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Li Y.,Changan University | Li Y.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Wang Z.,Changan University | Duan F.,Changan University | And 4 more authors.
Geotectonica et Metallogenia

The relationship clearly show orogeny-coupled basin formation between Wuerkashier Mountain and E Min basin in West Junggar. The boundary of the basin is somewhat parallel to the orogenic belt. The sedimentary rocks in the "mountain" area include the Silurian-Carboniferous marine terrigenous clastic rocks and volcanic rocks, whereas in the "basin" area sedimentary rocks consist of the Permian continental molasse and Neogene red glutenite and accumulation of Quaternary river terraces, with a typical marine-continental double layered structure. The edge of the basin is limited by the Barleik foreland thrust belt. "Mountain" area develop such thrust nappe as shovel type thrust fault, snakeheads structure and imbricate fan structure. This indicates that the combination of "basin"-"mountain" is a typical foreland basin system. E Min foreland basin formed in the Early Permian, and belongs to the "Premature" foreland basin, which is characterized by weak impact of the later thrust deformation and obvious features of the early structure of foreland basin. This achievement provides important information for basin analysis, tectonic evolution, sedimentation and orogeny-coupled basin formation of the E Min basin as well as the West Junggar basin. © 2016, Science Press. All right reserved. Source

Yang G.,Changan University | Yang G.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Li Y.,Changan University | Li Y.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits
Earth Science Frontiers

With deepening of the study, the oceanic island basalts (OIB) formed in different times have been identified in Central Asian Orogenic Belt (CAOB). West Junggar is located in southwestern margin of the CAOB, and contains many ophiolitic mélange belts with OIB basalts. The basalts show pillow structure and closely associate with ultrabasic rock, gabbro, massive basalt, limestone and purple siliceous rock. Geochemical studies show pillow basalts are characterized by alkaline affinity with high TiO2 (major>2.5%), light rare earth elements (LREE) enrichment, no obvious Nb and Ta negative anomalies. They are very similar to typical OIB, suggesting that they may have been formed in the oceanic plate and plume-related seamount setting. Based on developmental stage analysis for seamounts, we think that the seamounts in West Junggar at least had grown into the explosive stage, because of lots of pillow lavas. The volcanic rocks or volcaniclastic sediments in seamounts were enriched in large ion lithophile elements (LILE) and high field strength elements (HFSE). Therefore, the subduction of seamounts would have strongly affected the geochemical properties of volcanic rocks in arc and back-arc area. In fact, the Devonian-Carboniferous volcanic rocks in West Junggar contain seamount signal. Therefore, seamount subduction model may be better to explain the petrogenesis of volcanic rocks with OIB in West Junggar. In addition, there is a potential resource effect by seamount subduction, so we should study the indicator of the subduction of the paleo-seamounts and island chains, in order to provide a reliable basis for exploring gold, copper, and some other mines. © 2015, Editorial Office of Earth Science Frontiers. All right reserved. Source

Liu S.,Changan University | Liu S.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Li R.,Changan University | Li R.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | And 5 more authors.
Geotectonica et Metallogenia

The Mayuan stratabound Pb-Zn deposit in Nanzheng, Shaanxi province, is located in the southern margin of the Beiba Arch, at the northern margin of the Yangtze Plate. The orebodies are stratiform and hosted in breciated dolostone of the Sinian Dengying Formation. The ore minerals are primarily sphalerite and galena, and the gangue minerals comprise of dolomite, quartz, barite, calcite, and solid bitumen. There are vein and cloddy types of hydrothermal dolomite. The C, O, Sr isotopes and REE geochemistry of the two types of dolomite and surrounding rocks were analyzed. The results show that the δ13C (0.18‰), δ18O (-7.39‰), and 87Sr/86Sr (0.70967) values of the early vein dolomite are similar to those of the host rock of the Sinian dolostone (δ13C: -3.2‰-1.33‰; δ18O: -9.2‰- -3.85‰; 87Sr/86Sr: 0.70890-0.70994), indicating that the C, O and Sr were derived from the dissolution of the host rock. The positive Eu anomalies (average δEu=1.78) might indicate that the dolomite was formed in a strongly reductive environment. The cloddy dolomite has δ13C (-2.51‰-0.93‰) values similar to the host rock, however, the δ18O (-12.91‰- -10.95‰) values lower than the host rock, and ΣREE (3.14×10-6) contents and 87Sr/86Sr (0.71146) ratios higher than the host rock (ΣREE: 1.6×10-6; 87Sr/86Sr: 0.70890-0.70994). The results show that the cloddy dolomite might have precipitated from a high temperature fluid flowed through felsic basement and overlying clastic rocks (in which the ΣREE and 87Sr are much higher). So, it is likely that the early vein-type dolomite is related to the early low temperature compaction fluid which was stored in the Sinian Dengying Formation, and the late (ore forming stage) cloddy-type dolomite is related to the moderate temperature fluid cycling in the Paleozoic strata and the basement. © 2015, Science Press. All right reserved. Source

