Distribution of mantle-melt interaction zone: A petrological exploration tool for podiform chromitite deposits in the Kalaymyo ophiolite, Myanmar

Abstract

Podiform chromitite deposits in the Kalaymyo ophiolite, Myanmar, are hosted by replacive dunites and harzburgites with varying degrees of mantle-melt interaction. Combining petrography and spinel and whole-rock compositions of harzburgites from the Bophi-Vum area, one of the ultramafic massifs of the Kalaymyo ophiolite, we investigated petrological and geochemical indicators of the mantle-melt interaction in the harzburgites and their spatial relationship with the location of chromitites.Two end-member types of mantle harzburgites with distinct textures and compositions are recognized in the study area. Low-Cr# (Cr-spinel Cr# < 30; Cr# = molar Cr/(Cr + Al) × 100) harzburgites represent residual mantle peridotites after low degree of partial melting. They are characterized by high whole-rock Al2O3, CaO, and TiO2 contents with a negative correlation between spinel Cr# and TiO2 contents, following the partial melting model trend of the depleted mid-ocean ridge basalt (MORB) mantle. The Cr-spinels from the low-Cr# harzburgites are lobate and vermicular and occur in association with orthopyroxenes, which is typical features of residual harzburgites. On the other hand, the high-Cr# (Cr-spinel Cr# > 30) harzburgites mostly have lower whole-rock Al2O3 (< ~1.4 wt%), CaO (< ~1.3 wt%), and TiO2 (< ~0.04 wt%) contents than the low-Cr# harzburgites, indicating lower modal abundances of pyroxenes. The positive correlation between spinel Cr# and TiO2 contents in the high-Cr# harzburgites suggests their metasomatic origin from the interaction between the low-Cr# harzburgite and island-arc tholeiitic or boninitic melts. The Cr-spinels from the high-Cr# harzburgites, recrystallized during the mantle-melt interaction, are mostly euhedral and associated with olivine.Geochemical maps of the spinel Cr#, whole-rock Al2O3, and CaO contents for the mantle harzburgites show that the distribution of the high-Cr# harzburgites, i.e., the mantle-melt interaction zone, is closely associated with the locations of the dunite and chromitite outcrops. This spatial relationship suggests the potential use of the distribution of mantle-melt interaction zone for podiform chromitite exploration in the study area.