The origin of the Kheis Terrane and its relationship with the Archean Kaapvaal Craton and the Grenvillian Namaqua province in Southern Africa
- Van Niekerk, Hermanus Stephanus
- Authors: Van Niekerk, Hermanus Stephanus
- Date: 2009-01-29T12:08:52Z
- Subjects: Groups (Stratigraphy) , Sedimentary rocks , Structural geology , Plate tectonics , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:14852 , http://hdl.handle.net/10210/1974
- Description: D.Phil. , The tectonic history of the Kheis Terrane and its relationship with the Namaqua-Natal Metamorphic Province (NNMP) along the western margin of the Kaapvaal Craton were the focus of this study. Major issues addressed in this study are the origin and timing of formation of the Kheis Terrane and the recognition and definition of terrane boundaries in the area. Results of detailed measured sections across the Kheis Terrane, heavy mineral provenance studies, 40Ar/39Ar analyses of metamorphic muscovite, U-Pb SHRIMP dating of detrital zircon grains from 12 samples from the Kheis- and Kakamas Terranes and one igneous body from the Kakamas Terrane are presented. A new stratigraphic unit, the Keis Supergroup, comprising the Olifantshoek-, Groblershoop- and Wilgenhoutsdrif Groups, is defined. The base of the Keis Supergroup is taken at the basal conglomerate of the Neylan Formation. The Mapedi- and Lucknow Formations, previously considered part of the Olifantshoek Group, are now incorporated into the underlying Transvaal Supergroup. The Dabep Fault was found not to represent a terrane boundary. Rather, the Blackridge Thrust represents the boundary between the rocks of the Kheis Terrane and the Kaapvaal Craton. Provenance studies indicate that the rocks of the Keis Supergroup were deposited along a passive continental margin on the western side of the Kaapvaal-Zimbabwe Craton with the detritus derived from a cratonic interior. Detrital zircon grains from the rocks of the Keis Supergroup of the Kheis Terrane all gave similar detrital zircon age populations of ~1800Ma to ~2300Ma and ~2500Ma to ~2700Ma. The Kaapvaal Craton most probably never acted as a major source area for the rocks of the Keis Supergroup because of the lack of Paleo- to Mesoarchean zircon populations in the Keis Supergroup. Most of the detrital zircon grains incorporated into the Keis Supergroup were derived from the Magondi- and Limpopo Belts and the Zimbabwe Craton to the northeast of the Keis basin. The rock of the Kakamas Terrane was derived from a totally different source area with ages of ~1100Ma to ~1500Ma and ~1700Ma to ~1900Ma which were derived from the Richtersveld- and Bushmanland Terranes as well as the ~1166Ma old granitic gneisses ofthe Kakamas Terrane. Therefore the rocks of the Kheis- and Kakamas Terranes were separated from each other during their deposition. Detrital zircon populations from the Sprigg Formation indicate that it this unit was deposited after the amalgamation of the Kheis- and Kakamas Terranes and therefore does not belong to the Areachap Group. Results provide clear evidence for a tectonic model characterised by the presence of at least two Wilson cycles that affeected the western margin of the Kaapvaal Craton in the interval between the extrusion of the Hartley lavas at 1.93Ga and the collision with the Richtersveld tectonic domain at ~1.13Ga. According to the revised plate tectonic model for the western margin of the Kaapvaal- Zimbabwe Craton, the Neylan Formation represents the initiation of the first Wilson Cycle, with rifting at ~1927Ma ago, on the western margin of the Kaapvaal-Zimbabwe Craton. The metasedimentary rocks of the Olifantshoek Group were deposited in a braided river environment which gradually changed into a shallow marine environment towards the top of the Olifantshoek Group in the Top Dog Formation. The metasedimentary rocks of the Groblershoop Group were deposited in a shallow, passive or trailing continental margin on the western side of the Kaapvaal-Zimbabwe Craton. The rocks of the Wilgenhoutsdrif Group overlie the Groblershoop Group unconformably. This unconformity is related to crustal warping as a volcanic arc, represented by the metavolcanics of the Areachap Group, approached the Kaapvaal-Zimbabwe Craton from the west. The rocks of the Keis Supergroup were deformed into the Kheis Terrane during the collision of the Kaapvaal-Zimbabwe Craton, Areachap Arc and the Kgalagadi Terrane to form the Kaapvaal-Zimbabwe-Kgalagadi Craton. This event took place sometime between 1290Ma, the age of deformed granites in the Kheis Terrane and 1172Ma, the initiation of rifting represented by the Koras Group. This is supported by 40Ar/39Ar analyses of metamorphic muscovite from the Kheis Terrane that did not provide any evidence for a ~1.8Ga old Kheis orogeny (an age commonly suggested in the past for this orogeny). This collisional event resulted in the deformation of the