Triassic magmatism and metamorphism in the Antarctic Peninsula: Identifying the extent and timing of the Peninsula Orogeny

The mid to Late Triassic marks an episode of magmatism, deformation and metamorphism along the proto-Pacific margin of the Antarctic Peninsula and Patagonia. Calc-alkaline magmatism at ~227 Ma developed in a convergent margin setting across the central Antarctic Peninsula and North Patagonian Massif. Two distinct deformation and metamorphic events have been identified at ~221 Ma and ~207 Ma based on new U-Pb zircon ages from a metamorphic orthogneiss complex, investigated for the first time, from the elevated plateau region of central Palmer Land. These two events are interpreted to date the timing of the multi-phase Peninsula Orogeny, which correlates with the Chonide Event of central Patagonia. The onset of deformation in the Antarctic Peninsula is linked to tectonic events in central Patagonia and is associated with non-collisional slab dynamic processes during flat slab subduction in the Late Triassic. No consistent tectonic regime is evident during the mid-to Late Triassic episodes of deformation and metamorphism, but an initial period of extension/transtension (mid-Triassic) and a compressional regime in the Late Triassic is favoured in the Antarctic Peninsula and Patagonia. The newly acquired metamorphic ages provide no clear evidence for a segmented terrane model for the Antarctic Peninsula, as Late Triassic metamorphic ages are identified from across the central and eastern domains. New U-Pb zircon ages are also presented from a suite of strongly foliated granitoids that cross-cut the Triassic orthogneisses. They are dated in the interval 140–136 Ma and represent an episode of Early Cretaceous magmatism, transtensional deformation and widespread metamorphism across northwest and central Palmer Land.