Geochemistry of the fault gouge record information on fault behaviors and environmental conditions.We investigated variations in the mineralogical and geochemical compositions of the fault gouge sampled from the margi...Geochemistry of the fault gouge record information on fault behaviors and environmental conditions.We investigated variations in the mineralogical and geochemical compositions of the fault gouge sampled from the margin zone(MZ)to the slip central zone(CZ)of the fault gouge in the Beichuan-Yingxiu surface rupture zone of the Wenchuan Earthquake.Results show that the clay minerals contents increase from the MZ to CZ,and the quartz and plagioclase contents slight decrease.An increasing enrichment in Al_(2)O_(3),Fe_(2)O_(3),and K_(2)O are observed toward the CZ;the decomposition of quartz and plagioclase,as well as the depletion of Si O_(2),Ca O,Na_2O,and P_(2)O_(5)suggest that the alkaline-earth elements are carried away by the fluids.It can be explained that the stronger coseismic actions in the CZ allow more clay minerals to form,decompose quartz and plagioclase,and alter plagioclase to chlorite.The mass loss in the CZ is larger than that in MZ,which is maybe due to the more concentrated stress in the strongly deformed CZ,however other causes will not be excluded.展开更多
Fluid-rock interaction plays a critical function in physical and chemical processes associated with the formation and evolution of oil and gas reservoir space.In the diagenetic stage of shallow burial,the dissolution ...Fluid-rock interaction plays a critical function in physical and chemical processes associated with the formation and evolution of oil and gas reservoir space.In the diagenetic stage of shallow burial,the dissolution of carbonate rocks by acidic fluids is conducive to the development of secondary pore space in reservoirs.In contrast,the free drift experiment based on water bath instrument can simulate the dissolution process of carbonate rocks in shallow burial environment effectively.In order to study the shallow burial dissolution mechanism of carbonate rocks in different acid solutions,14 samples of typical carbonate rocks of Sinian,Cambrian,Ordovician,Permian and Triassic ages in the Tarim and Sichuan basins,China were used.The dissolution experiments on carbonate rocks in sulfuric acid,acetic acid,hydrochloric acid,silicic acid and carbonic acid at shallow burial temperature(30℃≤T≤90℃)were carried out using a water bath instrument.The PHREEQC software was used to simulate the dissolution of carbonate minerals,in order to compare the results of constant temperature water bath experiment.The results show that acid solutions have significant dissolution effect on shallow burial carbonate rocks when T=50–60℃,which corresponds to the burial depth of 1500–2000 m in the Tarim Basin and 1110–1480 m in the Sichuan Basin.However,there were obvious differences in the dissolution and reformation of carbonate rocks in different acids.In particular,sulfuric acid solution produced by thermochemical sulfate reduction can significantly promote the dissolution of carbonate rocks,especially dolomitic limestone.Moreover,the dissolution of limestone reservoirs is stronger than that of dolomite reservoirs in shallow burial.The results will provide new insights into the study of dissolution laws and influencing factors of reservoir spaces and the evaluation and prediction of carbonate reservoirs in China.展开更多
Jadeitites are formed either through direct precipitation from Na-Al-Si rich fluids(P-type),or by replacement of magmatic protoliths(R-type)in subduction zones.They are valuable targets for investigating the mobility ...Jadeitites are formed either through direct precipitation from Na-Al-Si rich fluids(P-type),or by replacement of magmatic protoliths(R-type)in subduction zones.They are valuable targets for investigating the mobility behavior and chemical composition of subduction zone fluids.The Rio San Juan Complex(RSJC)in the northern Dominican Republic hosts both P-and R-type jadeitites and jadeite-rich rocks,which provide ideal samples for addressing such issues.Here,we present trace element and Sr-Nd-O-Si isotope compositions of RSJC jadeitites and related rocks.Most samples show similar REE patterns,trace element distributions and δ^(18)O values to those of plagiogranite protoliths,indicating the predominance of R-type origin in RSJC.The P-type samples exhibit slightly higherδ^(30)Si values(−0.15‰to 0.25‰)than that of R-type samples(−0.20‰to 0.08‰),which place above the igneous array.The low(^(87)Sr/^(86)Sr)_(i)(0.70346 to 0.70505)and highεNd(t)values(4.6 to 6.8)of the P-type jadeitites and quartzites,along with relatively lowδ^(18)O values(4.7‰to 6.4‰)of their forming fluids,indicate that the fluids are likely derived from the altered basaltic crust rather than from oceanic sediment.However,the estimated jadeitite-and quartzite-forming fluids exhibit distinctδ^(30)Si values(0.76‰to 0.99‰and-0.48‰to-0.08‰,respectively),implying an evolution of the fluids that modified the Si isotopic compositions.Since fluid metasomatism and related desilication process could have lowered the whole-rock δ^(30)Si values,the heavy Si isotope compositions of the R-type samples are produced from the external fluids.Combing Rayleigh distillation and binary mixing simulations,we propose that fluids derived from altered oceanic crust obtained high δ^(30)Si values after crystallization of minerals enriched in light Si isotopes.The P-type jadeitites are formed through direct precipitation from this fluid.As the plagiogranite protoliths were continuously replaced by this fluid,the formed R-type samples(jadeitites and quartzites)also exhibit high δ^(30)Si values.Such rocks could significantly alter the Si isotope compositions of local mantle when they are deeply subducted at convergent plate margins.展开更多
