Geological Journal of China Universities

Study on Strucure Model of Metallogenic Series

ZHAI Yu-sheng, PENG Run-rain, WANG Jian-ping, DENG Jun

2003, 9(4): 510-519.

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The study from the single deposits to the metallogenic series and metallogenic system is an important progress in the study of metallogeny．In the course of probing into the theory of metallogenic series，their physical structure attracts attention．In this paper，the inner structures of metallogenic series are classified into 3 types：the material structure，the spatial structure and the temporal structure．The material structure comprises homologue，diversity，succession and complementarity between all kinds of ores and ore deposits．The spatial structure of metallogenic series includes paragenesis，zonation，transition，compactness and superposition between different kinds of ores an d ore deposits．The temporal structure comprises time-limit．stage asymptotics and paroxysm ． This paper gives some examples to explain the forming conditions of these structures，which have an reference effect to understand the metallogenic regularities and to guide the ore prospecting．

A Discussion on the Regional Mineralizing Pedigree of the Ore Deposits in the Northern Margin of the North China Landmass

CHEN Yuchuan1, XUE Chun-ji2, WANG Deng-hong3, LI Hua-qin4, Lu Yuan-fa4

2003, 9(4): 520-535.

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The metallogenic series is composed of a group of ore deposits that formed at the same tectonic unit and during certain tectonic period，and show the genetic relations．The metallogenic series type is made up of several metallogenic series that appear in the similar tectonic environment and possess generality and individuality．The evolution and distribution of the regional mineral deposits may be characterized by mineralizing pedigree which is the frontiers in the metallogenic series research．The importance and method of studying the mineralizing pedigree are discussed in this paper． The North China landmass experienced a 1ong crustal evolution history and is an important mineralizing region with evident ore-forming and prospecting potentiality．In this paper the mineralizing ages of many mineral deposits were determined and collected ，the important mineral deposits are tabled on the basis of ore-forming ages, 18 metallogenic series are classified and their distribution regularities are studied. The mineralizing pedigree research shows that this region mainly underwent 4 stages of crust evolution and the ore deposits were formed in the Archean shield，in the Proterozoic continental or margin rifts，in the Paleozoic proliferation fold belts and their covers，an d in the Mesozoic tectono-magrrmtic belt successively．With the proceeding crust evolution，the mineral deposit types tended to be diversified ，the mineralizing controls changed from “stratabound” to “magmatic rocks”．and the ore-formation processes tended to be more complex．There are 3 mineralizing peaks：the late Archean period, the end of the early Proterozoic to middle Proterozoic period, and the middle-late Jurassic-early Cretaceous period ．The mineralizing ages are concentrated at 3 000～2 500 Ma，1 900～1 400 Ma and 180～ 140 Ma, respectively． The mineralizing pedigree well responds to the crust evolution and indicates that the oxidation-reduction potential of the seawater and atmosphere was evidently increased from the Archean to the Proterozoic era in the northern margin of the North China landmass．

A Brief Review for the Study on Genesis of the Submarine Volcanic Exhalative Sedimentary Deposits in South China

Zhu Jin-chu

2003, 9(4): 536-544.

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Many stratiform and stratabound Cu，Pb，Zn，Fe，Au，Ag，Sn，S mineral deposits are found in South China．They were interpreted as hydrothermal or skarn type in origin up to early 1970’s．In middle 1970’s Professor Xu Keqin proposed a submarine volcanic exhalative sedimentation-hydrothermal superimposition origin for these mineral deposits，specifically formed in the fault depression environment．Led by Prof．Xu，the academic staff and students in the Department of Earth Sciences，Nanjing University conducted a large amount of investigations in this field and gained significant achievements．Nowadays this point of view is recognized by most domestic investigators and supported by geological exploration practice．

A Humble Opinion on the “Potassic and Sodic Two Mantle Alkali-Rich Magma Systems”

WANG Lian-kui, XIA Bin, ZHANG Yu-quan, CHEN Gen-wen

2003, 9(4): 545-555.

