Volume loss and defluidization history of Barbados

Abstract

The basal complex of Barbados island is a tectonic amalgam of Eocene strata accreted at an outer deformation front at the end of Eocene time. The structures and porosity‐depth function of such sediments give clues to the succession of pore volume loss episodes, each of which must have been accompanied by defluidization. The basal complex evolved as a perpetually shallow, low‐temperature mass which underwent little or no unroofing in its 36 m.y. history in the accretionary prism. In its early phase of deformation, the accretionary structure formed by thrust imbrication, perhaps with little concurrent volume loss. Burial compaction followed tectonic thickening during accretion, causing probable large pore volume loss within limits of 0–70% of the initial volume of the imbricate stack. A late phase of tectonics has affected Barbados and a wide region of the structural high since 20 Ma. Such tectonics reactivated faults in the basal complex which acted as channelways for deep‐seated and perhaps shallow fluids to emerge from the structural high. The late stage tectonics also caused local basins for deposition of sediment cover and emplacement of thrust nappes of forearc basin strata above the basal complex. Such top loading caused a renewed phase of burial compaction and loss of about 37% or more of the pore volume that existed at the onset of late stage tectonics.