Abstract:

Abstract:The Guanghua Formation in Longjiang Basin deposited continuously and is exposed in integrity, with abundant fossils of Jehol Biota, making it one of the key sections to probe the origin, evolution and radiation of the Jehol Biota in the middle of Da Hinggan Mountains. This study carried out a precise measurement for the section of Guanghua Formation. It is believed that the Guanghua Formation conformably overlies andesitic welded tuff of the Longjiang Formation, with part covered unconformably by basalt of the Ganhe Formation. Three lithological units have been recognized from bottom to top. Systematic sampling and identification for corresponding biota fossils were carried out, and this has greatly enriched the biota category of Jehol Biota in the middle of Da Hinggan Mountains. Based on newly collected fossils and previously published data, authors established the assemblages of various fossils in the middle of Da Hinggan Mountains, which include limbs, ostracods, plant fossils, insects and others, and further discussed their characteristics. The LAICPMS UPb zircon chronology study of the lower to middle sections of Guanghua Formation reveals that the Jehol Biota in the Longjiang Basin occurred at time of 1254±14Ma to 1201±11Ma, with an span of roughly about 500 million years, reflecting that the Jehol Biota throve from early to middle Apter period. According to paleontological characteristics and our previous studies, it can be concluded that the paleoenvironment of the Jehol Biota in the Longjiang Basin may be the intermittent or seasonal lakes, and the paleoclimate should be in the warm and humid seasonallychanging warm zone, accompanied by the short term arid climate.

Abstract:Tibet is located in the QinghaiTibet Plateau and characterized by complex geological structure and new intense tectonic activities. Tibet hosts abundant geothermal resources, ranking the first in national reserves of geothermal resources identified. The QinghaiTibet Plateau undergoes frequent tectonic activities due to strong northsouth extrusion. Change of geological stresses resulted in formation of a series of structural belts. The observation station in Naqu of Tibet is placed on the secondary tectonic belt of BangongcuoNujiang deep faulting in the northern part of Tibet, which are controlled by both nearNWtrending faulting and NStrending faulting. Existing data show that new tectonic movement in the observation area was active, manifesting that the deep huge faulting is still active. To study the deep electric structure of the observation area, three magnetotelluric profiles were investigated to analyze spatial distribution features and formation mechanism of geothermal resources. The shallow strata of observation area are mainly presented by 1D/2D structure and deep strata by 2D/3D structure. 2D and 3D magnetotelluric data inversion were also performed, yielding 2D and 3D electric models of for 3kmdeep shallow strata. This study carried out 2D magnetotelluric inversion using continuous media inversion method and 3D magnetotelluric inversion using REBOCC 3D inversion code, and comprehensively interpreted 2D and 3D electric structures based on hydrogeological investigation results. Research results show that horizontal electrical gradient belt of 2D geoelectric structure in the observation area reflects a fault, with distinct feature of vertical layering; low resistance layers in the high resistance layers reflect a deep complex structure in the observation area; local high resistance bodies of 3D geoelectric structure represent active range of intrusive rocks and low resistance area reflects spatial distribution of geothermal resources in the observation area. Geothermal resources results from infiltration of surface rivers along secondary fractures, and therefore, geothermal activities are controlled by faulting structure.

Abstract:The deformation of Mw 66 Earthquake on Nov25, 2016 in West Kunlun Mountain was observed from two directions using by Sentinel1 SAR databased InSAR technology. Based on the tectonic background, this study obtained a centimeterscale 3D deformation field and then verified its accuracy through comparison with surface ruptures and focal mechanism of this earthquake. InSARbased deformation field provides some recognition for the coseismic deformation and neotectonic movement patterns. ①The differences of coseismic deformation manifests the extension of seismogenic fault along the piedmont of West Kunlun mountain, striking 104°, 70km long and dipping SSE, which are characterized by mainly normal slip with dextral strikeslip. ②The coseismic deformation covers an elliptic area of about 100 km long and 60 km wide, showing multiple centers and multiple directions, with hanging wall subsiding 10~15 cm, horizontal sliding 2~6 cm, and footwall sliding 8~14 cm and vertical deformation of only3~1cm. Vertical deformation of hanging wall and footwall presents tensile features of four quadrants, in agreement with results of strikeslip shearing. ③Coseismic deformation is dominated by mode of elastic rebound, that is, the longterm tectonic stress was the driver for uplifting and northward intrusion of this region, while the local geomorphologies, i.e. surface rupture and graben basin, were the result of elastic rebound. ④The persistent uplift in the NE margin of Pamir plateau and structural deformation of normal faulting by this earthquake has confirmed the synorogenic extension model of the Muji basin (ieKougur extension), rather than the result of NWtrending extension of rightslip Karakoram faulting activity.

