Oldest rocks from Peninsular India : evidence for Hadean to Neoarchean crustal evolution
- Santosh, M., Tsunogae, T., Mohan, M. Ram, Shaji, E., Yang, Qiong-Yan, Satyanarayanan, M.
- Authors: Santosh, M. , Tsunogae, T. , Mohan, M. Ram , Shaji, E. , Yang, Qiong-Yan , Satyanarayanan, M.
- Date: 2014
- Subjects: Earth - Crust , Earth - History , Geology, Stratigraphic - Archaean , Rocks - India
- Type: Article
- Identifier: uj:5481 , S1342-937X(14)00326-8 , http://hdl.handle.net/10210/13542
- Description: The evolution of continental crust during Hadean and Archean and related geodynamic processes provide important clues to understand the early Earth history. Here we report evidence for Hadean and Eoarchean crust from the fringe of the Coorg Block, one of the oldest crustal blocks in Peninsular India. We present geological, petrological, and geochemical data, together with zircon U-Pb ages and Lu-Hf isotopes from a suite of metaigneous (granitoids, diorite, charnockite, metavolcanics) and metasedimentary (quartz mica schist, calcareous schist, ferruginous quartzite and BIF) rocks. Petrological and geochemical studies indicate that the igneous suite formed from subductionrelated arc magmatism, and that the sedimentary suite represents an imbricated accretionary package of continental shelf sequence and pelagic components. Mineral thermometry suggests metamorphism under temperatures of 710-730°C and pressures up to 8kbar.
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- Authors: Santosh, M. , Tsunogae, T. , Mohan, M. Ram , Shaji, E. , Yang, Qiong-Yan , Satyanarayanan, M.
- Date: 2014
- Subjects: Earth - Crust , Earth - History , Geology, Stratigraphic - Archaean , Rocks - India
- Type: Article
- Identifier: uj:5481 , S1342-937X(14)00326-8 , http://hdl.handle.net/10210/13542
- Description: The evolution of continental crust during Hadean and Archean and related geodynamic processes provide important clues to understand the early Earth history. Here we report evidence for Hadean and Eoarchean crust from the fringe of the Coorg Block, one of the oldest crustal blocks in Peninsular India. We present geological, petrological, and geochemical data, together with zircon U-Pb ages and Lu-Hf isotopes from a suite of metaigneous (granitoids, diorite, charnockite, metavolcanics) and metasedimentary (quartz mica schist, calcareous schist, ferruginous quartzite and BIF) rocks. Petrological and geochemical studies indicate that the igneous suite formed from subductionrelated arc magmatism, and that the sedimentary suite represents an imbricated accretionary package of continental shelf sequence and pelagic components. Mineral thermometry suggests metamorphism under temperatures of 710-730°C and pressures up to 8kbar.
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Lithostratigraphy and depositional environment of the Archaean Nsuze Group, Pongola Supergroup
- Authors: Cole, Edward George
- Date: 2014-07-21
- Subjects: Sedimentation and deposition - South Africa - KwaZulu-Natal , Sedimentation and deposition - Swaziland , Geology, Stratigraphic - Archaean
- Type: Thesis
- Identifier: uj:11722 , http://hdl.handle.net/10210/11447
- Description: M.Sc. (Geology) , Please refer to full text to view abstract
- Full Text:
- Authors: Cole, Edward George
- Date: 2014-07-21
- Subjects: Sedimentation and deposition - South Africa - KwaZulu-Natal , Sedimentation and deposition - Swaziland , Geology, Stratigraphic - Archaean
- Type: Thesis
- Identifier: uj:11722 , http://hdl.handle.net/10210/11447
- Description: M.Sc. (Geology) , Please refer to full text to view abstract
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Stratigraphy of the Archean Mozaan Group in the Kubuta-Mooihoek area, Swaziland
- Authors: Nhleko, Noah
- Date: 2012-08-22
- Subjects: Geology, Stratigraphic - Archaean , Geology - South Africa - KwaZulu-Natal
- Type: Thesis
- Identifier: uj:2980 , http://hdl.handle.net/10210/6405
