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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 {2. {3. and Crustal Evolution,Ministry of education,china School of Earth and Space Sciences,peking university,beijing 100871,china 1. The key laboratory of {2. {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 12.8±17 Ma and 42.±2. Ma, respectively, and euhedral prismatic zircons from the parametamorphic schist (W05-9) display U-Pb isotopic discordia intercept ages of 12.6±74 Ma and 2.0±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 1142.12. Ma, and its ε Nd (t) = -4.{2. These geochronological data suggest that these Precambrian metamorphic basement blocks within eastern segment of the Central Tianshan Tectonic Zone can be produced during 1140—12.0 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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The late Paleoproterozoic extension event:aulacogens and dyke Swarms in the North china craton

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Progress in Natural Science:Materials International 2006年第2期16卷 201-208页

作者： HOU Guiting, LI Jianghai, LIU Yulin and QIAN Xianglin (key laboratory of {2. {3. and Crustal Evolution, School of Earth and Space Sciences, peking university, beijing 100871, china) [a]key laboratory of {2. {3. and Crustal Evolution School of Earth and Space Sciences Peking University Beijing China

The extension structures and tectonic implication in the North china Craton ( NCC) are discussed in this paper based on the mafic dyke swarms and geochronology, combining with the geochronology of aulacogens. The late Paleoproterozoic time is the important turning point in the Precambrian evolution of the NCC. The extension system (e.g. aulacogens and dyke swarms) is widespread in the NCC, which marks the carbonization of the NCC with the rigid characteristic similar to the modern plate. The paleostress field modeling suggests that the dyke swarms and aulacogens are arogenic extension marking the start of the supercontinent, not synorogenic and post-orogenic extension. The mafic dyke swarms in the NCC mainly ranged from 1.83.to 1.77 Ga. The extension of the NCC is very limited brittle extension, the average extension ratio is only 0.3.% given by mafic dyke swarms extension calculation, so most of extension in the NCC is contributed by the aulacogens. The mafic dyke swarms are related with the aulacogens in the origin.

关键词： North china craton late Paleoproterozoic aulacogens mafic dyke swarms extension.

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The attenuation anisotropy of mudstones and shales in subsurface formations

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Science china Earth Sciences 2005年第11期48卷 1882-1890页

作者： SHI Ge1 & DENG Jixin1,2.1. The key Labratory of orogenic {2. and Crustal Evolution, School of Earth and Space Sciences,{3., beijing 100871, china 2. Geophysical Prospecting key Lab (CNPC), university of Petroleum, beijing 102.49, china 1. The key Labratory of orogenic {2. and Crustal Evolution School of Earth and Space Sciences Peking University 100871 Beijing China 2. Geophysical Prospecting key Lab (CNPC) University of Petroleum 102249 Beijing China

We have measured the relationships in the laboratorial condition between the at-tenuation in three samples of mudstones and shales as well as two samples of layered sand-stones and the alteration in direction, confining pressure and pore fluid. The relative contributions of different attenuation mechanisms are also discussed. Studies show that the attenuation in dry and saturated samples is strongly related to pressure and direction. The attenuation coefficient of P-wave propagating parallel to bedding (PH ) is less than that of P-wave propagating vertical to bedding (PV ), while the attenuation coefficient of S-wave both propagating and vibrating parallel to bedding (SH ) and that of S-wave propagating vertical to bedding while vibrating parallel to bedding (SV1) are less than that of S-wave propagating parallel to bedding while vibrating verti-cal to bedding (SV ). Under oil saturated conditions, the Biot flow attenuation acts as the domi-nant mechanism for waves propagating parallel to bedding, while the frame anelastic attenuation and squirt flow attenuation seem to play important roles in condition of propagation vertical to bedding.

