| 1. |
- H, Minnaar, et al.
(författare)
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Lithostratigraphy of the Mesoproterozoic Bethesda Formation.
- 2017
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Ingår i: South African Journal of Geology. - 0371-7208. ; 120:1, s. 187-192
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Tidskriftsartikel (refereegranskat)abstract
- The Bethesda Formation forms part of the Areachap Group, a volcano-sedimentary unit affected by the 1.2-1.0 Ga tectonothermal event in the Namaqua Sector of the Mesoproterozoic Namaqua-Natal Metamorphic Province. It comprises mainly pale brown biotite- and muscovite-rich metapelitic and quartzitic schist and gneiss with subordinate amphibolite, quartzite and calc-silicate rocks. It is commonly migmatitic with pegmatitic leucosomes and intrusive veins, but is generally weathered and poorly exposed. The extrusion of volcanic rocks in the Areachap Group is constrained between 1.30 and 1.24 Ga, whereas the Bethesda Formation is younger than 1224 ± 20 Ma based on detrital zircon dating. The regional foliation of the Areachap Group generally strikes northwesterly, reflecting isoclinal F2 folding which obscures contact relationships. Upper amphibolite facies metamorphism in the Bethesda Formation at about 18 km depth is dated at 1205 ± 16 Ma. The close association of the Bethesda Formation with the calc alkaline metavolcanic Jannelsepan Formation, with which it is in contact, suggests that they both formed in a volcanic arc setting shortly before the onset of the Namaqua orogeny. The Areachap Group as earlier defined, included the Sprigg, Van Wykspan, Rateldraai, Bethesda and Jannelsepan Formations in the Upington area. Lithological correspondence between the Bethesda Formation and the quartzo-feldspathic Van Wykspan and contact-metamorphic Rateldraai Formations suggests that these formations should be included in the Bethesda Formation, as implemented here. The conglomeratic Sprigg Formation might be younger than the other formations of the Areachap Group, but more data on detrital zircons is needed to evaluate this. For practical reasons the original name Bethesda Formation for this mappable unit is retained in preference to the lithodemic unit name Bethesda Schist, despite the lack of primary characteristics, way-up and base or top criteria.
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| 2. |
- Minnaar, H., et al.
(författare)
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Lithostratigraphy of the Mesoproterozoic Jannelsepan Formation
- 2017
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Ingår i: South African Journal of Geology. - : Geological Society of South Africa. - 1012-0750 .- 1996-8590. ; 120:1, s. 193-200
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Tidskriftsartikel (refereegranskat)abstract
- The Jannelsepan Formation forms part of the 1.30 to 1.24 Ga Areachap Group. It is a pre-tectonic calc-alkaline volcano-sedimentary unit in the 1.2 to 1.0 Ga Namaqua Sector of the Namaqua-Natal Metamorphic Province. The main rock types are amphibolites with subordinate clinopyroxene or biotite. Although some primary volcanic textures have been identified, primary features are generally poorly preserved. Minor interlayered units include felsic metavolcanic rocks, pelitic schists and calc-silicate rocks which may represent primary marls. Field and geochemical evidence suggests that the Jannelsepan Formation represents metamorphosed basaltic to intermediate lavas and associated sedimentary rocks which formed in a subduction-related arc setting.
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| 3. |
- Colliston, W. P., et al.
