Transverse intra-arc rifting: Palaeogene Wagwater Belt, Jamaica

Abstract

The Wagwater belt in eastern Jamaica is an exceptionally well exposed example of a transverse intra-arc rift formed during an abrupt transition from convergent to strike-slip tectonics. The belt consists of the uplifted Wagwater half-graben containing at least 5.6 km of coarse clastic terrestrial sedimentary rocks, which is overlain and flanked by a much wider basin filled with about 1.2 km of upward-fining, marine sedimentary rocks. Neogene strike-slip movements structurally inverted the half-graben and exposed thick sections of both the half-graben and overlying basin. Early(?) Palaeocene-Early Eocene rifting preceded the Middle Eocene formation of oceanic crust in the Cayman Trough pull-apart basin and affected a 50000 km 2 area near the eastern distal end of the pull-apart. Fifteen half-grabens, identified in Jamaica and in offshore areas using seismic profiling, range in strike from north-east to north-west. Rifts in Jamaica are presently oblique to the generally east-west strike of plutons and sedimentary facies belts within a Maestrichtian-Palaeocene(?) island arc. Based on their apparent relationship to the strike of the enclosing palaeo-arc, we interpret the Jamaican rifts as ‘transverse intra-arc rifts’. Following the deposition of Palaeocene redbeds and evaporites (Wagwater Formation) in the half-graben, subsidence was widespread in a marine sedimentary basin. This marine basin was filled in Early Eocene time by marine conglomerates (Port Maria and Albany Members of the Richmond Formation), sandstone and siltstones (Roadside Member), and, finally, in the latest Early Eocene to Earliest Middle Eocene time, by a calcareous mudstone (Langley Member). A bimodal suite of volcanic rocks (Newcastle and Nutfield Volcanics) was erupted during the deposition of the Wagwater Formation and the Roadside Member. The structure and tectonic setting of transverse intra-arc basins in Jamaica is somewhat similar to rifts of the Neogene Pannonian basin in Hungary. In both areas, an abrupt transition between convergent and strike-slip tectonics resulted in transverse intra-arc rifts striking almost perpendicular to a dying volcanic arc. Transverse intra-arc rifts may be common features of small, arc-fringed plates such as the Caribbean and Pannonian plates that respond quickly to collision by strike-slip motion towards an unopposed oceanic free face.