Is South-eastward Crustal Flow Possible around East Himalayan Syntax? - New Insights from SINOPROBE Magnetotellurics Array Data

Abstract:

The south-eastward expansion of Tibet plateau in eastern Tibet is considered a key process for understanding the large scale uplift and crustal thickening without significant concomitant crustal shortening. However, the geodynamic processes creating this iconic process is still unclear and hotly debated. Two popular geodynamic models, namely crustal flow at mid-to-lower crustal depths and coherent deformation between the crust and lithospheric mantle, are commonly appealed to as the expansion’s driving mechanism. However, neither of these mechanisms is able to reconcile all of the abundant geological and geophysical data. In this study we present a three-dimensional (3D) geo-electrical model, derived from SINOPROBE magnetotelluric (MT) array data, which reveals the geo-electrical and rheological structure in southeast Tibet that brings new insights into the region. Instead of continuous NW-SE conductive channels proposed in previous two-dimensional (2D) MT studies, a large-scale N-S directed resistive structure is revealed to disconnect the conductors from the crust to the upper mantle, arguing against the model of south-eastward (downslope) channel flow. Furthermore, distinct NNE directed conductive anomalies, which are perpendicular to the surface structures, are identified in the mid-to-lower crust. We interpret these anomalies as distributed NNE oriented crustal flow channels, which might cause the azimuthal clockwise extension around East Himalayan Syntax and partly contributed to the south-eastward expansion of eastern Tibet.