Abstract:The SankuanggouZhuanghuhe area is located in the north of the Duobaoshan metallogenic belt in Heilongjiang Province, NE China. Tectonicmagmatichydrothermal activities in the area are complicated, resulting in the formation of Sankuanggou skarn type deposits and Zhuanghuhe hydrothermal vein deposits. This study investigated geochronological, petrograpic and geochemical characteristics of magmatite rocks in the Sankuanggou and Zhuanghuhe areas. Twoperiod magmatic rocks have been identified: Hercynian rhyolite in Zhuanghuhe (288 Ma~294 Ma) and Hercynian Granite porphyry in Zhuanghuhe (297 Ma~303 Ma), and Yanshanian granite in Sankuanggou (172~179 Ma) and quartz diorite in Zhuanghuhe (165~176 Ma). Oreforming magmatic rocks in the SankuangouZhuanghuhe area are high Si and Al, alkalirich typeI granite, and enrichment of LILEs (such as Rb, Sr, Ba, and K), and depletion of HSFEs (such as Nb, Ta, and Ti), with distinct fractionation of HREE and LREE, and δEu loss. This study suggests that rhyolite and granite porphyry in Zhuanghuhe formed in active continental margin and was the result of subduction of the paleo Asian Ocean in the Hercynian period. The Yanshanian granite in Sankuanggou and quartz diorite in Zhuanghuhe are related to mineralization and enrichment, and the mineralization in the two areas was closely related to the subduction of the paleo Pacific in Yanshanian period.

Abstract:The Hongqiling magmatic NiCu sulfide deposits are situated at the southern margin of the eastern section of the Xing’anMongolian Orogenic Belt. Over 30 mafic and ultramafic intrusions consisting mainly of peridotite, pyroxenite and gabbro crop out in the mining area. This paper analyzed the nature of parent magma, and PGE depletion and tectonic setting of these orebearing maficultramafic intrusions of the Hongqiling intrusions using geochemical study of major elements, trace elements and PGE. Analysis of major elements and trace elements shows that the Hongqiling intrusions are characterized by high MgO (2875%) and low TiO2 (044%), enrichment of light rare earth element (LREE) and depletion of high field strength elements (HFSE), as well as extremely low ΣPGE（averaging 208×10-9）and high Cu/Pd（averaging 2916×103）. These features suggest that they have the same magmatic source. Based on olivineliquid equilibrium and mass balance, the calculated compositions of the parental magma for the Hongqiling NiCu Sulfide deposit is a high Mg basaltic magma with MgO of 1074% and FeO of 778%, respectively. Immiscible separation of sulfides likely resulted in extremely loss of PGEs in the Hongqiling orebearing intrusions during early evolution of parental magma of the Hongqiling intrusions. Combined with the evolution history of the eastern segment of the Central Asian orogenic belt, it can be concluded that the Hongqiling intrusions formed in the late Triassic postcollisional extensional environment, with formation of the deposits affected by the slab breakoff after subduction of the Ancient Asian ocean.

