Abstract
In the southern Tibetan plateau, which is considered to be the ongoing India–Eurasia continental collision zone, tracing of the Indian crustal front beneath Tibet is still controversial. We conducted deep subsurface electrical modeling in southern Tibet and discuss the geometry of the front of the Indian crust. Three areas along the Yarlung-Zangbo river zone for which previous magnetotelluric (MT) data are available were inverted independently using a three-dimensional MT inversion algorithm ModEM. Electrical horizontal slices at different depths and north–south oriented cross sections at different longitudes were obtained to provide a geoelectrical perspective for deep processes beneath the Tethyan Himalaya and Lhasa terrane. Horizontal slices at depths greater than − 15 km show that the upper crust is covered with resistive layers. Below a depth of − 20 km, discontinuous conductive distributions are primarily concentrated north of the Yarlung-Zangbo sutures (YZS) and could be imaged from mid- to lower crust. The results show that the maximum depth to which the resistive layers extend is over − 20 km, while the mid- to lower crustal conductive zones extend to depths greater than − 50 km. The results indicate that the conductive region in the mid- to lower crust can be imaged primarily from the YZS to south of the Bangong-Nujiang sutures in western Tibet and to ~ 31°N in eastern Tibet. The northern front of the conductive zones appears as an irregular barrier to the Indian crust from west to east. We suggest that a relatively less conductive subsurface in the northern portion of the barrier indicates a relatively cold and strong crust and that the front of the Indian crust might be halted in the south of the barrier. We suggest that the Indian crustal front varies from west to east and has at least reached: ~ 33.5°N at ~ 80°E, ~ 31°N at ~ 85°E, and ~ 30.5°N at ~ 87°E and ~ 92°E.
Highlights
As the largest and most recent orogenic plateau in the world, the Tibetan plateau is becoming one of the focuses of geoscience technique application and a natural laboratory to research global geodynamics and climate change
The results showed that the lowvelocity zone (LVZ) along the inclined portion of the Main Himalayan Thrust (MHT) indicates that the wet melting was induced by dehydration of the Indian lower crust, while the LVZ above the Indian lower crust was best explained by dehydration melting due to strain heating (Nabelek and Nabelek 2014)
The mid- to lower crust is imaged as conductive layers which were interpreted as ductile zones with partial melting enhanced by plates’ motion and/or dehydration
Summary
As the largest and most recent orogenic plateau in the world, the Tibetan plateau is becoming one of the focuses of geoscience technique application and a natural laboratory to research global geodynamics and climate change. The Himalaya and Lhasa terranes are considered to be the front area of the continental collision and the possibility of delamination and a ‘Moho doublet’ with the subduction of the Indian plate is generally agreed upon (Kind et al 2002; Nabelek and Nabelek 2014; Wittlinger et al 2009; Zhao et al 2011). We reprocessed previous MT data that were deployed in southern Tibet (Fig. 1) and obtained a three-dimensional (3D) electrical model to study deep structures and processes beneath the collision zone at the crustal scale. The Lhasa terrane, which is considered as an Andean-type active continental margin prior to the initial collision (Mo et al 2008; Yin and Harrison 2000), contains roughly E–W sedimentary strata and magmatic rocks (Zhao et al 2009). Nine BBMT stations trend roughly in E–W direction and were deployed in 2007. (2) B, 20 BBMT stations from line800 (Gyirong-Cogen profile) and 23 sites from line-900 (Tingri-Comai profile) that were deployed in 2001 and
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