Special Features
The tectonics of the Caribbean region feature a plethora of interesting and unique properties. This area of the Earth is the site of the discovery of black smokers and hydrothermal vents, a rare rift-rift-rift triple junction, thought-provoking hotspots, the longest and fastest subduction zone in the world, the largest earthquake ever recorded and a famous plate motion that had massive global implications.
The Galapagos Spreading Centre (GSC) is a classic divergent plate tectonic boundary separating the Nazca Plate from the Cocos Plate southwest of Central America (Tao et al., 2011). This mid-ocean ridge is famous for the discovery of black smokers and hydrothermal vents, which are of massive importance to biological research and mineral exploration (Tao et al., 2011). Just a short distance away from these hydrothermal vent sites is the Galapagos Triple Junction, a rare rift-rift-rift (RRR) triple junction which separates the Pacific, Nazca and Cocos Plates (Searle et al., 1985). The unique setting of an RRR triple junction makes it an invaluable site for scientific research, as it enables a better understanding of how plates deform internally near plate boundaries, as well as the relationship between this deformation and upwelling mantle material (Smith et al., 2013).
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Though interesting geologic features are peppered throughout the Caribbean region, the Nazca Plate undoubtedly reigns supreme. At 7500 km in length, the Nazca Plate is home to the longest subduction zone in the world as it obliquely subducts beneath the South American Plate (Klotz et al., 2001). Furthermore, this subduction zone features the fastest subduction rate on the planet at approximately 61 mm/year (Norabueana et al., 1999), and it is also the site of the largest earthquake ever recorded on the planet, the M 9.5 Valdivia earthquake (Kanamori and Cipar, 1976).
However, the most interesting feature of the Nazca Plate is its abundance of hotspots, an enigmatic phenomenon that is famously controversial among geologists. There are four hotspots to be precise: the Juan Fernandez, San Felix, Easter and Galapagos (Ray et al., 2012). Simply defined as intraplate regions of volcanism, the origin and development of hotspots are both fascinating and mysterious. On one hand, it is commonly thought that these volcanic regions are powered by anomalously hot underlying mantle, which is attributed to mantle plumes rising as thermal diapirs from the core-mantle boundary (Foulger, 2010). On the other hand, a more recent hypothesis suggests that it is not high temperatures that cause the volcanism, but rather that lithospheric extension enables the passive rising of melt from shallow depths (Foulger, 2010). Though the mantle plume hypothesis has been the generally accepted one, there is an increasing awareness of the lack of evidence supporting deep mantle sources, and conversely a growing body of support for the plate theory and the tectonic and shallow mantle processes it invokes (Foulger, 2010). Given the lack of overwhelming evidence either way, we may well be entering the height of the hotspot controversy and witnessing the initiation of a major turn in geologic dogma. The Galapagos hotspot and the other hotspots of the Nazca Plate will undoubtedly be of central importance to future research, given their ideal settings as what is commonly believed to be classic plume sites. |
Durham University's profile for Gillian Foulger, one of the leading proponents of alternative models to the mantle plume hypothesis:
https://community.dur.ac.uk/g.r.foulger/ Plate Vs Plumes: A Geological Controversy:
http://ca.wiley.com/WileyCDA/WileyTitle/productCd-1405161485.html A website dedicated to the origin of hotspot volcanism:
http://www.mantleplumes.org/index.html |
Another interesting feature of the tectonics of the Caribbean region is the historical motions of the Panama Plate. Closure of the Isthmus of Panama about 3 myr ago catalyzed dramatic changes in the Earth’s climate and biosphere (Schmittner et al., 2004). The Greenland ice sheet grew to a massive extent and the climate-dominating ice age cycles commenced (Schmittner et al., 2004). Disruption of water exchange between the Atlantic and Pacific Oceans led to different evolutionary paths of marine species on either side of the land bridge, while terrestrial life colonized an entire subcontinent (Schmittner et al., 2004). Specifically, models have put forth the interesting idea that the end result of this closure was decreased marine productivity in the North Atlantic and North Pacific, and increased marine productivity in the equatorial Pacific (Schmittner et al., 2004). Moreover, reduced inflow of fresher, higher-elevation Pacific water into the Atlantic led to increased salinity and northward heat transport, the latter of which caused increased snowfall and subsequently may have triggered glaciation (Schmittner et al., 2004).
