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Plate tectonic gemstones
Robert J. Stern, Geosciences Dept., The University of Texas at Dallas, Richardson, Texas 75083-0688, USA. Posted online ahead of print 9 May 2013; http://dx.doi.org/10.1130/G34204.1.
Humans have used, sought, and traded gemstones for thousands of years, uniquely linking art, economics, and geology, from the dawn of civilization until now. In contrast, the theory of plate tectonics, which explains how Earth's crust and upper mantle is divided into independent plates, has only existed for about 50 years. Gemstones mostly form where special conditions of pressure, temperature, and chemical composition occur, and sometimes these conditions can be linked to plate tectonic processes. Plate boundaries are dynamic geologic environments where conditions for gemstone formation occur, especially at convergent plate boundaries, where plates are subducted, sinking back into Earth's interior. In this paper, a team of U.S., Japanese, and Canadian geoscientists identify two gemstones -- ruby and a type of jade (jadeite) -- that form at two types of convergent plate boundaries, in subduction zones and where continents collide. Jadeite forms where seafloor (oceanic crust) is subducted -- for example, around the Pacific Ocean, in Central America, New Zealand, and SE Asia. In contrast, ruby forms where two continents collide, for example now beneath the Himalayas, where India and Asia are colliding, and in east Africa, where east and west Gondwana collided 550 million years ago. This new understanding of "plate tectonic gemstones" provides a new perspective on how plate tectonics functions and also suggests
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