The Middle Ordovician subsalt Majiagou Formation in the Ordos Basin comprises pervasively dolomitized shallow marine limestone and is a major reservoir rich in natural gas resources.Four types of dolomite matrix and c...The Middle Ordovician subsalt Majiagou Formation in the Ordos Basin comprises pervasively dolomitized shallow marine limestone and is a major reservoir rich in natural gas resources.Four types of dolomite matrix and cement were identified based on petrographic textures:(very)finely crystalline,non-planar to planar-s matrix dolomite(Md1);finely to medium crystalline,planar-s to planar-e matrix dolomite(Md2);microbialites comprising dolomite microcrystals(Md3);and finely to coarsely crystalline dolomite cement(Cd).The Md1 and Md2 dolomites were controlled by alternating lagoon-shoal facies and haveδ13C values(−1.89 to+1.45‰VPDB for Md1,−1.35 to+0.42‰VPDB for Md2)that fall within or are slightly higher than the coeval seawater,suggesting the dolomitizing fluid of evaporated seawater.Md2 dolomite was then subjected to penecontemporaneous karstification by meteoric water and burial recrystallization by sealed brines during diagenesis,as indicated by its relatively lowerδ18O values(−8.89 to−5.73‰VPDB)and higher 87Sr/86Sr ratios(0.708920–0.710199).Md3 dolomite comprises thrombolite and stromatolite and is interpreted to form by a combination of initial microbial mediation and later replacive dolomitization related to evaporated seawater.Cd dolomite was associated with early-formed karst system in the Md2 host dolomite.The lowestδ18O values(−11.78 to−10.18‰VPDB)and 87Sr/86Sr ratios(0.708688–0.708725)and fluid inclusion data(Th:123–175°C)indicate involvement of hydrothermal fluid from which the Cd dolomite precipitated during deep burial.These results reveal the multi-stage dolomitization history of the Majiagou Formation and provide new constraints on fluid origins and dolomites evolution during deep burial in old superimposed basins,such as the Ordos Basin and elsewhere.展开更多
Characteristics of ore forming fluids as inferred from detailed studies of inclusions indicate that pegmatites may have different origins. For example, the granitic pegmatite at Mufushan is originated from magma diffe...Characteristics of ore forming fluids as inferred from detailed studies of inclusions indicate that pegmatites may have different origins. For example, the granitic pegmatite at Mufushan is originated from magma differentiation at 1100-200℃, while the No.3 Pegmatite Vein in Xinjiang may owe its origin to a pegmatitic magma produced via metamorphic anatexis at 1140-200℃. Pegmatite fluids of the above two types are a melt liquid system and may evolve into a solid melt or solid liquid system that would have a critical bearing on metasomatism and intergranular solutions. The Minxi pegmatite, on the other hand, resulted from metamorphic differentiation, with its fluid (formed at 400-180℃) exhibiting many features of metamorphism. Pegmatites of different origins are distributed in tectonic units of different characters and are different both in the nature of ore forming fluid and in the source of ore metals. This concept of polygene launches a challenge to the traditional belief that pegmatite is exclusively originated from magma differentiation and may be helpful for the establishment of a new theory of pegmatite genesis.展开更多
On the basis of results of the studies of primary fluid inclusions, and the hydrogen and oxygen isotope data, the authors concluded that the early-stage ore-forming fluid from the Jinchangqing gold (copper) ore deposi...On the basis of results of the studies of primary fluid inclusions, and the hydrogen and oxygen isotope data, the authors concluded that the early-stage ore-forming fluid from the Jinchangqing gold (copper) ore deposit is a kind of sulfate type hot brine characterized by medium temperature and salinity, genetically related to the late-stage ore-forming fluid derived from an acidic and more reductive environment. However, the late-stage ore-forming fluid is a sort of low temperature and low salinity chloride-type hot brine which originated from a lower pressure, acidic and more oxidative environment. In general, the ore fluids were derived from the late-stage, or largely from the early-stage groundwater-derived meteoric water, which has a 12‰-17‰ heavier oxygen isotopic composition than the original rain water (δ{}+{18}O={-15.3‰}), and were formed during gold mineralization as a product of oxygen isotope exchange during the reaction between ore-forming fluid and wall rocks under a lower water/rock ratio condition.展开更多
