Frontispiece 1. Generalized cross section through Barbados accretionary prism showing changes in density in the transition from the proto-decollement to the decollement zone (Moore et al., 1998b). Blue density curve is reference from undeformed sediments on the oceanic plate at Site 1044 and is compared to each site to the west. Red curves are density values at all other sites. Note that from Sites 1047 to 948 there is a general increase in density due to deformation induced collapse of the sedimentary fabric. Site 1045 shows a 14m-thick low-density anomaly in the decollement zone that produces a negative polarity seismic reflection (see Frontispiece 2).

Frontispiece 2. Maps of: A) peak seismic reflection amplitude from the decollement zone (DiLeonardo et al., in press) and B) density inferred from the inversion of the decollement zone reflection (Zhao et al., 2000). Note the general increase in density from east to west starting at the deformation front, a trend that is also apparent in the individual log signatures (Frontispiece 1). Note, also, the area of negative seismic polarity that shows up as the area of reduced density in the inversion and emphasizes the patchy nature of the density decrease with underthrusting along the decollement thrust zone.

References

DiLeonardo, C. G., Moore, J. C., Nissen, S., and Bangs, N., in press, Control of Internal Structure and Fluid Migration Pathways Within the Barbados Ridge DTcollement Zone by Strike-Slip Faulting: Evidence From Coherence and 3-D Seismic Amplitude Imaging: Geological Society of America.

Moore, J. C., Klaus, A., Bangs, N., B., B., Bncker, C., Brnckmann, W., Erickson, S., Hansen, O., Ireland, P., Horton, P., Major, C., Moore, G., Peacock, S., Saito, S., Screaton, J., J., S., Stauffer, P., Taymaz, T., and Teas, P., 1998b, Consolidation patterns during initiation and evolution of a plate-boundary decollement zone: Northern Barbados accretionary prism: Geology, v. 26, p. 811-814.

Zhao, Z., Moore, G., Bangs, N. L., and Shipley, T. H., 2000, Spatial variations of the decollement/protodecollement zone and their implications: a 3-D seismic inversion study of the Northern Barbados accretionary prism: Island Arc, v. 9, p. 219-236.