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摘要:A study of the morphological and microstructural characteristics of helcionelloids from the Nanjiang area (north Sichuan, China) at the northern Yangtze Platform was undertaken, in order to understand their phylogenetic position. Helcionelloids fossils from the Kuanchuanpu Formation of the Changtanhe–Maolinzi section include 7 genera and 11 species. There are distinct differences in the degree of shell bending, the apical morphology and apex position, the outline of the aperture and the height of the shell, all of which constitute important identification features. Although helcionelloid apices exhibit varying degrees of rotation towards the aperture, they do not show any signs of evident distortion. A pair of basally-symmetrical muscle scars are discovered on the shells of helcionelloids (such as Bemella simplex), showing a distinct difference when compared with those of the stem-group gastropod (e.g., Pelagiella). The prismatic shell layer of helcionelloids has been observed, which are common components in Cambrian molluscs, but differ significantly from the dense layer microstructure found in contemporary molluscs. The microstructures, muscle scars and morphological characteristics demonstrate that helcionelloids represent a stem-group of molluscs.

摘要:The rhynchonellide brachiopod Dzieduszyckia Siemiradzki is widely distributed in the Lower Famennian strata, and exhibits a wide range of morphological variations among populations. 1272 autochthonous Devonian Rongxian Dzieduszyckia fossils were collected from three populations in South China, namely the Dazhai, Dalong, and Longmi sections. A series of quantitative morphological analyses were conducted to understand the morphological variation among populations and identify the triggers responsible for such variations. The results show that the Dazhai population differs significantly in morphospace from the Dalong and Longmi populations, while the latter two exhibit more similar morphological features, suggesting that geographic distribution may play a key role in affecting Dzieduszyckia morphology. The Longmi population shows a distinct morphospace from the Dazhai population and an overlapped morphospace with the Dalong population, indicating that habitat may not be the controlling factor. Lastly, the Dazhai and Dalong populations share some morphological similarities, but the Dazhai and Longmi populations occupy completely different morphospaces, indicating that evolution had a greater impact on phenotypic divergence than habitat. Our findings suggest that geographic distribution is the predominant factor influencing the morphological variation of Dzieduszyckia, while evolution and living habitat are less significant, the former of which might play a more important role.

摘要:Tectonic stress fields are the key drivers of tectonic events and the evolution of regional structures. The tectonic stress field evolution of the Tanlu fault zone in Shandong Province, located in the east of the North China Craton (NCC), may have preserved records of the NCC’s tectonic history. Borehole television survey and hydraulic fracturing were conducted to analyze the paleo and present tectonic stress fields. Three groups of tensile fractures were identified via borehole television, their azimuths being NNW–SSE, NW–SE and NE–SW, representing multiple stages of tectonic events. Hydraulic fracturing data indicates that the study region is experiencing NEE–SWW-oriented compression and nearly-N–S-oriented extension, in accordance with strike-slip and compression. Since the Cretaceous, the orientation of the extensional stress has evolved counterclockwise and sequentially from nearly-NW–SE-oriented to NE–SW-oriented and even nearly N–S-oriented, the stress state having transitioned from strike-slip-extension to strike-slip-compression, in association with the rotating and oblique subduction of the Pacific Plate beneath the NCC, with the participation of the Indian Plate.

摘要:As typical carbonate geothermal reservoirs with low porosity in northern China, the Jixianian System in the Xiong’an New Area is the main target for geothermal fluid exploration. The Jixianian System comprises the Gaoyuzhuang, Yangzhuang, Wumishan, Hongshuizhuang, and Tieling formations. The characteristics, formation periods, and controlling factors of reservoir tectonic fractures have been determined based on analyses of outcrops, cores, thin sections, and image logs. The results show that unfilled fractures account for over 87% and most tectonic fractures are high-angle shear fractures with angles concentrated at 40° to 70° and the fracture porosity increases linearly with an increased fracture aperture. Within the same tectonic setting and stress field, the lithology and layer thickness are the dominant factors governing the development of tectonic fractures, which are the most developed in dolomites and thin layers. Tectonic fractures were most likely formed in regions near faults or areas with larger stress gradients. The tectonic fractures in the carbonate geothermal reservoirs are roughly divided into four sets: NNW–SSE and NNE–SSW oriented ‘X’-conjugated shear fractures formed from the Paleozoic to the pre-Yanshanian Movement; NE–SW-oriented shear fractures, formed in episode B of the Yanshanian Movement, occurred at the Early Cretaceous; nearly E–W-oriented tensional fractures formed in the late Yanshanian Movement at the Late Cretaceous to Paleogene, and NEE–SW-oriented shear fractures formed during the Himalayan movement.

