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geochemical cycling during subduction initiation:Evidence from serpentinized mantle wedge peridotite in the south Andaman ophiolite suite

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Geoscience Frontiers 2018年第6期9卷 1755-1775页

作者： Abhishek Saha M.Santosh Sohini Ganguly C.Manikyamba Jyotisankar Ray Jagadish Dutta CSIR-National Institute of Oceanography Dona PaulaGoa 403 004India School of Earth Science and Resources China University of GeosciencesBeijing100083China Department of Earth Sciences University of AdelaideAdelaideSA 5005Australia Department of Earth Science Goa UniversityTaleigao PlateauGoa 403206India CSIR-National Geophysical Research Institute Uppal RoadHyderabad500 007India Department of Geology University of Calcutta35Ballygunge Circular RoadKolkata700 019India

The ophiolite suite from south Andaman Islands forms part of the Tethyan Ophiolite Belt and preserves the remnants of an ideal ophiolite sequence comprising a basal serpentinized and tectonised mantle peridotite followed by ultramafic and mafic cumulate units, basaltic dykes and spilitic pillow basalts interlayered with arkosic wacke. Here, we present new major, trace, rare earth(REE) and platinum group(PGE) element data for serpentinized and metasomatized peridotites(dunites) exposed in south Andaman representing the tectonized mantle section of the ophiolite suite. geochemical features of the studied rocks, marked by Al_2 O_3/TiO_2 > 23, LILE-LREE enrichment, HFSE depletion, and U-shaped chondrite-normalized REE patterns with(La/Sm)N > 1 and(Gd/Yb)N <1, suggest contributions from boninitic mantle melts. These observations substantiate a subduction initiation process ensued by rapid slab roll-back with extension and seafloor spreading in an intraoceanic fore-arc regime. The boninitic composition of the serpentinized peridotites corroborate fluid and melt interaction with mantle manifested in terms of(i) hydration, metasomatism and serpentinization of depleted, MORB-type, sub-arc wedge mantle residual after repeated melt extraction; and(ii) refertilization of refractory mantle peridotite by boninitic melts derived at the initial stage of intraoceanic subduction. Serpentinized and metasomatized mantle dunites in this study record both MOR and intraoceanic arc signatures collectively suggesting suprasubduction zone affinity. The elevated abundances of Pd(4.4-12.2 ppb) with highΣPPGE/∑IPGE(2-3) and Pd/Ir(2-5.5) ratios are in accordance with extensive melt-rock interaction through percolation of boninitic melts enriched in fluid-fluxed LILE-LREE into the depleted mantle after multiple episodes of melt extraction. The high Pd contents with relatively lower Ir concentrations of the samples are analogous to characteristic PGE signatures of boninitic magmas and might have resulted by the infiltration of boninitic melts i

关键词： South Andaman Ophiolite Mantle peridotite Metasomatism geochemical cycling Subduction initiation

geochemical characteristics and genetic type of a lithium ore (mineralized) body in the central Yunnan Province, China

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China Geology 2019年第3期2卷 287-300页

作者： Bai-dong Sun Jun-ping Liu Xiao-hu Wang Yan Dao Gui-xiang Xu Xiao-zhuang Xue-qing Guan Wei Wang Dong-hu Song Yunnan Institute of Geological Survey Kunming 650216China Kunming University of Science and Technology Kunming 650093China Chengdu Center China Geological SurveyMinistry of Natural ResourcesChengdu 610081China

Lithium ore (mineralized) bodies in the area A of central Yunnan Province belong to a sedimentary-type, which are controlled by stratum. The studied ore (mineralized) body mainly occurs in the Middle Permian Liangshan Formation. This work described the morphology, structures, main ore types and geochemical characteristics of this ore body in detail, and discussed the ore-forming material source, occurrence state of lithium and the formation mechanism of lithium ores to clarify the prospecting marks. In the further exploration, comprehensive evaluation of the lithium resources of known bauxite ore bodies in central Yunnan Province should be strengthened, and the exploration of hidden lithium ore bodies should be intensified in order to discover more large and super-large lithium orebodies, which will fill the gap of the national demand for lithium resources, and promote the national defense construction and new energy industry development.

