Sulfur isotopic composition of modern seafloor hydrothermal sediment and its geological significance

A total of 1 264 sulfur isotopic values for modern seafloor hydrothermel sediments from different hydrothermal fields have been collected.On this basis,combining our sulfur isotpic data for surface hydrothermal sediments from the Jade hydrohtermal field in the Okinawa Trough and the TAG hydrothermal field in the Mid-Atlantic Ridge,respectively,and comparing the sulfur isotopic compositions and analyzing their sources of sulfur in seafloor hydrothermal sediments from different geologic-tectonic setting,the results show that:(1) sulfur isotopic values of sulfides and sulfates in modern seafloor hydrothermal sediments are concentrated in a narrow range,δ 34S values of sulfides vary from 1×10 -3 to 9×10 -3,with a mean of 4.5×10 -3 (n=1042),δ 34S values of sulfates vary from 19×10 -3 to 24×10 -3,with a mean of 21.3×10 -3(n=217);(2) comparing the sulfur isotopic compositions of hydrothermal sediments from the sediment-hosted hydrothermal fields,the range of sulfur isotopic values for hydrothermal sediments from the sediment-free hydrothermal fields is narrow relatively;(3) the differences of sulfur isotopic compositions in sulfides from different hydrothermal fields show the differences in the sources of sulfur.The sulfur of hydrothermal sulfides in the sediment-free mid-ocean ridges is mainly from mid- ocean ridge basalt,and partially from the reduced seawater sulfate,and it is the result of partially reduced seawater sulfate mixed with basaltic sulfur.In the sediment-hosted mid-ocean ridges and the back-arc basins,the volcanics,the sediments and the organic matters also can offer their sulfur for forming hydrothermal sulfides;(4)the variations of sulfur isotopic compositions and the different sources of sulfur for hydrothermal sediments may be attributed to the various physical-chemical characteristics of hydrothermal fluids,the magmatic evolution and the different geologic-tectonic settings of seafloor hydrothermal systems.

Characteristics of strike-slip inversion structures of the Karatau fault and their petroleum geological significances in the South Turgay Basin,Kazakhstan

The Karatau fault is one of the important strike-slip faults in central Asia,and the South Turgay Basin is located towards its northern end.Detailed seismic interpretation indicated that the strikeslip tectonism of the Karatau fault weakened gradually from west to east in the South Turgay Basin.Typical flower structures developed on the section,and strike-slip faults showed an echelon pattern on planar view.The Karatau strike-slip fault affected the South Turgay Basin in two periods：（1） The South Turgay strike-slip pull-apart rift basin formed as a result of regional extensive stress in the Early-Middle Jurassic,characterized by the juxtaposition of horsts and grabens.The formation of horsts provided favorable reservoir spaces for later hydrocarbon accumulation,and different filling stages of grabens controlled different reservoir-forming factors in grabens.（2） Two stages of tectonic inversion occurred in the Late Jurassic and Late Cretaceous and played a crucial role in the final shape of the structure in the South Turgay Basin.The oil and gas migrated to form reservoirs and mainly concentrated in the horsts,graben slopes and in both sides of the strike-slip fault zone.In the case of the degree of accumulation of petroleum,the factor explaining why horsts are better than grabens is the strike-slip pull-apart of the South Turgay Basin,and the structure inversion of the South Turgay Basin explains why the west graben is better than the east one.Overall,the Karatau strike-slip fault played a very important role in the formation of the South Turgay Basin and its hydrocarbon accumulations.

Precise Dating and Geological Significance of the Caledonian Shangyou Pluton in South Jiangxi Province