CAJNOZOIC and Mesozoic in North Tarim are predominantly a set of terrestrial detrital formations. In thereservoir sandstones in the area, albite is one of the widely developed authigenic mineral. Micro-structural evid...CAJNOZOIC and Mesozoic in North Tarim are predominantly a set of terrestrial detrital formations. In thereservoir sandstones in the area, albite is one of the widely developed authigenic mineral. Micro-structural evidence shows that diagenetic albite occurs as euhedral crystals in the pore, and replaces feldsparand other detritus along cleavage and micro-crack. EPMA analyzing found that some of the alteration product has a chemical composition between purealbite and the replaced detrital feldspar. For example, composition of replaced alkali feldspar is betweenmicrocline and albite, and content of altered plagioclase decreases continuously. This has been regardedas direct evidence for fluid replacement, for feldspar crystallized from solution or magma is usually withfixed chemical composition. Taking alkali feldspar as an example, although Kf and Ab forming completeisomorphous admixture in high temperature, they exsolved out as two relative pure phases while temperature decreases.展开更多
The Tianqiao Zn–Pb–Ag deposit in SW China,hosted by Devonian and Carboniferous limestone and clay rocks,is composed of sulfides such as sphalerite,galena,and pyrite.Pyrite is present in different paragenetic stages ...The Tianqiao Zn–Pb–Ag deposit in SW China,hosted by Devonian and Carboniferous limestone and clay rocks,is composed of sulfides such as sphalerite,galena,and pyrite.Pyrite is present in different paragenetic stages and can be divided into four types based on textures and mineral assemblages.Pyrite from the adjacent Shanshulin deposit(Py-SSL)is also used for comparison.Py1 shows framboid texture with grain diameter up to 1 mm and was commonly replaced by sphalerite.Py2 is characterized by overgrowth texture and displays inner oscillatory zoning.Py2 is associated with abundant sphalerite and galena.Py3 shows replacement relics textures where galena fills the fractures of pyrite.Py4 is a euhedral to subhedral crystal disseminated in dolomite and is characterized by deformation and fragmentation textures.Minor sphalerite and galena are associated with Py4.Py-SSL is subhedral and disseminated in dolomite,similar to Py4.Py1 was formed by a diagenetic or sedimentary process,whereas Py2 and Py3 were formed by multiple stages of ore fluids.Py4 and Py-SSL were formed at the carbonate-sulfide stage,but Py4 suffered from deformation after its formation.Py1,Py2,and Py3 are characterized by relative enrichment of Sb,Cu,and As,in contrast to Py4 and Py-SSL with higher Cr,W,Ge,Sn,Tl,Ni,and Ga contents.However,critical metals such as Ge,Ga,and In in pyrite are generally lower than10 ppm,which are not economically important.The trace element variation in Tianqiao pyrite with paragenesis results from fluid evolution in the Pb–Zn ore system and competition with co-precipitating minerals.Diagenetic and ore-forming hydrothermal fluids are responsible for the formation of different types of pyrite.Ore-related pyrite from the Tianqiao and Shanshulin deposits has Co and Ni distribution features similar to pyrite from sedimentary pyrite and submarine hydrothermal vents,different from those in volcanogenic massive sulfide,iron oxide-copper–gold,and porphyry Cu deposits,indicating their derivation of relatively low-temperature(<~250°C)hydrothermal fluids,similar to basin brines or seawater.,via fluid-rock interaction.This conclusion is also supported by the sulfur isotope composition of sulfides which are 13.0–13.5%,and 15.6–20.5%for Tianqiao and Shanshulin deposits,respectively.展开更多
The composition of quartz inclusions and trace elements in ore indicate that gold\|bearing fluid in the Xiadian gold deposit, Shandong Province, stemmed from both mantle and magma, belonging to a composite origin. Bas...The composition of quartz inclusions and trace elements in ore indicate that gold\|bearing fluid in the Xiadian gold deposit, Shandong Province, stemmed from both mantle and magma, belonging to a composite origin. Based on theoretical analysis and high temperature and high pressure experimental studies, gold\|bearing fluid initiative localization mechanism and the forming environment of ore\|host rocks are discussed in the present paper. The composite fluid extracted gold from rocks because of its expanding and injecting forces and flew through ore\|conducive structures, leading to the breakup of rocks. The generation of ore\|host faults and the precipitation of gold\|bearing fluid occurred almost simultaneously. This study provides further information about the relationships between gold ore veins and basic\|ultrabasic vein rocks and intermediate vein rocks, the spatial distribution of gold ore veins and the rules governing the migration of ore fluids.展开更多
