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

Abstract

Geochemical and isotopic UPb SHRIMP and SmNd studies in three granitic plutons from the Pan-African Neoproterozoic/Cambrian Saldania Mobile Belt, southwestern South Africa supports differences in the sources and timing of emplacement of the main plutons related to the Cape Granite Suite as established by previous researchers. The Phase I, early syn-tectonic Darling Batholith Granitoid reflects an overall peraluminous chemical signature compatible with derivation mainly from melts extracted from paraderived crustal sources (Sa1 association). The Phase II, late to post-tectonic Robertson Pluton, reflects affinities to the Australian l-type granites (1a association). Despite the good structural constraints on the syn- and post-tectonic origin, 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 isotopic studies were also carried out for both plutons, as well as for the Riviera Granite, another phase II (1a association) pluton. The initial ε Nd (550 Ma) 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 for Robertson and 1243 Ma for Riviera. Despite the small databank, a dominant Mesoproterozoic (∼ 1600 Ma) crust may be seen as the best candidate to explain the model T DM ages obtained. All the data largely overlap with others recently obtained for other plutons within the Cape Granite Suite and cast doubts on the current correlation between Saldania and the southeastern Brazilian, Dom Feliciano Belts.