Abstract: Ophiolite and Ophiolitic Complexes in the Philippines

Graciano P. Yumul, Jr.

An ophiolite complex is defined as an oceanic crust- mantle sequence composed of pillow basalts, sheeted dike/sill complexes, high-level gabbros, mafic and ultramafic cumulate rocks, and residual peridotites. A similar sequence that lacks a portion of this rock suite is termed an ophiolitic complex. A compilation of the existing database and interpretation of available petrological and geochemical information on the Philippine ophiolite and ophiolitic complexes show the following. (1) The Philippine basement is composed of metamorphic blocks, ophiolite and oceanic crust/mantle sequences of mid-ocean ridge, marginal basin, ocean island, and island-arc derivations. (2) There is no systematic younging of the different mantle-crust sequences in any direction of the island-arc system. This is opposite to what has been observed in other circum-Pacific areas (e.g., Siberia, Japan, and the United States west coast). (3) Emplacement of the different ophiolite/ophiolitic complexes involved subduction related thrusting, onramping, and strike-slip mechanism. (4) Almost all of the Philippine ophiolite/ophiolitic complexes exhibit supra-subduction zone (SSZ) signatures. (5) Cr. Ni, volcanic-hosted massive sulfides and platinum group of minerals, are dominantly associated with the SSZ complexes.

Aside from offering constraints on the accretion/amalgamation history of the Philippine island-arc system, the recognized geochemical and tectonic relationships in the different ophiolite/ophiolitic complexes show them to be promising exploration playgrounds in the search for specific metallic minerals.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994