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Quantitative structural analyses and numerical modelling of ...

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ETG 6 - 2 SCHULMANN ET AL.: STRAIN DISTRIBUTIONthus allowing extrusion only in the vertical direction.Fossen <strong>and</strong> Tik<strong>of</strong>f [1998] suggested boundary conditionswhere zones <strong>of</strong> transpressive deformation are able to growthor shrink vertically as well as horizontally along strike.[5] Fossen <strong>and</strong> Tik<strong>of</strong>f [1993] defined two types <strong>of</strong> transpressionon the basis <strong>of</strong> the orientation <strong>of</strong> the instantaneousstretching axes: (1) pure-shear-dominated transpression inwhich v 1 <strong>and</strong> v 3 (eigenvectors <strong>of</strong> instantaneous straincorresponding to maximum <strong>and</strong> minimum elongation)define a vertical plane <strong>and</strong> the v 1 (lineation) is vertical,<strong>and</strong> (2) wrench-dominated transpression in which v 1 <strong>and</strong> v 3are horizontal, while the v 2 (intermediate eigenvector) isvertical. Pure-shear-dominated transpression operates whenthe angle between relative plate convergence direction <strong>and</strong>plate boundary is greater than 20° [Pinet <strong>and</strong> Cobbold,1992], <strong>and</strong> the main axis <strong>of</strong> finite strain is always vertical. Inwrench-dominated transpression acting at an angle <strong>of</strong> convergence(a) <strong>of</strong>

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