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-lived, arc-orthogonal, ductile transfer fault that preserves a history of regional Mesozoic compressional basement deformation and extensional arc pluton emplacement in the Antarctic Peninsula magmatic arc. 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 (D1), brecciation of marble and mylonitization of gneiss by Late Jurassic to Early Cretaceous sinistral shear during the peninsula-wide Palmer Land orogeny (D2), Early Cretaceous dextral transtension with emplacement of gabbro and garnet leucogranite between 140 and 135 Ma (D3), 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 (D4); this is responsible for the current geometry of the shear zone. The Auriga Nunataks shear zone transferred motion between arc-parallel compressional and extensional structural elements and by hosting plutons appears to have acted like a leaky transform fault during episodes of regional extension.

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