The Basement Property And Evolution Of The Northern Junggar Basin By In-situ Analysis Of Zircon U-Pb Chronology And Trace Element

Property and evolution of basements of the northern Junggar Basin are very important for basic scientific questions, not only for the regional pattern of reconstruction of the Paleo-Asian Ocean, but also for basin tectonic lightfaces palaeogeography to restore as well as its oil and gas exploration in recently years. This paper is based on regional geological structure, investigate outcrop in the Lower Cretaceous sandstone samples in DLS and cores from the Lu Liang uplift of the northern Junggar Basin Carboniferous volcaniclastic rocks and Permian-lower Cretaceous sandstone samples. Simultaneous in situ determination of U-Pb age and trace elements in zircon by LA-ICP-MS research zircon samples of different times and litho logy. Discussion on the basement times, material composition and evolution characteristics of the northern Junggar Basin at the time of the chain. Mainly achieved understanding as follows:1. On the basis of the analysis in the regional geological structure and lithostratigraphic units, sequence stratigraphic frameworks of the structural layer of the Junggar Basin are established. The comparison of the relationship the statistical distribution of the age data of between ophiolitic melange and typical granite is disscued. By the analsis that the north regional Paleozoic ocean basin is490Ma±and410Ma±two peak event of expansion at least, the Late Carboniferous-Early Permian (315-290)Ma is important tectonic transition period for Paleo-oceanic basin seduction-collision closed and it’s turned to intercontinental deformation system.2. By use of zircon U-Pb LA-ICP-MS in situ, the Carboniferous pyroclastic and the Mesozoic sandstone samples are analyzed and its statistical distribution of ages. The northern Junggar Basin zircon U-Pb ages is built and it has obtained quantitative peak age record and its distribution sequence of north regional basement and covers the tectonic evolution of the event.(1) According to regional Carboniferous-Lower Cretaceous lithostratigraphic units of the statistical analysis of the zircon U-Pb ages, showed that the northern Junggar Basin and its adjacent areas have complex tectonic events in the chronology. Precambrian3022～2102Ma,1747～1202Ma,996～915Ma,885～544Ma four age groups and the early-mid Paleozoic539～420Ma,419～356Ma,354～300Ma age groups and their corresponding490Ma±,410Ma±,330Ma±age of peak is found. This age ranges indicate that not only3.0Ga continental basementsexisted in the Junggar basin and adjacent areas but also mutiple evolutionary apisodes occurred during the formation of the basement. (2) The northern Junggar Basin Lu-liang uplift Carboniferous volcanic rock samples of zircon U-Pb dating with the area in the Late-Mid Proterozoic have two ranges of peak age of1447～1410Ma,885-559Ma, and the early-mid Paleozoic536～420Ma,401～360Ma,359～303Ma age ranges and their corresponding the peak age of490Ma±,356Ma±and336Ma±. This is indicating that the basement time is at least1.4Ga, and its formation and evolution of the north basin is mutiple.(3) Regional tectonic evolution of the sedimentary cover has experienced Permian299～250Ma, Mesozoic210～176Ma,175～148Ma and147～132Ma in Pre-Mesozoic and its corresponding peak age of290Ma±,180Ma±,163Ma±,140Ma±four major tectonic events indicate that the sedimentary cover of the northern Junggar Basin experienced a complex tectonic evolution of multi-stage process.3. The northern of Junggar Basin and its adjacent areas of different rock strata unit before the Permian (>300Ma) zircon trace element analysis, showed that bedrock material is mainly experienced multiple compositional evolution stage. The Early-Precambrian (3022～1202Ma) is mafic, along with the acidic rocks; Eate-Precambrian (996～544Ma) is mafic increaseed and acid rock reduced than Early-Precambrian; Early Paleozoic (539～420Ma)is mafic, along with the acid rock; early late Paleozoic (419-356Ma) is acid rock, accompanied by mafic rocks; the late middle Paleozoic (354～300Ma) is mafic rocks, accompanied by acidic rocks. They fall into the contineatal zircon range in U/Yb-Hf and Y plots. The overall indication that the basement of northern Zhunggar basin and its adjacent areas may existed at Archean3Ga, and the evolution of the complexity of the multi-stage continental crust basement.4. Lu-liang uplift Carboniferous pyroclastic rock drilling core samples of different age groups zircon trace element analysis, showed that the basement rock types of the Junggar basin is mainly the syenite, basalt, dolerite, larvikite and granitoids composed of mafic intrusive activities basenment. Early-Precambrian mainly is mafic rocks; the late Precambrian mafic and acidic rocks; early Paleozoic mainly is mafic rocks, along with the acid rock; late Paleozoic early is acid rock, accompanied by mafic rocks; mid-late Paleozoic is mafic rocks, accompanied by acidic rocks. They are in U/Yb-Hf and Y diagram fall into the contineatal zircon range, generally reflect the evolution of the basin area from the Proterozoic to the late Paleozoic Carboniferous of complex continental basement material.