Chinese University of Geosciences

Beijing, China

Chinese University of Geosciences

Beijing, China
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Zhang Y.,Peking University | Song S.,Peking University | Yang L.,Peking University | Su L.,Chinese University of Geosciences | And 4 more authors.
Lithos | Year: 2017

Oceanic plateaus with high-Mg rocks in the present-day oceanic crust have attracted much attention for their proposed mantle-plume origins and abnormally high mantle potential temperatures (Tp). However, equivalent rocks in ancient oceanic environments are usually poorly preserved because of deformation and metamorphism. Here we present petrological, geochronological and geochemical data for pillow lavas from Cambrian ophiolites in the Lajishan and Yongjing regions of the South Qilian Accretionary Belt (SQAB), from the southern part of the Qilian Orogen, northern China. Three rock groups can be identified geochemically: (1) sub-alkaline basalts with enriched mid- ocean ridge basalt (E-MORB) affinity; (2) alkaline basalts with oceanic island basalt (OIB) features, probably derived from partial melting of an enriched mantle source; and (3) picrites with MgO (18–22 wt%). Cr-numbers [Cr# = Cr/(Cr + Al)] of spinels from the picrites suggest 18–21% degree of partial melting at the estimated mantle potential temperature (Tp) of 1489–1600 °C, equivalent to values of Cenozoic Hawaiian picrites (1500–1600 °C). Zircons from one gabbro sample yielded a U–Pb Concordia age of 525 ± 3 Ma, suggesting the oceanic crust formed in the Cambrian. Available evidence suggests that Cambrian mantle plume activity is preserved in the South Qilian Accretionary Belt, and influenced the regional tectonics: “jamming” of the trench by thick oceanic crust explains the emplacement and preservation of the oceanic plateau, and gave rise to the generation of concomitant Ordovician inner-oceanic island arc basalts via re-organisation of the subduction zones in the region. © 2017 Elsevier B.V.

Cai Z.,Chinese Academy of Geological Sciences | Xu Z.,Chinese Academy of Geological Sciences | Xu Z.,Nanjing University | Cao H.,Chinese Academy of Geological Sciences | And 3 more authors.
Journal of Structural Geology | Year: 2017

The West Muztaghata Shear Zone (WMSZ) and Kuke ductile shear zone (KS) are located at the western and eastern margins, respectively, of the Muztaghata gneiss dome (MD) in the northeast Pamir. We report new geological data, including quartz fabric analyses, zircon U-Pb ages, and mica 40Ar-39Ar ages, to constrain the geometry, kinematics and evolution time of the WMSZ and KS. The presence of garnet and kyanite in the mylonites from the WMSZ indicate that the shear zone roots into the lower crust. The deformation characteristics of mylonites of the WMSZ show top-to-W or SW shear sense, and formed at mid-high temperatures. Zircons from high-grade mylonites and synkinematic leucogranites record a consistent U-Pb ages of ∼20 Ma, interpreted to reflect high-grade metamorphism and partial melting in the northeast Pamir in the early Miocene prior to ductile shearing along the WMSZ. The adjacent undeformed 12 Ma Kuzigan pluton, indicates deformation along the WMSZ ceased by then. 40Ar-39Ar dating results for mica show that the WMSZ underwent continued exhumation to the middle-upper crust until ∼12–8 Ma. To the east, the KS has E-dipping foliations with a top-to-E normal shear sense and preserves low to medium deformation temperature fabrics. Previous data and new biotite dating from the KS yield 40Ar-39Ar ages of ∼12–8 Ma, indicating broadly synchronous activity along the KS in the middle Miocene. Integrated with previous studies, our results suggest that continuous India-Asia convergence led to thickening of the Pamir crust, which propagated from south to north, initiating in the South Pamir in the late Eocene and advanced through the North Pamir around 20 Ma. This was immediately followed by rapid exhumation during east-west stretching and dome formation, broadly coeval but slightly outlasting exhumation of the other Central Pamir gneiss domes. © 2017 Elsevier Ltd

Luo Z.-B.,Chinese University of Geosciences | Zhang H.-F.,Chinese University of Geosciences | Li S.-R.,Chinese University of Geosciences
Kuangwu Yanshi/ Journal of Mineralogy and Petrology | Year: 2012

