X-ray-diffraction Study of Fe-2+ -Mg Order-disorder In Ortho-pyroxene - Some Kinetic Results

Saxena, S. K.; Domeneghetti, M. C.; Molin, Gianmario; Tazzoli, V.

Kinetic rates of Fe2+-Mg disordering in three orthopyroxenes (mean value of XFe = Fe2+/(Fe2++Mg) = 0.175,0.482,0.770 respectively) have been determined employing heating experiments and single crystal X-ray structural refinements. Disordering rate constants (K) (550800° C) for two pyroxenes are given by: ln (K) = 27.107(±5.177)–32062(±783)T–1(XFe = 0.175) ln (K) = 16.142(±0.057)–18227(±423)T–1(XFe = 0.770) The distribution coefficients KD (representing a steady state of disordering FeM2 + MgM1 lrhar FeM1 + MgM2) are given by: ln KD = 5.016(±0.223)-7033(±1473) T–1(XFe = 0.175) ln KD = 1.988(±0.122)-3809(±913)T–1(XFe = 0.770) These distribution coefficients provide the constraint of the disordering reaction on the value of the equilibrium constant for Fe2+-Mg order-disorder. Until the low temperature dependence of KD is well constrained, the calculation of cooling rates of pyroxenes and host rocks cannot be done reliably.

Titolo:	X-ray-diffraction Study of Fe-2+ -Mg Order-disorder In Ortho-pyroxene - Some Kinetic Results
Autori:	S. K. SAXENA M. C. DOMENEGHETTI MOLIN, GIANMARIO V. TAZZOLI mostra contributor esterni nascondi contributor esterni
Data di pubblicazione:	1989
Rivista:	PHYSICS AND CHEMISTRY OF MINERALS
Abstract:	Kinetic rates of Fe2+-Mg disordering in three orthopyroxenes (mean value of XFe = Fe2+/(Fe2++Mg) = 0.175,0.482,0.770 respectively) have been determined employing heating experiments and single crystal X-ray structural refinements. Disordering rate constants (K) (550800° C) for two pyroxenes are given by: ln (K) = 27.107(±5.177)–32062(±783)T–1(XFe = 0.175) ln (K) = 16.142(±0.057)–18227(±423)T–1(XFe = 0.770) The distribution coefficients KD (representing a steady state of disordering FeM2 + MgM1 lrhar FeM1 + MgM2) are given by: ln KD = 5.016(±0.223)-7033(±1473) T–1(XFe = 0.175) ln KD = 1.988(±0.122)-3809(±913)T–1(XFe = 0.770) These distribution coefficients provide the constraint of the disordering reaction on the value of the equilibrium constant for Fe2+-Mg order-disorder. Until the low temperature dependence of KD is well constrained, the calculation of cooling rates of pyroxenes and host rocks cannot be done reliably.
Handle:	http://hdl.handle.net/11577/2505544
Appare nelle tipologie:	01.01 - Articolo in rivista

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