rocks of the Keis Supergroup into the Kheis Terrane sometime between 1290Ma and 1172Ma.The second Wilson cycle was initiated during rifting along the Koras-Sinclair-Ghanzi rift on the Kaapvaal-Zimbabwe-Kgalagadi Craton at ~1172Ma. It was followed soon after by the initiation of subduction underneath the Richtersveld cratonic fragment at ~1166Ma after which the rocks of the Korannaland Group were deposited. The closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment occurred about 50Ma later (~1113Ma, the age of neomorphic muscovite in the metasedimentary rocks of the Kakamas Terrane) and resulted in the large open folds characterising the Kheis terrane and NNMP. Detrital zircon populations in the Sprigg Formation show that this formation does not belong to the Areachap Group and that it was deposited after the closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment at ~1113Ma. The Areachap Group can be extended towards the north and into Botswana along the Kalahari line where it forms the boundary between the Kaapvaal-Zimbabwe Craton to its east and the Kgalagadi Terrane to its west. The Areachap Terrane is thus related to the collision of the Kaapvaal-Zimbabwe Craton and Kgalagadi Terrane and was deformed a second time during the oblique collision of the Richtersveld cratonic fragment with the combined Kaapvaal-Zimbabwe-Kgalagadi Craton. The extension of the Areachap Group to the north along the Kalahari line opens up new exploration prospects for Coppertontype massive sulphide deposits underneath the Kalahari sand.
- Full Text:
- Authors: Van Niekerk, Hermanus Stephanus
- Date: 2009-01-29T12:08:52Z
- Subjects: Groups (Stratigraphy) , Sedimentary rocks , Structural geology , Plate tectonics , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:14852 , http://hdl.handle.net/10210/1974
- Description: D.Phil. , The tectonic history of the Kheis Terrane and its relationship with the Namaqua-Natal Metamorphic Province (NNMP) along the western margin of the Kaapvaal Craton were the focus of this study. Major issues addressed in this study are the origin and timing of formation of the Kheis Terrane and the recognition and definition of terrane boundaries in the area. Results of detailed measured sections across the Kheis Terrane, heavy mineral provenance studies, 40Ar/39Ar analyses of metamorphic muscovite, U-Pb SHRIMP dating of detrital zircon grains from 12 samples from the Kheis- and Kakamas Terranes and one igneous body from the Kakamas Terrane are presented. A new stratigraphic unit, the Keis Supergroup, comprising the Olifantshoek-, Groblershoop- and Wilgenhoutsdrif Groups, is defined. The base of the Keis Supergroup is taken at the basal conglomerate of the Neylan Formation. The Mapedi- and Lucknow Formations, previously considered part of the Olifantshoek Group, are now incorporated into the underlying Transvaal Supergroup. The Dabep Fault was found not to represent a terrane boundary. Rather, the Blackridge Thrust represents the boundary between the rocks of the Kheis Terrane and the Kaapvaal Craton. Provenance studies indicate that the rocks of the Keis Supergroup were deposited along a passive continental margin on the western side of the Kaapvaal-Zimbabwe Craton with the detritus derived from a cratonic interior. Detrital zircon grains from the rocks of the Keis Supergroup of the Kheis Terrane all gave similar detrital zircon age populations of ~1800Ma to ~2300Ma and ~2500Ma to ~2700Ma. The Kaapvaal Craton most probably never acted as a major source area for the rocks of the Keis Supergroup because of the lack of Paleo- to Mesoarchean zircon populations in the Keis Supergroup. Most of the detrital zircon grains incorporated into the Keis Supergroup were derived from the Magondi- and Limpopo Belts and the Zimbabwe Craton to the northeast of the Keis basin. The rock of the Kakamas Terrane was derived from a totally different source area with ages of ~1100Ma to ~1500Ma and ~1700Ma to ~1900Ma which were derived from the Richtersveld- and Bushmanland Terranes as well as the ~1166Ma old granitic gneisses ofthe Kakamas Terrane. Therefore the rocks of the Kheis- and Kakamas Terranes were separated from each other during their deposition. Detrital zircon populations from the Sprigg Formation indicate that it this unit was deposited after the amalgamation of the Kheis- and Kakamas Terranes and therefore does not belong to the Areachap Group. Results provide clear evidence for a tectonic model characterised by the presence of at least two Wilson cycles that affeected the western margin of the Kaapvaal Craton in the interval between the extrusion of the Hartley lavas at 1.93Ga and the collision with the Richtersveld tectonic domain at ~1.13Ga. According to the revised plate tectonic model for the western margin of the Kaapvaal- Zimbabwe Craton, the Neylan Formation represents the initiation of the first Wilson Cycle, with