HENRY, PIERRE, Laboratoire de Geologie de l'ENS (CNRS URA 1316), Paris, France; and PIERRE LABAUME, LGIT (CNRS), Universite Joseph Fourier, Grenoble, France
Abstract: Numerical Model of Transient Fluid Flow along the Barbados Wedge Decollement
Modeling the thermal consequences of steady state as well as transient state fluid flow along the decollement and comparison of the modeling results with temperature profiles obtained in Barbados drill holes (CORK long term monitoring experiment) imply that the basal decollement is and has not been, at least in the last few thousand years, the main conduit for fluid flow. Pore fluid and mineral vein chemistry do, however, imply that episodic fluid flow occurred along the decollement and has been more active in the past. Diffusion models applied to the chloride anomaly observed at the top of the decollement indicate that the last flow event is 1500-4000 years old but, although it may have caused a detectable thermal anomaly at the time of flow, this thermal anomaly has probably now diffused away. In situ permeability measurements show a strong dependence of permeability on pore pressure. A decollement model taking into account this non-linear effect shows that the propagation of a pressure front associated with a flow pulse is possible with characteristic times of a few hundreds to a few thouzand years, compatible with those inferred from the chlorinity profiles. The pore pressures measured with the CORKs are insufficient to allow sliding along the decollement according to the Coulomb wedge model. It is therefore likely that motion along the decollement occurs mostly during pressure pulses, a conclusion supported by the structural relationship between mineral veins and decollement fabric.
AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California