Secondary Compaction through Area Loss during Accretion; A Sand Model Approach

摘要

Loss of area (volume) through secondary (tectonic) compaction is quantified by analysing sequential sections of a sand model shortened above a rigid substratum. Area balancing shows that the model wedge tectonically compacts during deformation and it looses up to 17% of its area at 50% shortening. During the deformation, the wedge does not undergo homogeneous compaction. Instead, the incremental compaction increases towards foreland (toe of the wedge) whereas the accumulative compaction increases towards the hinterland (rear of the wedge) most of (he area loss takes place within the youngest of the imbricates. Between two stages of imbricate formation, the model accrettonnry wedge lost 3.9% of its area of which 3% was taken up within the youngest of the imbricate sheets at the toe. Length balancing of three layers located at different depths (top, middle and bottom) were conducted to determine and compare the three strain components (layer parallel thickening, folding and imbrication) at different stratigraphic levels in the model accretionary wedge. The shallow top layer has taken 37% shortening by imbrication and folding and only 17% by layer parallel thickening as compared to 13.6% shortening by folding and imbrication and 41 % shortening by layer parallel thickening for the deeper bottom layer. The middle layer has intermediate values. These results suggest that ductile deformation dominates at depth. In natural accretionary wedges, area loss and layer-parallel thickening is accommodated for by secondary (tectonic) reduction of porosity, pressure solution of minerals and development of fabric.