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The uplift history of the Tibetan Plateau and Himalaya and its study approaches and techniques: A review. WANG Cheng-Shan DAI Jin-Gen LIU Zhi-Fei SHU Li-Dong LI E-Lin GU Guo-Dong 2009, 16(3): 1-30.  Abstract ( 2419 )   PDF (4095KB) ( 2614 )    The uplift history of Tibetan Plateau and Himalaya is the key boundary condition in many Cenozoic geological events. Thus it profoundly affects the interpretation of the geological processes ranging from global cooling to the changes of Asian environments during the Cenozoic. Although various proxies have been applied, many of debates on the timing of the surface uplift of Tibetan Plateau and Himalaya still exist. The main reason is some of the proxies are problematic in themselves. Therefore, it is necessary to review these proxies together and to reassess their significances for the uplift of Tibetan and Himalaya. On the basis of our studies in northcentral Tibet, as well as the existing possible estimates, we provide a new model for the growth of Tibetan Plateau: Lhasa and Qiangtang terranes gained their elevations during Eocene time, whereas its northern area was still low and southern area was under sea level at that time. The ProtoTibetan Plateau expanded throughout the Neogene toward its present southern and northern margins in the Himalaya and Qilian Mountains. Related Articles | Metrics

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Accretionary orogenesis in the active continental margins. YUAN Si-Hua BO Gui-Tang WANG Li-Quan JIANG Xin-Qing YIN Fu-Guang ZHANG Mo-Beng ZHUO Jie-Wen 2009, 16(3): 31-48.  Abstract ( 2382 )   PDF (3714KB) ( 1790 )   Abstract:  The paper reviewed the history and progress of research in accretionary orogenesis, and considered the accretionary orogenesis an important way of continental accretion throughout the entire earth history. We supposed that the formation and evolution of orogenic belt could be explained by the evolution of composite arcbasin systems in the active continental margins, and the formation of super orogenic system was closely related to the composite arcbasin systems formed on one or two sides of an ocean, which were controlled by the subduction of longlived oceanic lithosphere. Accretionary orogenic systems in the active continental margins were built up by a series of collision and accretionary orogenies, including arcarc and arccontinent collision, accretion of forearc and backarc subduction complex, and collage of oceanic plateaus/islands/seamounts and exotic blocks (terranes). Convergent crustal consumption zone formed when the longlived oceanic lithosphere was eventually eliminated; the super orogenic complex was formed by the interconnection of orogenic systems that were transformed from the composite arcbasin systems on both sides of longlived oceanic lithosphere. Subsequently the super orogenic system was superimposed by the continentcontinent collision orogeny and intracontinental compression/extension, which caused more complexities. The convergent crustal consumption zone, therefore, is the key to understanding the formation and evolution of orogenic systems. All kinds of orogenic processes of composite arcbasin systems in the active continental margins were actually the courses of accretionary orogenesis. The study of composite arcbasin systems is very important for subdividing the orogenic minute architecture, and also basic for understanding the components, textures and structures of orogenic systems. The postorogenic intracontinental tectonic evolution was also controlled by the evolution histories of composite arcbasin systems. The composite arcbasin systems and continental margin systems provide more comprehensive records of Wilson cycles than fossil oceanic lithosphere. According to the ideas of composite arcbasin systems, a new model for the evolution of Tethyan ocean has been proposed, that the Gangdese belt had been controlled by the subduction of the Tethyan oceanic lithosphere since the Carboniferous, then an accretionary orogeny toward the ocean took place since the Triassic, and finally the Tethyan ocean vanished at the end of the Early Cretaceous. Related Articles | Metrics

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Mesozoic deformation of Dabashan curvilinear structural belt of Qinling orogen HU Jian-Min SHI Wei JU Hong-Jie CHEN Gong WU Guo-Li TIAN Mi 2009, 16(3): 49-68.  Abstract ( 2235 )     Abstract:  The Dabashan structural belt is a part of south Qinling Mountains, which has been regarded as a foreland thrusting belt of the collisional belt of the north and south China plates. The results of the researches show that the curvilinear structural belt, to the south of ChengkouFangxian thrust fault in the Dabashan mountains, has undergone strong superimposed deformation during the Mesozoic. The Dabashan curvilinear structural belt is composed of linear folds with curvilinear fold hinges and some curvilinear thrust faults (D2), which was formed during the major phase of deformation of south Dabashan. In the western curvilinear structural belt, the folds of D2 with fold axes of nearly south to north trending superimposed on the early wide folds with axis of nearly west to east (D1), and formed a typical cross superimposed structure. In the central and eastern parts, fold axes of D2 were gradually turned to nearly eastwest. The geological mapping shows that there existed a phase of deformation that the fold axes were of north to nearly south to north direction before the formation of the curvilinear structural belt. Based on the deformational sequence, deformed strata, and regional geology, the authors believe that the time of D1, both in western and in central and eastern Dabashan curvilinear structural belt, is the late Triassic to the early Jurassic. It is possible that the deformation D1 was related to the collision between north China block and Yangtze block. On the other hand, the geological relationship, geochronology and AFT data show that the main deformation time of D2, is about the late Jurassic to the early Cretaceous(160110 Ma). So the Dabashan curvilinear structural belt recorded two phases of deformation which were formed during different tectonic settings. It is of great significance for the understanding of the evolution of Qinling orogen. Related Articles | Metrics

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TRIASSIC AND JURASSIC TECTONICS IN THE EASTERN YANSHAN BELT, NORTH CHINA: INSIGHTS FROM THE CONTROVERSIAL DENGZHANGZI FORMATION AND ITS NEIGHBORING UNITS Gregory A Davis1 Meng Jiafeng2 Cao Wenrong3 Du Xingqiang3 2009, 16(3): 70-86.  Abstract ( 1987 )   PDF (5287KB) ( 782 )   Abstract:  The Jurassic geology of the NiuyingziDengzhangzi area of western Liaoning province south of Lingyuan has challenged geologists for many years. Its most controversial structural element is a narrow (0.11.5 km), subvertical, faultbounded panel of Middle Proterozoic Changzhougou quartzite and, locally, higher Changcheng System units. The 35 kmlong, NNEstriking panel is bordered on the west by the subvertical Daqizi fault (new name) and the steep, largely eastoverturned Late TriassicEarly Jurassic Dengzhangzi Formation. It is bordered on the east by the subvertical Zhuzhangzi fault (new name) and westdipping Middle Jurassic Guojiadian Formation strata. Previous structural interpretations have favored ideas that the Daqizi fault is a steep normal fault with Dengzhangzi side down, and that the Zhuzhangzi fault is a steep reverse fault with Guojiadian side down. We disagree with both interpretations and present evidence that both faults have formed during previously unrecognized Jurassic tectonic events. The Daqizi fault is interpreted as a late Early Jurassic to early Middle Jurassic westdirected thrust fault placing Changcheng strata across lowerplate Dengzhangzi strata. Both upper and lower plates were then folded. The Zhuzhangzi fault was originally a normal fault bounding a Guojiadian halfgraben that formed during an episode of previously unrecognized Middle Jurassic extension. The fault was localized along the folded, eastdipping contact between Changzhougou quartzites and overlying shales of the Chuanlinggou Formation. As the fault developed, detached hanging wall Chuanlinggou and higher Changcheng strata above the Changzhougou quartzite were dropped down and buried beneath the halfgraben fill. The geometry of the DengzhangziChangzhougouGuojiadian structural assemblage was subsequently modified by late Middle Jurassic or early Late Jurassic contraction. Among its effects were (1) reverse fault inversion of the Zhuzhangzi normal fault and (2) eastward YangzhangziWafangdian thrusting of Jixian strata across the Changcheng faultbounded panel and its neighboring Jurassic units. Steepening and eastward overturning of Dengzhangzi strata occurred at this time. The results of our study indicate that the Jurassic tectonic history of the western Liaoning area was considerably more complicated than believed earlier. Related Articles | Metrics