Abstract:Urad Middle Banner (Wulatezhongqi) in Inner Mongolia is tectonically located in the northwestern margin of North China Craton, belonging to the LangshanBaiyan Obo epicontinental rifting. Regionally, maficultramafic intrusions are distributed discontinuously along central Inner Mongolia, forming a 400kmlong, 30kmwide magmatic belt. This belt hosts lots of CuNi (PGE) deposits/ occurrences, with the smallmedium sized Kebu CuNi deposit occurring in the Kebu massif. The Kebu massif, cropping out over an area of 45km2, consists of gabbro and olive facies. The gabbro facies is dominant litholgical facies for massif, whereas the olive facies hosts the main orebodies. The two facies occur together and present a transition relation. In this study, LAICPMS UPb dating of zircons yielded an age of 2581±18Ma (MSWD=23) for the Kebu plagioharzburgite, suggesting a Late Permain magmatic event. Geochemical analysis results show that the maficultramafic rocks from the Kebu massif belong to the tholetiitic series. These rocks are relatively enriched in large ion lithophile elements (eg. Rb, Sr, Ba,) and depleted in high field strength elements (eg. Nb, Ta, Zr, Hf, Ti), with rightinclined REE distribution pattern and (La/Yb)N value of 247~1129. According to the Fo and Ni values of olivine which contains the highest Fo, MgO and FeO contents of parent magma were estimated to 101% and 121% respectively, indicating that the parent magma of the Kebu intrusion is a highMgO tholetiitic basalt. The comprehensive analysis shows that the Kebu maficultramafic intrusion might form in the postcollisional tectonic setting, with magmatic source consisting of asthenospheric material and mantle wedge material, both of which were contaminated by previously subducted fluids. Crystallization fractionation of Fe and Mgrich minerals (such as olivine and pyroxene) and contamination of Sirich crust material might have played a key role in Ssaturation and subsequent sulfide segregation.

Abstract:Detailed field work helped identify threedifferent assemblages of rocks occurring in the Hebukesaier ophiolitic mélange in the northern region of West Junggar. They are typical ophiolite unit mainly consists of metamorphic peridotite, gabbro, diabasic dike, basalt and chert; ocean island unit mainly consists of OIB, which coexists closely with silicolit, silica mudstone and limestone; and postcollision volcanic rock unit is mainly metarhyolite. Gabbro and diabase in ophiolite are characterized by slight enrichment or depletion in light rare earth elements and low (a/Yb)N ratios of 054~318, no obvious Eu anomalies, indicating that both are of EMORB and NMRB characteristic. The ocean island basalt shows relatively high contents of Al2O3 (366%~1583%), TiO2 (262%~315%) and Na2O+K2O (571%~7%), and displays an obvious rightleaning pattern with a high content of rare earth elements. Metarhyolites exhibit relatively high SiO2 and K2O contents, and extremely low MgO, CaO and MnO contents, enrichment of incompatible elements (K, Rb, Th, U and Pb), obvious depletion of Sr, P and Ti, and weak depletions of Nb and Ta. Geochemical characteristics indicate that metarhyolites may be formed in a postorogenic extension setting. LAICPMS UPb 〖JP2〗dating on zircons from metarhyolite yieldes a weighted mean 206Pb/238U〖JP〗 age of 435±2 Ma. Metarhyolites cut through or intruded different units of ophiolite (peridotite, diabase and basalt), suggesting that the Paleoocean basin of Hebukesaier ophiolite had been closed before late Early Silurian.

Abstract:Weijing compound granite of Hercynian to Yanshanian periods, located at the SinoMongolia boundary, belongs to the results of the extension of crust thickening subsequent to closure of the MongolOkhotsk Ocean. Apatite fission track age of the Weijing granite ranges from 767 to 538 Ma. Based upon the thermal simulation, the Weijing granite undergone a rapid uplifting and denudation event during the Late Cretaceous, but was in a very stable lowspeed denudation setting without obvious tectonic event during the whole Cenozoic period. The Late Cretaceous tectonic thermal event which the Weijing granite experienced corresponds to the angular unconformity between the Early and Late Cretaceous in its northern and eastern faulted basins (such as Erlian, Haila’er, and Songliao basins), which represents a tectonic inversion events. Due to the fact that the northern margin of North China Craton (NCC) was affected by the tectonic thermal event, this event might be closely related to the rapid subduction of the Izanagi Plate into the East Asian continent. Combined with low temperature thermal chronology data, the Late Cretaceous tectonic event might influence the west of Weijing granite and east of the Mandula area. Thermal simulation results demonstrate that the Weijing granite denudates at a speed of about 01 to 02 mm/a. Present topography of the eastern part in the northern margin of the North China has taken a shape likely since the Cenozoic, but not during early or middle Mesozoic. Study of uranium mineralization indicates that a largescale mineralization occurred in both mudstones of the upper Cretaceous Erlian Formation and sandstones of the lower Cretaceous Saihan Formation in the Erlian basin. All these uranium mineralization followed uprising event of the western margin of the basin in the late Cretaceous, and uranium in the Ubearing oxide fluid, leached from the Ubearing Weijing granite, migrated continuously into the orebearing mudstones and sandstones. Hence, uplift and denudation of the Weijing granite is an important factor controlling uranium mineralization in the basin and the timing of uplift is basically consistent to uranium mineralization in the Erlian basin.

