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15 January 2018 Previous Issue    Next Issue

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Structural style and kinematics of the Mesozoic Xuefengshan intraplate orogenic belt, South China Block YAN Danping,QIU Liang,CHEN Feng,LI Lin,ZHAO Lei,YANG Wenxin,ZHANG Yixi 2018, 25(1): 1-13.  DOI: 10.13745/j.esf.yx.2017-5-16 Abstract ( 518 )   PDF (4099KB) ( 996 )   One of the key scientific issues related to tectonics of the South China Block focuses on the nature of the JiangnanXuefeng orogenic belt. In this study, structural style and kinematics of five tectonic units, namely the Xiangzhong composite thrust belt, Xuefengshan thickskinned thrust belt, FanjingshanZouma domal belt, troughlike faultfold thrust belt and ejective thinskinned thrust belt, are identified along a geological crosssection of the Xuefeng orogenic belt with detailed profiles of regional geology, deformation and seismic interpretation. Our study shows: (1) The Xiangzhong composite thrust belt in the eastern Xuefeng orogenic belt is represented by the Longshan composite tectonic dome. This dome has structural style of the SEdipping thrust faultrelated Mesozoic chevron anticline, which overprinted the EWstriking Caledonian anticline. (2) The Xuefengshan thickskinned thrust belt is bordered by the Dayong thrust fault to the west, and outcrops extensively the shallow metamorphic Banxi Group. This belt has the NW faultrelated folds with smaller slip flatramp fault, where flat developed along the weak layers within the Banxi group while ramp cuts upward, thus producing the broad syncline and tight anticline, respectively. The flatramp fault also resulted in the Neoproterozoic Banxi Group thrusting over the Paleozoic, and the formation of the Yuanma Basin and klippes and tectonic windows. (3) The FanjingshanZouma domal belt is represented by the Fanjingshan tectonic dome. This dome has the structural style of faultrelated fold, with SEdipping flatramp thrust fault and hangingwall anisomerous box anticline, which outcrops the early Neoproterozoic Fanjingshan Group in the core. Thus the Fanjingshan tectonic dome was produced by thickskinned thrust. (4) The troughlike faultfold thrust belt contains a series of NEstriking parallel box anticlines and chevron synclines. The Cambrian outcrops in the core of the box anticlines while the SinianNeoproterozoic Banxi Group involves deep in the deformation. The fault developed imbricate faultrelated fold in the shallow and basement involved faultfold in the deep, making it an active duplex thrust fault. (5) The ejective thinskinned thrust belt, situated between the Huayingshan and Qiyueshan faults, is represented by chevron anticline and box syncline with SEdipping flatramp thrust fault produced by faultpropagation folding. All five tectonic units have deformations involving the Upper TriassicLower Jurassic and are unconformably covered by the Upper Cretaceous, indicating deformations occurred in the middlelate Mesozoic, and likely followed a “younging” trend from SE to NW. Therefore, this paper has proposed a new kinematic model, which contains essential features of the faultrelated folds, fold evolution, and the Mesozoic intraplate progressive orogeny along the Xuefeng Mountain. Related Articles | Metrics

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The Paleozoic deformational characteristics and tectonic significance of the Wengan Dome in the Southwest Yangtze Block SONG Zhidong,QIU Liang,ZHANG Yue,ZHANG Yixi 2018, 25(1): 14-32.  DOI: 10.13745/j.esf.yx.2017-5-15 Abstract ( 206 )   PDF (4308KB) ( 471 )   The Early Paleozoic, a key and widespread tectonic event, occurred between the Devonian and PreDevonian in the Yangtze Block. Different models on the event, such as the three episodes, two episodes and continued changing in paleogeographic patterns, have been proposed. This paper focuses on the Wengan Dome in the Southwest Yangtze Block, which has well preserved and exposed Early Paleozoic deformation. Six geologic crosssections of the Weng’an dome were used for the detailed divisions of the tectonic layers; analyses of structural styles, tectonic superposition and deformational sequence with chronological constraints were also performed. The results suggest that the Wengan Dome is essentially a tectonic superimposed dome. The dome experienced at least two deformations since the Paleozoic, namely the Early Paleozoic deformation D1 and Yanshanian deformation D2. The D1 deformation is represented by the EWtrending folds, strikeslip to thrust faults and EWtrending approximate to vertical interval cleavages—all resulted from SN vertical extrusion; it is seen in the CambrianSilurian and underlying tectonic layers. The EWtrending structures of the D1 deformation were intercepted and superimposed by the D2 deformation. This indicates that the D1 deformation formed before the angular unconformity between the tectonic layers of the CambrianSilurian and the Upper Devonian to Middle Triassic. According to the distribution of the detrital zircons, the Early Paleozoic era occurred later than ca. 438 Ma in the Wengan Dome. Geological investigation presented in this study, and numerous data published in recent years, further support the hypothesis that the Early Paleozoic tectonic deformation appeared first in the southern area of the South China Block before propagating to the north. Related Articles | Metrics

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The Mesozoic-Cenozoic deformation sequences of the Badu complex anticline and their significance for the evolution of the Nanpanjiang Basin YANG Wenxin,YAN Danping,QIU Liang,CHEN Feng 2018, 25(1): 33-46.  DOI: 10.13745/j.esf.yx.2017-5-13 Abstract ( 453 )   PDF (2445KB) ( 519 )   The Nanpanjiang Basin, located at the junction of the South China and Indochina blocks, is regarded as the foreland basin of Indosinian orogen. Due to the MesozoicCenozoic tectonic superimposition, the structural style of the basin is complex as superposed folds are common. Accordingly, the Badu domelike complex anticline in the middle of the Nanpanjiang Basin was chosen as the study object. Combining surface deformation analysis with deeper seismic profile interpretation and zircon geochronology of diabase, we reconstructed the structural styles and deformation sequences. The Badu complex anticline, which has a Devonian core and limbs of Permian and Triassic, is an arcshaped fold with northward axis. At the deep level, the structure is dominated by a NEdirecting duplex; at the middle and shallow level, there are Ndirected imbricates with faultrelated folds. The magmatic zircon from diabase yielded a youngest age population of 62 Ma, indicating a possible contemporaneous uplifting. Integrating structural styles at different levels, the deformation sequence of the region was divided into three deformations, D1, D2 and D3. D1, the duplex, was caused by Indosinian subduction; D2, the imbricate, was a result of Indosinian compression; and D3, represented by normal faults and diabase dykes, was a result of the Late Yanshanian extension. The formation and evolution of the Badu complex anticline is a typical example of the superimposition of the Nanpanjiang foreland Basin, which shows that the foreland basin of Indosinian underwent subduction, compression, tectonic transition from compression to extension during the Yanshanian, and finally uplifting in the Cenozoic era. Related Articles | Metrics

