Development of the Mosquitia Megafan in Response to Mantle Upwelling beneath Central America

The 23,000 km² alluvial plains of eastern Honduras and northeastern Nicaragua are low elevation (less than 50 meter AMSL) savanna grasslands crossed by the Patuca and Cocos rivers that drain 45,000 km² of the Central America highlands. We recognize the subareal plain as an active stream-dominated “megafan” based on its morphology, size and from exploration well data and offshore seismic profiles on the Nicaragua Rise. Offshore, the top of the Miocene seismic horizon extends between 100 and 150 km into the Caribbean Sea. Age constraints from industry wells show the pulse of clastic deposition began in the Pliocene and continue today. During the Pleistocene low-stands the mega-fan prograded across the shallow (less than 50 meters deep) upper Nicaragua Rise. The Patuca River flowed through the Sutawala windgap of the Colon mountains and combined with the Cocos to form a single fluvial system near the axis of the megafan.

Northern Central America has uplifted between one- and two-km since the beginning of the Pliocene creating its extensive highlands. Timing of the uplift coincides with the beginning of eruption of mantle-derived behind the arc basalts distinct from the Central America arc lavas. Both the uplift and mafic volcanism are attributed to mantle upwelling and possibly slab breakoff. The Mosquitia megafan developed as a depositional response to the uplift produced by the mantle upwelling. The Mosquitia megafan tectonic setting differs from other fans in that it is not directly associated with a convergent or collisional setting.