Lateral uniformity of India Plate strength over central and eastern Nepal

Abstract

The current understanding of the Himalayan lithosphere stems mostly from cross-sections through the range at the longitude of the Kathmandu Basin. In this paper we laterally extend the analyses of structures and rheology along the Nepal Himalayas between the Pokhara valley and the Arun river. We take advantage of available information and a new data set including gravity measurements and a receiver function profile. It appears that the geometry of the Moho inferred from seismological profiles and long-wavelength gravity anomalies does not exhibit major East-West variations within the 350-km-wide study area. Using thermomechanical modelling, we show that the northward deepening of the Moho observed along profiles perpendicular to the main thrust faults can be interpreted simply as the bending of a strong India Plate. This result suggests a gradual mechanical decoupling between the crust and the mantle, leading to a northward decrease of the effective elastic thickness of the Indian lithosphere from ∼75 km to ∼25 km beneath the Ganga Basin and the Tibetan Plateau, respectively. Our results also confirm (partially) eclogitized lower Indian crust beneath southern Tibet. At shorter wavelengths, the observed gravity profiles exhibit some small lateral variations that can be interpreted in terms of east-west variations of the thickness of subsurface geological structures such as the Ganga Basin and the Tethyan Sedimentary Sequence.

Imaging the Moho and the Main Himalayan Thrust in Western Nepal With Receiver Functions

“…In Western Nepal, the distance over which the Moho reaches its maximum depth differs from Central Nepal (Figure ; Nábělek et al, ): The gentler descent ends further north, north of the Higher Himalaya, at nearly 80‐km depth beneath southern Tibet (Xu et al, ). This may reflect a slightly different flexural rigidity of the India plate in Western Nepal compared to Central Nepal, although there is no significant difference in flexure West and East of our profile in Nepal as seen by gravity anomalies and numerical modeling (Berthet et al, ), unlike further toward NW India and to the Eastern Himalaya (Hammer et al, ; Hetényi, Cattin, et al, ; Lyon‐Caen & Molnar, ).…”

Late Neogene tectonically driven crustal exhumation of the Sikkim Himalaya: Insights from inversion of multithermochronologic data

“…Flexure is simulated as bending of a thin elastic plate and applied incrementally over each model time step. North of the MFT, the elastic effective thickness of the Indian plate inferred from Bouguer anomaly profile ranges between 35 and 25 km in eastern Nepal [ Berthet et al ., ] and 20 and 15 km in Bhutan [ Hammer et al ., ] accordingly, we use a fixed intermediate value of 20 km in Sikkim.…”

Along‐strike variations in the Himalayan orogenic wedge structure in Bhutan from ambient seismic noise tomography

“…Although the Himalayan orogen is traditionally considered to be highly cylindrical, with lithotectonic units and first‐order structures that can be followed along its entire strike, investigations over the past years point to significant along‐strike variations at the lithospheric scale. The expression of these variations is clearly seen in the surface relief [ Bookhagen and Burbank , ], gravity anomalies [ Berthet et al ., ; Hammer et al ., ; Hetényi et al ., ], foreland basin depth [ Burbank et al ., ], and sampled by several seismological experiments [e.g., Rai et al ., ; Monsalve et al ., ; Guo et al ., ; Huang et al ., ; Nabelek et al ., ; Caldwell et al ., ]. Deviations from cylindrical structure are also indicated in the upper crust by tectonic klippen and windows, like the pronounced Tista‐Rangit double‐window in Sikkim [e.g., Landry et al ., ] or the crystalline Kathmandu klippe in Central Nepal [ Stöcklin , ].…”