Abstract

Accretionary complex rocks on the Diego Ramirez Islands of southern Chile formed during subduction along the convergent Pacific margin of Gondwanaland. Tectonic melange was produced during a sequence of deformation phases that included early (prelithification?) strata) disruption; isoclinal folding and ductile shearing associated with dynamothermal metamorphism; and postmetamorphic cataclastic flow and brittle faulting. Stratal disruption and melange formation are interpreted to have begun during initial underthrusting beneath the accretionary prism, and to have continued by ductile processes at deeper levels during progressive underthrusting-underplating. Pervasive cataclastic shearing to produce a later generation of melange, followed by slip along two generations of discrete fault zones, occurred as underplated material was tectonically transported to progressively higher levels within the accretionary prism. The multiple stages of melange formation reflect strata) disruption in distinct deformation regimes associated with different structural levels of the accretionary prism.

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