# Kinematic strain localization

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State: Serval

Version: author

State: Serval

Version: author

Serval ID

serval:BIB_2D203F2D14BB

Type

**Article**: article from journal or magazin.

Collection

Publications

Fund

Title

Kinematic strain localization

Journal

Earth and Planetary Science Letters

ISSN-L

0012-821X

Publication state

Published

Issued date

2010

Peer-reviewed

Oui

Volume

300

Pages

197-204

Language

english

Abstract

Deformation within a steady-state compressional orogen, i.e., where

tectonic accretion is, on geological time scales, balanced by surface

erosion, can best be described by a stationary velocity field.

Instantaneous deformation results from spatial gradients in the velocity

field, whereas total accumulated strain results from the integration of

this instantaneous deformation along material paths following the flow

lines defined by the velocity field. We have synthesized the net strain

distributions for rocks exposed at the surface of such an orogenic

system using simple, linear velocity fields corresponding to (a) simple

shear within a dipping shear zone and (b) pure vertical shear. In both

cases we demonstrate the development of surface patterns of finite

strain accumulation that do not reflect the geometry of the assumed

velocity field in a simple manner. Large gradients in finite strain

arise as a consequence of the geographic variation in particle residence

time imposed by the surface boundary, even for the limiting case where

no instantaneous strain gradient exists. Such patterns of deformation

are often recognised in exhumed orogenic systems, but have commonly been

assumed to reflect more complex velocity fields resulting from

nonlinear, localizing crustal rheologies. We therefore demonstrate that

caution should be exercised in interpreting observed strain patterns

because a proportion of the observed strain localization must be

attributed to this purely kinematic (or geometric) effect - and this

proportion may be significant in many systems. Such kinematic effects

should be quantified, and subtracted from observed strain distributions

before they are used to infer the rheological behavior of crustal rocks.

We also suggest that in a simple shear (thrust) setting, kinematic

strain localization may in fact nucleate strain softening on the side of

the deforming region that is stable or fixed with respect to the Earth's

surface and thus be responsible for the asymmetry that characterizes the

large majority of thrust systems. (C) 2010 Published by Elsevier B.V.

tectonic accretion is, on geological time scales, balanced by surface

erosion, can best be described by a stationary velocity field.

Instantaneous deformation results from spatial gradients in the velocity

field, whereas total accumulated strain results from the integration of

this instantaneous deformation along material paths following the flow

lines defined by the velocity field. We have synthesized the net strain

distributions for rocks exposed at the surface of such an orogenic

system using simple, linear velocity fields corresponding to (a) simple

shear within a dipping shear zone and (b) pure vertical shear. In both

cases we demonstrate the development of surface patterns of finite

strain accumulation that do not reflect the geometry of the assumed

velocity field in a simple manner. Large gradients in finite strain

arise as a consequence of the geographic variation in particle residence

time imposed by the surface boundary, even for the limiting case where

no instantaneous strain gradient exists. Such patterns of deformation

are often recognised in exhumed orogenic systems, but have commonly been

assumed to reflect more complex velocity fields resulting from

nonlinear, localizing crustal rheologies. We therefore demonstrate that

caution should be exercised in interpreting observed strain patterns

because a proportion of the observed strain localization must be

attributed to this purely kinematic (or geometric) effect - and this

proportion may be significant in many systems. Such kinematic effects

should be quantified, and subtracted from observed strain distributions

before they are used to infer the rheological behavior of crustal rocks.

We also suggest that in a simple shear (thrust) setting, kinematic

strain localization may in fact nucleate strain softening on the side of

the deforming region that is stable or fixed with respect to the Earth's

surface and thus be responsible for the asymmetry that characterizes the

large majority of thrust systems. (C) 2010 Published by Elsevier B.V.

Create date

07/10/2012 19:46

Last modification date

03/03/2018 14:28