The Jinchang gold deposit is located in the eastern part of the Songnen Block of Xingmeng orogenic belt. It is indicated that,from the country rock alteration patterns and fluid inclusions data,the deposit is a porphyry-style gold deposit. Geological and geochronological data reveal that gold mineralization is most likely to be related to the Yanshanian porphyrytic magmatism. In order to shed light on the prospective exploration of the gold deposit,mineral geothermobarometers are used to study the forming conditions of the quartz diorite porphyrites underneath the No. 18 ore body. It is showed that the solidified temperatures of the quartz diorite porphyrites are 700 °C∼735 °C ,pressures are 0. 63 MPa∼l. 3 MPa, with the corresponding depths of 2 km∼4 km,similar to the mineralization depth (2. 1 km∼3. 2 km). Based on the characteristics of the porphyry metallogenic system,it is considered that the Jincharrg gold mine still have great potential prospection for further exploration.

Song S.,Peking University | Song S.,Durham University | Niu Y.,Durham University | Wei C.,Peking University | And 2 more authors.
Lithos | Year: 2010

The Gongshan block near the Eastern Himalayan Syntaxis is a fault-bounded block at the northern tip of the triangle-shaped Indochina continent (NIC). Exposed in this block are late Paleozoic (Carboniferous to Permian) strata and a north-south belt of intermediate to felsic batholiths (i.e., Gaoligongshan magmatic belt). The contact between the Gaoligongshan batholiths and Carboniferous/Permian strata is characterized by a series of high-grade metamorphic gneisses with leucosome granite veins (i.e., the so-called "Gaoligong Group"). U-Pb SHRIMP and LA-ICP-MS dating of zircons indicate that these gneisses are actually metamorphosed Paleogene sediments containing inherited Archean to Cretaceous detrital zircons (from 2690 to 64. Ma) and have undergone medium- to high-pressure granulite-facies metamorphism at ~ 22. Ma. Leucosome and S-type granite of 22-53. Ma by anatexis are ubiquitous within high-grade metamorphic rocks in the southern part of the Gongshan block. An Early Paleozoic gneissic granite and granitoid intrusions of Jurassic, Cretaceous and Oligocene-Miocene ages are also recognized in NIC blocks. These ages suggest that the NIC differs distinctly from the Indian continent, the Greater and Lesser Himalaya zones, and the Yangtze Craton, but resembles the Lhasa Block in terms of Paleozoic to Mesozoic magmatism and detrital zircon ages. This offers an entirely new perspective on the tectonic evolution of the Gongshan block in particular and of the history of the Lhasa Block in the context of the India-Asia continental collision in general. Furthermore, the high-grade metamorphism in the NIC indicates a strong crustal thickening (vs. strike-slip shearing) event during much of the Eocene to the Oligocene (~ 53-22. Ma) that has brought the Paleogene sediments to depths of greater than 25. km. Continuous northward convergence/compression of the Indian Plate at the Eastern Himalayan Syntaxis may have led to the clockwise rotation, southeastward extrusion and extension of the southeastern part of the Indochina continent. © 2010 Elsevier B.V.

Luo Z.,Chinese University of Geosciences | Luo Z.,Northwest University, China | Zhang H.,Chinese University of Geosciences | Zhang H.,Northwest University, China | Diwu C.,Northwest University, China
Acta Petrologica Sinica | Year: 2012

The Huai'an area of Northwest Hebei stands on the central-north of the North China Craton (NCC). Intermediat pyroxene-granulite in this area can provide important clues for the timing of regional metamorphism. The mineral assemblages indicate that it was undergone mid-pressure granulite metamorphism and overlapped by amphibolite facies retrograde. Zircon U-Pb, Lu-Hf isotope and trace elements compositions are analyzed. As a result, zircon cores with oscillatory zoning exhibit various 207Pb/206Pb ages in range of 2542-1902Ma (1σ. They show a positive relations with Th/U (0. 10-1. 92) ratios, σHREE (59. 1 × 10-6-452 × 10 -6) and εHf(t) values, indicating their different degrees of lattice recrystallization due to the postdated metamorphism. Zircon grains with the most concordant and old ages yield a mean 207Pb/ 206Pb age of 2471 ±18 Ma (2σ, MSWD =6.1). This age is interpreted to be the emplacement age of the protolith rocks. Their depleted Hf model ages of tDM and tDM c vary in range of 2550-2621Ma (peak at 2586Ma), and 2596-2716Ma (peak at 2665Ma), respectively. Whereas, they have εHf(t) values of 4. 1-6. 7, indicating that the protolith rocks is dominately derived from the Late Archean juvenile crust. The metamorphic over growth zircons occurring as metamorphic new-single grains or as zircon mantles overgrowth around the magmatic zircon cores, yield U-Pb ages varying from 1865Ma to 1782Ma, with relatively low Th/U (<0. 10), 176Lu/177Hf (<0. 0001), and HREE abundance. They yield a mean 207Pb/206Pb age of 1831 ±7Ma (2σ, MSWD = 2. 5). We interpret this age to be the age of granulite to amphibolite retrograde metamorphism. The Tiin-zircon temperatures record their formation temperatures in range of 683-714°C which are highly consistent with the temperatures from granulite to amphibolite retrograde metamorphism. Therefore, the isotopic ages of 1850-1800Ma might be representative of the stage of regional crust uplift postdating the Late Palaeoproterozoic cratonization.

