Analysis of global geochemical datasets obtained through analyses of dated zircon grains show that Earth experienced a peak in the degree of crustal recycling about 1.2 to 1.1 billion years ago, during the Grenvillian Superevent that resulted in amalgamation of supercontinent Rodinia. That the high values were never reached prior or subsequent to this event suggests that this interval represents a climax in Earth's mountain-building cycle, which Martin Van Kranendonk and colleagues postulate arose from a Goldilocks (just right) combination of large plates on a warmer, more rapidly convecting Earth. Prior to the Grenvillian superevent, plates were smaller and less rigid, precluding high degrees of crustal recycling, whereas continued cooling after the Grenvillian superevent resulted in slower drift rates and lower orogenic intensity.
Mantle upwelling and initiation of rift segmentation beneath the Afar Depression
J.O.S. Hammond et al., Department of Earth Science and Engineering, Imperial College London, SW7 2AZ London, UK, and School of Earth Sciences, University of Bristol, BS8 1RJ Bristol, UK. Posted online ahead of print on 29 April 2013; http://dx.doi.org/10.1130/G33925.1.
Plate tectonics continually reshape Earth's surface, breaking apart continents over millions of years. In this study, J.O.S. Hammond and colleagues use seismology to image beneath the Afar depression, the northern extreme of the East Africa rift and the only place on land undergoing the final stages of continental breakup. They record distant earthquakes on seismometers deployed across East Africa and, much like a d
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