Abstract:Based on the previously research, the research group of Key Laboratory of Continental Tectonics and Dynamics has achieved lots of great progress in the study of the continental dynamics of the Tibetan Plateau, especially in the evolution of Tethys and the growth of the Tibetan Plateau during the past decade. These achievements can be summarized as follows:(1) The Hypothesis on Tibetan Plateau as a orogenic plateau was proposed; (2) the reconstruction of the tectonic framework and the Tibetan-Tethys system; (3) the discovery of in situ diamond and deep mantle-derived mineral group in the ophiolites distributed along the Neotethyan suture zone; (4) the understanding of the subduction mechanism of the Neotethy oceanic basins; (5) the role of magmatism formed in the early stage of the Indo-Asian collision for the exhumation of Himalaya; (6) the establishment of the 3D models of the collisional orogeny and exhumation of the Himalaya; (7) the new proposal on the extrusion of the SE Tibetan Plateau:‘crustal bending and decouple’; (8) the subduction-related, collision-related and continental gneiss domes with Tibetan Plateau; (9) the tectonic setting and the Wenchuan Earthquake mechanism on the eastern margin of the Tibetan Plateau; (10) Numerical modeling of the Indo-Asian collisional process. This paper aims to communicate with and stimulate interest among global geologists to make further development in the continental dynamics of the Tibetan Plateau.

Abstract:High resolution magnetic susceptibility and detailed rock magnetism studies of the Yingxiu-Beichuan fault zone were conduced on the field section at Bajiaomiao, Hongkou Town. The systematic analysis reveals the existence of quite a few high magnetic susceptibility fault rock zones. A brown layer fault rock has the following features:(1) the highest magnetic susceptibility, (2) significant characteristics of magnetite new formation, and (3) similar demagnetization behavior of natural remanent magnetization and anhysteretic remanent magnetization. The principal mechanism responsible for the high magnetic susceptibility of the brown fault rock was most likely caused by the production of new magnetites from iron-bearing paramagnetic minerals. These new magnetites might be formed by frictional heating on slip planes along a seismic fault. Combined with the analytical result of the core from the first drill hole of the Wenchuan Earthquake Fault Scientific Drilling Project (WFSD-1), the authors hold that the presence of high magnetic susceptibility fault gouges in the same country rock can be considered to be an indicator of earthquakes or seismic signatures. Quite a few layers of high magnetic susceptibility fault rocks indicate that strong earthquake repeatedly occurred alongWenchuan earthquake fault zone.

Abstract:The Lishui Basin is a typical Cretaceous volcanic basin developed in Zhejiang Province of southeastern China. Five rock samples collected from interbedded volcanic tuffs of this basin were analyzed by using LA-MC-ICPMS zircon U-Pb method, which yielded weighted mean ²⁰⁶Pb/²³⁸U ages of (114±1) Ma, (114±2) Ma, (118±1) Ma, (122±1) Ma and (112±1) Ma, respectively.These dating results, in conjunction with regional sedimentary and structural contact relationships, led the authors to divide the volcano-sedimentary sequences into two rock suites:the lower rock suite, consisting of Guantou and Chaochuan Formations, was deposited in 124-112 Ma, whereas the upper rock suite, corresponding to Chaochuan Formation, was deposited in 104-91 Ma. Their generations resulted from two stages of crustal extensional events during the Early Cretaceous. These sedimentary data, coupled with structural analysis and tectonic stress field inversion, support the argument that the Lishui basin underwent two cycles of tectonic evolution, and each was dominated by alternate stress episodes of NW-SE extension and NW-SE compression. The NW-SE extension accommodated the initial opening and sediment infilling of the basin, which might have originated from the back-arc extension induced by the rollback of the subducted Paleo-Pacific slab during the Early Cretaceous. The NW-SE compression led to tectonic inversion, and was responsible for the unconformity between the Upper and Lower Cretaceous strata, which was probably associated with the variations of the subducted slab dynamics or the collision between the eastern Asian margin and the West Philippine Block. The alternate extensional and compressional episodes reflect variation of geometries and dynamics of subducted slab in a back-arc extensional setting.

