Geochemistry and mineralogy of the Eocene-Oligocene volcanic sequence, southern Sierra Madre Occidental, Juchipila, Zacatecas, Mexico

Abstract

The Sierra Madre Occidental (SMO) volcanic province of western Mexico is a remnant of a broad continental-margin orogenic belt formed as a result of mid-Tertiary subduction of the Farallon plate beneath Mexico. The most voluminous rocks exposed in the SMO are rhyolitic ash-flow tuffs (AFT) erupted throughout most of the province from 36 to 27 Ma. Two other magmatic eposides recorded in the SMO include an Eocene event (53-40 Ma) characterized by mafic-intermediate composition lava flows, and a post-ignimbrite event (29-20 Ma) characterized by the eruption of extension-related basaltic-andesites. This paper presents new data for an area in the southern SMO which has evidence for both Eocene and Oligocene volcanism. -from Authors