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Structural style and sandbox modelling of the Laizishan Dome in the Nanpanjiang Basin, South China WANG Jibin,YAN Danping,QIU Liang,TANG Xiangli,YANG Wenxin,ZHU Lutao 2018, 25(1): 47-64.  DOI: 10.13745/j.esf.yx.2017-5-19 Abstract ( 385 )   PDF (3924KB) ( 524 )   The Nanpanjiang Basin develops a series of tectonic domes which control the distribution of lowtemperature mineralization. An example is the typical Laizishan Dome, it controls the Lannigou giant gold deposit in the southwest Guizhou Province. Based on the statistics of strata attitude around the Laizishan Dome, the studied area was subdivided into NW and NE subregions through π circle projection analysis, and the fold type in the subregion was confirmed to be upright horizontal anticline by cross section and geometric projection analysis. Selection of axial plane cleavages was made based on statistics of all cleavages and parallel relationship between cleavage and axial plane of fold in the subdistrict. According to crosscutting relationships of axial plane cleavages, and age of strata and related intrusion involved in the deformation, the sequence offold development in the subdistrict and age of deformation were constrained, consequently inferring that the NWSE and NNESSWtrending anticlines were developed in the early and late Yanshanian, respectively.In the structural analysis based on the stratigraphic strength, strata shortening and deformation boundary conditions, four groups of sandbox simulation experiments with two sandbox models were designed to study the process and types of tectonic compounding and conjunction; and factors affecting the superposed deformation are discussed. The simulation results suggest that the Laizishan Dome is the result of superposition the NNEand NWtrending buckling folds,and the type of superposition is a migration of fold superimposition. Furthermore, the two folds correspond to the lateral extrusion to the Nanpanjiang Basin by the Xuefengshan uplift during the early Yanshanian, and the largescale thrusting from NW to SE in southwest Guizhou during the late Yanshanian, respectively. The results also show that difference in rock strengths and deformation intensities are the main factors affecting the styles and types of superimposition:when strength difference is large, the weak layer affects the structural styles of the upper and lower hard layers;when later stage deformation is weak, limited or migrating superimposed fold is formed,otherwise it forms the oblique crossing or crossing superimposed fold; and phased deformation leads to tectonic compound superposition,whilecoinstantaneous deformation or lesser difference in deformation velocity results in curved tectonic conjunction superposition. Related Articles | Metrics

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Structural and background anomaly characteristics of Pb, Zn, Ag, As, Sb of the Jiache Dome, Northeast Yunnan Province HAN Yangguang,YAN Danping,MU Dan,QIU Liang,KANG Ning,CHEN Feng 2018, 25(1): 65-79.  DOI: 10.13745/j.esf.2018.01.005 Abstract ( 562 )   PDF (2906KB) ( 475 )   Northeastern Yunnan, located in the southwestern part of the Yangtze Block, developed a series of tectonic domes hosting low temperature or closely related deposits. Research on the structural origin and properties of these tectonic domes is beneficial for revealing the regularity of regional low temperature ore formation. The Jiache Dome in northeast Yunnan situates near Awang and Jiache towns. Compared with other domes in the area, the Jiache Dome developed a complete structurerock assemblage, typical of the regional tectonic domes. Focusing on the structural features of the Jiache Dome, the structural origin and deformation sequences of tectonic domes, characteristics of background anomaly of low temperature metallogenic elements, and occurrence of Pb, Zn, Ag, As, Sb elements were determined in this work, through detailed geological investigation, structural analysis, key stratum sample collection, geochemical and EMPA analyses, in combination with regional background data. By completing three crosscutting structural profiles of the Jiache Dome, it is discovered that the dome has experienced at least three stages of structural deformation (D1, D2, D3): D1 period developed consequent flow layer deformation, possibly of the Caledonian age; D2 period formed the NEE trending buckling fold with a supposed deformation age of the Indosinian; D3 period resulted in the NNE trending buckling fold, whose deformation age is postulated to be the Yanshanian. Results of geochemical analyses show that lowgrade metamorphic rocks in the Kunyang Group (for example muddy and silty slate) have background anomaly values 3 to 5 times higher than background levels for Pb, Zn, Ag, Sb, As and siltstone in the Chengjiang Formation of Sinian. Similarly, dolomite and black shale in the Dengying Formation exhibit background anomaly levels 3 to 5 times higher than background values for Pb, Ag, and As. And part of black shales in the Yuhucun Formation of the lower Cambrian show background anomaly values 5 times higher than background values for Pb, Zn, Ag, Sb, As. EMPA analysis suggests that these low temperature oreforming elements are mainly hosted in the primary pyrite. Results of structure analyses further show that the main body of the dome formed over the superposed NNE and NEEtrending folds, and it has experienced multistage tectonic superposition and transformation. Related Articles | Metrics

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Deformation sequence and geochronological constraints on the metamorphism of the Bikou terrane, northwestern margin of the Yangtze Block XU Chenguang,YAN Danping,GU Shuhang,MENG Xiangkun,QIU Liang，Michael L.WELLS,WANG Jibin,MA Fang 2018, 25(1): 80-94.  DOI: 10.13745/j.esf.yx.2017-5-14 Abstract ( 306 )   PDF (3574KB) ( 595 )   The Bikou terrane lies on the northwestern margin of the Yangtze Block. It comprises pelitic rocks in the north and maficintermediate volcanic rocks in the south. Rocks in the north metamorphosed into phyllite and mica schist, while rocks in the south experienced greenschistblueschist facies metamorphism. Presently, there are no detailed analyses on the deformation sequence and regional metamorphism of the Bikou terrane; geochronological constraints for regional metamorphism are also lacking. As a result, nature of the Bikou terrane and age of regional metamorphism and tectonic settings are not known, causing controversy over the orogenies of West Qinling and Longmen Mountain. Here, after detailed field study and structural analysis, we divided the Bikou terrane deformation sequence into three stages, D1, D2 and D3. D1 is marked by tight fold, foliation S1 and mineral lineation L1; D2 is normal ductile shear dipping to the south, transforming thrust faults and resulting in formation of Jurassic halfgraben basins; and D3, formed in the sinistral strikeslip thrust in the Himalayan, is characterized by brittle deformation. In this study, we obtained UPb zircon age of 227.2±6.2 Ma from deformed felsic veins in the Bikou terrane. Since the undeformed intrusive plutons after D1 deformation yielded age of 226215 Ma in previous studies, the age of regional metamorphism in the Bikou terrane is constrained at ca. 220 Ma. Therefore we infer that, D1 formed during subduction and collision between the North and South China blocks in the Late Triassic, when regional metamorphism of the Bikou terrane occurred, and D2 and D3 were related to eastward expansion of the Tibetan Plateau. Related Articles | Metrics

