Palaeoarchaean (3.3 Ga) mafic magmatism and Palaeoproterozoic (2.02 Ga) amphibolite-facies metamorphism in the Central Zone of the Limpopo Belt: New geochronological, petrological and geochemical constraints from metabasic and metapelitic rocks from the Venetia area

摘要

We present new geochronological, geochemical, and petrological data of metapelitic and metabasitic rocks of the Krone metammorphic terrane, which forms the floor to the Venetia Klippen Complex in the Central zone of the Limpopo Belt. The combined datasets provide evidence that the metabasic rocks are relies of tholeiitic basalts that were emplaced during the Palaeoarchaean at 3.32 Ga and that these rocks - together with associated metapelitic rocks - underwent a Barrovian-type metamorphic overprint during the Palaeoproterozoic at 2.015 Ga. This is constrained by cathodoluminescence and in-situ laser ablation SF-ICP-MS analyses of zircon and monazite in thin sections. It is further supported by P-T pseudosection calculations in conjunction with observed mineral assemblages, mineral zoning patterns, and rock textures. the petrological results provide evidence that the rocks of the Krone metamorphic terrane underwent a prograde P-T increase from about 570 degrees C/4.5 kbar to 680 degrees C / 6.5 kbar, followed by a retrograde decompression-cooling to 550 degrees C/4 kbar. The new results in combination with previously published P-T-t data therefore support an interpretation wherein the rocks of the Krone Metamorphic Terrane and the overlying Venetia Klippen Complex contain relies of the same Palaeoarchaean (3.3 to 3.0 Ga) terrane, which was affected by granite intrusions at 2.60 to 2.65 Ga, and subsequently exposed and overlain by clastic sediments between 2.60 and 2.03 Ga. All rocks then experienced an amphibolite-facies metamorphic overprint in response to think-skin fold-and-thrust tectonics during the Palaeoproterozoic at 2.02 Ga.