Processes of formation and filling of a Mesozoic back-arc basin on the island of South Georgia

South Georgia contains a diverse suite of rocks representing different stages in the development of a back-arc basin on the Gondwana margin during the Mesozoic. Basin formation initially involved intrusion of large gabbroic plutons into deformed paragneisses and calc-alkaline rocks of a magmatic arc, and then extension of this crust by dyke emplacement. Partial melting of the metasediments formed a migmatitic aureole around the basic rocks. Rifting of this thinned continental crust led to the emplacement of mafic crust composed of lavas, dykes and plutonic gabbros with oceanic crustal characteristics. On an upper slope marginal to the arc, the mafic crust is overlain by a thinly bedded sequence of tuffs and mudstones deposited by turbidity currents. Overlying andesitic volcaniclastic rudites, deposited by debris flows, represent a major channel-fill sequence. The basin was filled by thick sequences of both arc-derived volcaniclastic sandstones and silicic detritus with a continental provenance. The volcaniclastic sediments form a fault-controlled aggrading system, deposited by high- and low-density turbidity currents in an elongate basin.

Details