TY - JOUR

T1 - Experimental investigation of reactions between two-mica granite and boron-rich fluids

T2 - Implications for the formation of tourmaline granite

AU - Cheng, Lining

AU - Zhang, Chao

AU - Yang, Xiaosong

AU - Qi, Dongmei

AU - Zhou, Yongsheng

AU - Holtz, Francois

N1 - Funding information: We appreciate the comments from two anonymous reviewers that helped us to considerably improve the manuscript. We are grateful to Qingbao Duan, Yongmei Shang and Yu Yang for their assistance with the fieldwork. We thank Ulrich Kroll for his help of experiment and Dominik Mock, Xi Ma for their assistance of SEM analysis. Xiaoyan Li is appreciated for beneficial discussions. This work was supported by the National Natural Science Foundation of China (Grant No. 41672197) and the China Scholarship Council (CSC).

PY - 2019/10

Y1 - 2019/10

N2 - 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.

AB - 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.

KW - Fluid-rock reactions

KW - High pressure and high temperature experiment

KW - Himalaya

KW - Leucogranite

KW - Tourmaline

UR - http://www.scopus.com/inward/record.url?scp=85074161586&partnerID=8YFLogxK

U2 - 10.1007/s11430-019-9442-y

DO - 10.1007/s11430-019-9442-y

M3 - Article

AN - SCOPUS:85074161586

VL - 62

SP - 1630

EP - 1644

JO - Science China Earth Sciences

JF - Science China Earth Sciences

SN - 1674-7313

IS - 10

ER -