Early Paleozoic geodynamic evolution of the Eastern Central Asian Orogenic Belt:Insights from granitoids in the Xing'an and Songnen blocks

摘要

The early Paleozoic tectonic framework and evolutionary history of the eastern Central Asian Orogenic Belt(CAOB)is poorly understood.Here we present zircon U-Pb geochronology,whole rock geochemistry,and Sr-NdHf isotope data of the early Paleozoic granitoids in eastern CAOB to investigate the petrogenesis and geodynamic implications.The early Paleozoic granitoids from the Songnen Block yield zircon U-Pb ages of 523-490 Ma,negative εNd(t)values of-6.7 to-0.8,and values of-8.6 to 7.1,indicating they were generated by partial melting of ancient crustal materials with various degrees of mantle contribution.They generally show affinities to A-type granites,implying their generation from an extensional environment after the collision between the Songnen and Jiamusi blocks.In comparison,the early Paleozoic granitoids from the Xing’an Block have zircon U-Pb ages of 480-465 Ma,εNd(t)values of-5.4 to 5.4,andεHf(t)values of-2.2 to 12.9,indicating a dominated juvenile crustal source with some input of ancient crustal components.They belong to I-type granites and were likely related to subduction of the Paleo-Asian Ocean.The statistics of TDM2 Hf model ages of the granitoids indicate that the Erguna and Jiamusi blocks contain a significant proportion of Mesoproterozoic crystalline basement,while the Xing’an Block is dominated by a Neoproterozoic basement.Based on these observations,the early Paleozoic evolutionary history of eastern GAOB can be divided into four stages:(1)before 540 Ma,the Erguna,Xing’an,Songnen,and Jiamusi blocks were discrete microcontinents separated by different branches of the Paleo-Asian Ocean;(2)540-523 Ma,the Jiamusi Block collided with the Songnen Block along the Mudanjiang suture;(3)ca.500 Ma,the Erguna Block accreted onto the Xing’an Block along the Xinlin-Xiguitu suture;(4)ca.480 Ma,the Paleo-Asian Ocean started a double-side subduction beneath the united Erguna-Xing’an and Songnen-Jiamusi blocks.