PETROLOGY AND GEOCHEMISTRY OF A BASINAL TERRANE METAMORPHIC ASSEMBLAGE, SANTA ROSA RANGE, NEVADA: IMPLICATIONS FOR LOCAL LATE CRETACEOUS MAGMATISM

Ongoing research into Mesozoic magmatism in northwestern Nevada suggests that this magmatism may have been petrogenetically influenced by local framework rocks. New LA-ICPMS U-Pb zircon analyses from metaluminous to peraluminous late Cretaceous granitoid intrusions in the Santa Rosa Range (SRR) of northwestern Nevada yield abundant inherited zircon core ages that correlate to published detrital zircon ages from metasedimentary rocks of the Basinal Terrane. This correlation implies that an ancient sedimentary component is involved in granitoid petrogenesis and suggests the potential that the locally exposed metamorphic host rocks may be source reservoirs or contaminants for the magmatism. Therefore, a suite of metamorphic rocks from the SRR were collected to investigate possible relationships between the SRR granitoid intrusions and their local metamorphic hosts. This suite broadly represents the composition of metasedimentary rocks exposed within the Basinal Terrane, allowing for larger regional comparisons. Samples were collected away from granitoid contacts and aureoles to minimize effects of meter-scale geochemical exchange between the granitoids and their hosts; contact metamorphic hornfels materials were avoided. The metamorphic suite represents five of the six formations exposed within the SRR and is characterized predominantly by phyllite with minor quartzite. Despite being petrographically homogeneous, our new geochemical analyses reveal major and trace element heterogeneities within the phyllites, for example: SiO₂ (59 -77 wt%); MgO (0.1-2.5 wt%); Al₂O₃ (10-21 wt%); K₂O (0.9-4.0 wt%); Ba (162-1557 ppm); Rb (40-177 ppm); Sr (49-293 ppm); V (15-125 ppm); and Sc (3-18 ppm). Element-element relationships suggest the following preliminary conclusions: 1) the exposed metamorphic suite does not appear to be a dominant melt source or bulk contaminant in granitoid production and 2) bulk assimilation of exposed metamorphic hosts may exert a minor influence restricted to granitoid margins. The role of host rock partial melting and subsequent magma mixing as a contributor to granitoid evolution currently is under investigation.