摘要:Gneisses with anatectic characteristics from the Liansan island in the Sulu UHPM (ultra-high pressure metamorphic) belt were studied for petrography, titanite U-Pb dating and mineral geochemistry. Three origins of garnets are distinguished: metamorphic garnet, peritectic garnet and anatectic garnet, which are formed in the stages of peak metamorphism, retrograde anatexis and melt crystallization, respectively. The euhedral titanite has a high content of REE and high Th/U ratios, which is interpreted as indicating that it was newly-formed from an anatectic melt. The LA-ICP-MS titanite U-Pb dating yields 214–217 Ma ages for the titanite (melt) crystallization. The distribution of trace elements varies in response to the different host minerals at different stages. At the peak metamorphic stage, Y and HREE are mainly hosted by garnet, Ba and Rb by phengite, Sr, Nb, Ta, Pb, Th, U and LREE by allanite and Y, U and HREE by zircon. During partial melting, Y, Pb, Th, U and REE are released into the melt, which causes a dramatic decline of these element contents in the retrograde minerals. Finally, titanite absorbs most of the Nb, U, LREE and HREE from the melt. Therefore, the different stages of metamorphism have different mineral assemblages, which host different trace elements.

摘要:Cenozoic potassic–ultrapotassic igneous rocks are widespread in the southeastern Tibetan Plateau. Their petrogenesis and magmatic processes remain subject to debate in spite of numerous publications. Almost all of the Cenozoic extrusive and intrusive rocks in the Yao’an area, western Yunnan Province, SW China, are geochemically shoshonitic, collectively termed here the Yao’an Shoshonitic Complex (YSC). The YSC is located in the (south)easternmost part of the ENE?WSW-trending, ~550 km-long and ~250 km-wide Cenozoic magmatic zone; the latter separates the orthogonal and oblique collision belts of the India–Eurasia collision orogen. Previously published geochronological and thermochronological data revealed that the rocks of the YSC were emplaced over a short timespan of 34–32 Ma. This and our new data suggest that the primary magma of the YSC likely was formed by partial melting of ancient continental lithospheric mantle beneath the Yangtze Block. This part of the continental lithospheric mantle had likely not been modified by any oceanic subduction. Fractionation crystallization of an Mg- and Ca-bearing mineral and Ti-Fe oxides during the magmatic evolution probably account for the variable lithologies of the YSC.

摘要:We report the oxide, element geochemistry and Nd isotopic geochemical data of apatite in the middle Pleistocene medium- and fine-grained trachyte in the Tianchi volcanic area (TVA) of Changbai Mountain, discussing the relationship between apatite and the composition of the whole rock. The purpose is to use the apatite geochemical data to constrain the evolutionary process of trachytic magma and the petrogenesis of trachyte in the cone-forming period of the Tianchi volcano. Apatite (Ca5(PO4)3(OH, F, Cl)) is a common accessory mineral that occurs widely in volcanic rocks in the TVA. The apatites in the trachyte are mainly subhedral–anhedral, having the characteristics of magmatic apatite. In terms of oxide and element geochemistry, they have homogeneous Al2O3, SiO2, MgO, P2O5, K2O, CaO and heterogeneous TiO2, with high F content. They are generally enriched in Th, U and LREEs, depleted in Nb, Ta, Zr, Hf and HFSEs, showing negative Ba, Sr and Ti anomalies, similar to those of the whole-rock host trachytes. The ratios of high (La/Yb)N, low δEu (Eu/Eu*), Sr/Y value and ΣREE content in apatite, and the F, Sr, Y, Th/U, La/Sm, and Nd/Tb with ΣREE and δEu anomalies showed a linear correlation, all of those indicating that the host magma has the characteristic of high differentiation. The apatite grains generally having 147Sm/144Nd, 143Nd/144Nd ratios and εNd(t) values of 0.1072–0.1195, 0.5123–0.5126 and ?3.49 to ?0.10, respectively, are similiar to those of the host rock. The Nd model ages TDM1 are 949–803 Ma in apatite. Combined with the εNd(t) value of the apatite core (?7.06 to ?3.49), we conclude that the initial magma of the host trachyte was derived from the partial melting of Proterozoic crustal material and there was an assimilation of wall rocks during its evolution.