rifting at ~1927Ma ago, on the western margin of the Kaapvaal-Zimbabwe Craton. The metasedimentary rocks of the Olifantshoek Group were deposited in a braided river environment which gradually changed into a shallow marine environment towards the top of the Olifantshoek Group in the Top Dog Formation. The metasedimentary rocks of the Groblershoop Group were deposited in a shallow, passive or trailing continental margin on the western side of the Kaapvaal-Zimbabwe Craton. The rocks of the Wilgenhoutsdrif Group overlie the Groblershoop Group unconformably. This unconformity is related to crustal warping as a volcanic arc, represented by the metavolcanics of the Areachap Group, approached the Kaapvaal-Zimbabwe Craton from the west. The rocks of the Keis Supergroup were deformed into the Kheis Terrane during the collision of the Kaapvaal-Zimbabwe Craton, Areachap Arc and the Kgalagadi Terrane to form the Kaapvaal-Zimbabwe-Kgalagadi Craton. This event took place sometime between 1290Ma, the age of deformed granites in the Kheis Terrane and 1172Ma, the initiation of rifting represented by the Koras Group. This is supported by 40Ar/39Ar analyses of metamorphic muscovite from the Kheis Terrane that did not provide any evidence for a ~1.8Ga old Kheis orogeny (an age commonly suggested in the past for this orogeny). This collisional event resulted in the deformation of the rocks of the Keis Supergroup into the Kheis Terrane sometime between 1290Ma and 1172Ma.The second Wilson cycle was initiated during rifting along the Koras-Sinclair-Ghanzi rift on the Kaapvaal-Zimbabwe-Kgalagadi Craton at ~1172Ma. It was followed soon after by the initiation of subduction underneath the Richtersveld cratonic fragment at ~1166Ma after which the rocks of the Korannaland Group were deposited. The closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment occurred about 50Ma later (~1113Ma, the age of neomorphic muscovite in the metasedimentary rocks of the Kakamas Terrane) and resulted in the large open folds characterising the Kheis terrane and NNMP. Detrital zircon populations in the Sprigg Formation show that this formation does not belong to the Areachap Group and that it was deposited after the closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment at ~1113Ma. The Areachap Group can be extended towards the north and into Botswana along the Kalahari line where it forms the boundary between the Kaapvaal-Zimbabwe Craton to its east and the Kgalagadi Terrane to its west. The Areachap Terrane is thus related to the collision of the Kaapvaal-Zimbabwe Craton and Kgalagadi Terrane and was deformed a second time during the oblique collision of the Richtersveld cratonic fragment with the combined Kaapvaal-Zimbabwe-Kgalagadi Craton. The extension of the Areachap Group to the north along the Kalahari line opens up new exploration prospects for Coppertontype massive sulphide deposits underneath the Kalahari sand.
- Full Text:
Basin analysis of the Mesoproterozoic Bushmanland group of the Namaqua Metamorphic Province, South Africa
- Authors: McClung, Craig Randall
- Date: 2008-06-12T05:35:38Z
- Subjects: Geology , Geochemistry , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:2666 , http://hdl.handle.net/10210/610
- Description: The Mesoproterozoic Bushmanland Subprovince of northwestern South Africa forms the western continuation of the transcontinental Namaqua-Natal Metamorphic Province, a crustal domain affected by the 1020-1220 Ma Namaquan Orogeny. Cross-cut by several large faults, the Bushmanland Subprovince can be subdivided into a southern Garies Terrain and northern Aggeneys Terrain. The supracrustal rocks of the Aggeneys Terrain (i.e. Bushmanland Group), comprise a thin (<1 km thick) metavolcano-sedimentary succession composed of a very consistent, shallow marine duplex of sandstone-shale to chemogenic metasedimentary and metavolcanic rocks that have undergone multiple phases of deformation and metamorphism. Since the discovery of the Broken Hill-type (BHT) mineralization in the Aggeneys-Gamsberg district (~440 Mt, 5.2% Cu+Zn+Pb) in the early 1970’s, controversy has persisted regarding the stratigraphy of the Bushmanland Group, its lateral correlation throughout the Aggeneys Terrain, environment and age of deposition, as well as classification and origin of its base-metal sulfide ± barite deposits. For these reasons, the present study primarily focuses on two aims, namely: (1) regionally based comprehensive lithostratigraphic, geochemical and geochronologic analysis of the Bushmanland Group to be used in the construction of a basin model; and (2) petrographic and geochemical analyses of Fe-Mn-rich rocks and barites to determine if they are related to base-metal mineralization and if so, to what extent. New lithostratigraphic data for the Bushmanland Group indicate that it can be subdivided into two subgroups and thirteen formations