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Geochronology and Geochemistry of the Radiolarian Cherts of the Mada'er Area,southwestern tianshan:Implications for Depositional Environment

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Acta Geologica Sinica(English Edition) 2011年第4期85卷 801-813页

作者： KANG Jianli ZHANG Zhaochong ZHANG Dongyang HUANG He DONG Shuyun ZHANG Su State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences Beijing 100083China Tianjin Institute of Geology and Mineral Resources Tianjin 300170China

In the southwestern tianshan,the geologic ages of many strata and their depositional environments are still poorly constrained because of complex *** Mada＇er area is located in the Kuokesaleling belt,southwestern *** cherts from the former Wupata＇erkan Group contain abundant radiolarian fossils,including 10 species which are identified as late Devonian to early Carboniferous in *** chert samples have SiO_2 contents ranging from 88.80 wt%to 93.28 wt%, and 2.02 wt%to 3.72 wt%for Al_2O_*** SiO_2/Al_2O_3 ratios of all samples vary from 23.84 to 46.11, much lower than those of the pure cherts（80-1400）.These values suggest that the cherts contain high ratios of terrigenous *** Al_2O_3/（Al_2O_3＋Fe_2O_3）ratios vary between 0.64 and 0.77,whereas V and Cu concentrations range from 10.92 ppm to 26.7 ppm and from 2.15 ppm to 34.1 ppm respectively. The Ti/V ratios vary from 25.53 to *** total REE concentrations of the cherts are between 30.78 ppm and 59.26 ppm,averaging 45.46 ***（La/Ce）_N ratios range from 0.81 to 1.12,and 0.88-1.33 for（La/Yb）_N,averaging 1.09,which suggests a continental margin ***,it is inferred that the cherts formed in a residual sea environment during the late Devonian to early Carboniferous time,which suggests that the collision between the Karakum-Tarim and Kazakhstan-Junggar plates did not occur at the *** addition,the regional geological information indicates that the study area experienced a post-collision stage during the early Permian,and thus it is likely that the collision between the two plates took place in the late Carboniferous.

关键词： radiolarian cherts geochemistry depositional environment southwestern tianshan China

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Geochemical characteristics and tectonic implications of HP-UHP eclogites and blueschists in southwestern tianshan, China

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Progress in Natural Science:Materials International 2006年第6期16卷 624-632页

作者： AI Yongliang, ZHANG Lifei, LI Xuping and QU Junfeng (MOE Key Laboratory of Orogenic Belt and Crust Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China School of Geosciences and Resources, China University of Geosciences, Beijing 100083, China) MOE Key Laboratory of Orogenic Belt and Crust Evolution School of Earth and Space Sciences Peking University Beijing 100871 China School of Geosciences and Resources China University of Geosciences Beijing 100083 China

Four rock assemblages in correspondence with two different tectonic settings have been recognized in the NEE-SWW extending HP-UHP metamorphic belt in southwestern tianshan, northwest China. Eclogite assemblage EC1 is geochemically akin to alkaline within-plate oceanic island basalt (OIB). EC2 shows affinity to enriched mid-oceanic ridge basalt (EMORB). Rare earth element (REE) and other immobile trace element characteristics of blueschist assemblage BS1 resemble those of normal mid-oceanic ridge basalt (NMORB). These three assemblages are likely formed on a seamount setting, and the prevalent presence of carbonate minerals and om-phacite quartzite stripes/gobbets suggests ancient pelagic sediments including marls are probably developed upon the basaltic seamount. Whereas the geochemical characteristics of BS2 assemblage are of volcanic arc basalt-type. The seamount with the pelagic sediments on it is brought into the subduction zone, and volcanic arc basalts formed on the active continental margin and trench sediments are eroded and enwrapped in the subducting mass, they are altogether subjected to high to ultrahigh pressure metamorphism and subsequent exhumation towards surface. The HP-UHP metamorphic belt is thus interpreted as a subduct ion-accretionary complex formed by tectonic juxtaposition and imbrication of seamount, seafloor, trench and volcanic arc sequences during oceanic crust subduction.

关键词： southwestern tianshan HP-UHP metamorphic belt snbduction-accretion complex trace element geochemistry.

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Evolutionary Significance of Pylentonemid Radiolarians and Their Late Devonian Species from southwestern tianshan,China

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Acta Geologica Sinica(English Edition) 2006年第5期80卷 647-655页

作者： LIU Yu HAO Shougang Department of Geology Peking University Beijing 100871

A group of radiolarian fossils with a complete morphological gradient of increasing polarization are reported from upper Devonian successions in southwestern tianshan, China. Specifically, the important transitional mophotypes, Pylentonema transitorum sp. nov., Archocyrtium medium sp. nov. and Quadrapesus transitivus sp. nov, were found. Based on the fact that the new transitional radiolarian fossils resemble more closely to pylentonemids （cyrtoid nassellarians） than to entactinids （spumellarians） in morphology, they are assigned to pylentonemids. Pylentonemids share characters of both the Nassellaria （e.g., horned cephalis, basal opening with pylome） and Spumellaria （e.g., system of trabecular spicules）, and they are thus of evolutionary significance. The evolutionary trend from spumellarians to nassellarians is characterized by （1） internal spicule： from simple trabecular spicules to complicate components （A;Ir,II;D;V;Lr,Li;MB）; （2） polarization of the radiolarian tests due to rearrangment of spine, from radial to an axial symmetry; （3） the gradual formation of a basal opening （aperture, pylome, or podome）; and the transition from a pseudopylome, a primative pylome with a narrow margin on the outer shell, to a true pylome rimmed with a narrow, elevated impermite wall.

