Cenozoic plutonism geochemistry in the extra-andean southern Patagonia as evidences of arc migration process

Abstract

In this work, we present the results of the first study which involves most of several cenozoic satellite plutons located in a 'back-arc' position in west Patagonia, south of the present Chile Triple-Junction. 4 plutons were studied in the northern tip, and 3 in the southern one. The petrographic and geochemical character of these plutons is different enough between them to propose a further classification for them: alkaline (sensu stricto): only the Monte Balmaceda Igneous complex, in the southern extremity; "intra-plate transitional" calc-alkaline: Río de Las Nieves and San Lorenzo plutons in the northern area, and the Torres del Paine Igneous Complex, in the southern area; and "arc transitional" calc-alkaline: the Paso de Las Llaves and Cerro Negro del Ghío plutons in the northern area, and the Cerro Donoso Pluton in the southern area. The "transitional" character, together with the plutons location, and regional context, can be explained by a Mio-Pliocene eastward arc migration coeval with the beginning of the Chile Rise subduction . Slab flattening hypothesis is favoured to explain the arc-migration, and together with the different length and time of arrival of the Chile Rise segments, contributed to the plutons heterogeneous geochemistry.