Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
History of geology wikipedia , lookup
Geology of Great Britain wikipedia , lookup
Large igneous province wikipedia , lookup
Great Lakes tectonic zone wikipedia , lookup
Geological history of Earth wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Baltic Shield wikipedia , lookup
Algoman orogeny wikipedia , lookup
Marine geology of the Cape Peninsula and False Bay wikipedia , lookup
Geological mapping and geochronology of the Kaaimans Group rocks along the coast south of George, Western Cape, South Africa Miller D.S1, de Wit M.J2, Armstrong R.A3 1. AEON (Africa Earth Observatory Network), and Department of Geoscience, Faculty of Science Nelson Mandela Metropolitan University, South Africa, Email: [email protected] 2. AEON (Africa Earth Observatory Network), Faculty of Science Nelson Mandela Metropolitan University, South Africa, Email: [email protected] 3. Research School of Earth Science, The Australian National University, Canberra 0200, A.C.T., Australia, Email: [email protected] ABSTRACT Precambrian basement rocks of the Cape Fold Belt are not well understood with respect to their paleogeographic relationship during the formation of the supercontinent Rodinia (middle to late Proterozoic) and its subsequent break up into continental fragments that later amalgamated to form Gondwana (early Palaeozoic). A series of Pre-Cape inliers outcrop along the western and south-eastern parts of South Africa, which represent tectonic windows that allow testing of these different paleogeographic models. Metasediments and intrusives (syn-tectonic granite and mafic dykes) of one of these terranes, the Kaaimans Group outcrop along the coast south of George. Previous work done on phase relations and mineral compositions indicate a poly-metamorphic history associated with these rocks. On a regional scale they do not exceed greenschist facies except where they were superimposed locally by low to medium grade contact metamorphism related to the intrusion of syn-tectonic granite. Evidence from petrogenetic grids indicate temperatures as low as 450°C and pressures between 2 and 3 kbar. Mafic meta-dykes are recrystallised to greenschist assemblages and display the same structure as the enclosing metasediments. The dykes do not cut the granite suggesting their age be bracketed by the onset of sedimentation of the Saldanian basin and intrusion of the syn-orogenic Pan-African granites. These dykes contrast with a younger generation of mafic dykes that cut the granite near Blougat. U/Pb isotope analyses from the intrusive (Rooiklip) granite, and detrital zircons associated with the upper metasedimentary sequence of the Kaaimans Group in its present position were dated using the SHRIMP. The maximum age of deposition is 1020 Ma after the youngest group of zircons in the metasediments and a minimum age constrained by the age of the intrusion of the granite at 532 ±5 Ma. Concordant detrital zircon dates are prevalent between 1030-1290 Ma, with subordinate groups at 1600 Ma, and 1800-2100 Ma. These data implies an important contribution of late-Neoproterozoic (Kibaran) terranes to these sediments, possibly from the Namaqua-Natal Belt and indicate that the sediments are not likely Neoproterozoic in age. KEYWORDS: Cape Fold Belt, Kaaimans Group, Pan African Orogeny, Saldanian Belt Inkaba yeAfrica : 9th Annual Workshop, Germany - 2012