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Formation processes and deformation modeling for post-orogenic dome structures of the North Dabie XIANG Bi-Wei WANG Yong-Sheng Dazhi Jiang SHU Guang ZHANG Bi-Long XIE Cheng-Long 2009, 16(3): 87-101.  Abstract ( 2120 )   PDF (3329KB) ( 1845 )   Abstract:  The North Dabie dome resulted from the postorogenic extension in Early Cretaceous. The NWWstriking, NNEdipping XiaotianMozitan shear zone in the northern boundary of the dome is a normal sinistral, ductile shear zone whereas the NWstriking, SEdipping WuheShuihou shear zone in the southern boundary is a dextral reverse, ductile shear zone. Field structural investigation, analyses of quartz Caxis fabric, kinematics and deformation temperatures as well as deformation modeling for the two shear zones demonstrate that they originated from the same subhorizontal, midcrustlevel ductile shear zone with shear sense of toptoNWW(280°) and dominance of simple shear deformation. Thereafter, this subhorizontal shear zone outcropped at the boundaries of the dome due to exhumation related to doming of the North Dabie associated with massive magmatism in the Early Cretaceous. Deformation modeling indicates that the present North Dabie dome occurs as an antiform with an EW trending axis, and the western segment of the dome experienced more intensely doming than the eastern. It can be concluded from the development that the socalled North Dabie dome belongs to typical metamorphic core complex in the Dabie orogenic belt. Related Articles | Metrics

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The characteristics of different structure layers and tectonic implications since late Paleozoic in Kalamaily Area, Xinjiang TUN Run-Jiang ZHANG Yuan-Yuan TAN Jia-Yi GUO Shao-Jie 2009, 16(3): 102-109.  Abstract ( 1915 )   PDF (1948KB) ( 949 )   Abstract:  The lithostratigraphical system in Kalamaily Area since the Carboniferous is composed of three suits of tectonostratigraphic sequences. They are: (1) an orogenic base sequence characterized by ophiolite mélange belt with cleavages and tight folds; (2) a postcollision tectonic layer of Carboniferous with most broad folds; and (3) an intercontinental basin tectonic layer of Permian to Jurassic full of both highangle normal faults and gentle folds. They represent the characteristics of sedimentformation of preCarboniferous collision stage, Carboniferous postcollision stage and intraplate faultcontrolled depression stage of Permian, respectively. Related Articles | Metrics

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Coupling and formation mechanism of continental intraplate basin and orogen—Examples from the QinghaiTibet Plateau and adjacent basins LI De-Wei JIA Xi-Beng XU Li-Gui 2009, 16(3): 110-119.  Abstract ( 2289 )   PDF (1454KB) ( 977 )   Abstract:  There are very close relationship between orogenic belts and sedimentary basins, which show some features including interdependence of their spatial structures, mutual compensation of their materials, interaction of their tectonics, and simultaneity of their tectonic evolutions. A unified formation mechanism of continental orogenic belts and sedimentary basins is presented as follows: The lower crustal ductile flow from basin to orogen driven by thermal energy related to upwelling mantle plume in continental intraplate or vertical diaper movement of dehydration and magma of subduction plate on active continental margin, resulted in the denudation of upper crust and surface in orogenic belt and sediment in basin, and led to a circulative movement of different states of rocks between basin and orogen, and between lower crust and upper crust. The typical coupling between the QinghaiTibet Plateau and adjacent basins occurred in the intraplate tectonic setting. The formation of the QinghaiTibet Plateau was not caused by the collision between India Plate and Eurasia Plate, but by intraplate basinmountain coupling driven by lower crustal flow. The intraplate basinmountain coupling process of the QinghaiTibet Plateau can be divided into two stages: (1)Intraplate orogeny and basinforming stage; (2)Isostatic mountain building and basin margin subsiding stage. The spatialtemporal evolution of the intraplate orogeny and basinforming of the QinghaiTibet Plateau and related basins was shown by the evolution sequence proceeding from the north and east, to the middle, and finally to the south of the QinghaiTibet Plateau in the corresponding periods from 180120 Ma, 6530 Ma, to 237 Ma, and was represented by extensive intraplate faulting, folding, block movement, magmatism and metallogeny.  Rapid uplift and strong erosion of the QinghaiTibet Plateau as a whole and rapid settlement and molasse formation of the depressions on the margins of the peripheral basins resulting from gravity isostasy since 3.6 Ma, characterized by pulsative uplift and settlement, crustscale vertical movement, integral rapid uplift of the plateau, local subsiding of basin margin, and considerable variations in topography and environment occurring in 3.6 Ma B.P., 2.5 Ma B.P., 1.81.2 Ma B.P., 0.8 Ma B.P., 0.15 Ma B.P., etc. Synchronous evolution of continental intraplate basinorogeny system underwent tectonic transformation from extension to compression, with the transformation from active movement of basin to active movement of orogeny. NonAnderson lowangle detachment, wavy thrust fault and abnormal conjugate strikeslip fault were formed by lower crustal flow and intraplate basinorogen coupling. Related Articles | Metrics