High-pressure(HP)or ultrahigh-pressure(UHP)rutile-quartz veins that form at mantle depths due to fluid-rock interaction can be used to trace the properties and behavior of natural fluids in subduction zones.To explore...High-pressure(HP)or ultrahigh-pressure(UHP)rutile-quartz veins that form at mantle depths due to fluid-rock interaction can be used to trace the properties and behavior of natural fluids in subduction zones.To explore the fluid flow and the associated element mobility during deep subduction and exhumation of the continental crust,we investigated the major and trace elements of Ti-rich minerals.Additionally,U–Pb dating,trace element contents,and Lu–Hf isotopic composition of zircon grains in the UHP eclogite and associated rutile-quartz veins were examined in the North Qaidam UHP metamorphic belt,Yuka terrane.The zircon grains in the rutile-quartz veins have unzoned or weak oscillatory zonings,and show low Th/U ratios,steep chondrite-normalized patterns of heavy rare earth elements(HREEs),and insignificant negative Eu anomalies,indicating their growth in metamorphic fluids.These zircon grains formed in 4313 Ma,which is consistent with the 4322 Ma age of the host eclogite.As for the zircons in the rutile-quartz veins,they showed steep HREE patterns on one hand,and were different from the zircons present in the host eclogite on the other.This demonstrates that their formation might have been related to the breakdown of the early stage of garnet,which corresponds to the abundance of fluids during the early exhumation stage.The core-rim profile analyses of rutile recorded a two-stage rutile growth across a large rutile grain;the rutile core has higher Nb,Ta,W,and Zr contents and lower Nb/Ta ratios than the rim,indicating that the rutile domains grew in different metamorphic fluids from the core towards the rim.The significant enrichment of high field strength elements(HFSEs)in the rutile core suggests that the peak fluids have high solubility and transportation capacity of these HFSEs.Furthermore,variations in the Nb vs.Cr trends in rutile indicate a connection of rutile to mafic protolith.The zircon grains from both the rutile-quartz veins and the host eclogite have similar Hf isotopic compositions,indicating that the vein-forming fluids are internally derived from the host eclogite.These fluids accumulated in the subduction channel and were triggered by local dehydration of the deeply subducted eclogite during the early exhumation conditions.展开更多
As demonstrated by a great amount of geologic and experimental evidences, RE of rock systems may be mobilized during fluid-rock interaction when solutions are rich in F -, Cl -, CO 3 2-, HCO 3 -, CO 2, HPO 4...As demonstrated by a great amount of geologic and experimental evidences, RE of rock systems may be mobilized during fluid-rock interaction when solutions are rich in F -, Cl -, CO 3 2-, HCO 3 -, CO 2, HPO 4 2-, HS -, S 2-, SO 4 2-, though little has been known about the mobilizing mechanism of these anions or ligands. The fractionation of RE resulted from hydrothermal alterations, i. e., fluid-rock interactions, are distinctive. One set of field data implies the preferential mobility of the LRE, while another set of field observations demonstrates the dominant mobilization of the HRE, and some theoretical prediction is not consistent with the field evidence. The Eu anomalies caused by fluid-rock interaction are complex and compelling explanation is not available due to inadequate experimental approaches. To know the exact behavior of RE during fluid-rock interaction and to solve the contradiction between some theoretical predictions and field observations, the following works remain to be done: (1) experimental investigations of RE mobility and fractionation as a function of fluid chemistry, e.g., the activity of F -, Cl -, CO 3 2-, HCO 3 -, CO 2, HPO 4 2-, HS -, S 2-, SO 4 2-, etc.; (2) experimental determination of RE mobility and fractionation as a function of T, P, pH, E h and water/rock ratios; (3) investigation of the mechanism and the controlling factors of RE partitioning between hydrothermal minerals and fluids. It was demonstrated that RE mobility is a potentially useful method for exploration.展开更多
Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming ...Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming processes of Yinshan deposit. It is not sufficient to show the mobility only by the absolute abundance of trace elements changes before and after alteration. This can simply result from dilution or concentration if other elements are added to or removed from the rock. As shown by that in Yinshan deposit, less than 20% of the increment of RE was caused by the 'condensed' of leaching some of major elements (e.g. Si, Na) from the rock. The principal factor which should be responsible for the higher contents of RE in altered rock is the addition of RE into the rock by hydrothermal fluids. Eu is selectively leached from the altered sericite phyllite by a mild acidity and reducing fluid which is characterized by much lower LRE/HRE ratio and a large positive Eu anomaly. A major effect on the RE patterns is the tendency to develop relatively flatter chondrite-normalized patterns. The RE characteristics may be used to distinguish between small and large ore bodies at a later stage of exploration.展开更多
The Koyna region of Maharashtra located in the western part of the~65 Myr old Deccan traps province,overlying the Neoarchean cratonic granitoid basement of peninsular India,has been experiencing recurring seismicity s...The Koyna region of Maharashtra located in the western part of the~65 Myr old Deccan traps province,overlying the Neoarchean cratonic granitoid basement of peninsular India,has been experiencing recurring seismicity since 1962 after the impoundment of the Shivajisagar Reservoir behind the Koyna Dam.展开更多
Discriminations in a local chemical, fluidal, mechanical and thermal processes in a shear zone will lead to metallogenic differentiation in a local section. This paper, based on the general geological setting of the S...Discriminations in a local chemical, fluidal, mechanical and thermal processes in a shear zone will lead to metallogenic differentiation in a local section. This paper, based on the general geological setting of the Shibangou gold deposit in Xixia, Henan, deals with petrological and petrochemical samples of altered rocks in the metallogenic section and of mylonites in the non\|metallogenic section of a selected shear zone. The discriminations in fluid\|rock interaction and petrological mass balance between altered rocks near the orebody and mylonites in the shear zone are discussed as well. The results show that the petrological volume of altered rocks in the metallogenic section of the shear zone is almost always dilatant and the mylonite volume in the non\|metallogenic section is almost always lost. Major elements in altered rocks from the metallogenic section and in mylonites from the non\|metallogenic section always show a tendency of being enriched and depleted, respectively. Fluid\|rock ratios in the mylonites (Nu=\{93.68-468.40\}) are larger than those of the altered rocks (Nc\+s\-\{(Ⅳ)\}=\{36.11-216.67\}). The gain and loss of major and trace elements from the altered rocks and mylonites in the shear zone are a composite process to be imported and exported by percolating fluids as well as of the loss and dilatancy of rock volume.展开更多
Hydrogen and oxygen isotope studies were carried out on mineral separates from high to ultrahigh pressure metamorphic rocks at Huangzhen and Shuanghe in the eastern Dabie Mountains, East China. The δ18O values of ecl...Hydrogen and oxygen isotope studies were carried out on mineral separates from high to ultrahigh pressure metamorphic rocks at Huangzhen and Shuanghe in the eastern Dabie Mountains, East China. The δ18O values of eclogites cover a wide range of ?5‰ to+9‰, but the δD values of micas fall within a narrow range of ?85% to ?70‰. Both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals, with reversed fractionations between omphacite and garnet in some eclogite samples. The δ18 O values of ?5‰ to ?1‰ for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent meteoric water-rock interaction prior to plate subduction. The preservation of oxygen isotope heterogeneity in the eclogites implies a channelized flow of fluids during progressive metamorphism caused by rapid subduction. Retrograde metamorphism has caused oxygen and hydrogen isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was internally buffered in the stable isotope compositions.展开更多
The Irtish techonic zone,as an example,is presented to study fluid-rock interactions during overthrusting the deformation process at the depth of middle-lower earth crust.The results show that there were compicuous fl...The Irtish techonic zone,as an example,is presented to study fluid-rock interactions during overthrusting the deformation process at the depth of middle-lower earth crust.The results show that there were compicuous fluid actions in the meantime of deformation and many deformational and differential microstructures related to fluid-rock interactions provided direct evidence of fluid actions.Fluid,as a medium of mass transfer,played an important role in the loss and getting of chemical compositions in deformed rocks during tectono-dynamic lithogeneous processes in which rock alterations from protolith(volcanics)through mylonite to migmatite and finally to migmatitic granite took place.The loss and getting of chemical compositions can he calculated by means of major and trace elements.Using the calculated results and SiO_2 solubility,the calculation fluid(mass)/rock(volume)ratio is 10~3-10~5g fluid/m^3 rock.The possible fluid resources are dehydration reactions of pore water and mineral water within protoliths(marine mid-acid volcanics)and foodwaU rocks during tectono-rise pressure and temperature processes.The fluid flow migrated from deep to shallow positions of the earth crust along the large-scale thrusting fault,penetrative cleavage,and S-C foliation.Fluid mass transportation resulted in chemical composition alterations in deformed rocks. Within overthrusting zone under the compressive orogenic background,the major mechanism of mass transportation is infiltration or advection in the open system.展开更多
Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and frac...Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and fracture characteristics of Zhangzhou granite were investigated under fluids with different pH values.Subcritical crack growth index(SCI)was reduced in both acidic and alkaline fluids compared with the neutral environment,with reduction percentages of 9.8%e31.9%under acidic environment(pH=1-5)and 8.3%e17.5%under alkaline environment(pH=10-14),respectively.In contrast,the weakening effect of fluid pH values on critical stress intensity was less than that of SCI.Scanning electron microscopy(SEM)results showed that grain boundaries were prone to dissolution compared to the basal surface,proving that subcritical cracks preferentially propagate along the grain boundaries.Fracture toughness was insensitive to fluid pH values in the short term but sensitive to solution salinity.Considering mineral compositions and contents,a rock dissolution rate was defined,and a SCI prediction model was proposed,which was demonstrated to be capable of estimating variations in SCI under various fluid environments for different rock types and could provide valuable insights for engineering applications and environmental assessments.展开更多
基金supported by the research grant from Institute of Crustal Dynamics,China Earthquake Administration(No.ZDJ2019-02)。
文摘Geochemistry of the fault gouge record information on fault behaviors and environmental conditions.We investigated variations in the mineralogical and geochemical compositions of the fault gouge sampled from the margin zone(MZ)to the slip central zone(CZ)of the fault gouge in the Beichuan-Yingxiu surface rupture zone of the Wenchuan Earthquake.Results show that the clay minerals contents increase from the MZ to CZ,and the quartz and plagioclase contents slight decrease.An increasing enrichment in Al_(2)O_(3),Fe_(2)O_(3),and K_(2)O are observed toward the CZ;the decomposition of quartz and plagioclase,as well as the depletion of Si O_(2),Ca O,Na_2O,and P_(2)O_(5)suggest that the alkaline-earth elements are carried away by the fluids.It can be explained that the stronger coseismic actions in the CZ allow more clay minerals to form,decompose quartz and plagioclase,and alter plagioclase to chlorite.The mass loss in the CZ is larger than that in MZ,which is maybe due to the more concentrated stress in the strongly deformed CZ,however other causes will not be excluded.
基金jointly supported by the Science and Technology Development Project of PetroChina Hangzhou Institute of Petroleum Geology(No.RIPED-2020-JS-51008)the Naturacl Science Foundation of China(Nos.41872250,41802159)。
文摘Fluid-rock interaction plays a critical function in physical and chemical processes associated with the formation and evolution of oil and gas reservoir space.In the diagenetic stage of shallow burial,the dissolution of carbonate rocks by acidic fluids is conducive to the development of secondary pore space in reservoirs.In contrast,the free drift experiment based on water bath instrument can simulate the dissolution process of carbonate rocks in shallow burial environment effectively.In order to study the shallow burial dissolution mechanism of carbonate rocks in different acid solutions,14 samples of typical carbonate rocks of Sinian,Cambrian,Ordovician,Permian and Triassic ages in the Tarim and Sichuan basins,China were used.The dissolution experiments on carbonate rocks in sulfuric acid,acetic acid,hydrochloric acid,silicic acid and carbonic acid at shallow burial temperature(30℃≤T≤90℃)were carried out using a water bath instrument.The PHREEQC software was used to simulate the dissolution of carbonate minerals,in order to compare the results of constant temperature water bath experiment.The results show that acid solutions have significant dissolution effect on shallow burial carbonate rocks when T=50–60℃,which corresponds to the burial depth of 1500–2000 m in the Tarim Basin and 1110–1480 m in the Sichuan Basin.However,there were obvious differences in the dissolution and reformation of carbonate rocks in different acids.In particular,sulfuric acid solution produced by thermochemical sulfate reduction can significantly promote the dissolution of carbonate rocks,especially dolomitic limestone.Moreover,the dissolution of limestone reservoirs is stronger than that of dolomite reservoirs in shallow burial.The results will provide new insights into the study of dissolution laws and influencing factors of reservoir spaces and the evaluation and prediction of carbonate reservoirs in China.
