Mantle geothermometry: experimental evaluation and recalibration of Fe–Mg geothermometers for garnet-clinopyroxene and garnet-orthopyroxene in peridotite, pyroxenite and eclogite systems

Abstract The reliability of eight Fe–Mg exchange geothermobarometers for garnet-bearing peridotites, pyroxenites and eclogites has been examined using a database comprised more than 300 published peridotite, pyroxenite eclogite experiments conducted from 10 to 70 kbar 850 > 1650 $$^\circ{\rm C}$$ ? C . We have tested geothermometers suitable range mantle lithologies, including websterite, harzburgite, wehrlite eclogite. All maintained an average difference in experimental calculated temperature (T) $$\left( {\Delta {\text{T}} = {\text{T}}_{{\exp - { }}} {\text{T}}_{{{\text{calc}}}} } \right)$$ ? T = exp - calc less $$\pm$$ ± 50 °C with standard deviation $$\Delta {\text{T}}$$ between 150 °C. Most performed well across narrow ln $${\text{Kd}}_{{{\text{Fe}} {\text{Mg}}}}^{{{\text{A}} {\text{B}}}}$$ Kd Fe Mg A B (where {\text{B}}}} =$$ $$\frac{{\left( {{\text{Fe}}_{{\text{A}}} \times {\text{Mg}}_{{\text{B}}} \right)}}{{({\text{Fe}}_{{\text{B}}} {\text{Mg}}_{{\text{A}}} )}}$$ × ( ) ), however, systematic overestimation underestimation T were observed outside the optimal $${\text{lnKd}}_{{{\text{Fe}} lnKd Increases pressure (P) adversely affected several geothermometers, particularly those calibrated empirically natural samples. previously calibrations garnet-clinopyroxene geothermometer unable reliably reproduce both peridotite compositions, which hinders their confident application datasets. To improve state geothermobarometry we used our recalibrate (1) geothermometer, (2) garnet-orthopyroxene geothermometer. Each recalibrated extended P, T, compositional range. inclusion eclogitic calibration permits peridotitic/pyroxenitic assemblages equilibrated under wide PT conditions upper mantle. Using multiple linear regression solve lnKd, found following expressions best reproduced (?) dataset: $${\text{T}}_{{{\text{Fe}} {\text{Mg}}}}^{{{\text{grt}} {\text{cpx}}}} (}^{ \circ {\text{C)}} }\frac{3356.34}{{\left( {\left( 0.008 {\text{P }}\left( {{\text{kbar}}} \right)} \right) + \left( {0.259 {\text{X}}_{{{\text{Ca}}}}^{{{\text{grt}}}} {0.914 {\text{X}}_{{{\text{Mg}}}}^{{{\text{grt}}}} 0.159 {\text{Jd}}^{{{\text{cpx}}}} {{\text{ln}}\left( {{\text{ Kd}}_{{{\text{Fe}} 1.265} \right)}} 273{ }$$ grt cpx C) 3356.34 0.008 P kbar + 0.259 X Ca 0.914 0.159 Jd ln 1.265 273 {\text{opx}}}} }\frac{1851.85}{{\left( 0.007 1.83 1.08} 273$$ opx 1851.85 0.007 1.83 1.08 where, $${\text{X}}_{{{\text{Ca}}}}^{{{\text{grt}}}} $$\frac{{{\text{Ca}}}}{{\left( {{\text{Ca}} {\text{Fe}} {\text{Mg}}} \right)}}$$ , {{\text{Fe}}_{{{\text{grt}}}} {\text{Mg}}_{{{\text{opx}}}} \right)}}{{({\text{Fe}}_{{{\text{opx}}}} {\text{Mg}}_{{{\text{grt}}}} )}} , $$\frac{{{\text{Mg}}}}{{\left( $${\text{Jd}}^{{{\text{cpx}}}} {\text{Na}} {\text{Cr}} 2 {\text{Ti}}$$ Na Cr 2 Ti {\text{Mg}}_{{{\text{cpx}}}} \right)}}{{({\text{Fe}}_{{{\text{cpx}}}} )}},$$ all elements on basis 12 oxygen anions garnet 6 clino- orthopyroxene. Fe 2+ total Fe. Our updated resolve issues earlier calibrations, poor performance at elevated P limitations. An improvement precision accuracy demonstrated through dataset, second independent set data, off craton settings. Iterative estimates datasets compare widely such as Taylor (1998) two-pyroxene solvus anticipate that this contribution will provide important reference be future studies inclusions diamond mantle-derived xenoliths.