(författare)
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Geochronological constraints on the Hartbees River Thrust and Augrabies Nappe: New insights into the assembly of the Mesoproterozoic Namaqua-Natal Province of Southern Africa
- 2015
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268. ; 265, s. 150-165
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Tidskriftsartikel (refereegranskat)abstract
- The region around Augrabies in the Namaqua sector provides insights into the processes that formed the Namaqua-Natal tectonic Province. Progressive ductile shear deformation during the long lasting Namaqua Orogeny was coeval with the global Grenvillian Orogeny. The Mesoproterozoic Namaqua-Natal Province is composed of severely deformed and metamorphosed rocks in terranes bounded by major thrust and shear zones. The interpreted research results deal with events around the Hartbees River Thrust, a suture zone where the granulite grade Grunau (Kakamas) terrane was overthrust onto the amphibolite grade Bladgrond (Bushmanland) terrane. The series of distinct deformation stages D-1-D-6 that have been identified during previous research in the western regions of the Namaqua sector, is also discernible in the study region around Augrabies. Microbeam geochronological techniques were used to date zircons from four samples of a granitic rock (the Karama'am Augen Gneiss) intrusive into the Hartbees River Thrust zone, and of a sample of granite (the Augrabies Granite) from the core of a large allochthonous sheath fold nappe in the Grunau terrane. The mean crystallisation age of the Karama'am intrusive is 1108 +/- 4 Ma and of the Augrabies Granite 1168 +/- 6 Ma. The sheath fold core of the latter granite is enclosed in the sheetlike Rooipad Granite (Riemvasmaak Granite) previously determined to be 1155 +/- 7 Ma. Crustal residence times deduced from Lu-Hf isotopic compositions of zircon cores and xenocrysts, cluster around 1710 Ma for the Augrabies Granite and about 200 Ma older for the Karama'am Granite Gneiss (with the oldest date at 2069 Ma). Collectively the available data enable reconstruction of the sequence of Namaqua Orogeny deformation stages: terrane assembly (D-1) at similar to 1195 Ma with metamorphism at 1191 +/- 12 Ma, pervasive folding and thrusting (D-2) at 1168 +/- 6 Ma, formation of major sheath and coaxial folds (D-3) at 1155 +/- 7 Ma, late open folds (D-4) at 1090 +/- 16 and a late metamorphism (coeval with major shear zones D-5-D-6?) at 1018 +/- 11 to 1024 +/- 14 Ma. (C) 2015 Elsevier B.V. All rights reserved.
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| 4. |
- Cornell, David H., 1948, et al.
(författare)
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Precise microbeam dating defines three Archaean granitoid suites at the southwestern margin of the Kaapvaal Craton.
- 2018
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 304, s. 21-38
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Tidskriftsartikel (refereegranskat)abstract
- Precise microbeam U-Pb zircon dates have been determined for 17 granitoid samples which crop out along the southwestern margin of the Kaapvaal Craton. In the Marydale High two main types of granitoid are distinguishedmainly by their normative Quartz - Alkali Feldspar – Plagioclase mineral proportions. The Draghoender Granite type is generally tonalitic to trondhjemitic and some samples have very low heavy Rare Earth Elements, probably originating as melts of eclogitic protoliths. Their ages vary by ~50 Ma from 2946 ±9 Ma to 2892 ±6 Ma (2σ), reflecting a long period of magmatism possibly due to subduction. The granodioritic to monzogranitic Skalkseput Granite type intrudes the Draghoender granite in places and has a coherent age of 2901 ±14 Ma. These two granite types thus overlap in time and space. The more evolved Skalkseputs type could have been derived by melting of the Draghoender type during assembly of the Kaapvaal Craton by collision of the Kimberley and Witwatersrand Terranes. A third granite type is exemplified by the 2721 ±6 Ma monzogranitic Steenkop Granite Gneiss which occurs south of Prieskapoort, and corresponds in age to a 2718 ±8 Ma monzogranite dyke which intrudes a 2871 Ma Skalkseput monzogranite. The previous age of 2718 ±8 Ma for the Skalkseput Granite probably also dated a Steenkop-type dyke. A basal conglomerate to the Zeekoebaard Formation of the Ventersdorp Supergroup has a single 2720 ±4 Ma detrital zircon population. South of the Marydale High a narrow strip of Draghoender-type Granite extends to Franzenhof where it is exposed in a Dwyka glacial outwash surface and is dated at 2931 ±9 Ma. The southernmost exposures of granite are windows in the Dwyka group about 130 km southeast of Marydale on both sides of the Doornberg Fault. The 2905 ±7 Ma Maritzdam Granite which is basement to Ventersdorp Supergroup volcanic rocks at Kuip is monzogranitic and corresponds to the Skalkseput type. On the southwest side of the Doornberg Fault the 2907 ±4 Ma Welgevonden Granite underlies Marydale Group volcanic rocks, showing that the Kaapvaal basement extends across the fault.
