Petrological and mineralogical characteristics of Hongshishan mafic-ultramafic complex in Beishan area,Xinjiang: Implications for assimilation and fractional crystallization.

Abstract

Fractional crystallization and assimilation constrain lithological composition and fraction, and play a key role in the formation of intrusive complex. Both processes can modify mineral compositions and the order of crystallization and have important significances for petrogenesis and associated metallogenesis. Hongshishan mafic-ultramafic complex in Beishan area ( Xinjiang) displays gradual transition in lithology and mineral modal, which demonstrates fractional crystallization. Si, Na, Al, Ca in plagioclase and Si, Al, Ti, Ca, Mg in clinopyroxene have systematic variations and indicate assimilation in different extent. Whereas, olivine and spinel are not sensitive to assimilation process, but multiple magma injection in terms of Fo, Ni and Cr , Ti contents. These assumptions inferred from mineral chemistry are consistent with those from whole rock compositional variations. Therefore, mineral chemistry is an alternative tool to trace magma evolution.