Abstract

FERRACUTTI, G.; BJERG, E.  and  MOGESSIE, A.. Petrology and geochemistry of mafic-ultramafic rocks in the Las Águilas River-of the Manantiales stream area, San Luis. Rev. Asoc. Geol. Argent. [online]. 2007, vol.62, n.3, pp.405-416. ISSN 0004-4822.

Geological mapping was completed in the area between Las Águilas River and the Manantiales stream in San Luis province due to the absence of a detailed geologic map of the mafic-ultramafic bodies which occur in this region. Also the lack of petrographic and geochemical information constituted a draw back when attempting to relate surface and subsurface rocks. In this contribution a geological map of the area and the petrological- geochemical nature of the different igneous rocks are presented. The mafic-ultramafic bodies are in contact with the metamorphic basement trough high angle faults and sometimes by intrusive relationships. At Las Higueras and Virorco bodies it was possible to identify igneous rock outcrops with layered magmatic texture of the non-uniform and with intermittent regularity type. These bodies were affected by deformation-metamorphism and alteration processes. As a result not only in the mineralogy of the rocks was changed, but also spatial position of the units was affected as revealed by the disposition of the layering of the mafic rocks. The rare earth patterns normalized to chondrite allow the identification of a magmatic differentiation process, with the largest rare earth enrichments corresponding to the most evolved rocks. The ultramafic rocks rare earth contents indicate that the magmatic crystallization was controlled by the formation of olivine and orthopyroxene.

Keywords : Mafic-ultramafic rocks; Petrography; Geochemistry; San Luis.

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