Stress and deformation in subduction zones: Insight from the record of exhumed metamorphic rocks
Bernhard Stöckhert, 2002. "Stress and deformation in subduction zones: Insight from the record of exhumed metamorphic rocks", Deformation Mechanisms, Rheology and Tectonics: Current Status and Future Perspectives, S. de Meer, M. R. Drury, J. H. P. de Bresser, G. M. Pennock
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High pressure (HP) and ultrahigh (UHP) metamorphic rocks are exhumed from subduction zones at high rates on the order of plate velocity (cm/year). Their structural and microstructural record provides insight into conditions and physical state along the plate interface in subduction zones to depths of >100 km. Amazingly, many identified (U)HP metamorphic rocks appear not to be significantly deformed at (U)HP conditions, despite their history within a high strain rate mega-shearzone. Other (U)HP metamorphic rocks seem to be deformed exclusively by dissolution-precipitation creep. Indications of deformation by dislocation creep are lacking, apart from omphacite in some eclogites. Available flow laws for dislocation creep (extrapolated to low natural strain rates, which is equivalent to no deformation on the time scales of subduction and exhumation, i.e., 1 to 10 Ma) pose an upper bound to the magnitude of stress as a function of temperature along the trajectory followed by the rock. Although the record of exhumed (U)HP metamorphic rocks may only be representative of specific types or evolutionary stages of subduction zones, for such cases it implies: (1) strongly localized deformation; (2) predominance of dissolution-precipitation creep and fluid-assisted granular flow in the shear zones, suggesting Newtonian behaviour; (3) low magnitude of differential stress; which (4) is on the order of the stress drop inferred for earthquakes; and (5) negligible shear heating. These findings are easily reconciled with exhumation by forced flow in a low viscosity subduction channel prior to collision, implying effective decoupling between the plates.
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Deformation Mechanisms, Rheology and Tectonics: Current Status and Future Perspectives
The motion and deformation of rocks are processes of fundamental importance in shaping the Earth, from outer crustal layers to the deep mantle. Reconstructions of the evolution of the Earth therefore require detailed knowledge of the geometry of deformation structures and their relative timing, of the motions leading to deformation structures and of the mechanisms governing these motions. This volume contains a collection of 22 papers on field, experimental and theoretical studies that add to our knowledge of these processes. They are a mixture of review papers oh selected topics in the field of structural geology and tectonics and papers on current issues and new techniques and are grouped into four themes:
The effect of fluids on deformation
The interpretation of microstructures and textures
Deformation mechanisms and rheology of crust and upper mantle minerals
Crust and lithosphere tectonics
The volume will appeal to researchers in the fields of structural geology and tectonophysics, both in academia and industry.