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MesoCenozoic tectonothermal pattern of the Pearl River Mouth Basin: constraints from zircon and apatite fission track data LI Shubo,WANG Yuejun,WU Shimin 2018, 25(1): 95-107.  DOI: 10.13745/j.esf.yx.2017-5-20 Abstract ( 295 )   PDF (3719KB) ( 514 )   As a representative of the epicontinental rift basin in the northern South China Sea, the Pearl River Mouth Basin is an ideal study area for a better understanding of the tectonic evolution of the South China Block and time limit of the opening of the South China Sea. This paper presents the apatite and zircon fission track dating results from basins Paleozoic gneissic and Cretaceous granitic drill samples. The zircon fission track apparent age ranges from 131.7 to 97.9 Ma, younger than their formation time; the apatite track apparent age falls between 79.7 and 61.9 Ma; at 11.3713.16 μm, the apatites fission track lengths show a cooling or mixing pattern. The geothermal simulation show that distinctive uplifting and cooling processes were present in different sites, cooling event took place earlier, and the uplifting rate was slower in the south than in the north in the Cenozoic. It is inferred that the basins basement uplifted about 6 km since the late Cretaceous when it experienced several episodes of rapid uplift in the late Cretaceous, the Shenhu tectonic event at Paleocene, the second scene of the Zhuqiong tectonic event, and the Nanhai tectonic event at Oligocene (before 26 Ma). During the Nanhai tectonic event, the uplift began earlier in the east than in the west. The timing of the rapid uplift is consistent with the timing of slipstrike of the Red River Fault, and the uplift shows good correlation with the basin formation. Our data provide important constraints on the extension of the South China Sea. It is confirmed that the basement uplift of the Pearl River Mouth Basin was a result of a conjuncture of the subduction of the Pacific Plate, collision of the IndianEurasian Plate and extension of the South China Sea. Related Articles | Metrics

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Studies on tectonic setting, sedimentary environment and mineralization mechanism of the Yinmin copper deposit in Yunnan Province DAI Hongzhang,LIU Jiajun,ZHU Wenbing 2018, 25(1): 108-124.  DOI: 10.13745/j.esf.yx.2017-5-21 Abstract ( 400 )   PDF (3035KB) ( 477 )   The Yinmin deposit is an important deposit in the Dongchuan copper ore field in Yunnan Province. It has two mineralization types, one is the FeCu deposit of Xikuangshan type from the Yinmin Formation of the Kunyang Group, the other is the Cu deposit of Dongchuan type from the Luoxue Formation. In this paper, major and trace elemental analyses were combined with thermodynamic calculation to reveal rock characteristics, tectonic setting, sedimentary environment, and mechanism of migration and accumulation of iron and copper. Results show that the Yinmin and Luoxue formations mainly consist of dolomites and siliceous dolomites with dolomitic sandstone as a minor component. Comprehensive analyses of various diagrams, such as 100(Fe2O3/SiO2)100(Al2O3/SiO2), Fe2O3/TiO2Al2O3/(Al2O3+Fe2O3), LaThSc and ThCoZr/10 graphs, indicate that the contents of carbonate samples from the two formations were consistent with an active continental margin sedimentary system. Discrimination diagrams of redox environment, such as V/Cr, V/(V+Ni) and Ce/La, indicate that the Yinmin and Luoxue formations were deposited in a deep water to semideepwater transitional dysaerobic basin. Thermodynamic calculation results show that iron and copper transported mainly in the form of Cl complex. First, temperature, Eh and f(S2) decreased while pH increased in the oreforming system as oreforming fluid transported to the surface and mixed with the reduced water. Then instability occurred in the complexes of copper and iron. Finally, oxides including hematite and magnetite, sulfides including pyrite, chalcopyrite, bornite and chalcocite changed sequentially with changes in the physical and chemical environment, and formed the ferrocopper and copper ore bodies of the Xikuangshan and Dongchuan types, respectively. Related Articles | Metrics

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Sources of oreforming material of typical PbZn deposits in the SichuanYunnanGuizhou metallogenic province: constraints from the SPb isotopic compositions KONG Zhigang,WU Yue,ZHANG Feng,ZHANG Changqing,MENG Xuyang 2018, 25(1): 125-137.  DOI: 10.13745/j.esf.yx.2017-10-4 Abstract ( 509 )   PDF (3931KB) ( 581 )   The SichuanYunanGuizhou (ChuanDianQian) PbZn metallogenic province, located along the western margin of the Yangtze block, comprises more than 400 ore deposits or prospects. The average Pb and Zn grades of its 200 Mt ore reserve are 5 and 10 wt%, respectively. The PbZn ore bodies mainly distributed as stratoid or veintype within the Sinian to Permian carbonate rocks, suggesting a typical epigenetic PbZn mineralization. In this study, isotope data of S and Pb sulfides from 21 deposits were compiled to reveal the source of oreforming materials, and provide guidance for further prospecting. The δ34S values of most sulfide minerals range from +9.0‰ to +28.6‰, similar to the SiniantoPermian seawater sulfate (+8.0‰ to +38.7‰). It suggests that S in sulfides mainly came from thermochemical sulfate reduction (TSR) of the hoststrata seawater sulfate. In addition, thermal decomposition of sulfurbearing organic matter could provide part of reduced sulfur in mineralization in some PbZn deposits. The Pb isotopic compositions of sulfides in the research area indicate four possible Pb sources: (1) Pb of the Tangjia deposit originated mainly from the basement rocks; (2) Pb in the Jinshachang, Lemachang and Lehong deposits mainly came from basement rocks containing radiogenic Pb isotopes and cap rock organicrich sediments; (3) Pb of the Huize, Tianbaoshan, Maozu, Yinchanggou, Daliangzi, Yunluhe, Maoping, Fule, Shanshulin and Tianqiao deposits originated primarily from basement rocks and oreforming fluid of multiple metalbearing brine mixing in the cap stratum, and partly from Permian Emeishan basalt; (4) Pb of the Qingshan, Chipu, Yinchangpo, Shaojiwan and Banbanqiao deposits mainly came from sedimentary rocks, and partly from basement rocks. The multiple SPb isotope composition in typical PbZn deposits is indicative of mixed origin for oreforming materials in the metallogenic province. Related Articles | Metrics

