Week 5 : Converging Plates - Barbados Ridge Accretionary Complex

Tectonics of the Lesser Antilles Chain of Islands (Source: Gailler et al. 2017)

I chose to visit the Lesser Antilles chain of islands. It is located east of the Caribbean plate where it borders with the North and South America plates. The region is an active subduction zone, where the oceanic crust of the South American Plate is being thrust under the Caribbean Plate, at a mean rate of around 2 cm/yr. The subduction process created the volcanic arc of islands that is the Lesser Antilles, from the coast of Venezuela to the Virgin Islands.

I decided to focus mainly on the Barbados Ridge accretionary complex, which is considered the largest (300km wide and 20 km thick) of its kind on the Earth. The island of Barbados, which is the crest of the complex, picked my interest for being among the few places on Earth where an active accretionary wedge is visible above sea level.

Schematic cross-section of the Barbados subduction zone. (Source: Speed et al., 2012)

It was formed following the accretion of sediments since the Eocene and deformation under the compressional type of tectonic forces. The sediments are sandy turbidites coming from Venezuela’s Orinoco River and deposed onto the ocean floor. As the South American Plate dives below the Caribbean one, these sediments are scraped off and incorporated into the accretionary complex. 

Parts of the island present a sequence of thrust faults that apparently deformed the Eocene turbidites into several pronounced folds. The rocks involved were observed by Terri Cook and Lon Abbott as follows: “[…] in places, overlain by remnants of an oceanic allochthon consisting of forearc basin sediments that were thrust eastward over the Barbados accretionary prism along a roof thrust”.

Folds in the Barbados Accretionary Prism (Source: Cook and Abbott, 2017)

Work cited:

Terri Cook and Lon Abbott, Barbados Beckons https://www.geoexpro.com/articles/2017/05/barbados-beckons