Late Paleozoic Volcanic Rock And The Implicaiton To The Tectonic Evolution Of The Northern Yili Block,Xinjiang

The Central Asian Orogenic Belt is a natural laboratory for studying the process of accretionary orogenic and crustal growth.The Yili Basin located in the southwestern segment of the CAOB.Late Paleozoic magmatic rocks are extensively exposed in the Yili Basin,the forming background and geological exploration meaning attracted many research teams to focus on this around the world.During the past 30 years,two distinct different tectonic settings,extension or convergence,are considered to related to the same magmatism in the Yili Basin,so unravelling the mechanism and process of the mantle-crust has important geological significance for the Late Paleozoic growth.In this contribution,we conducted field inverstigations,zircon U-Pb dating,whole-rock geochemical and Sr-Nd isotopic studies on the magmatic rocks from the Boluokenu Range,compare these results to Awulale Range,Wusun Range.Exploring the interacte mechanism of late Paleozoic crust and mantle in the northern margin of Yili,and clarifying the internal intrincity of magmatic activity.The following achievements have been withdrawn in this study: 1.The new zircon U-Pb data obtained in this study,375 Ma and 350 Ma,combined with previously published results put constraints on the late Paleozoic arc magmatism.According to studies in this paper,the magmatic activity time of the northern margin of Yili is concentrated at 350~380Ma,there is no gradient decrease from west to east as previous results stated along the north margin of Yili basin.The geological characteristics and petrological formation indicates its tectonic background similar to the magmatic rock in mature continental arc settings.2.The magmatic activity of the Mt.Yishijilike and Mt.Boluokenu is almost the same period,but the start time is relatively late;and the start time of Mt.Awulale magmatism is close to the end of the Boluokenu and lasts until the Late Carboniferous.3.The primitive magma of the Late Paleozoic volcanic rocks in the northern margin of the Yili Block has high-Aluminum properties.Part of the mediate-acid volcanic rocks are formed by the crystallization of the primitive magma,part of which is formed in the remelting of the new crust,and part of which is formed in the mixing of the two.4.By comparing the isotopic data of the Dahalajunhsan Formation volcanic rock in the Yili Block indicate that the Boluokenu volcanic rocks has a wide range of Nd isotope variation under the compression background of the subduction setting(?Nd(t)=-4.79~+4.10),while the Mt.Awulale volcanic rocks have a concentrated Nd isotope character of the mantle source(?Nd(t)=-3.51~+7.34).The former may be related to the transition from the Devonian-Carboniferous to the tensile stress transition,which may be related to the retreatment of the Permian oceanic plate or recession of the trench.5.The MELTS simulation indicate the primitive magma is hydrous,and the main differentiation process occurs in the shallow crust.The EC-AFC iterative calculation indicated that the early stage volcanic rocks have more lower crust components and the late stage volcanic rocks gradually transition to the middle-upper crust.