Structural evolution of the magmatic arc in northern Palmer Land, Antarctic Peninsula

In northern Palmer Land, Antarctic Peninsula, the magmatic arc has developed by the interaction of compressional and extensional tectonics. Periods of magmatism and arc compression in the Early Jurassic and Early to middle Cretaceous separate periods of arc and backarc extension in the Middle to Late Jurassic and Tertiary. Sheeted migmatite complexes and orthogneiss are mostly Jurassic arc plutons emplaced into older paragneiss. Heterogeneous regional deformation produced major shear zones, and the orientation of shear zones, foliation, and banding describe a fan diverging upward from the center of the arc. Mafic dikes and steep extensional shear zones throughout northern Palmer Land and thick amygdaloidal basalt sheets in northeastern Palmer Land are related to Jurassic extension of the arc and formation of a backarc basin filled by thick clastic sediments (Mount Hill and Latady formations). The arc and backarc were intensely deformed during the Cretaceous. Penetrative deformation of the backarc basin sedimentary rocks produced east verging folds; whereas the arc was deformed by discrete east directed thrust zones as much as 1 km thick. Previously, the metamorphic rocks in northern Palmer Land were considered as part of a pre‐late Paleozoic basement or as the roots of the Gondwanian orogen. Most of them are now shown to be deformed plutons of the Mesozoic magmatic arc. The deformation on the west side of the peninsula may be due to trench‐directed thrusting; whereas the deformation on the east side may be the result of backarc basin closure.