U-PbSHRIMP and Sm-Nd age constraints on the timing and sources of the Pan-African Cape Granite Suite, South Africa

Geochemical and isotopic U-Pb SHRIMP and Sm-Nd studies in three granitic pl utons from the Pan-African Neoproterozoic/Cambrian Saldania Mobile Belt, so uthwestern South Africa supports differences in the sources and timing of e mplacement of the main plutons related to the Cape Granite Suite as establi shed by previous researchers. The Phase I, early syn-tectonic Darling Batho lith Granitoid reflects an overall peraluminous chemical signature compatib le with derivation mainly from melts extracted from paraderived crustal sou rces (Sal association). The Phase II, late to post-tectonic Robertson Pluto n, reflects affinities to the Australian I-type granites (la association). Despite the good structural constraints on the syn- and post-tectonic origi n, the U-Pb ages point to a broadly synchronous crystallisation episode at 547 +/- 6 Ma and 536 +/- 5 Ma, respectively. In addition to U-Pb, Nd isotop ic studies were also carried out for both plutons, as well as far the Rivie ra Granite, another phase II (1a association) pluton. The initial epsilon(N d) (550 MB) based on a depleted mantle model range from -3.5 (Darling), to -3.1 (Robertson) and to -2.6 (Riviera). The Nd mean crustal residence ages are 1559 Ma for Darling, 1626 Ma far Robertson and 1243 Ma for Riviera. Des pite the small databank, a dominant Mesoproterozoic (similar to 1600 Ma) cr ust may be seen as the best candidate to explain the model T-DM ages obtain ed. All the data largely overlap with others recently obtained for other pl utons within the Cape Granite Suite and cast doubts on the current correlat ion between Saldania and the southeastern Brazilian, Dom Feliciano Belts. ( C) 2000 Elsevier Science Limited. All rights reserved.