Abstract:Discovery of theUpper Ordovician in the North China Craton and determination of its geological time has received considerable concerns. By verifying the previous records of conodont and graptolite in the top part of the Ordovician carbonate sequences at different localities, this study defined top of the Taoqupo Formation in Yaoxian County within the closure position (44973 Ma, the early Katian) of graptolite Diplacanthograptus spiniferus Biozone. This position represents the highest sequence of the Orvocician in North China. However, The Stratigraphic Chart of China (2014) placed the top of the Taoqupo Formation around the division line between Qiantangjiangian and Hirnantian Stages (4456 Ma), with the latter slightly higher than the end position of the graptolite biozone. The difference is evident and needs absolute age data. This study found one layer of bentonite at the lower part (about 5m to the bottom) of the Taoqupo Formation in Yaoxian. Geochemical data of bentonite samples reveal that they are potassiumrich feature (K2O＞Na2O), with K2O content of 381% close to the average value (475%) of 17 Ordovician bentonite samples from the southern margin of the Ordos Basin. Zircon LAICPMS UPb dating shows that the bentonite bed emplaced at 4537±33 Ma (MSWD = 025). Considering sampling sequences and relatively quick sedimentary rate of the limestone, it can be concluded that the bottom of the Taoqupo Formation is at 454 Ma (late Sandbian Stage). The age obtained in this paper is consistent with the previously obtained data, with deviation within the error range, indicating that the age in this paper is credible. Therefore, the bottom boundary of the Taoqupo Formation in The Stratigraphic Chart of China (2014) should shift downward appropriately.

Abstract:The Lianzigou gold deposit is an integral part of the Jialu gold orefield in the Xiaoqinling region, with orebodies occurring mainly within highly metamorphic gneiss of the Qincanggou Formation of the Archaeozoic Taihua Group. The orebodies occur as veins and are controlled by the NEtrending structural fracture altered zone, with the trending direction parallel to NEtrending major faulting. On both sides of orebodies are the alteration zonation characterized by potassicsilicification, sericitizationsilicificationpyritization, chloritizationepidotization from core to the rim of the orebodies. The H and O isotopic compositions show that oreforming fluids comprised mainly mixture of magmatic water and meteoric water. HeAr isotope results demonstrate mixing feature of crustal and mantlederived components. The sulfur isotopic compositions in sulfides indicate that ores are characteristic of enrichment of light sulfur, which maybe result from sulfur isotope fractionation during the process of mineralization. The ore lead isotopic compositions are relatively homogeneous, suggesting a possible source of the Taihua Group (wallrock) for lead in ores. The H, O, S and Pb isotope compositions indicate the waterrock interaction during mineralization. The early K+rich alkaline oreforming fluid mixed with the shallow fluid and then fully reacted with the wall rock to exchange materials and energy through waterrock reaction, generating potassic alteration zone in the wall rock. With mineralization continuing, the oreforming hydrothermal fluids changed physicchemical conditions and carried Au to migrate in the forms of Au(HS)2- and Au(HTe)2-, finally resulting in precipitation and enrichment of gold in a more favorable environment.

Abstract:The middlelate Early Cambrian represents a key point in the history of life. Marine facies carbonatic rocks of the Lower Cambrian Longwangmiao Formation in east Chongqing preserve the record of coeval seawater carbon isotopic change. Based on carbon isotopic data which are preserved effectively in seawater, analysis about 61 samples of carbonatic rocks shows valid δ13CVPDB values of +27‰ to -43‰, presenting a trend from decreasing to increasing. δ13C values in the middle to lower part of the formation shows big shifting, with frequent occurrences of positive and negative carbon isotope excursions, which correspond to positive (~4‰) and negative excursion (~5‰) globally. δ13C values at the upper part fluctuated slightly, but generally in a positive way. The carbon isotopic compositions of the Longwangmiao Formation varied with sea level change, tempestites and (or) biological evolutions. At the earlymiddle stage of the Longwangmiao Formation, frequent fluctuations of sea level and voluminous involvement of terrestrial clasts resulted in extensive development of tempestites. Worse stability of sea environment and progressive decrease of biodiversity led to decreasing of sea productivity and frequent fluctuation of carbon isotopic compositions and multiple δ13C negative excursions. During the middlelate stage of the Longwangmiao Formation, longterm slow rising of sea level and low development of storm deposition formed a stable oceanic environment and resulted in increasing biodiversity, which improved primitive productivity and caused even distribution of carbon isotope with most δ13C positive. The rapid negative excursion of δ13C values in carbonatic rocks in the eastern Chongqing area might attribute to deposition of tempesite in a shallow water setting with relatively abundant terriestial clasts.

