Deep-sea drilling team may have gotten sample they wanted

The scientific team that drilled into the sea floor off Costa Rica has gone home while the drilling ship, the JOIDES Resolution, is tied up in Curaçao for refitting.

The expedition may have recovered some of the gabbro it sought at Hole 1256D. However efforts to clean the existing hole took much of the expedition’s time.
Said the 21 scientists to the Resolution crew:

“Hole 1256D is the best chance for understanding some of the most fundamental processes operating on our planet; to understand how the great tectonic plates are formed. Expedition 335 has saved and resuscitated Hole 1256D, cleaned the hole of choking cuttings, and preserved it for future expeditions. We will be back!”

The hole reached 1,500 meters (about 4,900 feet) during a 2005 expedition. But when the new expedition arrived some 900 kilometers, about 560 miles, off Costa Rica’s Pacific coast, there were many blockages and problems to surmount, according to the weekly reports of the team. The current drilling only reached 1,521 meters below the sea floor, about 4990 feet. However the drilling crew

stabilized the hole with cement in several places to give quick access for a future expedition, the scientists reported.

Scientists recovered one 1.4-kilogram rock that may be the much-sought gabbro. That and other specimens will be analyzed extensively

Before the mission scientists explained that Oceanic crust is formed along mid-ocean ridges by the cooling of magma produced by the partial melting of mantle rocks. If the magma reaches the surface of the ocean floor, it cools rapidly, forming the basalts that make up the vast majority of the upper oceanic crust.  However, if the magma crystallizes more slowly at depth, the rock that is formed is called gabbro. The oceanic crust is therefore made up of a surface layer of basalt underlain by deeper gabbro. And that is what the team sought.

The drilling was into the Cocos tectonic plate, which is one of the causes of earthquakes in Costa Rica when it collides with the Caribbean plate.

The Resolution is special ship that allows deep ocean drilling. Its rig entered and left the hole deep beneath the Pacific some 24 times, according to the crew’s report.

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