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| 5. |
- Jochum, K. P., et al.
(författare)
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MPI-DING reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios
- 2006
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Ingår i: Geochemistry Geophysics Geosystems. - 1525-2027. ; 7:15 Febr
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Tidskriftsartikel (refereegranskat)abstract
- [1] We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties ( at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive ( isotope dilution) and comparative bulk ( e. g., INAA, ICPMS, SSMS) and microanalytical ( e. g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.
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| 6. |
- Moen, H. F. G., et al.
(författare)
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Lithostratigraphy of the Mesoproterozoic Wilgenhoutsdrif Group
- 2017
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Ingår i: South African Journal of Geology. - : Geological Society of South Africa. - 1012-0750 .- 1996-8590 .- 0371-7208. ; 120:1, s. 201-208
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Tidskriftsartikel (refereegranskat)abstract
- The Mesoproterozoic metamorphic formations of the Wilgenhoutsdrif Group underlie a large area around the Orange River east of Upington. The quartzitic Grootdrink Formation occurs at the base of the sequence and contacts with older units are either unconformable or along thrusts. The Zonderhuis Formation is a sequence of low-grade pelitic phyllites and impure quartzites with subordinate lenses of metavolcanic rocks and serpentinite. The Leerkrans Formation is thought to follow conformably and consists of deformed basaltic and quartz-porphyritic lavas and volcanogenic metasediments. The entire group is isoclinally folded and foliated, with greenschist facies metamorphic parageneses, and is altered by carbonate veins and epidotisation. The age of felsic volcanic rocks is reliably established at 1289 or 1293 Ma with 2 sigma errors of 9 Ma. The Wilgenhoutsdrif Group now forms part of the Kaaien Terrane of the Namaqua-Natal Province. It may have formed in a continental back-arc basin at about the same time as the arc-related volcanic rocks of the Areachap Group formed by subduction of an ocean basin to the west, prior to similar to 1.2 Ga Namaqua terrane assembly by collisions with the Kaapvaal-Rehoboth Craton.
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| 7. |
- Mohammad, Yousif, 1976, et al.
(författare)
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Geochemistry and Ar-Ar muscovite ages of the Daraban Leucogranite, Mawat ophiolite, northeastern Iraq: Implications for Arabia-Eurasia continental collision
- 2014
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Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120. ; 86, s. 151-165
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Tidskriftsartikel (refereegranskat)abstract
- Daraban Leucogranite dykes intruded discordantly into the basal serpentinized harzburgite of the Mawat Ophiolite, Kurdistan region, NE Iraq. These coarse grained muscovite-tourmaline leucogranites are the first leucogranite dykes identified within the Mawat Ophiolite. They are mainly composed of quartz, K-feldspar, plagioclase, tourmaline, muscovite, and secondary phologopite, while zircon, xenotime, corundum, mangano-ilemnite and cassiterite occur as accessories. The A/CNK value of the granite dyke samples varies from 1.10 to 1.22 indicating a strongly peraluminous composition. CaO/Na2O ranges from 0.11 to 0.15 and Al2O3/TiO2 from 264 to 463, similar to the strongly peraluminous (SP) granites exposed in ‘high-pressure’ collision zones such as the Himalayas. Ar–Ar muscovite step-heating dating yields 37.57 ± 0.25 and 38.02 ± 0.53 Ma plateau ages for two samples which are thought to reflect either their magmatic emplacement or resetting during collision-related metamorphism. Mineral chemistry shows evidence of both primary and secondary types of muscovite, with cores favouring the magmatic interpretation and slight effects of a late syn-serpentinization fluid seen at the rims. Geochemical features of Daraban Leucogranite dykes favour a syn-collisional tectonic setting. They probably formed in response to the continental collision between Eurasia and Arabia during the initial stage of the opening of the Gulf of Aden at 37 Ma. The muscovite ages and geochemical features of Daraban Leucogranite are strong evidence for the timing of the continental collision between northeastern Arabia and Eurasia in Kurdistan region of Iraq.
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| 8. |
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| 9. |
- Roelofse, F., et al.
