The Electrical Structure of the Tibetan-Himalayan Orogen
Abstract
The Tibetan Plateau is the type location for the study of continent-continent collision. During the period 1992-2001 the INDEPTH project collected comprehensive, high quality geophysical and geological data across the entire north-south extent of the Tibetan plateau. This project was developed in large part through the perseverance, insight and efforts of Doug Nelson. While the early phase was focussed on seismic reflection acquisition, Doug Nelson was largely responsible for the inclusion of other geophysical techniques during phases II and III of INDEPTH. A key part of this diversification was the inclusion of magnetotelluric (MT) exploration during INDEPTH-II in 1995. Over four field seasons (1995-2001), MT data were collected across the entire plateau, including each of the major tectonic features of the plateau. Previous presentations have focussed on relatively local structures based on an initial analysis of the MT data. In this presentation, a more comprehensive analysis will be presented, and which uses TE, TM and vertical magnetic field data. MT data collected in Ladakh and Nepal by other researchers will also be included. Key features that the MT surveys have shown include: (1) A high conductivity layer at a depth of 15-20 km that is present over the entire plateau. This layer extends both north-south (from Himalaya to the Kunlun Shan) and east-west (at least 78-92 degrees E) and is concluded to be due to a combination of partial melting and aqueous fluids. (2) In the Qiangtang and Songpan Ganze terranes of northern Tibet, this layer is underlain by an upper mantle with a relatively low resistivity (10-20 ohm-m). This is incompatible with whole scale underthrusting of Asian lithosphere. (3) In southern Tibet the conductive layer has a higher conductance, and it is thus more difficult to image the electrical structure of the underlying upper mantle. However, very long period data at some MT stations give evidence that the upper mantle is relatively resistive.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.S61D..03U
- Keywords:
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- 7218 Lithosphere and upper mantle;
- 8102 Continental contractional orogenic belts;
- 8110 Continental tectonics: general (0905)