Ni-in-garnet geothermometry in mantle rocks: a high pressure experimental recalibration between 1100 and 1325 °C

Abstract The temperature-dependent exchange of Ni and Mg between garnet olivine in mantle peridotite is an important geothermometer for determining temperature variations the upper diamond potential kimberlites. Existing calibrations Ni-in-garnet show considerable differences estimated above below 1100 °C hindering its confident application. In this study, we present results from new synthesis experiments conducted on a piston cylinder apparatus at 2.25–4.5 GPa 1100–1325 °C. Our experimental approach was to equilibrate Ni-free Cr-pyrope-rich starting mixture made sintered oxides with natural capsules (Ni olv ≅ 3000 ppm) produce charge comprised entirely peridotitic pyrope trace abundances (10–100 s ppm). Experimental runs products were analysed by wave-length dispersive electron probe microanalysis (EPMA) laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We use partition coefficient distribution our capsule $$\left( {{\text{lnD}}_{{{\text{grt}}/{\text{olv}}}}^{{{\text{Ni}}}} ; \frac{{{\text{Ni}}_{{{\text{grt}}}} }}{{{\text{Ni}}_{{{\text{olv}}}} }}} \right)$$ lnD grt / olv Ni ; , Ca mole fraction ( $${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Ca}};$$ X grt Ca Ca/(Ca + Fe Mg)), Cr $${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Cr}};$$ Cr Cr/(Cr Al)) develop formulation that performs more reliably datasets than existing calibrations. updated defined here as: $$T \left(^\circ{\rm C} \right)=\frac{-8254.568}{\left(\left( {\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Ca}} \times 3.023 \right)+\left({\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Cr}} 2.307 \right)+\left({\mathrm{lnD}}_{\frac{\mathrm{grt}}{\mathrm{olv}}}^{\mathrm{Ni}} - 2.639 \right)\right)}-273\pm 55$$ T ∘ C = - 8254.568 × 3.023 + 2.307 lnD olv Ni 2.639 273 ± 55 where $${\mathrm{D}}_{\mathrm{grt}/\mathrm{olv}}^{\mathrm{Ni}}= \frac{{\mathrm{Ni}}_{\mathrm{grt}}}{{\mathrm{Ni}}_{\mathrm{olv}}},$$ D , ppm, $${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Ca}}$$ = Mg) garnet, $${\mathrm{X}}_{\mathrm{grt}}^{\mathrm{Cr}}$$ Al) garnet. can be applied xenoliths or monomineralic xenocrysts derived disaggregation source. calibration used as single grain assuming average concentration ppm. To maximise reliability estimates geothermometer, provide users data quality protocol method which all EPMA LA-ICP-MS analyses prior geothermometry. uncertainty has been rigorously propagated incorporating analytical uncertainties. have found maximum associated ± 55 improved performance demonstrated through application previously published natural, well-characterised variety datasets, including diamondiferous Diavik Ekati kimberlite pipes Lac de Gras field, Canada. better aligns using those widely (Nimis Taylor, Contrib Mineral Petrol 139:541–554, 2000) enstatite-in-clinopyroxene confirms improvement relative versions geothermometer.