2020, Volume 27 Issue 1
    20 January 2020
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    The status and development trend of geothermal resources in China
    WANG Guiling,LIU Yanguang,ZHU Xi,ZHANG Wei
    2020, 27(1): 1-9. 
    DOI: 10.13745/j.esf.2020.1.1

    Abstract ( 445 )   PDF (9843KB) ( 1023 )  

    China is well endowed with geothermal resources that is widely distributed with distinctive distribution pattern and regional characteristic. In this work, we systematically summarized the recent nationwide achievements in geothermal energy developments. Shallow geothermal resources are extensively available throughout the country. For 336 above prefecturelevel cities, the annual recoverable amounts of shallow geothermal and hydrothermal resources were equivalent to 700 million and 1.9 billions tons of standard coal, respectively; the prospective amount of hot dry rock resources was equivalent to 856 trillion tons of standard coal. We also discussed the typical genetic mechanism of hydrothermal and hot dry rock resources. Rapid progresses of geothermal energy development and utilization technology have seen increasing shallow geothermal and hydrothermal resources explorations year by year. However, technical bottlenecks and imperfections still need to be resolved urgently in the areas of geothermal resource genesis, exploration and utilization management. In order to promote an healthy and orderly development of geothermal industry, future improvements should be focus on enhancing studies of resource genesis and geothermal tectonics and exploration technology, advancing geothermal technology and development and utilization demonstrations, assessing shallow geothermal and hydrothermal resources in key areas, and perfecting developmental and exploration methodologies for dry hot rock geothermal resource.

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    Discussion on the mechanism of deep geothermal energy transmission
    LUO Wenxing,SUN Guoqiang,ZHOU Yang,LIU Demin,CHEN Qi
    2020, 27(1): 10-16. 
    DOI: 10.13745/j.esf.2020.1.2

    Abstract ( 112 )   PDF (2595KB) ( 413 )  

    Based on deductive testing of previous mechanistic models of geothermal energy generation, we deduced the dynamic process of “internal heat transfer from the deep to the shallow surface of the earth”. We also discussed the mechanism of deep geothermal energy transmission from a few basic laws (first principles) through deductive reasoning. From a physical perspective, geothermal energy is essentially the result of thermal energy transfer from the Earth’s interior to the shallow crust. According to the first principle, the possible transmission process can be inferred by deductive method. The first principle of deep thermal energy transmission consists of five basic concepts: definition of temperature, principle of thermal expansion and contraction, Archimedes principle, thermal radiation and second law of thermodynamics and comparative efficiencies of three heat transfer modes of conduction and convection. Combined with the known Earth’s spherical structure, it can be seen from deductive reasoning that the liquid outer core begins to flow under the migration of the solid inner core, resulting in upwelling of mantle plume due to local fluid aggregation. The mantle plume occurs at the interface of another earth sphere, where the uplift force of underplating creates a convex geometry and produces a baking heating effect. As a result, the rheological property of the baked upper materials is enhanced to cause lateral flow, so that the vertical movement of the substance is converted into horizontal motion. The horizontally flowing hot matter accumulates to a certain extent and rises upward to produce vertical motion. Such vertical and horizontal movements are constantly changing, eventually transferring thermal energy from the center of the Earth’s deep core to the shallow crust. This energy transfer can lead to seafloor expansion, plate movement, basinmountain coupling, etc., and also form different levels of heatcontrol structure systems. The earthscale thermostatic tectonic system may be divided into several subsystems: the Earth’s core that is a heatgenerating structure; the liquid outer core that is a heat storage structure; mantle plums and high temperature fluids occurring at each sphere constitute the heatconducting structures; and volcanoes, hot springs and earthquakes on the Earth’s surface form the heatdissipating structures. The lateral flow of quasisolid rheological materials in continental crust is the main controlling factor for the formation of dry hot rock, which is of great significance for geothermal exploration of dry hot rock.

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    The development and outlook of the deep aquifer thermal energy storage (deepATES).
    HUANG Yonghui,PANG Zhonghe,CHENG Yuanzhi,KONG Yanlong,WANG Jiyang
    2020, 27(1): 17-24. 
    DOI: 10.13745/j.esf.2020.1.3

    Abstract ( 187 )   PDF (6344KB) ( 324 )  

    The deep aquifer thermal energy storage (deepATES) is a technology that uses deep aquifer (> 500 m) as the thermal storage medium. Storage and recovery of thermal energy are achieved by extracting and injecting groundwater from deep aquifers through groundwater wells. Using geothermal energy as basic carrier, deepATES achieves balancing among multiple energy resources, and guarantees a steady supply of energy. DeepATES is an effective and critical technology for matching up heat supply and demand over time and space. In this paper, we presented a comprehensive review of the worldwide development of deepATES projects and summarized its thermal performance indicators. Thereby, we investigated the key processes and dominant hydrogeological and operational parameters controlling the thermal recovery efficiency of a deepATES system. We further discussed the technological bottlenecks in deepATES on the basis of previous researches. The last but not least, we evaluated and predicted the economic and market potentials of the deepATES system.

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    Geothermal regime of the lower reaches of Yangtze River and implications for resource exploration
    ZHU Ge,LIU Shaowen,LI Xianglan,WU Di
    2020, 27(1): 25-34. 
    DOI: 10.13745/j.esf.2020.1.4

    Abstract ( 56 )   PDF (10524KB) ( 219 )  

    Geothermal energy, considered as one of new and emerging energies, has attracted increasing attention from academia and industry recently, owing to its huge potential and desirable attributes. Regional geothermal characteristics and deep temperature estimation are of great significances for geothermal energy exploration and utilization. The lower reaches of the Yangtze River in Eastern China is a region with welldeveloped socioeconomic conditions and extremely large energy demand. However, the current regional geothermal regime is not well understood and needs further update with newly acquired geothermal data to provide insights into energy potential assessment in the region. In this article, we outlined the presentday geothermal gradient and heat flow pattern of the Lower Yangtze and estimated the temperatures at 10005000 m depth by integrating previously available regional geothermal data and newly measured thermal properties. The results showed that the geothermal regime of the Lower Yangtze area is mainly controlled by the neotectonics within the area. The geothermal gradient ranged from 16 to 41 ℃/km, with most areas between 1825 ℃/km and an exception of 2835 ℃/km in the northern Jiangsu area. While the heat flow varied from 48 to 80 mW/m2  with a mean value of 60 mW/m2, high heat flow was also found in the northern Jiangsu area and near the TanLu fault zone, indicating the Lower Yangtze area is of a moderate to high geothermal regime favorable for hydrocarbon generation and geothermal energy exploitation. The estimated temperaturesatdepth were 3054 ℃ at 1000 m, 5095 ℃ at 2000 m, 65130 ℃ at 3000 m, 80170 ℃ at 4000 m, and 100210 ℃ at 5000 m. Generally, the geothermal gradient showed a remarkable SWNE striking, with high temperature anomalies distributed in the southern Anhui and northeastern Jiangsu areas, suggesting potential targets of geothermal energy utilization in the two areas. In addition, we also determined the isothermal depth patterns at 60 and 120 ℃. On the basis of geological, geochemical and geothermal conditions, we propose that the Lower Cambrian Hetang Formation and the Permian Longtan Formation of the northern Jiangsu area are the preferable hydrocarbon targets. In terms of regional geothermal energy utilization, the shallow (14002100 m) and deep (21003000 m) geothermal energy in the northern Jiangsu area can be used for heating and power generation or other industrial utilizations, respectively.