关键词： radiolarian spumellarian nassellarian entactinids pylentonemids phylogenetic evolution Late Devonian southwestern tianshan

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A subduction channel model for exhumation of oceanic-type high-pressure to ultrahigh-pressure eclogite-facies metamorphic rocks in SW tianshan,China

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Science China Earth Sciences 2016年第12期59卷 2339-2354页

作者： LI JiLei GAO Jun WANG XinShui Key Laboratory of Mineral Resources Institute of Geology and GeophysicsChinese Academy of Sciences

High-pressure(HP) and ultrahigh-pressure(UHP) eclogites exposed in collisional orogens are widely regarded to record the history of crustal rocks that were subducted to mantle depths and exhumed back to the *** into subduction and exhumation processes plays an important role in understanding the nature and evolution of subduction zones,geodynamics and plate *** contrast to continental-type HP to UHP metamorphic rocks that are dominated by felsic lithology,oceanic-type HP to UHP metamorphic rocks are dominated by mafic eclogites and thus have greater density,and their exhumation needs to overcome large barriers and may involve complicated tectonic *** exhumation of HP to UHP rocks is mainly influenced by the internal buoyancy,however,the external tectonic forces(such as channel flow) also act as effective exhumation drivers;in addition,effects of tectonic settings(such as slab rollback and breakoff) should take into *** HP-UHP metamorphic terrane in southwestern tianshan,which mainly comprises of metasediments with interlayered metamafic lenses and blocks,represents a typical accretionary melange associated with deep subduction of oceanic ***,the exhumation mechanisms of these once deeply buried HP-UHP rocks are still under *** on the field occurrences,petrographic features,peak metamorphic P-T conditions and ages of the eclogites/blueschists and their metasedimentary country rocks,a "sediment-type subduction channel" model is advocated in this study to appraise/decipher the formation and evolution of southwestern tianshan HP-UHP metamorphic ***-cyclic metamorphic eclogites record the multistage burial-exhumation cycling manipulated by convective flow in a channel-like interface between the plates,giving robust evidence for the presence of a subduction *** addition,this study summarizes some remaining geotectonic problems and research perspectives concerning the southwestern tianshan HP-UHP me

关键词： Eclogite High-pressure metamorphism Oceanic crust Exhumation Subduction channel southwestern tianshan

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Phase Equilibrium Modeling of Retrograded Eclogite at the Kekesu Valley, Eastern Segment of SW tianshan Orogen and Tectonic Implications

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Journal of Earth Science 2018年第5期29卷 1060-1073页

作者： Bin Xia Qin Yang Neng-Song Chen Zhiqiang Zhou School of Earth Sciences China University of Geosciences State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences Center for Global Tectonics China University of Geosciences

In this study, we report newly found strongly retrograded eclogite blocks in the Kekesu Valley, eastern segment of southwestern tianshan, northwestern China. Based on detailed petrographi- cal studies and mineral chemistry analyses, we constrain P-T evolution of two representative samples via phase equilibrium modeling method using THERMOCALC software. The peak stage is evidenced by the primary inclusions of omphacite＋glaucophane＋lawsonite （inferred）＋chlorite＋white mica in garnet. Using grossular and pyrope isopleth thermobarometry in garnet, the P peak conditions for this stage were con- strained to be -23 kbar, 480-500℃ and the T peak conditions were constrained to be 19-20 kbar, 500-520℃. Subsequent exhumation led to the transformation of lawsonite to epidote. Using Si-in- phengite barometry, the P was constrained to be 16-20 kbar at T of 500-520 ℃ for this stage. Further retrograde stage was evidenced by the mineral assemblages of glaucophane＋garnet＋epidote＋paragonite＋ chlorite＋white mica＋quartz. Later stage retrogression is evidenced by glaucophane＋epidote＋chlorite＋ quartz＋white mica＋albite＋aetinolite with P of 5-9 kbar when T〈490 ~C, indicating the eclogite may have been exhumed to the middle crust level and overprinted by blueschist-greenschist facies metamorphism. The results show that eclogite at the eastern segment of SW tianshan shares similar P-T path to the HP rocks from the western segment, implying a similar P-T evolution for these rocks.

关键词： eclogite P-T path phase equilibria southwestern tianshan Kekesu Valley.

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