Recent geophysical evidence shows that a wedge shaped region of serpentinized mantle occurs in the cold, shallow forearc above dehydrating slabs in several well-studied subduction zones. The volume of water potentially stored in the forearc is huge, depending on the degree of serpentinization of the forearc mantle. Dehydration occurs from the serpentinized forearc mantle in active subduction zones for 10 to 25 Ma as the age of the subducting plate becomes younger and the slab warmer or in relict forearcs after subduction ceases. Kirby et al. (2006) proposed that this deep, long-term water source could facilitate fault slip in San Andreas Fault System at low shear stresses in a broad region above the wedge and mobilize deep- seated serpentinite blocks. We further extend this idea and proposethat huge strike-slip fault systems in suture zones are made mobile and exhumation of high/ultrahigh-pressure metamorphic belts is rheologically facilitated by a weakening due to the release of pressurized water from the serpentinized forearc mantle. This process may also apply to the formation of some plate boundaries in active and passive margins. Dehydration weakening of former forearcs might, therefore, be a very important process in Earth's tectonic history.
問い合わせ先：土屋 卓久 TEL （089）927-8198
E-mail takut@sci.ehime-u.ac.jp