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    Screening of hot dry rock in the south-central part of the Bohai Bay Basin
    ZHANG Ying,FENG Jianyun,LUO Jun,HE Zhiliang,WU Xiaoling
    2020, 27(1): 35-47. 
    DOI: 10.13745/j.esf.2020.1.5

    Abstract ( 73 )   PDF (12123KB) ( 276 )  

    The Bohai Bay Basin is the main battleground of oil and gas exploration in North China. A large amount of drilling, logging and temperature data have been collected  through oil and gas exploration and development. Based on the analysis of temperature data, we found significant heat anomalies in the depression zone of this area, indicating potential for hot dry rock resource exploitation in the Jizhong, Huanghua, Linqing and Jiyang depressions. In these areas, carbonate and metamorphic rocks, such as Archean gneiss, mainly developed in the buried hill or uplift area in Lower Palaeozoic and Mesoproterozoic reservoirs, with proper burial depth, high temperature (≥180 ℃) and certain natural pore and permeability conditions. According to the calculations of geothermal gradient in the four depressions, the average geothermal gradient in 4000 and 5000 m deep drilling wells ranged between 3.073.32 and 2.963.27 ℃/100 m, respectively; and temperature reached 180 ℃ at 43096261 m buried depth, which is the range of target buried depth of hot dry rock. The depth of hot dry rocks reaching 180 ℃ varied greatly in different depressions.  Three sets of preMesozoicLower Paleozoic, Proterozoic and Archean buried hill thermal reservoirs are the most promising types of hot dry rock thermal reservoirs. For instance, we found buried Ordovician limestone and Cambrian and Middle Proterozoic dolomite in the Jizhong depression, mainly buried Ordovician limestone in the Huanghua depression, buried CambrianOrdovician limestone and Archean metamorphic rock in the Jiyang depression, and buried Ordovician limestone in the Linqing depression. The main exploration target is the concave and convex areas with buried depths of 30005000 m. Buried hills, such as Hexiwu and Changyangdian in the Jizhong depression, Nandagang and Qianmiqiao in the Huanghua depression, Zhuangxi and Gubei in the Jiyang depression, Machang and Wenliu in the Linqing depression, are favorable for the exploration and development of hot dry rocks as well as deep oil and gas.

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    Analysis of geothermal resources potential for hot dry rock in the Subei Basin
    LIU Demin,ZHANG Genyuan,GUAN Junpeng,ZHANG Shuo,ZHANG Jingqi
    2020, 27(1): 48-54. 
    DOI: 10.13745/j.esf.2020.1.6

    Abstract ( 107 )   PDF (4774KB) ( 478 )  

    The Subei Basin, a MesozoicCenozoic faultdepression,  developed on the preSinian System basement and Paleozoic marine platform deposits. From the Yanshanian Period, the area underwent large scale magmatic and volcanic tectonic activities and deposited ultra thick Cenozoic strata in the continuously active oceaniccontinental tectonic belt. This unique structural environment provides relatively high geothermal flow values and large geothermal gradient, therefore huge geothermal resource potential, in the Subei Basin. Based on the comprehensive investigation of regional geothermal geology, combined with synthesized analysis of geological structural characteristics, collected geothermal data and geophysical information, we preliminarily infer that there are not only shallow mediumlow temperature geothermal resources, but also high temperature hot dry rock(HDR) resources in the deep part of the region. We believe that the geothermal resources of HDR mainly come from the deep mantle and are the results of lithospheric thinning, mantle uplifting and the extensional cracking of crust since the Cenozoic. According to the scientific criteria of resources selection, the predominant prospecting area in the basin has abundant dynamic heat sources, excellent heat conduction channels, largescale thermal reservoirs and good thermal insulation cap rocks. Based on these analyses of HDR potential, we established a genetic model to provide reference for further exploration and development in the basin.

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    Analysis on the occurrence condition of geothermal resources of hot dry rock in Guangxi.
    KANG Zhiqiang,ZHANG Qizuan,GUAN Yanwu,LIU Demin,YUAN Jinfu,YANG Zhiqiang,LU Jipu,WANG Xinyu,ZHANG Qinjun,ZHANG Meiling,ENG Minhao
    2020, 27(1): 55-62. 
    DOI: 10.13745/j.esf.sf.2019.12.4

    Abstract ( 93 )   PDF (12728KB) ( 297 )  

    Conventional wisdom has long regarded Guangxi as a resourcespoor region for its lack of coal, oil and gas resources. Indeed, Guangxi has an extremely unsustainable energy structure with most energy imported from other provinces or foreign countries. However, Guangxi is located at the intersections of the Eurasian, Indian and Pacific plates, thus has relatively thin crust, well developed fault system and large volcanic rock outcrops with high radioactive elemental content. In fact, southeast Guangxi has good heat generation and storage conditions. Based on the Earth Gravitational Model 2008 (EGM2008), we recalculated the crustal structure and crystalline basement interface in Guangxi using Parker-Oldenburg’s algorithm. We analyzed the conditions for dry hot rock formation by integrating previous basic geological survey and elemental geochemical and geothermal geological data. We concluded that dry hot rock formation conditions are met in the Beibu gulf Basin and Yulin and Yujiang Depressions. These areas can be used for hot dry rock prospective survey in the next exploration.

