The Auriga Nunataks shear zone places new tectonic and temporal constraints on the Mesozoic evolution of West Antarctica. The shear zone is a long-lived, are-orthogonal, ductile transfer fault that preserves a history of regional 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 strike. Marble, graphite-bearing pyroxene-granulite, granodiorite-diorite, amphibolite, and gabbro are deformed to mylonite and marble-hosted tectonic breccia. The Mesozoic history of the shear zone is interpreted as follows: emplacement of granodiorite-diorite at circa 206 Ma during Early Jurassic dextral transtension and metamorphism that peaked at circa 188 Ma (D-1), brecciation of marble and mylonitization of gneiss by Late Jurassic to Early Cretaceous sinistral shear during the peninsula-wide Palmer Land orogeny (D-2), Early Cretaceous dextral transtension with emplacement of gabbro and garnet leucogranite between 140 and 135 Ma (D-3), and mid-Cretaceous, ocean-vergent thrusting and sinistral transpression between 125 Ma and 80 Ma, with a peak at circa 110 Ma that folded, mylonitized, and brecciated preexisting plutonic and metamorphic rocks (D-4); this is responsible for the current geometry 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 during episodes of regional extension.
