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The evolution of magmatic activity along the Pacific margin of southern South America and West Antarctica is considered in terms of the alignment, timing and petrogenesis of calc-alkaline granitoid emplacement. Distinct lower Paleozoic, upper Paleozoic to Triassic, and Triassic/earliest Jurassic belts in north-central Chile trend gradually across the continent into Argentina. Granitoids of similar ages also occur in the Antarctic Peninsula and adjacent parts of West Antarctica, although their linear distribution is not well known. These early granitoids were derived from magmas that contained a significant component of the deep continental crust close to the zone of melting. The Paleozoic belts are transected by mid-Jurassic to Tertiary plutonic belts, which are parallel to the Pacific coast throughout the region. The initial 87Sr/86Sr ratios of these younger granitoids decrease with time, suggesting a diminishing continental input, perhaps due to deeper melting in the mantle during extensional phases in a migrating subduction regime.

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