四川南江坪河超基性-碱性岩体矿物学与地球化学研究

STUDY ON MINERALOGY AND GEOCHEMISTRY OF THE PINGHE ULTRABASIC ALKALINE ROCK BODY, NANJIANG, SICHUAN

对四川南江坪河岩体的主要造岩矿物、岩石化学、微量元素和稀土元素地球化学，以及同位素进行了研究。结果表明钛铁霞辉岩、霓霞岩和磷霞岩具有明显的演化趋势，形成于较高的温压条件下，是一个成因密切的岩石系列。霞石正长岩，碱性正长岩和闪长岩则与之既有相似之处又有区别。据Ｓｒ、Ｎｄ同位素和稀土特征推测，该岩石系列可能由交代地幔高程度批式熔融形成，而霞石正长岩等则为同源岩浆晚期结晶分异的产物。

In the Pinghe ultrabasic alkaline rock body, jacupirangite, ijolite and urtite with the same mineral species, some similar and progressive evolutional features in petrochemistry , trace element and REE geochemistry show that they belong to the same genetic series and formed under higher pressure and temperature environment. Nepheline syenite in this rock body, exhibiting obvious different mineral compositional and petrochemical characteristics, formed under a rather lower pressure and temperature condition . As to the trace element and REE geochemistry, some similarities and differences can be seen between the nepheline syenite and the above mentioned rock series. Some isotopic parameters are got as follow. ε Nd is -1.90,ε Sr +76.89 and I Sr 0 7094 in the Pinghe rock body. Based on the isotopic and REE features, it is suggested that the jacupirangite ijolite urtite series may come from a metasomatic mantle source with a rathe high degree batch melting mode, and that the nepheline syenite,diorite etc. might be a late fractional crystallization product from a cogenetic magma.