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Petrogenesis of Songshugou dunite body in the Qinling orogenic belt, Central china: Constraints from geochemistry and melt inclusions

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Science china Earth Sciences 2005年第8期48卷 1146-1157页

作者： SU Li1,2, SONG Shuguang3.& ZHOU Dingwu1 1. key laboratory of Continental Dynamics of the ministry of {3., department of geology, Northwestern university, Xi’an 710069, china 2. The Geological Lab Center, china university of Geosciences (Beijing), Beijing 100083. china 3. key laboratory of orogenic belts of the ministry of education, department of geology, peking university, Beijing {13., china 1. key laboratory of Continental Dynamics of the ministry of {3. Department of Geology Northwestern University 710069 Xi’an China 2. The Geological Lab Center China University of Geosciences 100083 (Beijing)Beijing China 3. key laboratory of orogenic belts of the ministry of education Department of Geology Peking University 100871 Beijing China

The Songshugou dunite body, which occupies an area of about 20 km2, is the largest ultramafic massif in the eastern Qinling orogenic belt, Central china. The major compo-nent of this body is dunitic rocks including mylonitic dunite and coarse-grained dunite; they oc-cupy about 95 vol% of the total body. Petrography, mineral composition, major and trace ele-ments and primitive melt inclusions have been investigated in this paper; all revealed that this dunite body is the product of melt-rock interaction by porous percolation flow. In comparison with dunite sills or veins in harzburgite from the basal part of Oman ophiolite, this dunite body is characterized by lower contents of Al2O3. CaO and HREE but higher content of highly incom-patible elements and Zr and Hf. The LREE enriched patterns and primitive mantle normalized spidergrams of trace elements are also different from the Oman dunite. Combining with melt in-clusions observed in olivines, we conclude that this dunite body is the product of large- scale porous percolation flow of high-MgO melts within depleted mantle peridotites. The high-MgO magma, in essence, was most probably produced at the hot head of an upwelling mantle plume. The occurrence of the Songshugou dunite body is closely associated with the activity of mantle super-plume in Neo-Proterozoic era in the Yangtze Craton.

关键词： Songshugou dunite body, geochemistry, melt inclusion, mantle plume, Qinling orogenic belt.

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Anatomical reinvestigation of Archaeopteris macilenta from the Upper Devonian(Frasnian) of South china

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Journal of Systematics and Evolution 2011年第6期49卷 590-597页

作者： Yun GUO De-Ming WANG(key laboratory of orogenic {3. and Crustal Evolution,department of geology,peking university,Beijing 100871,china) (key laboratory of orogenic {3. and Crustal Evolution Department of Geology Peking University Beijing 100871 China) *Correspondence: De-Ming WANG *Correspondence: E-mail: dmwang@*** Tel.: 86-10-62761095 Fax: 86-10-62751187.

Archaeopteris macilenta is one of the most widespread plants in the Late *** on fossils from the Frasnian Huangjiadeng Formation,Yichang District of Hubei Province,for the first time we study in detail the anatomy of this progymnosperm plant in South *** axes are protostelic with three xylem sympodia and lack secondary *** axes are eustelic,bearing eight sympodia and a thin band of secondary *** symmetrical sympodia of mesarch primary xylem produce traces of appendages in a spiral *** macilenta and ***(***)are dominant in the Frasnian and Famennian,*** with these two species from other tectonic plates indicate consistent stelar *** spread,continuous occurrence,and identical anatomy during the Late Devonian indicate that Archaeopteris survived the Frasnian-Famennian extinction *** this time,endemic genera and cosmopolitan taxa,including Archaeopteris,suggest the palaeogeographic isolation of South china and certain associations with other plates.

关键词： anatomy Archaeopteris Late Devonian palaeogeography progymnosperms South china.

