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Yang G.,Chang'an University | Yang G.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Li Y.,Chang'an University | Li Y.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | And 5 more authors.
Earth-Science Reviews | Year: 2015

The Central Asian Orogenic Belt (CAOB, also known as the Altaid Tectonic Collage), one of the largest and long-lived accretionary orogens in the world, developed from ca. 600. Ma to 250. Ma by multiple accretions of terranes of different origin. Despite extensive research aimed at understanding tectonic evolution of the CAOB and the evolution of the Paleo-Asian Ocean, the subduction-accretion mechanism of the CAOB remains controversial. The West Junggar, northwestern China, is located in the southwest of the CAOB and consists of Paleozoic ophiolitic mélanges, arcs and accretionary complexes.The ophiolitic mélanges in West Junggar are generally complicated and usually consist of metamorphic peridotite (serpentinite), cumulates, gabbros, basaltic lavas (pillows), and abyssal radiolarian cherts. However, sheeted dike complexes are extremely rare and, where present, usually form small, isolated bodies. The formation age of ophiolitic mélanges in West Junggar has been determined generally as early Paleozoic except for the Darbut and Karamay ophiolitic mélanges with the age ranging from Early-Middle Devonian to Late Carboniferous. The Darbut and Karamay ophiolitic mélanges have distinct unconformable or fault contacts with Lower Devonian to Lower Carboniferous volcano-sedimentary rocks consisting mainly of sandstone, basalt, tuff and volcanic breccia. The strata deposited on the Tangbale and Mayile ophiolitic mélanges are early Paleozoic and dominated by Ordovician-Silurian volcano-sedimentary rocks.The alkaline basalts in the Tangbale, Mayile, Darbut and Karamay ophiolitic mélanges occur as tectonic blocks within the mélanges which are composed of pelagic limestones, siliceous mudstone and radiolarian chert, possessing formation characteristics of seamounts (oceanic islands/plateaus). The alkaline basalts are characterized by LREE enrichment and HREE depletion, very weak or no Eu anomalies, and no obvious Nb, Ta and Ti negative anomalies, suggesting typical OIB affinity. The OIB-type rocks in ophiolitic mélanges are considered as accreted seamount fragments in West Junggar accretionary complex, and may represent mantle transition zone plume-related magmatism within the Paleo-Asian Ocean. Therefore, we propose the following tectonic evolutionary history of the West Junggar.The seamounts formed in West Junggar as well as the Paleo-Asian Ocean at Neoproterozoic. With progressive evolution of the Paleo-Asian Ocean, subduction of the oceanic lithosphere commenced during late Cambrian to early Ordovician, resulted in the seamounts eventually accreted in the fore-arc with oceanic fragments forming the Tangbale and Mayile ophiolitic mélanges. As retreat of the subducting slab, the subduction-accretion processes may have continued in the late Paleozoic, given rise to form the Darbut and karamay ophiolitic mélange with the OIB-type rocks from seamounts. Based on our observations, and in combination with previous work, we suggest that the intra-plate magmatism in the CAOB might generally continuous during the development of the Paleo-Asian Ocean from the Late Neoproterozoic to the Mesozoic. Therefore, we present a new model that is multiple intra-oceanic subduction with seamount accretion for the CAOB, which can better explain the tectonic evolution of the CAOB. © 2015 Elsevier B.V.

Zha X.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Lu Z.,Petrochina
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2016

It is a valid approach to explore the tectonic evolution and origin by comparative chronological research of the rocks in the northern margin of Qaidam basin characterized by outcropped basement rocks and frequent magmatic activities. Dakendaban Rock Group (DRG) is one of the dominant crystal basement rocks of Oulongbuluke block. A study was carried out on material composition, deformation and metamorphism of the banded migmatitic gneiss, biotite plagioclase gneiss, two-mica plagioclase quartz schist sampled from the DRG, and the gneissic quartz diorite that intruded the DRG. The zircons from DRG samples yield nearly unanimous two peak age of about 460 Ma and peak age of about 430 Ma by LA-ICP-MS zircon U-Pb isotopic analyses. Combined with the regional tectonic processes, we maintain that the age of about 460 Ma is the geological response to the tectono-magmatism caused by ultradeep continental subduction in the North Qaidam. The metamorphic age about 430 Ma is consistent with the crystallization age (429.0±4.1 Ma) of the gneissic quartz diorite. Combined the chronolgical data with geochronological analyses on the gneissic quartz diorite, and the zircon REE data from DRG samples, it proves that the metamorphism of about 430 Ma is closely related to the homochronous tectono-thermal event. The obvious depletion of HFSE, including Nb, Ta, Zr, Hf, and the Pb enrichment demonstrate that the characteristics of the gneissic quartz diorite are related to the plate subduction which formed the active continental margin. This study provides important information for further revealing the tectonic properties and the evolution of the tectono-thermal event at Early Paleozoic in western Oulongbuluke bolck. © 2016, Editorial Department of Earth Science. All right reserved.

