The Caribbean region has a plethora of convergent plate boundaries, some of which have resulted in a significant presence of accretionary wedges. As one plate subducts beneath another, some of the overlying material is scrapped off the subducting plate, and is juxtaposed against the material of the overlying plate (Saffer et al., 2006). It is in this manner that the accumulation of ocean floor materials such as pelagic sediments, pillowed basalts, and ophiolites occurs (Barber et al., 1989).
Mechanisms behind Accretionary Wedges
A notable characteristic of accretionary wedges is the “taper angle”. This is the angle between the top of the wedge and the bottom. As the bottom plate is driven beneath the overlying plate, some sediments are scraped off and accumulate, while others are underthrust. As pressure mounts, the high pressure gradient results in a rapid decrease in porosity, from >50% pre-subduction to <15% within 20 km of the trench (Saffer et al., 2006). The result of this decrease in porosity is a dewatering of the subducting sediments (Bray and Karig, 1985). The end result, however, is a net increase in pore pressure, which reduces the effective stress. This allows for the mechanical stability of accretionary wedges which have low taper angles (Saffer et al., 2006). Taper angle is also dependent on other factors, such as the thickness of subducting sediments, plate velocity, and the presence of faults (Saffer et al., 2006). The expelled water may manifest itself as mud volcanoes, which are observed in Venezula, Panama, and Barbados (Aslan et al., 2011; Reed et al., 1989; Martin et al., 1996).
The decrease in porosity also has effects which reach further than the overall taper angle. As the pore fluid is expelled, the sediments lithify and become more competent (Zhao et al., 1986). The sediments which have accumulated at the front of the edge have not been subjected to high pressures, and as a result they have not lithified. They are thus mechanically incompetent, and deform as the plate continues to subduct beneath them. This is the cause of the characteristic convex downwards shape at the front of accretionary wedges (Zhao et al., 1986).
The decrease in porosity also has effects which reach further than the overall taper angle. As the pore fluid is expelled, the sediments lithify and become more competent (Zhao et al., 1986). The sediments which have accumulated at the front of the edge have not been subjected to high pressures, and as a result they have not lithified. They are thus mechanically incompetent, and deform as the plate continues to subduct beneath them. This is the cause of the characteristic convex downwards shape at the front of accretionary wedges (Zhao et al., 1986).
Locations of Interest
The northern Andes are certainly the most prominent accretionary wedge in the Caribbean region. They formed from 199.6 Ma to 23.02 Ma, as a result of the subducting Nazca plate (Ramos, 1999). As a result of primarily accreting oceanic basement rocks, there are obducted ophiolites, in addition to metamorphic rocks up to the blue schist facies (Ramos, 1999). The specifics of the Northern Andes are discussed on the "Suprasubduction Zone Microplates" page.
The Samana complex in the Dominican Republic is a metamorphic region which records a complex, high pressure accretionary wedge (Escuder-Viruete et al., 2011). This accretionary event was initiated approximately 60 Ma, as a high pressure, low temperature metamorphic accretionary wedge and then switching to a second regime, of decompression and retrograde metamorphism approximately 33 Ma (Escuder-Viruete et al., 2011). There are other similar high pressure accretionary areas on the northern coast of Hispaniola and Cuba, which are the result of a collision with the North American plate (Escuder-Viruete et al., 2013)
Similarly, Barbados has an accretionary wedge between it and the North American plate, with a convergent rate of ~3cm/a (Zhao et al., 1986). The Barbados wedge is unusually wide, approximately 300 km (Zhao et al., 1986). The thickness of sediments being subducted/accreted also varies greatly, reaching 7 km near the Orinoco River delta, to just 700 m further from shore (Zhao et al., 1986).
References
Aslan, A., Warne, A. G., White, W. A., Guevara, E. H., et al. (2001). Mud volcanoes of the Orinoco Delta, Eastern Venezuela. Geomorphology, 41. 323-336.
Bray, C. J., and D. E. Karig (1985), Porosity of sediments in accretionary prisms and some implications for dewatering processes. Journal of Geophysical Research, 90. 768–778.
Barber, T., Brown, K. (1989). Mud diapirism: the origin of melanges in accretionary complexes. Geology Today, 89-94.