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Tectonic genesis of the Santaishan peridotite in western Yunnan and its geological significance: evidence from geology, mineralogy and petrogeochemistry WANG Yixuan,WANG Genhou,YUAN Guoli，WANG Xingjun,Lu Yong,LIN Yu 2018, 25(1): 138-156.  DOI: 10.13745/j.esf.yx.2017-6-11 Abstract ( 473 )   PDF (3033KB) ( 421 )   GangdiseTengchong Block is one of most significant components of EastTethyan orogenic belt and therefore is the key to explore the evolution of Tethys. An outcrop of Santaishan ophiolites tectonically located in the GaoligongRuili fault zone and exposed as part of an accretionary complex, consist mainly of dunites and harzburgites that are dominated by Mgperidotites (Fo=9093), enstatite (En=8992) and Crspinel (Cr# =5478). Highly depleted modal, mineral and bulk rock compositions of the dunites and harzburgites indicate both rocks were residues from high degree partial melting (25%35%) in the spinel stability field. These rocks, lacking typical MORBtype chondritenormalized Rare Earth Element (REE) patterns, display a pattern of slightly enriched LREE and weak depletion of HREE. These characteristics, combined with the rocks' mineral and wholerock compositions, which lie between those of abyssal and forearc peridotites, imply that the selective enrichments of LREE and Pb were the result of meltrock interactions. This study suggests a twostage model for the genesis of peridotites, i.e., these rocks originated from a MORB upper mantle source and were subsequently trapped to form part of a mantle wedge above a subduction zone. Comparative observations on the ophiolitic massifs along the entire YZSZ (Yarlung Zongbo Suture Zone) further suggest that the tectonic setting of the Santaishan ophiolites is similar to YZSZ. Related Articles | Metrics

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Genesis and metallogenic model of the Shuiyindong gold deposit, Guizhou Province: evidences from highresolution MultiElement Mapping and in situ sulfur isotopes of Aucarrying pyrites by NanoSIMS ZHAO Jing,LIANG Jinlong,LI Jun,NI Shijun,XIANG Qirong 2018, 25(1): 157-167.  DOI: 10.13745/j.esf.yx.2018.01.011 Abstract ( 544 )   PDF (3486KB) ( 507 )   The Shuiyindong gold deposit is a typical large Carlintype gold deposit. It is located in the “Golden Triangle” area crossing Yunnan, Guizhou and Guangxi provinces where arsenian pyrite and arsenopyrite are the significant Aucarrying minerals with invisible gold. In this study, Back Scattered Electron (BSE) imaging and highresolution MultiElement Mapping by NanoSIMS show that the pyrites usually have the zonal texture containing lower Au, As in the core and higher Au, As and Cu in the overgrowth rim. The trace element pattern implies that the ore fluid is Au, As, Curich during the pyrite overgrowth stage. In addition, highresolution NanoSIMS mapping reveals that the Aurich rim is composed of several unevenly distributed fine subzones, marked by the banded pattern of Au, As and Cu due to episodic hydrothermal fluid variation. Meanwhile, in situ sulfur isotopic analysis of pyrite shows that the δ34S values of cores and rims range from 1.3‰ to 6.5‰ and -3.5‰ to 7.4‰, respectively, focusing generally around 0‰. This result, combined with similar gold deposits around the world, indicates that sulfur is likely originated from the deep magmatic source contaminated by sedimentary sulfur. Finally, a magmatichydrothermal model is proposed for the Shuiyindong gold deposit. It suggests that the As and Aubearing acid magmatic fluid upwelled along the deep fault to fill or react with Ferich wall rocks, which led to the deposition of gold; in addition, the meteoric water might have been involved in the ore formation. Related Articles | Metrics

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Fluid inclusion characteristics of the Weilasituo Sn polymetallic ore deposit, Inner Mongolia, China GUO Lixiang,LIU Jianming,ZENG Qingdong,JIANG Hucan,LIU Hongtao 2018, 25(1): 168-181.  DOI: 10.13745/j.esf.yx.2018.01.012 Abstract ( 482 )   PDF (2324KB) ( 402 )   The Great Xingan Range tin metallogenic belt is the only mineable tinpolymetallic belt in northern China. The newly discovered Weilasituo Sn polymetallic ore deposit in Inner Mongolia, in the southern Great Xingan Range, is a part of the XinganlingMongolian Orogenic Belt in the eastern Central Asian Orogenic Belt. The deposit is a largescale porphyryhydrothermal vein type Snpolymetallic ore deposit, its mineralization is mainly hosted in the top portion of the quartz porphyry and quartz veins above it. Based on the crosscutting relationship of veins and ore structure, we recognized four metallogenic stages during the formation of the western Weilasituo SnZn polymetallic ore deposit, namely the dropletlike SnZn in quartzporphyry (stage Ⅰ), molybdenum (stage Ⅱ), quartzcassiteritewolframite (stage Ⅲ) and quartzpolymetallic sulphides (stage Ⅳ) mineralization. Fluid inclusions can be divided into three types: liquid and vaporrich twophase aqueous inclusions, and daughter mineralbearing threephase inclusion. Microthermometric analyses indicate that the homogenization temperature of dropletlike SnZn mineralization in quartz porphyry varied from 324 to 333 ℃, with salinity of 6.5%7.5% NaCleqv and density around 0.730.74 g/cm3. The fluid inclusions from quartz porphyrystyle mineralization exhibit a homogenization temperature range of 201324 ℃, with salinity and density of 3.4%9.9% NaCleqv and 0.730.92 g/cm3, respectively, consistent with the characteristics of moderatehigh homogenization temperature, low salinity and moderate density fluids in this deposit. The analytical results by laser raman spectroscopy suggest that the composition of the oreforming fluid is mainly H2O in the liquid phase and CH4, CO2 and H2O in the vapor phase. The data obtained by δ18O and δD analyses imply that the oreforming fluids in the quartz vein mineralization stage originated from the mixture of magmatic and meteoric waters, with magmatic water as the main component. Therefore, the principle mechanism for the deposit mineralization was mixing of magmatic and meteoric waters followed by a cooling period during fluid evolution. Related Articles | Metrics