Abstract:Zircon U-Pb chronology and geochemistry of the biotite monzonitic granite from Shihahe area of Urad Middle Banner were studied systematically to investigate its formation age and tectonic background. The weighted average age obtained by zircon LA-ICP-MS U-Pb method is(274.99±0.71)Ma, which represents its formation age. The biotite monzonitic granite belongs to subaluminous-weakly peraluminous I-type and calc-alkaline series, with its A/CNK being 0.93-1.10 and σ being 2.01-2.88. The total REE (ΣREE) is lower, LREE values are higher and HREE is lower, with LREE/HREE ratio varying from 9.86 to 15.63, indicating that LREE and HREE differentiated intensely. Eu has insignificant anomalies or weakly negative anomalies. In the primitive mantle normalized trace elements spider diagram, the biotite monzogranite is enriched in large ion lithophile elements Rb and K while depleted in high field strength element Nb, similar to features of normal arc granitic rock. According to tectonic setting as well as emplacement time and characteristics of geochemistry of the biotite monzogranite from Shihahe area, it is inferred that the rocks were formed in an active continental margin environment, and the upper limit of conversion from ocean crust subduction to continent collision was later than late Early Permian.

Abstract:Garnet granites in Helin-Liangchang zone of central Inner Mongolia are strongly peraluminous granites. The age of garnet granites obtained by zircon LA-ICP-MS U-Pb method is 1923-1958 Ma, indicating Paleoproterozoic. The analyses of their geochemical characteristics indicate that the source area was made up of graywackes, and the partial melting temperature was relatively high, suggesting post collision stage magmatite activity characteristics. Considering the regional geological features, the garnet granites should be the product of partial melted graywackes which existed at the bottom of the earth's crust, heated by the basaltic magma with high temperature under the relatively high temperature conditions (above 875℃). The melting happened when Yinshan block and Erduosi block collided in the early Paleoproterozoic and turned from convergence to extension, companied by the underplating of basaltic magma.

Abstract:Located at the junction of North China Plate intersection, Tarim plate and Kazakhstan plate, Beishan area is characterized by nearly EW-trending tectonic-magmatic activity. The rocks mainly include rhyolite, rhyolitic breccias-containing debris crystal tuff, dacitic crystal tuff, andesitic crystal tuff and a small amount of dacite. They can be divided into two sections based on features and rock eruption spatial superposition relationship. Geochemistry shows that rhyolites have high SiO₂ content (77.05%~77.52%) and low TiO₂(0.06%-0.19%), CaO (0.38%-1.04%), MgO (0.09%-0.17%) content with K₂O/Na₂O higher than 1. They are relatively enriched in large ion lithophile elements (LILE) Rb and K, while depleted in high field strength elements (HFSE) Nb, Ta, P and Ti. The total amount of light rare earth elements (ΣLREE average value being 127.55×10^-6) is significantly higher than that of the heavy rare earth elements (ΣHREE average value being 10.92×10^-6), and LREE fractionation obviously ((La/Yb)_N varies from 6.37 to 7.88, with an average of 7.05, whereas (La/Sm)_N varies from 4.51 to 4.61, with an average of 4.55. Eu has obvious negative anomaly (δ Eu average value being only 0.62). Petrological and geochemical characteristics indicate that the tectonic setting was a continental-margin-arc. Zircon U-Pb age is 318.5±1.2 Ma for rhyolite by LA-IC-MS method. Combined with regional geological features, the authors believe that Baishan Formation in Fengleishan formed in the Late Carboniferous.

Abstract:There are large-scale intermediate-acid intrusive rocks distributed in the north of western Junggar, Xinjiang. The rocks formed during late Carboniferous to early Permian. The typical plutons include pyroxene diorite, quartz diorite and granodiorite. The Kuoyitasi intrusion is among one of them. It has SiO₂ values of 52.40%-67.53%, high Al₂O₃ content (14.92%-17.85%) and Na content, and low K and MgO content. Rittman values (δ) of the samples vary from 1.47 to 1.98, and the FeO^T/MgO values are between 1.01 and 1.69. The REE patterns are characterized by LREE enrichment and slight Eu anomalies with obvious fractionation between LREE and HREE. The geochemical characteristics suggest that the Kuoyitasi intrusion formed in a post-collisional extensional tectonic environment, and should be formed earlier than the collision time of east Junggar terrain. The rocks were probably derived from partial melting of the lower crust which was intruded by mafic magmas.

