The Lithospheric Structure of the Solonker Suture Zone and Adjacent Areas: Crustal Anisotropy Revealed by a High-Resolution Magnetotelluric Study

The closure of the Paleo-Asian Ocean along the Solonker Suture Zone (SSZ) during the Late Permian and Triassic represented the final stage in the formation of the Central Asian Orogenic Belt between the Siberian Craton and the North China Craton. In order to better understand the structure and formation of this ancient plate boundary, a high-resolution magnetotelluric (MT) profile was collected in 2010-2012 with both broadband and long-period MT data. Dimensionality analysis showed that a 2-D analysis was valid. Both 2-D isotropic and anisotropic resistivity models were derived from the joint inversion of MT and tipper data. The high-resolution mapping achieved in this study is due to the closely spaced MT stations (2-3km). The major south dipping conductive layer was detected beneath the SSZ and found to be electrically anisotropic with the highest conductivity in the down dip direction. This feature was interpreted as evidence for southward subduction forming the suture. Previous studies of electrical anisotropy in Paleoproterozoic orogens have reported electrical anisotropy with the maximum conductivity in the strike direction. The high conductivity has been interpreted as being due to graphite or sulfides concentrated in fold hinges. In contrast to these studies, the Solonker Suture conductor shows an enhanced conductivity in the dip direction. The difference between these situations could be explained if the Solonker Suture has the fold axes rotated by high strain into the strike direction. This would result in the highest conductivity being parallel to the dip direction.