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New evidences for dating of the Middle Jurassic Wanbao Formation in the Longjiang Basin, western margin of Heilongjiang Province SHI Zhensheng,LI Xizhe,DONG Dazhong,QIU Zhen,LU Bin,LIANG Pingping 2018, 25(1): 182-196.  DOI: 10.13745/j.esf.yx.2017-5-22 Abstract ( 329 )   PDF (2337KB) ( 333 )   Jurassic stratigraphy of the eastern Daxinganling region, which covers the western margin of Heilongjiang Province, China, has not been a high priority research. For many years, coalbearing strata determination of the Middle Jurassic relies on regional correlation with the typical Middle Jurassic coalbearing Wanbao Formation of western Jilin Province. Now for the first time, we discovered a set of Middle Jurassic coalbearing strata in a new round of geological survey in the region. In this paper, we determined the accurate forming age of 2 tuffs from the Wanbao Formation of the Longjiang Basin to be 165.2±1.7 Ma and 162.1±1.6 Ma. In addition, abundant megaplant fossils were collected from these strata, which were found to represent the NeocalamitesConiopterisRaphaelia assemblage, indicating EarlyMiddle Jurassic age. Sporepollen study on the megafossils reached similar assessment. We conclude that the Wanbao Formation formed in the Middle Jurassic, most probably in the late Middle Jurassic. Geochemical analyses show that the 2 tuffs were made of peraluminous calcalkaline volcanic rocks containing high Si, Al, low Ca, P, and enriched light rare earth elements with REE pattern gently tilting to the right and negative Eu anomaly. The enriched large ion lithophile elements Cs, Th, U, and depleted high field strength elements Nb, Ti, Zr, imply that the source rocks are crust genetic types. Volcanic activity of Wanbao period may be related to the dual role of the evolution of the ancient Pacific Plate and the evolution of the MongolianOkhotsk suture zone, and is more closely related to the evolution of the MongolianOkhotsk suture zone. Currently the Wanbao Formation of the Middle Jurassic represents an important newly discovered strata for the oil and gas exploration. Here, we provide reliable geochronological and biostratigraphic evidence not only for the classification and comparison of the Middle Jurassic coalbearing strata in the eastern Daxinganling Region, but also for the formation and evolution history of the Longjiang Basin. Related Articles | Metrics

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U-Pb dating and its implication for the clastic sedimentary rocks in the Rigain Pünco Formation in the Niu Mountain in Nyima County, Tibet HOU Engang,CHEN Yaofei,GAO Jinhan,WANG Genhou 2018, 25(1): 197-209.  DOI: 10.13745/j.esf.yx.2017-5-8 Abstract ( 256 )   PDF (3561KB) ( 400 )   The Qiangtang Block has become a geological research hotspot in recent years, however, its tectonic attributes, as well as the existence of ArcheanProterozoic basement in the block, have been controversial. In this work, using LAICPMS zircon UPb technique, we performed detrital zircon dating for the sedimentary samples from the Rigain Pünco Formation in the Niu Mountain in Rongma, Tibet. The results show: (1) The youngest age of detrital zircon is 215±2 Ma, equalling the maximum deposition age for the Rigain Pünco Formation. Combined with regional geological data, the deposition period was determined to be coincide with the Late Triassic NorianRhaetian stage. (2) The zircon grain age ranges between 580±6 and 212±2 Ma. The age peak at 298±2 Ma indicates the area was affected by the crustal thinning extensional stage magma activities during the PaleoTethys evolution in the Early Paleozoic. The age peak at 442±3 Ma shows that the area was affected by the magmatic activity due to the collision and accretion of the Caledonian Yangtze and Cathaysian plates in the Middle Paleozoic, and the provenance of the clastic rocks was the Yangtze continental margin. There is only one age occurrence at 650500 Ma, suggesting the provenance region was almost unaffected by the panafrican magmatism. (3) Clastic zircon appears in relatively small amount and ages from 1091±6 to 757±6 Ma, showing that the area was affected by the tectonic magmatic thermal events of the GrenvilleJinningian in the southern Qiangtang Block. (4) A large number of detrital zircons are dated between 3214±7 and 1380±15 Ma, they account for 60% of total zircon samples from the Rigain Pünco Formation. The age peaks at 1875±5 and 2531±6 Ma show that, the Qiangtang block was affected by the Proterozoic crystalline basement main stage tectonicthermal events, and the late Archean supercontinent split global events, hence providing a strong evidence for the existence of ArcheanProterozoic basement rocks in the Qiangtang Block. Related Articles | Metrics

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Magnetic anomaly in eastern China and adjacent sea, and its tectonic significance WU Zhaocai,GAO Jinyao,SHEN Zhongyan,YANG Chunguo,ZHANG Tao 2018, 25(1): 210-217.  DOI: 10.13745/j.esf.yx.2016-11-49 Abstract ( 238 )   PDF (4247KB) ( 476 )   On the basis of the latest shipboard magnetic data merging with the world digital magnetic anomaly, we have calculated the reduction to the pole (RTP) anomaly, pseudogravity anomaly, analytic signal and tilt angle, and used the wavelet decomposition and frequency spectrum analysis for the RTP anomaly. The results revealed the magnetic signature of the main tectonics in eastern China and adjacent sea. The distributions of paleocontinental nucleus in the North China block were indicated as well as the boundaries of Yangzi block. It was pointed out that the volcanic belt in the coastal area of Zhejiang and Fujian provinces connects to the Dongsha Uplift, and both of them are Mesozoic subduction volcanic arc. The NWoriented fault may be the boundary fault in which PaleoTethys tectonic domain converted to the Pacific tectonic domain, and controlled the subduction process during the Late Mesozoic and the conversion from the active continental margin to the passive continental margin since the Mesozoic at the Northern South China Sea continental margin. Related Articles | Metrics

