Abstract:Several decades of geological investigations and specific research in southern China have greatly deepened our understanding of the Pre Devonian tectonics of Southern China as follows. ① In southeast China, the metamorphic rocks, overlain unconformably by the Devonian sediments, host graptolites, trilobites and Brachiopoda, suggesting the rocks are Neoproterozoic to early Paleozoic in age, and the metamorphic rocks in the Wuyi Yunkai area, such as the Chencai and Dikou complexes with metamorphic ages of 460~440Ma, are proved to be the products of the Caledonian orogeny rather than of the pre Sinian orogeny. Therefore, South China is not a pre Sinian Cathaysia old land, but a Caledonian orogen. The high grade metamorphic rocks in the Wuyi Yunkai area, which underwent the severest tectonism and magmatism in the South China orogen, might be the rock for the orogen. ② During the pre Devonian, Southern China was divided into three tectonic units: the South China Sea platform (Indochina South China Sea platform), the South China orogen and the Yangtze paraplatform. During the Neoproterozoic, the South China orogenic belt was characterized by volcanic and volcaniclastic rocks, and by terrigenous clastic rocks in early Paleozoic but no reliable ophiolitic suite recorded. The Nd model ages and inherited zircon ages for widespread granites in the South China orogen suggest the Archean to Proterozioc in age, illustrating that there should be an ancient continental crust beneath the orogenic belt. Lithofacies paleogeographic research shows that terrigenous clastics of lower Paleozoic rocks in South China were derived from the South China Sea platform. And biostratigraphic and tectonic studies indicate a transitional relation between the Yangtze paraplatform and the South China orogen. It can be inferred that the Yangtze paraplatform, South China orogen and South China Sea platform should belong to one continental plate, the Southern China plate. ③ The latest isotopic dating indicates that the Shuangqiaoshan, Sibao and Lengjiaxi groups are the Neoproterozoic metamorphic rocks rather than the Mesoproterozoic ones; that is to say, they resulted not from the Greville orogeny (1300~1000Ma), but from the Sibao or Wuling orogeny (820Ma). Therefore, southern China should be part of the Gandwana continent rather than part of Rodinia supercontinent.

Abstract:Regional thrust systems have been discovered along the Lung’erni Angdarco belt of paleo oil reservoirs in the southern Qiangtang Basin. The Jurassic oil bearing dolomite and marine hydrocarbon source rocks thrust southward along gentle dipping faults over the Upper Cretaceous red beds in the eastern and western Beileico, northwestern Lung’erni, southeastern Bilogco Lake and surrounding areas of the Luxungco Lake, and the Middle Jurassic oil bearing carbonate and clastic sedimentary rocks thrust southward over the Triassic dark clastic rocks in northwestern Angdarco Lake, which formed variety of thrust sheets, thrust slices, nappes and structural windows. High resolution 2D seismic reflection profile reveals duplex thrust systems at different depths occur in the Lung’erni Angdarco paleo oil reservoirs. The oil bearing dolomite of the Middle Jurassic Buqu Formation in Bilogco moved southward along the upper duplex thrust for about 7~11 km and 12~15 km, resulting in the formation of the Lung’erni and Deruri palaeo oil reservoirs. The underlying Triassic and Carboniferous Permian sheets thrust in a large scale from north to south along lower duplex thrust, with frontiers of the thrust offset by the northward thrust faults. Field observation indicates that many thrust sheets and nappes of Jurassic limestone and dolomite occur in the transition zone between the paleo oil reservoir belt in the south of Central Qiangtang Uplift and the oil seepage zone in the north of Central Qiangtang Uplift. The explanation for the deep seismic reflection profile further suggests that the Triassic and Jurassic marine hydrocarbon source rocks in the northern Qiangtang Basin thrust southward over the Central Qiangtang Uplift to form the Middle Jurassic oil bearing dolomite and paleo oil reservoirs in the Beileico and Luxungco Lakes, southern Qiangtang basin. It can be inferred that uplift of the oil bearing dolomite and Jurassic hydrocarbon source rocks caused by regional southward thrust in the Late Cretaceous Early Tertiary led to formation of the Lung’erni Angdarco paleo oil reservoirs.