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“The potassic and sodic mantle alkali-rich magma systems” are the integral of all igneous rocks that are formed in a short geological period，and include the ultrabasic，basic，intermediate and acidic alkali-rich rocks along deep faults．The integral of potassic rocks is named potassic mantle alkali-rich magma system ，and the integral of sodic rocks is named sodic mantle alkali-rich magma system．The study for Ailaoshan—Jing shajiang potassic alkali, rich igneous rocks belt show that in intrusion depth，these rocks can be hypogene，hypabyssal and extrusive；in lithology，they can be ultrabasic，basic，intermediate and acidic；and in alkalinity most rocks are alkaline and weakly alkaline．Their striking features are K>Na，high potassium and alkali-rich．In petrochemistry，these rocks are generally highly alkaline(Na20+K2O range from 4.55% to 12.5%)，potassium -rich(K20/Na20 ratio is 1.15—3.20)，with high CaO (2.20% ～14.9%)，high Rb，Sr，Ba，Th，U ，and low Rb/Sr．The total contents of rare earth elements are higher．the light rare earth elements are strongly enriched．and the 8Eu values are low ．Most Isr values range from 0.705 to 0.706．INd range from 0.512305 to 0.512630．The Sr-Nd-Pb isotopic data imply that the magma of this rock belt was derived from EM II type mantle source．and probably directly came from a kind of potassic mantle．The Anning river sodic alkali, rich igneous rock belt are also hypogene，hypabyssal and extrusive in intrusion depth，ultrabasic，basic，intermediate and acidic in lithology and mostly are alkaline and weakly alkaline in alkalinity．Most of sodic alkali-rich rocks are high in Na20+K20 (5.67%～14.44%)，sodium-rich(the K2O/Na20 ratio is 0.22～0.90)，with high contents of Ti02(0.15%～6.44%)and large ion lithophile elements．Nb，Ta，Zr and Rb/Sr are relatively higher．The contents of light rare earth elements are lower than those of potassic rock belt，but u values are higher，and sometimes even positively abnorrea1．J values range from 0．705 to 0．706．INd value is about 0.512630．These rocks are similar to the igneous rocks in the rift area derived from mantle．They are mainly derived from mantle multi-period sodic alkali-rich magma and multi-stage evolved．The study shows that there are not only potassium -rich mantle source areas，but also sodium -rich mantle source areas．These mantle magmas were form ed in the deep mantle under the high pressure an d high temperature conditions．As the passageway of magma uprising，the ultra-deep faults are important for formation of the potassic and sodic mantle alkali-rich magma systems．

My Thinking about Granite Geneses of South China

ZHOU Xin-min

2003, 9(4): 556-565.

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The characteristics，genetic models and tectonic frameworks of the granites for four geological periods in South China are described and discussed in this paper．Several geological problems of South China which are worth further thinking over are raised by the present author

Sm-Nd Isotope Dating and Geological Implications for the Mesoproterozoic Mamianshan Group in Fujian Province

WANG He-nian1, LING Hong-fei1, ZHOU Li-ya1, YANG Feng-gen1, WANG Yin-xi2

2003, 9(4): 566-572.

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The Marnianshan Group in the middle part of Fujian Province is developed along the Zhenghe-Dapu deep fault zone which is an important geological boundary in Fujian and even in South China．Dating and study on genesis of the Mamianshan Group are important approach to characterize the Zheng he-Dapu deep fault zone，and to better understand the formation and evolution of the Cathaysia block．Samples collected from three sections yield three isochrons with consistent ages within error ranging from 1.73～1.77 Ga and with high initial ENd(t)values．This suggests that the Mamianshan metamorphic basic volcanic rocks were formed in the Mesoproterozoic rather than in the Caledonian period．This also suggests that the Zhenghe—Dapu deep fault zone was active as early as in the Mesoproterozoic when it was a premature rift Zone and that the Mamianshan meta-volcanic rocks were products of the rifting in the Cathaysia．The high initial ENd(t)values (+7.6～+10.9)of the Mamianshan meta-volcanic rocks suggest that they were derived from highly depleted mantle．This implies that this mantle produced large amount of crustal matters be fore the Mesoproterozoic probably in the Paleoproterozoic，which supports the existence of Cathaysia with main Paleoproterozoic crust most of which was later destroyed or reworked

Subdivision，Discrimination Criteria and Genesis for A Type Rock Suites

LIU Chang-shi, CHEN Xiao-ming, CHEN Pei-rong, WANG Ru-cheng, HU Huan

2003, 9(4): 573-591.