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    Analysis of structural controls of geothermal resources in the NW-SE trending BoluoDayawan fault depression in Huizhou City, Guangdong Province
    ZHANG Genyuan,LIU Demin,ZHANG Jingqi,WEN Chen,KANG Zhiqiang,GUAN Junpeng
    2020, 27(1): 63-71. 
    DOI: 10.13745/j.esf.2020.1.8

    Abstract ( 84 )   PDF (14459KB) ( 431 )  

    The BoluoDayawan fault depression (BDFD) is located in the Pearl River Mouth Basin in southwestern Guangdong Province, bordering in the north by Yangtze block and the west by Youjiang block of the Eurasian plate. At the beginning of the Cenozoic, intense tectonic activities, such as frequent magmatic intrusions, volcanic eruptions, strong earthquakes, and other neotectonics, occurred continuously in the studying area, owing to the presentday configuration of interactions between oceaniccontinental systems and westwards directed oblique subduction of the Pacific plate beneath the Eurasia plate. The BDFD is in the active tectonic coast belt of southeastern China, one of the Pacific Fire Ring’s (PFR) most spectacular and productive areas of large scale of magmatic, young volcanic and geothermal manifestation. In particular, the depression hosts an exceptionally vigorous active geothermal province which coupled with its high surface heat flow and temperature gradient, is as big as all southern China continent. Structures of the geothermal anomalies have been characterized by the NWtrending normal faults surrounded by the BDFD due to extension; inside the structures developed thick continental clastic deposits, large area of outcropped granite intrusions with rich thermogenic elements, and numerous high temperature hot springs exposed along the NWtrending linear BDFD, inductive to a huge geothermal system. Abundant hotwaterdominated geothermal resources stored in shallow sedimentary layers have been exploited and utilized by previous hydrogeological and geothermal survey. However, deeper HDR geothermal energy exploration is limited by current technology and economic conditions. From the experience of geothermal energy exploration around the world, the relationship between geological condition and temperature distribution is crucial in HDR exploration. Here, we studied the depths of a variety of Moho’s surface and Curie point isotherm and the distribution of the Bouguer gravity anomalies patterns under the BDFD, by a comprehensive multidisciplinary (gravity, magnetic, electric, seismic characteristics, etc) analysis of geophysical data. Aa a result, we derived preliminarily the crustal geological structure and temperature conditions. Considering both HDR geothermal energy generation principles and basic regional tectonic background, we infer that the heat source for HDR is derived from mantle diapirism which caused the crustmantle material nonuniform flow after producing partial melting. The melting position occurs at the bottom of continental crust region with huge upward heat transfer to the shallow layers. The ascending hot material and huge vertical stress leads to the Cenozoic new deep faults and subsidence of shallow terrain. Eventually, massive heat transfers to upper crustal rock mass through high thermal conductivity stratigraphy units and accumulates to form HDR thermal reservoir. The fracturing neotectonics superimpose on the previous Yanshanian tectonic system and reactivate the whole fault structures, facilitating heat exchange for the migrating shallow cold water. The tectonic mechanism and role of linear thermal uplift extension as shown in the conceptual model are in agreement with knowledge from other HDR geothermal studies.

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    Analysis of hot-dry geothermal resource potential in southeastern Guangxi
    SUN Minghang,LIU Demin,KANG Zhiqiang,GUAN Yanwu,LIANG Guoke,HUANG Xiqiang,YE Jiahui,GUO Shangyu,SUN Xingting,TANG Wei,FENG Minhao
    2020, 27(1): 72-80. 
    DOI: 10.13745/j.esf.2020.1.9

    Abstract ( 49 )   PDF (12179KB) ( 257 )  

    As an important part of geothermal resource, hot dry rock (HDR) is regarded as future clean energy with great developmental prospect and research value. Here, we studied southeastern Guangxi by reexamining the basic geological, geophysical and geochemical data. We carried out field investigations of tectonicmagmaticsedimentary formation system, lithospheric structure, characteristics of presentday geothermal field and distribution of earthquakes and hot springs to explore the potential of dryheat geothermal resources in southeastern Guangxi. The results show that the lithosphere is relatively thin with two lowvelocity layers about 6 and 2 km thick at above 25 and 68 km, respectively, indicating presence of slippage type ductile shears and high temperature geological bodies. In this area, Indosinian granites can provide stable supply of radiogenic heat materials (mean U concentration 5.41×10-6; Th 18.38×10-6; K2O 4.43%), whilst Cenozoic volcanic activities (OIB) provide a channel for the upwelling of deep thermal material while replenishing large amounts of geothermal energy. Indeed, we observed obvious geothermal anomalies in southeastern Guangxi: in BeihaiNanning, terrestrial heat flow was at 80100 mW/m2 with geothermal gradient above 30 ℃/km; in Qinzhou and Hepu, MesozoicCenozoic fault basins possess rich HDR geothermal resources that the sedimentary cap was of low cracking, porosity and thermal conductivity. Our research of dry heat geothermal potential will assist energy structural adjustment, ecological environmental optimization and industrial transformation and upgrading in Guangxi.

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    Classification of geothermal resources based on engineering considerations and HDR EGS site screening in China.
    HE Zhiliang,ZHANG Ying,FENG Jianyun,LUO Jun,LI Pengwei
    2020, 27(1): 81-93. 
    DOI: 10.13745/j.esf.2020.1.10

    Abstract ( 83 )   PDF (10087KB) ( 193 )  

    In the context of geothermal energy, hot dry rock (HDR) is naturally heated crustal rock with a temperature above 180 ℃ that has little fluid and therefore can provide commercially useful thermal energy. HDR exists everywhere at varying depths. When its temperature not high enough for electricity generation, it often can supply sufficient heat for a variety of direct uses such as space heating and food or chemical processing. If only a small fraction of its thermal reserve can be accessed routinely with existing drilling methods, it would represents an essentially inexhaustible supply of heat, potentially capable of contributing substantially to the world's energy needs. As one of the essential unconventional resources, exploration and production of HDR resource can duplicate the success of shale oil and gas by using mature technologies such as hydraulic fracturing, drilling and completion techniques, reservoir engineering and so on. Although a wide variety of methods can be suggested for extracting energy from hot dry rock, the simplest—probably the most economical—one is to imitate nature by circulating water through it. Usually this will require somehow creating connected pores within the hot rock with enough exposed surface so that heat can be extracted by circulating water at useful high temperatures and rates over long periods of time. Again, a variety of methods can be suggested for producing the required flow passage and heattransfer area, of which, hydraulic fracturing, i.e., enhanced or engineering geothermal system (EGS) technology, is the chosen one for the initial investigation in HDR program. During exploration of HDR geothermal resources by EGS technology, site screening is one of the most crucial step leading to ultimate success. The overall goal of the EGS program is to demonstrate the commercial feasibility of geothermal energy derived from hot dry rock. Therefore, its principal objectives are to confirm that the potential HDR resource is indeed large and accessible, develop a commercialized technology base for extracting the energy therefrom, and verify that the environmental and social consequences of HDR development are acceptable. On the consideration of resource, engineering and economics of geothermal exploration, middle to deep geothermal resources can be classified into two types: hydrothermal and HDR. The latter constitutes dry quality reservoir, dry inferior reservoir and dry nonreservoir rocks, according to reservoir porosity and permeability. The dry quality and inferior reservoirs are most suitable for ESG technology applications. The amount of natural reserves for the five geothermal resources are pyramidlike and with exploration difficulty increasing from top to bottom. Far more common, at depths of high rock temperatures, the combination of temperature, pressure and mineral deposition reduces any preexisting permeability to a value too low to permit natural formation of an exploitable hydrothermal reservoir. This is a typical HDR situation. Occasionally, however, because of some geologic barrier, a hot permeable formation is not reached by the groundwater circulation thus unproductive of geothermal fluids. In this situation, permeability may vary widely, but usually is very low. Based on considerations of geological resources including burial depth, temperature, lithology and physical properties of the reservoir, thickness and fault development of caprock, engineering technology such as drilling and completion techniques, reservoir deformation, management and operation, and market requirement and economy, we propose an evaluation method and key indices for EGS site screening by combining trifactor analysis and multitier index calculation. To test and verify this method, we selected 17 candidate regions in China with HDR geothermal resource advantages for HDR EGS site screening. After evaluation and optimization, we determined that the Yangbajing hightemperature geothermal region in Tibet and the buried hill geothermal region of the Jiyang depression in the Bohai Bay basin are among the best successful candidates for the superior zones for EGS testing.

