Diamond in the summit The tiny crystal in this image is an inclusion of diamond surrounded by the mi

Diamond in the summitThe tiny crystal in this image is an inclusion of diamond surrounded by the mineral orthopyroxene. It tells a story of a voyage hundreds of kilometers and tens of millions of years long. It was found today at the roof of the world.In the high part of the Himalayas, there are bodies of what we call “ophiolites”. An ophiolite is a block of mafic and ultramafic rocks stuck in the middle of a continent. These types of rocks – basalts and peridotites – are most commonly found as part of the ocean crust and upper mantle. Finding them in the middle of a continent is typically thought to require faulting, and a lot of it.There is a line of ophiolites running through the Himalayan mountains, from West to East. These ophiolites are thought to represent the original boundary between Asia and India. When the Tethys ocean between India and Asia closed, tiny bits of ocean crust and upper mantle were stuck in-between, forming these ophiolites. This orthopyroxene is a mantle mineral found in one of those ophiolites, and the diamond is trapped as an inclusion inside that larger mineral. The scalebar on this diamond, 10 μm, is 1/100th of a millimeter long, so these grains are extremely tiny.The diamond grains were found and published about in a recent paper by scientists from UT Arlington and the Wadia Institute of Himalayan Geology. The presence of diamond tells part of the story of these rocks before they were accreted to the continent.Diamond isn’t stable in the uppermost 100 kilometers of the planet Earth. It requires great pressures to form diamond from available carbon. The diamonds must have formed in these rocks when they were deeper than 100 kilometers in the mantle. Long before these rocks became part of the continent, they were deep in the mantle where the diamond formed. The mantle was brought upward beneath a mid-ocean ridge, where it eventually became part of the shallow ocean lithosphere. When India and Asia collided, this little bit of mantle was stripped off and trapped in-between Asia and India.How deep did these diamonds form? We know they must have been 100 kilometers deep, but they could have been much deeper. The scientists looked at other inclusions in the rocks and found C-H fluids trapped in some inclusions and remnants of a different mineral called Wadsleyite as well. Those compounds are only commonly stable along with diamond at depths greater than 400 kilometers.The best estimate of the researchers, therefore, is that these diamonds formed about 400 or 500 kilometers deep in the planet Earth. They were carried near to the surface by plate tectonics, dragged along as the Indian ocean crust moved towards Asia, and then folded and faulted into the ophiolite, where they are found today.-JBBImage source and original paper:http://bit.ly/2vwlCJr -- source link

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