The genetic relationship between different types of granite is critical for understanding the formation and evolution of granitic magma. Fluid-rock interaction experiments between two-mica leucogranite and boron-rich ...The genetic relationship between different types of granite is critical for understanding the formation and evolution of granitic magma. Fluid-rock interaction experiments between two-mica leucogranite and boron-rich fluids were carried out at 600–700°C and 200 MPa to investigate the effects of boron content in fluid and temperature on the reaction products. Our experimental results show that tourmaline granite can be produced by reactions between boron-rich fluid and two-mica granite.At 700°C, the addition of boron-rich fluid resulted in partial melting of two-mica granite and crystallization of tourmaline from the boron-rich partial melt. Increasing boron concentration in fluid promotes the melting of two-mica granite and the growth of tourmaline. No melt was produced in experiments at 600°C, in which Fe, Mg and Al released from biotite decomposition combined with boron from the fluid to form tourmaline under subsolidus conditions. The Na required for tourmaline crystallization derived from Na/K exchange between feldspar and the K released by biotite decomposition. The produced tourmaline generally has core-rim structures, indicating that the composition of melt or fluid evolved during tourmaline crystallization.Based on the experimental results, we propose that tourmaline granite veins or dikes can be formed by the reactions between boron-rich fluids, presumably produced by devolatilization of boron-bearing granitic magma, and incompletely crystallized granite at the top of the magma chamber. This 'self-metasomatism' involving boron-rich fluid in the late stage of magma crystallization could be an important mechanism for the formation of tourmaline granite.展开更多
The effects of melt composition,temperature and pressure on the solubility of fluorite(CaF2),i.e.,fluorine concentration in silicate melts in equilibrium with fluorite,are summarized in this paper.The authors present ...The effects of melt composition,temperature and pressure on the solubility of fluorite(CaF2),i.e.,fluorine concentration in silicate melts in equilibrium with fluorite,are summarized in this paper.The authors present a statistic study based on experimental data in literature and propose a predictive model to estimate F concentration in melt at the saturation of fluorite(CFin melt^Fl-sat).The modeling indicates that the compositional effect of melt cations on the variation in can be expressed quantitatively as one parameter FSI(fluorite saturation index):FSI=(3Al^NM+Fe^2++6Mg+Ca+1.5Na-K)/(Si+Ti+Al^NF+Fe^3+),in which all cations are in mole,and Al^NF and Al^NM are A1 as network-forming and network-modifying cations,respectively.The dependence of CFin melt^Fl-sat on FSI is regressed as:CFin melt^Fl-sat=1.130-2.014·exp(1000/T)+2.747·exp(P/T)+0.111·CmeltH2O+17.641·FSI,in which T is temperature in Kelvin,P is pressure in MPa,CmeltH2O is melt H2O content in wt.%,and CFin melt^Fl-sat is in wt.%(normalized to anhydrous basis).The reference dataset used to establish the expression for conditions within 540-1010℃,50-500 MPa,0-7 wt.%melt H2O content,0.4 to 1.7 for A/CNK,0.3 wt.%-7.0 wt.%for CFin melt^Fl-sat.The discrepancy of CFin melt^Fl-sat between calculated and measured values is less than±0.62 wt.%with a confidence interval of 95%.The expression of FSI and its effect on CFin melt^Fl-sat indicate that fluorine incorporation in silicate melts is largely controlled by bonding with network-modifying cations,favorably with Mg,Al^NM,Na,Ca and Fe^2+in a decreasing order.The proposed model for predicting CFin melt^Fl-sat is also supported by our new experiments saturated with magmatic fluorite performed at 100-200 MPa and 800-900℃.The modeling of magma fractional crystallization emphasizes that the saturation of fluorite is dependent on both the compositions of primary magmas and their initial F contents.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41672197)the China Scholarship Council(CSC)
文摘The genetic relationship between different types of granite is critical for understanding the formation and evolution of granitic magma. Fluid-rock interaction experiments between two-mica leucogranite and boron-rich fluids were carried out at 600–700°C and 200 MPa to investigate the effects of boron content in fluid and temperature on the reaction products. Our experimental results show that tourmaline granite can be produced by reactions between boron-rich fluid and two-mica granite.At 700°C, the addition of boron-rich fluid resulted in partial melting of two-mica granite and crystallization of tourmaline from the boron-rich partial melt. Increasing boron concentration in fluid promotes the melting of two-mica granite and the growth of tourmaline. No melt was produced in experiments at 600°C, in which Fe, Mg and Al released from biotite decomposition combined with boron from the fluid to form tourmaline under subsolidus conditions. The Na required for tourmaline crystallization derived from Na/K exchange between feldspar and the K released by biotite decomposition. The produced tourmaline generally has core-rim structures, indicating that the composition of melt or fluid evolved during tourmaline crystallization.Based on the experimental results, we propose that tourmaline granite veins or dikes can be formed by the reactions between boron-rich fluids, presumably produced by devolatilization of boron-bearing granitic magma, and incompletely crystallized granite at the top of the magma chamber. This 'self-metasomatism' involving boron-rich fluid in the late stage of magma crystallization could be an important mechanism for the formation of tourmaline granite.
基金This study was supported by the National Natural Science Foundation of China(No.41902052)the German Research Foundation(DFG)(No.BE 1720/40).
文摘The effects of melt composition,temperature and pressure on the solubility of fluorite(CaF2),i.e.,fluorine concentration in silicate melts in equilibrium with fluorite,are summarized in this paper.The authors present a statistic study based on experimental data in literature and propose a predictive model to estimate F concentration in melt at the saturation of fluorite(CFin melt^Fl-sat).The modeling indicates that the compositional effect of melt cations on the variation in can be expressed quantitatively as one parameter FSI(fluorite saturation index):FSI=(3Al^NM+Fe^2++6Mg+Ca+1.5Na-K)/(Si+Ti+Al^NF+Fe^3+),in which all cations are in mole,and Al^NF and Al^NM are A1 as network-forming and network-modifying cations,respectively.The dependence of CFin melt^Fl-sat on FSI is regressed as:CFin melt^Fl-sat=1.130-2.014·exp(1000/T)+2.747·exp(P/T)+0.111·CmeltH2O+17.641·FSI,in which T is temperature in Kelvin,P is pressure in MPa,CmeltH2O is melt H2O content in wt.%,and CFin melt^Fl-sat is in wt.%(normalized to anhydrous basis).The reference dataset used to establish the expression for conditions within 540-1010℃,50-500 MPa,0-7 wt.%melt H2O content,0.4 to 1.7 for A/CNK,0.3 wt.%-7.0 wt.%for CFin melt^Fl-sat.The discrepancy of CFin melt^Fl-sat between calculated and measured values is less than±0.62 wt.%with a confidence interval of 95%.The expression of FSI and its effect on CFin melt^Fl-sat indicate that fluorine incorporation in silicate melts is largely controlled by bonding with network-modifying cations,favorably with Mg,Al^NM,Na,Ca and Fe^2+in a decreasing order.The proposed model for predicting CFin melt^Fl-sat is also supported by our new experiments saturated with magmatic fluorite performed at 100-200 MPa and 800-900℃.The modeling of magma fractional crystallization emphasizes that the saturation of fluorite is dependent on both the compositions of primary magmas and their initial F contents.
