The broadest application of intracrystalline Fe2+-Mg partitioning between the M1 and M2 crystallographic sites in the pyroxene structure is the determination of the closure temperature (Tc) of the exchange reaction, that provides important constraint on the cooling rate of the pyroxene-bearing host rocks (e.g. Ganguly and Domeneghetti 1996). Although this approach has been successfully developed (Domeneghetti et al. 2013 and references therein) and applied for orthopyroxene and pigeonite-bearing rocks, relatively few data are available for clinopyroxenes (e.g., Ghose and Ganguly 1982). The most recent calibration (for both kinetic and equilibrium) for clinopyroxenes (cpxs) has been provided by Brizi et al. (2000) and Brizi et a. (2001) respecively. Calculations performed for cpxs in some Earth and planetary contexts (e.g., Malgarotto et al. 1993a,b; Abdu et al. 2009), provided (i) Tc consistent among different samples and coherent with their respective geological setting; (ii) cooling rates for different samples from the same context in significant disagreement one to another. In order to account for these discrepancies Domeneghetti et al. (2013) and Alvaro et al. (2014) further investigated this issue performing a new 'ex situ' equilibrium annealing study combined with high-resolution single-crystal X-ray diffraction (HR-SC-XRD) experiments on augite crystals from Miller Range nakhlite (MIL 03346,13) in order to obtain a new thermometric calibration for nakhlites. Our new calibrated geothermometer allows to reconcile over a wide range of temperatures the inconsistencies observed before.
Pyroxene Fe-Mg exchange reaction and its application to planetary studies
Fioretti AM
2015
Abstract
The broadest application of intracrystalline Fe2+-Mg partitioning between the M1 and M2 crystallographic sites in the pyroxene structure is the determination of the closure temperature (Tc) of the exchange reaction, that provides important constraint on the cooling rate of the pyroxene-bearing host rocks (e.g. Ganguly and Domeneghetti 1996). Although this approach has been successfully developed (Domeneghetti et al. 2013 and references therein) and applied for orthopyroxene and pigeonite-bearing rocks, relatively few data are available for clinopyroxenes (e.g., Ghose and Ganguly 1982). The most recent calibration (for both kinetic and equilibrium) for clinopyroxenes (cpxs) has been provided by Brizi et al. (2000) and Brizi et a. (2001) respecively. Calculations performed for cpxs in some Earth and planetary contexts (e.g., Malgarotto et al. 1993a,b; Abdu et al. 2009), provided (i) Tc consistent among different samples and coherent with their respective geological setting; (ii) cooling rates for different samples from the same context in significant disagreement one to another. In order to account for these discrepancies Domeneghetti et al. (2013) and Alvaro et al. (2014) further investigated this issue performing a new 'ex situ' equilibrium annealing study combined with high-resolution single-crystal X-ray diffraction (HR-SC-XRD) experiments on augite crystals from Miller Range nakhlite (MIL 03346,13) in order to obtain a new thermometric calibration for nakhlites. Our new calibrated geothermometer allows to reconcile over a wide range of temperatures the inconsistencies observed before.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
