Preliminary Studies On U-Pb Geochronology Of Zircon And Tectonic Implications In Laofengkou, West Junggar, Xinjiang

The study area is located in north-central part of West Junggar late Paleozoic hyperplasia orogenic belt.Tectono-magmatic events of high precision chronology restricted to set the plate tectonic evolution and adopted dynamic mechanism has very important scientific significance.Based on the Plate Tectonic Theory, we conducted a detailed field geology survey on granite chronology. By analyzing the morphology, U-Pb age and geochemical characteristics of rare earth elements of nine samples of granite or sedimentary zircon, we indentified the time limits of tectonic events for each period, analyzed the division of magma intrusion stages, and determined the relationship in connection between magma and strata, and inversed orogenic belt tectonic evolution proceeses of West Jungar. The results show that:1) It found that there are four geological ages and twelve intrusions periods in study area, by intrusion stages of the granite intrusions. For the construction of the West Junggar tectono-magmatic event provides high precision chronology basis.2)"Malasu gourp" formation was originally recongnized as lower Devonian Series. However, the U-Pb age of LA-ICP-MS zircon of the granitoid in Akeqiaoke intrusion into "Malssu gourp" is410.5±2.9Ma, which shows it is the product of early magma activity in early Devonian. U-Pb age of LA-ICP-MS zircon of the pyroclastic rocks in Akeqiaoke is389Ma. As a result, from the evidence of there ages, the contanct relationship between the granitoid in Akeqiaoke and the granitoid in Akeqiaoke are in fault contact.3) U-Pb age of LA-ICP-MS zircon in kulumusu moyite is324.3±8.2Ma. The originally unrecognized the upper Carboniferous strata was intruded by kulumusu moyite.Thus, the age of this strata should be earier than324.3±8.2Ma, according to our results, we recognized it as the lower carboniferous strata.4) By using LA-ICP-MS methods to analazed geochemical characteristics of REE for nine zircon samples, we found that most of the zircon showed relatively loss in LREE, while enrichment in HREE. They were chareterized as left assault type, and Ce has the positive abnormal, while Eu has the negative abnormal. The charactereristics analysis of REE of zircon indicated that both of rock formation and stata were comed from the partial melting of crustal material, In addition to Akeqiaoke rock from plate subduction of partial melting away.5) The study area can be divided into tectono-magmatic sequence:late Silurian-early Devonian (425Ma-405Ma), representative for Akeqiaoke granodiorites, rocks formed in the plate subduction melting; early Carboniferous (325Ma-320Ma), representative for Kulumusu rock and Hatu rock, formed in post-collision and stretch setting, from partial melting of crustal material; late Carboniferous (318Ma-300Ma) representative for Kezilekeya rock and Seerdeng rock, both formed in the earth’s crust (lithosphere) thinning of the tectonic environment after post-collision; early Permian (299Ma-290Ma) representative for North Seerdeng rock (291Ma)...