Chen B.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Chen B.,Xian Institute of Geology and Mineral Resources | Zhu Y.F.,Peking University
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2015

Ma gmatic high-An plagioclase (An80-100) crystallizes at the early stage of basaltic melt evolution. Due to the restricted conditions under which high-An plagioclase can form and preserve, it can help constrain the crystallization environment and petrogenesis of the host magma. High-An plagioclase ( An80-100) bearing diorite outcrops in Baikouquan, West Junggar, Xinjiang. It was dated to be 316.9 ± 2.9Ma ( MSWD = 1.5) by zircon SHRIMP. The high-An plagioclase occur as irregular patches in the predominant plagioclase of diorite. The major and trace elements and Sr-Nd isotopic data match the trend of the contemporary intrusions in this region. Detailed petrological and mineralogical studies demonstrate the high-An plagioclase are antecryst which belong to the magmatic system producing the host but are not directly a consequence of the crystallization of the host. They came from an earlier pulse of magma and which are incorporated in a later pulse. Based on the Al-in-amphibole geobarometer, the diorite crystallized at 1.2 ~ 2. 9kbar, which is compatible with the condition for the high-An plagioclase formation. The crystallization of high-An plagioclase n Baikouquan diorite suggests a H20-rich and depleted primary magma, and has a profound implication on the magmatic system.

Yang Z.,Chang'an University | Yang Z.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Chao H.,Chang'an University | Chao H.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | And 2 more authors.
Earth Science Frontiers | Year: 2016

Qinling orogenic belt is a famous orogenic belt in central China, and it is also a typical intra-continental orogenic belt of continental tectonics. This type of orogenic belt did not undergo subduction of ocean crust to form such orogenic belt with main suture zone. It is not the collision orogenic belt that formed by the interaction between North China plate and Yangtz plate, and also not so-called composite orogenic belt. According to the composition, structural characteristics of different depth, cross-bridge structure, structural style in the transformation of basin and mountain, the structural characteristics of Shangxian-Danfeng tectonic zone and Mianxian-Lueyang tectonic zone as well as the distinct north-south direction structures in the central orogenic system (Qinling), the non-plate features of these characteristics are discussed. On the basis of above discussion, the thrust-Choula(or Choula) tectonic model for the formation of Qinling intra-continental orogenic belt is built. © 2016, Editorial Office of Earth Science Frontiers. All right reserved.

Sun N.,Chang'an University | Sun N.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Sun N.,CAS Institute of Vertebrate Paleontology and Paleoanthropology | Li X.,CAS Institute of Vertebrate Paleontology and Paleoanthropology | And 4 more authors.
Holocene | Year: 2016

Understanding the features of the paleoclimate and paleoenvrionment from key areas is crucial for predicting the climate variation of the future. In this study, fossil charcoal coupled with high-accuracy accelerator mass spectrometry (AMS) 14C dating from the Guanzhong Basin is analyzed to reconstruct the paleoclimate. Here, the coexistence approach (CA) was applied, and the result showed that the mean annual temperature (MAT) was about 14.8°C, and the annual precipitation (AP) was about 831.1 mm in the Guanzhong Basin during 6200–5600 cal. a BP. Comparing the climate between the mid-Holocene and present in the Xi’an area, the MAT was about 1.1°C higher than today and the AP was about 278 mm higher than today, similar to the modern climate of the Hanzhong area in the southern Qinling Mountains. © 2016, © The Author(s) 2016.

Yangwei F.,Northwest University, China | Yangwei F.,Xian Institute of Geology and Mineral Resources | Yangwei F.,Xi'an Jiaotong University | Yangwei F.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | And 3 more authors.
Acta Geologica Sinica | Year: 2015

