Geochemical and Isotopic Heterogeneities along an Island Arc---Spreading Ridge Intersection: Evidence from the Lewis Hills, Bay of Islands Ophiolite, Newfoundland

This study focuses on the origin of magma heterogeneity and the genesis of refractory, boninite-type magmas along an arc---ridge intersection, exposed in the Lewis Hills (Bay of Islands Ophio-lite). The Lewis Hills contain the fossil fracture zone contact between a split island arc and its related marginal oceanic basin. Three types of intrusions, which are closely related to this narrow tectonic boundary, have been investigated. Parental melts in equilibrium with the ultramafic cumulates of the Pyroxenite Suite are inferred to have high MgO contents and low Al2O3, Na2O and TiO2 contents. The trace element signatures of these Pyroxenite Suite parental melts indicate a re-enriched, highly depleted source with 01 mid-ocean ridge basalt (MORB) abundances of the heavy rare earth elements (HREE). Initial eNd values of the Pyroxenite Suite range from ÿ15 to 06, which overlap those observed for th