Experimental recalibration of the Cr-in-clinopyroxene geobarometer: improved precision and reliability above 4.5 GPa

Abstract The pressure dependence of the exchange Cr between clinopyroxene and garnet in peridotite is applicable as a geobarometer for mantle-derived Cr-diopside xenocrysts xenoliths. most widely used calibration (Nimis Taylor Contrib Miner Petrol 139: 541–554, 2000; herein NT00) performs well at pressures below 4.5 GPa, but has been shown to consistently underestimate above GPa. We have experimentally re-examined this reaction over an extended pressure, temperature, compositional range using multi-anvil, belt, piston cylinder apparatuses. Twenty-nine experiments were completed 3–7 1100–1400 °C variety compositionally complex lherzolitic systems. These are conjunction with several published experimental datasets present modified widely-used NT00 Cr-in-clinopyroxene (Cr-in-cpx) single crystal geobarometer. Our updated calculates P (GPa) function T (K), CaCr Tschermak activity $$\left( {a_{{{\text{CaCrTs}}}}^{{{\text{cpx}}}} } \right)$$ a CaCrTs cpx , Cr/(Cr + Al) (Cr#) clinopyroxene. Rearranging results into 2 n polynomial multiple linear regression found following expression pressure: $$P\left( {{\text{GPa}}} \right) = 11.03 \left( { - T{ }\left( {\text{K}} \right){\text{ ln}}(a_{{{\text{CaCrTs}}}}^{{{\text{cpx}}}} ) \times 0.001088{ }} {1.526 {\text{ln}}\left( {\frac{{{\text{Cr}}\#^{{{\text{cpx}}}} }}{{T{ \right)}}} \right)} \right){ }$$ P GPa = 11.03 + - T K ln ( ) × 0.001088 1.526 Cr # where $${\text{Cr}}\#^{{{\text{cpx}}}} {\frac{{{\text{Cr}}}}{{{\text{Cr}} {\text{Al}}}}} Al $$a_{{{\text{CaCrTs}}}}^{{{\text{cpx}}}} {\text{Cr}} 0.81 \cdot {\text{Cr}}\#^{{{\text{cpx}}}} {{\text{Na}} {\text{K}}} \right),$$ 0.81 · Na , all mineral components calculated assuming six oxygen anions per formula unit Temperature (K) may be through geothermometers, however, we recommend crystal, enstatite-in-clinopyroxene (en-in-cpx) geothermometer. uncertainty our propagated by incorporating analytical uncertainties. that estimates 4 4–6 GPa 6 associated uncertainties 0.31, 0.35, 0.41 respectively. Pressures Cr-in-cpx good agreement 2–7 900–1400 those estimated from two-phase geobarometers based on solubility alumina orthopyroxene coexisting garnet. Application suites well-equilibrated lherzolite pyroxenite xenoliths Diavik-Ekati kimberlite Argyle lamproite pipes confirm accuracy precision geobarometer, show PT revised result systematically steeper paleogeotherms higher lithosphere?asthenosphere boundary compared original calibration.