Metamorphism of the Permo-Triassic Cape Fold Belt and its basement, South Africa |
| |
Authors: | H E Frimmel P G Fölling R Diamond |
| |
Institution: | (1) Department of Geological Sciences, University of Cape Town, Rondebosch, South Africa, ZA |
| |
Abstract: | Summary The Permo-Triassic Cape Fold Belt around the southern tip of Africa consists of a thick sequence of Palaezoic siliciclastic
sedimentary and pre-Cape basement rocks believed to be of Pan-African age. Both the basement rocks and the supracrustal rocks
of the Cape Supergroup display only low metamorphic grades. Application of chlorite, chlorite-chloritoid Fe-Mg exchange, and
calcite-graphite carbon isotope geothermometry to rocks from the unconformable contact between pre-Cape basement and the Cape
Supergroup made it possible to distinguish pre-Cape and syn-Cape metamorphic overprints. During Pan-African metamorphism temperatures
of up to middle greenschist facies conditions (around 400 °C) were reached, whereas lowermost greenschist facies conditions
(around 300 °C) were not exceeded during the 220–290 Ma Cape orogeny. In the past, most if not all of the pre-Cape basement
rocks, which form the Pan-African Saldania Belt, were considered to be of Neoproterozoic age. A hiatus of about 100 °C observed
between two adjacent limestone horizons that previously had been grouped together into a single formation at the bottom of
the allegedly Neoproterozoic Kango Group indicates that almost all of this group is syn- to post-orogenic with respect to
the Pan-African orogeny. A revision of the stratigraphy of the Kango Group is therefore suggested. Only its lowermost member
is truly Pan-African and probably related to about 620–740 Ma post-Sturtian cap carbonates in other Pan-African belts of southern
Africa. The remainder of the Kango Group reflects the successive development of two stages of orogen-related intra-continental
basins: The older stage led to a typical syn-orogenic foreland basin related to tectonic loading in the Gariep and Damara
orogenic belts further north(west) between 570 and 540 Ma; the younger is believed to have formed either a further foreland
basin or an intra-orogen pull-apart basin caused by later tectonic loading in the Ross orogenic belt and its continuation
into the southern Saldania Belt between 510 and 480 Ma.
Received May 7, 2000;/revised version accepted January 15, 2001 |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|