Sub-volcanic intrusions and the link to global climatic and environmental changes:
- Svensen, Henrik H, Planke, Sverre, Neumann, Else-Ragnhild, Aarnes, Ingrid, Marsh, Julian S, Polteau, Stéphane, Harstad, Camilla H, Chevallier, Luc
- 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.
- Full Text:
- Date Issued: 2018
- 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.
- Full Text:
- Date Issued: 2018
Petrology and geochemistry of peridotite xenoliths from the Letlhakane kimberlites, Botswana
- Stiefenhofer, Johann, Viljoen, K S, Marsh, Julian S
- Authors: Stiefenhofer, Johann , Viljoen, K S , Marsh, Julian S
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149705 , vital:38876 , https://doi.org/10.1007/s004100050272
- Description: The diamondiferous Letlhakane kimberlites are intruded into the Proterozoic Magondi Belt of Botswana. Given the general correlation of diamondiferous kimberlites with Archaean cratons, the apparent tectonic setting of these kimberlites is somewhat anomalous. Xenoliths in kimberlite diatremes provide a window into the underlying crust and upper mantle and, with the aid of detailed petrological and geochemical study, can help unravel problems of tectonic setting.
- Full Text: false
- Date Issued: 1997
- Authors: Stiefenhofer, Johann , Viljoen, K S , Marsh, Julian S
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149705 , vital:38876 , https://doi.org/10.1007/s004100050272
- Description: The diamondiferous Letlhakane kimberlites are intruded into the Proterozoic Magondi Belt of Botswana. Given the general correlation of diamondiferous kimberlites with Archaean cratons, the apparent tectonic setting of these kimberlites is somewhat anomalous. Xenoliths in kimberlite diatremes provide a window into the underlying crust and upper mantle and, with the aid of detailed petrological and geochemical study, can help unravel problems of tectonic setting.
- Full Text: false
- Date Issued: 1997
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
The Marinkas Quellen Carbonatite Complex, southern Namibia: carbonatite magmatism with an uncontaminated depleted mantle signature in a continental setting
- Smithies, Robert H, Marsh, Julian S
- Authors: Smithies, Robert H , Marsh, Julian S
- Date: 1998
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149736 , vital:38879 , https://doi.org/10.1016/S0009-2541(98)00029-1
- Description: The Marinkas Quellen Carbonatite Complex, in southern Namibia, forms part of the ca. 490–550 Ma Kuboos-Bremen Igneous Province, a zone of alkaline igneous rocks that intrude the Mesoproterzoic to Paleoproterozoic Namaqualand Metamorphic Province and Neoproterozoic platform sediments. The carbonatite complex includes Ca-rich, Mg-rich and Fe-rich carbonatites as well as late ferrocarbonatite dykes that show extreme enrichments in Mn, REE and Th. Compared to most carbonatites, those at Marinkas Quellen are generally depleted in most trace elements, particularly Ba and the LREE.
- Full Text: false
- Date Issued: 1998
- Authors: Smithies, Robert H , Marsh, Julian S
- Date: 1998
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149736 , vital:38879 , https://doi.org/10.1016/S0009-2541(98)00029-1
- Description: The Marinkas Quellen Carbonatite Complex, in southern Namibia, forms part of the ca. 490–550 Ma Kuboos-Bremen Igneous Province, a zone of alkaline igneous rocks that intrude the Mesoproterzoic to Paleoproterozoic Namaqualand Metamorphic Province and Neoproterozoic platform sediments. The carbonatite complex includes Ca-rich, Mg-rich and Fe-rich carbonatites as well as late ferrocarbonatite dykes that show extreme enrichments in Mn, REE and Th. Compared to most carbonatites, those at Marinkas Quellen are generally depleted in most trace elements, particularly Ba and the LREE.
- Full Text: false
- Date Issued: 1998
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
The emplacement of class 1 kimberlites: part 2, petrographic evidence
- Skinner, E M W, Marsh, Julian S
- Authors: Skinner, E M W , Marsh, Julian S
- Date: 2006
- Language: English
- Type: text , Long abstract
- Identifier: http://hdl.handle.net/10962/132740 , vital:36878
- Description: This paper has been prepared specifically for the September 2006, Kimberlite Emplacement Workshop, Saskatoon, Canada. To this end, emphasis is placed on a big bang/ bottom-up model for the emplacement of Class 1 kimberlite pipes first presented by Clement and Reid (1989) and reinforced by Skinner and Marsh (2004). In this part (Part 2) petrographic evidence is presented in support of evidence provided by the synthesis of specific geological features as presented in Part 1.
