Post-orogenic shoshonitic magmas of the Yzerfontein pluton, South Africa: the ‘smoking gun’ of mantle melting and crustal growth during Cape granite genesis?

Abstract

International audienceThe post-orogenic Yzerfontein pluton, in the Saldania Belt of South Africa was constructed through numerous injections of shoshonitic magmas. Most magma compositions are adequately modelled as products of fractionation, but the monzogranites and syenogranites may have a separate origin. A separate high-Mg mafic series has a less radiogenic mantle source. Fine-grained magmatic enclaves in the intermediate shoshonitic rocks are autoliths. The pluton was emplaced between 533 ± 3 and 537 ± 3 Ma (LA-SF-ICP-MS U–Pb zircon), essentially synchronously with many granitic magmas of the Cape Granite Suite (CGS). Yzerfontein may represent a high-level expression of the mantle heat source that initiated partial melting of the local crust and produced the CGS granitic magmas, late in the Saldanian Orogeny. However, magma mixing is not evident at emplacement level and there are no magmatic kinships with the I-type granitic rocks of the CGS. The mantle wedge is inferred to have been enriched during subduction along the active continental margin. In the late- to post-orogenic phase, the enriched mantle partially melted to produce heterogeneous magma batches, exemplified by those that formed the Yzerfontein pluton, which was further hybridised through minor assimilation of crustal materials. Like Yzerfontein, the small volumes of mafic rocks associated with many batholiths, worldwide, are probably also low-volume, high-level expressions of crustal growth through the emplacement of major amounts of mafic magma into the deep crust

Implications for sedimentary transport processes in southwestern Africa: a combined zircon morphology and age study including extensive geochronology databases

“…Another potential source of Cambrian-Ediacaran zircon in the lower Orange River is located to the south: the Saldania Belt (e.g. Andersen et al 2018b;Chemale et al 2010;Clemens et al 2017). Here, particularly those parts of the belt that drain to the Atlantic Benguela Current have a high potential to deliver detrital material via coast-parallel inner shelf-transport (de Decker 1988)-including possible short-distance aeolian transport on land-to the north.…”

Shoshonitic enclaves in the high Sr/Y Nyemo pluton, southern Tibet: Implications for Oligocene magma mixing and the onset of extension of the southern Lhasa terrane

“…6c). The simplest explanation for this observation is a source composed of pyroxenites rather than peridotites in the metasomatized lithospheric mantle (Clemens et al, 2017). Furthermore, the MMEs are characterized by strong depletion in HREEs, conventionally taken to indicate the presence of garnet or amphibole in the source region (or during fractionation) ( Fig.…”

Adakite‐Like Potassic Magmatism and Crust‐Mantle Interaction in a Postcollisional Setting: An Experimental Study of Melting Beneath the Tibetan Plateau

“…Underplating of this kind provides an important mechanism for crustal growth (Annen, 2005;Clemens et al, 2017;Zhao et al, 2009). It also provides a heat source for the melting of crustal materials (Clemens, 2003) together with a source of the high LILE required for the production of adakite-like potassic magmas (Figure 4; see also Wang et al, 2018).…”

“…However, the genesis of postcollisional adakite-like potassic rocks has remained controversial (Castillo, 2012). Proposals have included (1) high-pressure crystal fractionation of shoshonitic mafic magmas (Macpherson et al, 2006;Ribeiro et al, 2016), (2) partial melting of lithospheric mantle modified by sediment metasomatism (Conticelli et al, 2015;Foley et al, 1987;Liu et al, 2014;Mallik et al, 2016;Miller et al, 1999;Turner et al, 1996;Yang et al, 2015), (3) partial melting of thickened lower crust (Chung et al, 2003;Long et al, 2015;Ou et al, 2017;Wang et al, 2005), and (4) partial melting of mafic materials in a thickened lower crust with the input of enriched mantle-derived magma (Clemens et al, 2017;Hou et al, 2004;Hou et al, 2017).…”