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    Site selection and developmental prospect of a hot dry rock resource project in the Matouying Uplift, Hebei Province
    QI Xiaofei,SHANGGUAN Shuantong,ZHANG Guobin,PAN Miaomiao,SU Ye,IAN Lanlan,LI Xiang,QIAO Yongchao,ZHANG Jianyong
    2020, 27(1): 94-102. 
    DOI: 10.13745/j.esf.2020.1.11

    Abstract ( 54 )   PDF (13386KB) ( 929 )  

    As a significant component of geothermal resources, hot dry rock (HDR) geothermal energy has attracted increasing attention due to its clean, stable and renewable characteristics and great potential of geothermal power generation. Hot dry rock research is still at the early stage in China. Here, based on analysis of HDR exploitation projects around the world, we proposed several geothermal and geological indices for HDR evaluation and showed that the Matouying Uplift has great HDR exploitation potentials. Taking the HDR resource project in the Matouying Uplift as an example, we discussed the rules and indices for site selection through analyses of cap and reservoir rock conditions and deep geothermal anomaly. We also built a conceptual model of the drilling area in the Matouying Uplift for estimating temperatures of deep geothermal reservoirs.

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    Hydrogeochemical anomaly of mercury in the hightemperature geothermal waters in the Rehai hydrothermal area in Tengchong, Yunnan and its indications
    GUO Qinghai,WU Qifan
    2020, 27(1): 103-111. 
    DOI: 10.13745/j.esf.sf.2019.9.7

    Abstract ( 77 )   PDF (6320KB) ( 285 )  

    Mercury (Hg) is a typical undesirable constituent in the environment. One of potential sources of environmental mercury is deep geothermal systems. However, systematic studies on geothermal mercury are sparse. Here, we conducted a hydrogeochemical study on Hg in hot springs in the Rehai hydrothermal area in the Tengchong volcanic region. The results showed that Hg is rich in the neutral hot springs in the Rehai area but was not detected in most acidic Rehai hot springs. Moreover, the geothermal mercury in Rehai, like chlorine, a typical magmaderived component, primarily comes from magmatic fluid. In the neutral hot springs, Hg(II) is the predominant form of mercury. Complexation of Hg2+ with different sulfide species directly determines Hg(II) speciation, but hot spring pH values can also have an effect to some degrees by controlling sulfide speciation. Because Hg(II) is not prone to volatilization, the neutral hot springs generally have high mercury concentrations. However, volatile Hg(0) is the major form of mercury in acidic Rehai hot springs due to their much higher redox potentials, resulting in very low total mercury concentrations in acidic springs. Mercury in neutral hot springs can be an effective indicator for fault distribution in Rehai, because mercury concentration in ascending neutral spring waters varies distinctively depending on the water cooling process along fault. Geothermal mercury is of great significance for studying the structures of hydrothermal systems.

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    The application of FixAl and isotopic methods in the study of flowback fluids from Enhanced Geothermal Systems (EGS).
    TIAN Jiao,PANG Zhonghe,ZHANG Rui
    2020, 27(1): 112-122. 
    DOI: 10.13745/j.esf.2020.1.13

    Abstract ( 46 )   PDF (5420KB) ( 111 )  

    Enhanced Geothermal Systems (EGS) is an emerging technology for exploiting the geothermal resource in hot rocks with low permeability. The flowback fluid injected into the deep reservoir to extract heat, reflects not only the physicochemical properties of the reservoir but also efficiency of the geothermal resource exploitation. FixAl method and oxygen isotope thermometry have been used widely in natural geothermal systems. In this study, we focused on the applicability of these two methods in EGS flowback experiment. Based on flowback fluids data collected from typical EGS around the world, we evaluated chemical equilibrium states of minerals and flowback fluids and calculated underground fluids thermal exchange temperatures using FixAl method. Using isotope model we verified the mixing and displacement processes of brine. Our studies validated the usefulness of these two methods in EGS research. Moreover, we showed that the chemical characteristics of flowback fluid can be useful in determining brine content of flowback fluids, identifying dissolution of magmatic volatiles and additive residues after reservoir renovation, and predicting scaling trend or corrosiveness of fluids. Future work should focus on indepth studies of chemical properties of flowback fluids through experiments and modeling, so as to establish a scientific evaluation model for deep geothermal resource extraction.

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    Geochemical characteristics of geothermal fluids and water-rock interaction in geothermal reservoirs in and around the Gonghe Basin, Qinghai Province
    MA Yuehua,TANG Baochun,SU Shengyun,ZHANG Shengsheng,LI Chengying
    2020, 27(1): 123-133. 
    DOI: 10.13745/j.esf.2020.1.14

    Abstract ( 64 )   PDF (2423KB) ( 342 )  

    Investigations of the geochemical compositions of geothermal fluids as well as their movements and geneses are of great significance for the exploration and exploitation of hydrothermal resources. Currently, the exploitation and utilization of geothermal resources in Qinghai Province are not well developed, and more seriously, there is a lack of systematic studies on the geochemical features of the geothermal fluids there. The Gonghe Basin of Qinghai Province, located in the northern margin of the QinghaiTibet Plateau, is a rift basin formed in the early Cenozoic where abundant geothermal resources occur. With the geothermal areas in and around the basin as the study areas, we determined the geochemical compositions of the geothermal fluids and investigated the waterrock interactions occurring in the reservoirs based on systematic geochemical sampling and subsequent hydrochemical analyses. The results showed that the SiO2 concentrations of the geothermal waters displayed an increase trend from the Lower Pleistocene and Neogene reservoirs within the Gonghe Basin to the Ela and Waligong tectonicmagmatic belts, implying that the reservoir temperatures increased in the same way. The dissolution of primary aluminosilicate minerals and the formation of hydrothermally altered minerals in the reservoirs are the predominant hydrogeochemical processes controlling the concentrations of major cations in the geothermal waters, while the leaching of salty minerals during the infiltration of the recharging waters and the runoff and upflow of the geothermal waters made a substantial contribution to the occurrence of major anions, especially SO2-4 and Cl-.

