GEOCHEMISTRY OF EARLY CRETACEOUS ALKALINE RHYOLITES FROM HULUN LAKE, DAXING’ANLING AND ITS TECTONIC IMPLICATIONS
Ge Wenchun1,2, Li Xianhua1, Lin Qiang2, Sun Deyou2, Wu Fuyuan2, Yun Sunghyo3
1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640; 2. College of Earth Sciences, Jilin University, Changchun 130061; 3. Department of Earth Science, College of Education, Pusan National University. Pusan 609-735, Korea
The upper part of rhyolites within the Shangkuli Formation in the Hulun Lake region, northern Daxing’anling, is characterized by high SiO2 (75.41%~77.32%), total alkaline-rich (Na2O+K2O=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 A1-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.
Ge Wenchun,Li Xianhua,Lin Qiang et al. GEOCHEMISTRY OF EARLY CRETACEOUS ALKALINE RHYOLITES FROM HULUN LAKE, DAXING’ANLING AND ITS TECTONIC IMPLICATIONS[J]. Chinese Journal of Geology, 2001, (2): 176-183.