Stratigraphic correlation of the Awahab and Tafelberg Formations, Etendeka Group, Namibia, and location of an eruptive site for flood basalt volcanism
- Marsh, Julian S, Milner, Simon C
- Authors: Marsh, Julian S , Milner, Simon C
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6738 , http://hdl.handle.net/10962/d1007552 , http://dx.doi.org/10.1016/j.jafrearsci.2007.04.004
- Description: Detailed field and geochemical investigations in the vicinity of the type section of the Tafelberg Formation of the early Cretaceous Etendeka Group, NW Namibia, have revealed the existence of a large eruptive vent in the lower part of the regional volcanic sequence produced by Strombolian and Vulcanian eruptions. The vent is filled with the thick, differentiated, ponded Kudu-Run olivine-rich basaltic flow, which has a distinctive low Zr/Y geochemical signature as well as a Tafelberg-type tabular basalt and the Nil Desperandum latite. Field evidence indicates that the Kudu-Run basalt and the latite were erupted from fissures located within the vent. Associated with the vent is an extensive pyroclastic apron extending from the vent edge and which is interbedded with the regional stratigraphy. Blocks of Precambrain basement lithologies occur within this deposit and indicate that the vent was excavated to a depth of at least 350 m below the palaeosurface at that time. The original Tafelberg Formation type section described by Erlank et al. [Erlank, A.J., Marsh, J.S., Duncan, A.R., Miller, R.McG., Hawkesworth, C.H., Betton, P.J., Rex, D.C. 1984. Geochemistry and petrogenesis of the Etendeka volcanic rocks from SWA/Namibia, 195–247. In: Erlank, A.J. (Ed.), Petrogenesis of Volcanic Rocks of the Karoo province. Special Publication of the Geological Society of South Africa, vol. 13, 395 p.] the Tafelberg Gully section, crosses from the lower part of the regional sequence into the intra-vent sequence and returns to the regional sequence higher up. In doing so it includes some of the localized intra-vent flows and excludes a number of flows which are part of the regional sequence in its lower part, thus rendering it inappropriate as a type section. A revised type section for the Tafelberg Formation is described by combining the upper part of the Tafelberg Gully section with a new section of 14 flows at the base of the regional sequence in the Tafelberg North (TBN) section some 2 km N of the Tafeleberg Gully. Distinctive flows in the TBN section can be mapped southwards where their precise stratigraphic relationship to the northward-thinning Springbok and Goboboseb Quarts Latite members of the Awahab Formation can be demonstrated. These stratigraphic relationships are entirely consistent with palaeomagnetic reversal stratigraphy and demonstrate that the same N–R–N polarity sequence occurs in the type sections of the Awahab and Tafelberg formations. Thus, the Awahab and Tafelberg magma systems were contemporaneous but the Tafelberg system outlived that of the Awahab. The Awahab system was built from eruptive centres located S of the Huab River whereas the Tafelberg vents were located further north. , Full text article access in Journal of African Earth Sciences, 48 (5). pp. 329-340. Available: http://dx.doi.org/10.1016/j.jafrearsci.2007.04.004
- Full Text: false
- Date Issued: 2007
- Authors: Marsh, Julian S , Milner, Simon C
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6738 , http://hdl.handle.net/10962/d1007552 , http://dx.doi.org/10.1016/j.jafrearsci.2007.04.004
- Description: Detailed field and geochemical investigations in the vicinity of the type section of the Tafelberg Formation of the early Cretaceous Etendeka Group, NW Namibia, have revealed the existence of a large eruptive vent in the lower part of the regional volcanic sequence produced by Strombolian and Vulcanian eruptions. The vent is filled with the thick, differentiated, ponded Kudu-Run olivine-rich basaltic flow, which has a distinctive low Zr/Y geochemical signature as well as a Tafelberg-type tabular basalt and the Nil Desperandum latite. Field evidence indicates that the Kudu-Run basalt and the latite were erupted from fissures located within the vent. Associated with the vent is an extensive pyroclastic apron extending from the vent edge and which is interbedded with the regional stratigraphy. Blocks of Precambrain basement lithologies occur within this deposit and indicate that the vent was excavated to a depth of at least 350 m below the palaeosurface at that time. The original Tafelberg Formation type section described by Erlank et al. [Erlank, A.J., Marsh, J.S., Duncan, A.R., Miller, R.McG., Hawkesworth, C.H., Betton, P.J., Rex, D.C. 1984. Geochemistry and petrogenesis of the Etendeka volcanic rocks from SWA/Namibia, 195–247. In: Erlank, A.J. (Ed.), Petrogenesis of Volcanic Rocks of the Karoo province. Special Publication of the Geological Society of South Africa, vol. 13, 395 p.] the Tafelberg Gully section, crosses from the lower part of the regional sequence into the intra-vent sequence and returns to the regional sequence higher up. In doing so it includes some of the localized intra-vent flows and excludes a number of flows which are part of the regional sequence in its lower part, thus rendering it inappropriate as a type section. A revised type section for the Tafelberg Formation is described by combining the upper part of the Tafelberg Gully section with a new section of 14 flows at the base of the regional sequence in the Tafelberg North (TBN) section some 2 km N of the Tafeleberg Gully. Distinctive flows in the TBN section can be mapped southwards where their precise stratigraphic relationship to the northward-thinning Springbok and Goboboseb Quarts Latite members of the Awahab Formation can be demonstrated. These stratigraphic relationships are entirely consistent with palaeomagnetic reversal stratigraphy and demonstrate that the same N–R–N polarity sequence occurs in the type sections of the Awahab and Tafelberg formations. Thus, the Awahab and Tafelberg magma systems were contemporaneous but the Tafelberg system outlived that of the Awahab. The Awahab system was built from eruptive centres located S of the Huab River whereas the Tafelberg vents were located further north. , Full text article access in Journal of African Earth Sciences, 48 (5). pp. 329-340. Available: http://dx.doi.org/10.1016/j.jafrearsci.2007.04.004
- Full Text: false
- Date Issued: 2007
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
Volcanic rocks of the Witwatersrand Triad, South Africa. II: petrogenesis of mafic and felsic rocks of the Dominion Group
- Marsh, Julian S, Bowen, M P, Rogers, N W, Bowen, T B
- Authors: Marsh, Julian S , Bowen, M P , Rogers, N W , Bowen, T B
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140443 , vital:37889 , https://doi.org/10.1016/0301-9268(89)90075-2
- Description: A bimodal suite of volcanic rocks builds the bulk of the Dominion Group which, with an age of ∼ 2.72 Ga, is the oldest cover sequence overlying the granite-greenstone Archaean basement of the Kaapvaal craton in the western Transvaal, South Africa. The basic lavas are relatively rich in SiO2 (50–58%) and aphyric and exhibit a large compositional range. This variation is typically tholeiitic in that it is characterized by strong enrichment of Ti, Fe, and V in differentiated lavas.
- Full Text: false
- Date Issued: 2003
- Authors: Marsh, Julian S , Bowen, M P , Rogers, N W , Bowen, T B
- Date: 2003
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140443 , vital:37889 , https://doi.org/10.1016/0301-9268(89)90075-2
- Description: A bimodal suite of volcanic rocks builds the bulk of the Dominion Group which, with an age of ∼ 2.72 Ga, is the oldest cover sequence overlying the granite-greenstone Archaean basement of the Kaapvaal craton in the western Transvaal, South Africa. The basic lavas are relatively rich in SiO2 (50–58%) and aphyric and exhibit a large compositional range. This variation is typically tholeiitic in that it is characterized by strong enrichment of Ti, Fe, and V in differentiated lavas.
- Full Text: false
- Date Issued: 2003
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
New chemical analyses of the Suurberg volcanic rocks and their significance in relation to Mesozoic volcanism in Southern Africa
- Marsh, Julian S, Lock, B E, Fuchter, W H
- Authors: Marsh, Julian S , Lock, B E , Fuchter, W H
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133231 , vital:36951
- Description: Volcanic rocks are found associated with several of the late Mesozoic basins of southern South Africa. Bentonites are known from Plettenberg Bay and, according to an unconfirmed report, they are also found in the Worcester Basin, while vitric tuffs have been recorded from east of Oudtshoorn. The most extensive occurrences, however, are those of the Suurberg Group, which crops out sporadically around the margins of the Algoa Basin.
- Full Text:
- Date Issued: 1979
- Authors: Marsh, Julian S , Lock, B E , Fuchter, W H
- Date: 1979
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/133231 , vital:36951
- Description: Volcanic rocks are found associated with several of the late Mesozoic basins of southern South Africa. Bentonites are known from Plettenberg Bay and, according to an unconfirmed report, they are also found in the Worcester Basin, while vitric tuffs have been recorded from east of Oudtshoorn. The most extensive occurrences, however, are those of the Suurberg Group, which crops out sporadically around the margins of the Algoa Basin.