The Jinshan gold deposit is located in the Northeast Jiangxi province,South China,which related to the ductile shear zone.It contains two ore types,i.e.the alteration-type ore and the goldbearing quartz vein ore.Rb-Sr...The Jinshan gold deposit is located in the Northeast Jiangxi province,South China,which related to the ductile shear zone.It contains two ore types,i.e.the alteration-type ore and the goldbearing quartz vein ore.Rb-Sr age dating is applied to both gold-bearing pyrite in the alteration-type ore and fluid inclusion in the gold-bearing quartz vein to make clear the time of the gold mineralization of the Jinshan deposit.Analytical results of this study yielded that the age of the alteration-type ore bodies is about 838±110Ma,with an initial 87Sr/86Sr value of 0.7045±0.0020.However,the age of the gold-bearing quartz vein-type ore is about 379±49Ma,and the initial 87Sr/86Sr is 0.7138±0.0011.Based on the age data from this work and many previous studies,the authors consider that the Jinshan gold deposit is a product of multi-staged mineralization,which may include the Jinninian,Caledonian,Hercynian,and Yanshanian Periods.Among them,the Jinninian Period and the Hercynian Period might be the two most important ore-forming periods for Jinshan deposit.The Jinninian Period is the main stage for the formation of alteration-type ore bodies,while the Hercynian Period is the major time for ore bodies of gold-bearing quartz vein type.The initial values of the 87Sr/86Sr from this study,as well as the previous isotope and trace element studies,indicate that the ore-forming materials mainly derived from the metamorphic wall rocks,and the ore-forming fluids mainly originated from the deep metamorphic water.展开更多
Several aspects related with Lorentz force are discussed in the light of the presence of vibrating strings. Strings are considered as a compact,?tension and viscosity-free incompressible liquid. The motion of a charge...Several aspects related with Lorentz force are discussed in the light of the presence of vibrating strings. Strings are considered as a compact,?tension and viscosity-free incompressible liquid. The motion of a charge particle, obviously, represents the “line of vortex” in the medium of fluid. The term (VXB) turns out to be the natural consequence of Vortex dynamics. The present investigation also reveals the nature of the magnetic field and explains why and how this additional term takes part in Lorentz force.展开更多
Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysi...Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.展开更多
The origin of grain dolomite in M55 Member of Ordovician Majiagou Formation in northwestern Ordos Basin was studied by geochemical and petrological tests on core samples.Observation of cores,thin sections and casting ...The origin of grain dolomite in M55 Member of Ordovician Majiagou Formation in northwestern Ordos Basin was studied by geochemical and petrological tests on core samples.Observation of cores,thin sections and casting thin sections,analysis of cathodoluminescence,X-ray diffraction,microscopic sampling of trace elements,laser samplingδ18O andδ13C,and fluid inclusion homogenization temperature were conducted.The results show that the dolomite is the product of recrystallization of micritic to crystal powder dolomite rather than the product of dolomitization of grain limestone.In the spherical grains are residual gypsum and halite pseudo crystals identical with those in the host micritic dolomite.The spherical particles of dolomite has similar trace elements andδ18O andδ13C characteristics to micritic dolomite.Furthermore,Mn/Sr ratio of the fine-medium dolomite between the dolomite grains is about 5-8,while Mn/Sr ratios of calcite in limestone,micritic dolostone in micritic dolomite,and micritic and powdery dolomite are about 0-2,indicating that the dolomite experienced strong diagenesis.Homogenization temperature of inclusions of fine-medium dolomite is about 148.19°C,higher than that of inclusions in micritic to crystal powder dolomite(about 122.60°C),which also supports the conclusion that the grain dolomite experienced burial diagenesis and negative shift ofδ18O andδ13C.Theδ18O,δ13C values of micritic to crystal powder dolomite match with the negative migration,but those of calcite in limestone don’t.It is of great significance to elucidate the genesis of"dolomite recrystallization"for the prediction of such dolomite reservoirs.展开更多
