The Mesozoic Sedimentary Records On The Eastern Margin Of Jiamusi Block And Its Response To The Subduction History Of The Paleo-Pacific Plate

The Jiamusi block was affected by both the Late Paleozoic Paleo-Asian Ocean tectonic domain and the Early-Mesozoic Paleo-Pacific tectonic domain.However,the duration of subduction of the Paleo-Pacific plate beneath the Jiamusi block remains controversial.To constrain this timing,we analyzed detrital components,used zircon fertile factors for correction and dated detrital zircons from Late Triassic Nanshuangyashan Formation and Late Jurassic Yunshan Formation sandstones in the Jiamusi block.Results show that both formations have high quartz content,low rock fragments and low feldspar contents,indicating recycled orogenic belt and arc orogenic belt sources.To avoid the influence of zircon abundance in source rocks,303 granite zircon element and dating data from the Jiamusi block were collected for zircon fertile factor correction.According to the Zr element content,source rocks were divided into three groups: A.Cretaceous granitoids(112-92 Ma),B.Late Paleozoic-Early Mesozoic granitoids(338-209 Ma),C.Early Paleozoic granitoids(538-446Ma)and Neoproterozoic granitoids(996-722Ma),with zircon fertile factors of 1.0,1.5 and 1.3,respectively.After correction,detrital zircons in Late Triassic samples show a dominant ca.245 Ma age peak and secondary ca.474 Ma and ca.230 Ma peaks.Detrital zircons in Late Jurassic samples show a dominant ca.494 Ma age peak and a secondary ca.265 Ma peak.The sediment sources of Late Triassic Nanshuangyashan Formation include Jiamusi block,Xingkai block,and a Late Triassic magmatic arc near the study area.The sediment sources of Late Jurassic Yunshan Formation include Jiamusi block and Xingkai block.The sediment source areas of both formations have similarities,indicating that the eastern margin of Jiamusi plate was under post-arc compression environment in the Late Triassic and Late Jurassic.Therefore,we infer that subduction of Paleo-Pacific plate beneath the eastern margin of Jiamusi block had started before Late Triassic and continued until Late Jurassic.