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A model of contractional structure for transition belt between Kuche Depression and Southern Tianshan Uplift QI Jia-Fu LEI Gang-Lin LI Meng-Gang XIE Hui-Wen YANG Shu-Jiang 2009, 16(3): 120-128.  Abstract ( 2079 )   PDF (2375KB) ( 867 )   Abstract:  The structural features of the Cenozoic contractional deformation in the transition belt between Kuche depression and southern Tianshan uplift have been revealed by geological outcrop, seismic data, welllog and CEMP(Continuous Electromagnetic Profile)data; it is found that these features are difficult to be interpreted by the typical “Atype” subduction model. This article advances a “nonsubduction” contractional deformation model, i.e., the “delaminating contraction and vertically stacking” model. The “delaminating contraction” means that different structural levels developed their own contractional structural style owing to the detachments caused by the salt rock of PaleoceneEocene and the coalbearing series of Jurassic. The “vertically stacking” means that the stronger deformation zones within various levels were stacked up vertically, and the thinskin contractional deformation of cover detachment was stacked up on the top of the basementinvolved contractional deformation, so that the detachment fault could not develop into a regional detachment fault with great horizontal displacement. Detachment folds were developed in the overlying sequence of PaleoceneEocene salt rock, but a fault system assembled with basementinvolved reverse fault, thrust, and inverse fault or normal fault was developed in the underlying sequence of PaleoceneEocene salt rock or Jurassic coalbearing series. The cover folds show the structural pattern with a closed anticline and an open syncline. The asymmetric anticline was detached within salt rock of PaleoceneEocene or coalbearing series of Jurassic and was cut off by a break thrust in the steep limb. A series of basementinvolved thrust with highangle dipping to southern Tianshan dominate the contractional deformation in the basement. A miniscale imbricate wedge thrust system was developed in the footwall of basementinvolved thrust with a highangle dip, and a basementcored faultedanticline was developed in the hanging wall. Most of fault systems in the lower level probably vanished toward the salt rock of PaleoceneEocene or coalbearing series of Jurassic; the highangle basementinvolved thrust tipped upward to the core of detachment anticline in the shallower level, so that the salt rock or coalbearing series was an important transfer level. The highangle basementinvolved thrust may have been formed by the reverse displacement of a preexisting normal fault and led to the local structural deformations. The occurrence of the highangle thrust or the reverse of the preexisting normal fault may be attributed to the dynamics of vertical shearing caused by the uplift of southern Tianshan. Related Articles | Metrics

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Recognition and exploration of structural wedges—A case study of the southern margin of Junggar Basin GUAN Shu-Wei LI Ben-Liang HE De-Fa John H Shaw CHEN Zhu-Xin 2009, 16(3): 129-137.  Abstract ( 1692 )   PDF (2938KB) ( 978 )   Abstract:  Two basic conditions are necessary for structural wedges forming: one is at least two connected fault segments that bound a triangular or wedgeshaped fault block, and the other is the contrary slip transfer directions of these two fault segments. When the backward slip cut through the overlying stratum, folds were formed on the forelimb of structural wedge, which can also be used as the direct evidence to infer the deep wedging. Structural wedges are very typical in the southern margin of Junggar Basin and exhibit a variety of shapes and styles imbricated each other out of sequence. In the east part of the Southern Junggar Basin, the deep structural wedges at the mountain fronts, which are composed of several PaleozoicMesozoic faultbend folds, propagated northward along the coal layer of middle Jurassic; all slip transferred southward along back thrusts, above which the first row of anticlinal belt developed. While the first row anticline was plunging westward, part of slip started to transfer northward and formed the second and third rows of antclinal belts at the ramps. So the elevating and plunging between these three anticlinal belts imply the displacement transfer in the southnorth direction. The deep structures of the second and third rows of antclinal belts in the Southern Junggar Basin are composed of several imbricate hinge wedgeshaped fault blocks, which usually have small lateral extension, but may have independent reservoir system and different hydrocarbongaswater characteristics. In the exploration, it is a key procedure to define the wedges trend and lateral change in threedimensional space subtly, then drilling the target wedge that has been precisely defined based on the progress of seismic acquisition, processing and interpretation. Related Articles | Metrics

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Redefinition of the suture zone between the JuggarKazakhstan and Tarim Plates in Eastern Tianshan, Xinjiang, China and its significance MU Ge-Da-Er-·Za-Ri ZHANG Xiao-Fan TUN Zhao-Ning TUN Chang-Zhi CHEN Chuan 2009, 16(3): 138-148.  Abstract ( 1926 )   PDF (2988KB) ( 886 )   Abstract:  Under guidance of the theory of plate tectonics, according to geology, geophysical and geochemical exploration,  remote sensing data, and  comprehensive analysis of research results about the plate tectonics in Eastern Tianshan Orogenic Belt, we redefined the location of suture zone between the JunggarKazakhstan  and Tarim Plates, and concluded that the zone among Kangur and Aqqikkudug faults is the suture zone between the JunggarKazakhstan and Tarim Plates in  Eastern Tianshan Orogenic Belt. The above suture zone has an independent tectonic unit that possesses its material entity, its special tectonics and structures. It also controls the polymetallic metallogenic belt in Eastern Tianshan. Consequently, the suture zone played an important role in mineralization and spatial distribution of copper, nickel, gold, silver and other polymetallic deposits. Related Articles | Metrics

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Characteristics of the Cenozoic deformation in basin/range coupling regions on both sides of Tianshan Mountains and its geodynamics CHEN Zheng-Le LU Ke-Gai WANG Guan CHEN Bai-Lin LI Li JIANG Rong-Bao CUI Ling-Ling GONG Gong-Liang 2009, 16(3): 149-159.  Abstract ( 2249 )   PDF (2479KB) ( 789 )   Abstract:  Cenozoic deformation is well developed in the basin/range coupling regions on both sides of Tianshan Mountains, where is also a natural laboratory for studying the coupling dynamics of basin and range. Based on the comprehensive analysis of prior data and field measurements, and the analyses by ourselves, we mainly present in this paper the characteristics of Cenozoic deformation in both sides of Tianshan Mountains. It is obvious that the Cenozoic deformation in the south and north sides of Tianshan Mountains are both similar and different. The deformation transferred from the range to the basin, and the initiative time of the deformation in the south side is older than that in the north, and the crustal shortening and its rate in the south are larger than those in the north. The deformation in both sides also shows a segmental similarity in EWdirection, displaying a special deformation pattern of rhombic symmetry. Basement thrust systems are developed in the north side of Bogda Mountain (eastern Tianshan Mountains) and in the southwest side of western Tianshan Mountains. Strikeslip faulting took place not only in the south of the eastern Tianshan Mountains, but also in the north of the western Tianshan Mountains. Series of rows composed of folds and thrust systems grow on both sides of the central Tianshan Mountains. The comprehensive study suggests that the similarity and difference of the deformation resulted from the fardistance effect of the collision between the India and Asia Blocks and convergence afterward, and the earlypreserved relatively rigid prePaleozoic blocks and largescale fault systems within the LatePaleozoic Tianshan orogeny led to the formation of the Cenozoic deformation pattern of rhombic symmetry. Related Articles | Metrics