关键词： mudstone, shale, attenuation, anisotropy, attenuation mechanism

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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 {2. of Continental Dynamics of the Ministry of education of{3., Northwest university, Xi’an 710069,{3. 2. College of Earth Science and Land resources, Chang’an university, Xi’an 710054,{3. 3. The {2. of Orogen and Basin of the Ministry of education,{12., beijing 100871,{3. 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 experi{2.al 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 >2.0 km in depth. This may provide new evidence for further discussion of the dynamic mechanism of the formation and evolve{2. 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 of Paleoproterozoic Luyashan charnockitic rocks in Shanxi Province: Constraints from Geochemistry and Nd isotope

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Progress in Natural Science:Materials International 2006年第2期16卷 183-191页

作者： LIU Chaohui, LIU Shuwen, LI Qiugen, WANG Yueran, DANG Qingning, GU Libing, YANG Bin and ZHAO Fengsan (key laboratory of {2. {3. and Crustal Evolution, Ministry of education School of Earth and Space Sciences, peking university, beijing 100871, china) [a]key laboratory of {2. {3. and Crustal Evolution Ministry of Education Beijing China [b]School of Earth and Space Science Peking University Beijing China

Luyashan charnockite pluton mainly consists of monzonite, adamellite, charnockite and syenogranite, which are characterized by the enrichment of TiO2. P2.5, K2., Zr, Nb, Y, Pb, La, Ce, Ba and a higher K2./Na2. and depletion of MgO, CaO, Mg#, Th, U and lower Sr/Ba and rb/Ba. The negative correlations between Zr, Nb, Ce and SiO2.are distinct from I-type granites. Iso-topically Luyashan charnockite plutons are relatively uniform in Nd isotope, displaying initial εNd(t) (-5.9{2.to -6.97) and Nd depleted mantle model ages (2.67 Ga to 2.78Ga). These features indicate that Luyashan charnockitic magma derived from pre-existing late Archean crustal sources and the partial melting of mafic granulites probably under exceptionally high temperature with CO2.rich fluid. The garnet is a main residual phase during the partial melting. The original dry charnockitic magma experienced crystal fractionation of pyroxene, plagioclase, apatite and ilmenite during early crystallization. The geochemical evidence suggests that the Luyashan charnockitic magma was probably generated in the post-collision thermal relaxation and uplift tectonic setting after the main collision ( - 1850 Ma) between the Eastern and Western continental blocks.

关键词： Luyashan charnockite geochemistry Sm-Nd isotopes petrogenesis Paleoproterozoic.

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Phase equilibria of HP–UHP mica-schists in Jiangling, Eastern Dabieshan orogen

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Progress in Natural Science:Materials International 2009年第8期19卷 973-982页

作者： Hang Chu a, Chunjing Wei a, Shangguo Su b a MOE key laboratory of {2. {3. and Crustal Evolution, School of Earth and Space Sciences, peking university, beijing 100871, china b china university of Geosciences, beijing 100083. china [a]MOE key laboratory of {2. {3. and Crustal Evolution School of Earth and Space Sciences Peking University Beijing 100871 China [b]China University of Geosciences Beijing 100083 China

The HP–UHP metamorphic terrane of Jiangling, eastern Dabieshan comprises extensively distributed granitic gneisses, mica-schists and numerous eclogite blocks. The mica-schists generally contain garnet, phengitic muscovite, biotite, plagioclase, quartz, rutile and a small amount of epidote and hornblende. Study on petrography and phases equilibria in the NCKMnFMASH system indicates that the present mineral assemblages in mica-schists are not in equilibrium. The earlier stage of mineral assemblage represented by garnet and phengite reflects a HP–UHP condition. The garnet compositions and the phengite Si contents give a PT condition of 580–600 °C at 2.6–2.8 GPa. The garnet zonation records an earlier progressive metamorphic process which may be associated with the appearance of glaucophane, jadeite and lawsonite. The later stage of mineral assemblage characterized by the presence of biotite and plagioclase reflects a PT condition of 62.–63. °C at 0.9–1.1 GPa, belonging to the HP amphibolite facies. The main mineral assemblage in micaschists from the Jiangling region has recorded a complete HP–UHP metamorphic process.

