摘要
Intrusive rocks are widespread in the Binbalechagan, Dongwuqi, Inner Mongolia Autonomous Region. This paper selectes coarse-medium grained syenogranites (CMGS) in the region for isotope chronological and geochemical studies. By zircon SHRIMP U-Pb dating, weighted mean age of (220.4 ± 2.5) Ma(MSWD = 0.83) is obtained. The zircon oscillatory rings are well developed with typical pattern of magmatic zircon, so the result may represent the diagenetic age of the granite. CMGS is characterized by K enrichment, peraluminous, LREE relatively enriched, substantial negative Eu anomalies, HREE with weak negative gradient, Ba with obvious nega- tive anomalies, Rb and Th relatively enriched, other incompatible elements relatively depleted, both Y and Yb lower than the normalized values of ocean ridge granite. CMGS probably formed under post-orogenic extension setting after the convergence between the Siberian plate and Sino-Korean plaeo-plate.