Abstract:This study presents bulk petrogeochemistry and zircon U-Pb dating results for the Niuzhi monzonitic porphyry in Mojiang, Yunnan. LA-ICP-MS zircon U-Pb dating results show that the Niuzhi monzonitic porphyry formed in the Late Permian (263.5±1.7 Ma). The Niuzhi monzonitic porphyry is characterized by SiO₂ content of 55.30%-74.37%, alkali (Na₂O+K₂O) 2.56%-7.57%, and Na₂O higher than K₂O. It is enriched in LREE and Sc, Co, Cs, As, and depleted in Cr, Ni, Zn, Rb, Sr, Ba, Zr, Ta, Th, U, W, with negative Eu anomalies (δ Eu 0.74-1.06). According to the diagrams, the Niuzhi monzonitic porphyry formed in the tectonic environment of island arc-continent or continental-arc collision, indicating that the branch of Paleo-Tethys Ocean or arc basin in Ailaoshan tectonic belt may have been closed in the Late Permian (263.5±1.7 Ma).

Abstract:The Weijia tungsten deposit, located in the Tongshanling area of western Nanling metallogenic belt, is a newly discovered giant skarn tungsten deposit, with its orebodies mainly occurring at the contact zone between the Xianglinpu granite and Devonian carbonate rock. To determine the timing of the emplacement of the Xianglinpu granite and associated mineralization, the authors collected two kinds of granite, i.e., granite porphyry and quartz porphyry, from the Xianglingpu pluton for zircon LA-MC-ICP-MS U-Pb dating. The results show that the zircon U-Pb ages of granite porphyry and quartz porphyry are (157.8±0.9) Ma (MSWD=1.06) and (158.3±1.4) Ma (MSWD=0.2), respectively, suggesting that their emplacements were coeval within error and they were derived from the same magma source. In addition, the captured zircons from granite porphyry yielded the weighed mean U-Pb age of (435.0±3.1) Ma (MSWD=0.6), which recorded the Caledonian tectonic-magmatic event in this area. Based on the contact relationship between skarn tungsten orebodies and granite, the authors hold that the emplacement of Xianglinpu granite and associated tungsten mineralization occurred at ca.158 Ma, which coincided well with the large-scale mineralization of the Nanling in Middle-Late Jurassic (150-160) Ma. The constraint of the Late Jurassic Weijia skarn-type tungsten deposit implies the great potential of the late Jurassic skarn-type tungsten mineralization in western Nanling W-Sn metallogenic belt.

Abstract:The Weishan pluton is located in western Yunnan, close to the Ailao Mountain-Honghe River fault zone. It comprises monzonite porphyry and quartz monzonite porphyry. The LA-ICP-MS zircon U-Pb dating suggests that the pluton was emplaced in Eocene, with the age of (38.5±0.6) Ma. The Weishan pluton is peraluminous, with ASI from 1.09 to 1.44. All the samples have high K₂O content (4.50% to 4.98%) and K₂O/Na₂O ratios (1.10 to 1.41). The granitoids show adakitic affinities, such as high Al₂O₃, Sr, low HREE and Y content and the absence of negative Eu anomalies. The Weishan pluton has higher ε_Nd(t) and lower I_Sr values than the coeval peraluminous plutons from western Yunnan, indicating the contribution of mantle material to the formation of the pluton. All the geochemical data imply that the Weishan pluton was likely derived from partial melting of the sedimentary or metasedimentary rocks of thickened crust, triggered by underplating of basaltic magmas. Due to the early emplacement age, the Weishan pluton was not likely related to the left-lateral displacement of the Ailao Mountain-Honghe River shear zone.

