新疆北山地区红石山镁铁-超镁铁岩体的岩石矿物学特征:对同化混染和结晶分异过程的启示

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

结晶分异和同化混染是侵入岩体形成过程中控制岩相成分和分异程度的主导因素.探讨这两个因素在岩浆演化过程中的作用阶段及对矿物成分变化的影响对揭示岩体成因和成矿具有重要意义.新疆北山地区的红石山镁铁-超镁铁岩体钻孔剖面上岩相和各种矿物含量的渐变特征反映了岩浆演化的结晶分异过程.长石中Si、Na、Al、Ca和单斜辉石中Si、Al、Ti、Ca、Mg的系统变化揭示不同程度的同化混染作用.橄榄石和尖晶石对同化混染作用的反应较为迟缓,但其Fo、Ni和Cr#、Ti对新鲜岩浆注入较为敏感.这些矿物化学对岩浆演化过程的推断与全岩成分变化的指示相一致.因此,矿物化学在研究岩浆演化方面将会发挥重要作用.

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 W, 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.