Metasomatism and Slow Slip: Talc Production Along the Flat Subduction Plate Interface Beneath Mexico (Guerrero)

Talc-rich rocks are common in exhumed subduction zone terranes and may explain geophysical observations of the subduction zone interface, particularly beneath Guerrero, Mexico, where the Cocos plate subducts horizontally beneath North America and episodic tremor and slow slip (ETS) occurs. We present petrologic models exploring (a) the degree of silica metasomatism required to produce talc in serpentinized peridotites at the pressure-temperature conditions of the plate interface beneath Guerrero and (b) the amount of silica-bearing water produced by rocks from the subducting Cocos plate and the location of fluid pulses. We estimate the volumes of talc produced by the advection of silica-rich fluids into serpentinized peridotites at the plate interface over the history of the flat-slab system. In the ETS-hosting region, serpentinites must achieve similar to 43 wt. % SiO2 to stabilize talc, but minor additions of silica beyond this produce large volumes of talc. Our models of Cocos plate dehydration predict that water flux into the interface averages 3.9 x 10(4) kg m(-2) Myr(-1) but suggest that only where subducting basalts undergo major dehydration reactions will sufficient amounts of silica-rich fluids be produced to drive significant metasomatism. We suggest that talc produced by advective transport of aqueous silica alone cannot account for geophysical interpretations of km-thick zones of talc-rich rocks beneath Guerrero, although silica-bearing fluids that migrate along the plate interface may promote broader metasomatism. Regions of predicted talc production do, however, overlap with the spatial occurrence of ETS, consistent with models of slow slip based on the frictional deformation of metasomatic lithologies.