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Kinetics of antigorite dehydration: A real-time X-ray diffraction study

Abstract : Antigorite dehydration has been studied in situ using time-resolved X-ray diffraction (XRD) in the 1.1–5.5 GPa pressure range. The sequence of XRD spectra reveals that the high-temperature stability limit of antigorite is decreased by 50–100 °C under H2O-unsaturated conditions. The decomposition of antigorite into the high-temperature products, forsterite + enstatite, proceeds via an intermediate assemblage of forsterite and a “talc-like” phase, observed within a temperature interval of 130 ± 20 °C. The analysis of the transformation-time data using the Avrami model suggests that the breakdown of antigorite and the “talc-like” phase is kinetically controlled by surface growth processes at the edges of grains. The overall transformation rates are 10 to 100 times faster than those observed in water-saturated experiments, and show that the H2O activity is a strong driving force for dehydration. The breakdown of antigorite in subducting oceanic mantle with such kinetics would result in a fluid discharge rate of the order of 10− 6 to 10− 8 s− 1. This is faster than the viscous relaxation of serpentinites, and could lead to brittle failure or weakening of pre-existing faults. This provides an explanation for the seismicity in the lower plane of double seismic zones.
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Submitted on : Thursday, September 28, 2006 - 10:04:02 AM
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Jean-Philippe Perrillat, Isabelle Daniel, Kenneth Koga, Bruno Reynard, Hervé Cardon, et al.. Kinetics of antigorite dehydration: A real-time X-ray diffraction study. Earth and Planetary Science Letters, Elsevier, 2005, 236, pp.899-913. ⟨10.1016/j.epsl.2005.06.006⟩. ⟨hal-00101748⟩



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