关键词： Sedimentary-type lithium deposit Stratified deposit geochemical characteristics Metallogenic mechanism Mineral resources exploration engineering Yunnan Province China

Comprehensive geochemical/hydrochemical and geo-thermometry analysis of Unai geothermal field, Gujarat, India

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Acta Geochimica 2019年第1期38卷 145-158页

作者： Manan Shah Anirbid Sircar Nahid Shaikh Karan Patel Darshan Sharma Dwijen Vaidya School of Petroleum Technology Pandit Deendayal Petroleum University Wipro Limited Centre of Excellence for Geothermal Energy Pandit Deendayal Petroleum University

The knowledge of water temperature produced from a geothermal reservoir and its composition is of utmost importance in designing utilization strategies, the surface production facilities and in selecting the material to be used. Unai hot springs are located in the southern part of Gujarat, India with discharge temperatures varying from 51 to 56 ℃. With the aim of developing Unai as a potential geothermal field and exploiting it in the future, geochemical and geothermometrical study was undertaken. The samples were collected from various Unai geothermal location and analysis of chemical composition of water obtained from different wells was done. The concentration of Silica, carbonate and ions like Na and Cl have been analyzed to delineate the path of water movement in the subsurface and classify the reservoir based on the enthalpy.The ratio of the concentration of ions like Na^+ and K^+ and the relative proportions of various sets of ions were also used to characterize the geothermal reservoir and the reservoir fluid by the use of ternary diagrams. Na–K–Ca,Chalcedony, quartz, and Silica geo-thermometers have been studied. The present study also envisages the importance of graphical representations like Piper diagram,Scholler etc. to determine variation in hydrochemical facies and to understand the evolution of hydrochemical processes in the Unai geothermal field respectively. The study yields the conclusion that the reservoir under consideration is a low enthalpy reservoir with temperature ranging from 60 to 80 ℃.

关键词： Geothermal energy Hydrochemical geochemical Geothermometery Renewable energy

Molecular Organic geochemical Characteristics and Coal Gas Potential Evaluation of Mesozoic Coal Seams in the Western Great Khingan Mountains

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Acta Geologica Sinica(English Edition) 2020年第2期94卷 409-417页

作者： QU Yue SHAN Xuanlong DU Tiantian DU XianLi ZHAO Rongsheng College of Earth Sciences Jilin UniversityChangchun 130061China Key Laboratory for Evolution of Past Life and Environment in Northeast Asia Jilin UniversityMinistry of EducationChangchun 130061China College of Mining Engineering Heilongjiang University of Science&TechnologyHarbin 150022China

Coal-bearing strata are widespread in the western Great Khingan Mountains. Abundant coal resources have been found in the Jurassic Alatanheli Groups, the Cretaceous Bayanhua Groups, the Damoguaihe Formation and the Yimin Formation. The organic geochemical characteristics were analyzed in combination with hydrocarbon source rock evaluation and molecular organic geochemistry experiments, and the coal gas potential of coal seams was evaluated. The source rock evaluation results indicated that the Mesozoic coal samples have the characteristics of high organic matter abundance(TOC>30%), low maturity(Ro values of approximately 0.6%), and type Ⅲ composition. The hydrocarbon generation potentials of the Alatanheli Groups and Bayanhua Groups are high, while the generation potentials of the Damoguaihe Formation and the Yimin Formation are low. The results of geochemistry show that the depositional environment of the coal seam was a lacustrine, oxidizing environment with a low salinity, and the source of the organic matter was mainly higher plants. Affected by weak degradation, the coal seams mainly formed low-maturity gas of thermal catalytic origin. The Cretaceous coal seams contain a large amount of phytoplankton groups deposited in a low-stability environment affected by a transgression event, and the potential range varied widely. For the Jurassic coal seams, the depositional environment was more stable, and the coal seams feature a higher coal-forming gas potential.

