摘要
本文根据地质和地球化学的研究提出本区紫苏花岗岩主要是由英云闪长质、花岗闪长质岩浆侵位之后经麻粒岩相变质而形成的。根据地球化学特征,本区的紫苏花岗岩可分为大离子亲石元素亏损的北区(太平寨—三屯营)和大离子亲石元素较富集的南区(水厂—松汀),它们的地球化学差异反映了其形成时构造条件的不同。
Charnockites in Qianan-Qianxi area, Eastern Hebei province, range from intermediate to felsic end members in chemical composition. Al_2O_3, TFeO, CaO, Na_2O and TiO_2 decrease in a linear fashion with increasing SiO_2. The trends indicate that the source rocks of charnockites are mainly igneous rocks. Geochemical and field data indicate that the igneous reeks were transformed into charnockite protoliths by partial melting. In the course of partial melting the garnet, hornblende and plagioclase were important mineral phases. The degree of hornblende and garnet fractionation played an important role for the fractionation of light and heavy REE, on the other hand, plagioclase and hornblende affected mainly Eu behaviour in the charnockite protoliths.
Charnoekitism (granulite facies metamorphism) took place right after the emplacement of the charnoekite protoliths, during the charnorkitism, rich-CO_2 fluid extracted large ion lithophile(LIL)elements and H_2O from the charnockite protoliths, consequently, hydrogeneous minerals (biotite and hornblende) were dewatered and transformed into anhydrogeneous minerals (hypersthene and diopside), eventually, charnockites were formed.
The charnockites in the north part of this area deplete large ion lithophile elements and REE content is lower, whereas, the chacnockites in the south part of the area are enriched these elements and REE content is higher. The differences are related to both of the composition of the protoliths and fluid discharge and CO_2/H_2O ratio in the fluid resulted by the emplacement of the protoliths in differently tectonic conditions.
出处
《岩石矿物学杂志》
CAS
CSCD
1990年第3期193-202,共10页
Acta Petrologica et Mineralogica