that are directly correlatable throughout the terrain as well as similar supracrustal successions in neighboring portions of the Namaqua Metamorphic Province. The base of the Bushmanland Group (Wortel Subgroup) comprises a thin (250-350 m thick) sequence of interbedded upward-coarsening psammo-pelitic schists and mature quartzite (i.e. meta-orthoquartzites) of the Namies Schist Fm., Pella Quartzite Fm., Bloemhoek Fm. and laterally equivalent Kangnas Fm. In contrast, the metasedimentary rocks of the unconformably overlying Kouboom Subgroup can be separated into facies terrains divided by the Pofadder-Tantalite Valley Shear Zone (PTV Shear Zone). West of the PTV Shear Zone the Kouboom Subgroup is characterized by a thin (205-225 m thick) succession of interbedded mature quartzites and pelitic schists. East of PTV Shear Zone the Kouboom Subgroup encompasses a thick (~1250 m thick) succession of calc-silicate rocks hosted by biotite to calc-silicate-rich schists and metagreywackes. The Koeris Fm., a variably thick (0-650 m) succession of psammitic schists, metaconglomerates and ortho-amphibolites unconformably overlies the Kouboom Subgroup. Geochemical provenance and detrital zircon core populations of the Wortel Subgroup suggest the metasedimentary rocks were derived from the Paleoproterozoic continental island arc rocks of the Vioolsdrift Intrusive Suite and Gladkop Suite, as well as an unidentified sedimentary/metasedimentary succession. Deposition took place in a passive continental margin environment between 1140 to 1650 Ma. In contrast, the unconformably overlying Kouboom Subgroup is characterized by larger plutonic derived zircons of the basement rocks to the Orange River Group, suggesting deposition in a tectonically active environment marked by repeated periods of tectonic uplift. In addition, new age constraints reveal that deposition in the upper part of the Kouboom Subgroup (possibly upper part of the Gams Fm.) was synchronous with emplacement of the Little Namaqualand Suite (~1190 Ma) into the lower portions, i.e. Wortel Subgroup, of the Bushmanland Group. The geochemical attributes and detrital zircon populations of metagreywackes from the Driekop Fm. suggest they were eroded from the newly exposed, i.e. fresh to poorly weathered, intrusions of the Little Namaqualand Suite, indicating a renewed period of tectonic uplift. Lastly, unlike the other lithologic units of the Bushmanland Group, the Koeris Fm. exhibits four detrital zircon age populations at 1125-1325, 1605-1695, 1730-1910 and 1935-2075 Ma. The older sub-populations indicate sediment derivation from various units of the Richtersveld Subprovince and Steinkopf Domain, while the younger sub-populations suggest derivation from various units in the Rehoboth Inlier of Namibia and the Gordonia Terrain to the east. The provenance signature of the younger subpopulation implies that deposition of the Koeris Fm. occurred after continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. With regards to the base-metal deposits of the Aggeneys-Gamsberg district, petrographic and geochemical analysis of the Bushmanland Group Fe-Mn-rich rocks suggests that they can be subdivided into several types: (1) primary Fe-Mn-rich metasedimentary rocks; (2) magnetite-amphibole-rich Fe-Mn-rich rocks; (3) coticules; and (4) epigenetic Fe-Mn-rich rocks. Primary Fe-Mn-rich metasedimentary rocks occur throughout the western and central portions of the study area and appear to have been formed through the deposition of Fe-Mn-rich hydrogenous precipitates in areas of localized sediment starvation. However, as illustrated by the primary Fe-Mn-rich metasedimentary rocks of the Lemoenpoort prospect, a syn-diagenetic, hot (>250°C), metalliferous hydrothermal fluids infiltrated and altered these hydrogenous Fe-Mnrich metasedimentary rocks, resulting in the deposition of base-metal sulfides, formation of magnetite-amphibolite-rich Fe-Mn-rich rocks, as well as hydrothermal alteration of the siliciclastic wall rocks to form coticules. The spatial restriction of epigenetic Fe-Mn-rich rocks to shear zones, high Fe2O3 T (ca. 65 wt %), low ΣREE (ca. 13 ppm), presence of recrystallized quartz crystals, elevated concentration of Cu in some occurrences and general similarities with some hydrothermal iron/iron-oxide copper-gold (IOCG) deposits, suggests that the epigenetic Fe-Mn-rich rocks may have formed during prograde metamorphism. Low concentrations of SrO (0.5 ± 0.2 wt %), highly radiogenic Sr/ Sr ratios (0.7164 ± 0.0028), elevated δ S (27.3 ± 4.9 ‰) and δ O (7.7 ± 3.1 ‰) values in the barites, as compared to contemporaneous Mesoproterozoic seawater, suggests precipitation of stratiform and stratabound barite layers in the Bushmanland Group occurred through mixing of an evolved continental crustal source and contemporaneous seawater sulfate, 87 86 34 18 modified by bacterial sulfate reduction. Most