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This paper discusses the necessity for subdivision of A type suites into A1 and A2 subtypes and the judging criteria to distinguish them，based on new data obtained in study on A type suites in north Guangdong province and the data published in Chinese and overseas literature． The A type suites can be divided into two subtypes and three groups(A1 subtype：AS group；A2 subtype：ALAG group and AAG group)．The A1 subtype(AS group)is usually SiO2-undersaturated，metaluminous，and peralkaline-alkaline rocks，which include feldspathide syenites, a1kaline syenites and phonolites ．They are essentially characterized by existence of more or lass amount of feldspathide minerals such as Sodalite，nepheline，leucite etc．The A2 subtype is usually Si02-oversaturated，alkaline-subalkaline granitic rocks，which include the peraluminous，subalka1ine A type granites (ALAG group)，and the metaluminous，alkaline A type granites (AAG group)．Distinguishable from the ALAG group，the AAG group generally contains more or less amount of Ca-Na-or Na-pyroxenes and amphiboles ．Geochemically，the A1 subtype has relatively lower Si02(54.13％～61.29％)，higher ALK (12.65％～ 13.50％)，NK／A (0.85～1.03)，chlorine(50×10-6 ～9600×10-6)，R2(623，average，the same below)，Nb/Ta (15.69)，Zr／Hf(36.17)，Eu/Eu* (0.60)，LREE/HREE (15.18) and zircon．saturation temperature(833℃ )，and relatively lower R1(-263)，10^4 Ga/A1(2.4)，Y/Nb(0.34，similar to OIB source materials)and relatively lower fluorine(50×10-6～3523×10-6)．In contrast to A1 subtype，the AAG group of A2 subtype has relatively higher SiO2(71.93％-76.28％)，lower ALK(7.81％～9.80％)，chlorine(26×10-6～500×10I6)，R2 (318，in average，the same below)，Nb／Ta(13.09)，Eu／Eu* (0.29)and LREE/HREE (7.57)，and higher R1(2295)，10^4 Ga/A1 (3.93)，Y (1.64，similar to IAB source materials)，higher fluorine(6OO×10-6 ～1900×10-6)and zircon-saturation temperature(883℃ )．The ALAG group of A2 subtype is similar in geochemical properties to the AAG group，but is peraluminous．Using a series of diagrams of R1-R2，Y/Nb-Yb/Ta, Nb-Y - Ce and Nb/Ta-Nb，the A type suites can be readily distinguished into A1 and A2 subtype ．Based on the Nd，Sr isotopic data and using the mixing model of depleted mantle endmember and bulk crust endmember, it is calculated that the source materials for most A2 subtype granites of seven rock bodies are dominated by depleted mantle endmember component(68％～78％)．The mixing model of depleted mantle endmember and enriched mantle endmember shows that the source material components for A1 type rock suites are composed of EM4DM96-EM17DM83，and the enriched mantle endmember comprises only a minor proportion．

New Discussion on the South China-Type Massive Sulphide Deposits Formed on Continental Crust

GU Lian-xing1, HU Wen-xuan1, NI Pei1,HE Jing-xiang2, XU Yue-tong3, LU Jian-jun1, LIN Chun-ming1, LI Wei-qian1

2003, 9(4): 592-608.

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There are more than 20 massive sulphide deposits within upper Paleozoic basins in South China．These deposits occur at the transitional parts from elastic rocks to carbonates adjacent to the bottom of the marine transgression sequences，and are accompanied with minor bimodal volcanites and voluminous exhalites in the host strata．Principal mineral parageneses in the ores are formed by metamorphic reactions．Metals and mineral phases commonly exhibit stratigraphycally vertical and lateral zonations，which were produced by a combination of exhalation-diagenesis，post-ore remobilization，reworking and overprinting．Footwall mineralisations in the form of veins ，breccias and disseminations under massive sulphide layers have been found representing sub-seafloor pathways of ore-forming fluids． Accompaying alterations featured by silicification， sericitization and K-feldspathization can be interpreted to represent the silicon and potassium-rich characteristics of the continental crust．As stratigraphical equivalents to massive sulphides but form ed under more oxidizing environments，exhalative iron-manganese ore layers are often underlain by vein-type lead-zinc an d gold mineralizations．Such a type of upper Palaeozoic disconcordant hyarothermal mineralizations in basement sequences should be paid great attention to during mineral prospecting in South China． Ore-forming basins in the Nanling region were initiated on a post-Caledonian highly-matured contiental crust，whereas the lower Yangtze basin was situated on a basement evolving towards a passive continental margin．Contrasting compositional and metallogenic features of upper Palaeozoic massive sulphide deposits indicate difference in crustal maturity between these two regions during ore formation．Tungsten and tin are characteristic elements of massive sulphides formed on matured continental crust．Deposits in South China are distinct from those of the Sullivan-type in their close association with well-defined volcanic rocks，in their more abundant industrial metal varieties ，and in their strong reworking and overprinting by late-stage granitic magmas and magmatic fluids，and thus are worthy to accept the term South China-type deposits and to be regarded as representative of massive sulphide deposits formed on intensely attenuated continental crust．

