TY - JOUR

T1 - Tracing the evolution and distribution of F and Cl in plutonic systems from volatile-bearing minerals

T2 - A case study from the Liujiawa pluton (Dabie orogen, China)

AU - Zhang, Chao

AU - Holtz, Francois

AU - Ma, Changqian

AU - Wolff, Paul Eric

AU - Li, Xiaoyan

N1 - Funding Information: their thoughtful and critical comments that significantly improved the manuscript. We also thank Jochen Hoefs for his efficient editorial handling and helpful comments. This work was jointly funded by the German Science Foundation (project HO 1337/26), the National Nature Science Foundation of China (grants 90814004 & 40334037), and the China Geological Survey (grant 1212011121270). C. Zhang sincerely acknowledges the China Scholarship Council (CSC) and the German Academic Exchange Service (DAAD) for granting scholarships and China University of Geosciences (Wuhan) for offering an outstanding doctoral student research fund. Copyright: Copyright 2012 Elsevier B.V., All rights reserved.

PY - 2012/6/29

Y1 - 2012/6/29

N2 - Fluorine and chlorine play an important role in magmatic differentiation, hydrothermal alteration, and related mineralization processes, but tracing their evolution in magmatic and especially plutonic systems is not an easy task. The F and Cl in melts can be estimated from F and Cl concentrations in minerals, provided that partitioning between minerals and melts are constrained. Based on available partitioning models between mineral/melt, mineral/fluid, and melt/fluid, a set of equations has been derived to determine F and Cl concentrations in melts from the compositions of amphibole, biotite, and apatite. The new calculation procedure has been applied to a plutonic system, the Liujiawa pluton, eastern Dabie orogen (China). Cl and F concentrations in amphiboles, biotites, and apatites from different rock types (gabbronorite, two-pyroxene diorite, clinopyroxene diorite, and hornblende gabbro) have been determined by electron microprobe. Most amphiboles show a negative correlation between log(Cl/OH) and Mg-number and a positive correlation between log(F/OH) and A-site occupation. Biotites from the gabbronorite and two-pyroxene diorite show a slight positive correlation between log(Cl/OH) and Mg, which is however not the case for the clinopyroxene diorite. Apatites from all the samples are rich in F and show negative correlations between Cl and F concentrations. In our case study, we demonstrate that the Cl concentration in melt remains approximately constant at 1,000-2,000 ppm over the major crystallization interval, but decreases strongly at near solidus temperatures as a result of fluid exsolution. The F concentration in melt remains nearly constant at ca. 2,000-3,000 ppm at high temperatures as well as near solidus conditions, indicating that it is not largely affected by fluid exsolution because of its strongly preferred incorporation into melt. Interestingly, the evolution of Cl and F concentrations in melt with magmatic differentiation is similar to that determined in volcanic systems, suggesting that the evolution of Cl and F in melts during crystallization and late magmatic stages at depth (plutonic systems) is similar to that observed in volcanic systems during decompression and degassing.

AB - Fluorine and chlorine play an important role in magmatic differentiation, hydrothermal alteration, and related mineralization processes, but tracing their evolution in magmatic and especially plutonic systems is not an easy task. The F and Cl in melts can be estimated from F and Cl concentrations in minerals, provided that partitioning between minerals and melts are constrained. Based on available partitioning models between mineral/melt, mineral/fluid, and melt/fluid, a set of equations has been derived to determine F and Cl concentrations in melts from the compositions of amphibole, biotite, and apatite. The new calculation procedure has been applied to a plutonic system, the Liujiawa pluton, eastern Dabie orogen (China). Cl and F concentrations in amphiboles, biotites, and apatites from different rock types (gabbronorite, two-pyroxene diorite, clinopyroxene diorite, and hornblende gabbro) have been determined by electron microprobe. Most amphiboles show a negative correlation between log(Cl/OH) and Mg-number and a positive correlation between log(F/OH) and A-site occupation. Biotites from the gabbronorite and two-pyroxene diorite show a slight positive correlation between log(Cl/OH) and Mg, which is however not the case for the clinopyroxene diorite. Apatites from all the samples are rich in F and show negative correlations between Cl and F concentrations. In our case study, we demonstrate that the Cl concentration in melt remains approximately constant at 1,000-2,000 ppm over the major crystallization interval, but decreases strongly at near solidus temperatures as a result of fluid exsolution. The F concentration in melt remains nearly constant at ca. 2,000-3,000 ppm at high temperatures as well as near solidus conditions, indicating that it is not largely affected by fluid exsolution because of its strongly preferred incorporation into melt. Interestingly, the evolution of Cl and F concentrations in melt with magmatic differentiation is similar to that determined in volcanic systems, suggesting that the evolution of Cl and F in melts during crystallization and late magmatic stages at depth (plutonic systems) is similar to that observed in volcanic systems during decompression and degassing.

KW - Amphibole

KW - Apatite

KW - Biotite

KW - Chlorine

KW - Dabie orogen

KW - Fluorine

KW - Pluton

KW - Silicate melt

UR - http://www.scopus.com/inward/record.url?scp=84867576467&partnerID=8YFLogxK

U2 - 10.1007/s00410-012-0778-9

DO - 10.1007/s00410-012-0778-9

M3 - Article

AN - SCOPUS:84867576467

VL - 164

SP - 859

EP - 879

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 5

ER -