Abstract:Based on comprehensive analysis of the structure and coal hosting features in coal fields, in addition analysis of the typical structural profiles in the northwest、northeast、east and south of Junggar Basin, ascertained the basic structural pattern as follows: Firstly, the existing tectonic framework of Junggar Basin was finalized during the middle to late period of Himalayan movement. Chronically in the nealy south north compress stress field, showing alternating depressions and uplifts、belts in S N and blocks in E W in general; Secondly, intense structral deformation around the basin margin but gradually weak and shallow in the center, showing concentric ring shape structure on the whole, revealing the dynamical、kinematical and geometrical features controlled by orogenic belts around the basin and stress field from edge to inside; Thirdly, the large scale coal accumulation occurred in the extension/weak compress tectonic stress field during early middle Jurassic epoch; Fourthly, the thrust belts around the basin maybe the potential prospective areas for coal resource exploration and exploitation.

Abstract:The Tian Shan is characteristic of typical intra continent activities and hosts one thrusting zone in the southern margin of Junggar basin. The thrusting zone presents mainly as several rows of anticline and thrust fault which are parallel to trending of the maintains. Field investigation and mapping show that one thrust fault was developed within the core of the Manasi and Tugu anticlines and one thrust fault in the north wing of the anticline, both of which resulted in the formation of stream terrace deformation and fault escarpment. Drilling data, along with seismic data, show the existence of several north trending thrusting faults in the Manasi anticline, and the north wing and core of the Tugu anticline, and of hidden Dongwan anticline beneath these faults and syncline between the Qingshuihe and Qigu anticlines. Interpretation of ETM remote data and 2D seismic data indicates that the Dongwan anticline was an active superimposed dural thrust structure, which resulted in a series of out of sequence thrusting imbricated faults developed shallowly in the Qinshuihe and the Qigu anticlines. The seismic interpretation for growth and stratum unconformity also suggests that the buried Dongwan anticline is a synchronous duplex and ‘out of sequence’ thrust fans was mainly formed from late Miocene to present. We follow the Boyer’s synchronous thrust model to interpret the structural styles of the South Junggar thrust and fold belt which differs from a relatively simple hinterland to foreland (piggy back) progression of thrusting, in which older thrusts were assumed to become deactivated as new thrusts propagated toward the foreland. The mode of synchronous thrusting indicates that during the development of dual thrust structure triggered by deep sequential thrusting, the synchronous thrusting in the subsurface can produce out of sequence thrusting at the surface, similar to imbricated thrust fault.

Abstract:The Daba Shan region with its unique tectonic setting and rich petroleum resources is attracting people’s interest to conduct much in depth research. Based on the finite difference method and the elastic plastic constitutive model with two dimensional plane strain, this study carried out a series of numerical simulations for the Daba Shan foreland and thrust belt. The results show that the foreland area has the relatively weak detachment in the Lower Middle Triassic which includes gypsum and salt, which led to the main decollement surface transferring from the lower stratum in hinterland into the higher stratum in foreland. The distribution of Lower Middle Triassic detachment and syntectonic sedimentation put limitation on the position of the Zhenban Thrust, through which strong shortening strain in the hinterland was transmitted from basal detachment of lower Sinian into higher detachment of Lower Middle Triassic. Long term activity of the Zhenba thrust and Chenkou thrust might have accommodated more than half of total shortening strain of the Daba Shan foreland and thrust belt. After syntectonic sedimentation, the shallow Jura type folds in the foreland area propagated forward while those old faults in hinterland continued to thrust and rotate clockwise, thus forming an out of order thrusting sequence. Propagation of the main thrusts, which is different from classic piggyback mode, has shortening strain resulting from subduction of the footwall of main fault deeply into the backland. The simulation results are similar to the geological prototype of the Daba Shan foreland and thrust belt, illustrating that using finite difference software to simulate geological structure is feasible.

