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Granitoids in Chile

Luis Aguirre
Luis Aguirre
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January 01, 1983

Granitoid rocks are exposed in nearly forty per cent of Chile. The main periods of emplacement, indicated by isotopic data and stratigraphic relations, are Carboniferous, Jurassic, Cretaceous, and Tertiary, and they approximately coincide with the ages of the principal orogenic phases recorded in the country. The commonest rock types, regardless of age, are granodiorite and tonalite, but the compositional range is broad, and diorite, granite, quartz diorite, and gabbro are common.

The Paleozoic granitoids intrude stratified formations from Late Ordovician to latest Permian in age and are intruded by Cretaceous and Tertiary plutons. Their contacts are sharply discordant in some localities and transitional, accompanied by widespread migmatization, in others. A close relationship between the Paleozoic granitoids and high-temperature, low-pressure metamorphic series is well known in Central Chile. The Paleozoic granitoids are closely related in space with rhyolitic volcanic rocks of Permo-Triassic age in the Andes of north Central Chile.

The Mesozoic and Cenozoic (Andean) granitoids cut rocks ranging in age from Paleozoic to Late Tertiary. Their transgressive contact relations indicate a post-kinematic character, and thermal aureoles are present in several regions. Mineral deposits, especially copper, iron, molybdenum, and zinc are genetically related to these granitoids. The Tertiary granitoids are richer in alkalis than those of the Mesozoic, and some are directly associated with porphyry copper deposits. A genetic relation between the Tertiary granitoids and Pliocene andesitic flows has been suggested on the basic of Rb/Sr ratios. The age of the Andean granitoids decreases from west to east, and the initial Sr87/Sr86 ratio of granitoids, with ages ranging from mid-Cretaceous to Quaternary, shows a systematic west to east increase from 0.7022 to 0.7077, which indicates a change in the locus of melting.

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GSA Memoirs

Circum-Pacific Plutonic Terranes

J. A. Roddick
J. A. Roddick
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Geological Society of America
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January 01, 1983




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