importantly, δ O values suggest possible minimum temperatures of formation ranging from 18 <150°C for the Gamsberg deposit to >250°C for occurrences in the Aggeneys area. These obvious differences in temperature of formation are in good agreement with the Cu-rich, Ba-poor nature of the sulfide mineralization characteristic of the Aggeneys deposits versus the Cu-poor, Ba-rich character of the Gamsberg deposit. In conjunction with this, the isotopic and petrographic arguments favor a sub-seafloor replacement model for the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment-water interface as a true sedimentary exhalite appears more acceptable. Data obtained in the present study, combined with the results of previous investigations can be used to develop a comprehensive model for the geological evolution of the Aggeneys Terrain and Namaqua Metamorphic Province. The tectono-sedimentary evolution of the Aggeneys Terrain and Namaqua Metamorphic Province is marked by two important tectonic events separated by an episode of tectonic quiescence. Extrusion and deposition of the metavolcano-sedimentary rocks of the Orange River Group at 1908 Ma marks the start of the Orange River Orogeny. vii Prior to emplacement of the Vioolsdrift Intrusive Suite, the Orange River Group appears to have undergone a period of folding and low-grade metamorphism [D1/M1] that was subsequently followed by emplacement of the Main Phase Vioolsdrift Intrusive Suite roughly dated at 1890 Ma. Rapidly following emplacement of these intrusions, the lower crustal rocks of the Richtersveld Subprovince underwent a second, higher, amphibolite-facies metamorphic event [M1B] from 1870-1840 Ma. This event may have resulted in lower crustal melting and emplacement of the Gladkop Suite into an unknown package of metasediments or metasedimentary rocks south of the present day Orange River at roughly 1820 Ma. The Gladkop Suite was subsequently subjected to high-grade metamorphism at 1800 Ma. The Orange River Orogeny was terminated by emplacement of the Late Phase Vioolsdrift Intrusive Suite at approximately 1765 Ma and later northward-directed thrusting. Following termination of the Orange River Orogeny, deposition of the Bushmanland Group began in a tectonically stable environment marked by punctuated periods of tectonic activity that lasted until emplacement of the Little Namaqualand Suite at 1190 Ma. The detrital zircon populations of the Pella Quartzite Fm. and Koeris Fm. support (a) regional correlation of these stratigraphic units throughout the study area, (b) confirms sediment derivation from various local source terrains and (c) suggests a maximum depositional age of 1650 Ma. Furthermore, new age constraints reveal initiation of the O’okiepian Episode (Namaquan Orogeny), characterized by regional-scale mid- to high-grade contact metamorphism, was synchronous with emplacement of the Little Namaqualand Suite and deposition of the upper Kouboom Subgroup. Furthermore, the detrital zircon populations for the Driekop Fm. (upper Kouboom Subgroup) contain a large population of 1190 Ma (i.e. O’okiepian-age) detrital cores, suggesting a renewed period of tectonic uplift. Analogously, age constraints for the Koeris Fm. indicate a maximum depositional age of 1130 Ma, as well as derivation from a number of local and exotic source terrains indicating that deposition of the Koeris Fm. must have occurred in response to continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. Furthermore, these new age constraints also constrain the timing of D2-D3 deformation to between 1130-1080 Ma and regional peak metamorphism to 1020- 1040 Ma. , Prof. N.J. Beukes Prof. J. Gutzmer
- Full Text:
- Authors: McClung, Craig Randall
- Date: 2008-06-12T05:35:38Z
- Subjects: Geology , Geochemistry , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:2666 , http://hdl.handle.net/10210/610
- Description: The Mesoproterozoic Bushmanland Subprovince of northwestern South Africa forms the western continuation of the transcontinental Namaqua-Natal Metamorphic Province, a crustal domain affected by the 1020-1220 Ma Namaquan Orogeny. Cross-cut by several large faults, the Bushmanland Subprovince can be subdivided into a southern Garies Terrain and northern Aggeneys Terrain. The supracrustal rocks of the Aggeneys Terrain (i.e. Bushmanland Group), comprise a thin (<1 km thick) metavolcano-sedimentary succession composed of a very consistent, shallow marine duplex of sandstone-shale to chemogenic metasedimentary and metavolcanic rocks that have undergone multiple phases of deformation and metamorphism. Since the discovery of the Broken Hill-type (BHT) mineralization in the Aggeneys-Gamsberg district (~440 Mt, 5.2% Cu+Zn+Pb) in the early 1970’s, controversy has persisted regarding the stratigraphy of the Bushmanland Group, its lateral correlation throughout the Aggeneys Terrain, environment and age of