Abstract:With the objective of understanding the seismic sequences, styles, evolution and control factors of Cambrian platform slope system in the Tahe oilfield, northern Tarim, this study discusses the origin of platform, forming environment of unconformities, and marine source rocks using high precision three dimensional (3D) seismic data of secondly acquisition and comprehensive interpretation of the conventional 3D seismic and drilling data. Sixteen seismic sequences have been identified in the Tahe oilfield. SQ6, SQ7 and SQ11 are developed with LST, and other sequences consist of TST and HST, characterized by asymmetrical cycles with quick transgression and slow regression. Cambrian carbonate platform in the Tahe oilfield generally presents a large progradational platform with features of longitudinal aggradation, eastward overlap and eastward migration of platform margins successively. The platform margin migrated more than 40 kilometers from west to east. Cambrian carbonate platform originated from the north slope of the Tazhong uplift, experiencing the evolution of ramp, flat topped shelf and rimmed shelf platform. Initial topography, relative sea level changes, extension activities, basement subsidences and paleoclimate played different control roles in different evolution stages, and paleoclimate and wind direction also played remarkable control role in the development of Middle Late Cambrian rimmed shelf.Regional unconformities were developed within the top surfaces between Xiaoerbulak Fm. and Cambrian, and also in the shelf edges of middle Cambrain Shayilik Fm. and Awatag Fm. in Middle Cambrian, respectively. All these unconformities formed in a tensional environment. The Cambrian marine hydrocarbon source rocks in the Tahe oilfield are well developed, especially with the Yuertus Formation distributed throughout the region, and the slope basin source rocks of Wusongger Fm., Awatag Fm. and Upper Cambrian are distributed in the eastern Tahe oilfield.

Abstract:The Kaladawan area of Altun Mountains is located in the central segment of the Hongliugou Lapeiquan structural belt, which is bounded by the NE striking Altun strike slip faults to the north and the E W trending northern Altun fault. The area is widely developed with volcanic sedimentary rocks, which were determined to be Mesoproterozoic in age by previous studies. In this study zircon SHRIMP U Pb dating for the intermediate felsic volcanic rocks from the volcanic sedimentary rocks was conducted and yielded an age of 477~485 Ma, which confirms the existence of intermediate and felsic magmatic activity in the Kaladawan area during early Paleozoic. Petrogeochemical study also indicates that the volcanic rocks reflect the tectonic setting of active continental margin (Island arc) and magma source is characteristic of I type and I S transition type. In combination with dating and tectonic setting tracing of the ophiolitic mélange, high pressure metamorphic mudstone, eclogite, intermediate felsic intrusive rocks in the Hongliugou Lapeiquan structural belt, the authors suggest that the intermediate felsic volcanic rocks in the Kaladawan area are related to a tectonic setting of active continental margin (Island arc) and the age is roughly consistent with the final phase of ophiolitic mélange, representing that the syn collision intermediate felsic volcanic rocks resulting from the subduction of oceanic crust process. The Hongliugou Lapeiquan structural belt can be divided into 3 evolutional stages: ①a period of oceanic crust expansion in the Late Proterozoic Cambrian (the age of ophiolitic mélange is 510~580Ma and the expansion was slightly earlier); ②a period of subduction collision of oceanic crust plates in Early Ordovician Middle Ordovician early (the age of intermediate acidic volcanic rocks (including intrusive rock and volcanic rock) is 477~488Ma, part of granite has an age of 467Ma and high pressure metamorphic rocks of regressive metamorphism age is 479~491Ma); ③a period of post collision to extension in Late Ordovician Silurian (the ophiolitic mélange metamorphic basement is 450～455Ma in age, which represent final emplacement of ophiolitic mélange, and collision and post collision S type granite has the age of 417~431Ma, which shows the post collision to extension settings).

