Discovery And Tectonic Significance Of Unconformity Between Devonian And Metamorphic Basement In Fujin Uplift

Jiamusi massif is a very important tectonic unit in the east of Northeast China. Jiamusi massif is metamorphic and consolidation in the early Early Paleozoic and it formed magmatic arc in Permianthe.Between this important geological period, how Jiamusi massif experienced tectonic and sedimentary evolution become an important scientific problem.The authors studied the unconformity in conglomeratic sandstone-quartz sandstone and granitic gneiss in Fujin uplift of northeastern Jiamusi Massif. Later,we put emphasis study on its petrology, geochemistry and isotope chronology.The CL images reveal that most zircons have core rim texture. Based on the LA-ICP-MS zircon dating,the cores age was significantly older and all greater than 944+9Ma.The main age range is between 1456Ma-1805Ma.The edge of the zircon age is smaller,mainly 530+5Ma,543+5Ma and 504+4Ma.This age is consistent with the age of the facies metamorphism and the role of granitic magma in Jiamusi massif.The geochemical characteristics show that ω (SiO2), ω(Na2O), ω(K2O) values of the granitic rocks are 58.78-77.15%,0.07-3.16%,2.89-6.19%.ω(P2O5), ω(MnO2) content is low,0.04-0.13%,0.43-1.08%.These geochemical features suggest that the Fujin granitic rocks are slightly peraluminous and are of highly fractionated S-type granite.Gneiss in Fujin uplift belongs to volcano arc granitoids.500Ma about the granite may be the product of the environment of the same collision or collision.The U-Pb ages for zircons from quartz sandstone are all more than 465 Ma, of which are mainly concentrated in the age of 470-520 Ma, and just a small amount of ages are more than 800 Ma.The regional geological data show of Jiamusi massif is lack of the Ordovician-Silurian strata.The eastern margin has the early Devonian shallow marine sedimentary strata and the isotopic age of the fossil based on the exact fossils are in the Devonian Volcanic Rocks, zircon ages ranged from 386-392Ma.In view of the Ordovician-Silurian strata is absence,the information obtained from the clastic zircon age does not exist in the Devonian.Time limit on the deposition of quartz sandstone is more exact for the Early Devonian.The above evidence shows that after the early Paleozoic metamorphic consolidation of Jiamusi massif,During the period from Ordovician to Silurian it is uplifted tectonic background until the Early Devonian,then the eastern edge of is beginning of the deposition.Jiamusi Massif was undergone long-time uplift and erosion until Early Devonian, then the eastern part of the whole was turn into passive continental margin.