Abstract:The pre-collision magmatism took place in the accretionary wedges of many orogens. This paper presents the geological features of Langxian tonalite stock, zircon U-Pb data, and geochemical and Sr-Nd isotopic data for the tonalite to discuss whether island-arc type magmatism took place in the accretionary wedges of Yarlung Zangbo belt. The results indicate that the deformation degree of stock is distinctively lower than that of its wall rocks which comprises ophiolite mélange (145.7±2.5 Ma), and the age of the stock is (92.58±0.72)Ma (MSWD=1.8). The diorite is characterized by calc-alkaline series, and high Mg, Na, abundances of compatible elements (Cr=71.48×10^-6-86.74×10^-6, Co=22.32×10^-6-23.52×10^-6, Ni=33.51×10^-6-36.31×10^-6). The rock is enriched in Rb, Ba, Th, Pb, U, K, and depleted in Nb, Ta, Zr, Hf(Ti). REE patterns show strong enrichment of LREE and depletion of HREE (La_N/Yb_N=6.95-7.44), with indistinct Eu anomaly (δEu=0.82-0.91). Meanwhile, the values of ε_Nd(t) vary from 2.68 to 3.23. Based on these results in combination with previous data, the authors suggest that Langxian diotite intrusion was formed in an accretionary wedge island arc setting, related to southward migration of the Yarlung Zangbo subduction, and derived from the magma mixture of depleted mantle and subduction accretionary complex in the ocean ridge subducting at 90 Ma or so.

Abstract:In this paper, the authors studied detrital zircon geochronology of the Cambrian-Ordovician sedimentary rocks sampled from the southern Hunan to northeastern Guangxi area by using LA-ICP-MS and obtained 239 groups of effective age data, with the ages ranging from 3146 Ma to 474 Ma. Most of the data are concentrated in five periods, i.e., 2633-2473 Ma (peak value around 2500 Ma), 1880-1521 Ma (peak value around 1650 Ma), 1146-911 Ma (peak value around 970 Ma), 896-720 Ma (peak value around 800 Ma) and 682-474 Ma (peak value around 520 Ma). All the four samples recorded Paleoarchean-Mesoarchean information, and their ages are concentrated on 1146-911 Ma and 896-848 Ma, suggesting that the Grenville and Rodinia orogeny events profoundly influenced the study area. Moreover, the authors obtained a large number of ages representing the Pan-African time, implying that the global Pan-African event significantly affected the Cathaysia Block and its adjacent regions. Combined with previous researches, the authors hold that the study area is located in the southeast of the southwestern section of the collision orogenic belt between the Yangtze block and the Cathaysia block. The strata in the study area received material sources from the two blocks with the material from the Cathaysia block being dominant.

Abstract:The Dapai Fe-Pb-Zn polymetallic ore deposit in Yongding County of southwestern Fujian Province is a large-sized polymetallic deposit discovered in recent years. Zircon SHRIMP U-Pb dating of Dapai altered granodiorite is (127±1.8) Ma, equal to the Re-Os isotopic age (133.5±4.1) Ma of the granodiorite porphyry. Both ages are consistent with the age of Makeng and Pantian iron ore deposit in the same area, indicating genetic relation between the granitic magmatism and the Fe-Pb-Zn metallogenesis in the area, with the main metallogenic epoch being Yanshanian. Based on the previous research results and data obtained by the authors, it is inferred that the Dapai Fe-Pb-Zn polymetallic ore deposit belongs to stratabound skarn-porphyry type composite deposit.

Abstract:The Weilasito Sn-Zn-Cu deposit is located in Keshiketen, Inner Mongolia, at latitude 44°5'5"N, longitude 117°29'53"E. The mineralization styles include granite-type Sn-Zn at the top of the granite, quartz vein type Sn-Zn ore near the granite, Cu-Zn sulfide vein and Pb-Zn-Ag sulfide vein distal from the granite. Based on petrology, geology and geochemistry of elements and chronology, the authors recognized the granite magma revolution, the origin of the deposit and the relations between the mineralization styles. LA-ICP-MS zircon U-Pb dating yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 139.5±1.2 Ma(MSWD=3.3)for the alkali feldspar granite pluton. There are multilevel phenocrysts in the pluton, and the crystallization sequence is albite-quartz-K-feldspar-albite-quartz, topaz, cassiterite, and sphalerite. The granite rich in SiO₂ and Rb, Cs, Nb, Ta, W, Mo, Bi, Cu, Zn, In etc., poor in Al₂O₃, TiO₂, TFe₂O₃, CaO and Sr, Ba etc., the An value of the albite is lower than 0.3, similar to data of the granite of Sn-W deposits in the Nanling belt. Late magma experienced magmatic-hydrothermal transitional stage as well as gradual continuous evolution to hydrothermal stage. The Si rich, F rich and S rich fluid phases were separated from the magma to form the droplets (pocket) of quartz, topaz, cassiterite-sphalerite respectively in the granite-type Sn-Zn ore. The fluid inclusions are melt, melt-fluid and liquid respectively. The granite-type Sn-Zn ore formed at the top of pluton at the magma-hydrothermal transitional stage, the quartz vein-type Sn-Zn ore occurs at the outer part and the sulfide-vein Cu-Zn, Pb-Zn-Ag ore of the hydrothermal stage occurs distal from the rock body. All of the ores and the plutons comprise the magmatic hydrothermal tin polymetallic metallogenic system. In Xilin Gol-Chifeng area, there are some Pb-Zn-Ag veins (deposits and/or mineralization) related to the acidic intrusive rocks. There probably exsit large-sized hydrothermal tin (tungsten) polymetallic deposits in the depth.