Abstract:In this study,we carried out an REE geochemical study of lowermiddle Silurian organicrich bedded cherts and underlying Sinian volcanic rocks in the regions of northern Ruoergai (Zoigê) County in Sichuan and Diebu (Têwo) County in Gansu, central China. The aim of this study was to understand the origin of rare earth elements in hydrothermal cherts and factors affecting REE patterns, and establish a corresponding model. 28 samples of cherts from one drilling core and two profiles were studied using petrographic analysis, scanning electron microscopy (SEM) analysis, major and rare earth element analyses. 14 samples of volcanic rocks from one profile were investigated using major elements and REE analyses. Petrographic and SEM analyses of black hydrothermal cherts show that the black cherts have typical features of deposition structure and weak latestage metamorphism. The TAS diagram of lower Sinian volcanic rocks suggests that they are dominantly felsic volcanic rock, with minor being mafic volcanic rocks. Combined with previous results, comparison analysis of underlying Sinian volcanic rocks and overlying middleearly Silurian hydrothermal siliceous rock draw the following conclusions. (1) Tensional tectonic setting is an essential dynamic factor for formation of hydrothermal chert, REEs of which mainly derived from hydrothermal fluids, ancient seawater (mixed in continental matters). (2) Relative abundances of the REEs in hydrothermal cherts have a threshold, below which LREEs’ distribution pattern is consistent with that of hydrothermal fluids while HREEs’ distribution patterns consistent with that of underlying volcanic rocks; and above which LREEs’ distribution presents the characters of mixing of hydrothermal fluid with ancient water (terrestrial material). The LREE patterns of hydrothermal cherts are consistent with that of upper crust, while HREE patterns are consistent with that of underlying volcanic rocks. Therefore, hydrothermal chert deposited in a certain condition can indicate paleodepositional structure environment.

Abstract:Researchers at both home and abroad divide mica minerals into two or three categories, which are named highAl, mediumAl and lowAl sericites based on wavelength of spectral AlOH absorption. Although some concern was paid on their minerageny, no systematic specific study has been carried out. With CASI/SASI airborne hyperspectral data obtained for the Xuemisitan area, and based on implementation of mineral mapping, a systematical comparison study was conducted on origins of highAl, mediumAl and lowAl sericites. Based on field geological observation and sampling in the Xuemisitan area, this study analyzed samples of three kinds (highAl, mediumAl and lowAl sericites) of altered rocks using hyperspectal measurement, AlOH absorption wavelength calculation and statistics, microscope observation of thin section, X ray diffraction of bulk rock, and X ray diffraction of clay minerals. In combination with fluid metallogenic theory and minerageny, this study also analyzed their forming mechanism. The results show that highAl sericite underwent intensive alteration and altered minerals of mica include sericite and illite, accompanied by pyrophyllite and finegrain quartz. By contrast, lowAl sericite underwent medium alteration, and altered minerals are dominantly illite and andreattite, and more chlorite, with minor laumonite. HighAl sericite altered rocks contain relatively higher contents of quartz and clay, but relatively lower contents of Kfeldspar, plagioclase and calcite than that of the lowAl series. LowAl sericite altered rocks contain low contents of quartz and clay, but relatively high contents of plagioclase, Kfeldspar and calcite. Combined with detailed mineralogy studies, this study concludes that the highAl sericite identified by hyperspectral may form in the hydrothermal fluid environment with comparatively high temperature and slight acid and the lowAl sericite formed in fluid environment of comparatively low temperature and slight alkaline. This understanding is of great significance for application of hyperspectral mineral mapping information and interpretation of deep exploration information.