INTERACTIONS BETWEEN FOREARC BASIN STRATIGRAPHY AND ACCRETIONARY WEDGE GROWTH UNDER THE CRITICAL TAPER THEORY

Forearc basins are an important component along subduction zones, which store sediments derived from the source area on or behind accretionary wedges. Although the basin stratigraphy can record history experienced by the basin during its evolution, the interactive processes between the basin and the wedge remain poorly understood. In order to investigate such processes, simple forearc basins were numerically reproduced with building up of accretionary prisms under the critical wedge theory in terms of changes in the sediment fluxes along the subduction zone. Variable fluxes include Q_s (sediment supply to the basin from the source area), Q_in.T (sediments filling the trench), and Q_out.T (sediments subducted from the trench into the subduction channel). Sediment input rate to the basin (Q_in.FAB) was determined by Q_s and accommodation generated by growth of the accretionary wedge. The results indicated the stratigraphic patterns depended on degree of filling (underfilled or overfilled) and the volume balance between supplied sediments (Q_s) and depositional space. The strata deposited in the underfilled phase were characterized by trenchward progradation of deposition and onlapping contacts on both landward and trenchward margins of the basins. On the other hand, in the overfilled phase, the deposits were tilted landward, and the depocenter migrated landward. Intervals of little sediment influx to the basin marked major stratigraphic boundaries, and were caused by sediment supply-limited or accommodation-limited case. The latter case can produce condensed sections in the stratigraphy and can possibly lead to the development of submarine canyons as conduits for sediments bypassing. Fluctuations in sediment fluxes and their balance significantly influenced on stratigraphic patterns in forearc basins. The basin stratigraphy is key to knowing how subduction zones evolve through interactions with changing surface processes.