The Permian to late Triassic magmatic evolution of SW Pangea: Reconciling evidence from Patagonia and the Antarctic Peninsula

Abstract

The geodynamic setting across the Paleozoic to Mesozoic transition in Patagonia and the Antarctic Peninsula (SW Pangea) has been strongly debated. Hypotheses of terrane accretion, episodes of shallower to flattened subduction, long-lived stages of crustal extension, or even subduction arrest have been variably proposed. We have compiled and re-evaluated the available whole-rock geochemistry and zircon Hf-isotope data for Permian to Triassic rocks from Patagonia and the Antarctic Peninsula, and compared these findings with the orogenic events in these regions.We have identified that two orogenic cycles occurred along the SW margin of Pangea during the Permian-Triassic interval, namely the Gondwanide and Chonide/Peninsula orogenies. Both orogenies coexisted with the development of magmatic arcs; the Permian arc exhibits an overall I-type signature that switched to A-type towards ca. 240 Ma, whereas the Triassic arc has an S-type signature in the Antarctic Peninsula and intraplate features in Patagonia. The Hf isotope data for zircon exhibit broadly subchondritic values, suggesting significant crustal presence in the magmatic source during both cycles. The short- and long-term temporal behavior of the isotopic trends suggests variations that may be attributable to the participation of primitive and/or evolved sources. We conclude that the geochemical and isotopic signatures of the magmas, together with different styles of crustal deformation, resulted from the interaction of the upper and lower plates, consistent with the evolution of an accretionary-type margin along SW Pangea during Permian and Triassic times.