Abstract:Located on the southern margin of the Geza island arc, the Tongchanggou porphyry deposit is a large-sized Mo(Cu) polymetallic deposit discovered in recent years in southwest Sanjiang region. In this paper, the authors investigated the sources of minerals through sulfur and lead isotope tracer study. Testing results show that the δ³⁴S values of ore sulfides vary in the range of -0.7‰-+3.8‰, 0.79‰ on average. The variation range is very small, which indicates a single source of the sulfur isotope and displays the characteristics of magmatic source sulfur isotopic composition. The lead isotopic composition of ore minerals is characterized by ²⁰⁶Pb/²⁰⁴Pb ranging from 18.3325 to 18.694, ²⁰⁷Pb/²⁰⁴Pb ranging from 15.588 to 15.663, and ²⁰⁸Pb/²⁰⁴Pb ranging from 38.454 to 39.008, exhibiting relatively stable Pb isotopic composition and showing the normal lead characteristics. There is a significant positive correlation between lead isotopic composition and characteristic parameters (△β and △γ, V₁ and V₂). Lead structural model identification and genetic classification comprehensive analysis suggest that the lead isotopes of the Tongchanggou porphyry Mo(Cu) deposit were mainly derived from the depth and show the crust-mantle mixed source characteristics. The mineralization had a close relationship with Yanshanian magmatic intrusion, with the minerals of the strata also making some contribution.

Abstract:In this paper, the authors described the geological features of the the Dadengge gold polymetallic deposit, analyzed major elements, REE, sulfur isotope, δD_V-SMOW-δ¹⁸O_H2O, and fluid inclusions, and then summarized the geochemical features so as to find the ore-forming genesis and physicochemical conditions. Major element analyses show that the alteration zone gained SiO₂, K₂O but lost Na₂O, Al₂O₃, CaO during alteration. The sulfur isotope composition ranges between 7.0‰ and 7.1‰ δ³⁴S_CDT, suggesting that the sulfurs were of the same origin, being a unified source. The δD_V-SMOW values range from -83.68‰ to -116.95‰, and theδ¹⁸O_H2O values range from -2.57‰ to 8.35‰, suggesting that the mineralizing fluids were derived from the mixed magmatic and meteoric water. The mineralizing process took place under the condition of medium temperature (86-429℃) and low salinity (1.74%-22.38% NaCl_eq), and the mineralizing fluid might have been a CO₂-H₂O-N₂-NaCl system. The mineralizing fluids of the main mineralization stage exhibited feature of multiple sources, and the change of physicochemical conditions and fluid immiscibility were the important mechanisms for deposition and enrichment of gold and other mineralizing elements.

Abstract:Located in northwest Yunnan, the Beiya gold deposit is a skarn porphyry type gold polymetallic deposit with rich alkali. The distribution of orebodies is related to structure and porphyry, which constitutes the basis for the application of the tectonogeochemical method. Through R type cluster analysis and factor analysis, the authors recognized two combinations of elements. One is Au-Ag-Fe-Cu-Sb-Hg-Sn-Pb-Co-Mo, and the othor is Zn-Pb. Then the authors used them to draw a tectono-geochemical map, which included the combination of elements and anomalies. With the map, the authors detected the migration direction of the ore-forming fluid and the location of the orebody. It is held that the Bijia Mountain has a relatively good exploration potential.

