【摘要】 大兴安岭呼伦湖一带的上库力组第 3段流纹岩具有高硅 (Si O2 =75.41 %～77.32 % )、富碱 (Na2 O+K2 O=7.98%～ 8.74% )、富 Y、Nb、Zr及低 Al、Mg、Ca、Ni、Cr、Ti和高 Ga/Al比值等特点 ,类似于 A型花岗岩 ,而与高度分异的 I型和 S型花岗岩有明显差别。该流纹岩的地球化学特征类似于 A1型花岗岩 ,且与该区 A型花岗岩同时 ,很可能是 A型花岗岩浆喷出相的产物。流纹岩的全岩 Rb- Sr等时线年龄 1 2 7± 5Ma,与伊列克得组玄武岩(1 2 5± 2 Ma)时代一致 ,两者构成了双峰式火山岩组合 ,形成于早白垩世岩石圈拉张环境。更多还原

【Abstract】 The upper part of rhyolites within the Shangkuli Formation in the Hulun Lake region, northern Daxing’anling, is characterized by high SiO 2 (75.41%~77.32%), total alkaline\|rich (Na 2O+K 2O=7.98%~8.74%), high Ga/Al, enriched in Y, Nb, Zr, and depleted in Al, Mg, Ca, Cr, Ti. Their chemical compositions are very similar to those of A type granites, but different from highly fractionated I and S type granites. These rhyolites, geochemically similar to those of A 1 type granites subdivided by Eby(1992), are the synchronous products of A type granite in this region. Five rhyolite samples yield a Rb Sr whole rock isochron age of 127±5 Ma, coeval with the age of 125±2 Ma of Yeliekede basalts in the Daxing’anling. It is therefore suggested that the bimodal magmatism occurred in a lithospheric extensional setting during the Early Cretacoues.更多还原