(författare)
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Lithostratigraphy of the Palaeoproterozoic Verena Granite
- 2020
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Ingår i: South African Journal of Geology. - : Geological Society of South Africa. - 1012-0750 .- 1996-8590. ; 123:1, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- The Verena Granite forms part of the Palaeoproterozoic Lebowa Granite Suite of the Bushveld Complex and was named after the village of Verena in the Mpumalanga Province of South Africa. It occurs over an area of similar to 600 km(2) and is intrusive into the Rooiberg Group, the Rashoop Granophyre Suite and the Klipkloof Granite. It is in turn intruded by the Makhutso Granite, the youngest known granite of the Lebowa Granite Suite. The Verena Granite is characterised by its coarse to very coarse-grained nature, its pinkish to reddish colours and its porphyritic texture defined by the presence of large perthitic K-feldspar phenocrysts within a finer grained groundmass of plagioclase (An(8-15)) and quartz. Geochemically it can be classified as an A-type granite that straddles the boundary between metaluminous and peraluminous compositions. The granite is enriched in REEs relative to chondrite and shows strong fractionation of the LREEs, a distinct negative Eu anomaly and little fractionation of the HREEs. U-Pb dating presented here places the age of the Verena Granite at 2052 +/- 9 Ma, which is the same as that of the published 2054 +/- 2 Ma age of the Nebo Granite. Currently no consensus exists regarding the petrogenesis of the Verena Granite. Doubts have been cast on a genetic link between the Verena Granite and the remainder of the Nebo Granite. A genetic link between the Klipkloof Granite and the Verena Granite appears likely, with the former possibly representing the rapidly chilled roof of the magmas that crystallised to form the latter. Lu-Hf isotope data on zircons are consistent with that from other units of the Lebowa Granite Suite. It also supports the unconventional model involving a common enriched mantle origin for all mafic and felsic units of the Bushveld Complex, with minimal input from older crust.
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| 10. |
- van Schijndel, Valby, et al.
(författare)
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Three episodes of crustal development in the Rehoboth Province, Namibia.
- 2011
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Ingår i: The Formation and Evolution of Africa: A Synopsis of 3.8 Ga of Earth History. Geological Society, London, Special Publications. ; 357, s. 27-47
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Tidskriftsartikel (refereegranskat)abstract
- The African continental crust was assembled by a series of orogenies over a period of billions of years mainly in Precambrian times. Tracing the build-up history of this stable crust is not always straightforward due to multiphase deformation and regions with poor outcrop. Episodes of metamorphism and magmatism associated with multiple Wilson cycles are recorded in zircons, which found their way into sediments derived from the hinterland. Dating of zircon populations in detrital rocks can hence provide age spectra which reflect the metamorphic and magmatic events of the region. Microbeam dating of detrital zircon is used to characterize the crustal development history of the Rehoboth Province of southern Africa. We investigated a quartzite of the Late Palaeo-Early Mesoproterozoic Billstein Formation, formed in a continental basin, and a quartz-feldspar arenite layer of the late Mesoproterozoic Langberg Formation conglomerates, immature sediments formed within a felsic volcanic system (both close to Rehoboth Town). The combined data indicate three episodes of crustal evolution in the Rehoboth Province. The oldest phase is only documented in the Billstein quartzite by three 2.98–2.7 Ga Archaean zircons. A Palaeoproterozoic phase between 2.2 and 1.9 Ga is older than any known exposures of the Rehoboth Province. The Billstein quartzite shows a main peak at 1.87 Ga, corresponding to the 1863±10 Ma Elim Formation. The Langberg sample reflects magmatism related to the entire Namaqua–Natal Wilson cycle between c. 1.32 and 1.05 Ga. The absence of zircons of that age range in the Billstein quartzite indicates a pre-Namaqua age for the Billstein Formation. Our data shows that there were at least three episodes of crustal development at 2.98–2.7 Ga, 2.05–1.75 and 1.32–1.1 Ga. We have documented the existence of a previously unrecognized 2.98–2.7 Ga Archaean crustal component, which was probably exposed in the Rehoboth Province during the Palaeoproterozoic and thus indicates a much longer geological history for the Rehoboth Province than previously known.
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