Nappe structures in the highly deformed proterozoic metasedimentary aggeneys-type sequence of western bushmanland, South Africa

Strydom, D.; Visser, J. N. J.

doi:10.1016/0301-9268(86)90020-3

Cited by 15 publications

(7 citation statements)

References 6 publications

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“…For the Pofadder terrane, the ORO intrusives suggest a marginal calkalkaline arc environment (isotopes: Barton, 1983;geochemistry: Read, 1977;structure: Blignault, 1975;. From a plate tectonic perspective, the NMO intrusives were generated during the final phases of a major continent-scale collisional event, associated with southwesterly directed transport of terranes (Blignault et al, 1983;Strydom and Visser, 1986;Van der Merwe, 1986;Van Aswegen et al, 1987;Colliston et al, 1989;1991;Van der Merwe and Botha, 1989;Jackson, 1992).…”

Section: Discussionmentioning

confidence: 97%

“…The hierarchial placement of the various intrusives follows from mapping and structural studies (Blignault et al, 1983;Colliston et al, 1986;1889;Strydom and Visser, 1986;Watkeys, 1986;Strydom et al, 1987;van Aswegen et al, 1987) and is corroborated by the available isotopic dates (Barton, 1983;Reid and Barton, 1983;Clifford et al, 1995;Robb et al, 1998). The distribution of the plutonic rocks for four of the terranes is illustrated in Figure 2.…”

Section: Regional Distributionmentioning

confidence: 95%

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The distribition and diagnostic features of deformed plutonic rocks in two terranes of the Namaque mobile belt along the Orange (Gariep) River, South Africa

Colliston

Schoch

2006

South African Journal of Geology

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ABSRACTTwo periods of deformation have been documented by detailed mapping in a strip of 3000 km 2 along the Orange (Gariep) River. The mapping has enabled field discrimination and regional correlation of well-exposed plutonic tectonites that volumetrically dominate the western part of the Namaqua mobile belt. The associated metasedimentary and metavolcanic successions that supplied tectonostratigraphic keys for correlation of rock units, were described in previous publications. Deformation took place during an orogenesis that may be termed the Orange River Event (ORO, ϳ2.0 to ϳ1.6 Ga, with associated calcalkaline magmatism) and the later Namaqua Event (NMO, ϳ1.2 to ϳ1.1 Ga, with associated granitic magmatism). The ORO magmatism includes the Vioolsdrif Suite, represented by outcrops of deformed leucogranite, adamellite, granodiorite and mafic rocks that were later intruded by small mafic complexes. The products of the NMO magmatism include various members correlated with the Little Namaqualand Suite (the Kabis, Pipeline, Swartmodder, Koeipoort, Mission, Coboop and Eendoorn gneisses).Textural properties of the metaplutonic rocks vary from very coarsely porphyroblastic (e.g. Eendoorn gneiss, megacrysts >10 cm) to fine even-grained (e.g. some Kabis gneiss). The megacrysts, invariably composite on microscopic scale, are deformed relicts of phenocrysts. Variation in strain is well illustrated by megacrysts that grade from nearly equidimensional to flattened, visible as pencil-shaped streaks on exposed surfaces. Several gneisses that appear to be unrelated because of different textural properties, merely record variation in strain intensity (e.g. the little deformed granodioritic occurrences at Vioolsdrif are coeval with severely deformed rocks at Pella, 150 km furthur to the east). Detailed structural-stratigraphic mapping and petrographic study helped to prevent unnecessary proliferation of names.Compressional tectonics were responsible for the general style of both orogeneses reflecting the effects of progressive ductile shearing rather than consecutive discrete deformational events. ORO intrusives belong to specific tectonic terranes and tend to be batholithic (in the Pofadder terrane). The grade of metamorphism was greenschist to amphibolite. The rapid tectonism of the subsequent NMO cycle led to terrane accretion and to granulite/upper amphibolite grade metamorphism. Associated granitic intrusives are not terrane-specific. The predominant sheet-like to phacolithic habits reflect emplacement during horizontal tectonism. Supracrustal Rocks Lithological Description Besondermeid FormationGarnet-biotite-sillimanite schist. Cammas FormationLayered sequence of white and green coloured metaquartzite with biotite-sillimanite schist, iron formation and conglomerate bands. Dabenoris FormationWhite and grey coloured metaquartzite with interbanded quartz-muscovite schist. Groothoek FormationMica-quartz schist. Guadom FormationMainly mafic metavolcanic rocks.. Hom FormationMainly felsic metavolcanic rocks. Hotson FormationRhyt...

