Zircon U-Pb dating of Late Paleozoic alkali-feldspar granite in Duobaoshan, Great Xing'an Range: Constrains on collision and assembly time of Xing'an and Songnen Blocks

This paper is the result of geological survey engineering.

Objective The Duobaoshan area of the Great Xing'an Range is located on the tectonic belt between the Xing'an block and the Songnen block in the east of the Xingmeng orogenic belt. In this paper, the chronology and petrogeochemistry of the Late Paleozoic alkali feldspar granites in the Duobaoshan area are used to constrain the time limit of the collision between the Xing'an block and the Songnen block.

Methods In this paper, the zircon U-Pb geochronology and the whole rock geochemistry were carried out.

Results The LA-ICPMS U-Pb ages of zircons from two alkali-feldspar granite samples were (300.3±2.0)Ma and (307.3±1.7) Ma, respectively. Two samples have the similar geochemistry characteristics, with high silicon (SiO₂= 69.70% to 77.42%), relatively high aluminum (Al₂O₃=11.60% to 15.05%), and high alkali (K₂O+ Na₂O=7.22% to 9.80%), low Ca and Mg (CaO=0.02% to 0.8%, MgO=0.02% to 0.48%), enrichment of Rb, Th, Zr and Hf, depleted of Ba, Sr, Nb and Ta, relatively high (Zr+Nb+Ce+Y). In addition, they also have significantly negative Eu anomalies, with the right-leaningdistribution of rare earth elements and high zircon saturation temperature, suggesting both of them are A-type granites.

Conclusions Combined with the regionally tectonical evolution, it is concluded that the alkali-feldspar granite formed at extensional geological background of post-collision regime, marking the end of the collision between the Xing'an block and the Songnen block.