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Composition of sandstone and heavy minerals implies the provenance of Kuqa Depression in Jurassic, Tarim basin, china

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Progress in Natural Science:Materials International 2005年第7期15卷 633-640页

作者： WU Chaodong, LIN Changsong, SHEN Yanping and FENG Xue ( key laboratory of orogenic {3. and Crustal Evolution, ministry of education, peking university, Beijing 100871, china department of Resources, china university of Geosciences, Beijing 100083. china) key laboratory of orogenic {3. and Crustal Evolution Ministry of Education Peking University Beijing 100871 China. department of Resources China University of Geosciences Beijing 100083 China

The petrological characteristics and heavy mineral assembly of the Jurassic System in Kuqa Basin are consistent with the tectonic evolution, which is the major factor controlling the filling process of Kuqa Basin. Controlled by the source areas at the both sides of the Basin, the matrixes are dominated by sedimentary rock, high-grade metamorphic rock, acid magmatic rock, and the highest heavy mineral assemblage of zircon-garnet-magnetite in the content. According to heavy mineral indexes, the Jurassic strata can be classified into three rhythmic units of heavy mineral. The lower sequence contains abundant heavy minerals and relatively high content of detritus and its matrixes primarily came form the recycling orogen. The assemblage of "zircon-garnet-magnetite" indicates that the sedimentary area in the early evolution period of the basin is relatively near the provenance. The middle sequence is different from the lower sequence in the heavy mineral assemblage and has the different characteristics from that of source rock. The heavy mineral assemblage is "garnet-zircon" with the highest content of garnet and its main matrices are the high-grade metamorphic rock, acid magmatic rock and hydrothermal vein at the northeastern edge of the basin. The middle and upper sequences are characterized by the clast provenance, which is primarily from the recycling orogen at the northern edge of the basin and secondarily from the southern uplift. As a result of the two provenances, the strata with apparent changes of heavy mineral assemblage and index better coincides with the interfaces of the secondary strata sequences, which reflects the denudation history and the filling process of the orogen at the northern edge of the basin.

关键词： sandstone components provenance analysis filling sequence tectonic evolution.

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Structures,kinematics,thermochronology and tectonic evolution of the Ramba gneiss dome in the northern Himalaya

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Progress in Natural Science:Materials International 2008年第7期18卷 851-860页

作者： Lei Guo,Jinjiang Zhang,Bo Zhang The key laboratory of orogenic {3. and Crustal Evolution,ministry of education,china School of Earth and Space Sciences,peking university,Beijing 100871,china The key laboratory of orogenic {3. and Crustal Evolution Ministry of Education China School of Earth and Space Sciences Peking University Beijing 100871 China

The Ramba gneiss dome,one of the north Himalayan gneiss domes,is composed of three tectono-lithologic units separated by an upper and a lower detachment ***-grade metamorphic Tethyan Himalayan sedimentary sequence formed the upper unit above the brittle upper detachment *** gneiss and a leucogranite pluton made up the lower unit beneath the ductile lower detach- ment *** middle-grade garnet-,staurolite-and andalusite-schist constituted the middle unit between the two faults,which may be that the basal part of the upper unit experienced detachment *** Ramba dome underwent three episodes of deformation in its tectonic *** first episode was a top-down-to-north-northwest sliding possibly related to the activity of the south Tibetan detachment system(STDS).The second episode was the dominant deformation related to a east–west extension,which resulted in a unique top-down-to-east kinematics and the major tectonic features of the *** third episode was a collapse sliding toward the outsides of the *** Ramba gneiss dome is possibly a result of the east–west extension and magmatic *** lower detachment fault is probably the main detachment fault separating the sedimentary sequence from the crystalline basement during the east–west extension in the dominant deformation *** diapir of the leucogranite pluton formed the doming shape of the Ramba gneiss *** pluton intruded in the core of the dome in a late stage of the dominant deformation,and its Ar–Ar cooling ages are about 6 *** indicates that the dominant deformation of the dome happened at the same time of the east–west extension represented by the north–south trending rifts throughout the northern Himalaya and southern ***,the formation of the Ramba gneiss dome should be related to this east–west extension.