- Description: M.Sc. , Known outcrops of the supracrustal Mesoarchean Mozaan Group of the Pongola Supergroup occur in north-eastern Kwazulu-Natal and southern Mpumalanga in South Africa, and southern Swaziland. Outcrops of the Mozaan succession in Swaziland are preserved in the Ntungulu-Mahlangatsha and Kubuta-Mooihoek areas. The succession is composed of polymictic conglomerate, poorly sorted scour based quartzite, orthoquartzite, shale, iron-formation, polymictic diamictite and lava. In the Kubuta- Mooihoek area a 3000m thick succession is preserved and correlates almost bed for bed with that in the Hartland area in South Africa. The succession is preserved from the Dipka member of the Sinqeni Formation at the base to the Tobolsk lava at the top. The depositional environment ranges essentially between fluvial and marine with two distinct glaciogenic diamictite units and one unit of lava near the top of the succession. Seven unconformity bounded sequences are recognised in the succession and from these a relative sea-level curve could be constructed. Trace element geochemistry of the shale reveals that the source area was predominantly felsic with a mafic component probably derived from the uplifted pre-Pongola granitoids and Nsuze Group. The petrography of the quartzite in the succession suggests a change in provenance from a low-lying deeply weathered to uplifted moderately weathered source area higher up in the stratigraphy. Part of the tectonic uplift may have been associated with isostatic rebound related to melting of continental glaciers. The Tobolsk lava is a continental flood basalt also possibly related to a tectonic uplift event. There are indications of sediment recycling in the upper part of the succession where conglomerates are predominantly composed of chert clasts A pretectonic quartz porphyry sill, folded with the strata, provides an upper age limit of 2837±5 Ma for the deposition of the Mozaan Group. The Mooihoek granite (2824±6 Ma) that intrudes and deforms the synclinal structure along its eastern flank, provides an upper age limit of the folding event. This suggests that the deformation of the Mozaan succession took place in the intervening 13 Ma period between 2824 and 2837 Ma ago.
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- Authors: Nhleko, Noah
- Date: 2012-08-22
- Subjects: Geology, Stratigraphic - Archaean , Geology - South Africa - KwaZulu-Natal
- Type: Thesis
- Identifier: uj:2980 , http://hdl.handle.net/10210/6405
- Description: M.Sc. , Known outcrops of the supracrustal Mesoarchean Mozaan Group of the Pongola Supergroup occur in north-eastern Kwazulu-Natal and southern Mpumalanga in South Africa, and southern Swaziland. Outcrops of the Mozaan succession in Swaziland are preserved in the Ntungulu-Mahlangatsha and Kubuta-Mooihoek areas. The succession is composed of polymictic conglomerate, poorly sorted scour based quartzite, orthoquartzite, shale, iron-formation, polymictic diamictite and lava. In the Kubuta- Mooihoek area a 3000m thick succession is preserved and correlates almost bed for bed with that in the Hartland area in South Africa. The succession is preserved from the Dipka member of the Sinqeni Formation at the base to the Tobolsk lava at the top. The depositional environment ranges essentially between fluvial and marine with two distinct glaciogenic diamictite units and one unit of lava near the top of the succession. Seven unconformity bounded sequences are recognised in the succession and from these a relative sea-level curve could be constructed. Trace element geochemistry of the shale reveals that the source area was predominantly felsic with a mafic component probably derived from the uplifted pre-Pongola granitoids and Nsuze Group. The petrography of the quartzite in the succession suggests a change in provenance from a low-lying deeply weathered to uplifted moderately weathered source area higher up in the stratigraphy. Part of the tectonic uplift may have been associated with isostatic rebound related to melting of continental glaciers. The Tobolsk lava is a continental flood basalt also possibly related to a tectonic uplift event. There are indications of sediment recycling in the upper part of the succession where conglomerates are predominantly composed of chert clasts A pretectonic quartz porphyry sill, folded with the strata, provides an upper age limit of 2837±5 Ma for the deposition of the Mozaan Group. The Mooihoek granite (2824±6 Ma) that intrudes and deforms the synclinal structure along its eastern flank, provides an upper age limit of the folding event. This suggests that the deformation of the Mozaan succession took place in the intervening 13 Ma period between 2824 and 2837 Ma ago.