关键词： HP–UHP metamorphism Phase equilibria Mica-schist Dabieshan

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Nd-Sr Isotopic Geochemistry of the Late Archean-Paleoproterozoic Granitoids in the Lüliang-Wutai Terrain,North china Craton,and Implications for Petrogenesis

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Acta Geologica Sinica(English Edition) 2006年第6期80卷 834-843页

作者： CHEN Bin, LIU Shuwen, WANG rui, CHEN Zhichao and LIU Chaoqun key laboratory of {2. {3. and Crustal Evolution, MOE School of Earth and Space Sciences, peking university, beijing 100871 peking Univ Key Lab Orgen Belts & Crustal Evolut MOE Sch Earth & Space Sci Beijing 100871 Peoples R China

In this paper we report geochemical and Nd-Sr isotopic data for a late Archean gneissic granitic pluton （Hengling pluton）, an early Paleoproterozoic complex （Xipan complex） and a late Paleoproterozoic granitic pluton （Yunzhongshan granites） from the Liiliang-Wutai terrain, North china, to trace the source of these late Archean-Paleoproterozoic granitoids and, particularly, to understand the nature and mechanism of continental growth at that time. The Hengling granitic gneisses （ca. 2.51 Ga） are characterized by high Na2. and LILEs, TTG-like rEE patterns （highly depleted HrEE and minor Eu anomalies） and moderately depleted Nd-Sr isotopic compositions （εNd（t） =1.2.2.7, ISr=0.7015-0.7019）, and were considered as being products of arc magmatism that was developed upon the North china craton. The Xipan complex （ca. 2.2.Ga） contain gabbroic diorite and monzonite, mostly being Na2.-rich, highly fractionated rEE patterns and isotopically enriched （εNd（t） =-1.5 to -4.1, Isr=0.703.-0.706）. The gabbroic diorites probably originated from melting of an enriched mantle source, but significantly contaminated by lower crustal material, and the monzonites probably represent a product of a mixture between the gabbroic dioritic magma and granitic melts of crustal origin. The Yunzhongshan post-collisional granitoids （ca. 1.8 Ga） are characterized by high-K affinity and highly-enriched and homogeneous Nd isotopic compositions （εNd（t）=-4.9 to -5.7）, although they split into two groups in terms of rEE patterns： one group showing elevated HrEE （and Sc, Y and Zr） with significant negative Eu anomalies and the other showing highly depleted HrEE and, to a lesser extent, mid-rEE with negligible Eu anomalies. These granites are genetically related to a process of extensional collapse of a thickened orogen. They formed through magma mixing between mantle-derived basaltic magmas and crust-derived granitic melts, followed by significant fractionation of ferromagnesian phases （like hornblende and C

关键词： geochemistry Nd-Sr isotopes granitoids late Archean-Paleoproterozoic Wutai-Lüliang

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Geochemical characteristics of Jurassic coal and significance for the evolution of the environment, Yanqi Basin, china

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Progress in Natural Science:Materials International 2006年第9期16卷 974-982页

作者： WU Chaodong , XU Youling, GUO Zhaojie1, QUAN Shujin, LI Yonglin and FENG Xue ( key laboratory of {2. {3. and Crustal Evolution of dep.r.ment of education, peking university, beijing 100871, china 3.d Geological Survey Brigade, Henan Bureau of Mineralogical and resources, Xinyang 476000, china Exploration & Development research Institute of Henan Oilfield, SINOPEC, Nanyang 473.3., china) [a]key laboratory of {2. {3. and Crustal Evolution of dep.r.ment of education Peking University Beijing China [b]3.d Geological Survey Brigade Henan Bureau of Mineralogical and Resources Xinyang China [c]Exploration & Development research Institute of Henan Oilfield SINOPEC Nanyang China

The Mesozoic strata of the Yanqi Basin consists of coarse debris with coal beds, characterized by the developments of coal seams of the Jurassic sediments whose main petrologic contents are glutenite, fine sandstone, mudstone, carbonaceous shale and coal. Based on the analyses of the minerals, trace elements and rEEs, we try to find geochemical characteristics of the coal seam formation process. The analysis results indicate that the contents of ash and sulfur are low while the content of phosphor is comparatively high, and that the specific value of Al2.3.SiO2.is relatively high and that of (Al2.3.+ SiO2./(Fe2.3.+ CaO+ MgO) is near 1. All these results indicate that the coal seams are formed in the relatively deep marsh, which is favorable for the evolvement of hydrocarbon at the diagenesis stage.

关键词： coal sedimentary geochemistry trace elements Jurassic.

