中国金伯利岩中的单斜辉石  

CLINOPYROXENES IN KIMBERLITES OF CHINA

作　　者：董振信[1] 

机构地区：[1]中国地质博物馆

出　　处：《地质学报》1992年第1期35-47,共13页Acta Geologica Sinica

摘　　要：本文对我国金伯利岩中,作为巨晶、粗晶、基质相矿物、与镁铝榴石和钛铁矿的连生体、深源岩石包体矿物及金刚石中包体矿物产出的单斜辉石的粒度、形态、颜色及蚀变壳、矿物种属、化学成分特征、端员组分、红外光谱等进行了研究。并与玄武岩中的巨晶及其深源岩石包体矿物、钾镁煌斑岩和云煌岩中的单斜辉石作了对比。研究了单斜辉石和镁铝榴石共生对。探讨了金伯利岩中单斜辉石的成因,形成的温、压条件及所反映出的金伯利岩体形成的构造环境,指出了该矿物在找寻金刚石矿工作中的指示标志。The principal conclusions of this work are as follows: (1) Clinopyroxenes in kimberlites are dominated by endiopside with subordinate diopside and minor salite and augite. (2) Megacryst and macrocryst clinopyroxenes in kimberlites occur as single crystals and typically as smooth rounded nodules. They often are covered with an altered coat consisting of very fine-grained serpentine and calcite aggregates. (3) Ca/(Ca+Mg) ratios (30.7％—44.07％) of megacryst clinopyroxenes are lower than those (40.37—55.83％) of macrocryst clinopyroxenes, but much lower than those (50.35％—57.68％) of clinopyroxenes occurring as ground mass phase. (4) Clinopyroxenes in kimberlites exhibit a large scatter in SiO_2 and Al_2O_3, contents, and a weak negative correlation exists between SiO_2 and Al_2O_3 contents. (5) Megacryst and macrocryst clinopyroxenes in limberlites are high-Al~Ⅵ and low-Al~Ⅵ in contrast, clinopyroxenes occurring as groundmass phase in kimberlites and inclusion mine- rals in basalts are low-Al~Ⅵ and high-Al~Ⅵ. Moreover, Al~Ⅵ of clinopyroxene inclusions in diamonds is much higher than Al~Ⅵ (6) Some macrocryst clinopyroxenes in kimberlites are compositionally, close to those of peridotke-pyroxenite inclusions in kimberlites, reflecting the former have been derived from the latter. (7) The coexisting clinopyroxenes and garnets m kimberlites and their inclusions are in an equilibrium state under variable P-T conditions. (8) The absorption band positions of infrared spectra for clinopyroxenes shift to the higher frequence with increasing Mg/(Mg+Ca). (9) P-T fields of formation of kimberlite clinopyroxenes in China are located near or on the shield geothermal curve, tallying with the fact that kimberlites occur tectonically within stable platforms. (10) Clinopyroxenes containing lower Al_2O_3, Ca/(Ca+Mg), Ca/(Ca+Mg+Fe) and CaAl_2SiO_6, (Tsch) and higher Mg/(Mg+Ca), Cr_2O_3 and Al~Ⅵ/Al~Ⅵ were formed at high T, especi

关 键 词：金伯利岩 单斜辉石 地球化学 

分 类 号：P588.125[天文地球—岩石学]