the granites of northern Patagonia and the Gastre Fault System in relation to the break -up of Gondwana

The transcurrent Gastre Fault System in central Patagonia, which is closely associated with subvolcanic granite emplacement, is recognized as a major dextral shear-zone and geological boundary. We propose its equivalence to a Late Triassic-Jurassic precursor of the Aghulas Fracture Zone, allowing dextral displacement of the Southern Patagonian Block relative to the rest of South America during the earliest rifting phase of Gondwana break-up. This model could explain some of the inferred movement of the Falkland/Malvinas Islands and alleviate geometrical problems inherent in reconstructions of the South Atlantic region. It can also explain unique geological features of southern Patagonia, such as the Upper Triassic to Lower Jurassic calc-alkaline granitoids of the North Patagonian Massif and the extensive silicic volcanism of Mid-Late Jurassic times. The magmatism is seen as a consequence of the mechanism of Gondwana disintegration and it is not necessary to invoke a relationship to deep mantle structure or plume activity.

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