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References
Foulger, Gillian. Plates Vs Plumes: A Geological Controversy. Hoboken: Wiley-Blackwell, 2010. Print.
Kanamori, H., & Cipar, J. J. (1974). Focal Process of the Great Chilean Earthquake May 22, 1960. Physics of the Earth and Planetary Interiors, 9(2), 128-136.
Klotz, J., Khazaradze, G., Angermann, D., Reigber, C., Perdomo, R., & Cifuentes, O. (2001). Earthquake Cycle Dominates Contemporary Crustal Deformation in Central and Southern Andes. Earth and Planetary Science Letters, 193(3-4), 437-446.
Norabuena, E. O., Dixon, T. H., Stein, S., & Harrison, C. G. A. (1999). Decelerating Nazca-South America and Nazca-Pacific Plate Motions. Geophysical Research Letters, 26(22), 3405-3408.
Ray, J. S., Mahoney, J. J., Duncan, R. A., Ray, J., Wessel, P., & Naar, D. F. (2012). Chronology and Geochemistry of Lavas from the Nazca Ridge and Easter Seamount Chain; An Approximately 30 myr Hotspot Record. Journal of Petrology, 53(7), 1417-1448.
Schmittner, A., et al. (2004). Global Impact of the Panamanian Seaway Closure. Eos, 85(49), 526-527.
Searle, R. C., Francheteau, J. (1985). Morphology and Tectonics of the Galapagos Triple Junction, Marine Geophysical Researches, 8, 95-129.
Smith, D. K., Schouten, H., Montesi, L., Zhu, W. (2013). The Recent History of the Galapagos Triple Junction Preserved on the Pacific Plate, Earth and Planetary Science Letters, 371-372, 6-15.
Tao, C., Li, H., Wu, G., Su, X., Zhang, G. (2011). First Hydrothermal Active Vent Discovered on the Galapagos Microplate, American Geophysical Union Fall Meeting 2011.
Foulger, Gillian. Plates Vs Plumes: A Geological Controversy. Hoboken: Wiley-Blackwell, 2010. Print.
Kanamori, H., & Cipar, J. J. (1974). Focal Process of the Great Chilean Earthquake May 22, 1960. Physics of the Earth and Planetary Interiors, 9(2), 128-136.
Klotz, J., Khazaradze, G., Angermann, D., Reigber, C., Perdomo, R., & Cifuentes, O. (2001). Earthquake Cycle Dominates Contemporary Crustal Deformation in Central and Southern Andes. Earth and Planetary Science Letters, 193(3-4), 437-446.
Norabuena, E. O., Dixon, T. H., Stein, S., & Harrison, C. G. A. (1999). Decelerating Nazca-South America and Nazca-Pacific Plate Motions. Geophysical Research Letters, 26(22), 3405-3408.
Ray, J. S., Mahoney, J. J., Duncan, R. A., Ray, J., Wessel, P., & Naar, D. F. (2012). Chronology and Geochemistry of Lavas from the Nazca Ridge and Easter Seamount Chain; An Approximately 30 myr Hotspot Record. Journal of Petrology, 53(7), 1417-1448.
Schmittner, A., et al. (2004). Global Impact of the Panamanian Seaway Closure. Eos, 85(49), 526-527.
Searle, R. C., Francheteau, J. (1985). Morphology and Tectonics of the Galapagos Triple Junction, Marine Geophysical Researches, 8, 95-129.
Smith, D. K., Schouten, H., Montesi, L., Zhu, W. (2013). The Recent History of the Galapagos Triple Junction Preserved on the Pacific Plate, Earth and Planetary Science Letters, 371-372, 6-15.
Tao, C., Li, H., Wu, G., Su, X., Zhang, G. (2011). First Hydrothermal Active Vent Discovered on the Galapagos Microplate, American Geophysical Union Fall Meeting 2011.