Forearc Sedimentation, Subduction Erosion and the Effect of Seamount Collisions in the Tonga Arc System
1996 American Geophysical Union Fall Meeting
Collision of the Louisville Ridge with the trench appears to have caused modest (< 300m), temporary uplift of the Tonga Platform at the point of collision. However, on the trench slope collision resulted in compression, greater uplift and arcward tilting of the basement, generating unconformities within the mid-slope terrace basins. Subsequent collapse of the forearc basement and resumption of extension results in the deposition of a new stratigraphic sequence unconformably overlying the older series, as recorded at ODP Site 841 during the middle Miocene. Rapid late Eocene subsidence of the mid-slope terrace at ODP Site 841, following subduction initiation in the mid Eocene, may be due to the formation of the trench at that time. Extensional unroofing of the arc basement during the formation of the trench resulted in the erosion of arc lower crustal dunite and mantle peridotite into mass flow conglomerates. Post-early Oligocene subsidence reflects slow, continuous subduction erosion of the outer forearc, with < 20-30 km being eroded from the plate margin since that time.