STRUCTURE OF THE BACK-ARC SPREADING BASINS AND THE FLUID REGIME IN THE MANTLE

Abstract

Seismic, geothermal, petrological and other data collected during the joint Soviet-Chinese-Japanese Project “Geotraverse: Pacific-China plain” are highly contradictory concerning their information on back-arc basins. The routine interpretation of the geothermal data leads, e.g. to the conclusion that the temperatures at depth are much higher than can be derived from other data. The discrepancies can be resolved by the back-arc spreading basins origin because of secondary mantle bulk or fluid convection. The inversion of the sign of the seismic velocity anomalies in the Pacific region at a depth of about 300 km can also be explained if active deep fluid regime is proposed. A new geotherm below the Mariana back-arc basin is proposed, and the velocity of the ascending mantle flow is estimated for this region.