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A challenge to the concept of slip-lines in extrusion tectonics

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Geoscience Frontiers 2011年第1期2卷 23-34页

作者： Yadong Zheng~(a,*),Erchie Wang~b,Jinjiang Zhang~a,Tao Wang~c a key laboratory of {2. {3. and Crustal Evolution,Ministry of education,School of Earth and Space Sciences, peking university,beijing 100871,china b Institute of geology and Geophysics,Chinese Academy of Sciences,beijing 10002.,china c Institute of geology,Chinese Academy of Geological Sciences,beijing 10003.,china [a] key laboratory of {2. {3. Crustal Evolution Ministry of Education School of Earth Space Sciences Peking University Beijing 100871 China [b] Institute of Geology Geophysics Chinese Academy of Sciences Beijing 100029 China [c] Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China

Wide-open V-shaped conjugate strike-slip faults in Asia are typically related to extrusion ***,the tectonic model based on the slip-line theory of plasticity has some critical problems associated with *** conjugate sets of slip-lines in plane deformation,according to the theory of plasticity should be normal to each another but,in reality,the angles between the conjugate strike-slip faults,which are regarded as slip-lines in extrusion tectonics in the eastern Mediterranean,Tibet-middle Asia,china and the Indochina Peninsular regions,are always more than 90°(on average～110°) in the direction of contraction. Another problem is that the slip-line theory fails to explain how,in some cases,e.g.,in the Anatolian area in the eastern Mediterranean,the extrusion rate is much higher than the indent *** two major problems are easy to solve in terms of the Maximum-Effective-Mo{2.(MEM) Criterion that predicts that orientations of the shear zones are theoretically at an angle of 54.7°and practically at angles of 55°±10°with theσ- or contractional *** orientations of the strike-slip faults that accommodate extrusion tectonics are,therefore, funda{2.ally controlled by the MEM *** extrusion is along the MEM-orientations,the extruding rate is normally higher than the indenting rate.

关键词： Extrusion tectonics Slip-line Wide-open V-shaped strike-slip faults MEM-Criterion Strain rate

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Science china Earth Sciences 2004年第10期47卷 896-911页

作者： ZHANG Changhou1,2. WU Ganguo1,2. WANG Genhou2. ZHANG Weijie2.& SONG Honglin2.1. key laboratory of Lithospheric Tectonics and Lithoprobing Technology,{2. {3. of Geosciences, Ministry of education of{2., beijing 100083.{2. 2. School of Earth Sciences and Mineral resources,{2. {3. of Geosciences, beijing 100083.{2. 1. key laboratory of Lithospheric Tectonics and Lithoprobing Technology China University of Geosciences Ministry of Education of China 100083 Beijing China 2. School of Earth Sciences and Mineral resources China University of Geosciences 100083 Beijing China

The northwest trending tectonic belt in the middle part of the Mesozoic intraplate Yanshan orogenic Belt, northeast Hebei Province, is composed of thrusts, extensional faults, strike-slip faults and syntectonic sedimentations as well. The northeastward basement-involved major thrusting deformation occurred between 174Ma and 168MaBP and was followed by an intrusion of the granitic plutonic rocks. As a part of the post-thrusting extensional deformations a northwest extending volcano-sedimentation system of Late Jurassic and Early Cretaceous formed in the southwest side of the belt. These volcano-sedimentary sequences are divided into Tuchengzi Formation, Zhangjiakou Formation, Yixian Formation and Jiufotang Formation re- spectively. They are characterized by southeastward migration as a result of the increasing down-dip slip displacement along the major extensional fault toward the southeast of the belt. The provenance area of the Jiufotang Formation north to it experienced southwestward thrusting during and after its later sedimentation. The thrusting in this stage resulted in the formation of an asymmetric footwall syncline with vergence to SW in the Jiufotang Formation in the NE side of the basin. Finally a dextral strike-slip deformation occurred along the NW tectonic belt. The striking tectono-geomorphological features and present seismic activities along this belt indicate that it has been being active since Cenozoic era and is still in the active state at present. This northwest extending tectonic belt was following the same direction and location as the existing fault systems within the basement as revealed by former geological and geophysical studies. So it is reasonable to infer the Mesozoic deformation along this belt to be a result of reactivation of the basement structures in a favorable tectonic stress field. The reactivation of basement struc- tures might be taken as one of the mechanisms of intraplate deformation and orogeny.

关键词： Yanshan orogenic Belt, northwest extending tectonic complex, thrust system, geochronology.

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