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The uplifting of Artux anticline by stages in the Late Quaternary, Southwest Tianshan YANG Xiao-Beng CHEN Li-Chun LI An DU Long DENG Qi-Dong 2009, 16(3): 160-170.  Abstract ( 1812 )   PDF (2816KB) ( 774 )   Abstract:  The interaction zone between southwest Tianshan and Tarim is located on the northeast side of Pamir; it is a region with several rows of active reverse faults and active fold zones, and the Artux anticline is one of the active folds. The Boguzi River originated from a glacier in Tianshan Mountains incises the middle segment of Artux active fold. Six pedestal terraces formed in the Late Quaternary had developed along the both banks of the Boguzi River at the site of Artux anticline. These terraces had been folded since its formation. The longitudinal profiles of the terraces have been measured at the Boguzi River by differential GPS. It is found that the terrace surfaces of T1, T2 and T4 dip north on the north limb of the Artux anticline and its slope direction is opposite to the flow direction of the Boguzi River. On the south limb of the Artux anticline, the terrace surfaces of T1, T2 and T5 dip south. The average slope angles of the terrace surfaces of T1, T2 and T5 are 09°, 1.2°, and 1.8°, respectively. These slope angles are larger than the average slope angle of presentday river bed (0.5°). Using the optically stimulated luminescence dating of finegrained quartz and finegrained mixed minerals by the “DoubleSMAR” procedure, we found out that the formation ages of T1, T2, T3, T4 and T5 terraces are about 25.0±2.6, 42.7±4.4, 63.1±6.3, 96.9±9.9 and 120±10 ka BP, respectively. The incision rates of the Boguzi River are nonuniform at different periods in the Late Quaternary. The incision rates of T3 and T4 terraces are 0.49 and 0.44 mm/a, respectively. The incision rates of T1, T2 and T5 terraces are 1.2 mm/a, 1.69 mm/a, and 1.36 mm/a, respectively. The three times of strong incision of the Boguzi River occurred at different periods of time which are (120±10)～(96.9±9.9) ka、(42.7±4.4)～(25.0±2.6) kaka and(25.0±2.6) ka to present, respectively. The accelerated incision may have been caused by the quickly uplifting of the Artux anticline at the corresponding period. Related Articles | Metrics

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A new insight into the thrust structures at the northwestern margin of Junggar Basin MENG Jia-Feng GUO Shao-Jie FANG Shi-Hu 2009, 16(3): 171-180.  Abstract ( 2023 )   PDF (1998KB) ( 923 )   Abstract:  The uppermost tectonic feature of the northwestern margin of Junggar Basin is a group of thrusts there. Disputes over these thrust structures are mainly about their formation time and attributes, and the relevant debate of whether the Junggar Basin is a faulted depression or a foreland basin. At the northwestern margin, granite and dyke swarms developed, suggesting that the studied area underwent an extension from 314 Ma to 255 Ma. The facts that the sedimentary scope of Jurassic is wider than that of Triassic and the alkali basalt developed in the early Jurassic indicate that the Junggar Basin underwent an extension and kept expansion in  Jurassic. The late Triassic strata unconformably overlying the granite indicates that the formation time of these thrust structures might be from the late Permian to the early Triassic, no later than the Late Triassic. The seismic profile of northwestern margin shows gentle and stable Permian strata in thrust fronts. As to Permian sedimentation, its major characteristics include volcanic development, positive cycle fining up in the long term, higher depositional rate, a steeptogentle pattern of subsidence curve, as well as higher paleogeothermal gradient and heat flow values. The main hydrocarbon traps are nonstructural traps, like lithostratigraphic traps, while the tectonolithological traps are the minority. Based on the analysis above, we believe that the thrust structures are short term inversion structures occurring between 314255 Ma extension and Jurassic extension, rather than large scale thrust belts associated with orogeny. Related Articles | Metrics

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The strain partition in the southern margin of the North China plate: A study of LuonanLuanchuan fault belt and the strong deformation belt in the northern margin of the Qinling orogenic belt SONG Chuan-Zhong LIN Sheng-Lian LI Jia-Hao CHEN Ze-Chao LIAN Yun CA Zhi-Chuan 2009, 16(3): 181-189.  Abstract ( 2334 )   PDF (1635KB) ( 961 )   Abstract:  The Qinling LuonanLuanchuan fault belt shows the kinematic characteristics of a sinistral oblique subduction with strike generally at 107° and dip to north at 65°. The subduction of Southern China plate strikes at 80° and dips at 42°; the motion direction of Southern China plate is 42°; and the angle between the plate motion direction and the southern boundary of the North China plate is 65°, with the convergence angle of 25°. The fold hinge line trending 290° in strong deformation zone of the northern margin of the Qinling belt is 15° oblique to the strike of the LuonanLuanchuan fault belt. The strike of reverse thrust shares basically the same direction with the fold hinge line. The majority of faults and the LuonanLuanchuan belt have the same kinematic polarity; both are the leftlateral strikeslip reverse fault. The strikes of strikeslip normal faults are mainly NESW. The nature of faults, the direction of distribution and kinematic characteristics are in accordance with the mode of stress function of plate convergence; the schistosity and gneissosity are characterized by 117°trending and an angle of 10° existing between them and the LuonanLuanchuan fault belt. The systematic observation of rock deformation characteristics, strikedip survey of foliation, finite strain measurement of rocks and noncoaxial progressive deformation analysis of rocks were completed in vertical section of the shear plane. The results show that there is a tendency that the included angle between the foliation and the strike of shear zone is increasing from south to north in the strong deformation zone of the northern margin of the Qinling belt. The shearing strains of rocks are descending in file and the deformation of the orogenic belt shows a feature of “triclinic symmetry”. Related Articles | Metrics

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A numerical simulating study of mechanical characteristic of superposed deformation in Daba Mountain Foreland WU Gong-Ling SHI Wei DONG Shu-Wen TIAN Mi 2009, 16(3): 190-196.  Abstract ( 1575 )   PDF (1663KB) ( 860 )   Abstract:  In this paper, by using nonlinear finite element numerical method, we have studied the mechanical characteristics, the interference patterns of superposed folds and the feature of the united arcshaped structures in Daba Mountain Foreland.  The evolution of a series of arcshaped structures has been demonstrated, and a group of boundary conditions adapted to the superposed deformation in this region has been obtained. The study shows that (1)the creep materials selected in our model were deformed greatly with time even under very small and slow variation of stress field, which made us possible to study the tectonic deformation through principal stress trajectory; that (2)the interference patterns of superposed folds in Daba Mountain Foreland are mostly perpendicular intersection, inclined intersection and in parallel roughly; that (3)the formation of Daba arcshaped structures is thought due to the action of northeastern boundary forces with two tectonic convergences at east and west part, but another arcshaped structure in Eastern Sichuan Basin assembled with Daba Mountain forming a convergent double arc is thought due to the action of the boundary forces from southeastern direction. Related Articles | Metrics

