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

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

Aug 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005e%26psl.236..899p&link_type=abstract

Earth and Planetary Science Letters, Volume 236, Issue 3-4, p. 899-913.

Computer Science

20

Scientific paper

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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