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Section: Discussionmentioning

confidence: 97%

Section: Regional Distributionmentioning

confidence: 95%

The distribition and diagnostic features of deformed plutonic rocks in two terranes of the Namaque mobile belt along the Orange (Gariep) River, South Africa

Colliston

Schoch

2006

South African Journal of Geology

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“…The Achab and Aroams gneisses reflect major magmatic events during the Namaqua Orogeny (correlated with the well-known Little Namaqualand and Spektakel Suites; Colliston and Schoch, 2000;Strydom et al, 1987). The inability of field Strydom and Visser, 1986;Colliston et al, 1989;Colliston and Schoch, 2002). I= Zone of lower strain with uninterrupted stratigraphy.…”

Section: Basementmentioning

confidence: 97%

“…It seems that many of the obtained dates reflect the time of metamorphism rather than that of deposition. Note that the entire supracrustal sequence was severely deformed (during the Namaqua Orogeny: D 1 -D 6 ; Colliston andSchoch, 2002, 2013;Strydom and Visser, 1986). Intrusives into the sequence were deformed as well, during D 1 -D 3 (e.g.…”

Section: Age Of Supracrustal Rocksmentioning

confidence: 97%

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Stratigraphy of the Mesoproterozoic Aggeneys Terrane, Western Namaqua Mobile Belt, South Africa

Colliston¹,

Schoch²,

Praekelt³

2012

South African Journal of Geology

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The stratigraphy of the Aggeneys Terrane is discussed, one of at least eleven tectono-stratigraphic terranes of the Namaqua mobile belt. The severe deformation of the region caused isoclinal folding, structural duplications and excisions everywhere, presenting a formidable obstacle to regional correlation of the stratigraphic sequences. Geological mapping of lithological types proves unable to characterize the supracrustal rocks. For compilation of the various metasedimentary sequences, detailed sequence mapping is required. The lateral continuity of characteristic sequence packages on dekametre scale and the systematic recording of defined polarity, enables unequivocal correlation and classification of the metasediments.The deformation of the Aggeneys Terrane resulted in different east-west trending strain domains: a northern zone of lower strain (zone I) with nearly uninterrupted stratigraphy, and a southern zone of higher strain (zone II) with fragmented stratigraphy wherein the supracrustal successions are preserved in mega sheath folds and fold nappes only. Because of the economic interest in Cu-PbZn deposits of one formation (the Gams Formation), most detailed studies have in the past been restricted to the disrupted zone. The complete stratigraphic column can however be compiled in the zone of lower strain, where it is apparent that the metasediments may be divided into six units. The units of the Aggeneys Subgroup (mentioned in descending order) are the Koeris, Gams, Hotson, T'hammaberg, Skelmpoort and Wortel Formations.In the zone of disrupted stratigraphy (zone II), the portions of the various formations preserved in specific fold nappe structures can be recognized easily in spite of facies variations, excisions and structural juxtapositions. Facies variations include differences in thickness and non-deposition. To illustrate all distributional aspects, maps and interpretations are presented for the regions around Swartberg (Black Mountain) and the Soutkloof fold nappe in the Aggeneys Hills (Aggeneysberge). It is concluded that the interpretational system employed for the Aggeneys Terrane, has powerful predictive properties. The system provides convincing modeling of the mechanisms controlling the stratigraphic development of the entire western Namaqua-Natal mobile belt.

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Thermal History and Tectonic Setting of the Namaqualand Granulites, Southern Africa: Clues to Proterozoic Crustal Development

Waters

1990

Granulites and Crustal Evolution

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Nappe structures in the highly deformed proterozoic metasedimentary aggeneys-type sequence of western bushmanland, South Africa

Cited by 15 publications

References 6 publications

The distribition and diagnostic features of deformed plutonic rocks in two terranes of the Namaque mobile belt along the Orange (Gariep) River, South Africa

The distribition and diagnostic features of deformed plutonic rocks in two terranes of the Namaque mobile belt along the Orange (Gariep) River, South Africa

Stratigraphy of the Mesoproterozoic Aggeneys Terrane, Western Namaqua Mobile Belt, South Africa

Thermal History and Tectonic Setting of the Namaqualand Granulites, Southern Africa: Clues to Proterozoic Crustal Development

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