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The present activity of the central and southern segments of the TanchengLujiang fault zone evidenced from relocated microseismicity and focal mechanisms ZHU Ailan,XU Xiwei,WANG Peng,REN Ye,SUN Dongjun 2018, 25(1): 218-226.  DOI: 10.13745/j.esf.yx.2016-11-54 Abstract ( 364 )   PDF (3663KB) ( 375 )   The TanchengLujiang Fault Zone (TLFZ) is the largest intraplate active tectonic deformation and strong historical seismicity zone in eastern China. It shows the segmentation feature in fault geometry and historical seismicity. We investigated the present activity of the central and southern segments of the TLFZ by analyzing the historical seismicity, relocated background seismicity and focal mechanism solutions. The background seismicity, resulting from the lingering aftershocks of the 1668 Tancheng earthquake sequence, aligns along the surface rupture zone of the 1668 Tancheng MS 8 earthquake extending roughly 340 km long from Sihong to Zhucheng. Both the earthquake rupture relic belt and the relocated background seismicity reveal that, the two Holocene active faults in the central segment, namely the ChangyiDadian fault and the AnqiuJuxian fault, involved in the rupture process during the 1668 Tancheng earthquake in the pattern of en echelon. The cross sectional profiles of the hypocenters delineate that the planes of the ChangyiDadian fault and AnqiuJuxian fault dipped to the southeast and northwest, respectively, with high dipping angles thus avoided merging in lower crust. The microseismicity belt represents the seismic rupture zone of the 1668 Tancheng earthquake, has high b values indicating this segment is not locked at present; in contrast, the north segment to Anqiu was not involved in the rupture and has low b values and low microseismicity rate, thus this segment may be locked. The focal mechanism solutions indicate that the maximum stress orientation in the central segment of the TLFZ is in the direction of NE; and the nodal plane of the mean solution with the same direction as the fault strike shows right lateral strike slip with some normal components. While in the southern segment, the maximum stress orientation turns to NEE near EW and shows right lateral strike slip with some thrust components. In the transition part of the central and southern segments from Suqian to Jiashan, as the focal mechanism solutions show, the maximum stress orientation is in the direction of NWW, which reflects the local stress state to be dominated by thrusting. Among these segments, the SihongJiashan segment experienced few historical earthquake and has a low microseismicity rate and is therefore more likely prone to accumulate stress at present. The relocated microseismicity concentrates at the intersections of the TLFZ and the northwest trending faults, illustrating the present activity of the NW trending faults and the thrust faulting on the TLFZ. Likewise at the southern end of the TLFZ, the relocated microseismicity aligns along the eastern segment of the NWW trending XiangfanGuangji fault, demonstrating the present activity of this segment. Related Articles | Metrics

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Surface rupture characteristics of the seismogenic structure of the Ludian MS 6.5 earthquake and identification and dating of related paleoearthquakes LI Xi,XU Xiwei,Zhang Jianguo,XIE Yingqing,YU Jiang,ZHANG Yanqi 2018, 25(1): 227-239.  DOI: 10.13745/j.esf.yx.2016-11-52 Abstract ( 243 )   PDF (3148KB) ( 340 )   After the Ludian MS 6.5 earthquake occurred, the distribution of aftershocks presented two possible directions, causing intensive debate over whether the seismogenic structure was the NE oriented ZhaotongLudian fault or a NW oriented secondary fault. Through detailed field investigation, we found that there were estimated 8 km long surface ruptures oriented N22°WN55°W along the line connecting Xiejiayingpan and Guangming villages and Wangjiapo. These ruptures are rightstepwise and leftlateral and with strikeslip components of 3035 cm overall and 4060 cm locally, demonstrating that the BaogunaoXiaohe fault is the seismogenic structure of the Ludian MS 6.5 earthquake. A large trench along the Xiaoyakou fault trough of the seismogenic structure opened, from which we identified four paleoearthquakes including the 2014 Ludian MS 6.5 earthquake and named them E1 through E4 from the oldest to the youngest. Eight charcoal samples were dated to constrain the ages of E1, E2 and E3 at 91908870 BC, 1000 BC900 AD, and 9101240 AD, respectively, and the youngest event E4 was associated with the 2014 Ludian MS 6.5 earthquake. This study illustrates that a 6.5 magnitude earthquake in the Yunan Region could produce surface rupture and leave its trace in the geologic record. Based on the surface rupture characteristics, image geometric discontinuity and the characteristic adelomorphic footprint of the paleoseismics found on the trench walls, it may conclude that the activity of the BaogunaoXiaohe fault was not very strong historically, and this fault represents a seismogenic structure of a moderately strong earthquake. Related Articles | Metrics

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Analysis of movement characteristics of the Longitudinal Valley Fault in eastern Taiwan, China based on GPS observations LI Haiyan,SHAO Zhigang,MA Hongsheng,WANG Peng,ZHANG Zhi 2018, 25(1): 240-251.  DOI: 10.13745/j.esf.yx.2017-2-38 Abstract ( 404 )   PDF (4632KB) ( 323 )   The Longitudinal Valley Fault is one of the faults with the most active dynamic action and crustal movement deformation in Taiwan, China. Its fault movement characteristic and strong seismic risk have been concerned by scholars. Using constraints from coseismic surface displacement and interseismic deformation observations between 1992 and 1999, this paper inverted the coseismic slip distribution of the 2003 Chengkung Earthquake (MW 6.8) and the interseismic slip characteristic of the Longitudinal Valley Fault. The results show that the northern Longitudinal Valley Fault was almost fully locked (locking fraction up to 0.9) to the depth of 27 km; the southern fault was partially locked (locking fraction ~0.5) with shallower locking depth (~12 km); and the locking fraction and locking depth in the central fault was between north and south. The epicenter of the 2003 Chengkung earthquake was near the transition zone between the creeping zone and the locked zone. Based on the coseismic slip distribution and interseismic slip characteristic results, and combined with the characteristics of historical earthquake fault rupture distribution, one can see that there was a difference in the form of fault movement between southern and northern Longitudinal Valley fault: the northern is mainly in the form of seismic slip, and the southern the form of seismic and aseismic slips. Since the 1951 HualianTaitung ML 7.3 earthquake sequence, the southern, central and northern faults have become capable of releasing the stored strain in a future MW 6.4, 7.0 and 7.4 earthquakes, respectively. In case of a cascading rupture, however, the accumulated strain under the entire Longitudinal Valley Fault can engender a MW 7.5 earthquake. Related Articles | Metrics

