TY - JOUR

T1 - Fluorine partitioning between titanite and silicate melt and its dependence on melt composition

T2 - Experiments at 50-200 MPa and 875-925°C

AU - Li, Xiaoyan

AU - Zhang, Chao

AU - Behrens, Harald

AU - Holtz, François

N1 - Publisher Copyright: © 2018 E.Schweizerbart'sche Verlagsbuchhandlung. Copyright: Copyright 2018 Elsevier B.V., All rights reserved.

PY - 2018/2/1

Y1 - 2018/2/1

N2 - We present experimental results constraining the partitioning of fluorine (F) between titanite and metaluminous silicate melt under H2O-saturated conditions at 50-200 MPa, 875-925°C. Resulting experimental melts are metaluminous with ASI values [aluminium saturation index, calculated as molar Al2O3/(CaO+Na2O+K2O)] falling in the range 0.68-0.97. Titanite crystals and coexisting melts have F contents that vary from 0.2 to 2.6 wt% and from 0.2 to 3.2 wt%, respectively. The calculated proportion of the F-O substitution is within 0.02-0.28 per formula unit, which is predominantly compensated by the substitution of Al and Fe3+ for Ti, as well as a subordinate amount of Ti-Mg2+ substitution. The mass-ratio partition coefficient DFTtn-melt is within 0.5-1.2, and there is little influence of pressure under the conditions investigated. However, the potential effect of temperature needs further investigation. DFTtn-melt is positively correlated with melt ASI, and can be predicted using the following relation: DFTtn-melt = 2:26 ∗ ASI - 1:05: This equation is valid only for metaluminous melts (ASI < 1). The effect of melt ASI on DFTtn-melt is related to structural properties of F-bearing melts, which can incorporate higher F concentrations at lower ASI. Assuming that the high-Ti titanite investigated here is subject to ideal mixing, we calculated a Margules parameter (WFmelt) of 48.6 ± 4.3 kJ/mol for F in silicate melt with a symmetric binary mixing model. The high value of WFmelt confirms that O-F mixing in silicate melt is far from ideal. The reliability of using of DFTtn-melt to calculate melt F contents has been checked by investigating plutonic rocks of the Liujiawa pluton in the Dabie orogen of eastern China. Our new estimates of melt F content are consistent with those derived from amphibole, biotite and apatite compositions.

AB - We present experimental results constraining the partitioning of fluorine (F) between titanite and metaluminous silicate melt under H2O-saturated conditions at 50-200 MPa, 875-925°C. Resulting experimental melts are metaluminous with ASI values [aluminium saturation index, calculated as molar Al2O3/(CaO+Na2O+K2O)] falling in the range 0.68-0.97. Titanite crystals and coexisting melts have F contents that vary from 0.2 to 2.6 wt% and from 0.2 to 3.2 wt%, respectively. The calculated proportion of the F-O substitution is within 0.02-0.28 per formula unit, which is predominantly compensated by the substitution of Al and Fe3+ for Ti, as well as a subordinate amount of Ti-Mg2+ substitution. The mass-ratio partition coefficient DFTtn-melt is within 0.5-1.2, and there is little influence of pressure under the conditions investigated. However, the potential effect of temperature needs further investigation. DFTtn-melt is positively correlated with melt ASI, and can be predicted using the following relation: DFTtn-melt = 2:26 ∗ ASI - 1:05: This equation is valid only for metaluminous melts (ASI < 1). The effect of melt ASI on DFTtn-melt is related to structural properties of F-bearing melts, which can incorporate higher F concentrations at lower ASI. Assuming that the high-Ti titanite investigated here is subject to ideal mixing, we calculated a Margules parameter (WFmelt) of 48.6 ± 4.3 kJ/mol for F in silicate melt with a symmetric binary mixing model. The high value of WFmelt confirms that O-F mixing in silicate melt is far from ideal. The reliability of using of DFTtn-melt to calculate melt F contents has been checked by investigating plutonic rocks of the Liujiawa pluton in the Dabie orogen of eastern China. Our new estimates of melt F content are consistent with those derived from amphibole, biotite and apatite compositions.

KW - Aluminium saturation index

KW - Fluorine

KW - Fluorite

KW - Partitioning

KW - Silicate melt

KW - Substitution

KW - Titanite

UR - http://www.scopus.com/inward/record.url?scp=85047059077&partnerID=8YFLogxK

U2 - 10.1127/ejm/2017/0029-2689

DO - 10.1127/ejm/2017/0029-2689

M3 - Article

AN - SCOPUS:85047059077

VL - 30

SP - 33

EP - 44

JO - European Journal of Mineralogy

JF - European Journal of Mineralogy

SN - 0935-1221

IS - 1

ER -