- Full Text:
- Date Issued: 1979
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
Petrology of the alkaline core of the Messum igneous complex, Namibia: evidence for the progressively decreasing effect of crustal contamination
- Harris, Chris, Marsh, Julian S, Milner, Simon C
- Authors: Harris, Chris , Marsh, Julian S , Milner, Simon C
- Date: 1999
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149746 , vital:38880 , https://doi.org/10.1093/petroj/40.9.1377
- Description: The Messum complex of NW Namibia, a part of the Paraná–Etendeka volcanic province, consists of a dominantly felsic central core, surrounded by older gabbros. The igneous rocks of the core can be divided, in order of decreasing age, into (1) a sub-alkaline suite, (2) an outer quartz syenite suite, and (3) an inner silica-undersaturated suite dominated by nepheline syenite. Compositional differences within the quartz syenite suite can be explained by fractional crystallization, but Sr- and O-isotope data indicate that these rocks contain a significant crustal component.
- Full Text: false
- Date Issued: 1999
- Authors: Harris, Chris , Marsh, Julian S , Milner, Simon C
- Date: 1999
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149746 , vital:38880 , https://doi.org/10.1093/petroj/40.9.1377
- Description: The Messum complex of NW Namibia, a part of the Paraná–Etendeka volcanic province, consists of a dominantly felsic central core, surrounded by older gabbros. The igneous rocks of the core can be divided, in order of decreasing age, into (1) a sub-alkaline suite, (2) an outer quartz syenite suite, and (3) an inner silica-undersaturated suite dominated by nepheline syenite. Compositional differences within the quartz syenite suite can be explained by fractional crystallization, but Sr- and O-isotope data indicate that these rocks contain a significant crustal component.
- Full Text: false
- Date Issued: 1999
Strontium isotope characterization of Karoo volcanic rocks
- Bristow, J W, Allsopp, H L, Erlank, Anthony J, Marsh, Julian S, Armstrong, R A
- Authors: Bristow, J W , Allsopp, H L , Erlank, Anthony J , Marsh, Julian S , Armstrong, R A
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/134176 , vital:37081 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6453595
- Description: Karoo volcanics of both mafic and felsic composition cover large areas of southern Africa, and are characterized by considerable ranges in their initial 87Sr/86Sr (i.e. Ro) ratios. Mafic volcanics from the eastern and western continental margins show the greatest range in Ro ratios, i.e. Lebombo-Nuanetsi area: 0.7035-0.7134 and Etendeka: 0.7030-0.7135 respectively. In the Central Karoo area the mafic rocks show a smaller spread of ratios: 0.7046-0.7094.
- Full Text:
- Date Issued: 1984
- Authors: Bristow, J W , Allsopp, H L , Erlank, Anthony J , Marsh, Julian S , Armstrong, R A
- Date: 1984
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/134176 , vital:37081 , https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetailamp;idt=6453595
- Description: Karoo volcanics of both mafic and felsic composition cover large areas of southern Africa, and are characterized by considerable ranges in their initial 87Sr/86Sr (i.e. Ro) ratios. Mafic volcanics from the eastern and western continental margins show the greatest range in Ro ratios, i.e. Lebombo-Nuanetsi area: 0.7035-0.7134 and Etendeka: 0.7030-0.7135 respectively. In the Central Karoo area the mafic rocks show a smaller spread of ratios: 0.7046-0.7094.
- Full Text:
- Date Issued: 1984
Karoo and Etendeks flood basalt provinces, southern Africa and the tectonic development of their adjacent margins:
- Marsh, Julian S, Watkeys, M K
- Authors: Marsh, Julian S , Watkeys, M K
- Date: 1996
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144868 , vital:38386
- Description: Southern Africa hosts remnants of two continental flood basalt provinces emplaced in association with fragmentation of Gondwana. The earliest is the 183 Ma Karoo Province whose relationship to continental breakup and sea floor spreading is complex. Geochemical stratigraphy, Ar-Ar Dating and palaeomagnetism indicate that Karoo mafic igneous rocks throughout Southern Africa were emplaced over a very short interval at 183 Ma.
- Full Text:
- Date Issued: 1996
- Authors: Marsh, Julian S , Watkeys, M K
- Date: 1996
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144868 , vital:38386
- Description: Southern Africa hosts remnants of two continental flood basalt provinces emplaced in association with fragmentation of Gondwana. The earliest is the 183 Ma Karoo Province whose relationship to continental breakup and sea floor spreading is complex. Geochemical stratigraphy, Ar-Ar Dating and palaeomagnetism indicate that Karoo mafic igneous rocks throughout Southern Africa were emplaced over a very short interval at 183 Ma.