Abstract:It has long been regarded that the only Early Paleozoic occurs in North Daba Mountain, but this idea may be challenged. The Taohekou Formation in North Daba Mountains is a volcanic sedimentary succession which preserves relatively complete sedimentary records. Detrital zircon U Pb ages from sandstone collected at the same position were measured by the LA ICP MS method in this study. 62 sets of age data were obtained for the samples 12YMN1 and 12YMN11, which have redefined the formation age of the Taohekou Formation and provided constraint on the evolution of early Paleozoic tectonic in North Daba Mountains. The ages of 11 young zircons indicate that the Taohekou Formation deposited no earlier than Early Devonian. The concordant ages of detrital zircons show that the Taohekou Formation was sourced mainly from trachyte, intrusive rocks and basalts with time range from 407Ma to 434Ma. The age and CL images for magmatic detrital zircons indicate that there occurred three stage magmatism, that is, Early Silunian, Middle Silunian and Early Devonian, corresponding to the intrusive rocks at 431~439Ma, trachyte of the Banjiuguan Formation at 4269Ma, and basalts of the Taohekou Formation at 4143Ma, respectively.

Abstract:The geochemical analysis of the amphibolite in the east of Qikeshan indicates it belongs to tholeiitic series with high SiO2 and Al2O3 contents of 46.99%~51.01% and 13.85%~15.82%, MgO and FeOT contents of 7.00%~7.71% and 12.4%~13.5%. Diagrams of MgO vs. SiO2, Al2O3, CaO and FeOT, Cr vs. Rb and Rb/Nb vs. Rb/Zr exhibit that partial melting and fractional crystallization has occurred in the magma evolution. And the slightly enrichment of light rare earth element (LREE) implies the magma has experienced a 10% to 20% of partial melting and low fractional crystallization. Zircon Lu Hf isotopic data reveal that the protolith was from the mantle derived magma which was slightly differentiated from the chondrite, and the liquid temperature of the magma was 1175~1251℃. Microanalytical dating shows the protolith has an age of 718±22Ma with a metamorphic age of 502±14Ma. The new data and previous studies indicate that the protolith was not the product of the Neoarchean Era, but formed in the expansion period after the assembly of the Neoproterozoic Rodinia supercontinent, and experienced the peak metamorphism of early Paleozoic South Altyn, revealing that the original ancient Tethys was closed in 502±14 Ma.

Abstract:The large Penglai 9 1 oilfield in the Bohai Bay Basin is the first discovered buried hydrocarbon reservoir of the Mesozoic granite. The geochemical characteristics and origin of the rocks provide important clues for the mechanism of Mesozoic tectonic environment of and continental crust growth of Bohai Bay Basin. A new age of 164±2 Ma was obtained for the Penglai 9 1 granitic pluton by LA ICP MS, and represents the formation age of the pluton consisting mainly of quartz monzodiorite，granodiorite and monzonitic granite．The study of major elements shows that the ω（SiO2）=6222%~7086%,ω（K2O）=329%~436%,ω（CaO）=171%~410%, AR=213~306，A/CNK=089~107, indicating that the pluton belongs to I type granite of high k calc alkaline series. The chondrite normalized REE patterns show a right dipping mode, enrichment in LREE and LILE, depletion in HREE and HFSE. The geochemical characteristics of the subduction zone components (SZC) display its close relation to the source region of magma. The granite is characterized by high contents of Sr, Sr/Y and La/Yb, and low contents of Y, Yb and Mg#, showing characteristics of adakite rock resulting from partial melting of thickening lower crust．The R1 R2 discriminant diagram and (Y+Nb) vs Rb tectonic diagram reveal that the granite was formed in the post collisional expansion stage. In conclusion, the Penglai 9 1 granite pluton were formed by partial melting of lower crustal materials including subduction materials in the crust thickening background due to the postcollisional extension. Its formation marks that the main collision of the Mesozoic continental convergent collision in the Bohai Bay basin had ended and entered post collisional extension stage from the compression of the main collisional stage during the period of 164 Ma, providing new evidence to further determine the Mesozoic continental collision process in the Bohai Bay basin in detail.