关键词： Ramba gneiss dome North Himalayan gneiss domes East–west extension

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C-isotope composition and correlation of the Upper Neoproterozoic in Keping area, Xinjiang

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Chinese Science Bulletin 2007年第4期52卷 504-511页

作者： HE XiuBin, XU Bei & YUAN ZhiYun The key laboratory of orogenic {3. and Crustal Evolution, peking university ministry of education of china School of Earth and Space Sciences, peking university, Beijing 100871, china The key laboratory of orogenic {3. and Crustal Evolution PekingUniversity Beijing 100871 China

C-isotope analysis of the carbonates in the Upper Neoproterozoic in Keping, Xinjiang indicates that the Qigebrak Formation and the Upper Sugaitbrak Formation mainly record positive C-isotope values, and a distinct positive excursion occurs in the lower part of the Qigebrak Formation. There are three negative excursions in the boundary between the Qigebrak Formation and the Cambrian, the uppermost and lowermost Upper Sugaitbrak Formation. These characters resemble those of the Upper Neoproterozoic in the Three-Gorge area, which suggests that the Upper Sugaitbrak Formation and Qigebrak Formation can be correlated with the middle and upper parts of the Doushantuo Formation and Dengying Formation, respectively. The negative excursion at the top of the Upper Sugaitbrak Formation corresponds to that at the top of the Doushantuo Formation, while the negative excursion at the bottom of the Sugaitbrak Formation can be correlated with that at the middle part of the Doushantuo Formation in the Three-Gorge area and that at the top of the Hangelchaok diamictites in the Quruqtagh area.

关键词：新疆柯坪地区晚震旦世 C同位素成分冰川作用

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Kinematics and dynamics of the Mesozoic orogeny and late-orogenic extensional collapse in the Sino-Mongolian border areas

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Science china Earth Sciences 2005年第7期48卷 849-862页

作者： ZHENG Yadong 1 & WANG Tao2 1. key laboratory of orogenic {3. and Crustal Evolution (peking university), ministry of education, Beijing 100871, china 2. Institute of geology, Chinese Academy of Geological Sciences, Beijing 10003., china key laboratory of orogenic {3. and Crustal Evolution (peking university) Ministry of Education Beijing 100871 China Institute of geology Chinese Academy of Geological Sciences Beijinq 100037 China

The Sino-Mongolian border areas underwent two important tectonic events during Mesozoic time after late Paleozoic orogeny: a late Triassic to earlier Jurassic contractional event that resulted in a large-scale south-vergent thrust during the orogeny and a late Jurassic-earlier Cretaceous extensional event in a north-south direction that formed a metamorphic core complex. The kinematic and dynamic analyses show that the thrust sheet moved southwards with a kinematic vorticity number of ca. -0.10 and sub-horizontal maximum compressive stress axis that belongs to a contraction-thickening shear. The upper plate of the late-orogenic detachment relatively moved in a 165°direction. The average kinematic vorticity in its earlier stage was 0.74 that belongs to simple shear dominated shearing and related to the maximum compressive stress axes dipping at ～66°, while the later average kinematic vorticity was ～0.55°that belongs to pure shear dominated shearing with sub-vertical maximum compressive stress axes. This suggests that the thrusting led to the crust thickened and the lower plate rocks that were originally located in the upper crust depressed through a brittle-ductile transition zone into the lower crust and became warmer. The heated rocks trended to uplift since their increasing volume and decreasing density while the loading of the upper-plate rocks increased due to the structural thickening. Under the combined effect of the loading and the thermal-uplifting, the ductile shear zone in between increased in its component of vertical pure shear. Once its pure-shear component exceeded its simple-shear one the ductile shear zone became an extension-thinned shear zone. This progressive transitional process reflects internal and essential temporal and spatial relationships: the extensional factor nucleated during the crust thickening by thrusting and increase of the extensional factor finally led to late-orogenic collapse.

关键词： Mesozoic thrusting,late-orogenic collapse,kinematic vorticity number,stress state.

