中国金伯利岩地球化学

本文利用了100多个金伯利岩的主要元素及微量元素分析结果,用Si/Mg、C.l——(SiO_2+Al_2O_3+Na_2O)/(MgO+2K_2O)、Mg/(Mg+Fe)比值及SiO_2、Al_2O_3及Na_2O含量研究了金伯利岩的混染程度。结果表明,绝大部分金伯利岩受到了混染作用的影响,它们的成分实际上不能代表形成这些岩石的岩浆的成分。金伯利岩的Al_2O_3和Na_2O的含量比其他碱性超基性及基性岩石的Al_2O_3和Na_2O含量低得多。含金刚石的金伯利岩比不含金刚石的金伯利岩的MgO、(Cr_2O_3+NiO)高,而TiO_2+Al_2O_3+Na_2O+K_2O+P_2O_5低。 我国金伯利岩中Cr-Al,Ni-Co,Ni-Cr,Ni-V,Sc-Ti,Zn-Ti,Ba-Sr,Zr-Hf,Nb-Ta,U-Th,K-Rb呈正相关关系。

GEOCHEMISTRY OF KIMBERLITES IN CHINA

More than 100 analyses of major and trace elements of kimberlites have been undertaken. Degree of contamination of analyzed kimberlites has been estimated by Si/Mg, C. I. =(SiO2 +Al2O3 + Na2O)/(MgO + 2K2O), Mg/(Mg + Fe), SiO2, Al2O3 and Na2O contents. Most of kimberlites were contaminated and their compositions in fact not represent the compositions of the magmas from which they formed. The Al2O3 and Na2O contents of kimberlites are extremely low relative to those of other alkaline ultrabasic and basic rocks. Diamond-bearing kimberlites are relatively richer in MgO, (Cr2O3 + NiO)contents and poorer in TiO2 + Al2O3 +Na2O+ K2O +P2O5 than diamond-free kimberlites.The mean abundances of compatible elements in kimberlites from China are: Cr 846ppm, Ni 69Qppm, Co 45ppm, Sc 19.96ppm Cu 156ppm, Zn 106ppm. Cr-Al, Ni-Co, Ni-Cr, Ni-V, Sc-Ti, Zn-Ti of kimberlites show positive correlations. The average and ranges of the incompatible elements of kimberlites from China are: Ba 835ppm(22.76-6030ppm), Sr 454ppm(109.7-1341ppm), Zr 308ppm (12.15-1113ppm), Nb 81ppm (12-48.72ppm), Ta 11ppm(10-18.5ppm), U 8.8ppm(0-32ppm), Th 70ppm(20-140ppm), Li 44.68ppm(2.69 148ppm), Rb 29ppm (10-60ppm). Ba-Sr, Zr-Hf, Nb-Ta, U-Th, K-Rb of kimberlites show positive correlations.