Abstract:The Xiangshan volcanic basin comprises volcano intrusive complexes that are composed of tuff, rhyolite dacite, porphyry rhyolitic dacite, porphyroclastic lava, coarse grained porphyry and porphyritic granite. The paper discussed the origin and evolution of these igneous rocks based on their whole rock major and trace elements, as well as Pb Sr Nd isotopes. Different lithologies have similar elemental and isotopic compositoins, indicating that they were derived from the same source region. The rocks are rich in silicon and alkali, low in calcium and magnesium. LREE and HREE differentiate significantly, REE distribution curve presents four component model and obvious negative Eu. Nd model ages(T2DM) of rhyodacite, Porphyroclastic Lava, rough spots granite porphyry and porphyritic granite is closer, respectively 167Ga, 166Ga, 166Ga and 163Ga, slightly lower than the residual zircon 207Pb/206Pb age (17879Ma) and the the oldest rocks exposed (amphibolite) of Cathaysian Block within the magmatic zircon SHRIMP U Pb age of (1766 ± 19Ma). There is a negative correlation between SiO2 and P2O5, combining the facieology and the two element mixed mode petrography of Sr Nd, calculating that the material source of the complexes has a small amount of mantle source involved, the average content of 2282%.; each sub cycle between the different rock types with diagenesis sequence, Na2O and K2O increased, but SiO2 content decreased gradually, may indicate that the magma has occurred in the differentiation of normal. acidic component is on the upside, and the partial distribution of basic components at the bottom, at the end of the first sub cycle or timeout period, acidic component join in the magma. The first subcycle variation degree is strong, the separation of plagioclase and potash feldspar, at the second sub cycles, mainly potassium feldspar. At the late Yanshan, Jiangxi in the dynamic background of the earth is different, gradually evolved into intra plate rift trend from south to north. In 141Ma~132Ma the Xiangshan area is post orogenicr, in the vicinity of 125Ma gradually evolved into an intraplate rift environment.

Abstract:The volcanogenic claystone, deposited globally, especially around the Tethyan Realm in the Permian Triassic Boundary (PTB), plays a significant role in understanding the triggering mechanism and associated geological events for the Latest Permian Mass Extinction (LPME). Here, we present research of claystones around the PTB on mineralogy, petrology and geochemistry, which has filled the blank in this area. The results show that the components of the PTB claystone are composed mainly of volcanogenic clays (illite, etc.), and phenocryst minerals (such as quartz, calcite, pyrite and magmatic zircon). Their geochemical compositions are characterized with high K2O and low Na2O, relative enrichment in Large ion Lithophile Element (LILE) and depletion in the High Field Strength Element (HFSE). All the features of the PTB claystone mentioned above suggest that the claystones are volcanogenic kalibentonite with protolith being intermediate felsic rhyodacite and source background of arc type magmatism. Compared with other PTB claystones found in other areas in South China, it can be inferred that all the PTB claystones have similar genesis and likely derived from felsic magmas eruption triggered by either continental collisions around paleo Tethys Ocean or subduction of Panthalassic Ocean along eastern margin of the Pangea Continent including South China plate, and characterized by multiple episodes. These intense volcanic activities in a global scale including the volcanism associated with extensive distributions of the PTB claystones may act as key causes responsible for the Latest Permian Mass Extinction

