Age and geology of granitoids in northeast Palmer Land, Antarctic Peninsula

Abstract

The Antarctic Peninsula preserves a long history of Late Paleozoic and Mesozoic magmatism that reflects dynamic processes along the southwestern Gondwanan convergent margin. Granitoid magmatism is widespread across the Peninsula and records a complex history of subduction, massive silicic volcanism, and metamorphism. However, direct field observations are rare due to the inaccessibility of many remote outcrops, particularly in the central sector of the Antarctic Peninsula. Robust petrochronological data are even more scarce, limiting the ability to connect rock exposures across large ice-covered areas. Plutonic rocks across parts of the southern Antarctic Peninsula (northeast Palmer Land) lack detailed characterisation and geochronological constraints. Here, UPb isotopes and trace elements (e.g., Ti, P, Ce, Eu, and other REEs) are analysed in zircon (n = 1148) from archived samples from Mount Faith, Mount Sullivan, and Engel Peaks to calculate the timing and nature of magmatic and metamorphic events. These data are supplemented with in situ and whole-rock geochemistry. The resulting magmatic crystallisation ages are Early Jurassic (188–179 Ma) for calc-alkaline, peraluminous, weakly S-type granitoids at all three locations. This novel age constraint for the Mount Faith Granite: (1) indicates it is distinct from all three granitoid emplacement phases at Mount Charity immediately south, and (2) provides an upper age limit on cross-cutting tholeiitic mafic dykes. Deformation of the Mount Faith Granite could reflect either post-crystallisation strain or syn-emplacement strain that deformed granitoids of the Subcordilleran Plutonic Belt. Early Cretaceous (116–120 Ma) recrystallisation of Early Jurassic zircon provide evidence of the first phases of the Palmer Land Event on the central Peninsula. New data presented here provide a detailed geochronology of granitoids in northeast Palmer Land that can be used for Mesozoic tectonic reconstructions.