基金supported by funds from the National Key Research and Development Program of China(Grant No.2024YFF0807302)National Natural Science Foundation of China(42273043,42173003)the International Visiting Professorship of USTC(2024BVR23).
文摘Jadeitites are formed either through direct precipitation from Na-Al-Si rich fluids(P-type),or by replacement of magmatic protoliths(R-type)in subduction zones.They are valuable targets for investigating the mobility behavior and chemical composition of subduction zone fluids.The Rio San Juan Complex(RSJC)in the northern Dominican Republic hosts both P-and R-type jadeitites and jadeite-rich rocks,which provide ideal samples for addressing such issues.Here,we present trace element and Sr-Nd-O-Si isotope compositions of RSJC jadeitites and related rocks.Most samples show similar REE patterns,trace element distributions and δ^(18)O values to those of plagiogranite protoliths,indicating the predominance of R-type origin in RSJC.The P-type samples exhibit slightly higherδ^(30)Si values(−0.15‰to 0.25‰)than that of R-type samples(−0.20‰to 0.08‰),which place above the igneous array.The low(^(87)Sr/^(86)Sr)_(i)(0.70346 to 0.70505)and highεNd(t)values(4.6 to 6.8)of the P-type jadeitites and quartzites,along with relatively lowδ^(18)O values(4.7‰to 6.4‰)of their forming fluids,indicate that the fluids are likely derived from the altered basaltic crust rather than from oceanic sediment.However,the estimated jadeitite-and quartzite-forming fluids exhibit distinctδ^(30)Si values(0.76‰to 0.99‰and-0.48‰to-0.08‰,respectively),implying an evolution of the fluids that modified the Si isotopic compositions.Since fluid metasomatism and related desilication process could have lowered the whole-rock δ^(30)Si values,the heavy Si isotope compositions of the R-type samples are produced from the external fluids.Combing Rayleigh distillation and binary mixing simulations,we propose that fluids derived from altered oceanic crust obtained high δ^(30)Si values after crystallization of minerals enriched in light Si isotopes.The P-type jadeitites are formed through direct precipitation from this fluid.As the plagiogranite protoliths were continuously replaced by this fluid,the formed R-type samples(jadeitites and quartzites)also exhibit high δ^(30)Si values.Such rocks could significantly alter the Si isotope compositions of local mantle when they are deeply subducted at convergent plate margins.
基金funded by the Fundamental Research Funds for National Universities, China University of Geosciences (Wuhan) and China Geological Survey (Grant Nos. 12120113032800, 21201011000150004, DD20190069)
文摘High-pressure(HP)or ultrahigh-pressure(UHP)rutile-quartz veins that form at mantle depths due to fluid-rock interaction can be used to trace the properties and behavior of natural fluids in subduction zones.To explore the fluid flow and the associated element mobility during deep subduction and exhumation of the continental crust,we investigated the major and trace elements of Ti-rich minerals.Additionally,U–Pb dating,trace element contents,and Lu–Hf isotopic composition of zircon grains in the UHP eclogite and associated rutile-quartz veins were examined in the North Qaidam UHP metamorphic belt,Yuka terrane.The zircon grains in the rutile-quartz veins have unzoned or weak oscillatory zonings,and show low Th/U ratios,steep chondrite-normalized patterns of heavy rare earth elements(HREEs),and insignificant negative Eu anomalies,indicating their growth in metamorphic fluids.These zircon grains formed in 4313 Ma,which is consistent with the 4322 Ma age of the host eclogite.As for the zircons in the rutile-quartz veins,they showed steep HREE patterns on one hand,and were different from the zircons present in the host eclogite on the other.This demonstrates that their formation might have been related to the breakdown of the early stage of garnet,which corresponds to the abundance of fluids during the early exhumation stage.The core-rim profile analyses of rutile recorded a two-stage rutile growth across a large rutile grain;the rutile core has higher Nb,Ta,W,and Zr contents and lower Nb/Ta ratios than the rim,indicating that the rutile domains grew in different metamorphic fluids from the core towards the rim.The significant enrichment of high field strength elements(HFSEs)in the rutile core suggests that the peak fluids have high solubility and transportation capacity of these HFSEs.Furthermore,variations in the Nb vs.Cr trends in rutile indicate a connection of rutile to mafic protolith.The zircon grains from both the rutile-quartz veins and the host eclogite have similar Hf isotopic compositions,indicating that the vein-forming fluids are internally derived from the host eclogite.These fluids accumulated in the subduction channel and were triggered by local dehydration of the deeply subducted eclogite during the early exhumation conditions.
