LAUSR

Abstract The Acoje block of the Eocene Zambales ophiolite (NW, Philippines) is a fragment of forearc lithosphere in the Western Pacific and hosts a world-class chromite deposit. The compositions of chromitites, dunites and harzburgites in the block are used to explore origin of ophiolitic chromite deposits during subduction initiation. Chromite grains in these rocks have a large range of Cr# [100 × Cr/(Cr + Al)]. Those in the cpx-rich harzburgites have the lowest Cr# range (15–35). Those in the chromitites have a bimodal Cr# distribution, ~45–48 and 73–76, confirming presence of both high-Al and high-Cr chromitites in the block. Those in the cpx-poor harzburgites and dunites have similar Cr#s, ranging from ~35 to 85. The TiO2 contents of chromite grains are generally