Abstract:The Daba Mountain passes through two tectonic units, namely, the Qingling orogenic belt and the Yangtz craton. Based on the 1:50000 stream sediment survey, the authors calculated the geochemical parameters of ore-forming elements and analyzed the distribution characteristics, element correlation and element anomaly assemblages. The results show that the study area might be a potential area for Pb, Zn, Ba, Cu and Mn deposits. It is concluded that the main metallogenic types in Qinling unit of the study area are low temperature epithermal Zn-Cu deposits and sedimentary type Ba deposits connected with the Silian-lower Cambrian black rocks. The main metallogenic types in Yangtze unit of the study area are low temperature epithermal Pb-Zn deposit related to the Cambrian carbonaceous rocks and sedimentary type Mn deposits which are connected with Cambrian and Silian carbonaceous rocks respectively. On such a basis, five prospective areas were delineated. Yangjiaping-Gedong area and Zhenping area are expected to be promising areas for Ba-Zn deposits, Huang'anba-Mihunzhen area for Zn-Cu deposits, Baiyangping area for Pb-Zn deposits and Xiuqi-Shifang area for Mn deposits.

Abstract:The Xindigou gold deposit in Inner Mongolia is a typical greenstone belt gold deposit. Microscope and scanning electron microscope were used to study the modes of occurrence of gold. 602 grains of native gold were recognized, including inclusion, fissure-filling, and intergranular and interlocking gold. The gold-hosting minerals are mainly pyrite and quartz, which account for 95% of the total gold-hosting minerals, and minor K-feldspar, sericite, siderite, limonite, tetrahedrite, sphalerite, galena were also identified. On the basis of statistics, the gold granularity is mainly characterized by micro extra particulate (0.2-5 μm), micro fine particulate (10-20 μm), microscopic medium (20-50 μm), and micro particulate (5-10 μm) grained gold, accounting for 32.23%, 26.91%, 20.6%, and 16.11%, respectively. The micro coarse-gained gold which was observed in the sample and under the microscope is relatively minor but plays an important role in the ore grade and total resource. Electron microprobe analysis and phase analysis show that gold occurs mainly as independent gold minerals. The gold minerals are mainly native gold and secondary electrum (the average fineness is 803), which indicates that gold was formed under the condition of medium temperature and depth.

Abstract:Following Jiaoshiba and Changning-Weiyuan areas, Huangjinba shale gas field in Zhaotong National Shale Gas Demonstration Area is the place where the shale gas exploration and development have received a good achievement. To systemically demonstrate the reservoir conditions for shale gas accumulation in the Huangjinba shale gas field and provide a reference for future exploration, the authors studied the Wufeng-Longmaxi shale gas reservoir in detail in such aspects as regional geological setting, reservoir petrology, physical properties and geochemistry. The results indicate that the stable regional tectonics and well-developed roof and floor formations are crucial factors for shale gas enrichment in this region. These good preserving conditions help the reservoir maintain a high pressure (pressure coefficient >1). High porosity (mean=4%) and TOC content (target bed >2%) of the reservoir provide good spaces for hydrocarbons, and cause the reservoir rocks to have high gas values (1.35-3.48 cm³/g, >2.50 cm³/g on average). The geochemical data of natural gas show that the predominant composition is CH₄(>97%), with minor compositions including C₂H₆, C₃H₈ and CO₂. The isotopic data of natural gas show that the C isotopic constituents of hydrocarbons have been preserved, indicating that the reservoir is closed or semiclosed. Nevertheless, the pore system of the reservoir is very complicated and heterogeneous, which leads to the low permeability of the reservoir, and such a condition should be carefully treated during stimulation processes. In general, the shale gas development potential of the Huangjingba gas field is good, and the production test shows that the gas production quantity of fractured vertical well is 0.5×10⁴-3.5×10⁴ m³/day/well, and the quantity for fractured horizontal well is 12×10⁴-40×10⁴ m³/day/well.

Abstract:Based on analyzing the distribution, thickness, area, total organic carbon content, thermal evolution, type of organic matter and petrographic composition of the shale on the southern margin of Junggar Basin, the authors hold that the Jurassic Badaowan, Sangonghe and Xishanyao Formation, the Permian Lucaogou Formation, Hongyanchi Formation and the Carboniferous strata are favorable formations for shale gas exploration. Through an analysis of enrichment conditions of favorable horizons of shale gas and by using the method of superimposing vitrinite reflectance (Ro) isoline, mudstone thickness isoline and total organic carbon content (TOC) contour, the authors determined that the Jurassic strata of the transition region of the northwestern margin of Homato anticline belt, Shawan sag and Monan convex, the Jurassic strata of transition region of Fukang sag and Fukang fracture belt, the Permian strata of Dabancheng sag and Yongfeng sag with shallow buried depth in Chaiwopu depression and the Carboniferous strata of Qigu fault fold zone with shallow buried depth ae favorable places for shale gas exploration.