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    Evaluation of geological conditions for the development of deep geothermal energy in China
    PANG Zhonghe,,LUO Ji,CHENG Yuanzhi,DUAN Zhongfeng,TIAN Jiao,KONG Yanlong,LI Yiman,HU Shengbiao,WANG Jiyang
    2020, 27(1): 134-151. 
    DOI: 10.13745/j.esf.2020.1.15

    Abstract ( 77 )   PDF (4434KB) ( 319 )  

    Deep geothermal energy refers to geothermal energy that lies deeper than 3000 meters below Earths surface. China is rich in deep geothermal energy, but how favorable are the exploitation conditions? Based on the principle of geothermal geology, in association with rock mechanics, we put forward an indicator system for evaluating the conditions of deep geothermal energy exploitation. We first assign values to each indicator using the expert scoring method; then we apply the principle of fuzzy mathematics to obtain a single value so as to assess the exploitation feasibility. This method considers the safety aspect of enhanced geothermal system (EGS) technology in the development of deep geothermal energy. It advocates adopting the concept of “soft stimulation”, different from the “rigid stimulation” which may induce earthquakes and other key factors not conducive to the healthy development of geothermal energy industry. It also emphasizes the reservoir properties and geophysical fields, expanding and supplementing the previous evaluation results. The established new method is more suitable for the actual geothermal geological conditions, i.e., tectonics dominant geothermal distribution in China. In other words, geothermal energy distribution is closely related to tectonic activities, the stress is relatively high, the crust is generally active with frequent earthquake events. This method makes full use of expert knowledge, adds the role of fuzzy mathematical comprehensive evaluation, and makes the quantitative results easy to compare and use. Therefore, this method is expected to better support decisionmaking. Based on the new assessment method and existing deep geothermal research and geothermal exploration results, we attempted to make a preliminary assessment of the geological conditions of deep geothermal energy development in nine regions of mainland China, including the northsouth geothermal zones in Tibet, the volcanic geothermal regions in western Yunnan Province, the central and eastern regions of Qinghai Province, Northeast and North China, and other regions. We revealed quantitative differences of regional geological conditions for geothermal exploitation, showing that continental China has complex geological conditions, often unfavorable to deep geothermal energy development.

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    Tracer test and simulation of thermal energy storage in carbonate rocks of the Xian County geothermal field.
    LI Tingxin,CAI Yongfeng,LIU Yanguang,LIU Guihong,ZHANG Hongliang,QIN Xiangxi
    2020, 27(1): 152-158. 
    DOI: 10.13745/j.esf.2020.1.16

    Abstract ( 88 )   PDF (2796KB) ( 189 )  

    The theoretical model of predicting thermal breakthrough in production well during geothermal recharge is still not perfect. In this paper, we carried out well recharge tracer test in the Xian County geothermal field and performed parameter inversion using the Comsol Multiphysics modeling software. We used the software’s theoretical framework to explain the tracer test data quantitatively and predict thermal breakthrough in heat mining wells. The results demonstrated a relatively low tracer recovery rate of 0.0225%, with one preferential passage of about 513.7 m long in the geothermal doublet well, indicating poor hydraulic connection between the doublet wells. After parametric analysis, we calculated the goodnessoffit R2 to be 0.7907, greater than 0.6, suggesting a strong correlation between the optimization result and measured value, therefore a good model fit. Our model predicts that 100 years of continuous exploitation will not cause thermal breakthrough.

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    Expansion of fracture network in granites via chemical stimulation: a laboratory study
    GUO Qinghai,HE Tong,ZHUANG Yaqin,LUO Jin,ZHANG Canhai
    2020, 27(1): 159-169. 
    DOI: 10.13745/j.esf.sf.2019.12.2

    Abstract ( 65 )   PDF (7594KB) ( 129 )  

    Enhanced geothermal system (EGS) has been used to extract heat from deep hot dry rock with low permeability by creating an artificial geothermal reservoir. Hydraulic fracturing, along with chemical stimulation, was usually adopted to improve the permeability of a target EGS reservoir. In this study, we collected granodiorite samples from the Gonghe basin of Qinghai Province and subjected them to a systematic chemical stimulation test by use of three chemical agents (sodium hydroxide, hydrochloric acid and mud acid) at three different injection rates. The results show that the permeability of the rock samples increased upon injection of hydrochloric acid or mud acid, with the latter bringing larger increases; whereas the application of sodium hydroxide solution reduced the permeability. Among the three chemical agents, mud acid exhibited the strongest ability of dissolving feldspar minerals in granodiorite; in contrast, quartz was eroded most severely by sodium hydroxide solution. Nevertheless, during the chemical stimulation test using sodium hydroxide solution, we saw amorphous silica or aluminosilicates precipitation due to excess dissolution of the primary minerals on the fracture surface; and precipitation resulted in microfracture filling which definitely had a negative effect on improving permeability. Thus, in general, mud acid is the best chemical agent for the target hot dry rock in this study. At a moderate injection rate (3 mL·min-1), mud acid can most effectively erode granodiorite samples and remarkably enhance sample permeability. Lowering injection rates, however, could cause secondary mineral precipitation and fracture filling therefore lowering sample permeability.

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    Principle and application of OpenGeoSys for geothermal energy sustainable utilization
    KONG Yanlong,HUANG Yonghui,ZHENG Tianyuan,LU Renchao,PAN Sheng,SHAO Haibing,PANG Zhonghe
    2020, 27(1): 170-177. 
    DOI: 10.13745/j.esf.2020.1.18

    Abstract ( 290 )   PDF (9446KB) ( 235 )  

    Numerical simulation is very useful in utilizing large scale geothermal energy, predicting reservoir response and optimizing exploitation procedure. Here we describe the OpenGeoSys (OGS) software used to simulate the complex processes in geoscience and hydrological applications, focusing on its application in geothermal energy utilization. OGS is based on an objectoriented finite element method concept and can deal with numerical simulation of thermohydromechanicalchemical processes in porous media. Case studies related to shallow geothermal energy (temperature and pressure prediction), hydrothermal energy (optimization on the distance between production well and reinjection well, scaling) and hot dry rock (hydraulic fracturing, permeability evolution) are shown with the purpose to help managing geothermal energy utilization.

