Geochemical Characteristics of Zoned Chromites in Peridotites from the Proterozoic Miaowan Ophiolitic Complex, Yangtze Craton: Implications for Element Mobility and Tectonic Setting

Abstract

The chrome spinel (chromite) in mantle peridotites from ophiolites can shed light on the formation and evolution process of ophiolites. Podiform chromites were found in the Late Proterozoic Miaowan ophiolitic complex (MOC), Yangtze Craton. Due to the metamorphism and intense deformation, most chromite grains in the MOC peridotites show typical chemical zoning (core-rim texture). The values of major and trace elements largely vary from core to rim within chromite grains, indicating that the chromites have undergone strong alteration and element mobility. Major and trace elements in the core parts of chromites are used to infer the tectonic origins and evolution of mantle peridotites in the MOC. The chromites from the MOC peridotites have higher Cr# values and lower Ni and Ga contents with respect to those from Phanero-zoic mantle peridotites, indicating a higher degree of depletion. In-situ major and trace elements (e.g., Ga) characteristics of podiform chromites in the MOC show that chromites from both harzburgites and dunites have strong subduction-related signatures, indicating that the MOC has formed in a supra-subduction setting which is consistent with the geological and geochemical data presented in previous studies.