埃塞俄比亚北部施瑞地区新元古界钾长花岗岩成岩过程浅析

Preliminary l Analysis on the Diagenetic Process of the Neo-proterozoic Moyite in Shire Region,Northern Ethiopia

通过对埃塞俄比亚北部施瑞地区新元古界钾长花岗岩做详细的野外地质调查、岩相学研究及岩体主量元素测试分析可知,施瑞地区新元古界钾长花岗岩成分含量较稳定,尤其是SiO_2和Al_2O_3的含量变化不大,说明在其形成岩体的原始岩浆均一化程度较高,该区花岗岩的基性组分含量较低,酸性和碱性组分含量高,表明该区花岗岩分异演化程度高.分异指数(DI)具有较高的值,固结指数SI普遍较小,说明本区岩浆分异结晶演化程度及酸性程度均很高,这也表明原始岩浆的结晶分异强烈.岩体主量元素低TiO_2和P_2O_5的特征,表明岩浆经历了显著的钛铁矿、磷灰石等矿物的分离结晶作用.从岩体Harker图解显示出成岩过程中存在部分矿物结晶分异出该岩浆体系.埃塞俄比亚北部施瑞地区新元古界钾长花岗岩应为结晶分异作用所形成.

Through the detailed field investigations, petrographic studies and major element tests on the neo-proterozoic moyite in the Shire region, Northern Ethiopia, it is known that the compositions of the neo-proterozoic moyite in the Shire region are pretty stable. Especially the contents of SiO2 and A12 03 have few variations, which indicate that the degree of homogenization of the primitive magma of the rock body is relatively high. The contents of the basic components of the gran- ite of the area are relatively low, and contents of the acedic and alkali components are relatively high, which indicate tlaat the degree of differentiation of the granite of the area is relatively high. The Differentiation Index （DI） has high values, and the Solidification Indexes （SI） are low, which indicate that the degrees of magmatic differentiation and crystallization and the acidic degree are both high and that the primitive magma experienced strong crystallization and differentiation. The low- SiO2 and low-A12 03 features of the major elements of the rock body indicate that the magma experienced prominent ilmenite and apatite crystallization and differentiation. From the Harker diagram of the rock body, it is observed that the part of the minerals are crystallized and differentiated from the magmatic system during the diagenetic process. The neo-proterozoic moyite in the Shire region of Northern Ethiopia are formed from differentiation and crystallization.