Zircon O and Hf isotopic constraints on the genesis of Permian-Triassic magmatic and metamorphic rocks in the Antarctic Peninsula and correlations with Patagonia

Abstract

The Permian–Triassic is a critical period for interpreting and understanding the development of West Antarctica and its correlations into Patagonia, South America. The Antarctic Peninsula preserves isolated outcrops of Permian–Triassic age magmatic and metamorphic rocks of granodiorite, orthogneiss, paragneiss and migmatites. Outcrops from the eastern margin of the Antarctic Peninsula (Eastern Domain) have the strongest affinity with continental Gondwana, and have igneous zircons with initial εHf values ranging from −2.8 to −21.6, and δ18O from 10.5 to 5.6‰. These values record a strong sedimentary influence on the magma source and imply crustal recycling. This is in concert with the extensive inherited zircon components that record late Mesoproterozoic–early Neoproterozoic ages, Cambrian and older Permian ages. U–Pb zircon ages for a ca. 202 Ma orthogneiss from the western Antarctic Peninsula (Central Domain) record the presence of a Permian protolith with zircon overgrowth at ca. 222 Ma due to partial melting. These zircon rims have initial εHf values of +1.5 to −0.9 and δ18O of 5.3 to 4.2‰, similar to those determined for the cores. This indicates that the new zircon crystallised from dissolution of partly dissolved cores. Our new data indicate strong similarities between the Eastern Domain of the Antarctic Peninsula and the southern tip of Patagonia, supporting a continuation of both areas, without the need for a great degree of geographical overlap during the Permian and Triassic.