The zircon SHRIMP dating age for the Shangyou granites is 464±11 Ma. The geological feature of the pluton is consistent with the isotopic age, which shows that it is a product of Caledonian orogenesis. The Shangyou granites are regarded as peraluminous crust-derived granites to possess the typical geochemical characteristics of calc-alkaline rocks on the active continental margin with enriched Si, K, Al （A/CNK -- 1.11 on average）, HREE, Rb, U, Th and heavily depleted V, Cr, Co, Ni, as well as Ti-Y, Nb-Ta, Zr, Sr, P and Ba, to be commonly corundum normative （av C -- 1.44）. The Shangyou granites with higher 87Sr/86Sr ratios （0.707126-0.712186）, ENd（t） values （-7.29 to -10.22） and （tDM） values （1.52-1.63 Ga）, which are considered to result from partial melting of continental crust metamorphic sedimentary rocks with relatively low of crust maturation degree corresponding to the Middle Proterozoic, to have some possible contributions of mantle-derived components. The Shangyou granites are regarded as post-collision granites, which were formed in a transitional tectonic setting from compression to extension in the Middle Ordovician period after the Yangtze plate was subducted beneath the Cathaysian plate. The Ar-Ar total ages of K-feldspar and biotite are 292.1 Ma and 295.5 Ma respectively, which have recorded information of a late-stage thermal alteration event.

Re-recognition of Tieshan “Syenite” and its Geological Significance in Zhenghe, Fujian Province

1 Introduction Tieshan Syenite crosses between Dongfeng and Zhangyuan’an in Zhenghe of Fujian province,occurs in the direction of 42°,Total length 8500m,width 600-800m and its Area of about 39km2.Outcrops of the mass are

Magnetostratigraphy of a Loess-Paleosol Sequence from Higher Terrace of the Daduhe River in the Eastern Margin of the Tibetan Plateau and Its Geological Significance

The eolian deposits distributed in the river valleys in the eastern margin of the Tibetan Plateau （TP） are very useful in neotectonic and paleoclimatic studies. Firstly, the climate in the eastern margin of the TP is mainly controlled by the Indian summer monsoon, and detailed studies on the loess-paleosol sequences in this region can provide valuable terrestrial evidence of past changes in the Indian summer monsoon. Secondly, the river terraces in the eastern margin of the TP are considered to be a sensitive recorder of neotectonism to reflect the timing and amplitude of the TP uplift.

New Discovery of the Late Triassic Terrigenous Sediments in the Great Xing＇＇an Range Region,NE China and its Geological Significance

Objective The Great Xing＇an Range is located in the eastern section of Central Asian Orogenic Belt（CAOB）.As a superposed position of multiple tectonic domains,its structural evoIlution has always been a focused issue of geological research.

Cassiterite U-Pb Date of the Yangbin Porphyry Tin Deposit in Zhejiang and its Geological Significance

Objective The Yangbin porphyry tin deposit in Taishun County of Zhejiang Province is one of the few porphyry-type tin deposits in South China, which is located in the middle portion of the Mesozoic volcanic active belt on the southeastern coast of China. The Yangbin granite porphyry is closely related to the tin mineralization in this region. Based on petrologic and Sr-Nd-Pb isotopic

Deep-water gravity flow deposits in a lacustrine rift basin and their oil and gas geological significance in eastern China

The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport of slide and slump,fluid transport of debris flow and turbidity currents are driven by gravity in deep-water lacustrine environment.The transformation between debris flow and turbidity current,and the transformation of turbidity current between supercritical and subcritical conditions are the main dynamic mechanisms of gravity flow deposits in a lake basin.The erosion of supercritical turbidity current controls the formation of gravity-flow channel.Debris flow deposition gives rise to tongue shape lobe rather than channel.Deep-water gravity flow deposits are of two origins,intrabasinal and extrabasinal.Intrabasinal gravity flow deposits occur as single tongue-shape lobe or fan of stacking multiple lobes.Extrabasinal gravity-flow deposits occur as sublacustrine fan with channel or single channel sand body.However,the nearshore subaqueous fan is characterized by fan of stacking multiple tongue shape lobes without channel.The differential diagenesis caused by differentiation in the nearshore subaqueous fan facies belt results in the formation of diagenetic trap.The extrabasinal gravity flow deposits are one of the important reasons for the abundant deep-water sand bodies in a lake basin.Slide mass-transport deposits form a very important type of lithologic trap near the delta front often ignored.The fine-grained sediment caused by flow transformation is the potential"sweet spot"of shale oil and gas.