摘要:As an important part of the early Mesozoic granites in the South Qinling tectonic belt (SQTB), the Guangtoushan pluton provides a material basis for research on the composition of magma sources and the effects of peritectic assemblage entrainment (PAE) on the changes in the granite composition. As shown by the results of LA-ICP-MS zircon U-Pb dating, the Guangtoushan pluton was emplaced during the Late Triassic (214–212 Ma) and was formed in the post-collision stage between the SQTB and the Yangtze plate. The collected samples had high SiO2 content and low Cr and Ni contents, indicating that the magmas did not undergo significant crust-mantle mixing during their evolution. The Guangtoushan granitoids were distributed along the trend line of magmatic fractional crystallization in the F–An–Or diagram. This result, combined with the relatively homogeneous Sr-Nd isotopic composition, implies that the Guangtoushan pluton underwent slight assimilation and contamination. As can be inferred from the comparison between the compositions of the Guangtoushan granitoids and various fluid-absent experimental melts, the magma sources of the Guangtoushan granitoids contain a variety of materials, such as graywackes, pyroclastic graywackes, and pelites and are not derived from lower crustal mafic rocks. The correlation between the maficity and the major and trace elements further indicates that the strongly peraluminous granitoids from the Guangtoushan pluton was formed by the partial melting of biotite-bearing crustal rocks and its magmatic evolution was accompanied by the entrainment of clinopyroxenes and accessory minerals.

摘要:The Dahongshan Fe-Cu (-Au) deposit is a superlarge deposit in the Kangdian metallogenic belt, southwestern China, comprising approximately 458 Mt of Fe ores (40% Fe) and 1.35 Mt Cu. Two main types of Fe-Cu (-Au) mineralization are present in the Dahongshan deposit: (1) early submarine volcanic exhalation and sedimentary mineralization characterized by strata-bound fine-grained magnetite and banded Fe-Cu sulfide (pyrite and chalcopyrite) hosted in the Na-rich metavolcanic rocks; (2) late hydrothermal (-vein) type mineralization characterized by Fe-Cu sulfide veins in the hosted strata or massive coarse-grained magnetite orebodies controlled by faults. While previous studies have focused primarily on the early submarine volcanic and sedimentary mineralization of the deposit, data related to late hydrothermal mineralization is lacking. In order to establish the metallogenic age and ore-forming material source of the late hydrothermal (-vein) type mineralization, this paper reports the Re-Os dating of molybdenite from the late hydrothermal vein Fe-Cu orebody and H, O, S, and Pb isotopic compositions of the hydrothermal quartz-sulfide veins. The primary aim of this study was to establish the metallogenic age and ore-forming material source of the hydrothermal type orebody. Results show that the molybdenite separated from quartz-sulfide veins has a Re-Os isochron age of 831 ± 11 Ma, indicating that the Dahongshan Fe-Cu deposit experienced hydrothermal superimposed mineralization in Neoproterozoic. The molybdenite has a Re concentration of 99.7–382.4 ppm, indicating that the Re of the hydrothermal vein ores were primarily derived from the mantle. The δ34S values of sulfides from the hydrothermal ores are 2‰–8‰ showing multi-peak tower distribution, suggesting that S in the ore-forming period was primarily derived from magma and partially from calcareous sedimentary rock. Furthermore, the abundance of radioactive Pb increased significantly from ore-bearing strata to layered and hydrothermal vein ores, which may be related to the later hydrothermal transformation. The composition of H and O isotopes within the hydrothermal quartz indicates that the ore-forming fluid is a mixture of magmatic water and a small quantity of water. These results further indicate that the late hydrothermal orebodies were formed by the Neoproterozoic magmatic hydrothermal event, which might be related to the breakup of the Rodinia supercontinent. Mantle derived magmatic hydrothermal fluid extracted ore-forming materials from the metavolcanic rocks of Dahongshan Group and formed the hydrothermal (-vein) type Fe-Cu orebodies by filling and metasomatism.