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Models for estimating carbon dioxide emission from coalfield fires and the study of the related key parameters CAO Daiyong,LIU Zhifei,YANG Guang,DU Xiaomin,DOU Xuqian,SONG Xianfeng,WANG Haiyan 2018, 25(1): 252-258.  DOI: 10.13745/j.esf.yx.2016-11-60 Abstract ( 278 )   PDF (2223KB) ( 236 )   It is the basis of emission reduction work to refine the list of carbon emissions. The aim of this study is to evaluate the carbon dioxide emission induced by coalfield fires in China. Based on coal oxygen complex action theory, two calculating methods based on “coal loss in combustion” and “gas emissions flux” were proposed with different research approaches. In these two carbon dioxide calculating methods, the parameters “discharge coefficient”, “emission factor α”, “emission flux” and “emission factor β” were explicitly defined; and then the approaches for acquiring these parameters were explained in detail: (1) “discharge coefficient” can be obtained from the experiment for simulating coal spontaneous combustion; (2) “emission factor α” can be obtained from the carbon dioxide adsorption experiment for surrounding rock and geological survey in coalfield; (3) “emission flux” can be obtained by the gas emission flux monitoring; (4) “emission factor β” can be obtained by the remote sensing interpretation with high resolution imageries. As a result, these two calculation models were used in the Wuda coal field to inspect whether the models can be used in actual operation. Related Articles | Metrics

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Evaluation of groundwater exploitation potentiality in the Hebei Plain based on Niche Theory YU Kaining,LIAO Anran 2018, 25(1): 259-266.  DOI: 10.13745/j.esf.yx.2016-11-58 Abstract ( 231 )   PDF (3244KB) ( 316 )   The groundwater exploitation potentiality evaluation, a part of the groundwater resources evaluation, is aimed at providing references for the groundwater management, planning and development. Traditional evaluation methods, using single indicator for evaluation, fail to take into account all the factors affecting the groundwater exploitation potential. Thus it is of great importance to develop a more comprehensive evaluation method and theory. The idea, that the spatial distribution and dynamic change of groundwater are not only affected by the socioeconomic development and exploitation technology, but also influenced by selfregulation, agrees with Niche Theory. In this paper, following a discussion on the definition of groundwater niche and its calculation formula and evaluation index system, the groundwater niche calculations, as well as analyses of groundwater niche clustering and exploitation potential were carried out in 9 cities in the Hebei Plain. The results were compared with those obtained using the traditional methods. As the results show, the evaluation method based on Niche Theory ranks the groundwater exploitation potential for the 9 cities, from high to low, as Tangshan, Xingtai, Handan, Baoding, Langfang, Hengshui, Shijiazhuang, Cangzhou and Qinhuangdao. Compared with the traditional methods, the two evaluation approaches yield similar ranking results with the exceptions of Baoding, Qinhuangdao and Langfang. The discrepancy demonstrates that the evaluation method based on Niche Theory, as described in this paper, is more comprehensive, scientific, rational and realistic. We believe Niche Theory will provide a new and may even be a paradigm shift in our approach for the evaluation of groundwater exploitation potentiality. Related Articles | Metrics

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Methodologies in calculating apparent background values of minor components in groundwater: a case study of the Liujiang Basin LIAO Lei,HE Jiangtao,PENG Cong,ZHANG Zhenguo,WANG Lei 2018, 25(1): 267-275.  DOI: 10.13745/j.esf.yx.2017-02-3 Abstract ( 288 )   PDF (4233KB) ( 367 )   Based on the extensive literature research of internationally adapted methodologies for the calculation of minor component background values, and after comparing and analyzing the relative strength of each method, a methodology combining hydrochemistry analysis and mathematical statistics was developed for the analysis of groundwater minor component apparent background values. Firstly, factor analysis was carried out on the minor and major components to establish their relationships. Next, the outliers of the major components were identified with the 3σ rule, and results were checked by using Piper graph, which was also used to determine macroscopically the obvious outliers of minor components related to hydrochemistry. Then the outliers of the minor components were identified by the iterative 2σ technique and probability graph method. Finally, the 95th percentiles for the outliereliminated data were taken as the apparent background values of the minor components. This methodology is useful in understanding the overall statistical characteristics, avoiding errors in threshold values due to subjectivity, and removing outliers efficiently. Comparing with the four frequentlyused mathematical statistics methods, this methodology, applied in the Liujiang Basin study, was shown to be more stable and reliable for calculating apparent background values of minor components, and able to explain the abnormal minor components and background constraints. The results show that the apparent background values of minor components in the Liujiang Basin shallow groundwater were 75.1, 27.4, 0.11, 0.30 and 0.32 mg/L for nitrate, metasilicic, acidaluminum, fluorine and bromine, respectively. The high nitrate value indicates that the extensive farming, husbandry and sewage discharge in the Liujiang Basin have inevitably influenced groundwater compositions in the area. Related Articles | Metrics

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A study of the impact of mining activities on the seepage of the dam and dam foundation of Yuecheng Reservoir WANG Zhuoran,WU Xiong 2018, 25(1): 276-285.  DOI: 10.13745/j.esf.yx.2017-02-4 Abstract ( 204 )   PDF (3217KB) ( 287 )    Yuecheng Reservoir belongs to the national key reservoir, while the reservoir area and the surrounding ground is a typical coalrich region, covering a large number of highquality coal resources. In order to study the impact of mining activities on the seepage of the dam and dam foundation, the dam was used as the research object and a safety limit in the upstream was set in this paper. By controlling the effective protection boundary of the dam and foundation, the impact depth and the impact degree of the mining on the shallow surface were controlled. The numerical simulation results showed that under the condition that the water level was 105.0 m upstream, 159.1 m downstream and the exploration impact distance was 2000 meters away from the dam, mining activities would not affect the permeability of the dam and the foundation. At the same time, it would not affect the permeability of the dam shoulder as well. Related Articles | Metrics

