The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous e...The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous experiments of the same type of rocks under dry conditions,and the former which is enriched in potassium has a lower melting point than the latter. It is con-sistent with the previous study. The melting temperature of eclogite increases with pressure,whereas potassic basalt has similar properties only at 1.5—2.5 GPa and>3.0 GPa, and at 2.5—3.0 GPa the melting temperature decreases with pressure. This can be explained as follows: (1)eclogite only has one hydrous mineral amphibole and the dehydous temperature is lower than thewet solidus of the rock. (2) Amphibole exists in potassic basalt at the pressures lower than 2.5GPa and phlogopite exists at pressures higher than 2.5 GPa, and the special compositions of bothminerals determine that amphibole has a dehydration temperature higher than or close to that ofthe wet solidus of the rocks, while phlogopite has a dehydration temperature lower than that ofthe wet solidus. On the other hand the features of the continuous solidus in the experiment ofhydrous eclogite were produced by the fact that the dehydration temperature of its amphibolelower than or close to the melting temperature of the hydrous conditions. So the melting tempera-ture lowers at higher pressures. Therefore, the composition of the rocks in the lithosphere and thetypes of hydrous minerals and their stable P-T conditions are the important factors controllingthe solidi of rocks. It can quite well explain the partial melting of rocks and the origin of the lowvelocity zone in the deep lithosphere.展开更多
Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of the...Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H2O-CO2-salt fluids at 750--800 ℃ and 5.5--6.2 kbar, partial melting, and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650--700 ℃. These processes caused local variations of water and alkali activity in the fluids, resulting in various mineral assemblages within the dehydration zone. The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H2O-CO2-（K, Na）Cl fluids at 750 and 800 ℃ and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）CI fluids is accompanied by partial melting at 750--800 ℃. Orthopyroxene-bearing assemblages are characteristic for temperature 800 ℃ and are stable in equilibrium with fluids with low salt concentrations, while salt-rich fluids produce clinopyroxene-bearing assemblages. These observations are in good agreement with the petrological data on the dehydration zones within the Sand River olthogneisses.展开更多
Experiments on the partitioning of Cu between different granitic silicate melts and the respective coexisting aqueous fluids have been performed under conditions of 850 °C, 100 MPa and oxygen fugacity(f O_2) buff...Experiments on the partitioning of Cu between different granitic silicate melts and the respective coexisting aqueous fluids have been performed under conditions of 850 °C, 100 MPa and oxygen fugacity(f O_2) buffered at approaching Ni–Ni O(NNO). Partition coefficients of Cu(DCu= cfluid/cmelt) were varied with different alumina/alkali mole ratios [Al_2O_3/(Na_2O·K_2O), abbreviated as Al/Alk], Na/K mole ratios, and Si O_2 mole contents. The DCu increased from 1.28 ± 0.01 to 22.18 ± 0.22 with the increase of Al/Alk mole ratios(ranging from 0.64 to 1.20)and Na/K mole ratios(ranging from 0.58 to 2.56). The experimental results also showed that DCuwas positively correlated with the HCl concentration of the starting fluid.The DCuwas independent of the Si O_2 mole content in the range of Si O_2 content considered. No DCuvalue was less than 1 in our experiments at 850 °C and 100 MPa, indicating that Cu preferred to enter the fluid phase rather than the coexisting melt phase under most conditions in the melt-fluid system, and thus a significant amount of Cu could be transported in the fluid phase in the magmatichydrothermal environment. The results indicated that Cu favored partitioning into the aqueous fluid rather than themelt phase if there was a high Na/K ratio, Na-rich, peraluminous granitic melt coexisting with the high Cl-fluid.展开更多
Experiments have been carried out for studying the melting characteristics of two representative types of granite complexes relating to tin ore deposits in Guangxi. The curves of the beginning melting of the Longxiang...Experiments have been carried out for studying the melting characteristics of two representative types of granite complexes relating to tin ore deposits in Guangxi. The curves of the beginning melting of the Longxiangai porphyritic biotite granite (LPBG), the Longxiangai granular biotite granite (LGBG), the margin phase and central phase of the rocks of the Pinyin granite (MPPG and CPPG) are determined by the experiments. The results of the experiments show that the temperature of the beginning melting points of the tin -bearing granite not only depends on the type and features of the rocks, but also varies with the total water vapour pressure (PH2O) and the one of the different granites decrease with the increasing pressure. In different ranges of the pressure,the variance gradient of the beginning melting points sharply varies. When PH2O is less than or equal to 136 MPa, the beginning melting temperatures of LPBG somewhat lower than those of LGBG ;Whe P H2O is larger than 136MPa,The beginning temperatures of LPBG are higher than those of LGBG. The beginning teperatures of CPPG are always higher than those of MPFG at the conditions of PH2O from 75 to 250 MPa.展开更多
基金Note:This study was supported by China National Natural Science Foundation Grant No.49070087.