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Nature of the Precambrian metamorphic blocks in the eastern segment of Central Tianshan:Constraint from geochronology and Nd isotopic geochemistry

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Science china Earth Sciences 2004年第12期47卷 1085-1094页

作者： LIU Shuwen,GUO Zhaojie,ZHANG Zhicheng,LI Qiugen & ZHENG Haifei The key laboratory of orogenic {3. and Crustal Evolution,ministry of education,china School of Earth and Space Sciences,peking university,Beijing 100871,china 1. The key laboratory of orogenic {3. and Crustal Evolution Ministry of Education China 2. School of Earth and Space Sciences Peking University 100871 Beijing China

Granitoid gneisses are widespread in Precambrian metamorphic blocks of eastern segment of the Central Tianshan Tectonic Zone, and they have intrusive contact relationships with their metamorphic sedimentary country rocks of Proterozoic Xingxingxia and Kawabulag groups. Zircon U-Pb ages from a granodioritic gneiss (IW11-1) and a parametamorphic schist (W05-9) are determined at the Weiya area. Euhedral prismatic zircons from the granodioritic gneiss (IW11-1) provide U-Pb isotopic discordia intercept ages of 1218±17 Ma and 426±26 Ma, respectively, and euhedral prismatic zircons from the parametamorphic schist (W05-9) display U-Pb isotopic discordia intercept ages of 1216±74 Ma and 290±15 Ma, respectively. A whole-rock Sm-Nd isotopic isochron is determined in augen granitoid gneiss samples at the Gang- gou-Kumishi area and we obtain the isochron age of 1142±120 Ma, and its ε Nd (t) = -4.3. These geochronological data suggest that these Precambrian metamorphic basement blocks within eastern segment of the Central Tianshan Tectonic Zone can be produced during 1140—1220 Ma, and occur a nearly homochronous metamorphism. Integrated to these geochronological data, Nd depleted mantle model ages (T DM ) and epsilon Nd(t) values of these granitoid gneiss samples indicate that they can derive from mixing in various scales both magmas from mantle and crust sources at a late Mesoproterozoic active continental margin tectonic environment. Similarity in geochronology, Sm-Nd isotopic geochemistry between Weiya-Xingxingxia, Pargangtag and Ganggou-Kumishi areas suggests that they could be a bigger uniform metamorphic basement block, which could be formed by the assembly of the supercontinent Rodinia and be separated by late geological processes.

关键词： Central Tianshan Tectonic Zone, Precambrian metamorphic blocks, granitoid gneisses, isotopic chronolo-gy, active continental margin, supercontinent Rodinia.

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Mesozoic thrusts and extensional structures in the Daqingshan orogen, Inner Mongolia, and their temporal and spatial relationship

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Progress in Natural Science:Materials International 2007年第2期17卷 177-186页

作者： QI Guowei, ZHANG Jinjiang , WANG Xinshe and GUO Lei ( key laboratory of orogenic {3. and Crustal Evolution, ministry of education, china School of Earth and Space Sciences, peking university, Beijing 100871, china Institute of geology, Chinese Academy of Geological Sciences, Beijing 10003., china) [a]key laboratory of orogenic {3. and Crustal Evolution Ministry of Education China [b]School of Earth and Space Sciences Peking University Beijing China [c]Chinese Academy of Geological Sciences Institute of Geology Beijing China

Three large-scale thrusts developed in the Daqingshan orogen, Inner Mongolia, with a northeast-east trending from Louhuashan to Suletu are described in this paper. These northwest-directed thrusts, together with the four tectonic belts (or tectonic sheets) separated by these faults, formed a typical thrusting system. The originally defined Hohhot metamorphic core complex may be a tectonic sheet, making the uppermost tectonic unit of the thrusting system and truncated by the Daqingshan detachment fault on top. The existing tectono-chronological studies showed that the thrusting of this region possibly happened at the same time as the extension along the top detachment fault. This presents that the contraction and extension in Daqingshan orogen were probably simultaneous. The structural pattern of the Daqingshan orogen can be correlated to the Himalayan orogen, and models for simultaneous thrusting and detachment in Himalaya may give a hint for explaining the development of the Daqingshan orogen.

关键词： Daqingshan thrust metamorphic core complex detachment fault contraction-extension transform Himalaya.