基金This study was supported by the National Science and Technology Major Projects of China(Grant Nos.2016ZX05004006-001-002 and 2016ZX05004002-001)PetroChina Science and Technology Project(Grant No.2019B-0406)the China Scholarship Council(No.201908080005)。
文摘The Middle Ordovician subsalt Majiagou Formation in the Ordos Basin comprises pervasively dolomitized shallow marine limestone and is a major reservoir rich in natural gas resources.Four types of dolomite matrix and cement were identified based on petrographic textures:(very)finely crystalline,non-planar to planar-s matrix dolomite(Md1);finely to medium crystalline,planar-s to planar-e matrix dolomite(Md2);microbialites comprising dolomite microcrystals(Md3);and finely to coarsely crystalline dolomite cement(Cd).The Md1 and Md2 dolomites were controlled by alternating lagoon-shoal facies and haveδ13C values(−1.89 to+1.45‰VPDB for Md1,−1.35 to+0.42‰VPDB for Md2)that fall within or are slightly higher than the coeval seawater,suggesting the dolomitizing fluid of evaporated seawater.Md2 dolomite was then subjected to penecontemporaneous karstification by meteoric water and burial recrystallization by sealed brines during diagenesis,as indicated by its relatively lowerδ18O values(−8.89 to−5.73‰VPDB)and higher 87Sr/86Sr ratios(0.708920–0.710199).Md3 dolomite comprises thrombolite and stromatolite and is interpreted to form by a combination of initial microbial mediation and later replacive dolomitization related to evaporated seawater.Cd dolomite was associated with early-formed karst system in the Md2 host dolomite.The lowestδ18O values(−11.78 to−10.18‰VPDB)and 87Sr/86Sr ratios(0.708688–0.708725)and fluid inclusion data(Th:123–175°C)indicate involvement of hydrothermal fluid from which the Cd dolomite precipitated during deep burial.These results reveal the multi-stage dolomitization history of the Majiagou Formation and provide new constraints on fluid origins and dolomites evolution during deep burial in old superimposed basins,such as the Ordos Basin and elsewhere.
文摘Characteristics of ore forming fluids as inferred from detailed studies of inclusions indicate that pegmatites may have different origins. For example, the granitic pegmatite at Mufushan is originated from magma differentiation at 1100-200℃, while the No.3 Pegmatite Vein in Xinjiang may owe its origin to a pegmatitic magma produced via metamorphic anatexis at 1140-200℃. Pegmatite fluids of the above two types are a melt liquid system and may evolve into a solid melt or solid liquid system that would have a critical bearing on metasomatism and intergranular solutions. The Minxi pegmatite, on the other hand, resulted from metamorphic differentiation, with its fluid (formed at 400-180℃) exhibiting many features of metamorphism. Pegmatites of different origins are distributed in tectonic units of different characters and are different both in the nature of ore forming fluid and in the source of ore metals. This concept of polygene launches a challenge to the traditional belief that pegmatite is exclusively originated from magma differentiation and may be helpful for the establishment of a new theory of pegmatite genesis.
基金Thisresearchprojectwasgrantedjointlybythe95’StateKeyScienceandTechnologyProjects(96 914 03 04),ResearchProjectsin95’KeyRegionsandZonessponsoredbytheoriginalNon ferrousMetalIndustry GeneralCompany(96 D 42),theStateKeyBasicResearch,Develop mentandPlanningProgram(G1999043208)andtheFoundationProjects ofYunnanProvincialEducationDepartment(0142104).
文摘On the basis of results of the studies of primary fluid inclusions, and the hydrogen and oxygen isotope data, the authors concluded that the early-stage ore-forming fluid from the Jinchangqing gold (copper) ore deposit is a kind of sulfate type hot brine characterized by medium temperature and salinity, genetically related to the late-stage ore-forming fluid derived from an acidic and more reductive environment. However, the late-stage ore-forming fluid is a sort of low temperature and low salinity chloride-type hot brine which originated from a lower pressure, acidic and more oxidative environment. In general, the ore fluids were derived from the late-stage, or largely from the early-stage groundwater-derived meteoric water, which has a 12‰-17‰ heavier oxygen isotopic composition than the original rain water (δ{}+{18}O={-15.3‰}), and were formed during gold mineralization as a product of oxygen isotope exchange during the reaction between ore-forming fluid and wall rocks under a lower water/rock ratio condition.