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Structural evolution of Dabashan Mountain: Evidence from ESR dating CHENG Mo-Jiang YANG Kun-Guang 2009, 16(3): 197-206.  Abstract ( 1886 )   PDF (2163KB) ( 1334 )   Abstract:  Fifty eight samples from tectogenetic α quartz veins in Dabashan Mountain have been studied by using ESR dating method. The results showed that the evolution history of the North Dabashan Mountain (N.DBS) since the Mesozoic can be divided into three stages: 24372015 Ma (the Late Triassic), 1656912 Ma (the Late Jurassic to the Early Cretaceous) and 686 Mapresent (the Cenozoic), while the South Dabashan Mountain (S.DBS) can be divided into another correspondent three stages: 170160 Ma (the Bajocian to the Callovian), 1473941 Ma (the end of the Late Jurassic to the Early Cretaceous) and 667 Mapresent (the Cenozoic). Thus, the S.DBS is closely related to the N.DBS in structural evolution. Axial plane cleavages and fracture cleavages that represent the major strong deformation period of the S.DBS were chiefly formed in about 1472941 Ma (the end of the Late Jurassic to the Early Cretaceous) with the deformational characteristics of a piggyback type. The ESR dating of quartz veins in fracture cleavages also showed that the two terminal strata (deformed before 160 Ma) of S.DBS were involved into deformation earlier than the middle sections (deformed after 140 Ma). Since the Cenozoic, the tectogenesis of S.DBS transformed to the uplift and extensional slipping movements and became stable gradually. The ESR dating results are consistent with other geochronology evidences very well. Related Articles | Metrics

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Geothermochronology and tectonic evolution of Eastern Altyn Tagh Mountains, Northwestern China CHEN Xuan-Hua YIN An George E Gehrels JIANG Rong-Bao CHEN Zheng-Le BAI Pan-Fei 2009, 16(3): 207-219.  Abstract ( 2073 )   PDF (2400KB) ( 2453 )   Abstract:  This paper gives the integrated analyses of geothermochronology and tectonic system evolution of eastern Altyn Tagh Mountains, northern QinghaiTibet Plateau. The eastern Altyn Tagh is considered to have developed from Archean continental core, through Proterozoic stable platform and continental rifting in the NeoProterozoic, to “Altyn Ocean” and trencharcbasin system in the Early Paleozoic plate subduction, collisional orogeny and arc magmatism (with a peak activity at 443 Ma) occurred through the Ordovician and the Early Silurian. After the closing of “Altyn Ocean” in the Carboniferous, the eastern Altyn Tagh entered into the stage of continental tectonic development, and had undergone two major tectonic events since then, which are Mesozoic extension appeared as Lapeiquan detachment faulting and Cenozoic strikeslip faulting on Altyn Tagh Fault. The regional thermal cooling history of the eastern Altyn Tagh was controlled by these tectonic events and the tectonic events developed there were recorded by the thermal cooling history. Various massifs developed in different time had experienced different cooling histories which are well depicted by the geothermochronologic data. Therefore, geothermochronology is a helpful method for understanding the regional tectonic evolution of eastern Altyn Tagh area. Related Articles | Metrics

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Postcollisional volcanism of Kalamaili suture zone TUN Xiao-Ai LIU De-Liang LI Zhen-Sheng 2009, 16(3): 220-230.  Abstract ( 2045 )   PDF (1625KB) ( 987 )   Abstract:  Kalamaili suture zone is an important plate boundary in north Xinjiang, and there are plenty of Neopaleozoic volcanic rocks around itThese volcanic rocks are enriched in LILEs and relatively depleted in HFSEs, and they are  also characterized by high Nb, Zr, TiO2 contents and Zr/Y, Nb/Y ratios, and  depleted SrNd isotopesThe characteristics of these volcanic rocks suggest that they were produced in postcollisional periodThe postcollisional volcanic rocks around Kalamaili suture zone become younger from west to east, which indicates that this suture zone entered postcollisional period gradually from west to east, and  reflects that the Kalamaili Ocean had been closed gradually from west to eastAs to the Kalamaili suture zone in postcollisional period, the lithosphere extended and thinned, and the asthenosphere materials upwelled and  melted partially, and intensive mantle convection occurred, leading to a plenty of mantlederived magmas underplating the suture zoneThe lithospheric mantle metasomatized by fluid in subduction period  melted partially under decompression and high temperature, the resulting melts contaminated the underplating asthenospheric materials, and the erupted lavas became the Neopaleozoic postcollisional volcanic rocks Related Articles | Metrics

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Neoproterozoic Jiaoziding peraluminous granite in the northwest margin of Yangtze Block：Zircon SHRIMP U-Pb age and geochemistry， and their tectonic significance FEI Xian-Chi LI Zuo-Chen DING Sa-Beng LI Rui-Bao FENG Jian-Bin SUN Yu ZHANG E-Feng 2009, 16(3): 231-249.  Abstract ( 2727 )   PDF (3246KB) ( 859 )   Abstract:  The granite of Jiaoziding dome core is located in backLongmenshan Area of the northwest margin of Yangtze Block. The study of granites zircon SHRIMP UPb geochronology and geochemistry is aiming at constraining its formation age and petrogenesis. The results show that the zircons of the samples in deformative granite and massive granite of the Jiaoziding granites have internal oscillatory zoning; zircons of the Jiaoziding granites have higher Th/U ratios（0.521.23， 0.321.16）and are igneous in origin. The results of zircon SHRIMP UPb dating for deformative granite and massive granite were （793±11） Ma and （792±11） Ma respectively，which indicates that the granite intrusions formed in Nanhua period of the late Neoproterozoic，and their formation times are fully coincident. The Jiaoziding granite is high in SiO2 （72.01％77.65％）and Al2O3（12.12％14.18％），and its A/CNK=0.951.13（1.04 on average）. It is a typical peraluminous granites，with supersaturation in Al and Si，and is identified as Stype granite. The abundance of ∑REE varies in the range of (75.8179.97)×10-6（77.89×10-6 on average）. The rocks show a LREE enrichment pattern and obviously weak to intermediate negative Eu anomalies. The trace element geochemistry is characterized evidently by negative anomaly of Ta，Nb，Ti，etc. and positive anomaly of Rb，Ba，Sr，etc. The granite emplaced by underplating of granitic magma，which formed through partial melting of sedimentary mainly of arenite，and is typical crust source petrogenesis. The Jiaoziding granite shows the characteristics of postcollisional granite, and is regarded as the postorogenic granite. Thus the granite intrusions are interpreted as syncollisional granites resulted from the crustal thickening caused by active continental margin subduction and arccontinent collision orogeny during the Neoproterozoic in the northwest margin of Yangtze Block. The granitic intrusion formed in a transitional environment from syncollision (compressional environment) to postcollision （extensional environment），and is the product of the initial breakup of Rodinia supercontinent. Related Articles | Metrics

