Gabbroic shallow intrusions and lava-hosted xenoliths in the Mount Taylor area, New Mexico

Abstract

—Recent detailed geologic mapping of six quadrangles encompassing Mount taylor volcano has revealed three small shallow intrusive bodies of olivine gabbro and a scoria cone containing 0.5 m long blocks of similar olivine gabbro. these gabbros resemble a large gabbro plug within the amphitheater of Mount taylor in age (3.26 to 2.68 Ma), mineralogy (plagioclase-clinopyroxene-olivine) and fine- to medium-grained texture (average grain size 0.55 to 1.25 mm). Major-element geochemistry indicates the shallow gabbros are similar to trachybasalt lavas erupted in and around Mount taylor from 3.2 to 1.7 Ma. in contrast, shallow olivine gabbros do not chemically resemble medium- to coarse-grained gabbroic xenoliths (mostly orthopyroxene-bearing norite) found in some trachybasalt lavas around Mount taylor. Co-magmatic trachybasalt and shallow gabbro bodies occur in other volcanic terrains (e.g., Stromboli, italy). Coarser grained gabbroic xenoliths co-existing with trachybasalt lavas are noritic and are believed to have a mantle or deep crustal source (e.g., Colton crater, aZ and Mauna Kea, hi). three small areas around Mount taylor have unusual upheaved structure that we postulate may be caused by intrusion of shallow small volume gabbro bodies: San Fidel Dome, Devil Canyon Dome and american Canyon uplift. a low amplitude (± 20 gamma) positive aeromagnetic anomaly above the Devil Canyon dome supports the interpretation that it is underlain by a magnetite-bearing mafic intrusion at depth.