexes and kimberlite nodules of deep-seated origin negates direct crystallochemical control of Al/Cr ratios of spinels by pressure.
- Full Text: false
- Date Issued: 1983
Alkaline rocks in the Kuboos-Bremen Igneous Province, southern Namibia: the Grootpenseiland and Marinkas Kwela Complexes
- Smithies, Robert H, Marsh, Julian S
- Authors: Smithies, Robert H , Marsh, Julian S
- Date: 1996
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145838 , vital:38471
- Description: The early Cambrian Kuboos-Bremen Igneous Province of northwestern South Africa and southern Namibia comprises a series of intrusive bodies that collectively encompass virtually the entire range of alkaline rock types. Two of these bodies, the Grootpenseiland and Marinkas Kwela Complexes lie immediately north of the Orange River and are amongst the few that show this wide lithological range on a local scale.
- Full Text:
- Date Issued: 1996
- Authors: Smithies, Robert H , Marsh, Julian S
- Date: 1996
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145838 , vital:38471
- Description: The early Cambrian Kuboos-Bremen Igneous Province of northwestern South Africa and southern Namibia comprises a series of intrusive bodies that collectively encompass virtually the entire range of alkaline rock types. Two of these bodies, the Grootpenseiland and Marinkas Kwela Complexes lie immediately north of the Orange River and are amongst the few that show this wide lithological range on a local scale.
- Full Text:
- Date Issued: 1996
An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt: Naude's Nek section (South Africa)
- Moulin, Maud, Fluteau, Frédéric, Courtillot, Vincent, Marsh, Julian S, Delpech, Guillaume, Quidelleur, Xavier, Gérard, Martine, Jay, Anne E
- 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.
- Full Text:
- Date Issued: 2011
- 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.
- Full Text:
- Date Issued: 2011
Asthenospheric and lithospheric sources for Mesozoic dolerites from Liberia (Africa): trace element and isotopic evidence
- Dupuy, C, Marsh, Julian S, Dostal, J, Michard, A, Testa, S
- Authors: Dupuy, C , Marsh, Julian S , Dostal, J , Michard, A , Testa, S
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140422 , vital:37887 , https://doi.org/10.1016/0012-821X(88)90067-2
- Description: Combined elemental, and Sr and Nd isotopic data are presented for Mesozoic dolerite dikes of Liberia (Africa) which are related to the initial stage of opening of the Atlantic Ocean.
- Full Text: false
- Date Issued: 2002
- Authors: Dupuy, C , Marsh, Julian S , Dostal, J , Michard, A , Testa, S
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140422 , vital:37887 , https://doi.org/10.1016/0012-821X(88)90067-2
- Description: Combined elemental, and Sr and Nd isotopic data are presented for Mesozoic dolerite dikes of Liberia (Africa) which are related to the initial stage of opening of the Atlantic Ocean.
- Full Text: false
- Date Issued: 2002
Basalt geochemistry and tectonic discrimination within continental flood basalt provinces
- Authors: Marsh, Julian S
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140412 , vital:37886 , https://doi.org/10.1016/0377-0273(87)90035-7
- Description: Continental flood basalts are usually regarded as a single tectonomagmatic entity but frequently quoted examples exhibit a variety of tectonic settings. In one well-studied, classic, flood basalt province, the Mesozoic Karoo province of southern Africa, magmatism occurred in the following tectonic settings: (a) continental rifting leading to ocean-floor spreading in the South Atlantic Ocean (Etendeka suite of Namibia); (b) stretched continental lithosphere and rifting not leading directly to ocean-floor formation (Lebombo suite of southeastern Africa); and (c) an a-tectonic, within-plate, continental setting characterized by an absence of faulting or warping (Lesotho highlands and Karoo dolerites of South Africa).
- Full Text: false
- Date Issued: 2003
- Authors: Marsh, Julian S
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140412 , vital:37886 , https://doi.org/10.1016/0377-0273(87)90035-7
- Description: Continental flood basalts are usually regarded as a single tectonomagmatic entity but frequently quoted examples exhibit a variety of tectonic settings. In one well-studied, classic, flood basalt province, the Mesozoic Karoo province of southern Africa, magmatism occurred in the following tectonic settings: (a) continental rifting leading to ocean-floor spreading in the South Atlantic Ocean (Etendeka suite of Namibia); (b) stretched continental lithosphere and rifting not leading directly to ocean-floor formation (Lebombo suite of southeastern Africa); and (c) an a-tectonic, within-plate, continental setting characterized by an absence of faulting or warping (Lesotho highlands and Karoo dolerites of South Africa).
