SU Hang1, LIU Xu-guang2, ZHENG Tao2, LIU Ying-xin2

(1. Heilongjiang Longkuang Resources Development Group Co., Ltd, Harbin 150036, China; 

2. Natural Resources Survey Institute of Heilongjiang Province, Harbin 150036, China)

Abstract: The Baliqiao area within the Lesser Xing’an Range is located in the tectonic transitional belt between the Xing’an and Songnen-Zhangguangcailing blocks in the eastern Xing-Meng orogen. The complicated multiple-stage tectonic events and frequently intensive magmatism occurred in the area. Geochronology and geochemistry of the Late Paleozoic alkali-feldspar granite in this area have been carried out in this paper, aiming to provide new constraints on the timing of collision between the Xing’an and Songnen－Zhangguangcailing blocks. LA-ICP-MS zircon U-Pb dating results show that the medium grained alkali-feldspar granite outcropped in the Baliqiao area was emplaced at 295.3 ± 0.7 Ma and it is an early Permian intrusion. Samples of the alkali-feldspar granite have SiO2 contents of 75.27-77.71 wt%, Na2O+K2O contents of 6.96-8.72 wt%, and Al2O3 contents of 11.45-13.28 wt%, with variable Na2O/K2O values of 0.27-1.05, A/CNK values of 1.00-1.51, indicating that it belongs to the peraluminous, high-K calc-alkaline granite. Those samples have rare earth element contents varying from 116.46×10-6 to 321.52×10-6, with high ΣLREE/ΣHREE and (La/Yb)N ratios of 3.07-9.65 and 1.70-6.91, respectively, and characteristics of the LREE enrichment and the HREE depletion. They have significantly negative Eu anomalies with δEu values varying from 0.21 to 0.34. They are relatively enriched in large ion lithophile elements (Rb, U) and Zr-Hf, but depleted in Nb and Ta, with high contents of Zr+Nb+Ce+Y. All these features are consistent with those of the A-type granite in post-orogenic extensional environment. In addition, their positive εNd(t) value of 3.66 suggests that the granite might be formed by magma derived from the partial melting of juvenile crust. The occurrence of such kind of alkli-fedspar granite might represent the extensional event after the collision and merging of the Xing’an and Songnen-Zhangguangcailing blocks, which might have occurred before the Early Permian. 

Keywords: alkali-feldspar granite; zircon U-Pb dating; geological significance; the Baliqiao area

ACTA MINERALOGICA SINICA Vol. 43, No. 5, 2023, Page 665