Song S.,Peking University | Niu Y.,Durham University | Niu Y.,Chinese Academy of Sciences | Su L.,Chinese University of Geosciences | And 2 more authors.
Geochimica et Cosmochimica Acta | Year: 2014

Modern adakite or adakitic rocks are thought to result from partial melting of younger and thus warmer subducting ocean crust in subduction zones, with the melt interacting with or without mantle wedge peridotite during ascent, or from melting of thickened mafic lower crust. Here we show that adakitic (tonalitic-trondhjemitic) melts can also be produced by eclogite decompression during exhumation of subducted and metamorphosed oceanic/continental crust in response to continental collision, as exemplified by the adakitic rocks genetically associated with the early Paleozoic North Qaidam ultra-high pressure metamorphic (UHPM) belt on the northern margin of the Greater Tibetan Plateau. We present field evidence for partial melting of eclogite and its products, including adakitic melt, volumetrically significant plutons evolved from the melt, cumulate rocks precipitated from the melt, and associated granulitic residues. This "adakitic assemblage" records a clear progression from eclogite decompression and heating to partial melting, to melt fractionation and ascent/percolation in response to exhumation of the UHPM package. The garnetite and garnet-rich layers in the adakitic assemblage are of cumulate origin from the adakitic melt at high pressure, and accommodate much of the Nb-Ta-Ti. Zircon SHRIMP U-Pb dating shows that partial melting of the eclogite took place at ~435-410. Ma, which postdates the seafloor subduction (>440. Ma) and temporally overlaps the UHPM (~440-425. Ma). While the geological context and the timing of adakite melt formation we observe differ from the prevailing models, our observations and documentations demonstrate that eclogite melting during UHPM exhumation may be important in contributing to crustal growth. © 2014 Elsevier Ltd.

Song S.,Peking University | Niu Y.,Durham University | Niu Y.,CAS Qingdao Institute of Oceanology | Su L.,Chinese University of Geosciences | And 2 more authors.
Earth-Science Reviews | Year: 2014

The North Qaidam ultra-high pressure metamorphic (UHPM) belt in the northern Tibetan Plateau records a complete history of the evolution of a continental orogen from prior seafloor subduction, to continental collision and subduction, and to the ultimate orogen collapse in the time period from the Neoproterozoic to the Paleozoic. Lithologies in this UHPM belt consist predominantly of felsic gneisses containing blocks of eclogite and peridotite.The 1120-900. Ma granitic and psammitic/pelitic gneisses compose the majority of the UHPM belt and is genetically associated with the previous orogenic cycle of Grenville-age, whereas protoliths of the HUPM eclogites are of both the 850-820. Ma continental flood basalts (CFBs) and the 540-500. Ma oceanic crust (ophiolite). The early stage of quartz-stable eclogite-facies metamorphism took place at ~. 445-473. Ma, the same age as that of the HP rocks in the North Qilian oceanic suture zone, representing the earliest subducting seafloor rocks exhumed and preserved. Coesite-bearing zircons from the metapelite and eclogite, diamond-bearing zircons from garnet peridotites constrain the UHP metamorphic age of ~. 438-420. Ma, which represents the timing of continental subduction at depths of 100-200. km, ~. 10-20. m.y. younger than the early stage of the Qilian seafloor subduction. Therefore, deep subduction of continental crust should be the continuation of oceanic subduction that is pulled down by the sinking oceanic lithosphere or pushed down by the overriding upper plate, which is an expected and inevitable consequence for the scenario of passive continental margins. Partial melting of subducted ocean crust might occur in response to continental subduction at ~. 435. Ma.The UHPM rocks started to exhume accompanied by mountain building and deposition of Early Devonian molasses in the North Qilian region at ~. 420. Ma. Decoupling of oceanic subduction zone and continent UHPM terranes may be attributed to the different exhumation path and mechanism between the subducted oceanic and continent crusts, or rollback of subduction zone. Decompression melting of UHP metamorphosed slab and continental crust during exhumation is responsible for the generation of adakitic melts and S-type granite. Mountain collapse and lithosphere extension happened in the period of ~. 400-360. Ma and formed diorite-granite intrusions in the UHPM belt, which marked the end of a complete orogenic cycle.This UHP metamorphic belt presents an example of multi-epoch tectonic recycles, represented by recombination of the Neoproterozoic Grenvillian orogenesis and the Early Paleozoic Caledonian orogenesis. © 2013 Elsevier B.V.