Escuder-Viruete, J., Perez-Estuan, A., Gabites, J., Suarez-Rodriguez, A. (2011). Structural development of a high-pressure collisional accretionary wedge: The Samaná complex, Northern Hispaniola. Journal of Structural Geology, 33. 928-950.
Escuder-Viruete, J., Valverde-Vaquero, P., Rojas-Agramonte, Y., et al. (2013). Timing of deformational events in the Río San Juan complex: Implications for the tectonic controls on the exhumation of high-P rocks in the northern Caribbean subduction–accretionary prism. Lithos, 177. 416-435.
Martin, J. B., Kastner, M., Henry, P., Le Pichon, X., Lallement, S. (1996). Chemical and isotopic evidencefor sources of fluids in a mud volcano field seaward of the Barbados accretionary wedge. Journal of Geophysical Research, 101(20). 325-345.
Ramos, V. A. (1999). Plate tectonic setting of the Andean Cordillera. Episodes, 22(3), 183-190.
Reed, D. L., Silver, E. A., Tagudin, J. E., Shipley, T. H., Vrolijk, P. (1989). Relations between mud volcanoes, thrust deformation, slope sedimentation, and gas hydrate, offshore north Panama. Marine and Petroleum Geology, 7. 44-54.
Saffer, D. M., Belkins, B. A. (2006). An Evaluation of factors influencing pore pressure in accretionary complexes: Implications for taper angle and wedge mechanics. Journal of Geophysical Research, 111.
Zhao, W. L., Davis, D. M., Dahleen, F. A., Suppe, J. (1986). Origin of Convex Accretionary Wedges: Evidence form Barbados. Journal of Geophysical Research, 91(10). 246-258.
"Mud Volcano." Wikipedia. Wikimedia Foundation, 27 Jan. 2014. Web. 30 Jan. 2014.
"Oceanic/continental: The Andes." The Geological Society of London. N.p., n.d. Web. 29 Jan. 2014.
Bray, C. J., and D. E. Karig (1985), Porosity of sediments in accretionary prisms and some implications for dewatering processes. Journal of Geophysical Research, 90. 768–778.
Barber, T., Brown, K. (1989). Mud diapirism: the origin of melanges in accretionary complexes. Geology Today, 89-94.
Escuder-Viruete, J., Perez-Estuan, A., Gabites, J., Suarez-Rodriguez, A. (2011). Structural development of a high-pressure collisional accretionary wedge: The Samaná complex, Northern Hispaniola. Journal of Structural Geology, 33. 928-950.
Escuder-Viruete, J., Valverde-Vaquero, P., Rojas-Agramonte, Y., et al. (2013). Timing of deformational events in the Río San Juan complex: Implications for the tectonic controls on the exhumation of high-P rocks in the northern Caribbean subduction–accretionary prism. Lithos, 177. 416-435.
Martin, J. B., Kastner, M., Henry, P., Le Pichon, X., Lallement, S. (1996). Chemical and isotopic evidencefor sources of fluids in a mud volcano field seaward of the Barbados accretionary wedge. Journal of Geophysical Research, 101(20). 325-345.
Ramos, V. A. (1999). Plate tectonic setting of the Andean Cordillera. Episodes, 22(3), 183-190.
Reed, D. L., Silver, E. A., Tagudin, J. E., Shipley, T. H., Vrolijk, P. (1989). Relations between mud volcanoes, thrust deformation, slope sedimentation, and gas hydrate, offshore north Panama. Marine and Petroleum Geology, 7. 44-54.
Saffer, D. M., Belkins, B. A. (2006). An Evaluation of factors influencing pore pressure in accretionary complexes: Implications for taper angle and wedge mechanics. Journal of Geophysical Research, 111.
Zhao, W. L., Davis, D. M., Dahleen, F. A., Suppe, J. (1986). Origin of Convex Accretionary Wedges: Evidence form Barbados. Journal of Geophysical Research, 91(10). 246-258.
"Mud Volcano." Wikipedia. Wikimedia Foundation, 27 Jan. 2014. Web. 30 Jan. 2014.
"Oceanic/continental: The Andes." The Geological Society of London. N.p., n.d. Web. 29 Jan. 2014.