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The mountainbuilding process of the Huangshan Mountain, East China, and its tectonic implications LUO Zhao-Hua LI De-Dong BO Ying HUANG Dan-Feng LIANG Chao 2009, 16(3): 250-260.  Abstract ( 2478 )   PDF (3271KB) ( 1501 )   Abstract:  Whether there was a glacier on the Huangshan Hill is a topic long in debate and the opponents take an advantageous position. One of the interpretations from the opponents is that the previous elevation of the Huangshan Hill can not satisfy the condition of the hill being covered with snow all the year round. Such view point is from the interpretation of geographers for the mountainbuilding process of the Huangshan Hill without considering the information from the Huangshan massif and regional geology. The Huangshan massif is a small Early Cretaceous composite batholith mainly consisting of four intrusive units as the following in order from central to rim and from early to late: Wenquan unit (fine granular Bimontzogranite), Yungusi unit (coarse and continuously heterogranular Bisyenogranite), Shiziling unit (porphyritic Bisyenogranite) and Gongyangshan unit (fine granular alkali feldspar granite with biotite). Such textural variation suggests that the Huangshan Hill has undergone synemplacement erosion, that the depth of magma emplacement decreased from early to late and that the emplacement process was driven by the tectonic pressing. Accordingly, the Kfeldspar phenocrysts of the Shizifeng unit are oriented in the same direction and the primary joints in the Yungusi unit are perpendicular to the contact interfaces with both neighbor units. Both above facts suggest forceful emplacement of the Huangshan granites. Therefore, the Huangshan massif was produced in compressing condition instead of stretching environment as interpreted by the previous authors. The new interpretation is in accordance with the analysis of sedimentary basins and regional structure deformations and indicates that the Huangshan was in orogenic condition and had thick crust. Comparing the magmaoriginated depth and the recent crust thickness, it is reasonable to interpret that the crust of the Huangshan district has been thinned about 1429 km since the late Cretaceous. Its geomorphic response is about 1.944.18 km. Accordingly, the elevation of the Huangshan at the late Cretaceous may have reached up to 26934776 m. Therefore, the Huangshan Hill is formed by differential erosion during the surface subsidence instead of by episodic rising. Related Articles | Metrics

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Fluid evidence of the formation and evolution of Daqingshan thrustnappe LIU Zheng-Hong XU Zhong-Yuan WANG Ge-Yong YANG Zhen-Sheng 2009, 16(3): 261-269.  Abstract ( 1843 )   PDF (1774KB) ( 1971 )   Abstract:  Fluid veins widely developed in the Daqingshan thrustnappe, and can be divided into filled veins and edged veins according to their occurrences. According to their age,the formation of the fluid veins can be classified into three phases: the first phase quartz veins, the second phase quartz veins and the late phase calcite veins. The types of fluid inclusions in the first phase quartz veins is relatively complex, which contain twophase aqueous, threephase CO2bearing, pure CO2 and single phase aqueous fluid inclusions, respectively; analytical data revealed that their forming solutions came from lower crust or upper mantle. The second phase quartz veins contain only twophase aqueous and single phase aqueous fluid inclusions; fluids came from meteoric water which interfused with magmatic water. The late calcite veins contain twophase aqueous and a few single phase aqueous fluid inclusions; fluids came from interlayer solutions. The evolution history of Daqingshan thrustnappe system is determined according to the deformation phases, time and the depth data of those different kinds of veins. The thrusting of IndoChinese occurred at 78 km in the crust, the  thrusting of middle Yanshanian occurred at 36 km in the crust and the  thrusting of late Yanshanian within 2 km in the crust. Related Articles | Metrics

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The chronological and geological implications of the Cenozoic basic magmatic activities in Piqiang Basin, Xinjiang, China LI De-Dong LUO Zhao-Hua HUANG Jin-Xiang WEI Yang LIANG Chao 2009, 16(3): 270-281.  Abstract ( 1924 )   PDF (2394KB) ( 855 )   Abstract:  Involved in the Cenozoic intraplate orogeny of southwestern Tianshan, the northwestern Tarim Basin had developed a series of NEtrending faults and faultrelated folds. The cause of the Cenozoic structural deformation in this region, however, remains currently in controversy. This paper aims to report the geology of the Cenozoic igneous rocks and their chronology, proposing that the structural deformation was the response of shallow crust to the mantlederived magmatism rather than the direct result of IndoAsia collision. There are many Cenozoic mafic dikes with NNW and NNE trend and nearly 90 dipping angle and four volcanic necks in the Piqiang basin. The dikes have intruded the Cenozoic lacustrine layers. Our SHRIMP UPb zircon ages determined for these igneous rocks for the first time indicate that the mafic dykes and necks were formed at about 46 Ma, while the whole rocks KAr isochron date yielded an age of (45.5±6.13) Ma. The results suggested that the magmatism appeared in the middle Eocene, almost 22 Ma earlier than the nappe structures (~24 Ma). In terms of the heat conduction model, we estimated that the distance of heat transfer from deep heat source was about 25 km. Considering that the underplating or intraplating mantlederived magmas may serve as the deep source of heat, we presume that the Cenozoic deformation of the northwest Tarim Basin may have been triggered by the Cenozoic magmatism. Related Articles | Metrics

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Major earthquakes by rheological diapirism of crustmantle material—Evidence from satellite gravity data BI Qi 2009, 16(3): 282-293.  Abstract ( 2462 )   PDF (2051KB) ( 1054 )   Abstract:  Satellite gravity field data recovered by digital global models with 2180 to 2360 order are mainly originated from the density variation in the depth of 1836 km, at which epicenters of most major structure earthquakes were located. Therefore, satellite gravity data can make great contribution to earthquake research.  The author has made a detailed analysis of the satellite gravity data over Wenchuan, Motuo, Zhongba, Jiashi  and Taiwan Areas in China, where earthquakes more than magnitude of 6 took place in recent several decades. It is surprising that the gravity field patterns over these areas are extremely similar, which is characterized by the following features: (1)Paired positive and negative anomaly.  (2)Epicenters usually were located between the pairs where the gradient of gravity field was the steepest.  (3)The value of positive peak increased and its width decreased at higher order field.  (4)The distance between positive and negative peaks varies in different tectonic background. (5)Different styles of crustmantle material diapirism in different stress fields. Geologically, rheological diapirism of high density crustmantle material could be a reasonable explanation to this unique pattern. The proposed high density growth index is a measurement of increase in density from deep to shallow. The passageways of diapirism for high density crustmantle plastic material may be formed by the crust faults or giant fault zones and detached strata.  The heterogeneity of crustmantle material reflects the complexity of dynamic processes in continental plate tectonics. Related Articles | Metrics

