Varying mantle sources of supra-subduction zone ophiolites: REE evidence from the Zambales Ophiolite Complex, Luzon, Philippines

Abstract

The Zambales Ophiolite Complex, a supra-subduction zone ophiolite, is characterized by three volcanic-hypabyssal rock units: the Coto Block volcanic-hypabyssal rocks, the Coto dikes intruded into the Coto residual peridotites and the Acoje Block volcanic-hypabyssal rocks. The first two groups exhibit transitional mid-ocean ridge-island arc characteristics while the latter reveals island arc affinity. Furthermore, these three volcanic rock suites are characterized by differing bulk REE, major-element, trace-element and mineral chemistries. The Coto Block volcanic-hypabyssal rocks [ (Ce Yb) n 0.4–1.0; TiO 2 0.50–1.50 wt.%; Zr 31–76 ppm; Y 13–31 ppm] have higher REE, Ti, Zr and Y than the Coto dikes [ (Ce Yb) n 0.3–0.8; TiO 2 0.52–0.94 wt.%; Zr 15–55 ppm; Y 10–27 ppm] and the Acoje Block volcanic-hypabyssal rocks [ (Ce Yb) n 0.2–0.3; TiO 2 0.26–0.86 wt.%; Zr 11–45 ppm; Y 10–23 ppm] arguing for an increasing degree of melting of the sources from the former to the latter. These data suggest the involvement of several mantle sources which have undergone different degrees of partial melting and LREE addition as evidenced by the presence of LREE-enriched basalts [ (Ce Yb) n 3–5] among the Coto Block volcanic-hypabyssal rocks. These results further illustrate the complexities involved in the generation and evolution of supra-subduction zone ophiolites.