A view into the subsurface of Mauna Kea volcano, Hawaii: Crystallization processes interpreted through the petrology and petrography of gabbroic and ultramafic xenoliths

Abstract

Xenoliths from the southern flank of Mauna Kea volcano form two broad categories. (1) Ultramafic: porphyroclastic dunite, wehrlite, and olivine clinopyroxenite (Fo89·4-83·6, clinopyroxene mg-number 90·3-86·3, spinel mg-number 57-42, spinel cr-number 70-52, no plagioclase); and granular wehrlite and olivine clinopyroxenite (Fo83-76) with plagioclase (An84-69) ± orthopyroxene, and Crmagnetite. (2) Gabbroic:granulargabbro, gabbrononte, and troctolite composed of olivine+ clinopyroxene frameworks (Fo82-74, mg-number 85-79) enclosing plagioclase (∼An79-69) ± orthopyroxene, and Fe-Ti oxides; and plagioclase ( 4 wt %). These Mauna Kea xenoliths are plutonic complements to postshield lavas (Hamakua Volcanics), and they identify that stage of volcano development with 15-5 wt % MgO magmas that underwent processes intrinsic to mafic-layered intrusions- e.g. in situ and gravity-settled crystallization, extensive differentiation, varieties of layering, mobilizations of late-stage, evolved liquids, compaction and convective disturbances in reservoirs.