Dong Z.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Dong Z.,Research Center for Orogenic Geology | Gu P.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Gu P.,Research Center for Orogenic Geology | And 6 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences

The adamellite develops in Yanchangbeishan of Lenghu area in Qinghai, which is located in the west segment of the north margin of Qaidam. The samples have higher SiO2 (74.98%-76.92%) and K2O (4.44%-5.93%) contents, but lower MgO (0.04%-0.07%) and CaO (0.43%-0.69%) contents. The Rittmann indices of the rock range in 2.43-2.79, which shows that it belongs to high potassium calc-alkaline series. The alumina saturation average index is 1.01, which indicates that the adamellite belongs to peraluminous granites. Moreover, the samples are intensively depleted in HFSEs (Nb, Ta), with enriched LILEs (K, Rb, Ba, Pb), reflecting the characteristics of island-arc magma. LA-ICP-MS zircon U-Pb dating shows that the formation age of the rock is 252±3 Ma. The zircon Hf isotope analysis reveals that 176Hf/177Hf ratios, varying in 0.282 958 to 0.283 032, have high positive εHf(t) (8.75-14.50) and two-stage Hf model ages (averaged at 385 Ma). In the 176Hf/177Hf -εHf(t) discrimation diagrams, these zircons are plotted nearly on the depleted mantle evolution line. It can be concluded that the rock chiefly derived from the new basaltic lower crust which is originated from depleted mantle. Based on the regional geological background and the geochemical characteristics of the masses, we consider that Yanchangbeishan adamellite bears similar characteristics of its primary magma with mafic-ultramafic rocks of Devonian, which were supposed to be originated from partial melting of the young basaltic lower crust related to subduction of Zongwulong small oceanic basin from south. Thereby, it reveals that the north margin of Qaidam was in volcanic arc or active continental margin tectonic environment during Permian epoch. ©, 2015, China University of Geosciences. All right reserved. Source

Xu X.Y.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Xu X.Y.,Research Center for Orogenic Geology | Li R.S.,Research Center for Orogenic Geology | Chen J.L.,MLR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | And 10 more authors.
Acta Petrologica Sinica

Based on our new geological investigation in the northern Xinjiang, a tectonic model of three Plates with two Belts and complex evolutionary history inversion from ocean to continent are revealed here. According to the evidence of geology, geophysics and detrital zircon U-Pb dating, a Precambrian block existing in southern Junggar Basin is recognized. By re-defining and re-interpreting the various tectonic units, this paper presents a new, improved standpoint for the tectonic characteristics of eastern Junggar and western Junggar. The eastern Junggar is a well-exposed accretionary wedge stretch from Mayebo in southeastern of Ertix tectonic belt to Wucaiwan in southern Kalamyli tectonic belt, and western Junggar is also a accretionary wedge developing from eastern Ertix tectonic belt to southern margin of Xiemishitai. Integrating our new field observations and interpretation of geological data from key areas, we suggest that the formation of Kazakhstan Plate in Early Paleozoic was caused by amalgamation between the Junggar-Tuha, Central Tianshan and Yili blocks, which define the Early Paleozoic orogeny in northern Xinjiang. According to the Devonian stratigraphy and sedimentary environments, the evolution of the ocean to the north of the Kazakhstan Plate from Early Devonian to Late Devonian is discussed, and the closure time of the ocean is identified in Late Devonian. On the other hand, this paper aims to amplify current understanding of the southern Tianshan Belt by describing it as a huge accretionary wedge, and the southern most suture zone between Siberia-Kazakhstan Union Plate and Tarim Plate which possibly closed at the end of the Early Carboniferous. Therefore, this paper presents an improved model for Late Paleozoic evolution of the northern Xinjiang area, which is a model of three Plates with two Belts. After the formation of the Kazakhstan Plate, there exist the Siberia Plate to the north, the Kazakhstan Plate in the middle and the Tarim Plate to the south, which was separated by the Junggar Belt and South Tianshan Belt, respectively. The collision between the Siberia Plate and Kazakhstan Plate occurred at about the latest Devonian, which formed the Siberia-Kazakhstan union Plate. Then the union Plate collide with the Tarim Plate possibly occurred at the end of the Early Carboniferous, which remark the terminal time of the oceancontinental transformation of Paleo-Asia Ocean in China. From Late Carboniferous to Early Permian, the whole northern Xinjiang area evolved into a continental extension and rift with thick piles of basaltic lavas and subordinate intermediate-silicis lavas. Source

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