The Ophiolite belt of Western Argentina, South America

HALLER MJ

London

Encuentro; Geological Association of Canada, Mineralogical Association of Canada Joint Annual Meeting; 1984

Geological Association of Canada & Mineralogical Association of Canada

A 1000 km long belt of mafic and ultramafic rocks extends along the eastern foothills of the Andes between 25º30’ and 30º South. The structurally deeper rocks of the sequence include harzburgites, wehrlites, diopsidites and dunites, which are partially or wholly serpentinized. In some cases the rocks are composed by actinolite, tremolite and zonal spinels, minerals which obliterate the original plutonic texture. Some of the ultramafics show foliation given by the iso-orientation of spinels and crisotiles. The structurally intermediate level consists of gabbros, some of them completely serpentinized. Remnant cumulus textures are recognizable in the serpentinized gabbros. The rocks of the upper level are formed by pillow-lavas and some lava sheets of a broad basaltic composition and are intruded by small gabbroic intrusive bodies. Thinn chert layers are interbedded in the pillow-lavas. The whole mafic and ultramafic sequence is tectonically disturbed and reverses faulting, over-thrusting and tectonic slices are common. The preliminary geochemical data suggest – as it was shown for the Troodos ophiolite - the presence of two distinct compositional suites of lavas.