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Geochronological grouping of granitoids in relation to the 1.2 Ga Namaquan Orogeny, South Africa.

Författare och institution:
A Pettersson (Institutionen för geovetenskaper); David H. Cornell (Institutionen för geovetenskaper)
Publicerad i:
IGC conference, Oslo, July 2009. Session: STT-03 Accretionary orogens: Character and processes, ( Abstracts ) s. 2008-08-09
Konferensbidrag, refereegranskat
Sammanfattning (abstract):
The Namaqua-Natal Province in South Africa partly encircles the Archean Kaapvaal Craton. The Namaqua sector in the west is a more than 400 km-wide belt of five terranes or subprovinces that collided and was accreted to the Kaapvaal Craton at ~1.2 Ga. This coincides with the time of Rodinias birth, along with many Mesoproterozoic belts. U-Pb zircon ages for a large number of granitoids, from a profile across the Namaqua Sector reveal several distinct episodes of crustal growth that took place prior to, during and after the main collision events at 1.2 Ga. The collisions induced deformation, crustal thickening and high grade metamorphism, termed the Namaquan Orogeny. Our data shows that the main magmatism in the sector can be regarded as grouped into Pretectonic (>1.22 Ga), Syntectonic (1.22-1.15 Ga) and Post-tectonic (1.1 Ga) Groups. Our geochronological classification bears little resemblance to earlier ones based on the degree of foliation in the rocks. Pretectonic crustal development started in the Bushmanland crust during the Archaean, now reflected by scarce xenocrystic and detrital zircon dates and Sm-Nd model ages. This was followed by the ~2.0 Ga Island Arc related Richtersveld Subprovince and few granitoids in the northwestern Bushmanland Terrane. In the foreland (Kaaien Terrane) and in the Areachap Terrane, pretectonic magmatism related to breakup events or arc magmatism in the 1.4 to 1.2 Ga interval can be found. Syntectonic magmatism is characterized by voluminous 1.22-1.15 Ga granitic intrusions across most of the sector. This event continued for some 70 Ma and went on longest in the Kakamas Terrane, situated at the center of the sector. A 1.1 Ga post-tectonic magmatic event is found in the eastern part of the sector, the Kaaien, Areachap and Kakamas Terranes, where it produced calc-alkaline gabbroic to granitic magmatism and volcanism. This is distinct from the High-T, low P metamorphism and diverse magmatism in the Bushmanland and Garies Terranes in the western part of the sector at 1.05-1.01 Ga. The majority of the granitoids formed in two periods, the Syntectonic tectonothermal event and the Post-tectonic, largely thermal event. The scarcity of pretectonic magmatic rocks in general suggests that the crust has been almost completely reworked by crustal melting during the early Namaquan tectogenesis.
Ämne (baseras på Högskoleverkets indelning av forskningsämnen):
Geovetenskap och miljövetenskap
Namaqua-Natal, granitoids, geochronology
Postens nummer:
Posten skapad:
2009-12-04 18:40

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