Crustal structure of the India-Asia collision zone, southern Tibet, from INDEPTH MT investigations

Project INDEPTH was initiated in 1992 to develop a better understanding of the deep structure and mechanics of the Himalaya-Tibet region, and magnetotelluric surveying was added during INDEPTH Phase II in 1995. Broadband and long period data were acquired in 1995 along a N-S transect crossing the India-Asia collision zone, the Yarlung-Zangbo suture, at ∼90°E longitude. However, these data failed to penetrate to the deep crustal and mantle depths due to low solar activity, and the presence of the thick conductive crust. Deep crustal and upper mantle information is key to test the model of subcretion to southern Tibet by the stiff Indian mantle lid. In order to try to obtain such information, and to test along-strike variability of the Yarlung-Zangbo suture zone, a magnetotelluric experiment was performed in 2001 roughly along longitude 92°E, containing an ultra-long period component. MT data were acquired at 28 locations along the new profile, with long period data at 15 of these, and ultra-long period data at five of these 15. Initial comparisons of the models generated from the 1996 and 2001 datasets indicate little variation in electrical conductivity structure along-strike.