Comparison in the Characteristics，Origin，and Related Metallogeny between Granites in Dajishan and Piaotang，Southern Jiangxi，China

HUA Ren-min, ZHANG Wen-lan, CHEN Pei-rong, WANG Ru-cheng

2003, 9(4): 609-619.

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Dajishan and Piaotang are two large tungsten deposits in southern Jiangxi Province，which are all related to granites of continental crust remelting type．Besides W as major product, the Dajishan deposit is also a deposit of Ta and Nb，whereas the Piaotang deposit is rich in Sn，Mo，and Ag．Major and trace element geochemistry of these two granites is studied ．Both granites are Si02, rich and peraluminous，higher in alkalies ，and rich in F and incompatible trace elements．However，the comparison between them shows that the Dajishan granite was formed by more highly evolved magma than the Piaotang granite． This might be the key factor that controlled the different metallogenic characteristics of these two deposits．The commonly used terms such as W-bearing granites ，Ta-Nb-bearing granites ， an d Li-F granites ，as well as the geodynamic setting for the granites ，is also briefly discussed in this paper

Geology，Distribution，Types and Tectonic Settings of Mesozoic Epithermal Gold Deposits in East China

MAO Jing-wen1 2, LI Xiao-feng2, ZHANG Zuo-heng2, WANG Yi-tian2, LI Hou-min1, HU Hua-bin1

2003, 9(4): 620-637.

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We preliminarily describe the basic characteristics of the epithermal gold deposits in East China．The epithermal gold deposits in East China can be divided into low-sulfidation and high-sulfidation types，which are related to granitic and alkaline series magmatic rocks．Except for the Zijinshan in Fujian province and the Tiantoushan in Anhui province，the others are low sulfidation epithermal gold deposits．The Guilaizhuang in the west Shandong and possibly the Yixingzhai in northwestern Shanxi are alkaline rock-related gold deposits．The epithermal gold deposits in East China are spatially distributed in the faulting-depressing volcanic basins or along the magmatic-volcanic zones in the uplift areas． Most of them are structurally continued by calderas ，craters，diatremes and related faults and hosted in volcanic rocks ，intrusions and surrounding strata．The alteration assemblages are mainly adularia-chalcedony-sericite for low-sulfidation gold deposits，and alunite-kaolinite-quartz(chalcedony)for high-sulfidation gold deposits．In genera1, the alterations in these Mesozoic gold deposits do not show the obvious zoning as those in the Cenozoic gold deposits in the southeast Pacific islands an d Japan．The ore-forming ages of the epithermal gold deposits in East China are within four pulses of 180—188 Ma，135—144 Ma，127—115 Ma an d 94—105 Ma．respectively．The former three pulses geodynamieally correspond to the extensional periods of post-collision orogenic process between North China and Yangtze cratons ，transformation of the tectonic regime from N to nearly EW —directions ，and significant thinning process of the lithosphere；The latter pulse is the products of the lithosphere extension in South China ．We suggest that all the epithermal gold deposits in East China are the products of magmatic heat events in the extensional tectonic setting within the continental margin．

Lithogeochemical Characteristics and Origin for Basaltic Lava from Renbu Ophiolite from Xizang(Tibet)，China

XIA Bin, WANG Ran, CHEN Gen-wen

2003, 9(4): 638-647.