文摘CAJNOZOIC and Mesozoic in North Tarim are predominantly a set of terrestrial detrital formations. In thereservoir sandstones in the area, albite is one of the widely developed authigenic mineral. Micro-structural evidence shows that diagenetic albite occurs as euhedral crystals in the pore, and replaces feldsparand other detritus along cleavage and micro-crack. EPMA analyzing found that some of the alteration product has a chemical composition between purealbite and the replaced detrital feldspar. For example, composition of replaced alkali feldspar is betweenmicrocline and albite, and content of altered plagioclase decreases continuously. This has been regardedas direct evidence for fluid replacement, for feldspar crystallized from solution or magma is usually withfixed chemical composition. Taking alkali feldspar as an example, although Kf and Ab forming completeisomorphous admixture in high temperature, they exsolved out as two relative pure phases while temperature decreases.
基金Guizhou Science Foundation,20171197,Yumiao MengCAS Hundred Talents Program,Y9CJ034000,Xiao-Wen Huang+1 种基金National Natural Science Foundation of China,42073043,Yumiao Meng,41673050,Xiao-Wen HuangScience and Technique Foundation of Water Resources Department of Jiangxi Province,202123YBKT10,Chun-Xia Xu。
文摘The Tianqiao Zn–Pb–Ag deposit in SW China,hosted by Devonian and Carboniferous limestone and clay rocks,is composed of sulfides such as sphalerite,galena,and pyrite.Pyrite is present in different paragenetic stages and can be divided into four types based on textures and mineral assemblages.Pyrite from the adjacent Shanshulin deposit(Py-SSL)is also used for comparison.Py1 shows framboid texture with grain diameter up to 1 mm and was commonly replaced by sphalerite.Py2 is characterized by overgrowth texture and displays inner oscillatory zoning.Py2 is associated with abundant sphalerite and galena.Py3 shows replacement relics textures where galena fills the fractures of pyrite.Py4 is a euhedral to subhedral crystal disseminated in dolomite and is characterized by deformation and fragmentation textures.Minor sphalerite and galena are associated with Py4.Py-SSL is subhedral and disseminated in dolomite,similar to Py4.Py1 was formed by a diagenetic or sedimentary process,whereas Py2 and Py3 were formed by multiple stages of ore fluids.Py4 and Py-SSL were formed at the carbonate-sulfide stage,but Py4 suffered from deformation after its formation.Py1,Py2,and Py3 are characterized by relative enrichment of Sb,Cu,and As,in contrast to Py4 and Py-SSL with higher Cr,W,Ge,Sn,Tl,Ni,and Ga contents.However,critical metals such as Ge,Ga,and In in pyrite are generally lower than10 ppm,which are not economically important.The trace element variation in Tianqiao pyrite with paragenesis results from fluid evolution in the Pb–Zn ore system and competition with co-precipitating minerals.Diagenetic and ore-forming hydrothermal fluids are responsible for the formation of different types of pyrite.Ore-related pyrite from the Tianqiao and Shanshulin deposits has Co and Ni distribution features similar to pyrite from sedimentary pyrite and submarine hydrothermal vents,different from those in volcanogenic massive sulfide,iron oxide-copper–gold,and porphyry Cu deposits,indicating their derivation of relatively low-temperature(<~250°C)hydrothermal fluids,similar to basin brines or seawater.,via fluid-rock interaction.This conclusion is also supported by the sulfur isotope composition of sulfides which are 13.0–13.5%,and 15.6–20.5%for Tianqiao and Shanshulin deposits,respectively.