Geochronology and geochemistry of the ore-bearing intrusion in the Longgen Lead-Zinc deposit in Tibet and its geological significance

1 Introduction The Longgen Lead-Zinc deposit is located in the southern Gangdise-Nyainqentantanglha plate and belongs to the western section of the Nyainqentantanglha copper-lead-zinc-silver metallogenic belt.In this paper,

40^Ar-39^Ar Dating of the Mahuaping W-Be deposit, Northwestern Yunnnan Province, China, and its Geological Significance

Objective Located near the intersection of Yangtze craton, Tibet- Sanjiang orogen and Songpan-Ganzi orogen of Northwest Yunnan Province, the Mahuaping deposit is a unique large -scale tungsten-beryllium-fluorite ore deposit ever discovered in this area. In recent years, many studies have been carried out in Sanjiang Tethyan metallogenic belt and aforementioned adjacent regions. To date, however, little attention has been paid to this deposit, for example, the geochronology of Mahuaping W-Be deposit still remains unsolved. In this study, we have pioneered research about muscovite 40Ar-39Ar age to better understand the geochronology of the Mahuaping W-Be deposit.

Newly Discovered Fluvial-Lacustrine Sediments in the Western Yangtze Block and their Geological Significance for the Emeishan Large Igneous Province

Objective The Emeishan large igneous province （ELIP） in SW China is the only one large igneous province in China recognized by international geologists. Previous studies of ELIP over past two decades indicate that the ELIP age, duration, scale and generation mechanism are still controversial. Among those scientific topics, some scholars suggest that ELIP is an example of up-doming prior to LIP formation, which was evidenced by： （1） The thickness of the Yangxin Formation （P^v） limestone unit, which lies directly beneath ELIP, reduces from the center of erosional area to the outer edge. （2） Paleo-karst surfaces are present. （3） The clastic rocks of alluvial fan deposits, from the eroded materials in the maximum uplifted area, developed surrounding the inner zone. However, other scholars urge that those so-called ＂alluvial fan＂ deposits are ＂hydromagmatic deposits＂, erupted or emplaced at or near sea level, and conclude that there was no pre-emptive uplift in ELIP. In order to constrain the above-mentioned scientific issue, we conducted detailed field geological investigations and systematically measured geological sections to provide new evidence by using sedimentary data.

Petrogeochemistry, geochronology and its geological significance of the granite from Baishipo Ag deposit, Dabie orogen

1 Introduction Granitoid magmas have been widely used as a natural probe for tracing the crustal evolution process(Martin et al.,2005).Mesozoic granitoids are widespread in the Dabie

Geochemical characteristics and geological significance of picritic rocks in Permian Tiaohu Formation from Santanghu Basin, Xinjiang, NW China

1 Introduction Santanghu Basin is located between the Armantai and Karamaili suture zone,at the junction of the Siberia,Kazakhstan and Tarim plates(Chen and Jahn,2004;Xiao et al.,2008).As an important part of the Central Asian

Late Paleoproterozoic-Neoproterozoic Multi-rifting Events Accompanied by Four Stages of Magmatism in the North China Craton and Their Geological Significance

An important Paleoproterozoic mobile belt event took place in the North China Craton(NCC),termed the Hutuo Movement.This has been interpreted as a cratonic reworking event with rifting-subduction-collision

Zircon U-Pb Dating of Leucogranite in Lhozag and Its Geological Significance

The Himalayan leucograite, which is typical production of continent-continent collision orogenic belt, has become a research hotspot of the Tibetan Plateau. The research on the leucogranite would help to verify and improve the continent-continent collision orogenic theory. （Huang et al., 2017; Fig. la）. Previous studies show the Himalayan leucogranite was mainly melted from crust materials （Guo and Wilson, 2012）. But it remains controversial for the formation model as to whether it formed from gathering of dikes or diaper of deep magma chambers.