Clark C.,Curtin University Australia | Healy D.,University of Aberdeen | Johnson T.,Curtin University Australia | Collins A.S.,University of Adelaide | And 3 more authors.
Gondwana Research | Year: 2015

The Southern Granulite Terrane in southern India preserves evidence for regional-scale high to ultrahigh temperature metamorphism related to the amalgamation of the supercontinent Gondwana. Here we present accessory mineral (zircon and monazite) geochronological and geochemical datasets linked to the petrological evolution of the rocks as determined by phase equilibria modelling. The results constrain the duration of high to ultrahigh temperature (> 900 °C) metamorphism in the Madurai Block to be c. 40 Ma with peak conditions achieved c. 60 Ma after the formation of an orogenic plateau related to the collision of the microcontinent Azania with East Africa at c. 610 Ma A 1D numerical model demonstrates that the attainment of temperatures > 900 °C requires that the crust be moderately enriched in heat producing elements and that the duration of the orogenic event is sufficiently long to allow conductive heating through radioactive decay. Both of these conditions are met by the available data for the Madurai Block. Our results constrain the length of time it takes for the crust to evolve from collision to peak P-T (i.e. the prograde heating phase) then back to the solidus during retrogression. This evolution illustrates that not all metamorphic ages date sutures. © 2014 International Association for Gondwana Research.

Song X.-W.,Chinese University of Geosciences | Zheng J.-M.,Chinese University of Geosciences | Fan X.-Y.,Sinochem Group | Xiao G.-J.,Petrochina
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2011

In Eastern China, the vast majority of Mesozoic and Cenozoic continental oil basins are dominated by thin-layer sand and shale depositing, the lithology and thickness of the stratums varies largely in the transverse direction, and the thicknesses of these stratums are far less than the vertical resolution of conventional seismic exploration. In order to predict thin inter-bedded reservoir effectively, this paper analyzed both the advantage and disadvantage of common time-frequency methods such as STFT, CWT, MPD, and analyzed experimental model and oilfield material, and the conclusions can be obtained: Compared with STFT and CWT, the MPD based on Ricker wavelet has a better resolution in analyzing thin interbeded reservoirs, and it can describe geology cube more objectively. According to seismic data and well log data from Pinghu oilfield, the MPD based on Ricker wavelet can describe the reservoir space more effectively, and it fits the distribution of reservoir with the actual well log data.

Xue J.,Chinese University of Geosciences | Li S.,Chinese University of Geosciences | Sun W.,Chinese University of Geosciences | Zhang Y.,Chinese University of Geosciences | And 2 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2013

Ore genesis and source of ore-forming materials are always be debated in the study of the metallogenic theory and ore prospecting. In the paper, helium and argon isotopic characteristics of the pyrite from five gold ore samples formed in different stages are analyzed. It is showed that the R/Ra ratio in the fluid ranges from 0.00833 to 3.61200, with an average of 1.40000; the 40Ar/36Ar ratio ranges from 465.7 to 4 674.7, the ratio of 4He/40Ar* varies from 0.36 to 1.36. The ratio of the mantle fluid in ore-forming fluid is from 3.73% to 45.87%, average value is 17.67%. Combined with the characteristics of H-O isotope, magmatic rock, wall rock alteration and fluid inclusion etc., it is suggested that ore-forming fluid belongs to the mixture of mantle-derived and crustal-derived fluid. It is mainly derived from the crust, and mixed by the mantle-derived fluid and the small amount of meteoric water in the metallogenic process.

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