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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 | Year: 2014

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.

Gao X.,Research Center for Orogenic Geology | Guo F.,CAS Guangzhou Institute of Geochemistry | Xiao P.,Research Center for Orogenic Geology | Kang L.,Research Center for Orogenic Geology | Xi R.,Research Center for Orogenic Geology
Lithos | Year: 2016

The Central Asian Orogenic Belt (CAOB) is the largest Phanerozoic accretionary orogen on Earth. The role that Precambrian continental microblocks played in its formation, however, remains a highly controversial topic. New zircon U-Pb age data and whole-rock geochemical and Sr-Nd-Pb isotopic studies on Permian (253-251 Ma) andesites from the Xi Ujimqin area provide the first evidence for the existence of a continental lower mafic crust in the eastern segment of the CAOB. These Permian lavas generally have chemical compositions similar to experimental melts of garnet pyroxenites. Based on Sr-Nd-Pb isotopic compositional differences, they can be further subdivided into two groups. Group 1 has moderately radiogenic Sr (87Sr/86Sr(i) = 0.7060-0.7062) and nonradiogenic Nd (εNd(t) = -9.0-8.3) and Pb (e.g., 206Pb/204Pb = 17.18-17.23) isotopic compositions similar to the ancient lower mafic crust beneath the North China Craton (NCC). Compared with Group 1, Group 2 has less radiogenic Sr (87Sr/86Sr(i) = 0.7051-0.7055), and more radiogenic Nd (εNd(t) = -0.2-+1.4) and Pb (e.g., 206Pb/204Pb = 18.04-18.20) isotopic compositions as observed in the Phanerozoic granitoids and felsic lavas of the CAOB. The combined geochemical and isotopic data indicate that Group 1 was derived from ancient lower mafic crust of the NCC affinity, with a residual assemblage of pyroxene + plagioclase + amphibole. The source for Group 2 was a mixture of ancient lower mafic crust and a juvenile crustal component, and melting left a residue of orthopyroxene + clinopyroxene + plagioclase + garnet + amphibole. Generation of these two types of late Permian andesites favors a model whereby breakoff of a subducted slab and subsequent lithospheric extension triggered extensive asthenospheric upwelling and melting of the continental mafic lower crust of the eastern CAOB. The discovery of ancient lower continental crust of the NCC affinity in the CAOB implies that the NCC experienced continental breakup during the opening and spreading of the paleo-Asian Ocean. © 2016 Elsevier B.V.

Gao X.,Research Center for Orogenic Geology | Xiao P.,Research Center for Orogenic Geology | Kang L.,Research Center for Orogenic Geology | Ji W.,Research Center for Orogenic Geology | Yang Z.,Research Center for Orogenic Geology
Geotectonica et Metallogenia | Year: 2015

Petrologic and geochemical analyses have been carried out in aiming to reveal the petrogenesis of the ‘Permian' sub-alkaline basalt of A'qiang volcanic sequence in West Kunlun orogen. The lower basalts exhibit tholeiitic feature and share similar incompatible trace element geochemistry to those of the oceanic plateau basalts, i.e., insignificant Nb-Ta anomaly, higher Nb/La ratios (0.49-1.46, average=0.98), LREEs enrichment relative to HREEs and flat HREE pattern. Their geochemical features indicate that the primitive magma was derived from a source of convective asthenosphere with involvement of EMII component. The upper basalt-andesite associations have similar trace element geochemical characteristics to the island arc basalt-andesite series, with enrichments in LREEs and LILEs and depletions in Nb, Ta and Ti. We suggest that the upper lavas were derived from an enriched lithospheric mantle, which had been previously modified by slab-released fluids and/or related sediments. Both types of mafic lavas experienced fractional crystallization of olivine, clinopyroxene and plagioclase. Our new results from the ‘Permian' tholeiitic basalts indicate multiple mantle sources beneath the eastern part of West Kunlun orogen, suggesting the existence of a continental margin rift or a back-arc basin during the late Paleozoic time. © 2015, Science Press. All right reserved.

Yun J.,Research Center for Orogenic Geology | Yun J.,China University of Geosciences | Gao X.-F.,Research Center for Orogenic Geology | Xiao P.-X.,Research Center for Orogenic Geology | And 2 more authors.
Geology in China | Year: 2015

