Direct evidence of active deformation in the eastern Indian oceanic plate


Geology, V. 26, No. 2, pp. 131-134.

Keywords: Wharton basin, strike-slip faulting, ninetyeast ridge, intraplate deformation


Christine Deplus - CNRS / Institut de Physique du Globe de Paris, case 89, 4 place Jussieu, 75252 Paris cedex 05, France

Michel Diament - Institut de Physique du Globe de Paris, case 89, 4 place Jussieu, 75252 Paris cedex 05, France

H�l�ne H�bert - Institut de Physique du Globe de Paris, case 89, 4 place Jussieu, 75252 Paris cedex 05, France

Guillaume Bertrand � Ecole Normale Sup�rieure, Laboratoire de G�ologie, 24 rue Lhomond, 75231, Paris cedex 05, France.

St�phane Dominguez - Laboratoire de G�ophysique et Tectonique, Universit� de Montpellier II, case 060, 4 place E. Bataillon, 34095 Montpellier cedex, France.

Jacques Dubois - Institut de Physique du Globe de Paris, case 89, 4 place Jussieu, 75252 Paris cedex 05, France

Jacques Malod - CNRS / Universit� de Bretagne Occidentale, 6 avenue Le Gorgeu, B.P. 452, 29275, Brest cedex, France.

Philippe Patriat - CNRS / Institut de Physique du Globe de Paris, case 89, 4 place Jussieu, 75252 Paris cedex 05, France

Bernard Pontoise - ORSTOM, UR14 Laboratoire de G�odynamique sous-marine, B.P. 48, 06230 Villefranche-sur-Mer, France.

Jean-Jacques Sibilla - Institut de Physique du Globe de Paris, case 89, 4 place Jussieu, 75252 Paris cedex 05, France



ABSTRACT


Conventional plate tectonics theory postulates that plates only deform on their boundaries. To the contrary, there is ample evidence of intraplate deformation in the equatorial Indian Ocean, west of the Ninetyeast aseismic ridge. Prior to this study, no direct evidence of deformation east of the Ninetyeast Ridge was available. We present the results of a multipurpose geophysical cruise showing that intraplate deformation also occurs in this area. Long, at least 1000 km, left-lateral north-south strike-slip faults are active and reactivate fossil fracture zones. This style of deformation is strikingly different from the east-west folds and reverse faults that affect the region west of the Ninetyeast Ridge. Contrasting processes of convergence at the northern plate boundaries can account for the two styles of deformation. West of the Ninetyeast Ridge there is a continent-continent collision, and east of the ridge oceanic lithosphere subducts along the Sumatra trench. The Ninetyeast aseismic ridge therefore appears to be a mechanical border separating two distinct deformed areas


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