- Full Text: false
- Date Issued: 2003
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
Compositionally diverse magmas erupted close together in space and time within a Karoo flood basalt crater complex:
- McClintock, Murray, Marsh, Julian S, White, James D L
- Authors: McClintock, Murray , Marsh, Julian S , White, James D L
- Date: 2008
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144966 , vital:38396 , https://doi.org/10.1007/s00445-007-0178-6
- Description: Geochemical data and mapping from a Karoo flood basalt crater complex reveals new information about the ascent and eruption of magma batches during the earliest phases of flood basalt volcanism. Flood basalt eruptions at Sterkspruit, South Africa began with emplacement of thin lava flows before abruptly switching to explosive phreatomagmatic and magmatic activity that formed a nest of craters, spatter and tuff rings and cones that collectively comprise a crater complex >40 km2 filled by 9–18 km3 of volcaniclastic debris.
- Full Text:
- Date Issued: 2008
- Authors: McClintock, Murray , Marsh, Julian S , White, James D L
- Date: 2008
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144966 , vital:38396 , https://doi.org/10.1007/s00445-007-0178-6
- Description: Geochemical data and mapping from a Karoo flood basalt crater complex reveals new information about the ascent and eruption of magma batches during the earliest phases of flood basalt volcanism. Flood basalt eruptions at Sterkspruit, South Africa began with emplacement of thin lava flows before abruptly switching to explosive phreatomagmatic and magmatic activity that formed a nest of craters, spatter and tuff rings and cones that collectively comprise a crater complex >40 km2 filled by 9–18 km3 of volcaniclastic debris.
- Full Text:
- Date Issued: 2008
Cretaceous erosion in central South Africa: evidence from upper-crustal xenoliths in kimberlite diatremes
- Hanson, E Kelsey, Moore, John M, Bordy, Emese M, Marsh, Julian S, Howarth, Geoffrey H, Robey, Julian van Aardt
- Authors: Hanson, E Kelsey , Moore, John M , Bordy, Emese M , Marsh, Julian S , Howarth, Geoffrey H , Robey, Julian van Aardt
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144978 , vital:38397 , https://doi.org/10.2113/gssajg.112.2.125
- Description: Twelve Group II and fourteen Group I kimberlite diatremes in central South Africa were examined for upper crustal xenoliths in order to estimate the extent of various lithological units of the Karoo Supergroup in the main Karoo basin at times of kimberlite eruption, the Cretaceous erosional history of the area, and the approximate vertical extent of the kimberlite diatremes prior to erosion. Sandstone and amygdaloidal basaltic lava xenoliths from the Karoo Supergroup were specifically selected as their modal mineralogies and geochemical compositions respectively can be attributed to specific stratigraphic positions within the Karoo Supergroup. Results indicated that, at the time of Group II kimberlite eruption (120 Ma), basaltic lavas of the Drakensberg Group covered the entire area, but by the time of Group I kimberlite eruption (85 Ma), they were restricted to the south-eastern half of the study area.
- Full Text:
- Date Issued: 2009
- Authors: Hanson, E Kelsey , Moore, John M , Bordy, Emese M , Marsh, Julian S , Howarth, Geoffrey H , Robey, Julian van Aardt
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144978 , vital:38397 , https://doi.org/10.2113/gssajg.112.2.125
- Description: Twelve Group II and fourteen Group I kimberlite diatremes in central South Africa were examined for upper crustal xenoliths in order to estimate the extent of various lithological units of the Karoo Supergroup in the main Karoo basin at times of kimberlite eruption, the Cretaceous erosional history of the area, and the approximate vertical extent of the kimberlite diatremes prior to erosion. Sandstone and amygdaloidal basaltic lava xenoliths from the Karoo Supergroup were specifically selected as their modal mineralogies and geochemical compositions respectively can be attributed to specific stratigraphic positions within the Karoo Supergroup. Results indicated that, at the time of Group II kimberlite eruption (120 Ma), basaltic lavas of the Drakensberg Group covered the entire area, but by the time of Group I kimberlite eruption (85 Ma), they were restricted to the south-eastern half of the study area.