基金TheprojectwasfinanciallysupportedjointlybytheNationalNaturalScienceFoundationofChina(No .4 0 172 0 36 )"TheKeyProgrovmofScienceandTechnologyResearch"(No .0037)sponsoredbytheMinistryofEducation theNationalClimbingPro gramofChina No .95 pre 2 5and 95 pr
文摘The composition of quartz inclusions and trace elements in ore indicate that gold\|bearing fluid in the Xiadian gold deposit, Shandong Province, stemmed from both mantle and magma, belonging to a composite origin. Based on theoretical analysis and high temperature and high pressure experimental studies, gold\|bearing fluid initiative localization mechanism and the forming environment of ore\|host rocks are discussed in the present paper. The composite fluid extracted gold from rocks because of its expanding and injecting forces and flew through ore\|conducive structures, leading to the breakup of rocks. The generation of ore\|host faults and the precipitation of gold\|bearing fluid occurred almost simultaneously. This study provides further information about the relationships between gold ore veins and basic\|ultrabasic vein rocks and intermediate vein rocks, the spatial distribution of gold ore veins and the rules governing the migration of ore fluids.
基金supported by the National Natural Science Foundation of China (No. 41202083, 40373025)the Research Award Fund for Outstanding Middle-aged and Young Scientist of Shandong Province (BS2013HZ024)
文摘The Jinshan gold deposit is located in the Northeast Jiangxi province,South China,which related to the ductile shear zone.It contains two ore types,i.e.the alteration-type ore and the goldbearing quartz vein ore.Rb-Sr age dating is applied to both gold-bearing pyrite in the alteration-type ore and fluid inclusion in the gold-bearing quartz vein to make clear the time of the gold mineralization of the Jinshan deposit.Analytical results of this study yielded that the age of the alteration-type ore bodies is about 838±110Ma,with an initial 87Sr/86Sr value of 0.7045±0.0020.However,the age of the gold-bearing quartz vein-type ore is about 379±49Ma,and the initial 87Sr/86Sr is 0.7138±0.0011.Based on the age data from this work and many previous studies,the authors consider that the Jinshan gold deposit is a product of multi-staged mineralization,which may include the Jinninian,Caledonian,Hercynian,and Yanshanian Periods.Among them,the Jinninian Period and the Hercynian Period might be the two most important ore-forming periods for Jinshan deposit.The Jinninian Period is the main stage for the formation of alteration-type ore bodies,while the Hercynian Period is the major time for ore bodies of gold-bearing quartz vein type.The initial values of the 87Sr/86Sr from this study,as well as the previous isotope and trace element studies,indicate that the ore-forming materials mainly derived from the metamorphic wall rocks,and the ore-forming fluids mainly originated from the deep metamorphic water.
文摘Several aspects related with Lorentz force are discussed in the light of the presence of vibrating strings. Strings are considered as a compact,?tension and viscosity-free incompressible liquid. The motion of a charge particle, obviously, represents the “line of vortex” in the medium of fluid. The term (VXB) turns out to be the natural consequence of Vortex dynamics. The present investigation also reveals the nature of the magnetic field and explains why and how this additional term takes part in Lorentz force.
文摘Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.
基金Supported by the China National Science and Technology Major Project(2016ZX05050).
文摘The origin of grain dolomite in M55 Member of Ordovician Majiagou Formation in northwestern Ordos Basin was studied by geochemical and petrological tests on core samples.Observation of cores,thin sections and casting thin sections,analysis of cathodoluminescence,X-ray diffraction,microscopic sampling of trace elements,laser samplingδ18O andδ13C,and fluid inclusion homogenization temperature were conducted.The results show that the dolomite is the product of recrystallization of micritic to crystal powder dolomite rather than the product of dolomitization of grain limestone.In the spherical grains are residual gypsum and halite pseudo crystals identical with those in the host micritic dolomite.The spherical particles of dolomite has similar trace elements andδ18O andδ13C characteristics to micritic dolomite.Furthermore,Mn/Sr ratio of the fine-medium dolomite between the dolomite grains is about 5-8,while Mn/Sr ratios of calcite in limestone,micritic dolostone in micritic dolomite,and micritic and powdery dolomite are about 0-2,indicating that the dolomite experienced strong diagenesis.Homogenization temperature of inclusions of fine-medium dolomite is about 148.19°C,higher than that of inclusions in micritic to crystal powder dolomite(about 122.60°C),which also supports the conclusion that the grain dolomite experienced burial diagenesis and negative shift ofδ18O andδ13C.Theδ18O,δ13C values of micritic to crystal powder dolomite match with the negative migration,but those of calcite in limestone don’t.It is of great significance to elucidate the genesis of"dolomite recrystallization"for the prediction of such dolomite reservoirs.