- Full Text:
- Date Issued: 1996
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
Karoo volcanic and intrusive rocks: Lesotho and Eastern Cape
- Authors: Marsh, Julian S
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144890 , vital:38388
- Description: The Karoo Igneous Province is one of the classic Mesozoic continental flood basalt provinces. At present erosion levels it comprises numerous eroded remnants of an extensive, thick volcanic sequence (largely lava flows) and a well-exposed subvolcanic intrusive complex of dykes and sheets which are particularly abundant in the underlying Karoo sedimentary strata.
- Full Text:
- Date Issued: 2013
- Authors: Marsh, Julian S
- Date: 2013
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144890 , vital:38388
- Description: The Karoo Igneous Province is one of the classic Mesozoic continental flood basalt provinces. At present erosion levels it comprises numerous eroded remnants of an extensive, thick volcanic sequence (largely lava flows) and a well-exposed subvolcanic intrusive complex of dykes and sheets which are particularly abundant in the underlying Karoo sedimentary strata.
- Full Text:
- Date Issued: 2013
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, G, Robey, J V A
- Authors: Hanson, E Kelsey , Moore, John M , Bordy, Emese M , Marsh, Julian S , Howarth, G , Robey, J V A
- 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, G , Robey, J V A
- 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
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
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 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
The mineralogy, petrology, and origin of the Merensky cyclic unit in the western Bushveld Complex
- Kruger, Floris J, Marsh, Julian S
- Authors: Kruger, Floris J , Marsh, Julian S
- Date: 1985
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136024 , vital:37329 , https://doi.org/10.2113/gsecongeo.80.4.958
- Description: The Merensky cyclic unit of the Bushveld Complex represents the first products to crystallize after the influx and mixing of a large new batch of magma in the chamber. Excluding the Merensky pegmatoid, the Merensky cyclic unit grades upward from an orthopyroxenite at the base, through norite to anorthosite at the top of the sequence. It is followed by the very similar Bastard cyclic unit.
- Full Text: false
- Date Issued: 1985
- Authors: Kruger, Floris J , Marsh, Julian S
- Date: 1985
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/136024 , vital:37329 , https://doi.org/10.2113/gsecongeo.80.4.958
- Description: The Merensky cyclic unit of the Bushveld Complex represents the first products to crystallize after the influx and mixing of a large new batch of magma in the chamber. Excluding the Merensky pegmatoid, the Merensky cyclic unit grades upward from an orthopyroxenite at the base, through norite to anorthosite at the top of the sequence. It is followed by the very similar Bastard cyclic unit.
- Full Text: false
- Date Issued: 1985
Geochemical stratigraphy of the Mohale Dame-Katse Dam areas, Lesotho. Report on contract LHDA, Mohale Tunnel: Sampling and Testing of Cores. Lesotho Highlands Tunnel Partnership (Mohale)
- Authors: Marsh, Julian S
- Date: 1996
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144857 , vital:38385
- Description: In monotonous basalt sequences, such as the Karoo basalt sequence in Lesotho, geochemistry can be a useful adjunct to stratigraphic studies. The acceptance of geochemical criteria in defining stratigraphic units arises from work in the Columbia River Group in NW SA (Swanson et al., 1979) and is now widely employed. It has recently been successfully applied in the Karoo basalts (Marsh et al., in press). In the current investigation a stratigraphic framework for construction work related to the Katse-Mohale tunnel has been developed using the compositions of basalt samples collected from a number of borehole cores in relation to the geochemical stratigraphy of Marshet al. (in press).
- Full Text:
- Date Issued: 1996
- Authors: Marsh, Julian S
- Date: 1996
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/144857 , vital:38385
- Description: In monotonous basalt sequences, such as the Karoo basalt sequence in Lesotho, geochemistry can be a useful adjunct to stratigraphic studies. The acceptance of geochemical criteria in defining stratigraphic units arises from work in the Columbia River Group in NW SA (Swanson et al., 1979) and is now widely employed. It has recently been successfully applied in the Karoo basalts (Marsh et al., in press). In the current investigation a stratigraphic framework for construction work related to the Katse-Mohale tunnel has been developed using the compositions of basalt samples collected from a number of borehole cores in relation to the geochemical stratigraphy of Marshet al. (in press).
- Full Text:
- Date Issued: 1996
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 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 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