tailieunhanh - Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

Certain studies were excluded because of methodological flaws or inadequate descriptions. We excluded studies in which the predictions were made on different sets of individuals. To include such studies would have left open the possibility that one method proved superior as a result of operating on cases that were easier to predict. For example, in some studies we excluded comparisons in which the clinicians were allowed to use a “reserve judgment” category for which they made no prediction at all (not even a probability of the outcome in question intermediate between yes and no), but the actuary was. | ELSEVIER TECTONOPHYSICS Tectonophysics 296 1998 61-86 Rheological heterogeneity mechanical anisotropy and deformation of the continental lithosphere Alain Vauchez Andrea Tommasi Guilhem Barruol Laboratoire de Tectonophysique Universite de Montpellier II et CNRS UMR 5568 - cc049 F34095 Montpellier cedex 5 France Received 26 March 1998 accepted 22 June 1998 Abstract This paper aims to present an overview on the influence of rheological heterogeneity and mechanical anisotropy on the deformation of continents. After briefly recapping the concept of rheological stratification of the lithosphere we discuss two specific issues 1 as supported by a growing body of geophysical and geological observations crust mantle mechanical coupling is usually efficient especially beneath major transcurrent faults which probably crosscut the lithosphere and root within the sublithospheric mantle and 2 in most geodynamic environments mechanical properties of the mantle govern the tectonic behaviour of the lithosphere. Lateral rheological heterogeneity of the continental lithosphere may result from various sources with variations in geothermal gradient being the principal one. The oldest domains of continents the cratonic nuclei are characterized by a relatively cold thick and consequently stiff lithosphere. On the other hand rifting may also modify the thermal structure of the lithosphere. Depending on the relative stretching of the crust and upper mantle a stiff or a weak heterogeneity may develop. Observations from rift domains suggest that rifting usually results in a larger thinning of the lithospheric mantle than of the crust and therefore tends to generate a weak heterogeneity. Numerical models show that during continental collision the presence of both stiff and weak rheological heterogeneities significantly influences the large-scale deformation of the continental lithosphere. They especially favour the development of lithospheric-scale strike-slip faults which allow strain to be

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