Geochemical and petrological data suggest that the gabbroic sequence and the volcanic rock series of the Camarines Norte Ophiolite Complex (CNOC) have affinity to back—arc basin materials having muted subduction traces. Major and trace element co-variation plots of the extrusive rocks point to crystal fractionation characterized by a tholeiitic trend and mixing of magmas with variable mantle sources as at least two of the magmatic differentiation processes that controlled their evolution. 'I`he crystallization order of the assemblage is ol -> pl —> Ca-pyroxene +/- opx, which is indicative of a MOR or BAB setting. These mineral phases are also observed in the gabbroic assemblage. The Mg# of the extrusive rocks indicate their highly evolved nature, while Ca, Al and Ti trends suggest that the mantle sources of the CNOC magmas are relatively fertile having undergone low degrees of partial melting. MORB -normalized incompatible multi-element plots andincompatible LILE and HFSE ratios also favor a MOR or marginal basin environment. Commonly utilized tectonic discrimination diagrams also show the dominance of the MOR/marginal basin signature with rare, but persistent, IA components. The lone sample from mainland Camarines Norte, on the other hand, consistently exhibits an IA character although partial melting trends suggests that it could not have been produced in a mature island arc setting.

Geochemical and geochronological evidences support a contiguous Bicol basement composed of a crust - upper mantle assemblage formed in a supra-subduction zone regime. This has significance in the evaluation of the basement complex’s potential to host economic concentrations of chromitites, massive sulfides and platinum-group minerals..