Influence of kinetics on the smectite to illite transition in the Barbados accretionary prism


  • Barbara Bekins,

  • Anne M. McCaffrey,

  • Shirley J. Dreiss


Low chloride pore fluids observed along faults in clay-rich accretionary complexes are commonly attributed to the release of interlayer water during the smectite to illite transformation. However, to date, there has been no thorough analysis of the location and quantity of fluids that may be generated by this mechanism. To address this problem, a temperature and time dependent rate expression describing the dehydration reaction was coupled to a kinematic model of the northern Barbados accretionary complex. Temperatures in the complex were estimated by modeling heat flow through the prism sediments as they thicken arcward. The sediments' temperature-time histories were computed using a model for the velocities of sediment motion through the complex. In this model the prism sediments follow uniformly diverging paths from the toe, while the underthrust sediments undergo uniaxial strain. The model predictions are validated against clay mineralogy data from Barbados Island mudstones. Our results show that the location of the peak dehydration rate is 20 km farther arcward in the underthrust sediments than in the prism complex. The fresh water produced by the reaction results in pore waters that are 10–30% fresher at a distance of 50–70 km from the prism toe. This constraint indicates a probable fluid migration path of more than 50 km from the reaction zone to the sites where freshened pore fluids have been observed. The peak rate of fluid production when expressed as the volume of fluid per volume of sediment per second is 2×l0−15.