Palynomorphs from Metamorphic Rocks in Southern Anhui and Their Geological Significance

The southern Anhui metamorphic terrane is traditionally regarded as a part of middle-lateProterozoic "Jiangnan Old Land". Based on the occurrence of palynomorphsAsperatopsophosphaera sp., Trachysphaeridium sp. and Nucellosphaeridium sp. (late

Identification of Greigite in the Pliocene Sediments of Qinghai Lake and Its Geological Significance

The Qinghai Lake in North China is the largest interior plateau lake in Central Asia, and is sensitive to climate change and the environmental effects of Tibetan Plateau uplift. An almost continuous 626 m long sediment core was drilled in an in-filled part of the southern lake basin in the Scientific Drilling at Qinghai Lake.

China's Shale Gas Geological Investigation and Prospecting Have Made Significant Progress

Since 2015, the China Geological Survey has implemented a major program of ＂Geology Survey of Land Energy Mineral Resources＂. Till now, a total of billions of RMB have been invested and seven engineering projects have been established, all of which has greatly enhanced the geological survey and exploration of China＇s continental shale gas in an attempt to overcome the oil and gas shortage.

Geochemical characteristics and geological implication of ferromanganese crust from CM6 Seamount of the Caroline Ridge in the Western Pacific

Ferromanganese crusts(Fe-Mn crusts)grow very slow and can be treated as condensed stratigraphic sections recording paleo-oceanographic environmental information and local key geological events during the mineralization process.Geochronology,textures,mineralogy,and geochemistry of a Fe-Mn crust sample from the CM6 Seamount of the Caroline Ridge in the Western Pacific Ocean were analyzed by means of electron probe microanalysis and X-ray diffraction.The Fe-Mn crust shows three layers in textural characteristics from bottom to top.The lower,middle,and upper layers presence mottled,botryoidal,and columnar textures,respectively.Ferruginous vernadite,Fe hydroxide,amorphous silicate minerals,calcite,quartz,and feldspar are the main minerals of the Fe-Mn crust.Using cobalt chronometry method,the cumulative growth time of the Fe-Mn crust was determined to be 11 Ma or 25 Ma,of which25 Ma is inconsistent with other lines of age constraint brought by dating of the substrate.The co-existence of abundant silicate minerals and bioclasts in the middle and lower layers of the Fe-Mn crust diluted the ferromanganese oxide deposits,thus affected the texture,minerals,and geochemical characteristics of the Fe-Mn crust.Variations in Mn Co,Ni,and other elements content and the burial of opal-A recorded the expansion of oxygen minimum zone(OMZ)in the upper layer of the Fe-Mn crust.In addition,the highreflectivity Fe-rich laminae might indicate the surrounding volcanic activity.The Fe-Mn crust sample was determined to be hydrogenic by electron probe micro-analyzer(EPM A).The findings help us understand the geochemical characteristics of the Fe-Mn crust in the Caroline Ridge Seamount in the Western Pacific and the variations of paleo-oceanographic environment clues borne by the Fe-Mn crusts.

Multi-scale fractures formation and distribution in tight sandstones—a case study of Triassic Chang 8 Member in the southwestern Ordos Basin

Fracture system is an important factor controlling tight oil accumulation in the Triassic Chang 8 Member,southwestern Ordos Basin,China.A systematic characterization of the multi-scale natural fractures is a basis for the efficient tight oil production.Based on outcrops,seismic reflections,well cores,well logs(image and conventional logging),casting thin sections,and scanning electron microscope observation,the multi-scale fractures occurrences and their influences on Chang 8 tight sandstone reservoirs are revealed.The results show that three periods of strike-slip faults and four scales of natural fractures developed,namely mega-scale(length>7×10^(7) mm),macro-scale(3.5×10^(5)<length<7×10^(7) mm),meso-scale(10<length<3.5×10^(5) mm),and micro-scale(length<10 mm)fractures.The mega-and macro-scale fractures developed by strike-slip faults are characterized by strike-segmentation and lateral zonation,which connect the source and reservoir.These scale fractures also influence the distribution and effectiveness of traps and reservoirs,which directly influence the hydrocarbon charging and distribution.The meso fractures include the tectonic,diagenetic,as well as hydrocarbon generation-related overpressure types.The meso-and micro-scale fractures improve the sandstone physical properties and also the tight oil well production performance.This integrated study helps to understand the distribution of multi-scale fractures in tight sandstones and provides a referable case and workflow for multi-scale fracture evaluation.