Thermodynamic calculation on the phase transformation and water release of subducted sediment from 10 to 35 kbar

Abstract

Thermodynamic calculation results of a clastic sediment composition (K 2O–Na 2O–CaO–MgO–FeO–Fe 2O 3–Al 2O 3–TiO 2–SiO 2–H 2O) at 10 to 35 kbar and 300–900 °C show that H 2O release of subducted sediment in subduction zone is mainly controlled by the metamorphic dehydrations of hydrous minerals: chlorite, muscovite, carpholite, paragonite, lawsonite and chloritoid. At lower (≤70 km) and deeper (≥70 km) depths in subduction zone, the dehydration temperature of sediment varies from 350–800 to 420–600 °C, respectively. Above 780 °C, hydrous minerals are broken down entirely in the system except for muscovite. The phase transition and dehydration of sediment may be responsible for the H 2O source of the shallow level fluid in young (hot) subduction zone and the deeper fluids in elder (cold) subduction zone.