- Full Text:
- Date Issued: 2006
- Authors: Skinner, E M W , Marsh, Julian S
- Date: 2006
- Language: English
- Type: text , Long abstract
- Identifier: http://hdl.handle.net/10962/132740 , vital:36878
- Description: This paper has been prepared specifically for the September 2006, Kimberlite Emplacement Workshop, Saskatoon, Canada. To this end, emphasis is placed on a big bang/ bottom-up model for the emplacement of Class 1 kimberlite pipes first presented by Clement and Reid (1989) and reinforced by Skinner and Marsh (2004). In this part (Part 2) petrographic evidence is presented in support of evidence provided by the synthesis of specific geological features as presented in Part 1.
- Full Text:
- Date Issued: 2006
The emplacement of class 1 kimberlites: part 1, evidence of geological features
- Skinner, E M W, Marsh, Julian S
- Authors: Skinner, E M W , Marsh, Julian S
- Date: 2006
- Language: English
- Type: text , Long abstract
- Identifier: http://hdl.handle.net/10962/132729 , vital:36877
- Description: This paper has been prepared specifically for the September 2006, Kimberlite Emplacement Workshop, Saskatoon, Canada. To this end, emphasis is placed on a big bang/ bottom-up model for the emplacement of Class 1 kimbertite pipes first presented by Clement and Reid (1989) and reinforced by Skinner and Marsh (2004). In this part (Part 1) the evidence of various geological features is presented.
- Full Text:
- Date Issued: 2006
- Authors: Skinner, E M W , Marsh, Julian S
- Date: 2006
- Language: English
- Type: text , Long abstract
- Identifier: http://hdl.handle.net/10962/132729 , vital:36877
- Description: This paper has been prepared specifically for the September 2006, Kimberlite Emplacement Workshop, Saskatoon, Canada. To this end, emphasis is placed on a big bang/ bottom-up model for the emplacement of Class 1 kimbertite pipes first presented by Clement and Reid (1989) and reinforced by Skinner and Marsh (2004). In this part (Part 1) the evidence of various geological features is presented.
- Full Text:
- Date Issued: 2006
The geochemistry of potassic lavas from Vulsini, central Italy and implications for mantle enrichment processes beneath the Roman region
- Rogers, N W, Hawkesworth, C J, Parker, R J, Marsh, Julian S
- Authors: Rogers, N W , Hawkesworth, C J , Parker, R J , Marsh, Julian S
- Date: 1985
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136034 , vital:37330 , https://doi.org/10.1007/BF00378265
- Description: Major and trace element and 143Nd/144Nd (0.51209–0.51216) and 87Sr/86Sr (0.70879–0.71105) isotope analyses are presented on a representative group of lavas from the Vulsini district of the Roman magmatic province. Three distinct series are identified; the high-K and low-K series are similar to those described from other Italian volcanoes, while the third is represented by a group of relatively undifferentiated leucite basanites which are thought to be near-primary mantle melts.
- Full Text: false
- Date Issued: 1985
- Authors: Rogers, N W , Hawkesworth, C J , Parker, R J , Marsh, Julian S
- Date: 1985
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136034 , vital:37330 , https://doi.org/10.1007/BF00378265
- Description: Major and trace element and 143Nd/144Nd (0.51209–0.51216) and 87Sr/86Sr (0.70879–0.71105) isotope analyses are presented on a representative group of lavas from the Vulsini district of the Roman magmatic province. Three distinct series are identified; the high-K and low-K series are similar to those described from other Italian volcanoes, while the third is represented by a group of relatively undifferentiated leucite basanites which are thought to be near-primary mantle melts.
- Full Text: false
- Date Issued: 1985
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
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
The petrology and significance of a stratiform mafic segregation pegmatite in a Karoo-aged dolerite sheet
- Mitchell, Andrew A, Naicker, S B, Marsh, Julian S, Dunlevey, J N
- 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.
- Full Text:
- Date Issued: 1997
- 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.
- Full Text:
- Date Issued: 1997
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
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
The Luderitz Alkaline Province, South West Africa II: metasomatism and assimilation in the contact aureole of the Granitberg Foyaite Complex
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132963 , vital:36913
- Description: Reactions between the Outer Foyaite magma of the Granitberg Complex and the sedimentary country rocks are striking. At sandstone contacts the magma has assimilated quartz-rich sedimentary material and a suite of pulaskites, peralkaline nordmarkites, and peralkaline granites have been generated by a complex process involving both assimilation and crystal fractionation.
