Abstract:

It has been more than 30 years since Simon Peacock proposed that the forearc mantle of the Cascadia subduction system is partially serpentinized. Geophysical evidence published since then strongly  supports his hypothesis. Similar observations in southwest Japan also point to the Nankaido subduction system as another warm-slab subduction system having serpentinized forearc mantle. Moreover, a rich set of seismic observations in both systems point to EPS phenomena related to the updip migration of fluids also occur. An important question is whether certain changes in subduction inputs at trenches that lead to warming of the forearc mantle could release this stored water into the forearc crust and/or updip into the interplate thrust zone and could influence the deep hydrology and rheology of the forearc crust and interplate thrust zone. I use as example of the former the San Andreas Fault System in the California Coast Ranges, suggest that such models give insights into independent phenomena in the distributed plate boundary of the Coast ranges, including the occurrence of block-and-matrix serpentinite melanges along the active faults of the California continental margin.