文摘As demonstrated by a great amount of geologic and experimental evidences, RE of rock systems may be mobilized during fluid-rock interaction when solutions are rich in F -, Cl -, CO 3 2-, HCO 3 -, CO 2, HPO 4 2-, HS -, S 2-, SO 4 2-, though little has been known about the mobilizing mechanism of these anions or ligands. The fractionation of RE resulted from hydrothermal alterations, i. e., fluid-rock interactions, are distinctive. One set of field data implies the preferential mobility of the LRE, while another set of field observations demonstrates the dominant mobilization of the HRE, and some theoretical prediction is not consistent with the field evidence. The Eu anomalies caused by fluid-rock interaction are complex and compelling explanation is not available due to inadequate experimental approaches. To know the exact behavior of RE during fluid-rock interaction and to solve the contradiction between some theoretical predictions and field observations, the following works remain to be done: (1) experimental investigations of RE mobility and fractionation as a function of fluid chemistry, e.g., the activity of F -, Cl -, CO 3 2-, HCO 3 -, CO 2, HPO 4 2-, HS -, S 2-, SO 4 2-, etc.; (2) experimental determination of RE mobility and fractionation as a function of T, P, pH, E h and water/rock ratios; (3) investigation of the mechanism and the controlling factors of RE partitioning between hydrothermal minerals and fluids. It was demonstrated that RE mobility is a potentially useful method for exploration.
文摘Rare earths in ores, altered and unaltered sericite phyllite, altered and unaltered dacite porphyry were determined in order to examine behaviors of rare earths in hydrothermal alteration associating with ore-forming processes of Yinshan deposit. It is not sufficient to show the mobility only by the absolute abundance of trace elements changes before and after alteration. This can simply result from dilution or concentration if other elements are added to or removed from the rock. As shown by that in Yinshan deposit, less than 20% of the increment of RE was caused by the 'condensed' of leaching some of major elements (e.g. Si, Na) from the rock. The principal factor which should be responsible for the higher contents of RE in altered rock is the addition of RE into the rock by hydrothermal fluids. Eu is selectively leached from the altered sericite phyllite by a mild acidity and reducing fluid which is characterized by much lower LRE/HRE ratio and a large positive Eu anomaly. A major effect on the RE patterns is the tendency to develop relatively flatter chondrite-normalized patterns. The RE characteristics may be used to distinguish between small and large ore bodies at a later stage of exploration.
基金conducted under the project sponsored by the Ministry of Earth Sciences,Govt.of India[Project Code-Mo ES/P.O.(Seismo)/1(374)/2019]
文摘The Koyna region of Maharashtra located in the western part of the~65 Myr old Deccan traps province,overlying the Neoarchean cratonic granitoid basement of peninsular India,has been experiencing recurring seismicity since 1962 after the impoundment of the Shivajisagar Reservoir behind the Koyna Dam.