关键词： coal source rocks molecular organic matter geochemical characteristics low-maturity gas coal gas western part of the Great Khingan Mountains

A Model of Hydrothermal Dolomite Reservoir Facies in Precambrian Dolomite, Central Sichuan Basin, SW China and its geochemical Characteristics

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Acta Geologica Sinica(English Edition) 2019年第1期93卷 130-145页

作者： GU Yifan ZHOU Lu JIANG Yuqiang JIANG Chan LUO Mingsheng ZHU Xun School of Geosciences & Technology Southwest Petroleum University Exploration Division PetroChina Southwest Oil & Gas Field Company Shunan Division of Petrochina Southwest Oil&Gas Field Company Exploration and Development Institute of Southwest Oil&Gas Field Company PetroChina

Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug(or pore), 2) intercrystalline pore, 3) residual inter-breccia vug(or pore), and 4) enlarged dissolved-fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine-medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids(average temperature 192°C). Fine-medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ^(18)O, significant enrichment of Mn-Fe and ^(87)Sr/^(86)Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono-hydrothermal events(i.e., the Xingkai Taphrogenesis of Late Sinian-Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness(e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids(such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement-rooted faults and associated grid-like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above-mentioned faults(including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon expl

关键词： hydrothermal dolomite reservoir facies geochemical characteristics Precambrian Dengying Formation central Sichuan Basin

Ophiolites of the Central Asian Orogenic Belt:geochemical and petrological characterization and tectonic settings

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Geoscience Frontiers 2019年第4期10卷 1255-1284页

作者： Harald Furnes Inna Safonova Department of Earth Science University of BergenAllegt.415007BergenNorway Sobolev Institute of Geology and Mineralogy 3 Koptyuga ave.Novosibirsk 630090Russia Novosibirsk State University 1Pirogova St.Novosibirsk 630090Russia

We present a compilation of published data(field,petrography,ages and geochemistry)from 73 ophiolitic complexes of the Central Asian Orogenic Belt.The ophiolitic complexes,ranging in age from Neoproterozoic to Triassic.have been geochemically classified as subduction-related and subductionunrelated categories applying recent,well-established discrimination diagrams.The subductionunrelated category is further subdivided into Mid-Ocean Ridge type(MOR),a common rift-drift stage and Plume type,and the subduction-related category is subdivided into Backarc(BA),Forearc(FA).Backarc to Forearc(BA-FA)and Volcanic Arc(VA)types.The four subduction-related types define highly different geochemical features,with the BA and FA types defining end members showing subduction influence of 10%-100%and 90%-100%subduction influence,respectively,and the two other types(BAFA and VA)define values between the two end members.The subduction-related category comprises79%of the examined ophiolites,of which the BA type ophiolites is by far the dominant group,followed by the BA-FA type,and with FA and VA types as subordinate groups.The Neoproterozoic and Ordovician complexes exhibit the highest,whereas those of Silurian age exhibit the lowest subduction-influence.Of the remaining 21%subduction-unrelated ophiolites,the MOR type dominates.Both the subductionrelated and subduction-unrelated types,in particular the latter,are commonly associated with alkaline basalts taken to represent ocean island magmatism.Harzburgite,dunite,gabbro and basalt are the common lithologies in all ophiolite types,whereas the BA-FA,FA and VA types generally contain intermediate to felsic rocks,and in the FA type boninites occur.The subduction-related ophiolites types generally show low metamorphic grade,whereas greenschist.amphibolite and blueschist grades occur in the subduction-unrelated and BA types.The highly different subduction contribution(from 0 to 100%in the MOR and FA,respectively),attest to variable dips of the subducting slab,as well as variable flux of s

关键词： geochemical classification Subduction-unrelated units Subduction-related units Subduction fingerprint Intra-plate magmas Arc erosion

Innovations on Assembled Techniques of geochemical Lithofacies and Their Applications in Basin Analysis and Exploration for Minerals in Basins

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Acta Geologica Sinica(English Edition) 2017年第S1期91卷 199-201页

作者： FANG Weixuan China Non-Ferrous Metals Resource Geological Survey BeijingChina100012

1 Introduction Research and development on assembled techniques of geochemical lithofacies is to be oriented,at the firstly,by technological issues or conundrum in methodology,and to be subsidiary directed by applications of theoretic basis in sedimentary basin analysis and explorations for minerals in the ore-hosting basin.However these are to be steered by integrated knowledge and cross-sectional study while they are focused on the core value and innovative technology.