Abstract:Groundwater salinization is attributed either to evaporation, dissolution or mixing. Seawater intrusion falls into the latter, i.e. mixture of fresh groundwater and seawater, which implies this mixture occurs not only in the dissloved salts but also in water molecules. To confirm the occurrence of mixing, it is important to make sure that both the solvent and solute have undergone the same degree of mixing. Note that besides seawater intrusion, fresh groundwater salinization may also be attributed to evaporation and (or) dissolution. In this study, by employing both the inert (δD, δ18O, Cl- and Br-) and reactive (major and minor elements) tracers, we analyzed these chemistry data of groundwater samples collected in Laizhou Bay to identify seawater intrusion. Samples were collected from coastal aquifer of south Laizhou Bay, including 6 in Laizhou city, 10 in Longkou and 9 in Shouguang. The sediments of Laizhou and Longkou mainly consist of silicate clasts, while Shouguang is mostly covered by carboantes, which are supposed to be supplied from the southern mountainous area. By stable isotopic analyses (δD and δ18O) combining the local geographical conditions in Laizhou, the groundwater samples due to precipitation recharge were determined. We next confirmed that the groundwater samples in Longkou is also directly recharged from local precipitation, whereas for Shouguang, based on the altitude effect and the local hydrological setting, we infer the groundwater is probably recharged from the precipitation of southern mountainous area. Cl- δ18O relation indicates that salinity is originated from the dissolution of evaporite by freshwater, rather than mixing with seawater. Br-/Cl- ratios confirmed the dissolution of evaporite, and it can also reflect the influence of man made pollutants and decomposition of organic matter in transgressive sediments. As reflected by the piper digram, the Longkou samples have undergone ion exchange reactions, and ion (HCO3-, H2SiO3, F-, Li+, Sr2+ and Ba2+) concentrations, which relate to the aquifer mineral composition, also reflect extensive water rock interaction. All samples are not indicatative of mixture of fresh water and sea water. Inert tracer analyses provide a framework for regional groundwater recharge, determine that the salinization of atmosphere water is due to evaporites dissolution, and also exclude the possibility of freshwater and seawater mixing. By comparing the element concentration ratios of groundwater and marine ratios, the deviation can be explained by water rock interaction, including dissolution, precipitation, ion exchange, and contaminants enter of local samples. Therefore, for groundwater salinization study in coastal zone, the first step is to determine the possibility of solvent mixing, which is followed by identifing the solute mixing and salt sources, using various chemical tracers.

Abstract:Black shales are a type of sedimentary rocks that are characterized by large variation in chemical compositions both spatially and temporally. Therefore, the chemical indices, such as CIA(MIA), CIW, CIX, PIA, STI, R, WIP, V, and W, which are based on relatively homogeneous geochemical compositions of different igneous rocks, can not be used to identify the weathering degrees of black shale because they can not differ chemical compositions of parent rocks from that of weathered black shales and have low sensitivity and other problems. Therefore, it is necessary to establish a new chemical index to identify the weathering degree of black shale. In combination with the one way ANOVA analysis and the multivariate discriminant analysis methods, this study conducted major elements analysis for the samples from fresh and weathered black shales of Lower Cambrian in central Hunan to define the differences of their chemical components. Establishment of major element discriminant method can further define chemical weathering index of weathering degree of black shales. It is shown that different major elements have different degree of influence on the chemical difference between the fresh and weathered black shales, and such influencing degree decreases with an order of TiO2>Al2O3>Fe2O3>LOI>MnO>CaO>SiO2>MgO>K2O>Na2O>P2O5. Chemical weathering index for identifying weathering degree of black shales (WB) can be established as follows: WB=288×ln(SiO2)+1667× ln(TiO2)+1052×ln(Al2O3)+562×ln(Fe2O3)-201×ln(MgO)+410×ln(CaO)-424×ln(K2O)-506×ln(Na2O)+507×ln(LOI)-15813. This new chemical index can overcome the weakness of all the existed chemical indices, and can be used to identify the weathering degree of black shale.