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Ultrahigh pressure (>7 GPa) gneissic K-feldspar (-bearing) garnet clinopyroxenite in the Altyn Tagh, NW china: Evi- dence from clinopyroxene exsolution in garnet

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Science china Earth Sciences 2005年第7期48卷 1000-1010页

作者： LIU Liang1,3. CHEN Danling1, ZHANG Anda1, SUN Yong1, WANG Yan1, YANG Jiaxi1,2 & LUO Jinhai1 1. key laboratory of Continental Dynamics of the ministry of {3. of china, Northwest university, Xi’an 710069, china 2. College of Earth Science and Land Resources, Chang’an university, Xi’an 710054, china 3. The laboratory of Orogen and Basin of the ministry of {3., peking university, Beijing {13., china key laboratory of Continental Dynamics Ministry of Education of China Northwest University Xi'an 710069 China laboratory of Orogen and Basin Ministry of Education Peking University Beijing 100871 China College of Earth Science and Land Resources Chang'an University Xi'an 710054 China

The exsolution of clinopyroxene and rutile in coarse-grain garnet is found in the gneissic K-feldspar(-bearing) garnet clinopyroxenite from Yinggelisayi in the Altyn Tagh, NW china. The maximum content of the exsolved clinopyroxene in the garnet is up to >5% by volume. The reconstructed precursor garnet (Grt1) before exsolution has a maximum Si content of 3.061 per formula uint, being of supersilicic or majoritic garnet. The peak-stage metamorphic pressure of >7 GPa is estimated using the geobarometer for volume percentage of exsolved pyroxene in garnet and the Si-(Al+Cr) geobarometer for majoritic garnet, and the temperature of about 1000℃ using the ternary alkali-feldspar geothermometer and the experimental data of ilmen- ite-magnetite solid solution. The protoliths of the rocks are intra-plate basic and intermediate ig- neous rocks, of which the geochemical features indicate that they are probably the products of the evolution of basic magma deriving from the continental lithosphere mantle. The rocks are in outcrops associated with ultrahigh pressure garnet-bearing lherzolite and ultrahigh pressure garnet granitoid gneiss. All of these data suggest that the ultrahigh pressure metamorphic rocks in the Altyn Tagh are the products of deep-subduction of the continental crust, and such deep- subduction probably reaches to >200 km in depth. This may provide new evidence for further discussion of the dynamic mechanism of the formation and evolvement of the Altyn Tagh and the other collision orogenic belts in western china.

关键词： Altyn Tagh gneissic K-feldspar (-bearing) garnet clinopyroxenite clinopyroxene exsolution in garnet ultra-high pressure metamorphism.

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Petrogenesis and significance of the Hongshan syenitic pluton,South Taihang: zircon SHRIMP U-Pb age, chemical compositions and Sr-Nd isotopes

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Progress in Natural Science:Materials International 2006年第2期16卷 192-200页

作者： ZHOU Ling and CHEN Bin (key laboratory of orogenic {3. and Crustal Evolution, MOE, School of Earth and Space Sciences, peking university, Beijing 100871, china) [a]key laboratory of orogenic {3. and Crustal Evolution MOE School of Earth and Space Sciences Peking University Beijing China

The Hongshan syenitic pluton (South Taihang) is mainly made up of hornblende syenite and minor granite. SHRIMP zircon dating yields a U-Pb age of 13.±2.7 Ma for the emplacement of the pluton, while biotite Rb-Sr isotopic data give an isochron of 120. 3.2.4 Ma. Hongshan syenites show low silica, high alkalis and LILE such as Sr, and exhibit negligible Eu anomalies or slightly positive anomalies in the REE patterns. The syenites show quite enriched isotopic compositions with Isr from 0.7052 to 0. 7102 and εNd(t) from -7.5 to - 11.1. Petrogenesis of the pluton can be that partial melting of an enriched lithospheric mantle gave birth to an alkali basaltic magma, which subsequently underplated in the lower crust and experienced a coupled fractionation of ferromagnesian phases like pyroxene and hornblende and minor ( china Plateau" in the Mesozoic.

关键词： syenite zircon SHRIMP Nd-Sr isotopes Taihang North china craton.

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