Qinling orogen is one of the five main repository distribution provinces of large scale graphite resources. Graphite occurrence strata are multitudinous including NeoArchaean group to Neopaleozoic. Mineral deposit types are complete consisting of crystal flaky graphite deposit and aphanitic graphite deposit, ore types of the former are main graphite gneiss, graphite schist and graphitized marble, and ore types of the latter are main graphite layer metamorphosised from coal bed and graphitic carbargilite. At present, most graphite deposits with low research degree only implement preliminary investigations of the graphite resource, which has a good prospect. Based on the basic material of dozens of graphite deposits, spots and plays discovered in the Qinling orogen, this paper applied geologic multidisciplinary analysis method to disclose the graphite deposit types of the Qinling orogen, mainly through outdoors geologic survey and specimen examination with analysis of some typical deposits: regional metamorphism crystal graphite deposits and thermo-contact metamorphic aphanitic graphite deposits, with the control of latitudinally trending regional tectonic, graphite deposits of the Qinling orogen distribute sublatitudinally trending three large ore belts: I the Neoarchean-Proterozoic basement crystal graphite enrichment deposits zone along the south margin of North China plate; II the Carboniferous intermountain basin group aphanitic graphite enrichment deposits zone near the Shangdan suture of the West Qinling; III Paleozoic crystal graphite enrichment deposits zone in the Qinling paleomicroplate of the west part of the East Qinling.Conclusions are reached from multiple inquiries: Qinling multi-cycle complex continental collision orogen zone has experienced multiple tectonic framework transformation and polyphase tectonic thermal event from NeoArchean Erathem adjointing multiple graphite tectonic mineralization cycle. In the light of chief control of mineralization and ore types, each of the three large graphite deposits belts of the Qinling orogen has its own genesis: I graphite deposits enriched metallogenetic zone is that regional tectogenetic movement from NeoArchaean caused polyphase metapepsis, which superimposed up and reconstructed NeoArchean Erathem to Proterozoic basement, forming regional metamorphic big flake crystal graphite deposits; II graphite deposits enriched metallogenetic zone is that polyphase regional tectogenetic movement associated with multiple heating caused by multiphase igneous intrusion, which resulted in original coal layers emerging multiple thermo-contact metamorphisms and formed thermo-contact metamorphic aphanitic graphite deposits. III graphite deposits enriched metallogenetic zone is that Palaeozoic cap-rock experienced polyphase metapepsis, forming regional metamorphic finely flake crystal graphite deposits. Comprehensive research of metallogenetic mechanism in graphite deposits and its associated profitable deposits of the Qinling orogen is importance for future exploration. © 2015 Geological Society of China.

Li R.,Chang'an University | Li R.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Qin X.,Chang'an University | Qin X.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | And 3 more authors.
Acta Geologica Sinica | Year: 2015

Field investigation combined with detailed petrographic observation indicate that abundant oil, gas, and solid bitumen inclusions were entrapped in veins and cements of sedimentary rocks in the Dabashan foreland, which were used to reconstruct the oil and gas migration history in the context of tectonic evolution. Three stages of veins were recognized and related to the collision between the North China block and the Yangtze block during the Indosinian orogeny from Late Triassic to Early Jurassic (D1), the southwest thrusting of the Qinling erogenic belt towards the Sichuan basin during the Yanshanian orogeny from Late Jurassic to Early Cretaceous (D2), and extensional tectonics during Late Cretaceous to Paleogene (D3), respectively. The occurrences of hydrocarbon inclusions in these veins and their homogenization temperatures suggest that oil was generated in the early stage of tectonic evolution, and gas was generated later, whereas solid bitumen was the result of pyrolysis of previously accumulated hydrocarbons. Three stages of hydrocarbon fluid inclusions were also identified in cements of carbonates and sandstones of gas beds in the Dabashan foreland belt and the Dabashan foreland depression (northeastern Sichuan basin), which recorded oil/gas formation, migration, accumulation and destruction of paleo-reservoirs during the D2. Isotopic analysis of hydrocarbon fluid inclusions contained in vein minerals shows that δ13C1 of gas in fluid inclusions ranges from -17.0‰ to -30.4‰ (PDB) and δD from -107.7‰ to -156.7‰ (SMOW), which indicates that the gas captured in the veins was migrated natural gas which may be correlated with gas from the gas-fields in northern Sichuan basin. Organic geochemical comparison between bitumen and potential source rocks indicates that the Lower Cambrian black shale and the Lower Permian black limestone were the most possible source rocks of the bitumen. Combined with tectonic evolution history of the Dabashan foreland, the results of this study suggest that oil was generated from the Paleozoic source rocks in the Dabashan area under normal burial thermal conditions before Indosinian tectonics and accumulated to form paleo-reservoirs during Indosinian collision between the North China block and the Yangtz block. The paleo-reservoirs were destroyed during the Yanshanian tectonic movement when the Dabashan foreland was formed. At the same time, oil in the paleo-reservoirs in the Dabashan foreland depression was pyrolyzed to transform to dry gas and the residues became solid bitumen. © 2015 Geological Society of China.