- Full Text:
- Date Issued: 2009
Cretaceous volcanic rocks of the Namibe Basin, southern Angola: report on a reconnaissance field and geochemical investigation
- Authors: Marsh, Julian S
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/67301 , vital:29070
- Description: publisher version , Mafic alkaline lavas and intrusions occur in the onshore Namibe Basin in southern Angola. The distribution and field relationships of these igneous rocks have been mapped and described by Carvalho (1961). During a reconnaissance field visit in June 2009 a suite of samples was collected for further investigation.
- Full Text:
- Date Issued: 2010
- Authors: Marsh, Julian S
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/67301 , vital:29070
- Description: publisher version , Mafic alkaline lavas and intrusions occur in the onshore Namibe Basin in southern Angola. The distribution and field relationships of these igneous rocks have been mapped and described by Carvalho (1961). During a reconnaissance field visit in June 2009 a suite of samples was collected for further investigation.
- Full Text:
- Date Issued: 2010
Distinct kimberlite pipe classes with contrasting eruption processes
- Skinner, E M W, Marsh, Julian S
- Authors: Skinner, E M W , Marsh, Julian S
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150603 , vital:38988 , https://doi.org/10.1016/j.lithos.2004.03.044
- Description: Field and Scott Smith [Field, M., Scott Smith, B.H., 1999. Contrasting geology and near-surface emplacement of kimberlite pipes in southern Africa and Canada. Proc. 7th Int. Kimb. Conf. (Eds. Gurney et al.) 1, 214–237.] propose that kimberlite pipes can be grouped into three types or classes. Classical or Class 1 pipes are the only class with characteristic low temperature, diatreme-facies kimberlite in addition to hypabyssal- and crater-facies kimberlite. Class 2 and 3 pipes are characterized only by hypabyssal-and crater-facies kimberlite.
- Full Text: false
- Date Issued: 2004
- Authors: Skinner, E M W , Marsh, Julian S
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150603 , vital:38988 , https://doi.org/10.1016/j.lithos.2004.03.044
- Description: Field and Scott Smith [Field, M., Scott Smith, B.H., 1999. Contrasting geology and near-surface emplacement of kimberlite pipes in southern Africa and Canada. Proc. 7th Int. Kimb. Conf. (Eds. Gurney et al.) 1, 214–237.] propose that kimberlite pipes can be grouped into three types or classes. Classical or Class 1 pipes are the only class with characteristic low temperature, diatreme-facies kimberlite in addition to hypabyssal- and crater-facies kimberlite. Class 2 and 3 pipes are characterized only by hypabyssal-and crater-facies kimberlite.
- Full Text: false
- Date Issued: 2004
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
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
Dyke swarms and associated lava formations in the northern Lebombo monocline, Karoo Large Igneous Province, South Africa
- Klausen, Martin B, Marsh, Julian S, Watkeys, M K
- 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.
- Full Text:
- Date Issued: 2006
- 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.
- Full Text:
- Date Issued: 2006
Emplacement of inflated Pāhoehoe flows in the Naude’s Nek Pass, Lesotho remnant, Karoo continental flood basalt province: use of flow-lobe tumuli in understanding flood basalt emplacement
- Jay, Anne E, Marsh, Julian S, Fluteau, F, Courtillot, V
- Authors: Jay, Anne E , Marsh, Julian S , Fluteau, F , Courtillot, V
- Date: 2018
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/60752 , vital:27826 , https://link.springer.com/article/10.1007/s00445-017-1189-6
- Description: Physical volcanological features are presented for a 710-m-thick section, of the Naude’s Nek Pass, within the lower part of the Lesotho remnant of the Karoo Large Igneous Province. The section consists of inflated pāhoehoe lava with thin, impersistent sedimentary interbeds towards the base. There are seven discreet packages of compound and hummocky pāhoehoe lobes containing flow-lobe tumuli, making up approximately 50% of the section. Approximately 45% of the sequence consists of 14 sheet lobes, between 10 and 52-m-thick. The majority of the sheet lobes are in two packages indicating prolonged periods of lava supply capable of producing thick sheet lobes. The other sheet lobes are as individual lobes or pairs, within compound flows, suggesting brief increases in lava supply rate. We suggest, contrary to current belief, that there is no evidence that compound flows are proximal to source and sheet lobes (simple flows) are distal to source and we propose that the presence of flow-lobe tumuli in compound flows could be an indicator that a flow is distal to source. We use detailed, previously published, studies of the Thakurvadi Formation (Deccan Traps) as an example. We show that the length of a lobe and therefore the sections that are ‘medial or distal to source’ are specific to each individual lobe and are dependent on the lava supply of each eruptive event, and as such flow lobe tumuli can be used as an indicator of relative distance from source.