The Wuluate Formation of Lower Carboniferous is distributed in the northern part of Western Kunlun Mountains. Associated with thick carbonate rock and thin marble, it is a set of volcano-sedimentary rocks mainly composed of grayish green pillow basalts and grayish white rhyolite. Based on the study of the chemistry of lavas, the authors hold that the major element values of the basalts are similar to the average values of tholeiite: SiO2 values vary between 52.10% and 54.42%, (Na2O/K2O)>1, TiO2(0.50%∼2.03%), and Mg# values are in the range of 52∼70. The ΣREE values of the samples range from 14.46×10-6 to 91.83× 10-6, whereas (La/Yb)N values vary between 0.46 and 1.69, respectively. All these characteristics are extremely similar to things of the E-BABB and different from features of OIB and N-MORB. The basalts show depletion of Rb, suggesting that the lower crust contamination existed in the magma processing. Rhyolite belongs to both calc-alkaline and high-K calc-alkaline volcanic rock series. Concentrations of REE are higher than those of basalts, the (La/Yb)N radios are between 1.30 and 11.99, and (La/Sm)N radios are from 1.15 to 4.07. All these features are similar to features of the lower crust. Different REE patterns and trace element features between the two rock types and the absence of trend from the basalts to the rhyolite imply that the rhyolite and basalt had different sources and origins. Trace element diagrams and regional geological characteristics indicate that the Wuluate Formation formed in an extension environment of the back-arc pull-apart condition. The study of the genetic characteristics of rocks suggest that the basalts resulted from 5% - 10% partial melting of spinel lherzolite in the depleted mantle, and were contaminated by the lower crust later. The heat carried by the mantle material led to the partial melting of the lower crust, and then the rhyolite was produced. Comprehensive studies show that the northern part of Western Kunlun Mountains was in a stretch tension environment (back - arc extensional environment) in the early Carboniferous, and the Wuluate Formation was the magmatic product of the tectonic event.

Wang K.,Research Center for Orogenic Geology | Wang K.,China University of Geosciences | Liu S.,China University of Geosciences | Jiang C.,China University of Geosciences | And 3 more authors.
Geotectonica et Metallogenia | Year: 2015

The northern Yangtze Block went through many periods of deformation, within which the early-period structural styles were destroyed and replaced by later ones. Fortunately, records of the early-period deformation styles are reserved in the Nanzhang area, which is tectonically located between the two arc-shaped fault-belts in the northern Yangtze Block: Daba Shan and Dahong Shan. Three phases of folding were recognized in the Dayang synclinorium area, namely the first stage NW-SE trending folds, second stage NE-SW trending folds, and the third stage E-W trending folds. The three phases of folding correspond to the tectonic deformations such as the northward subduction of the Yangtze Block with later intra-continental deformation, the northwest-ward thrusts of the Jiangnan-Xuefeng fold blets and the southwest-ward propagation of Daba Shan fault belts during the late Jurassic to early Cretaceous, respectively. ©, 2015, Science Press. All right reserved.

Bai J.-K.,Research Center for Orogenic Geology | Wang H.-L.,Research Center for Orogenic Geology | Zhu X.-H.,Research Center for Orogenic Geology | Xie C.-R.,Research Center for Orogenic Geology
Geology in China | Year: 2016

As the first named location of the Ordovician Zhongbao Group, Shihuigou area in Yongdeng County of North Qilian Mountain is an ideal place for the study of the Ordovician tectonic evolution of North Qilian orogenic belt. On the basis of the measured stratigraphic section, the Zhongbao Group in Shihuigou area can be divided into upper and lower part respectively: the lower part mainly consists of mafic-intermediate volcanic rocks and pyroclastic rocks, whereas the characteristics of the upper part is the existence of carbonate, cherts and siltstone interbedded with intermediate-basic pyroclastic rocks. Field investigation shows that there are many layers of cherts and strong deformation in the upper part of the Ordovician Zhongbao Group. According to the study of the rock assemblage, stratigraphic sequence, sedimentary facies, volcanic eruption facies, deformation features and spatial combination relationship, this set of special sedimentary strata are considered to be the typical olistostromes. Considering its internal structure and volcanic-sedimentary succession, the authors hold that the olistostromes should be deposited in the deep-water basin near the island arc, which belonged to a tectonic background of archipelagic ocean. The discovery of olistostromes in the Zhongbao Group provides reliable evidence for recovering and establishing the Ordovician sedimentary environment and paleogeographic evolution of the North Qilian orogenic belt. It also offers important sedimentologic evidence for further studying the trench-arc-basin system spatial pattern of the North Qilian orogenic belt.