关键词： sedimentary geochemical innovative technological subsidiary tectonic magmatic facies hydrocarbon volcanic

Discovery of Wolitu Pb-Zn deposit through geochemical prospecting under loess cover in Inner Mongolia, China

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Geoscience Frontiers 2017年第5期8卷 951-960页

作者： Fan Yang Mu Kong Huazhong Liu Jinsong Yu Shaoping Yang Zhihong Hao Dehui Zhang Kuang Cen School of Earth Sciences and Resources China University of Geosciences (Beijing) Beijing 100083 China Institute of Geophysical and geochemical Exploration Chinese Academy of Geological Sciences Langfang 065000 Hebei China UNESCO International Centre on Global-Scale Geochemistry Langfang 065000 Hebei China Key Laboratory of geochemical Exploration Ministry of Land and Resources China Langfang 065000 Hebei China

We report the finding of the Wolitu Pb-Zn deposit in Inner Mongolia, China, through a series of geochemical surveys. The Wolitu area, located in the loess-cover area in the Hure Banner, Tongliao City,Inner Mongolia, and neighboring the Horqin Sandy Land to the north, had no previous history of Pb-Zn mining or record of Pb-Zn mineralization. Our study identified a large Pb-Zn anomaly with potential zones of mineralization by stream sediment survey. Random rock sampling reveals limonitization at sporadic outcrops in the gullies. The high concentrations of Pb in the residual debris provided guidelines to fix the position for exploratory trench. Oxidized concealed orebodies were identified by trenching.Blind orebodies in veins hosted within the structural zone between slates and marbles of the upper Carboniferous Shizuizi Formation and the Permian granite were discovered by drilling. It is computed that the ore reserve may reach up to 540,000 tones with Pb grade of 1.27% and Zn of 1.9%. This case study is an excellent example for identifying potential polymetallic deposits in loess covered terrains using geochemical exploration.

关键词： geochemical exploration Loess-covered area Pb-Zn deposit Resource reserve Inner Mongolia

geochemical Characteristics and Prospecting Direction of the Hongwei-Xiongguan-Songheyi Dongshan Area in the Greater Xing’an Mountains, Heilongjiang Province

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Meteorological and Environmental Research 2019年第5期10卷 103-104,111页

作者： Wang Ziteng Shi Yajing Shi Jiayuan Du Bangyu Du Chunsheng State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Chengdu University of TechnologyChengdu 610059China Institute of Sedimentary Geology Chengdu University of TechnologyChengdu 610059China College of Earth Sciences Chengdu University of TechnologyChengdu 610059China Fifth Geological Exploration Institute of Heilongjiang Province Harbin 150000China Heilongjiang Geological Science Institute Harbin 150000China

The Daxinganling area collided during the Late Paleozoic.The study area Hongwei-Xiongguan-Songheyi Dongshan area is located at the superimposed transition site of the Paleozoic paleo-Asian tectonic-metallogenic domain and the Mesozoic-Cenozoic Pacific Ocean tectonic-mineralization area.It is a good ore-forming fluid channel and has very good ore metallogenic geological conditions.The comprehensive research and metallogenic prediction of the geological background and geochemical characteristics of this area are carried out.It is believed that this area has good prospecting potential,and the prospecting area is circled.Suggestions for further prospecting work in this area are put forward.

关键词： geochemical characteristics Prospecting direction The Greater Xing'an Mountains Heilongjiang Province