THE GEOLOGY OF THE TORRES DEL PAINE LACCOLITH, S-CHILE

The Torres del Paine intrusive complex (TPIC) is a composite mafic/granitic intrusion located in Patagonia/Chile. It consists of a basal mafic part (Paine-Mafic-Complex PMC, Michael 1984) and a beautifully exposed granitic laccolith (TPL). The TPIC has been dated by Halpern (1973) at 12±2 Ma. An improved geologic map, basic geometry and the emplacement of the TPIC is discussed here. The PMC forms the base of the Western and Central parts of the TPIC. It consists of two major phases, an early monzonite and a later olivine-gabbro. Igneous structures (layering, xenolith orientations, and major contacts) are vertical in the Western most part of the PMC (East of Lago Grey), while layering and major contacts were found to be sub-horizontal in the central and Eastern most parts of the PMC (Valle Francés). The roof of the PMC is flat to concave. The lower contact is only partially exposed, suggesting the form of a stock or maybe lopolith. Field evidence shows the intrusion of the granite to be after that of the PMC. The TPL intruded in the form of a laccolith along the top of the PMC, shooting into the host rock in the East (West of Rio Ascencio) and the South. The TPL is composed of at least a major porphyritic granite and a boarder phase - several meters to hundreds of meters wide - with a dominantly granophyric texture and abundant miaroles with locally fayalite. The later zone represents most likely a more mobile phase separated from the major porphyritic phase during intrusion. Pre-intrusive structural elements in the host rocks which were passively rotated indicate emplacement by ballooning of the laccolith, in agreement with the shallow emplacement depth(2-4 km). Our detailed field studies suggest that the TPL did not intrude along a thrust plane, in contrast to the proposal of Skarmeta and Castelli (1997). Based on the revised geologic map, profiles and structural data we argue for intrusion of the TPL along the roof of the PMC

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