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Shear strength of unsaturated expansive soil during wettingdrying cycles. XU Dan,TANG Chaosheng,LENG Ting,LI Yunsheng,ZHANG Yan,WANG Kan,SHI Bin 2018, 25(1): 286-296.  DOI: 10.13745/j.esf.yx.2016-11-62 Abstract ( 416 )   PDF (2004KB) ( 285 )   Expansive soil is highly sensitive to climate change. Understanding the response of engineering properties of expansive soil under wettingdrying cycles is therefore significant for revealing the disaster mechanism as natural expansive soil is subjected to periodic evaporation and infiltration. In this investigation, a series of shear tests were conducted on unsaturated remolded expansive soil which was subjected to three wettingdrying cycles. The influence of drying process, normal stress and wettingdrying cycles on shear strength behavior were analyzed and discussed. The results show that (1) during drying, specimen stiffness, shear strength, shear strength parameters (cohesion and internal friction angle), failure brittleness and peak strength loss increase with decreasing water content, while the shear displacement decreases accordingly; (2) higher normal stress gives rise to higher shear strength as well as residual shear strength, but lower peak strength loses, and fracture toughness of the specimen increases generally with increasing normal stress applied during shearing; (3) the shear strength behavior of unsaturated expansive soil is significantly influenced by wettingdrying cycles, during which both shear strength and cohesion increase first and then decrease, and reach their peak values at the second drying path; however, the internal friction angle is slightly influenced by wettingdrying cycles; (4) after the specimens were subjected to multiple wettingdrying cycles, the shear characteristics are similar to that of over consolidated soil, and the specimen presents more brittleness at failure; (5) the residual shear strength seems to be independent of drying process and wettingdrying cycles as the obtained values are generally kept around 100 kPa; and (6) shear strength of unsaturated expansive oil during wettingdrying cycles is significantly conditioned by suction, microstructure and cracking development; it is necessary to combine unsaturated soil mechanics and soil science to make an accurate evaluation. Related Articles | Metrics

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Determination of multiring structure and analysis on the deep structure of the Lunar Mare Imbrium Basin WANG Qinglong,LIU Jianzhong,GUO Dijun,JI Jinzhu,LIU Jingwen,WANG Juntao,LUO Lin 2018, 25(1): 297-313.  DOI: 10.13745/j.esf.yx.2016-11-30 Abstract ( 218 )   PDF (3346KB) ( 263 )   The Imbrium Basin is the largest lunar near side and the most researched multiring impact basin on the Moon that a substantial amount of studies has been done on the boundary restoration of its multiring structure. But so far most scholars have not reached a consensus on the initial shape of the multiring structure and neither on the multiring position/quantity, basin size, etc. This paper used GRAIL Freeair gravity anomaly and LOLA laser altimetry data to carry out a multisource data integration analysis. The results show that the Imbrium Basin has a three ring structure with eccentric circles of boundary feature; the diameters of the three rings are 1500 km, 1100 km and 665 km, respectively from the outside to the inside. Based on the Euler inversion results, there are two fault structures at different depths pertinent to the tectonic movement properties and directions in the central Imbrium Basin. The two fault structures are named (1) the deep fault structure, which is gradually inclined and extends inwardly at the depth >40 km; and (2) the shallow fault structure, which is gradually inclined and extends outwardly at the depth ≤40 km. Studies on material composition combined with geophysical characteristics show that the geological tectonic evolution of the Imbrium area can be mainly divided into two stages. Stage 1: The gradually inclined and inwardly extended structure at the depth >40 km formed from the main evolution of the internal dynamic that is a magmatic condensation process in the early stage of the Moon（4.53.85 Ga); it provides a channel for the generation, differentiation and migration of deep magma in the early stage of the moon. This structure fault represents the tectonic evolution stage of the deep magma ocean of the Imbrium area before the Imbrium Basin impacted. Stage 2: The gradually inclined and outwardly extended structure at the depth ≤40 km formed from two kinds of equally significant geological dynamic evolutions of internal and external dynamic of lunar geological processes in the late stage of the Moon（≤3.85 Ga), it provides a migration path for the different stages of the basaltic magma eruption or overflow to the lunar surface. This structure fault represents the tectonic evolution stage of the mare magmatism of different stages of basaltic magma eruption，filling overflow of the Imbrium area in the late stage of the moon after the Imbrium Basin impacted. Related Articles | Metrics

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Mineralogy of Mare Frigoris ZHANG Xiaomeng,ZHANG Xunyu,CHEN Yuan,CAI Wei,LU Yu,WU Yunzhao 2018, 25(1): 314-324.  DOI: 10.13745/j.esf.yx.2016-12-38 Abstract ( 442 )   PDF (2040KB) ( 413 )   Mineral composition of mare basalt reflects chemical composition of magma source together with physical and chemical environments of the rocks formation, which is significant for both researches of origin and evolution of the Moon and exploitation and utilization of lunar resource.In this study, an elongated mare was chosen as our research area, and Moon Mineralogy Mapper (M3) hyperspectral data was applied to mineral spatial distribution.Mare Frigoris was mapped and characterized into 25 basalt units based on multisource remote sensing data including spectrum, terrain and elements abundance.We extracted 169 spectra curves of fresh craters from M3 hyperspectral image.Spectral parameters such as absorption center and absorption band area ratio were obtained through data processing.Mafic mineral variation of Mare Frigoris basalt was acquired by analyzing reflectance spectras absorption features.Basalt units in eastern Frigoris are older, with mafic mineral dominated by clinopyroxene containing lower CaO compared to returned lunar samples, which is similar to older basalt units in Mare Serenitatis and Mare Imbrium.Basalt units of western Frigoris and Sinus Roris are younger and rich in olivine.And the late stage basalts in Oceanus Procellarum and Mare Imbrium show the same feature too.These widespread olivinerich basalts suggest the uniqueness in the global evolution of the moon.Geographically speaking, Frigoris is an individual mare, but its source region may have connections with mares around in consideration of mineral differences between western and eastern Frigoris as well as mineral similarities with mares at the same location. Related Articles | Metrics