Abstract:In this paper, the authors carried out detailed research on geochemical characteristics of the Suowa Formation mudstones from Well QZ3. The origin of organic matters and the sedimentary environment were investigated according to the characteristics of biomarkers. Abundant biomarkers, including n-alkanes, isoprenoid, terpanes and steranes from mudstones, were detected by GC and GC-MS. The n-alkanes have nC₁₇, nC₁₈, nC₂₃or nC₂₅ as the mean peaks. OEP values vary from 0.4 to 1.24, Pr/nC₁₇ from 0.68 to 0.99, Ph/nC₁₈ from 0.55 to 0.98, and Pr/Ph from 0.50 to 0.90. In the m/z191 GC-MS, C₃₀ hopane is most abundant in the terpanes, with the presence of tricyclic terpanes and gammacerane. In the m/z217 GC-MS, regular steranes are characterized by the highest abundances. The regular steranes C₂₇-C₂₈-C₂₉ααα 20R are distributed in the asymmetric "V" shape. C₂₉ααα 20S/(20S+20R) values vary from 0.30 to 0.49 and C₂₉αββ/(ααα+αββ) from 0.40 to 0.54. GC/MS characteristics of saturated hydrocarbon show that organic matter is characterized by mixed sources composed of phytoplankton, suggesting that organic matter is formed in a low-salinity anoxic environment. Different kinds of parameters indicate that the organic matter of the asphalts and mudstones is the peak of oil generation. At the same time, biomarker parameters of the asphalts and mudstones from QZ3 Well show similar characteristics in such aspects as organic matter source, sedimentary environment and maturity. They have very close genetic relationship.

Abstract:Z₂dn of Sichuan basin belongs to the last set of Neoproterozoic strata, and it is also the first sedimentary cover for Sichuan. The main lithology is the pure dolomite in light color, which underwent a complicated diagenesis, so its depositional environment is a topic of much controversy. Based on the field section in the periphery of the basin, drilling core, well logging data and analysis of analytical data, guided by petrology, sedimentology and petroleum geology theory, and combined with the modern stromatolites sedimentary characteristics, the authors analyzed characteristics of petrology, sedimentary environment of Dengying Formation. Some conclusions have been reached:① The rocks of Dengying Formation can be divided into 3 types and 12 subtypes. Poor algal section is mainly composed of dolomicrite, clotted dolomite and grained dolostone, mostly occurring at the early-middle stage of a complete sedimentary cycle. Rich alga section is mainly composed of straticulate dolostone, laminated dolomite and foam dolomite, mostly occurring at the middle-late stage of a complete sedimentary cycle. ② The sedimentary facies of Z₂dn of Sichuan basin is mainly shallow-water restricted platform facies, and it can be subdivided into 4 subfacies, i.e., algal mound, grain beach, flat and lagoon. The sedimentary facies of the study area is mainly algal mound, and the algal mound may be further subdivided into base, core, cap 3 microfacies. ③ Comprehensive analysis shows that the high quality reservoirs is obviously controlled by facies. In platform, the reservoirs of grained beach and algal mound, especially the composite body of "mound and beach complex", are of the best physical property, and gas exploration of Z₂dn should be carried out around the microbolite in Sichuan basin.

