Experimental study of the Fe-Mg exchange between garnet and biotite; constraints on the mixing behavior and analysis of the cation-exchange mechanisms

Other| December 01, 1997 Experimental study of the Fe-Mg exchange between garnet and biotite; constraints on the mixing behavior and analysis of the cation-exchange mechanisms C. K. Gessmann; C. K. Gessmann Universitaet Bonn, Mineralogisch-Petrologisches Institut, Bonn, Federal Republic of Germany Search for other works by this author on: GSW Google Scholar B. Spiering; B. Spiering Search for other works by this author on: GSW Google Scholar M. Raith M. Raith Search for other works by this author on: GSW Google Scholar American Mineralogist (1997) 82 (11-12): 1225–1240. https://doi.org/10.2138/am-1997-11-1218 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation C. K. Gessmann, B. Spiering, M. Raith; Experimental study of the Fe-Mg exchange between garnet and biotite; constraints on the mixing behavior and analysis of the cation-exchange mechanisms. American Mineralogist 1997;; 82 (11-12): 1225–1240. doi: https://doi.org/10.2138/am-1997-11-1218 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract New experimental data are presented for the Fe-Mg exchange between garnet and biotite in the temperature range 600–800 °C at 0.2 GPa. The Fe-Mg-Al mixing properties of biotite were evaluated and the garnet-biotite geothermometer was recalibrated. SEM observations and comparative laser granulometry show that solution-precipitation largely controls the cation exchange mechanism, involving about 50% of the mineral volume. Mass balance calculations emphasize the effectiveness of the experimental design: A high Gt/Bio ratio ensures that the garnet composition remains approximately constant and close to equilibrium, even if the entire garnet volume is not involved in the cation exchange. Progressively decreasing partition coefficients with decreasing Fe content of garnet indicate nonideal thermodynamic mixing behavior. The application of various garnet activity models support nearly ideal Fe-Mg mixing in garnet. The remaining nonidealities were attributed to nonideal Fe, Mg, and Al mixing in biotite as the initially binary biotite samples changed toward more aluminous compositions during the experiments. Adopting the standard state properties and the garnet-mixing model of Berman (1988, 1990), least square regressions reveal nearly ideal mixing of Fe and Mg in biotite with WFeMg = –2.3 ± 1.6 kJ/mol, while the difference between Fe-Al and Mg-Al interactions yield ΔWAl = –17.6 ± 2.4 kJ/mol (1 cation). This interaction parameter is strictly valid only for Tschermak-substituted [6]Al in biotite according to the operational substitution. Application of the suggested garnet-biotite geothermometer reproduces well the reference temperatures of experimental and natural garnet biotite assemblages. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.