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Journal of the Geological Society

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Discussion on the role of the Red River shear zone, Yunnan and Vietnam, in the continental extrusion of SE Asia Journal, Vol. 163, 2006, 1025–1036

^{1 1} CNRS, UMR 5570, Université de Lyon, Université Claud Bernard Lyon1, Ecole Normale Supérieure de Lyon, Laboratoire de Science de la Terre, UMR 5570 CNRS, 2 rue Dubois, Bat géode, la Doua, 69622 Villeurbanne, France (e-mail: herve.leloup@univ-lyon1.fr)
^{2 2} Tectonique et Mécanique de la Lithosphère, Institut de Physique du Globe de Paris, and Université Paris 7, CNRS, Paris, France
^{3 3} Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK (e-mail: mike.searle@earth.ox.ac.uk)

The first 20% of the full text of this article appears below.

P. H. Leloup, P. Tapponnier & R. Lacassin write: In his recent paper, Searle (2006) acknowledges that the 1000 km long Ailao Shan–Red River shear zone is a large Miocene left-lateral shear zone, but speculates that left-lateral slip started after 21 Ma and claims that the total finite offset remains unknown. From this he concludes that continental extrusion was only a relatively minor tectonic factor during the India–Asia collision, as long argued by other workers (e.g. England & Houseman 1986; Cobbold & Davy 1988; Dewey et al. 1989; Houseman & England 1993). We summarize below the field and geochronological evidence that makes us maintain a viewpoint in better accordance with facts.

Timing of left-lateral shear along the Ailao Shan–Red River shear zone. The Ailao Shan–Red River shear zone is composed mostly of high-grade metamorphic rocks and deformed granitoids with ubiquitous evidence for left-lateral shear parallel to the belt (e.g. Tapponnier et al. 1986, 1990; Leloup et al. 1993, 1995, 2001). The crystallization of the granitoids has been dated between 22 and 35 Ma (Fig. 1d–f), for example by Schärer et al. (1990, 1994) and Zhang & Schärer (1999), leading those workers to propose that left-lateral shear started at least c. 35 Ma ago. In contrast, Searle (2006) claims that all the deformed granitoids found within the shear zone predate left-lateral shear and that their crystallization ages should thus be interpreted to provide an upper limit for the onset of deformation, rather than a lower limit, thus suggesting a maximum age of 21 Ma for this deformation. A clear understanding of the P–T history and in situ deformation history of the intrusions, as well as of their relationships with surrounding paragneisses, is fundamental for . . . [Full Text of this Article]