deposition, as well as classification and origin of its base-metal sulfide ± barite deposits. For these reasons, the present study primarily focuses on two aims, namely: (1) regionally based comprehensive lithostratigraphic, geochemical and geochronologic analysis of the Bushmanland Group to be used in the construction of a basin model; and (2) petrographic and geochemical analyses of Fe-Mn-rich rocks and barites to determine if they are related to base-metal mineralization and if so, to what extent. New lithostratigraphic data for the Bushmanland Group indicate that it can be subdivided into two subgroups and thirteen formations that are directly correlatable throughout the terrain as well as similar supracrustal successions in neighboring portions of the Namaqua Metamorphic Province. The base of the Bushmanland Group (Wortel Subgroup) comprises a thin (250-350 m thick) sequence of interbedded upward-coarsening psammo-pelitic schists and mature quartzite (i.e. meta-orthoquartzites) of the Namies Schist Fm., Pella Quartzite Fm., Bloemhoek Fm. and laterally equivalent Kangnas Fm. In contrast, the metasedimentary rocks of the unconformably overlying Kouboom Subgroup can be separated into facies terrains divided by the Pofadder-Tantalite Valley Shear Zone (PTV Shear Zone). West of the PTV Shear Zone the Kouboom Subgroup is characterized by a thin (205-225 m thick) succession of interbedded mature quartzites and pelitic schists. East of PTV Shear Zone the Kouboom Subgroup encompasses a thick (~1250 m thick) succession of calc-silicate rocks hosted by biotite to calc-silicate-rich schists and metagreywackes. The Koeris Fm., a variably thick (0-650 m) succession of psammitic schists, metaconglomerates and ortho-amphibolites unconformably overlies the Kouboom Subgroup. Geochemical provenance and detrital zircon core populations of the Wortel Subgroup suggest the metasedimentary rocks were derived from the Paleoproterozoic continental island arc rocks of the Vioolsdrift Intrusive Suite and Gladkop Suite, as well as an unidentified sedimentary/metasedimentary succession. Deposition took place in a passive continental margin environment between 1140 to 1650 Ma. In contrast, the unconformably overlying Kouboom Subgroup is characterized by larger plutonic derived zircons of the basement rocks to the Orange River Group, suggesting deposition in a tectonically active environment marked by repeated periods of tectonic uplift. In addition, new age constraints reveal that deposition in the upper part of the Kouboom Subgroup (possibly upper part of the Gams Fm.) was synchronous with emplacement of the Little Namaqualand Suite (~1190 Ma) into the lower portions, i.e. Wortel Subgroup, of the Bushmanland Group. The geochemical attributes and detrital zircon populations of metagreywackes from the Driekop Fm. suggest they were eroded from the newly exposed, i.e. fresh to poorly weathered, intrusions of the Little Namaqualand Suite, indicating a renewed period of tectonic uplift. Lastly, unlike the other lithologic units of the Bushmanland Group, the Koeris Fm. exhibits four detrital zircon age populations at 1125-1325, 1605-1695, 1730-1910 and 1935-2075 Ma. The older sub-populations indicate sediment derivation from various units of the Richtersveld Subprovince and Steinkopf Domain, while the younger sub-populations suggest derivation from various units in the Rehoboth Inlier of Namibia and the Gordonia Terrain to the east. The provenance signature of the younger subpopulation implies that deposition of the Koeris Fm. occurred after continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. With regards to the base-metal deposits of the Aggeneys-Gamsberg district, petrographic and geochemical analysis of the Bushmanland Group Fe-Mn-rich rocks suggests that they can be subdivided into several types: (1) primary Fe-Mn-rich metasedimentary rocks; (2) magnetite-amphibole-rich Fe-Mn-rich rocks; (3) coticules; and (4) epigenetic Fe-Mn-rich rocks. Primary Fe-Mn-rich metasedimentary rocks occur throughout the western and central portions of the study area and appear to have been formed through the deposition of Fe-Mn-rich hydrogenous precipitates in areas of localized sediment starvation. However, as illustrated by the primary Fe-Mn-rich metasedimentary rocks of the Lemoenpoort prospect, a syn-diagenetic, hot (>250°C), metalliferous hydrothermal fluids infiltrated and altered these hydrogenous Fe-Mnrich metasedimentary rocks, resulting in the deposition of base-metal sulfides, formation of magnetite-amphibolite-rich Fe-Mn-rich rocks, as well as hydrothermal alteration of the siliciclastic wall rocks to form coticules. The spatial restriction of epigenetic Fe-Mn-rich rocks to shear zones, high Fe2O3 T (ca. 65 wt %), low ΣREE (ca. 13 ppm), presence of recrystallized quartz crystals, elevated concentration of Cu in some occurrences and general similarities with