- Full Text:
- Date Issued: 2018
- Authors: Jay, Anne E , Marsh, Julian S , Fluteau, F , Courtillot, V
- Date: 2018
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/60752 , vital:27826 , https://link.springer.com/article/10.1007/s00445-017-1189-6
- Description: Physical volcanological features are presented for a 710-m-thick section, of the Naude’s Nek Pass, within the lower part of the Lesotho remnant of the Karoo Large Igneous Province. The section consists of inflated pāhoehoe lava with thin, impersistent sedimentary interbeds towards the base. There are seven discreet packages of compound and hummocky pāhoehoe lobes containing flow-lobe tumuli, making up approximately 50% of the section. Approximately 45% of the sequence consists of 14 sheet lobes, between 10 and 52-m-thick. The majority of the sheet lobes are in two packages indicating prolonged periods of lava supply capable of producing thick sheet lobes. The other sheet lobes are as individual lobes or pairs, within compound flows, suggesting brief increases in lava supply rate. We suggest, contrary to current belief, that there is no evidence that compound flows are proximal to source and sheet lobes (simple flows) are distal to source and we propose that the presence of flow-lobe tumuli in compound flows could be an indicator that a flow is distal to source. We use detailed, previously published, studies of the Thakurvadi Formation (Deccan Traps) as an example. We show that the length of a lobe and therefore the sections that are ‘medial or distal to source’ are specific to each individual lobe and are dependent on the lava supply of each eruptive event, and as such flow lobe tumuli can be used as an indicator of relative distance from source.
- Full Text:
- Date Issued: 2018
Eruptive history of the Karoo lava flows and their impact on early Jurassic environmental change:
- Moulin, Maud, Fluteau, Frédéric, Courtillot, Vincent, Marsh, Julian S, Delpech, Guillaume, Quidelleur, Xavier, Gérard, Martine
- Authors: Moulin, Maud , Fluteau, Frédéric , Courtillot, Vincent , Marsh, Julian S , Delpech, Guillaume , Quidelleur, Xavier , Gérard, Martine
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145098 , vital:38408 , https://doi.org/10.1002/2016JB013354
- Description: This paper reports new paleomagnetic and geochronologic data from a ~1500 m thick composite section belonging to the Drakensberg group, the thickest remnant of the Karoo lavas in Northern Lesotho. Flow‐by‐flow analysis of paleomagnetic directions reveals 21 magnetic directional groups, corresponding to single eruptive events, and 16 individual lava flows. The new age determinations of lava flows range from 180.1 ± 1.4 to 182.8 ± 2.6 Ma. These data, combined with previous results, allow us to propose that the main part of the Drakensberg group and the Karoo intrusive complex dated around 181–183 Ma may have been erupted over a period as short as 250 kyr and may have coincided with the two main phases of extinction in the Early Toarcian. This scenario agrees well with the discontinuous rhythm of environmental and biotic perturbations in the Late Pliensbachian‐Toarcian interval.
- Full Text:
- Date Issued: 2017
- Authors: Moulin, Maud , Fluteau, Frédéric , Courtillot, Vincent , Marsh, Julian S , Delpech, Guillaume , Quidelleur, Xavier , Gérard, Martine
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145098 , vital:38408 , https://doi.org/10.1002/2016JB013354
- Description: This paper reports new paleomagnetic and geochronologic data from a ~1500 m thick composite section belonging to the Drakensberg group, the thickest remnant of the Karoo lavas in Northern Lesotho. Flow‐by‐flow analysis of paleomagnetic directions reveals 21 magnetic directional groups, corresponding to single eruptive events, and 16 individual lava flows. The new age determinations of lava flows range from 180.1 ± 1.4 to 182.8 ± 2.6 Ma. These data, combined with previous results, allow us to propose that the main part of the Drakensberg group and the Karoo intrusive complex dated around 181–183 Ma may have been erupted over a period as short as 250 kyr and may have coincided with the two main phases of extinction in the Early Toarcian. This scenario agrees well with the discontinuous rhythm of environmental and biotic perturbations in the Late Pliensbachian‐Toarcian interval.
