Complex N-S variations in Moho depth and V (p)/V (s) ratio beneath the western Tibetan Plateau as revealed by receiver function analysis

Author:	Murodov, D., Zhao, J.M., Xu, Q., Liu, H.B., Pei, S.P.
Abstract:	We present herein detailed images of the Moho depth and V-p/V-s ratio along ANTILOPE-1 profile beneath the western Tibetan Plateau derived from receiver function analysis. Along the ANTILOPE-1 profile, a rapidly northward-dipping Moho extends from similar to 50 km below the Himalaya to similar to 80 km across the Indus-Yarlung suture, shallowing to similar to 66 km under the central Lhasa terrane. The Moho depth shows a dramatic increase from similar to 66 km north of the Bangong-Nujiang suture to similar to 93 km beneath central Qiangtang terrane where it reaches the maximum depth observed along this profile before steeply rising to similar to 73 km. We interpret both the 15 and 20 km offsets of Moho depth occurring beneath the central Lhasa and central Qiangtang terranes as being related to the northern frontiers of the decoupled underthrusting Indian lower crust and lithospheric mantle, respectively. The Moho remains at a depth of similar to 70 km with a slight undulation beneath the northern Qiangtang and Songpan-Ganzi terranes, and then abruptly shallows to similar to 45 km near the Altyn Tagh Fault. The similar to 25 km Moho offset observed at the conjunction of the Tarim Basin and the Altyn Tagh mountain range suggests that the crustal shortening is achieved by pure shear thickening without much underthrusting. The average crustal V-p/V-s ratio changes from 1.66 to 1.80 beneath the Himalaya, the Lhasa terrane and the Tarim Basin indicating a felsic-to-intermediate composition. However, higher V-p/V-s ratios between 1.76 and 1.83 (except for a few outlying low values) are found beneath the Qiangtang and Songpan-Ganzi terranes, which could be attributed to the joint effects of the more mafic composition and partial melt within the crust. The Moho depth and V-p/V-s ratio exhibit complex N-S variations along this profile, which can be attributed to the joint effects of Indian lower crust underthrusting, the low-velocity zone of the mid-upper crust, crustal shortening and thickening, and other involved dynamic mechanisms.
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Page number:	895-906
Issue:	2
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PubYear:	2018
Volume:	214
Publication name:	Geophysical Journal International
Abstract:	We present herein detailed images of the Moho depth and V-p/V-s ratio along ANTILOPE-1 profile beneath the western Tibetan Plateau derived from receiver function analysis. Along the ANTILOPE-1 profile, a rapidly northward-dipping Moho extends from similar to 50 km below the Himalaya to similar to 80 km across the Indus-Yarlung suture, shallowing to similar to 66 km under the central Lhasa terrane. The Moho depth shows a dramatic increase from similar to 66 km north of the Bangong-Nujiang suture to similar to 93 km beneath central Qiangtang terrane where it reaches the maximum depth observed along this profile before steeply rising to similar to 73 km. We interpret both the 15 and 20 km offsets of Moho depth occurring beneath the central Lhasa and central Qiangtang terranes as being related to the northern frontiers of the decoupled underthrusting Indian lower crust and lithospheric mantle, respectively. The Moho remains at a depth of similar to 70 km with a slight undulation beneath the northern Qiangtang and Songpan-Ganzi terranes, and then abruptly shallows to similar to 45 km near the Altyn Tagh Fault. The similar to 25 km Moho offset observed at the conjunction of the Tarim Basin and the Altyn Tagh mountain range suggests that the crustal shortening is achieved by pure shear thickening without much underthrusting. The average crustal V-p/V-s ratio changes from 1.66 to 1.80 beneath the Himalaya, the Lhasa terrane and the Tarim Basin indicating a felsic-to-intermediate composition. However, higher V-p/V-s ratios between 1.76 and 1.83 (except for a few outlying low values) are found beneath the Qiangtang and Songpan-Ganzi terranes, which could be attributed to the joint effects of the more mafic composition and partial melt within the crust. The Moho depth and V-p/V-s ratio exhibit complex N-S variations along this profile, which can be attributed to the joint effects of Indian lower crust underthrusting, the low-velocity zone of the mid-upper crust, crustal shortening and thickening, and other involved dynamic mechanisms.
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