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    Comparative experimental study on physical and mechanical properties of granite after natural cooling and under realtime high temperature
    LUO Shengyin, DOU Bin, TIAN Hong, CHEN Jie, XIAO Peng, ZHANG Shitao
    2020, 27(1): 178-184. 
    DOI: 10.13745/j.esf.2020.1.19

    Abstract ( 81 )   PDF (7098KB) ( 149 )  

    The change of physical and mechanical properties of rock under high temperature has a direct impact on the development and utilization of hot dry rock resources and stability of underground reservoirs. Here, we studied granite through physical property and uniaxial compression testing with high temperature natural cooling and realtime temperature treatments. We analyzed and compared the physical and mechanical property changes of the specimens at different temperatures  under the two treatments. The results are as follows: (1) The mass of granite decreased with increasing temperature by 0.24% and 0.27%, respectively, while the volume of granite increased with increasing temperature by 4.21% and 3.53%, respectively, under the two treatments. (2) The peak strength and elastic modulus of the specimens decreased as a whole; at 600 ℃, the peak strength decreased by 49.81% and 37.19%, respectively;  elastic modulus decreased by about 34.35% and 26.13%, respectively; and the peak strain increased by 70.43% and 39.62%, respectively. (3) At below 400 ℃, mechanical properties of the specimens weakened less after natural cooling than under realtime temperature treatment, but the trend reversed at temperatures  higher than 400 ℃, and a high temperature inflection point appeared. The research results can provide reference for stability evaluation of hot dry rock resources and realtime high temperature rock in practical engineering.

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    Overview of enhanced geothermal system (EGS) based on excavation in China
    KANG Fangchao,TANG Chun’an
    2020, 27(1): 185-193. 
    DOI: 10.13745/j.esf.2020.1.20

    Abstract ( 113 )   PDF (5025KB) ( 154 )  

    Geothermal energy is a permanent, renewable, inexhaustible and clean energy stored in regosol, fluid and magmatic bodies in the Earth’s crust. Its exploitation and utilization, mainly hot dry rock (HDR), may become a meaningful way to solve the future energy crisis. The enhanced geothermal system (EGS) is the primary method used in the exploitation of HDR up till the present time. Because of the complexity of geological environment and dependency of hydraulic measures on natural fissures, most of EGS projects have many technical shortcomings, such as insufficient thermal storage volume and heat transfer area, low working fluid flow rate, low terminal temperature and induced earthquake risk, making largescale commercialization of DHR unachievable. The prospects of the enhanced geothermal system based on excavation technology (EGSE) inspired us to find breakthroughs  overcoming the technical difficulties and limitations of EGS. In this paper, we discussed EGSE in great detail on its operation fundamentals, engineering principles and technical advantages based on a conceptual model. By adopting mining technologies, such as excavation, blasting and caving, EGSE can significantly overcome geological environmental restrictions on thermal storage quality to form a unique fracturing system of geothermal reservoir as well as a special thermal energy exchange system. It has the advantages of building up customized thermal storage, forming sufficient heat transfer areas, maintaining stable working fluid flow rate and temperature, and reducing earthquake risks, thus provides a brandnew scheme for the commercialization of HDR geothermal energy.

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    Discussion on Cenozoic tectonic development and dynamics in South Tibet
    LIU Demin,YANG Weiran,GUO Tieying
    2020, 27(1): 194-203. 
    DOI: 10.13745/j.esf.sf.2019.11.29

    Abstract ( 126 )   PDF (5025KB) ( 403 )  

    Openingclosing tectonics is a hypothesis about the whole earth based on the theory that every tectonic movement on earth is openingclosing movement. It can explain some geological phenomena developing on the continents which can not be explained by plate theory. In this paper, using openingclosing theory, we analyzed the characteristics of tectonic units in South Tibet, and proposed that South Tibet can be divided into the gravitational detachment fault reformed thrust and normal faults. The field scientific investigation team found the Rongbusi normal fault when the mainstream opinion believed that the Tibetan plateau was formed by collisioncompression orogenesis in 1970s. We consider that the Rongbusi normal fault and the Main Central Thrust developed before the South Tibet detachment fault, and that the former two faults are the two boundaries of the South Tibet extrusion structure. The South Tibet detachment fault partially superimposes on the Main Central Thrust and manifests high angle following the Rongbusi normal fault in the north of Chomolangma. We believe that the three fault systems developed in different tectonic backgrounds and periods. The structural units such as klippes and windows, which were identified by previous researchers in southern Tibet, belong to thrust fault system but usually have no obvious features of extrusion or thrust; however, they have the characteristics of missing strata column as younger strata overlaying on the older ones. We consider the klippes and windows the results of later gravitational decollement and having clear characteristics of extension and slippery. Based on openingclosing theory, we believe that since Cenozoic, the study area had undergone multiple developmental stages such as oceanic crust expansion (opening) and subduction (closing), continental collision (closing) and intracontinental extension (opening). Geothermal energy from deep earth, gravitational potential energy from Earth's interior, and stress energy from tectonic movements, played a key role in the multistage development.

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    Applying the view of openingclosingrotating tectonics to study how the Earth’s interior is working.
    YANG Weiran,JIANG Chunfa,ZHANG Kang,GUO Tieying,YOU Zhendong
    2020, 27(1): 204-210. 
    DOI: 10.13745/j.esf.2020.1.22

    Abstract ( 79 )   PDF (2453KB) ( 179 )  