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An integrated field, geochemical and geochronological study of archaean rock units in Southern Swaziland
- Authors: Dlamini, Ntombifuthi
- Date: 2015-04-23
- Subjects: Geology, Stratigraphic - Archaean , Rocks - Swaziland
- Type: Thesis
- Identifier: uj:13561 , http://hdl.handle.net/10210/13700
- Description: M.Sc. (Geology) , This study represents the first detailed field, geochemical and geochronological study of Archaean rock units that crop out along the Ncotshane River in the southern part of Swaziland. These rock units were mapped as Mahamba Gneiss in the geological map of Swaziland (Wilson, 1982). However, field examination indicated that the area consists of a heterogeneous assemblage of serpentinite, amphibolite, gabbroic gneiss, quartzite, meta-ironstone, augen gneiss, granitic gneiss and diorite, all of which are intimately associated with weakly foliated granite and dolerite. Serpentinite is regarded to represent the metamorphosed equivalent of komatiite found in the Dwalile Supracrustal Suite, a correlate of the Onverwacht Group, on the basis of similar geochemical characteristics. The silicified part of the serpentinite may compare with silicified komatiite that are widely observed in the Onverwacht Group. It is equally possible however that the ultramafic rocks originated as intrusions that are widespread in the SE Kaapvaal craton and which include both Palaeoarchaean and Mesoarchaean layered complexes. No contacts with neighbouring rocks were observed, thus not allowing unequivocal differentiation between the different possibilities. Amphibolites represent metamorphosed equivalents of the Mozaan Group basalts based on their association with Mozaan quartzite. Gabbroic gneiss, which occurs in association with amphibolite, likely represents an intrusive equivalent of amphibolite.....
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- Authors: Dlamini, Ntombifuthi
- Date: 2015-04-23
- Subjects: Geology, Stratigraphic - Archaean , Rocks - Swaziland
- Type: Thesis
- Identifier: uj:13561 , http://hdl.handle.net/10210/13700
- Description: M.Sc. (Geology) , This study represents the first detailed field, geochemical and geochronological study of Archaean rock units that crop out along the Ncotshane River in the southern part of Swaziland. These rock units were mapped as Mahamba Gneiss in the geological map of Swaziland (Wilson, 1982). However, field examination indicated that the area consists of a heterogeneous assemblage of serpentinite, amphibolite, gabbroic gneiss, quartzite, meta-ironstone, augen gneiss, granitic gneiss and diorite, all of which are intimately associated with weakly foliated granite and dolerite. Serpentinite is regarded to represent the metamorphosed equivalent of komatiite found in the Dwalile Supracrustal Suite, a correlate of the Onverwacht Group, on the basis of similar geochemical characteristics. The silicified part of the serpentinite may compare with silicified komatiite that are widely observed in the Onverwacht Group. It is equally possible however that the ultramafic rocks originated as intrusions that are widespread in the SE Kaapvaal craton and which include both Palaeoarchaean and Mesoarchaean layered complexes. No contacts with neighbouring rocks were observed, thus not allowing unequivocal differentiation between the different possibilities. Amphibolites represent metamorphosed equivalents of the Mozaan Group basalts based on their association with Mozaan quartzite. Gabbroic gneiss, which occurs in association with amphibolite, likely represents an intrusive equivalent of amphibolite.....
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Composition and provenance of quartzites of the Mesoarchean Witwatersrand supergroup, South Africa
- Authors: Blane, Craig Harry
- Date: 2013-12-09
- Subjects: Quartzite - South Africa - Witwatersrand Supergroup , Geology, Stratigraphic - Archaean
- Type: Thesis
- Identifier: uj:7818 , http://hdl.handle.net/10210/8712
- Description: M.Sc.(Geology) , The Mesoarchean Witwatersrand Supergroup is a remarkably well preserved siliciclastic dominated cratonic platform succession located on the Kaapvaal Craton in South Africa. The vast gold resources which have been mined since 1886 make it relevant for study. The study aimed to identify significant provenance shifts throughout the depositional life of the basin which should be reflected in the in heavy mineral populations and the geochemical composition of the siliciclastic rocks. The study identified major changes in the source rock compositions through the basin lifespan and inferred major tectonic events during the life of the basin. It was found that the mechanical effects of sorting in different depositional environments