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The striations character of Ms 8.0 Wenchuan Earthquake and its application research ZHANG Jun-Long 2009, 16(3): 294-305.  Abstract ( 1764 )   PDF (3435KB) ( 3164 )   Abstract:  On May 12th, 2008, a great Ms 8.0 earthquake occurred in Wenchuan County, Sichuan Province. The BeichuanYingxiu fault extending about 220 km characterized by dextral strikeslip  faulting is one of the three main seismogenic faults along the Longmenshan Fault zone,  and its activity is much more important than the other two. The major shock had induced  clear striations presenting at some local places along  the rupture of the BeichuanYingxiu fault,  the location and size of the striations may  be the surface response to  the peak value of  the deep rupture. Based on the stress field reflected by the striations and on the  relationship between displacement and surface rupture length,  the BeichuanYingxiu rupture zone are able to be subdivided into three segments, namely the Hongkou subsection,  the Beichuan subsection and  the Nanba subsection. Among them, Hongkou subsection extends 2245 km, with coseismic displacement of 4.5 m with  σ1 stress in the direction of NWWNW,  which had undergone at least three phases of activation. It is indicated that  the phase Ⅲ is the most intensive reverse faulting which reconstructs the phaseⅠandⅡ dextral strike slip activity, which all  are controlled by the main shock. The Beichuan subsection extends 90100 km, with coseismic displacement of 3.5 m, and σ1 stress  in the direction of NWW and is approximately horizontal,  and its intensity is weaker than the phase III of Hongkou . The Nanba subsection extends 3550 km, with coseismic displacement of 2.5 m and  σ1  stress  in the direction of NWW characterized by nearly horizontal compression. The  σ1  azimuth is 180°different from those of  the south and middle segments,  and its intensity is similar to that of the phaseⅠandⅡ of the south segment. Related Articles | Metrics

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Basal characteristics and formation mechanisms of geological hazards triggered by the  May 12, 2008 Wenchuan earthquake with a moment magnitude of 8.0 HAN Jin-Liang TUN Shu-Ren HE Chu-Jun SUN Wei-Feng ZHANG Chun-Shan WANG Chao YANG Jin-Zhong DAN Ju-Song 2009, 16(3): 306-326.  Abstract ( 2737 )   PDF (6222KB) ( 1172 )   Abstract:  The Ms 80 May 12, 2008 Wenchuan earthquake triggered landslides, rock collapses and debris flows at more than 18 000 sites,  which directly caused about 20 000 fatalities. Landslides, rock collapses and debris flows were distributed along active faults, rivers, roads, highways and railways,  forming geological hazards chains.The peak ground acceleration is the strongest influence parameter, the second is topography,  and bedrock geology,  geomorphology, human activity are factors controlling earthquakeinduced landslides also. Rupture geneses of landslides and rock collapses clustered at or near ridge crests, and at convex knickpoint within ridge flanks, and it is found out that this topography had a strong effect on seismic waves, giving rise to a significant amplification of peak ground accelerations at those sites.We give a new model of rupture of landslides and rock collapses triggered by strong earthquake in mountainous area. Related Articles | Metrics

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The implications of strontium and helium isotopic compositions for the earthquake activity in the midwest of Hexi corridor, China DIAO Xia ZHANG Gui-Xia BO Gong-Qin TUN Jing RAO Wen-Bei 2009, 16(3): 327-332.  Abstract ( 2210 )   PDF (1102KB) ( 875 )   Abstract:  The Hexi Corridor (37°17′N to 42°48′N; 93°23′E to 104°12′E) is located in the northeast margin of Tibetan Plateau active block region. The deep fault zones trending WNW (northern boundary fault of the Qilianshan) and NNE (Altyn fault zone) are well developed. Medium and strong earthquakes ever occurred in history in these regions, especially at the junction region of Qilianshan seismotectonic zone and northsouth seismotectonic zone. After Wenchuan  earthquake Ms 80 occurred at 14:28:01.42 CST on 12 May 2008, all regions except Xinjiang, Jilin and Heilongjiang in China were affected by the great quake. It is a remarkable problem that how strong the coming earthquake in the Hexi seismic belt may be in the future time. In this paper, the authors have measured strontium and helium isotopic compositions of groundwater in Zhangye, Wuwei and Jiuquan Basins. It is concluded that the groundwater in these three basins are not originated from the runoff of Heihe River, Shiyanghe River or Shulehe River respectively, but from the supply of rainfall in the Qilianshan mountain front, which feeds the deep fault zones and then flows up over the Earth surface. The groundwater in different areas have different cycling routes. Therefore, the fault zones within the Hexi Basin are strongly active at present. The Yumen, Gaotai, Minle, and Yongchang Counties are located at or nearby the junction areas of the deep fault zones, so the occurrence probability of medium and strong earthquake in the future is quite high within the regions. It should be stressed to enhance the realtime monitoring of groundwater in the regions. Related Articles | Metrics

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Geomechanics modelling test on deformation fracture mechanism of mountain caused by earthquake HU Xiang-Ning WANG Lan-Sheng 2009, 16(3): 333-340.  Abstract ( 1427 )   PDF (1253KB) ( 1173 )   Abstract:  The deformation fracture of mountains caused by earthquake is a complicated evolved process. In this paper, three typical geomechanics modes are summarized and concluded, i.e. the outerinclining bedded landslide model, the highsteep block (layer) bedded slope collapsing model and the weak base landslide model, which are representative for the deformation fracture and instability of mountains in areas with high earthquake intensity. We have also indigenously developed, designed and explored a set of geomechanics modeling test equipment, models and techniques under vibration to conduct the mechanism modeling test of the three typical geomechanics models, concepts and models. Through the modeling reproduction test of the evolved process of deformation fracture, typical phenomena and important evidence of deformation fracture under vibration are shown and formation conditions, relevant factors and evolvement principles of typical earthquake instability mechanism are presented to offer scientific and reliable test data and evidences for further research and analysis. Related Articles | Metrics

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Tempestite of Akeshake Formation in Awulale Area,Western Tianshan and its significance LI Yong-Jun GAO Yong-Li TONG Li-Chi GUO Wen-Jie TONG Li-Meng 2009, 16(3): 341-348.  Abstract ( 1658 )   PDF (1743KB) ( 811 )   Abstract:  The Early Carboniferous Akeshake Formation in the Awulale Kuoerku Area, Western Tianshan, is mainly marked by carbonate rocks and clastic rock. In this set of strata, the bambooleaflike calcrudite belonging to storm deposit developed. The storm sedimentary structures include erosional structures, tearpull structures, stormsurge structures, storm eddy structures and quickly deposited structures after storm. These types of storm deposits that have been recognized include the bambooleaflike calcirudite with massive bedding, the bambooleaflike calcirudite and sandstone with graded bedding, the calcarenite with hummocky and hollow cross bedding and parallel bedding, the calcarenite and feldspathic litharenite with parallel bedding, the calcarenite and bioclastic silty calcirudite with wavy cross bedding, the calcisiltite and silty calcirudite with horizontal bedding, and the bioclastic silty calcirudite with homogeneous or horizontal bedding. These storm deposits may indicate the sedimentary environment being the shelf of low latitude zone in the Early Carboniferous. The discovery of the storm deposits is of significance in the interpretation of the Carboniferous pa1aeogeography,palaeoclimate, palaeotectonics and plate motion of Western Tianshan. Related Articles | Metrics

