摘要
熊耳群火山岩系熔岩占绝对优势,具有双峰式特点。在其变质或蚀变过程中,Na_2O、K_2O、CaO等活动组分被带入或带出,在拟定的ATF图上,熊耳群主体为拉斑玄武岩。REE和其他微量元素的特征与大陆裂谷拉斑玄武岩一致。它们形成在早、中元古代陆壳基底上的大陆裂谷发展过程中,该裂谷是秦岭古裂谷系的组成部分。
According to petrography, petrochemistry and trace elements geochemistry, the volcanic rocks of Xionger Group are of double model character. The primary rocks of intermediate-basic end are tholeiite and basalt-andesite, whereas those of acid end—acidic dasite and rhyolite. Andesite with content of SiO_2 59～63％ is rare.
The most common mineral association of Xionger Group is that of greenschist facies. There were two kinds of pyroxene, and the Ca-rich clinopyroxene is only relic primary mafic mineral and its composition closely approaches that of augite in tholeiite. It was from basalt within plate.
Besides, H_2O, CO_2, Na_2O, K_2O and CaO had been carried in or taken out. On the basis of many average chemical analyses from domestic and foreign refrenees, the author proposed a ATF diagram identifying the type of primary magma by means of inert components Al_2O_3, TiO_2 and Fe_2O_3+FeO+MgO, and determined that the type of primary magma of Xionger Group is tholeiite.
The characteristics of REE and other trace elements of Xionger Group are different from that of andesite, shoshonite, high-Al basahs, and alkalic basalt in continental rift. It closely approaches that of tholeiite in continental rift.
The tectonic setting of the volcanic rocks was thought to be a continental rift on the base of crust, It was a part of Qinling rift system.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1990年第2期20-29,共10页
Acta Petrologica Sinica
基金
中国科学院科学基金项目R850443"东秦岭-大别山古会聚带的形成机制
变质作用和岩浆活动"研究成果的一部分
关键词
熊耳群
火山岩
大陆
裂谷
地台
Continental rift
Xionger Group
Volcanic rocks
Double model
ATF diagram