- Full Text:
- Date Issued: 1975
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132963 , vital:36913
- Description: Reactions between the Outer Foyaite magma of the Granitberg Complex and the sedimentary country rocks are striking. At sandstone contacts the magma has assimilated quartz-rich sedimentary material and a suite of pulaskites, peralkaline nordmarkites, and peralkaline granites have been generated by a complex process involving both assimilation and crystal fractionation.
- Full Text:
- Date Issued: 1975
Geochemical variations in a long Karoo dyke, Eastern Cape
- Marsh, Julian S, Mndaweni, M J
- 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.
- Full Text:
- Date Issued: 1998
- 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.
- Full Text:
- Date Issued: 1998
The Luderitz Alkaline Province, South West Africa I: descriptive petrology of the Granitberg Foyaite Complex
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132951 , vital:36912
- Description: The Granitberg foyaite complex is one of three known alkaline igneous complexes, which, together with a dyke swarm, constitute the Liüderitz Alkaline Province of Lower Cretaceous age. The near-circular complex is emplaced into dolomites and sandstones of the Bogenfels Formation. A large fragment of these sedimentary rocks, originally forming the roof of the intrusion, is preserved in the centre of the complex.
- Full Text:
- Date Issued: 1975
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132951 , vital:36912
- Description: The Granitberg foyaite complex is one of three known alkaline igneous complexes, which, together with a dyke swarm, constitute the Liüderitz Alkaline Province of Lower Cretaceous age. The near-circular complex is emplaced into dolomites and sandstones of the Bogenfels Formation. A large fragment of these sedimentary rocks, originally forming the roof of the intrusion, is preserved in the centre of the complex.
- Full Text:
- Date Issued: 1975
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
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, A R
- 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
- 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
The late Archaean Dominion Group, South Africa: petrogenesis of flood-type basalts and their mantle sources
- Marsh, Julian S, Rogers, N W, Bowen, M P, Bowen, T B
- Authors: Marsh, Julian S , Rogers, N W , Bowen, M P , Bowen, T B
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131690 , vital:36721
- Description: The Dominion group has an age of 2.7 - 2.8 Ga and is the earliest of the cover sequences overlying the granite greenstone terrane in the western part of the Archaean Kaapvaal Craton, southern Africa. The Dominion group is largely built of volcanic rocks and is preserved over an area of 15,000 km² with a maximum thickness of 2.7 km.
- Full Text:
- Date Issued: 1988
- Authors: Marsh, Julian S , Rogers, N W , Bowen, M P , Bowen, T B
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131690 , vital:36721
- Description: The Dominion group has an age of 2.7 - 2.8 Ga and is the earliest of the cover sequences overlying the granite greenstone terrane in the western part of the Archaean Kaapvaal Craton, southern Africa. The Dominion group is largely built of volcanic rocks and is preserved over an area of 15,000 km² with a maximum thickness of 2.7 km.
- Full Text:
- Date Issued: 1988
Supplying lava eruptions in the Karoo Province, South Africa: a geochemical comparison of the volcanic sequence with intrusions in the main Karoo basin
- Authors: Marsh, Julian S , Mitha, V R
- Date: 2006
- Language: English
- Type: text , abstract
- Identifier: http://hdl.handle.net/10962/132873 , vital:36901
- Description: Magma supply for lava eruptions remains a poorly understood facet of continental flood volcanism. In the Karoo Province a vast complex of dolerite sheets and dykes is exposed in the main Karoo sedimentary basin underlying the flood basalt remnant of Lesotho (Drakensberg Group) suggesting that lavas were erupted locally from a widely distributed network of fissures.
- Full Text:
- Date Issued: 2006
- Authors: Marsh, Julian S , Mitha, V R
- Date: 2006
- Language: English
- Type: text , abstract
- Identifier: http://hdl.handle.net/10962/132873 , vital:36901
- Description: Magma supply for lava eruptions remains a poorly understood facet of continental flood volcanism. In the Karoo Province a vast complex of dolerite sheets and dykes is exposed in the main Karoo sedimentary basin underlying the flood basalt remnant of Lesotho (Drakensberg Group) suggesting that lavas were erupted locally from a widely distributed network of fissures.
- Full Text:
- Date Issued: 2006