Gao X.-F.,Research Center for Orogenic Geology | Xiao P.-X.,Research Center for Orogenic Geology | Kang L.,Research Center for Orogenic Geology | Zhu H.-P.,Shaanxi Geological Survey | And 3 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2013

This paper presents petrological and geochemical features and zircon U-Pb age of a suite of bimodal volcanic rocks in the Bulunkuole Group from the Taishuihai Massif, NW China. The zircon U-Pb dating results yield a mean 238U/206Pb age of 521.3±3.3 Ma, representing the extrusion time of the dacites in the Middle Cambrian, which indicates that the previously defined Paleoproterozoic Bulunkuole Group also includes early Paleozoic volcanic rocks. The basalts and dacites belong to low-K affinities. The basalts show enrichment in Rb, Ba, K and LREE, and depletion in Nb-Ta and Th, suggesting that they were derived from a previously metasomatized depleted mantle. The dacites also show more enrichment in LILE and Th, and larger depletion in Nb-Ta, Sr and Ti in comparison with the basalts. Different REE patterns and trace element features between the two rock types, and the absence of differentiation trend from the basalts to dacites, argue against the origin for the dacites as the differentiates of the basalts. Combining the dacites geochemical features and the experimental data suggest that they are melts of lower crustal mafic protoliths heated by contemporaneous underplating basaltic magmas at relatively low pressure conditions. The occurrence of the bimodal volcanic rocks reflects that the region experienced an extensional tectonic-magmatic event during early Paleozoic. The new data suggests that the previously defined "Paleoproterozoic Bulunkuole Group" includes at least three components: (1) the Paleoproterozoic khondalite series; (2) the Indo-Sinian high-pressure metamorphic complexes and (3) the early Paleozoic volcano-sedimentary associations.

Yu J.,Research Center for Orogenic Geology | Guo L.,Research Center for Orogenic Geology | Li J.,Research Center for Orogenic Geology | Smithies R.H.,Geological Survey of Western Australia | And 3 more authors.
Lithos | Year: 2016

Ordovician to Devonian sodic granites dominate the newly recognized Luotuojuan composite granite in the Lebaquan-Luotuojuan-Niujuanzi region of Beishan, along the southern margin of the Central Asian Orogenic Belt in NW China. The granites include sodic (K2O/Na2O > 0.5) tonalites with low Y (<7 ppm), Yb (<0.7 ppm), high Sr/Y (>68) that formed during at least two events at c. 435 and c. 370-360 Ma. Their compositions are consistent with high-pressure melting of basaltic crust, although relatively non-radiogenic Nd isotope compositions (εNd(t) + 0.9) require some crustal assimilation. The interpretation that these granites reflect melts of a subducted slab (i.e. adakite) is supported by independent local and regional geological evidence for an oceanic subduction-accretion setting, including a long history of calc-alkaline magmatism and the identification of a series of early Paleozoic ophiolite belts. Other sodic granites forming the Luotuojuan composite granite are mainly quartz-diorite and granodiorite formed between c. 391 and c. 360 Ma. These rocks are not adakites, having Sr concentrations and Sr/Y ratios too low and Y and Yb concentrations too high. They are low- to medium-K calc-alkaline rocks more typical of magmas derived through melting in a subduction modified mantle wedge. Compositional changes from sodic to potassic granites, over time frames consistent with subduction processes, suggest at least two separate cycles, or pulses, of hot subduction in the Lebaquan-Luotuojuan-Niujuanzi region. Although early Paleozoic adakites have been inferred to exist elsewhere in the Beishan region, many of the reported adakitic rocks have compositions inconsistent with melting of subducted oceanic lithosphere and so tectonic interpretation of hot subduction might not be valid in these cases. A study of regional granite data also shows not only that adakite magmatism does not extend into the Permian but that if subduction-accretion processes extended into the late Paleozoic, no typical subduction-related magmatism was preserved. New and published Nd isotope data from regional granites also requires at least the local presence of Proterozoic basement, or microcontinental slivers, in the evolution of the Beishan region. © 2016 Elsevier B.V.

Pan F.,Research Center for Orogenic Geology | Li J.,Research Center for Orogenic Geology | Xu Y.,Research Center for Orogenic Geology | Yue L.,Northwest University, China | And 4 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

Aridity of the Asian interior plays an important role in the accumulation of eolian deposits in both eastern (monsoon regime) and western China (westerly wind regime). A better understanding of the provenance of those eolian deposits (loess and red clay) will shed light on the history and mechanisms of Asian aridification. In eastern China, decrease in grain size from northwest to southeast shows that the Neogene red clay of the Chinese Loess Plateau (CLP) was derived from the desert and arid lands of northwestern China by the East Asian winter monsoon. However, in western China, outcrops are limited, and this is an obstacle to studies of the spatial variation of the provenance of eolian deposits. We use [Formula presented] geochronology of detrital zircons to determine the provenance of the Altun Red Clay, a recently discovered and continuous eolian deposit in western China. Our comparison of detrital zircon age spectra for the Altun Red Clay with those of potential source regions, and with results for the coeval red clay of the CLP, indicates that: 1. the main zircon age components of the Altun Red Clay are very different from those of the red clay on the CLP, suggesting that these deposits were sourced from different areas, and 2. the Altun Red Clay was likely sourced from the Taklamakan Desert, and transported via westerly winds. © 2016 Elsevier B.V.

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 | Year: 2015

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.

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