tended to obscure provenance shifts, but with careful evaluation of the various factors in play significant provenance shifts could be identified. It was found that these provenance shifts corresponded closely with major unconformity sequence boundaries identified by Beukes (1995). These major provenance shifts are a record of a major tectonic event during the development of the basin. The Hospital Subgroup records a passive trailing margin, fed by a combination of felsic and ultra-mafic source rocks. Within the Hospital Hill Subgroup, there is a trend of increasing ultramafic components in the source area with increasing stratigraphic height. This trend is believed to reflect progressive unroofing of tonalite and greenstone belt complexes over the life of the Hospital Hill Subgroup. At the base of the Promise Formation a basin wide unconformity is present, which marks a shift from mature shallow marine and outer shelf sediments of the Hospital Hill Subgroup to immature fluvial quartzites for the Government and Jeppestown Subgroups (Beukes, 1995). In addition to the major change in depofacies that was recognised by Beukes (1995), this study found evidence for a shift in provenance to generally more fractionated source rocks, that were heterogeneous, but well mixed. The presence of lithoclasts indicates a possible metamorphic component was also present in the source area. This is consistent with a source area containing granitoid batholiths, and granite plutonism which is associated with early subduction tectonics and volcanic arc formation during the deposition of the Government and Jeppestown Subgroups (Wronkiewicz and Condie, 1987 and Poujol, et al., 2003, Kositcin and Krapez, 2004). Another important basin wide unconformity is present at the base of the Johannesburg Subgroup, and marks another major provenance change. These rocks are chemically more mature than the Government and Jeppestown Subgroups and represent a shift to an immature fluvial depositional setting related to basin closure (Beukes, 1995). A shift to moderate Th:Sc and La:Sc suggests a less fractionated mix of source rocks. The disappearance of the lithoclasts indicates that the metamorphic source rocks no longer supplied material to the basin. A small increase in the chromite to zircon ratio also suggests that some unfractionated source rocks were present. The narrow range in Th:Sc, La:Sc, Nb:Y ratios suggests that a homogeneous source area is present, but this is contradicted by the highly variable zircon ages measured by Kositcin and Krapez (2004), so the narrow spread might indicate that the rocks are very well mixed. Zircon populations measured by Kositcin and Krapez (2004) suggest that source terrain of the Johannesburg Subgroup probably consisted of a mixture of the granitoid batholiths from which the Government and Jeppestown Subgroups are a derived as well as some intermediate igneous material with ages of 3000-2870 ma. This would reflect incorporation of syntectonic granitoid plutons into the source areas, Kositcin and Krapez, (2004). The Turffontein Subgroup rocks are very coarse and chemically mature, but they display poor to moderate sorting and rounding. The rocks were deposited in a fluvial environment but marine quartzites are not uncommon. It is believed that these rocks were transported in a high energy environment, but the duration of transportation was short. This allows for effective winnowing but insufficient time for physically mature rocks with well-rounded grains to develop, explaining the mature chemical composition but immature physical composition. The source rocks of the Turffontein Subgroup were probably the same as the Johannesburg Subgroup with the higher energy mode of transportation responsible for the observed increase in Zr:Ti ratio. It would also explain the scarcity of feldspars and chlorite in the Turffontein Subgroup. Th:Sc and Nb:Y ratios suggest highly fractionated source rocks, but care must be taken because the mature nature and coarse grainsize of these rocks make trace element analyses unreliable. The zircon population indicates the presence of 3090-3060ma (Kositcin and Krapez, 2004) granite batholiths, as well as 3000-2870 Ma (Kositcin and Krapez, 2004) syntectonic granite plutons, as well as ancient granitoid gneiss (Kositcin and Krapez, 2004) in the source area. This study has provided new support for a foreland basin origin of the Witwatersrand Supergroup, proposed by Beukes (1995), Beukes and Nelson (1995) and Nhleko (2003), resulting from orogenic collision of the Witwatersrand and Kimberley blocks along the western margin of the Witwatersrand block. The Amalia, Kraaipan and Madibe greenstone belts and Colesberg Magnetic Anomaly are probably the only remaining remnants of this orogeny today.
