Material transfer in accretionary wedges from analysis of a systematic series of analog experiments

Abstract

The structural evolution of accretionary wedges was modeled in a series of analog experiments with systematically varying initial boundary conditions. The two principle parameters investigated were basal friction and thickness of sediment Input (relative to subducted sediment Output). Material transfer (in terms of degree and location of accretion and erosion) is quantified as a function of these two parameters. Low basal friction produces long, thin wedges, by continuous frontal accretion of imbricate thrusts. Simultaneously, substantial basal erosion may occur, with little influence on the frontal dynamics. The formation of an outer arc high with an accompanying forearc basin depends upon the relative amount of basal erosion, the opening of the subduction window. Spacing of thrust faults is proportional to the layer thickness confirming the principle of self-similar wedge growth from critical wedge theory. High basal friction typically generates steep wedges, marked by an erosional, mass wasting frontal slope in the cases I ⪯ O. This is due to underthrusting and/or subduction of the entire sedimentary section. The case I < O also features the late development of normal faulting and an extensional forearc basin.For both low and high basal friction the material balance affects the wedge slope; erosive conditions (I < O) lead to steeper wedges than accretionary conditions (I > O). For low basal friction the primary modes of material transfer are frontal accretion and basal erosion. For high basal friction the primary modes of material transfer are underthrusting/underplating and frontal erosion. Applying the experimental results to active convergent margins, parallels may be drawn. Thus, the Barbados Ridge Complex is interpreted to be a good example of a low basal friction wedge with an accretionary material balance, while the Japan and Mariana margins provide examples of an erosive material balance.