The Auriga Nunataks shear zone: Mesozoic transfer faulting and arc deformation in northwest Palmer Land, Antarctica

The Auriga Nunataks shear zone places new tectonic and temporal constraints on the Mesozoic evolution of West Antarctica. The shear zone is a long-liv ed, are-orthogonal, ductile transfer fault that preserves a history of regi onal Mesozoic compressional basement deformation and extensional are pluton emplacement in the Antarctic Peninsula magmatic are. It forms an east-west trending positive flower structure 2.4 km wide, exposed along 5 km of stri ke. Marble, graphite-bearing pyroxene-granulite, granodiorite-diorite, amph ibolite, and gabbro are deformed to mylonite and marble-hosted tectonic bre ccia. The Mesozoic history of the shear zone is interpreted as follows: emp lacement of granodiorite-diorite at circa 206 Ma during Early Jurassic dext ral transtension and metamorphism that peaked at circa 188 Ma (D-1), brecci ation of marble and mylonitization of gneiss by Late Jurassic to Early Cret aceous sinistral shear during the peninsula-wide Palmer Land orogeny (D-2), Early Cretaceous dextral transtension with emplacement of gabbro and garne t leucogranite between 140 and 135 Ma (D-3), and mid-Cretaceous, ocean-verg ent thrusting and sinistral transpression between 125 Ma and 80 Ma, with a peak at circa 110 Ma that folded, mylonitized, and brecciated preexisting p lutonic and metamorphic rocks (D-4); this is responsible for the current ge ometry of the shear zone. The Auriga Nunataks shear zone transferred motion between are-parallel compressional and extensional structural elements and by hosting plutons appears to have acted like a leaky transform fault duri ng episodes of regional extension.