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Petrology and geochemistry of crustal and upper mantle xenoliths from the Venetia Diamond Mine – evidence for Archean crustal growth and subduction

Pacific Centre for Isotopic and Geochemical Research (PCIGR) and Mineral Deposit Research Unit (MDRU), Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Rd., Vancouver, British Columbia, Canada, V6T 1Z4, email: wpretorius{at}eos.ubc.ca
Department of Geology, Rand Afrikaans University, Johannesburg, South Africa, e-mail: jmb{at}na.rau.ac.za

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.

This article has been cited by other articles:

				J.M. Barton Jr., R. Klemd, and A. Zeh The Limpopo Belt: A result of Archean to Proterozoic, Turkic-type orogenesis? Geological Society of America Special Papers, January 1, 2006; 405(0): 315 - 332. [Abstract] [Full Text] [PDF]