THE ORIGIN OF RETROGRADE SHEAR ZONES IN THE NAPIER COMPLEX - IMPLICATIONS FOR THE TECTONIC EVOLUTION OF ENDERBY LAND, ANTARCTICA

Abstract

Retrograde shear zones (RSZs) in granulites at Fyfe Hills in the Napier Complex, East Antarctica, formed during a Late Proterozoic or Early Palaeozoic reactivation event. These RSZs preserve a structural and metamorphic record of excavation from depth equivalents of 6-8 kbar (20-26 km) to depth equivalents of 3-5 kbar (10-17 km). Excavation was essentially isothermal suggesting that the RSZs formed in an allochthonous terrain during crustal thickening by low-angle thrusting. Rehydration of the RSZs was accompanied, in part, by large-ion lithophile element enrichment and reduction in K/Rb, features which are attributed to: (1) the retrograde fluid having originated in continental crust that h..