Geological Society of America Abstracts with Programs. Vol. 44, No. 7, p.561
An andesitic dome from the eastern sector of the Transmexican Volcanic Belt, in central Mexico, allocates plutonic xenoliths (biotite-quartz-diorite and phlogopite-clinopyroxenite), and andesitic cogenetic dikes, constituting a metaluminous, medium-K, magmatic suite.The dome and dikes are high-silica adakites (60-61 wt%), with high values of Na2O (~4 wt%), Sr (>1000 ppm), and Sr/Y (>60) ratios. They are formed by plagioclase (labradorite-andesine), and zoned Ca-amphibole phenocrysts ranging from edenite to tschermakite. Oxydized amphibole rims are common.Xenoliths are high silica (70 wt%), high-alumina (Al2O3>15 wt%), Ba (599 ppm) and Sr (564 ppm), trondhjemitic (K20/Na2O<1) melts with plagioclase (labradorite-oligoclase), and mica (magnesian siderophyllite and ferroan phlogopite). On the other hand, clinopyroxenites show cumulate texture with high-Ca, green clinopyroxene (ferrian-diopside), phlogopite, and magnesio-hastingsite. The xenoliths are geochemically characterized by high values of MgO (12.55 wt%), Cr (950 ppm), and Ni (190 ppm).Likely, the dome emplacement is diapiric, formed from a hot, water rich, oxidized magma, with predominant amphibole fractional crystallization, with delayed plagioclase crystallization, at pressures between 7-6 kbar. Quartz-diorite xenoliths crystallized from a water-rich primitive felsic magma. Clinopyroxenites are an ultramafic, primitive cumulate rock, dominated by the fractional crystallization of ferromagnesian minerals.