柴北缘鹰峰环斑花岗岩矿物学特征及其岩石学意义

MINERALOGY FEATURE OF YINGEFNG RAPAKIVI GRANITE IN NORTH QAIDAM BASIN AND PETROLOGIC SIGNIFICANCE

柴北缘构造带中元古代鹰峰环斑花岗岩主要造岩矿物的研究结果表明，该岩体具pyterlitic型环斑结构，各主要矿物均具多世代特征。钾长石主要以卵形斑晶出现，出溶钠长石条纹极发育，出溶后主晶成分为Or94.57Ab5.25An0.18，钠长石条纹为Or0.71Ab97.59An1.7，推算出球斑均一化成分为Or66.41Ab32.95An0.64。岩浆结晶的斜长石以更长石为主，由于不同程度的蚀变使An降低成为钠质长石。黑云母多有不同程度的蚀变，析出磁铁矿和钛铁矿，析出铁后黑云母的n（Fe）/n（Fe＋Mg）=0.5~0.63，属Mg-Fe2＋-和Fe2＋-黑云母，原成分应更富铁。鹰峰岩体在矿物组成及主要矿物特征上与典型环斑花岗岩的相似，但也存在一些差异，这些差异有的是起因于加里东期的变质改造，有的反映了岩体形成环境和过程的特性。

Research on the main rock-forming minerals of Middle Proterozoic Subera Yingfeng rapakivi granite in the North Qaidam Basin tectonic belt indicates the magmatic body exhibits pyterlitic rapakivi texture, and each main mineral is polygenetic. K-feldspar mainly takes the form of oval phenocryst, and exsolved albite stripe is well-developed. After exsolving, the host crystal composition tunas out to be Or94.57 Ab5.25 An0.18; albite stripe composition OE0.71 Ab97.59 An1.7, and the calculated original compesition Or66.41Ab32.95An0.64. Plagioclase of magmatic crystallization is mainly oligoclase. Owing to varying-degree alteration, An decreased and albite appeared in large amounts. Most biotites have separated magnetite and ilmenite as the result of varying-degree alteration after separating, The values of n（Fe）/n（Fe ＋ Mg） in biotite range from 0.5 to 0.63, belonging to the biotite of Mg-Fe^2＋-and Fe^2＋ -, the original composition should be characterized by more iron. The Yingfeng magmatic body is similar to a typical rapakivi granite, but there are some differences, reflecting the characteristics of magmatic body-forming environment and processes.