Very similar microstructure, that is, the same phase aggregation is found in both experimentally deformed synthetic materials and natural ultramylonite. The stress-strain-rate relationship, grain-size dependent flow strength, and the achievement of large tensile stain on the synthetic samples indicate that the samples creeped due to grain boundary sliding (GBS). As a result of GBS, grain-switching events allow dispersed phases to contact grains of the same phase oriented in the direction of compression. Mineral phase mixing through GBS, which helps to retain fine grain size in rocks due to grain boundary pinning, has been speculated to occur during formation of mylonites. However, the results presented here by Takehiko Hiraga and colleagues contradict this hypothesis because mineral aggregation through GBS promotes demixing rather than mixing of the mineral phases. GBS processes alone will not promote a transformation of well-developed monomineralic bands to polymineralic bands during mylonitization.
Sea-level-induced seismicity and submarine landslide occurrence
Daniel S. Brothers et al., U.S. Geological Survey, Coastal and Marine Science Center, 384 Woods Hole Road, Woods Hole, Massachusetts 02543, USA. Published online 22 July 2013, http://dx.doi.org/10.1130/G34410.1.
The relationships between global climate change and marine geohazards remains poorly understood. This study by Daniel S. Brothers and colleagues investigates compelling linkages between rapid sea-level rise, bending of the lithosphere, and stress loading of crustal faults. Rupture of such faults may induce slope failure and generate submarine landslides, thus offering a new explanation for the temporal coincidence between many submarine landslides and rapid sea level rise between 16,000 and 8,000 years ago.
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Geological Society of America