摘要:The Goshgarchay Cu-Au deposit is located in the central part of the northwest flank of the Murovdagh region in the Lesser Caucasus. The Goshgarchay Cu-Au deposit is associated with Middle Jurassic volcanic and Late Jurassic–Early Cretaceous high-K calc-alkaline intrusive rocks. The Cu-Au mineralization is commonly related to quartz-sericite-chlorite alteration dominantly composed of chalcopyrite, gold, sphalerite, pyrite, bornite, hematite, covellite, chalcocite, malachite, and azurite. The Goshgarchay copper-gold deposit, which is 600 m wide and approximately 1.2 km long, is seen as a fault-controlled and vein-, stockwork– and disseminated type deposit. The Goshgarchay Cu-Au deposit predominantly comprises Cu (max. 64500 ppm) and Au (max. 11.3 ppm), while it comprises relatively less amounts Zn (max. 437 ppm), Mo (max. 47.5 ppm), Pb (max. 134 ppm), and Ag (max. 21 ppm). The homogenization temperatures and salinities of fluid inclusions in quartz for stage I range from 380°C to 327°C, and 6.9 wt% to 2.6 wt% NaCl eq., respectively. Th and salinities in quartz for stage II range from 304°C to 253°C, and 7.6 wt% to 3.2 wt% NaCl eq., respectively. The calculated δ34Sh2s values (?1.5‰ to 5.5‰) of sulfides and especially the narrow range of δ34Sh2s values of chalcopyrite and bornite (between ?0.07‰ and +0.7‰) indicate that the source of the Goshgarchay Cu-Au mineralization is magmatic. Based on the mineralogical, geochemical, fluid inclusion, and sulfur isotopic data, the Goshgarchay Cu-Au deposit represents a late stage peripheral magmatic-hydrothermal mineralization probably underlain by a concealed porphyry deposit.

摘要:To investigate the influence of diagenetic water media on the hydrogen isotopes of individual sedimentary aromatic compounds, a series of hydrous pyrolyses were conducted on herbaceous peat. Polycyclic aromatic hydrocarbons (PAHs) in hydrous pyrolysed samples and their hydrogen isotopic composition characteristics were studied. The aqueous medium demonstrated a significant influence on the hydrogen isotopic composition of the individual PAHs generated during pyrolysis. The results showed that the PAHs formed after pyrolysis in the presence of a saltwater medium with high δD value from a salt lake had a heavy hydrogen isotopic composition. The PAHs formed after pyrolysis in the presence of a fresh water medium with low δD value from a swamp had a light hydrogen isotopic composition. The difference in the average PAH δD value between the two hydrous experiments varied from –174‰ to –109‰, suggesting that the hydrogen isotopic composition of individual sedimentary PAHs can reflect the source of the diagenetic water medium. In addition, a comparative study found that the hydrogen isotopes of PAHs were superior to those of n-alkanes in the same sample for diagenetic water indications. The results indicated that the exchange of water-derived inorganic hydrogen and organic hydrogen was more intensive in freshwater experiments than in saltwater experiments. With an increase in the simulation temperature, the average δD value of PAHs generated in the hydrous simulation experiments showed an increasing trend, reflecting that the δD value of sedimentary PAHs formed with the participation of diagenetic water media was still closely related to the thermal maturity of organic matter. Comparative studies showed that the δD values of different types of organic compounds produced by hydrous pyrolysis of peat were in the order, PAHs > n-alkanes > methane.

摘要:The late Paleozoic Fengcheng Formation shale (LPF shale) in the Junggar Basin, NW China, is the oldest alkaline source rock discovered in the world, providing a unique perspective with which to explore organic matter (OM) enrichment in alkaline lake environments. Combined with the organic carbon isotope profile and paleoenvironmental proxies, this study reveals that the LPF shale was deposited in an arid climate with high salinity and a strong reducing environment, accompanied by frequent volcanic activity. High TOC values are concentrated in two intervals with frequent fluctuations in OM types. A negative excursion due to changes in sedimentary OM source is found in the δ13Corg profile. The excursion corresponds to the OM enrichment interval and is accompanied by abnormally high values of Sr/Ba and Sr/Cu. This implies that the extreme arid climate has led to high salinity, resulting in strong reducibility and changes in paleontological assemblages, which in turn controlled the differential enrichment of OM. The Fengcheng Fm. high-quality source rocks are the result of the combined action of climatic events, volcanism, high-salinity water environment and superior hydrocarbon-generating organisms. The results provide new insights into the formation conditions of terrestrial alkaline high-quality source rocks and the factors controlling alkaline OM enrichment.