    All Earth materials and processes perform opening and closing movements. The thermally (heat energy) driven upward movement can be defined as opening, while the gravity (potential) driven downward movement can be defined as closing. The overall openingclosing movement achieves synchronized unity and interdependency between vertical and horizontal movements through mutual opposition and transformation. So that, under rotational control and modulation, this movement transforms all Earth materials, tectonics, energies,  etc. from the state of disorder to order, and eventually builds up the dynamically stable and balanced openingclosingrotating tectonic system. Therefore, studying the unceasing cyclic evolution of formation, destruction and renovation of this dynamically stable and balanced tectonic system is the only basis and effective way for understanding the working of the  Earth’s interior. For that, we delineated eight vertical and one crustal (spherical) openingclosing tectonic cycles, and preliminarily established a 4dimensional working system of the Earth. The dynamically stable and balanced system is established through longterm working of the four natural laws, i.e., gravity balance, internal energy minimization (in crystallization), preferential growth orientation (normal to the Earth’s center) and horizontal homogeneity, among which gravity balance is the leading law. At about 4 Ga, mantle lithosphere was formed as a lid covering the hot Earth. This event initiated the stable openingclosingrotating tectonic system and entered the Earth into a prolonged dynamically stable and balanced evolutionary era. After that, each major geological event (loss of balance) had been either poking a hole into or tearing up the lithosphere, thus destructing Earth’s balance. But the rotating and openingclosing movements could quickly restore the balance and start a new cycle. Till now the Earth has passed through eight megacycles. Since plate tectonics only concerned with the destruction and restoration of the most recent four megacycles in developing its theory, it has limitations of time and space and cannot be called “global tectonics”.Earth is a living body. Its operating system—the inner structure and function—is rather perfect: the opening, closing, rotating and unbalancing movements form the movement system; its “blood” system comprises geofluid acting as “blood”, the Earth’s nucleus functioning as “heart” for “blood” supply and storage, and mantle plumes for channeling “blood”. And under the gravity balance criteria, four gravity balancing surfaces, four openingclosing transforming zones and two mass balancing lines on the sphere make up the Earth’s dynamic equilibrium system.Because transformation between “opening” and “closing” happens spontaneously and is selfadjusting, it can be the main motivator for the working of the Earth’s interior. In addition, external energy input can also be utilized by the mutual transforming mechanism of opening and closing.  Therefore, under the control of the rotating movement, interdependency, mutual opposition and transformation of the opening and closing movements are the major motivator for and basic dynamic mechanism of Earth’s interior working system.

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    Study on the dynamic mechanism of northward drift of the Indian Plate.
    LIANG Guanghe
    2020, 27(1): 211-220. 
    DOI: 10.13745/j.esf.2020.1.23

    Abstract ( 116 )   PDF (11364KB) ( 375 )  

    The Indian continental plate is an activated cratonic plate. Its northward drift and collision with Eurasian plate have been extensively studied, however, the dynamic mechanism of the northward drift is rarely noticed. Traditionally, it is believed that the seafloor spreading caused the northward drift of the Indian Plate, but the latest geophysical observations are contrary to this belief. Based on systematic analyses of geomagnetic anomaly characteristics, paleomagnetic measurements and seismic exploration profiles, we showed that the thickness of the Indian continental plate is about 40 km. We established a new continental drift model to illustrate that the dynamic mechanism of the northward drift is closely related to the continuous deep magma upwelling in the south part of the Indian Plate, such that the northward drift is self driven. This model can reasonably explain the power source of the Indian Plate drift; and it can also give a reasonable explanation about the dynamic mechanism of the leftlateral rotation of the Indian Plate. Finally, we discussed the origin of the abnormal highspeed drift of the Indian Plate between 8040 Ma and the cause of the Great Rift Valley in East Africa. This study provides a new dynamic mechanism for the continental drift model.

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    Role of circumferential-direction stress in crustal movement
    MAO Xiaoping,LUXU Linghong,WANG Xiaoming,FAN Xiaojie,GENG Tao,WANG Haochen
    2020, 27(1): 221-233. 
    DOI: 10.13745/j.esf.2020.1.24

    Abstract ( 108 )   PDF (16592KB) ( 424 )  

    It is still controversial what drives crustal movement. Although there are many competing theories, the magnitude of the driving force described in these theories is too small to drive crustal movement. In addition, many insitu stress measurements showed that the horizontal principal compressive stress is the largest of the three insitu stress components and considered as the crustal “anomaly” pressure, however, there is no unified mechanistic explanation for this observation. Therefore, it is necessary to find out what the source of the driving force is and why such horizontal stress dominants. Inspired by anticlinal structures and stone arch bridge that are supported by lateral force, and through stress analysis of the Earth model, we concluded that the crust, as a spherical shell, can experience lateral extrusion from its own weight, which acts as circumferentialdirection stress. Consistent with the insitu measured stress characteristics, this circumferentialdirection stress is derived from and greater than gravity. We estimated that the stress is about 900 MPa at 20 km depth, enough for driving plate movement (needs at least 500 MPa). Because, as asthenosphere can flow, stress will be released as long as there is a weak zone in the lithosphere above it, resulting  in relative motion between plates. The whole oceanic crust behaves like an arch bridge: under circumferentialdirection stress, it can insert into the deep part of the continental crust at the subduction zone, the weak area of the lithosphere, so the subduction zone bears part or even all of the weight of seafloor. Finally, we proposed that there is no structural force or collision force independent of gravity that can work independently, the circumferentialdirection stress is the only driving force strong enough for crustal movement.

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    Theory of earthquake triggering by the singularity of critical point behavior of water
    HU Baoqun,GAO Haidong,WANG Yun,LI Mangen,BAI Lihong,SUN Zhanxue
    2020, 27(1): 234-243. 
    DOI: 10.13745/j.esf.2020.1.25

    Abstract ( 81 )   PDF (1973KB) ( 292 )  

    Through the examination of a large number of seismic phenomena and  thermodynamical analysis of seismic processes, we found the common characteristics of earthquakes which included plane zonation, correlation with faults, multiple seismic layers occurring in the lithosphere, high conductivity and low velocity layers in the deep part of the affected area, close relationship with water, short and sudden main quake, abnormal behavior of some animals and plants, topographic and geomorphological changes, and geochemical, geophysical and meteorological anomalies. As a whole, these characteristics can be divided into two kinds: one  relates to faults affected by rock properties and force; and the other relates to water. In this study, focusing on fault depressurization and water phase transition, we improved the theory stating that the coupling of the singularity of critical point behavior of water during secondorder phase transition, and fault depressurization in lithosphere, triggers earthquake. On this basis, we proposed the theory of earthquake triggering by the singularity of  critica point behavior of water as follows: (1) Depressurization and water accumulation in brittle and ductile fractures (or zones) cause pressure decrease and temperature rise in some areas of crust and upper mantle; as temperature and pressure of water simultaneously reach the critical values of water, the second order phase transition is induced. (2) At the critical point of second order phase transition of water, change of water physicochemical properties is abrupt. In particular, sudden change of solubility of solids in water abruptly weakens the local mechanical properties of the crust and upper mantle, while thermal pressure (i.e. thermal stress) approaches infinity, according to the MieGrüneisen formula, as water CV approaches infinity during the second order phase transition. Fracturing depressurization causes the local temperature and pressure of the lithosphere to reach the critical values of water at the same time thus induces second order phase transition. These factors trigger the local hydrothermal explosion to form earthquake. And (3) Earthquake magnitude is positively correlated with the amount of local accumulation of water undergoing second order phase transition in faults. The critical behavior of water, i.e.,  sudden change of many physicochemical properties, is the source of various anomalies in geochemistry, geophysics, plant and animal growth, meteorology and so on, and is also the main indicator in earthquake monitoring.We also briefly discussed correlation between earthquakes and hydrothermal metallogeny or oil and gas formation or other geological processes. The theory we proposed here is mainly used to explain the mechanism of strong earthquakes in the Earth’s crust.

