Abstract

Petrographical and geochemical (i.e. mineral and whole rock major, REE) data, and geothermobarometry estimates for a suite of crustal and upper mantle xenoliths from the Venetia Diamond Mine suggest a major crust forming event involving both subduction and crustal thickening between ~3.0 to ~2.6 Ga. The compositionally diverse xenoliths of felsic to mafic amphibolite, and granulite, and eclogite are compatible with being the respective protolith and restites involved in partial melting. Conditions of melting are constrained by comparing the characteristics of the xenoliths from Venetia with those of experimental charges from recent amphibolite melting experiments. The resulting melt products are correlated with Throndhjemite-Tonalite-Granite (TTG) lithologies currently exposed in the Northern Marginal and Central Zones of the Limpopo Belt. Geochemical data for the eclogite xenoliths in this study suggest that they may be remnants of Archean oceanic crust which has had partial melt extracted from it during subduction, whereas the intermediate-felsic garnet-quartz xenoliths are compatible with being restites from melting shallow, more ferroan sources during crustal thickening. A new geotectonic model for the Limpopo Belt based on the xenolith data is suggested.

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