Mariana blueschist mud volcanism: Implications for conditions within the subduction zone

Several recently discovered active mud volcanoes on the nonaccretionary Mar iana convergent plate margin are erupting slab-derived fluids, serpentine m ud, and metamorphosed rocks from depths of as great as 25 km, Blueschist ma terials from the metamorphosed subducted plate are contained in the muds. P ore fluids indicate a depth dependence for decarbonation. The mud volcanoes record in situ conditions along the decollement, including pressure and te mperature conditions and physical properties within the subduction zone. Si milar mud-flow material occurs worldwide as "sedimentary serpentinite" depo sits in accreted fragments of former convergent margins, making this kind o f mud volcanism a more important phenomenon in convergent margins than prev iously recognized.