Petrology of the lower crust and upper mantle beneath southeastern Chihuahua, Mexico: a progress report.

Abstract

Xenoliths of lower crustal and upper mantle rocks occur in a host alkali basalt at the La Olivina peridot mine, Mexico. The ultramafic rocks are of three compositional groups distinguished by clinopyroxene chemistry similar to those from San Carlos, Arizona, Kilbourne Hole, New Mexico, USA, and Xalapasco de La Joya, San Luis Potosi (Mexico). The mantle xenoliths are of three textural groups: allotriomorphic granular (igneous?), porphyroclastic (metamorphic?) and granoblastic (metamorphic?). The lower crust xenoliths are mainly pelitic gneisses of uniform mineral assemblage, and pyroxene-granulites, mostly plagioclase-bearing, but some with scapolite instead. These xenoliths resemble those from Kilbourne Hole, and have been dated at approx 1400 m.y., which agrees well with Kilbourne Hole. It seems likely that the Precambrian craton underlying Kilbourne Hole extends SE into Mexico at least as far as La Olivina.-R.E.S.