文摘The experimental study on the melting of potassic basalt and eclogite with about 2% waterat 800-1300℃ and 1.0-3.5 GPa shows that the solidi of both rocks are significantly lower thanthose obtained from the previous experiments of the same type of rocks under dry conditions,and the former which is enriched in potassium has a lower melting point than the latter. It is con-sistent with the previous study. The melting temperature of eclogite increases with pressure,whereas potassic basalt has similar properties only at 1.5—2.5 GPa and>3.0 GPa, and at 2.5—3.0 GPa the melting temperature decreases with pressure. This can be explained as follows: (1)eclogite only has one hydrous mineral amphibole and the dehydous temperature is lower than thewet solidus of the rock. (2) Amphibole exists in potassic basalt at the pressures lower than 2.5GPa and phlogopite exists at pressures higher than 2.5 GPa, and the special compositions of bothminerals determine that amphibole has a dehydration temperature higher than or close to that ofthe wet solidus of the rocks, while phlogopite has a dehydration temperature lower than that ofthe wet solidus. On the other hand the features of the continuous solidus in the experiment ofhydrous eclogite were produced by the fact that the dehydration temperature of its amphibolelower than or close to the melting temperature of the hydrous conditions. So the melting tempera-ture lowers at higher pressures. Therefore, the composition of the rocks in the lithosphere and thetypes of hydrous minerals and their stable P-T conditions are the important factors controllingthe solidi of rocks. It can quite well explain the partial melting of rocks and the origin of the lowvelocity zone in the deep lithosphere.
基金supported by Russian Foundation for Basic Research(project 10-05-00040 to OGS)Russian President Grants for Young Scientists(MD-222.2012.5 to OGS)+1 种基金grant from the National Science Foundation of South Africa(GUN:20531 92 to DDvR)University of Johannesburg as a part of the Russian South African scientific collaboration
文摘Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H2O-CO2-salt fluids at 750--800 ℃ and 5.5--6.2 kbar, partial melting, and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650--700 ℃. These processes caused local variations of water and alkali activity in the fluids, resulting in various mineral assemblages within the dehydration zone. The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H2O-CO2-（K, Na）Cl fluids at 750 and 800 ℃ and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）CI fluids is accompanied by partial melting at 750--800 ℃. Orthopyroxene-bearing assemblages are characteristic for temperature 800 ℃ and are stable in equilibrium with fluids with low salt concentrations, while salt-rich fluids produce clinopyroxene-bearing assemblages. These observations are in good agreement with the petrological data on the dehydration zones within the Sand River olthogneisses.
文摘Experiments on the partitioning of Cu between different granitic silicate melts and the respective coexisting aqueous fluids have been performed under conditions of 850 °C, 100 MPa and oxygen fugacity(f O_2) buffered at approaching Ni–Ni O(NNO). Partition coefficients of Cu(DCu= cfluid/cmelt) were varied with different alumina/alkali mole ratios [Al_2O_3/(Na_2O·K_2O), abbreviated as Al/Alk], Na/K mole ratios, and Si O_2 mole contents. The DCu increased from 1.28 ± 0.01 to 22.18 ± 0.22 with the increase of Al/Alk mole ratios(ranging from 0.64 to 1.20)and Na/K mole ratios(ranging from 0.58 to 2.56). The experimental results also showed that DCuwas positively correlated with the HCl concentration of the starting fluid.The DCuwas independent of the Si O_2 mole content in the range of Si O_2 content considered. No DCuvalue was less than 1 in our experiments at 850 °C and 100 MPa, indicating that Cu preferred to enter the fluid phase rather than the coexisting melt phase under most conditions in the melt-fluid system, and thus a significant amount of Cu could be transported in the fluid phase in the magmatichydrothermal environment. The results indicated that Cu favored partitioning into the aqueous fluid rather than themelt phase if there was a high Na/K ratio, Na-rich, peraluminous granitic melt coexisting with the high Cl-fluid.
文摘Experiments have been carried out for studying the melting characteristics of two representative types of granite complexes relating to tin ore deposits in Guangxi. The curves of the beginning melting of the Longxiangai porphyritic biotite granite (LPBG), the Longxiangai granular biotite granite (LGBG), the margin phase and central phase of the rocks of the Pinyin granite (MPPG and CPPG) are determined by the experiments. The results of the experiments show that the temperature of the beginning melting points of the tin -bearing granite not only depends on the type and features of the rocks, but also varies with the total water vapour pressure (PH2O) and the one of the different granites decrease with the increasing pressure. In different ranges of the pressure,the variance gradient of the beginning melting points sharply varies. When PH2O is less than or equal to 136 MPa, the beginning melting temperatures of LPBG somewhat lower than those of LGBG ;Whe P H2O is larger than 136MPa,The beginning temperatures of LPBG are higher than those of LGBG. The beginning teperatures of CPPG are always higher than those of MPFG at the conditions of PH2O from 75 to 250 MPa.
