Sedimentary Record of Arc‐Continent Collision Along Mesozoic SW North America (Siuna Belt, Nicaragua)

Abstract

The western margin of the Caribbean Plate is a typical example where oceanic and continental terranes have amalgamated by subduction, collision, and strike-slip processes. The boundaries between these blocks, as well as their tectonostratigraphic records, are generally covered by younger deposits and dense tropical vegetation, which may hamper reconstructing the accretionary evolution of the convergent margin. In that context, the study of overlap sedimentary assemblages represents an important tool to constrain the accretion timing of terranes. In northern Central America, the geology of the suture zone between the Chortis Block and the exotic Siuna Intraoceanic Arc indicates that the two terranes were assembled together during a Hauterivian arc-continent collision (approximately 134-131 Ma). The exotic origin of the intraoceanic arc is based on the nature of metamorphic blocks within and the kinematics of the Siuna Serpentinite Mélange. The short duration of the collision event is suggested by coeval exhumation of the Siuna Serpentinite Mélange and Chortis-derived coarse sedimentation (El Amparo Formation) along the suture zone, rapidly followed by onset of pelagic sedimentation (Rio Matis Formation). Although the collision appears to have been short lived and preserved only in the suture zone, postcollisional extension affected intra-arc to back-arc settings of the Chortis Block and led to the formation of kilometer-thick extensional basins. We envisage that the convergent margin inboard of SW Mexico-represented by the fringing Guerrero Intraoceanic Arc and the Mixteca continental terrane-underwent similar postcollisional extension, whereas the western margin of the proto-Caribbean oceanic realm experienced onset of WSW dipping subduction beneath the accreted Siuna Intraoceanic Arc.