Abstract:Core ZK4 with a shallow depth of 28.3 m was drilled in the Yellow River Delta in 2007. Samples from the core were used in the laboratory to make detailed sedimentological observations and perform analysis of water content, organic carbon (Corg), total carbon (TC), and nutrient compositions. According to the stratigraphic analyses of core ZK1, seven sedimentary environments were recognized, and the historical evolutions of coastal wetlands were revealed. Chronologies, sedimentation rates and carbon accretion rates of the environments were revealed from AMS¹⁴C dating method, historical records of the Yellow River diversions, and comprehensive analyses by means of historic geography and sedimentary geology. The results show that total carbons, organic carbons and nutrients (except for element S) are all in good linear correlations, the accretion rates of Corg, TC, N and P have very significantly positive correlations with sedimentation rates shown as R>0.89, p<0.01, and the sedimentation rates are the main factor controlling accretion rates of Corg, TC, N and P. Although Corg concentrations are low (<1%) in the modern Yellow River Delta sediments, the high sedimentation rates have made the average accretion rate of Corg in the sediments come up to 2878.23 g/(m²·a), much higher than the values in other high-Corg wetlands in the world, and thus the modern Yellow River Delta can be considered to be a very good carbon sink due to its high sedimentation rate.

Abstract:Reservoir physical properties of volcanic rocks in Xujiaweizi fault depression are influenced obviously by the fracture developing extent. According to the survey of similar outcrops, the core observation, casting thin slice and imaging logging analysis data, in combination with stress field numerical simulation technology, the authors analyzed fracture types, trends, dip angles, lengths, densities, fillings and the factors influencing the fracture development of the volcanic reservoir. The result shows that fractures in the study area are mainly tectonic shear fractures, followed by diagenetic fractures. Four nearly WE-, NS-, NE-and NW-trending fracture groups are developed, mainly high angle fractures and inclined fractures, and the lengths and densities of these fractures change significantly. The main factors influencing the development of the volcanic rock fractures include ancient tectonic stress, lithology, volcanic edifice and fault. Therefore, the high value area of the ancient tectonic stress has good relationship with fracture developed area. In a variety of volcanic rocks, fractures in trachyte, agglomerate and rhyolite are relatively well developed. Fractures are mainly developed in the facies of volcanic crater and near-crater. Fractures are also developed on the upper wall of the fault with obvious stress disturbance and, with the increase of the distance from the fault, the extent of the fracture development decreases.

Abstract:As a new method of basin sedimentological research, the process-response theory is based on the earth system science. This kind of method is composed of process research and response research. The controlling role of the basin evolution in the sedimentary process is emphasized in this theory. The process-response theory was successfully applied to the study of lacustrine carbonate rocks in the 4^th member of Shahejie Formation (Es₄) within the mid-northern part of the western sag of Liaohe depression. The results show that the formation and distribution of lacustrine carbonate rocks are obviously controlled by basin evolution process in time and space. Based on the study of the Es₄ in the mid-northern part of the western sag of Liaohe depression, the authors hold that the sedimentary environment of lacustrine carbonate rocks has three key points. The first one is the suitable topography and hydrodynamic conditions. The second one is the favorable climate and water media, and the last one is the rich provenance supply and the dolomitic conditions. The application of the process-response theory, together with the research on the three key points and the comprehensive sedimentary model of lacustrine carbonate rocks, constitutes the basis for establishing the composite sedimentary model with more reference and guidance value.

Abstract:Metasedimentary rocks in Sinian-Cambrian Xunwu rock group of southern Jiangxi Province show obvious variation of SiO₂ values. Except for one sample with a relatively lower concentration, the average SiO₂ content is 63.01%. These rocks show comparatively high K₂O, Al₂O₃ and (TFeO+MgO) values and low Na₂O and CaO values. Compared with the concentrations of compatible trace elements, they are very close to values of Archaean Australian Shales (PASS), but their values are dramatically higher than values of the upper crust, and are consistent with the characteristics of high (TFeO+MgO) values, indicating that a certain amount of intermediate-basic components existed in the source region. Total REE concentrations are higher than those of the upper crust and PAAS. Nevertheless, , the chondrite-normalized REE patterns exhibit a slanting rightward shape with enriched LREE, flat HREE, obvious negative Eu anomalies and less obvious negative Ce anomalies, similar to features of the typical upper crust and PAAS. Based on the geochemical characteristics, the protolith should be terrigenous clastic rocks with intermediate maturity, and the provenance was mainly dominated by reconstructed felsic and granitic sediments from the upper crust, with partly contributed by certain amounts of intermediate-basic components. Immobile elements like high field-strength elements and rare earth elements reveal that the sedimentary environment was bathyal to abyssal and the tectonic background was the passive continental margin with rift systems. The results obtained by the authors shed some light on the tectonic attributes of southern China in Early Paleozoic from the perspective of sedimentary geochemistry.