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The basaltic lavas from Renbu ophiolite from Xizang(Tibet)are composed of finegrained plagioclase basaltic porphyrite，coarse-grained plagioclase basaltic porphyrite，and amygdaloidal pyroxene basalt．The analytical data show that their contents of potassium and natrium are relatively higher，and those of iron and phosphorus are also higher，but calcium and magnesium are comparatively deficient． Meanwhile，they have higher aluminum and lower titanium contents and belong to tholeiite rock series．LILE，such as Ba，Rb，Sr and HFSE，including Th，Ta，Nb，Zr and Hf are rich，but Cr，Ni and the other trace elements are relatively poor, total abundances of gale earth elements are comparatively high and they display the enriched distribution patterns of LREE，which shows that the basalts possess the characteristics of the typical oceanic island-arc．The Th/Ta ratios are between 1.03 and 1.53 an d the average value is 1.19．The La/Ta ratios are between 10.08 an d 13.26 and the average value is 12.2．The Th/Ta，La/Ta ratios an d the distribution pattern s of spidergrarms indicate that the Renbu lavas are oceanic non—SSZ basalts． Intergrating with the field geology and comparing with MORB．OIB and the other typical ophiolites ，we can draw a conclusion that Renbu ophiolite was probably formed in an initial marginal basin tectonic environment under the extension stress dynamics during the Neo-Tethys periods．

Geochemical Behavior of Incompatible Elements in Peraluminous Magmatic System and Its Mechanism- Fractionation of the coherent elemental pairs and the lanthanide tetrad effect in granitic magmas：Implications for melt-fluid interaction

LIU Cong-qiang, ZHANG Hui

2003, 9(4): 648-660.

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Based on the studies on apatites from the Altay No.3 granite pegmatite，Xinjiang，China．together with those peraluminous granites and pegmatites from various areas in the world，this paper discusses the fractionation of the coherent elemental pairs that have similar ionic radii and same valences ，and also the origin of the lanthanide tetrad effect． It is suggested that the fractionation of the coherent elemental pairs and occurrence of the lanthanide tetrad effect are genetically related to formation of volatile-rich fluid during magmatic evolution，and that the fractionation of the elemental pairs an d the intensity of the lanthanide tetrad effect ar1e dependent on the extent of fluid-melt interactions．

He-Ar Isotopic Systematics of Fluid Inclusions in Pyrites from PGE-Polymetallic Deposits in Lower Cambrian Black Rock Series，Southern China

SUN Xiao-ming1 2, WANG Min1, XUE Ting1, MA Ming-yang1, LI Yan-he3

2003, 9(4): 661-666.

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He-Ar isotopic compositions of fluid inclusions trapped in pyrites from some representative PGE-polymetallic deposits in Lower Cambrian black rock series in Southern China were analysed by using an inert gas isotopic mass spectrometer．The results show that the ore-forming fluid possesses a low 3He/4He ratio，varying between 0.43×10-8 and 26.39× 10-8，with an R/Ra value of 0.003～0.189．The 40Ar/36Ar are 258～ 287, closing to that of air-saturated water (ASW)．He-At isotopic indicator studies show that the ore-forming fluid was mainly composed of formation water or basinal hot brine an d spa water，while the content of mantle fluid or deep-derived magmatic water might be neglected ．The PGE-polymetallic mineralization might be related to evolution of Caledonian miogeosynclines distributed along southern margin of the South China Craton．In the Early Cambrian Period，the formation water(basinal hot brine)trapped in the Caledonian basins where accumulated extremely thick sediments was expelled and migrated laterally along strata be cause of the pressure generated by overlying sediments．The basinal ho t brine ascended along faults，mixed with sea water and finally deposited ore minerals．

U/Th and U/Pa Dating of Nanjing Man

CHENG Hai1, R．Lawrence．Edwards1, WANG Yong-jin2

2003, 9(4): 667-677.