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    Detailed study of the formation of Japanese islands based on tectonic evolution of basins in the East China Sea and Northern South China Sea.
    LIANG Guanghe
    2020, 27(1): 244-259. 
    DOI: 10.13745/j.esf.2020.1.26

    Abstract ( 168 )   PDF (1973KB) ( 370 )  

    The Japanese islands are located between the eastern edge of Asia and the western Pacific. The source and genetic mechanism of their formation have been extensively studied, but controversies still remain. Japan is traditionally considered to be part of the trench arc basin system formed by the Pacific subduction, but this notion contradicts geological observations. Based on topographical features, seismic exploration profiles, restoration of basin tectonic evolution history, paleomagnetic measurements and paleontological evidence, we systematically analyzed the tectonic migration of the Pearl River Mouth Basin, the Taiwan Southwestern Basin, the East China Sea Basin and the Okinawa Trough. The results showed that the Japanese continental plate drifted from two regions in the Cenozoic: Hokkaido came from the equator; and Honshu, Shikoku and Kyushu came from the edge of the South China continent. The genetic mechanism is closely related to the eastward drifting of the Eurasian plate splitting from the North Atlantic, and India’s collision with the Eurasian plate. In the process, the Japanese islands on the eastern edge of the Eurasian plate first cracked, then drifted. This new continental drift model can reasonably explain the formation mechanism and process of the trench arc basin system. It can also explain the formation mechanisms of the arcshaped island arc and the rich oil and gas deposits in the basin. This study provides a new dynamic mechanism for the continental drift model.

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    Geological features of opening-closing tectonics at different spatiotemporal scales
    WANG Jie,WU Haibo,LU Xiaofei,LI Xianrui
    2020, 27(1): 260-269. 
    DOI: 10.13745/j.esf.2020.1.27

    Abstract ( 81 )   PDF (7341KB) ( 193 )  

    “Openingclosing” tectonics is a new hypothesis for studying the opening and closing movements and evolution of the earth. Different spatiotemporal openingclosing tectonics have different geological features that need to be studied from different perspectives. In this paper, we demonstrated the applications of openingclosing tectonic theory in geotectonic division, seismic activity and interpreting modern geodesy results, by the examples of large openingclosing tectonic zones in the Mediterranean and medium sized in the eastern Dabie orogenic belt. The results showed that (1) the bordering regions of Asia, Europe and Africa can be divided into six tectonic assemblages: Russian, African and North, Central, South and East Asian tectonic assemblages; (2) earthquakes in the bordering regions are mainly distributed in Cenozoic openingclosing tectonic transition zones between tectonic assemblages; (3) the seismic profile and focal mechanism study indicated that the current tectonic movement in the MediterraneanTurkeyIranAfghanistan tectonic transition zone is dominated by “closing” motion; and (4) modern crustal deformation observations around the eastern Dabie orogenic belt, such as ground tilt and strain in the Shizishan, Huangmei and Macheng areas, and observations from GNSS and mobile gravity surveys in the area, indicate a low tendency for tectonic evolution from “closing” to “opening” on a short time scale, suggesting the “openingclosing” movement can be a common mechanism for some correlated tectonic events occurred simultaneously in the region.

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    Is negative buoyancy the primary force driving plate motion during the onset of subduction? A discussion on rock fracture mechanics
    ZHOU Hui,QIU Liang,YAN Danping
    2020, 27(1): 270-274. 
    DOI: 10.13745/j.esf.2020.1.28

    Abstract ( 71 )   PDF (3313KB) ( 360 )  

    Based on the method of rock fracture mechanics, we discussed in this paper the possibility of pulling force (negative buoyancy) exerted by subducting plate being the driving force for plate movement. Experimental results of rock fracture indicate that the lithospheric strength is very low, only about n×10 MPa, which is unlikely to bear the necessary n×102 MPa stress during the onset of subduction. In addition, results from tectonic modeling, thermal cracking, fatigue fracture, flexure of subducted slabs, subduction dehydration and melting process studies reveal that the idea of negative buoyancy of subducting plate being the driving force for plate movement is inconsistent with research observations.

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    Discussion on the Cenozoic tectonic evolution and dynamics of southern Tibet 
    LIU Demin, YANG Weiran, GUO Tieying, RU Jiangtao, XIONG Aimin
    2020, 27(1): 275-286. 
    DOI: 10.13745/j.esf.sf.2020.5.5

    Abstract ( 14 )  
    Opening-closing tectonics is a new idea for exploring the global tectonics, which holds that every tectonic movement of all materials and geological bodies on earth is characterized by opening and closing. The opening -closing tectonic view can be used to explain some geological phenomena developing in continents which cannot be reasonably explained by the theory of plate tectonics. Based on the available basic geological data and combining with the opening-closing view, we analyzed the divisions and characteristics of tectonic units in South Tibet, and propose that Tibet can be divided into gravitational detachment and detachment fault zones, which are superimposed thrust fault zones  and reconstructed normal fault zones, respectively. Although the mainstream opinion believed that the Tibetan Plateau is formed by collision-compression orogenesis, field investigation revealed the existence of the Rongbu Temple normal fault in the1970s. We consider that the Rongbu Temple normal fault and the Main Central Thrust (MCT) were formed earlier than the South Tibet detachment fault, and the former two  faults constitute the two boundaries of the southern Tibet extrusion structure. The South Tibet detachment fault partially superimposes on the MCT and manifests a relatively high angle in following the Rongbu Temple normal fault north of  the Chomolangma. We suggest that the three fault systems are the products of different periods and tectonic backgrounds. The tectonic units, such as klippes and windows identified by previo us researchers in southern Tibet, belong to thrust fault system but usually have no obvious extrusion or  thrust characteristics; however, they are characterized by missing strata columns as younger strata overlapping the older ones. These  klippes and windows should be the results of later gravitational decollement and must be characterized as extensions and slips, respectively. Based on opening-closing theory, we  suggest that since the Cenozoic the study area had undergone multistage development, which  can be divided into the oceanic crust expansion (opening) and subduction (closing) and the continental collision (closing) and intracontinental  extension (opening) stages. Geothermal energy from the deep earth, gravitational potential energy from the earth’s interior, and additional stress energy from tectonic movements, all played a key role in the multistage tectonic evolutionary process. 
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