Zhang G.S.,Chang'an University | Zhang G.S.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Zhang G.S.,Moscow State University | Bobrov A.V.,Moscow State University | And 2 more authors.
Geochemistry International | Year: 2016

The paper discusses the results of mineralogical and petrographic studies of spinel lherzolite xenoliths and clinopyroxene megacrysts in basalt from the Jixia region related to the central zone of Cenozoic basaltic magmatism of southeastern China. Spinel lherzolite is predominantly composed of olivine (Fo89.6–90.4), orthopyroxene (Mg# = 90.6–92.7), clinopyroxene (Mg# = 90.3–91.9), and chrome spinel (Cr# = 6.59–14.0). According to the geochemical characteristics, basalt of the Jixia region is similar to OIB with asthenospheric material as a source. The following equilibrium temperatures and pressures were obtained for spinel peridotite: 890–1269°C and 10.4–14.8 kbar. Mg# of olivine and Cr# of chrome spinel are close to the values in rocks of the enriched mantle. It is evident from analysis of the textural peculiarities of spinel lherzolite that basaltic melt interacted with mantle rocks at the xenolith capture stage. Based on an analysis of the P–T conditions of the formation of spinel peridotite and clinopyroxene megacrysts, we show that mantle xenoliths were captured in the course of basaltic magma intrusion at a significantly lower depth than the area of partial melting. However, capture of mantle xenoliths was preceded by low-degree partial melting at an earlier stage. © 2016, Pleiades Publishing, Ltd.

Xu X.Y.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Chen J.L.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Gao T.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Gao T.,Chang'an University | And 2 more authors.
Acta Petrologica Sinica | Year: 2014

Zircon LA-ICP-MS dating indicates that Jiangligou monzonite, Ayishan granodiorite, Dewulu granodiorite, Wenquan granodiorite, and Zhongchuan monzonite in the northern margin of Western Qinling terrane formed at 264 ± 1.4Ma, 241.6 ±4Ma, 233. 5 ± 1. 5Ma, 216. 2 ± 1. IMa, and 264. 2 ± 1. 3Ma, respectively. Geochemical data suggest that these granitic rocks are mainly belonging to high-K calc-alkalic series and minor rocks are calc-alkalic. The Jiangligou, Ayishan and Zhongchuan intrusions are prealuminous granites with ACNK > 1.05, however, the Wenquan and Dewulu intrusions are metalumious or prealuminous granites with ACNK value of 0. 95 ∼ 1. 05. They also have the geochemical characters of adakite and Himalaya-type granites. The granites of adakite and Himalaly-type with low Mg# may result from partial melting of basalts in thickened lower crust, which can provide some clues to the collision between the North China Plate and the Yangtze Plate and also direct Cu-Au prospecting.

Yang G.,Chang'an University | Yang G.,Key Laboratory for the study of Focused Magmatism and Giant Ore Deposits | Li Y.,Chang'an University | Li Y.,Key Laboratory for the study of Focused Magmatism and Giant Ore Deposits | And 5 more authors.
International Geology Review | Year: 2016

Zircon U–Pb geochronological and geochemical analyses are reported for a suite of the early Carboniferous volcanic rocks from West Junggar (Northwest China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded concordant weighted mean 206Pb/238U age of 345 ± 3 Ma, indicating the presence of early Carboniferous volcanic rocks in West Junggar. The early Carboniferous volcanic rocks consist of basalt, basaltic andesite, and andesite. Geochemically, all the samples bear the signature of ocean island basalt (OIB), and are characterized by alkaline affinity with minor variations in SiO2 compositions (45.13–53.05 wt.%), high concentrations of Na2O + K2O (5.08–8.89 wt.%) and TiO2 (1.71–3.35 wt.%), and LREE enrichment and HREE depletion ((La/Yb)N = 7.1–12.4), with weak Eu anomalies (Eu/Eu* = 0.9–1.1) and no obvious Nb, Ta, and Ti negative anomalies. These features suggest that the early Carboniferous volcanic rocks were derived from an OIB-related source that consists of oceanic lithosphere with ~1–3% degree partial melting of garnet lherzolite. From these observations, in combination with previous work, we conclude that the early Carboniferous alkaline volcanic rocks in Karamay region formed by upwelling of asthenospheric mantle through a slab window in a forearc setting during consumption of the West Junggar Ocean. Meanwhile, seamounts, which formed in the Late Devonian and were accreted and subducted in Karamay arc, also brought geological effects in the subduction zone. © 2016 Taylor & Francis

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