Ultramafic intrusives in the Sierra de Córdoba, Argentina

Abstract

?Ultramafic intrusives in the Sierra de Córdoba, Argentina?. Ultramafic bodies of Alpine type outcrop over a belt of 120 kilometers within the Precambrian basament of the Sierra de Córdoba. They occur on metamorphosed sedimentary rocks belonging to the amphibolite
facies and range from small pods to sill like masses up to one kilometer in length.

The intrusives with a small central core of relatively fresh bronzitite are bounded by a mass of serpentinite. The composition of the primary rock is: 10% to 15% olivine (Fo98-96), 80% bronzite (En88-84) and 5% to 10% chromite plus magnetite. Primary layering is represented by differentiates of olivine and chromite with layers of bronzite.

Chromite pods and lenses, sometimes rimmed by steatite borders, ranging from few centimeters up to one meter in width are made up of chromite and magnetite with minor picotite, augite and enstatite.

Metamorphic aureoles between the ultramafics and country rocks, as well as metamorphic differentiation processes, are described.