%0 Journal Article
%T Different Origins of the Fractionation of Platinum-Group Elements in Raobazhai and Bixiling Mafic-Ultramafic Rocks from the Dabie Orogen, Central China
%A Qing Liu
%A Quanlin Hou
%A Liewen Xie
%A Hui Li
%A Shanqin Ni
%A Yudong Wu
%J Journal of Geological Research
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/631426
%X Concentrations of the platinum group elements (PGEs), including Ir, Ru, Rh, Pt, and Pd, have been determined for both Raobazhai and Bixiling mafic-ultramafic rocks from the Dabie Orogen by fire assay method. Geochemical compositions suggest that the Raobazhai mafic-ultramafic rocks represent mantle residues after variable degrees of partial melting. They show consistent PGE patterns, in which the IPGEs (i.e., Ir and Ru) are strongly enriched over the PPGEs (i.e., Pt and Pd). Both REE and PGE data of the Raobazhai mafic-ultramafic rocks suggest that they have interacted with slab-derived melts during subduction and/or exhumation. The Bixiling ultramafic rocks were produced through fractional crystallization and cumulation from magmas, which led to the fractionated PGE patterns. During fractional crystallization, Pd is in nonsulfide phases, whereas both Ir and Ru must be compatible in some mantle phases. We suggest that the PGE budgets of the ultramafic rocks could be fractionated by interaction with slab-derived melts and fractional crystallization processes. 1. Introduction The platinum group elements (PGEs), including Os, Ir, Ru, Rh, Pt, and Pd, are strongly siderophile and chalcophile elements. They have similar geochemical behaviors during magmatic processes. Traditionally, the PGEs are subdivided into two groups, the compatible IPGEs (Os, Ir, and Ru) and the incompatible PPGEs (Rh, Pd, and Pt) [1]. It has been suggested that the IPGEs are refractory and tend to be retained in the mantle peridotites during partial melting [2]. In contrast, the PPGEs are concentrated in the base metal sulphides (e.g., pentlandite, chalcopyrite), which are released to the melts along with the molten sulfide melts [2]. Because of their unique geochemical characteristics, the PGEs can be used to identify the magma sources and unravel the complex petrogenetic processes, such as partial melting, melt percolation, and metasomatism in the mantle [1]. Mafic-ultramafic rocks have lower REE contents but higher PGE contents than other rocks, so the PGEs have advantages in studying their petrogenetic processes [1, 3¨C7]. In this study, we present the PGE data of both Raobazhai and Bixiling mafic-ultramafic rocks from Dabie Orogen, central China, to discuss their fractionation behaviours during magma evolution. The mechanisms of differentiation between these elements will be examined below, taking into account the geochemical affinities of the PGE and their partition in the mineral phases. The results also demonstrate that the PGEs can provide important information on the genesis
%U http://www.hindawi.com/journals/jgr/2012/631426/