- Full Text:
- Date Issued: 2017
Evolution of a strongly differentiated suite of phonolites from the Klinghardt Mountains, Namibia
- Authors: Marsh, Julian S
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140400 , vital:37885 , https://doi.org/10.1016/0024-4937(87)90023-5
- Description: Phonolites of Tertiary age occur as eroded tholoids, lava flows, ignimbrites, and coulees in the Klinghardt Mountains of southern Namibia. Sixty samples have been analyzed for major and trace elements and fourteen of these for 87SR 86SR. The phonolites lie close to the low-pressure cotectics in Q-Ne-Ks, in keeping with their petrography which indicates that most samples have phenocrysts of both nepheline and sanidine. Na has been variably lost from the rocks during crystallization and devitrification/alteration of hypocrystalline specimens.
- Full Text: false
- Date Issued: 2003
- Authors: Marsh, Julian S
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140400 , vital:37885 , https://doi.org/10.1016/0024-4937(87)90023-5
- Description: Phonolites of Tertiary age occur as eroded tholoids, lava flows, ignimbrites, and coulees in the Klinghardt Mountains of southern Namibia. Sixty samples have been analyzed for major and trace elements and fourteen of these for 87SR 86SR. The phonolites lie close to the low-pressure cotectics in Q-Ne-Ks, in keeping with their petrography which indicates that most samples have phenocrysts of both nepheline and sanidine. Na has been variably lost from the rocks during crystallization and devitrification/alteration of hypocrystalline specimens.
- Full Text: false
- Date Issued: 2003
Evolution of the continental lithosphere: evidence from volcanics and xenoliths in southern Africa
- Hawkesworth, C J, Erlank, Anthony J, Marsh, Julian S, Menzies, M A, Van Calsteren, Peter
- Authors: Hawkesworth, C J , Erlank, Anthony J , Marsh, Julian S , Menzies, M A , Van Calsteren, Peter
- Date: 1983
- Language: English
- Type: text , conference paper
- Identifier: http://hdl.handle.net/10962/133548 , vital:36989 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=9641566
- Description: The geology of southern Africa offers a rare opportunity to study the evolution of a segment of continental lithosphere because its rocks range in age from 3.6 Ga to recent, and over the last 200 Ma both the upper mantle and the crust have been sampled by Karoo and Tertiary volcanism and as xenoliths in kimberlite pipes.
- Full Text:
- Date Issued: 1983
- Authors: Hawkesworth, C J , Erlank, Anthony J , Marsh, Julian S , Menzies, M A , Van Calsteren, Peter
- Date: 1983
- Language: English
- Type: text , conference paper
- Identifier: http://hdl.handle.net/10962/133548 , vital:36989 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=9641566
- Description: The geology of southern Africa offers a rare opportunity to study the evolution of a segment of continental lithosphere because its rocks range in age from 3.6 Ga to recent, and over the last 200 Ma both the upper mantle and the crust have been sampled by Karoo and Tertiary volcanism and as xenoliths in kimberlite pipes.
- Full Text:
- Date Issued: 1983
Excursion to Granitberg and the Klinghardt Mountains, southern Namibia
- Authors: Marsh, Julian S
- Date: 1998
- Language: English
- Type: text , field guide
- Identifier: http://hdl.handle.net/10962/132118 , vital:36801
- Description: Three small subvolcanic intrusions (Granitberg, Pomona and Drachenberg) and associated dykes of Cretaceous age, occur between Bogenfels and Prinzen Bucht, S of Luderitz, Namibia. This field trip will chiefly be concerned with rocks that have crystallized from magmas of nepheline syenite composition.
- Full Text:
- Date Issued: 1998
- Authors: Marsh, Julian S
- Date: 1998
- Language: English
- Type: text , field guide
- Identifier: http://hdl.handle.net/10962/132118 , vital:36801
- Description: Three small subvolcanic intrusions (Granitberg, Pomona and Drachenberg) and associated dykes of Cretaceous age, occur between Bogenfels and Prinzen Bucht, S of Luderitz, Namibia. This field trip will chiefly be concerned with rocks that have crystallized from magmas of nepheline syenite composition.
- Full Text:
- Date Issued: 1998