some hydrothermal iron/iron-oxide copper-gold (IOCG) deposits, suggests that the epigenetic Fe-Mn-rich rocks may have formed during prograde metamorphism. Low concentrations of SrO (0.5 ± 0.2 wt %), highly radiogenic Sr/ Sr ratios (0.7164 ± 0.0028), elevated δ S (27.3 ± 4.9 ‰) and δ O (7.7 ± 3.1 ‰) values in the barites, as compared to contemporaneous Mesoproterozoic seawater, suggests precipitation of stratiform and stratabound barite layers in the Bushmanland Group occurred through mixing of an evolved continental crustal source and contemporaneous seawater sulfate, 87 86 34 18 modified by bacterial sulfate reduction. Most importantly, δ O values suggest possible minimum temperatures of formation ranging from 18 <150°C for the Gamsberg deposit to >250°C for occurrences in the Aggeneys area. These obvious differences in temperature of formation are in good agreement with the Cu-rich, Ba-poor nature of the sulfide mineralization characteristic of the Aggeneys deposits versus the Cu-poor, Ba-rich character of the Gamsberg deposit. In conjunction with this, the isotopic and petrographic arguments favor a sub-seafloor replacement model for the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment-water interface as a true sedimentary exhalite appears more acceptable. Data obtained in the present study, combined with the results of previous investigations can be used to develop a comprehensive model for the geological evolution of the Aggeneys Terrain and Namaqua Metamorphic Province. The tectono-sedimentary evolution of the Aggeneys Terrain and Namaqua Metamorphic Province is marked by two important tectonic events separated by an episode of tectonic quiescence. Extrusion and deposition of the metavolcano-sedimentary rocks of the Orange River Group at 1908 Ma marks the start of the Orange River Orogeny. vii Prior to emplacement of the Vioolsdrift Intrusive Suite, the Orange River Group appears to have undergone a period of folding and low-grade metamorphism [D1/M1] that was subsequently followed by emplacement of the Main Phase Vioolsdrift Intrusive Suite roughly dated at 1890 Ma. Rapidly following emplacement of these intrusions, the lower crustal rocks of the Richtersveld Subprovince underwent a second, higher, amphibolite-facies metamorphic event [M1B] from 1870-1840 Ma. This event may have resulted in lower crustal melting and emplacement of the Gladkop Suite into an unknown package of metasediments or metasedimentary rocks south of the present day Orange River at roughly 1820 Ma. The Gladkop Suite was subsequently subjected to high-grade metamorphism at 1800 Ma. The Orange River Orogeny was terminated by emplacement of the Late Phase Vioolsdrift Intrusive Suite at approximately 1765 Ma and later northward-directed thrusting. Following termination of the Orange River Orogeny, deposition of the Bushmanland Group began in a tectonically stable environment marked by punctuated periods of tectonic activity that lasted until emplacement of the Little Namaqualand Suite at 1190 Ma. The detrital zircon populations of the Pella Quartzite Fm. and Koeris Fm. support (a) regional correlation of these stratigraphic units throughout the study area, (b) confirms sediment derivation from various local source terrains and (c) suggests a maximum depositional age of 1650 Ma. Furthermore, new age constraints reveal initiation of the O’okiepian Episode (Namaquan Orogeny), characterized by regional-scale mid- to high-grade contact metamorphism, was synchronous with emplacement of the Little Namaqualand Suite and deposition of the upper Kouboom Subgroup. Furthermore, the detrital zircon populations for the Driekop Fm. (upper Kouboom Subgroup) contain a large population of 1190 Ma (i.e. O’okiepian-age) detrital cores, suggesting a renewed period of tectonic uplift. Analogously, age constraints for the Koeris Fm. indicate a maximum depositional age of 1130 Ma, as well as derivation from a number of local and exotic source terrains indicating that deposition of the Koeris Fm. must have occurred in response to continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. Furthermore, these new age constraints also constrain the timing of D2-D3 deformation to between 1130-1080 Ma and regional peak metamorphism to 1020- 1040 Ma. , Prof. N.J. Beukes Prof. J. Gutzmer
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Medicinal ethnobotany of the Kamiesberg, Namaqualand, Northern Cape Province, South Africa
- Authors: Nortje, Janneke Margaretha
- Date: 2011-08-20
- Subjects: Ethnobotany , Traditional medicine , Medicinal plants , Materia medica, Vegetable , Khoisan (African people) - Ethnobotany , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:2843 , http://hdl.handle.net/10210/6278
