A piece of mantle: São Pedro and São Paulo rocksAlmost a 1000km from the Brazilian coa

A piece of mantle: São Pedro and São Paulo rocksAlmost a 1000km from the Brazilian coast and 1800km from the African coast a 12.5m high archipelago shyly shows its face from the breaking waves. This is the archipelago of São Pedro and São Paulo rocks, a group of 15 small islets and rocks that although appearing small are actually part of something much bigger, the Mid-Atlantic Ridge. In reality the rocky pinnacles rise around 4000m from the ocean floor, it is one of the few places in the world where part of Mid Atlantic Ridge appears above the water (even when it is only 12,5m in height).An mid-ocean ridge is a spreading zone where magma well up to build a new oceanic crust. At slow spreading ocean ridges which have a small supply of upwelling magma oceanic core complexes (also known as megamullions) form long ridges parallel to the spreading ridge. Usually these seabed geological features have smooth domes or turtleback shapes lined with transverse ridges where the abyssal mantle is exposed. The rocks of Sao Pedro and Sao Paul are part of these domes made up of exposed abyssal mantle. In fact, it is the only location in the Atlantic where exposure above the ocean occurs. The rocks that are exposed are serpintinized abyssal mantle periodiote. Serpentinite forms when sea water intrudes down fractures and reacts with ultramafic rocks in the lower crust and upper mantle. Peridotite on the other hand is a ultramafic (rocks with low silica content) rock composed mostly of olivine and pyroxene minerals. Thus the archipelago offers are rare look into the oceanic lithosphere.Just below the ocean’s surface marine life thrives due to the rich flora and fauna surrounding the islets. This is the main reason that the archipelago is a paradise for a number of seabirds. Charles Darwin visited the archipelago in February of 1832. He listed the fauna he could find which at the time were: two birds, a crab, a tick, a fly (on the bird) and a moth.The islands are only 250m across, there is almost no vegetation (a constant sea spray prohibits growth) except for some algae and fungus and the only source of fresh water comes from rain. There is a lighthouse and a research station on the biggest island which is manned by 4 researchers for a period of 10 days a time.Here you can see how the pinnacles from São Pedro and São Paulo would appear from under water: http://thetim.es/1dTZInRImage: Copyright Eduardo Nicolau The main research station and lighthouse and a view of the underwater world.–BOReferences:Deborah K. Smith, Johnson R. Cann and Javier Escartín. 2006. Widespread active detachment faulting and core complex formation near 13° N on the Mid-Atlantic Ridge. Nature 442 27 July 2006.http://worldwildlife.org/ecoregions/nt1318http://www.whoi.edu/oceanus/viewArticle.do?id=2392http://bit.ly/15BHVyo -- source link

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