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Research on the characteristics of thinalternatingbed seismic waveform—A case study of the beach bar sandstones of Es4 in Boxing Sag HAN Hong-Wei 2009, 16(3): 349-355.  Abstract ( 1977 )   PDF (2183KB) ( 3193 )   Abstract:  Thinalternatingbeds exist commonly in rifted terestrial lake basin, like beach bar sandstones; they have some common characteristics, like the fast changes in horizontal direction and thinness of a single bed;these features, in addition to the low seismic data resolution, make the  seismic prediction difficult. In this study, we have analyzed all kinds of lithologic geophysical signatures in the area where the beach bar sandstones developed in Es4 in Boxing Sag, and analyzed the seismic reflection features of different lithologies and their combinations using an inversion model combined with actual well results. The study determined the seismic attributes, such as the seismic waveform structure and the ratio of the areas on both sides of the maximum of the seismic reflections from different sandstone combinations, and summed up the corresponding relationships of the thinalternatingbeds and their combination patterns with the attributes of each seismic reflection. Using these results, we have predicted exactly the development belt of reservoir in exploring the bank and dam body reservoir of Es4 in the west of Dongying Depression. Related Articles | Metrics

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Simulation of hydrocarbon generation and expulsion of low maturity oil shale DAO Shu SHANG Da-Zhen WANG Dong-Ying HU Gao LI Jing-Jing LIN Wen-Ji 2009, 16(3): 356-363.  Abstract ( 1935 )   PDF (1345KB) ( 742 )   Abstract:  The study of maturation evolution of source rocks is of great significance in evaluating the regional background of oil and gas generation. Low maturity oil shale of South Junggar was chosen as sample for thermal simulating experiment of source rocks in three different conditions, that is, without water but with variation in temperatures,  with various amount of water under the constant temperature, and with constant amount of water  under different temperatures. Based on the qualitative and quantitative testing of oil, gas, and solid residue, the changes in the phase state and hydrocarbon compositions were analyzed. The experimental result shows that in the first two kinds of  experiments, the ratios of oil generation both reached their peaks at 300 ℃, whereas the latter was higher than  the former experiment of the same temperature; in the third experiment, the oil generating reached its peak with 10 mLwater; during the stage of dry gas generation, gaseous hydrocarbon mainly came from heavy hydrocarbon cracking rather than high maturity kerogen itself. After thermal cracking at 400 ℃, the remaining ratio of oil generation decreased to its minimum being 5%; the amount of saturated hydrocarbon was high in conditions of low and extreme high temperatures, mainly composed of nalkanes. The amount of aromatic hydrocarbon, mainly composed of triaromatics and tetraaromatics, was highly variable in different temperatures, and reached its maximum at 400 ℃ and  lowered down to the minimum at  500 ℃, whereas the changes in the amount of the nonhydrocarbon and bitumen were contrary to that. Related Articles | Metrics

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Characteristics of saprolites formed from crystalline rock and clasolite in humid climatic regions and their development process XU Ze-Min 2009, 16(3): 364-373.  Abstract ( 1344 )   PDF (5935KB) ( 925 )   Abstract:  The saprolites derived from crystalline rock and clasolite and developed in slope unsaturated zones are usually sandwiched between residual or colluvial soil and weathered bedrock, and retained large structures such as bedding or fractures from their parent rocks. The color difference between saprolite blocks and their parent rocks is obvious and the texture and structure of the parent rock can be preserved in saprolites. Secondary clay minerals, quartz and ferrohydrite are most common in saprolites. Saprolites have spongy microtexture and are characterized by high porosity, high intrinsic permeability, high specific water capacity, low specific yield and low density. The development of saprolite is realized by the progressive propagation of the weathering front of low permeable rock blocks, and the condensate from the moisture and the unsaturated seepage flow are the key agents of the propagation process. The gaseous water molecules in unsaturated zones spread into the pore system of rock blocks at some depth and condense into liquid water which can dissolve rockforming minerals. In rainy season, the thin water film derived from precipitation on the surface of rock blocks in unsaturated zones absorbs the dissolution components of the rock block solution and carries them into saturated zones. At the same time, the dissolving capacity of solution between mineral grains in rock blocks is also restored. When the above process circulates to some extent, saprolitic crusts will be formed inside structural planes. Saprolitic crusts may absorb and store the liquid water flowing on their surfaces, and in dry season these saprolitic crusts provide unsaturated zones and weathering fronts of rock blocks with moisture. With the lapse of time, saprolitic crusts get thicker and thicker, corestones become smaller and smaller, and finally rock blocks evolve into saprolitic blocks. When all rock blocks within the research area have developed into saprolitic blocks, the rock mass turns into saprolite. Related Articles | Metrics

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Current research progress in petrology of carbonated eclogites CHEN Xiao-Ji ZHANG Li-Fei 2009, 16(3): 374-384.  Abstract ( 1710 )   PDF (1574KB) ( 918 )   Abstract:   Cycling of carbon into and out of the mantle plays a key role in the global carbon cycle and influences the CO2 budget of the Earths atmosphere. Subduction introduces carbon into the mantle, while volcanic outgassing releases it to the surface. Oceanic crust is mainly composed of basalts, and hydrothermal altered basalts contains several wt％ of carbonates (average 3wt％), which is a huge carbon sink for global carbon cycling. Carbonates (in the form of veins) within basalts can be delivered to the upper mantle until 300 km during oceanic crust subduction, thus produced carbonated eclogites. Partial melting of carbonated eclogites plays an important role in arc magmatism and volcanic outgassing. In this paper, we summarize up to now all reports of ultrahighpressure metamorphic areas of natural carbonated eclogite samples and compare with the recent progress in experimental petrology of altered MORB plus carbonate minerals and reach some basic conclusions of how carbonate minerals interact with silicate system (eclogitic) with progressively elevated temperature and pressure in subduction zones. What is more, we summarize the current research progress of phase equilibrium calculation of carbonated eclogites in NCFMASH+CO2 system and the H2OCO2 activity model, thus forecast the future phase relationship calculation of NCFMASH+CO2 system, which is important for global carbon cycling. Related Articles | Metrics