- Full Text:
- Authors: Blane, Craig Harry
- Date: 2013-12-09
- Subjects: Quartzite - South Africa - Witwatersrand Supergroup , Geology, Stratigraphic - Archaean
- Type: Thesis
- Identifier: uj:7818 , http://hdl.handle.net/10210/8712
- Description: M.Sc.(Geology) , The Mesoarchean Witwatersrand Supergroup is a remarkably well preserved siliciclastic dominated cratonic platform succession located on the Kaapvaal Craton in South Africa. The vast gold resources which have been mined since 1886 make it relevant for study. The study aimed to identify significant provenance shifts throughout the depositional life of the basin which should be reflected in the in heavy mineral populations and the geochemical composition of the siliciclastic rocks. The study identified major changes in the source rock compositions through the basin lifespan and inferred major tectonic events during the life of the basin. It was found that the mechanical effects of sorting in different depositional environments tended to obscure provenance shifts, but with careful evaluation of the various factors in play significant provenance shifts could be identified. It was found that these provenance shifts corresponded closely with major unconformity sequence boundaries identified by Beukes (1995). These major provenance shifts are a record of a major tectonic event during the development of the basin. The Hospital Subgroup records a passive trailing margin, fed by a combination of felsic and ultra-mafic source rocks. Within the Hospital Hill Subgroup, there is a trend of increasing ultramafic components in the source area with increasing stratigraphic height. This trend is believed to reflect progressive unroofing of tonalite and greenstone belt complexes over the life of the Hospital Hill Subgroup. At the base of the Promise Formation a basin wide unconformity is present, which marks a shift from mature shallow marine and outer shelf sediments of the Hospital Hill Subgroup to immature fluvial quartzites for the Government and Jeppestown Subgroups (Beukes, 1995). In addition to the major change in depofacies that was recognised by Beukes (1995), this study found evidence for a shift in provenance to generally more fractionated source rocks, that were heterogeneous, but well mixed. The presence of lithoclasts indicates a possible metamorphic component was also present in the source area. This is consistent with a source area containing granitoid batholiths, and granite plutonism which is associated with early subduction tectonics and volcanic arc formation during the deposition of the Government and Jeppestown Subgroups (Wronkiewicz and Condie, 1987 and Poujol, et al., 2003, Kositcin and Krapez, 2004). Another important basin wide unconformity is present at the base of the Johannesburg Subgroup, and marks another major provenance change. These rocks are chemically more mature than the Government and Jeppestown Subgroups and represent a shift to an immature fluvial depositional setting related to basin closure (Beukes, 1995). A shift to moderate Th:Sc and La:Sc suggests a less fractionated mix of source rocks. The disappearance of the lithoclasts indicates that the metamorphic source rocks no longer supplied material to the basin. A small increase in the chromite to zircon ratio also suggests that some unfractionated source rocks were present. The narrow range in Th:Sc, La:Sc, Nb:Y ratios suggests that a homogeneous source area is present, but this is contradicted by the highly variable zircon ages measured by Kositcin and Krapez (2004), so the narrow spread might indicate that the rocks are very well mixed. Zircon populations measured by Kositcin and Krapez (2004) suggest that source terrain of the Johannesburg Subgroup probably consisted of a mixture of the granitoid batholiths from which the Government and Jeppestown Subgroups are a derived as well as some intermediate igneous material with ages of 3000-2870 ma. This would reflect incorporation of syntectonic granitoid plutons into the source areas, Kositcin and Krapez, (2004). The Turffontein Subgroup rocks are very coarse and chemically mature, but they display poor to moderate sorting and rounding. The rocks were deposited in a fluvial environment but marine quartzites are not uncommon. It is believed that these rocks were transported in a high energy environment, but the duration of transportation was short. This allows for effective winnowing but insufficient time for physically mature rocks with well-rounded grains to develop, explaining the mature chemical composition but immature physical composition. The source rocks of the Turffontein Subgroup were probably the same as the Johannesburg Subgroup with the higher energy mode of transportation responsible for the observed increase in Zr:Ti ratio. It would also explain the scarcity of feldspars and chlorite in the Turffontein Subgroup. Th:Sc and Nb:Y ratios suggest highly fractionated source rocks, but care must be taken because the mature nature and coarse grainsize of these rocks make trace element analyses unreliable. The zircon population indicates the presence of 3090-3060ma (Kositcin and Krapez, 2004) granite batholiths, as well as 3000-2870 Ma (Kositcin and Krapez, 2004) syntectonic granite plutons, as well as ancient granitoid gneiss (Kositcin and Krapez, 2004) in the source area. This study has provided new support for a foreland basin origin of the Witwatersrand Supergroup, proposed by Beukes (1995), Beukes and Nelson (1995) and Nhleko (2003), resulting from orogenic collision of the Witwatersrand and Kimberley blocks along the western margin of the Witwatersrand block. The Amalia, Kraaipan and Madibe greenstone belts and Colesberg Magnetic Anomaly are probably the only remaining remnants of this orogeny today.
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