Thermal, chemical, and structural characteristics of fluid migration and fluid-rock interaction in a mid-Proterozoic shear zone, Manzano Mountains, New Mexico.

Abstract

The structure in the study area is dominated by a large, mid-Proterozoic shear zone that strikes NE and dips steeply SE. The zone had a NW directed tectonic transport direction during the shearing. Hydrothermal veining developed at several stages in the deformational history. Early fluids were relatively low in salinity and CO$\sb2$ content and flowed through the rock in small, pervasive structural sites produced by ductile deformation. Fluids migrating through the shear zone at progressively later times tended to be more focused along larger more brittle structures, and had higher salinity and CO$\sb2$ contents. The earliest veins show little alteration of the host rocks while progressively later veins show increasing amounts of wall rock alteration. Alteration near early veins is broadly characterized by increased Fe, Mg, Ca, and Al and decreased Si and K; later veins have increased Si and K, manifested by silicification, sericitization, +/$-$ sulfidization of the host rocks.