Deformation And Fluid Escape Related to Two Stages of Evolution of Seamount Subduction Offshore Costa Rica
Abstract
We have studied upper plate deformation and fluid flow related to the subduction of seamounts of the Cocos plate. New multibeam bathymetry, side scan sonar, high resolution seismics, sediment echosoundings and deep-towed video camera observations have been recorded over two of the most prominent features: Jaco and Parrita scars. The bathymetric highs observed upslope of both scars as well as their side walls are characterised by a complex morphostructural pattern shaped by two main sets of crosscutting faults: (1) radial normal faults, probably related to seafloor uplift due to seamount subduction and (2) linear compressive faults trending perpendicular to the direction of subduction (N130-N140). Surface deformation, mainly characterized by elongated short wavelength folding, has been observed on both structures and could be related to the combination of compressive stresses in front of the subducting seamounts and strike-slip motion on the lateral walls. However, some noticeable differences have been observed between both scars. The radial normal faults seem better developed upslope of Jaco scar and many sigmoidal structures might reveal strike-slip motions. Parrita scar is mainly controled upslope by folding and linear N140 trending faults. A number of highly reflective patches (100m to 1Km wide) have been observed in both areas and are attributed either to encrusted material related to fluid escape or mud flows injected through the crosscutting faults which may allow fluid ascension. Several hypotheses may explain the differences observed between both structures. (1) Parrita scar only 6 Km upslope from the deformation front is a more recently subducted seamount covered by a thinner sedimentary sequence than Jaco scar. This could explain why Parrita scar shows less important uplift and brittle deformation. (2) The Parrita seamount could also be a smaller seamount more easily subducted. Both hypotheses also account for the presence of a larger amount of reflective patches around Jaco scar, where compressive tectonics seems more important.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....5345H