Petrogenesis of heterogeneous mantle peridotites with Ni-rich olivine from the Pujada Ophiolite, Philippines

Abstract

Nickel (Ni) enrichment (>0.40 wt%) in olivine was previously recognized in mantle xenoliths and volcanic rocks. Though this enrichment is often attributed to subarc metasomatic processes, the occurrence of Ni rich olivines in mantle peridotites remains to be established. We found peridotites that randomly contain unusually high-Ni olivines (up to Ni = 0.53 wt%) from the mantle section of the Pujada Ophiolite, Philippines. The Pujada mantle peridotites can be classified into three groups based on their occurrence and spinel Cr#: Group I - massive lherzolites and harzburgites with Cr# = 0.10–0.40, Group II - lherzolite-dunite and harzburgite-dunite interlayers with Cr# = 0.10–0.40, and Group III - interlayered harzburgites and dunites with Cr# >0.40. Rare earth element composition of clinopyroxenes shows general light rare earth element (LREE) depletion and relatively flat heavy rare earth element (HREE) with minor LREE enrichment. The high-Ni olivines are associated to the occurrence of secondary orthopyroxenes, high modal abundance of orthopyroxenes (>30%) and LREE enrichment. The Ni enrichment in olivine is the result of the diffusion of Ni from a pyroxenitic melt. The crystallization of a hybridized melt formed by the combination of pyroxenite melt, primitive MORB melt and siliceous slab-derived melt, shows the same case of formation for the high Ni-olivine phenocrysts in alkali basalts from Hawaii, Kamchatka and the Mexican Volcanic Belt.

Keywords

• Pujada ophiolite
• Peridotites
• Ni-rich olivine
• Philippines