- Description: M.Sc. , Scientific relevance: Qualitative and quantitative data is presented that give a new perspective on the traditional medicinal plants of the Khoisan (Khoe-San), one of the most ancient of human cultures. The data is not only of considerable historical and cultural value, but allows for fascinating comparative studies relating to new species records, novel use records and the spatial distribution of traditional medicinal plant use knowledge within the Cape Floristic Region. Aim of the study: A detailed documentation and quantitative analysis of medicinal plants of the Kamiesberg area (an important Khoisan and Nama cultural centre) and their medicinal traditional uses, which have hitherto remained unrecorded. Materials and methods: During four study visits to the Kamiesberg, semi-structured and structured interviews were conducted with 23 local inhabitants of the Kamiesberg, mostly of Khoisan decent. In addition to standard methodology, a newly developed Matrix Method was used to quantity medicinal plant knowledge. Results: The Kamiesberg is an important center of extant Nama ethnomedicinal information but the knowledge is rapidly disappearing. Of a total of 101 medicinal plants and 1375 anecdotes, 21 species were recorded for the first time as having traditional medicinal uses and at least 284 medicinal use records were new. The relative importance, popularity and uses of the plants were quantified. The 97 newly documented vernacular names include 23 Nama (Khoekhoegowab) names and an additional 55 new variations of known names. The calculated Ethnobotanical Knowledge Index (EKI) and other indices accurately quantify the level of knowledge and will allow for future comparisons, not only within the Kamiesberg area but also with other southern African communities of Khoisan decent. Conclusion: The results showed that the Kamiesberg is an important focal point of Khoisan (Nama) traditional knowledge but that the medicinal plants have not yet been systematically recorded in the scientific literature. There are numerous new use records and new species records that are in need of scientific study. Comparative data is now available for broader comparisons of the pattern of Khoisan plants use in southern Africa and the study represents another step towards a complete synthesis of Cape Herbal Medicine.
- Full Text:
- Authors: Nortje, Janneke Margaretha
- Date: 2011-08-20
- Subjects: Ethnobotany , Traditional medicine , Medicinal plants , Materia medica, Vegetable , Khoisan (African people) - Ethnobotany , Namaqualand (South Africa)
- Type: Thesis
- Identifier: uj:2843 , http://hdl.handle.net/10210/6278
- Description: M.Sc. , Scientific relevance: Qualitative and quantitative data is presented that give a new perspective on the traditional medicinal plants of the Khoisan (Khoe-San), one of the most ancient of human cultures. The data is not only of considerable historical and cultural value, but allows for fascinating comparative studies relating to new species records, novel use records and the spatial distribution of traditional medicinal plant use knowledge within the Cape Floristic Region. Aim of the study: A detailed documentation and quantitative analysis of medicinal plants of the Kamiesberg area (an important Khoisan and Nama cultural centre) and their medicinal traditional uses, which have hitherto remained unrecorded. Materials and methods: During four study visits to the Kamiesberg, semi-structured and structured interviews were conducted with 23 local inhabitants of the Kamiesberg, mostly of Khoisan decent. In addition to standard methodology, a newly developed Matrix Method was used to quantity medicinal plant knowledge. Results: The Kamiesberg is an important center of extant Nama ethnomedicinal information but the knowledge is rapidly disappearing. Of a total of 101 medicinal plants and 1375 anecdotes, 21 species were recorded for the first time as having traditional medicinal uses and at least 284 medicinal use records were new. The relative importance, popularity and uses of the plants were quantified. The 97 newly documented vernacular names include 23 Nama (Khoekhoegowab) names and an additional 55 new variations of known names. The calculated Ethnobotanical Knowledge Index (EKI) and other indices accurately quantify the level of knowledge and will allow for future comparisons, not only within the Kamiesberg area but also with other southern African communities of Khoisan decent. Conclusion: The results showed that the Kamiesberg is an important focal point of Khoisan (Nama) traditional knowledge but that the medicinal plants have not yet been systematically recorded in the scientific literature. There are numerous new use records and new species records that are in need of scientific study. Comparative data is now available for broader comparisons of the pattern of Khoisan plants use in southern Africa and the study represents another step towards a complete synthesis of Cape Herbal Medicine.
- Full Text:
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