Researchers shed light on magma-seawater boundary
Scientists on the Integrated Ocean Drilling Program (IODP) Expedition 335 Superfast Spreading Rate Crust 4 have succeeded in recovering a set of heat-tempered basalts: these offer a comprehensive picture of the boundary between magma and seawater, something that has not been easy to get. Completing operations in Ocean Drilling Program (ODP) Hole 1256D, a deep scientific borehole over 1,500 metres below the seabed into the igneous crust of the Pacific Ocean, the research team sampled a full section of the intact oceanic crust down into gabbros (a group of coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt that represent 66 % of the ocean crust) in one of the planet's deepest 'hard rock' penetration sites of scientific ocean drilling, said the IODP in a statement. In cooperation with drillers, the team steadied, cleared and primed ODP Hole 1256D for further deepening. Led by the National Oceanographic Centre, Southampton at the University of Southampton in the United Kingdom and the Centre National de la Recherche Scientifique (CNRS) in France, the expedition was the fourth in a series of expeditions carried out in 2002 and 2005. According to the scientists, the biggest process active on Earth is the intrusion of gabbros. Over 12 cubic kilometres of new magma from the mantle intruded into the crust annually, they say, adding that minerals, chemistry and textures of gabbroic rocks preserve records of the processes that take place deep within the planet's mid-ocean ridges, where new ocean crust is formed. 'The formation of new is the first step in Earth's plate tectonic cycle,' says Professor Damon Teagle of the National Oceanographic Centre, Southampton. 'This is the principal mechanism by which heat and material rise from within the Earth to the surface of the planet. And it's the motion and interactions of Earth's tectonic plates that drive the formation of mountains and volcanoes, the initiation of earthquakes, and the exchange of elements (such as carbon) between the Earth's interior, oceans, and atmosphere.' For his part, Benoît Ildefonse of the CNRS and the Université Montpellier 2, says: 'Understanding the mechanisms that construct new tectonic plates has been a major, long-standing goal of scientific ocean drilling, but progress has been inhibited by a dearth of appropriate samples, because deep drilling (at depths greater than 1,000 meters into the crust) in the rugged lavas and intrusive rocks of the ocean crust continues to pose significant technical challenges.' ODP Hole 1256D is located around 900km west of Costa Rica in the Pacific Ocean, and 1,150km east of the linear submarine volcanic chain known as the East Pacific Rise. The hole is found in a crust that is 15 million years old, formed during a 'superfast' spreading at the ancient East Pacific Rise, when the newly developed plates were moving apart by over 200 millimetres per year (mm/yr). 'Although a spreading rate of 200 mm/yr is significantly faster than the fastest spreading rates on our planet today, superfast-spread crust was an attractive target because seismic experiments at active mid-ocean ridges indicated that gabbroic rocks should occur at much shallower depths than in crust formed at slower spreading rates,' Professor Teagle points out. 'In 2005, we recovered gabbroic rocks at their predicted depth of approximately 1,400 meters below the seafloor, vindicating the overall "Superfast" strategy.'For more information, please visit: Integrated Ocean Drilling Program (IODP):http://www.iodp.org/National Oceanographic Centre, Southampton:http://www.noc.soton.ac.uk/
Countries
France, United Kingdom