【摘要】 贺根山豆荚状铬铁矿是典型的高Al型铬铁矿（Cr^#=47.8～54.9,Mg^#=64.1～73.7）,其中的包体以硅酸盐矿物为主（包括橄榄石、斜方辉石、单斜辉石、韭闪石、钠长石）。根据包体形状、矿物组合及分布特征可将其划分为三类。第一类包体呈孤立单矿物相,主要包括橄榄石和单斜辉石,第二类包体由平衡共生的单斜辉石和斜方辉石构成,上述两类包体均具有被熔蚀的边,且零星分布在尖晶石中,属于捕虏晶成因。第三类包体属于熔融包体,具有多边形外形,包含复杂的矿物相并密集分布于尖晶石核部。利用尖晶石颗粒内部保存完好的单斜辉石以及单斜辉石和斜方辉石包体估算的温度（1148～1254℃）与压力（490～1290 MPa）表明,贺根山豆荚状铬铁矿矿床的形成深度为16～43 km。熔融包体中含大量钠长石和韭闪石,指示铬铁矿母熔体富集H₂O、Na和Si。与铬铁矿平衡母熔体的Al₂O₃含量（15.4%～16.3%）、TiO₂含量（0.3%～0.9%）和FeO/MgO比值（0.6～1.1）与低Ti拉斑玄武质熔体的类似。利用尖晶石和橄榄石包体计算获得铬铁矿原始熔体的MgO含量为～19.8%。贺根山豆荚状铬铁矿经历了深部预富集和浅部成矿两个阶段,其中浅部成矿作用涉及熔体与方辉橄榄岩反应以及演化的熔体与原始熔体混合等过程。更多还原

【Abstract】 The Hegenshan high-Al podiform chromitites have Cr^# values of 47.8～54.9 and Mg^# values of 64.1～73.7. The spinel-hosted inclusions from the chromitites principally consist of silicates which comprise olivine, orthopyroxene, clinopyroxene, pargasite and albite. Three types of inclusions could be identified based on mineral assemblages and distribution characteristics. The type 1 inclusions are monomineralic inclusions that consist of olivine and clinopyroxene. The type 2 inclusions are characterized by the coexistence of orthopyroxene and clinopyroxene. Both type 1 and type 2 inclusions are xenocrysts hosted by spinel. The type 3（3 a, 3 b, 3 c） are melt inclusions. Temperatures（1148～1254℃） and pressures（490～1290 MPa） based on clinopyroxene inclusions and coexisting clinopyroxene and othorpyroxene suggest depths of 16 km to 43 km. The compositions of melt inclusions suggest that the parental melt is rich in H₂O, Na, and Si. The calculated Al₂O₃, TiO₂ and（FeO/MgO） values of the parental melt corresponding to the Hegenshan podiform chromitites are 15.4%～16.3%, 0.3%～0.9% and 0.6～1.1, respectively, which are similar to low-Titholeiitic melt. Calculations based on spinel and olivine inclusions suggest that the primitive melt of the Hegenshan podiform chromitites has a high MgO content of 19.8%. The differences in composition between parental melt and primitive melt suggest an evolving process for primitive melt from high Mg to low Mg. This evolution is probably caused by melt-rock reaction and melt mixing. The genesis of Hegenshan podiform chromitites may have experienced a deep process and finally formed in a shallow mantle. The process in shallow mantle involves processes of the reaction between the melt and harzburgites and mixing of evolved melt and primitive melt.更多还原