文摘Discriminations in a local chemical, fluidal, mechanical and thermal processes in a shear zone will lead to metallogenic differentiation in a local section. This paper, based on the general geological setting of the Shibangou gold deposit in Xixia, Henan, deals with petrological and petrochemical samples of altered rocks in the metallogenic section and of mylonites in the non\|metallogenic section of a selected shear zone. The discriminations in fluid\|rock interaction and petrological mass balance between altered rocks near the orebody and mylonites in the shear zone are discussed as well. The results show that the petrological volume of altered rocks in the metallogenic section of the shear zone is almost always dilatant and the mylonite volume in the non\|metallogenic section is almost always lost. Major elements in altered rocks from the metallogenic section and in mylonites from the non\|metallogenic section always show a tendency of being enriched and depleted, respectively. Fluid\|rock ratios in the mylonites (Nu=\{93.68-468.40\}) are larger than those of the altered rocks (Nc\+s\-\{(Ⅳ)\}=\{36.11-216.67\}). The gain and loss of major and trace elements from the altered rocks and mylonites in the shear zone are a composite process to be imported and exported by percolating fluids as well as of the loss and dilatancy of rock volume.
基金Project supported by the Chinese Ministry of Science and Technology (Grant No. 95-Pre-39)the National Natural Science Foundation of China (Grant Nos. 49794042, 49473173 and 49453003)the Chinese Academy of Sciences (Grant No. KZ951-A1-401-5).
文摘Hydrogen and oxygen isotope studies were carried out on mineral separates from high to ultrahigh pressure metamorphic rocks at Huangzhen and Shuanghe in the eastern Dabie Mountains, East China. The δ18O values of eclogites cover a wide range of ?5‰ to+9‰, but the δD values of micas fall within a narrow range of ?85% to ?70‰. Both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals, with reversed fractionations between omphacite and garnet in some eclogite samples. The δ18 O values of ?5‰ to ?1‰ for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent meteoric water-rock interaction prior to plate subduction. The preservation of oxygen isotope heterogeneity in the eclogites implies a channelized flow of fluids during progressive metamorphism caused by rapid subduction. Retrograde metamorphism has caused oxygen and hydrogen isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was internally buffered in the stable isotope compositions.
基金the National Natural Science Foundation of ChinaNational Key Project 85-902-01-05Educational Bureau of the Chinese Academy of Sciences
文摘The Irtish techonic zone,as an example,is presented to study fluid-rock interactions during overthrusting the deformation process at the depth of middle-lower earth crust.The results show that there were compicuous fluid actions in the meantime of deformation and many deformational and differential microstructures related to fluid-rock interactions provided direct evidence of fluid actions.Fluid,as a medium of mass transfer,played an important role in the loss and getting of chemical compositions in deformed rocks during tectono-dynamic lithogeneous processes in which rock alterations from protolith(volcanics)through mylonite to migmatite and finally to migmatitic granite took place.The loss and getting of chemical compositions can he calculated by means of major and trace elements.Using the calculated results and SiO_2 solubility,the calculation fluid(mass)/rock(volume)ratio is 10~3-10~5g fluid/m^3 rock.The possible fluid resources are dehydration reactions of pore water and mineral water within protoliths(marine mid-acid volcanics)and foodwaU rocks during tectono-rise pressure and temperature processes.The fluid flow migrated from deep to shallow positions of the earth crust along the large-scale thrusting fault,penetrative cleavage,and S-C foliation.Fluid mass transportation resulted in chemical composition alterations in deformed rocks. Within overthrusting zone under the compressive orogenic background,the major mechanism of mass transportation is infiltration or advection in the open system.
基金financial support from the National Natural Science Foundation of China(No.52074349)China Scholarship Council(No.202206370108)the Hunan Provincial Innovation Foundation for Postgraduate(No.CX20230193).
文摘Subcritical crack growth(SCG)in fluid-rock interactions plays a crucial role in understanding crustal deformation and fracture network development.Using a double-torsion technique,the subcritical crack growth and fracture characteristics of Zhangzhou granite were investigated under fluids with different pH values.Subcritical crack growth index(SCI)was reduced in both acidic and alkaline fluids compared with the neutral environment,with reduction percentages of 9.8%e31.9%under acidic environment(pH=1-5)and 8.3%e17.5%under alkaline environment(pH=10-14),respectively.In contrast,the weakening effect of fluid pH values on critical stress intensity was less than that of SCI.Scanning electron microscopy(SEM)results showed that grain boundaries were prone to dissolution compared to the basal surface,proving that subcritical cracks preferentially propagate along the grain boundaries.Fracture toughness was insensitive to fluid pH values in the short term but sensitive to solution salinity.Considering mineral compositions and contents,a rock dissolution rate was defined,and a SCI prediction model was proposed,which was demonstrated to be capable of estimating variations in SCI under various fluid environments for different rock types and could provide valuable insights for engineering applications and environmental assessments.
