An extensive, crustally-derived, 3325 to 3310 Ma silicic volcanoplutonic suite in the eastern Pilbara Craton: evidence from the Kelly Belt, McPhee Dome and Corunna Downs Batholith

Abstract

New sensitive high resolution ion microprobe zircon U–Pb dating indicates that the eastern Pilbara Craton contains an extensive suite of variably deformed 3325 to 3310 Ma rhyolites, high-level quartz–feldspar porphyries and granitoids. These range in composition from Na-rich trondhjemite (low-K rhyolite) to K-rich monzogranite, with silica-rich (>68%) biotite (±hornblende) bearing porphyritic granodiorites and monzogranites most abundant. Initial volcanism accompanied regional extension at ∼3325 Ma and was followed by intrusion of high-level porphyritic stocks and emplacement of massive to foliated batholithic granitoids at ∼3315 Ma. The compositions of this volcano plutonic suite suggest that the most likely source for parent magmas is older continental crust with tonalite–trondhjemite–granodiorite suite compositions. Crustally-derived silicic volcanic rocks and granitoids have traditionally been considered rare in pre-3.0 Ga granitoid–greenstone terranes. Evidence from the eastern Pilbara indicates that magmatic recycling of continental crust has occurred at least as early as 3.3 Ga.