Bounds on strain in large Tertiary shear zones of SE Asia from boudinage restoration
R. Lacassin, P. H. Leloup and P. Tapponnier
Laboratoire de Tectonique, Mécanique de la Lithosphère, U.R.A. 1093 CNRS, Institut de Physique du Globe de Paris, 4 place Jussieu, 75252, Paris Cédex 05, France
Received 13 September 1991; accepted 27 July 1992. ; Available online 31 March 2003.
Abstract
We have used surface-balanced restoration of stretched, boudinaged
layers to estimate minimum amounts of finite strain in the mylonitic
gneisses of the Oligo-Miocene Red River-Ailao Shan shear zone
(Yunnan, China) and of the Wang Chao shear zone (Thailand). The
layer-parallel extension values thus obtained range between 250
and 870%. We discuss how to use such extension values to place
bounds on amounts of finite shear strain in these large crustal
shear zones. Assuming simple shear, these values imply minimum
total and late shear strains of, respectively, 33 ± 6 and
7 ± 3 at several sites along the Red River-Ailao Shan shear
zone. For the Wang Chao shear zone a minimum shear strain of 7
± 4 is deduced. Assuming homogeneous shear would imply
that minimum strike-slip displacements along these two left-lateral
shear zones, which have been interpreted to result from the India-Asia
collision, have been of the order of 330 ± 60 km (Red River-Ailao
Shan) and 35 ± 20 km (Wang Chao).
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Insigths from Tertiary deformation of SE Asia. |