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Evidence from China is crucial in order to understand hominid evolution，with age dating being critical to interpret the evidence． Homo erectus fossils， including two skulls and a tooth，were discovered interbedded with cave deposits in the suburbs of Nanjing in 1993 and 1994, and are referred to as“Nanjing Man”．U/Th ages of the calcite flowstone overlying the Nanjing Man fossils are 533+_15 12ka or 533+-35 30ka，if considered accurately．The[231Pa/235U] activity ratio of the flowstone is 0.998±0.006．indicating concordance of U/Th and U /Pa ages ．A stratigraphically younger stalagmite gives an age progression consistent with the internal stratigraphy of the stalagmite：465+-45 35 ka；398±15 ka；350±10 ka；260±8 ka and 160±2 ka．Our data indicate that Nanjing Man is older than 500 ka．We analyzed five animal teeth from the Nanjing site by TIMS．U/Th ages vary from 185 to 290 ka and U/Pa ages from 137 to 172 ka．For both U/Th and U/Pa ages, the each age is less than that of the dentine for the same tooth．In addition，the U/Pa age of each tooth subsample is less than its U/Th age by 24～40％．Thus，these teeth do not follow an early uranium uptake mode1．In a[234U /238U]vs．[230Th/238U]diagram，the tooth data plot in a field between early U uptake(EU)and linear U uptake(LU) curves．This indicates a U uptake history between the EU and LU model，which has been the general consensus on uptake history for these types of samples．In this case, both U/Th and U/Pa LU model ages will be the upper limit of the samples ．However，the U/Pa age may give a better estimation be cause it is not affected by the possible variation of input 234U/238U ratios．The minimum U/Pa LU model age is 1 Ma, which gives a constraint on the upper limit of Nanjing Man age．Although possible，it is not conclusive that Nanjing Man lives in marine 16O isotope stage 16(MIS16)．

A Two-Stage Model for Formation of the Dongguashan Cu-Au Deposit

LU Jian-jun, HUA Ren-min, XU Zhao-wen, GAO Jian-feng, LI Juan

2003, 9(4): 678-690.

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The Dongguashan Cu-Au deposit includes stratiform sulphide orebodies，and skarn and porphyry type orebodies．The stratiform orebodies occur between the Late Devonian sandstones and the Middle to Late Carboniferous carbonates．Detailed field and laboratory investigations revealed that these stratabound orebodies are massive sulphide deposit．The Late Juarassic magmatic rocks were brought to be in contact with the masive sulphide orebodies and caused them to be transformed and hydrothermally superimposed．The copper-bearing magmatic fluids replaced massive sulphides ores and formed chalcopyrite in them ．A two-stage model for the formation of the Dongguashan deposit can be established ．In the first ore-forming stage during the Middle Carboniferous period ，submarine exhalation sedimentation caused the formation of massive sulphide orebodies which contain dominantly pyrite，pyrrhotite，and some gangue minerals，but little copper-bearing sulphides．In the second stage at the Late Jurassic，magmatic hydrothermal fluids，on the one hand，formed the skarn and porphyry type of ore bodies ，on the other hand，overprinted the earlier massive sulphide orebodies ，and induced enrichment of large amounts of copper in the stratiform sulphide ores ．

Preliminary Study on Fluid Inclusion Planes for Dabie Mountain Granite

NI Pei, FAN Jian-guo, ZHOU Jin, DING Jun-ying, MA Dong-sheng, HUA Ren-min，, LING Hong-fei, JIANG Shao-yong

2003, 9(4): 691-700.

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The devolvement and migration of geo-fluids is controlled by regional stress．Fluid inclusion planes(FIP)are a bridge to link the geo-fluid and the stress．It is a useful means to investigate the migration of the geo-fluid under certain regional stress field．Fluid inclusion planes kept in the granites provide the best way for US to study the regional stress field change and the fluid evolution when the granites intrude into the country rocks and cool down at the crustal environment．This paper statistically surveys FIPs attitudes for three granitic intrusives in Dabie Mountain，Anhui province(Zhubeyuan，Tianzhushan and Sikongshan granites)．Microthermometric works were also done on the fluid inclusions in FIPs．It is revealed that the characteristics of FIPs in the Zhubeyuan and Tianzhushan grantes are similar ，but obviously different from the Sikongshan granite．The FIP in Zhubeyuan and Tianzhushan granites have preferred orientations of NE and NW W ．The NW W striking FIP are cross-cut by the NE striking FIP．The homogenization temperature, salinity and CO2 contents of the fluid inclusions in NW W striking FIP are higher than those of NE striking FIP, which indicate regional paleo-stress change from NWW to NE strike accompanying the intrusion and cooling of the above two granites，and fluids evolved from CO2—H2O-NaC1 type to H2O-NaCl type with declined temperatures and salinities．FIP in Sikongshan granite have preferred orientations of SN and EW ．The EW striking FIP are cross-cut by the SN striking FIP．While cooling, the Sikongshan granite experienced a regional stress field changing from EW to SN and fluid types changing from CO2-CH4-H2O-NaC1 type to H2O-NaC1 type with the declined fluid temperatures and salinities．

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