Upper mantle discontinuity structure beneath eastern and southeastern Tibet: New constraints on the Tengchong intraplate volcano and signatures of detached lithosphere under the western Yangtze Craton

Abstract

We present new constraints on the upper mantle transition zone structure beneath eastern and southeastern Tibet based on P wave receiver functions for a large broadband data set from two very dense seismic arrays. A clear depression of both the 410 km and 660 km discontinuities is detected west of the Red River fault relative to the east. The correlated topographic variations across the Red River fault are indicative of temperature changes in the upper mantle above the transition zone, which suggests that the fault is a deep‐rooted structure that penetrates into the upper mantle and separates Indochina from South China. West of the Red River fault, the transition zone thickness under the Tengchong volcano is found to be normal compared to the global average. This strongly suggests that the intraplate volcano may originate from slab tearing of the eastward subducting Indian plate at shallow depths in the upper mantle rather than from dehydration of a flattened plate within the transition zone. Our results further show that the 660 km discontinuity is significantly depressed under the western Yangtze Craton and that the transition zone therefore thickens by up to 20 km. This thickening is suggestive of lowered temperatures associated with a remnant of detached lithosphere in response to overlying asthenospheric escape flow in and around the western Yangtze Craton. In addition, we find that the transition zone thickness beneath much of the Sichuan Basin is similar to the global average.

Mantle transition zone discontinuities beneath the Indochina Peninsula: Implications for slab subduction and mantle upwelling

“…A numerical simulation study suggests that this upwelling is part of a return flow system induced by actively sinking slab segments and is capable of producing decompression melting in the upper mantle [ Faccenna et al , ]. A similar mechanism is involved in a recent RF study to explain low upper mantle velocities and Cenozoic volcanism in southwestern China, directly to the north of our study area [ Zhang et al , ].…”

P and S Wave Tomography Beneath the SE Tibetan Plateau: Evidence for Lithospheric Delamination

“…One mechanism suggests that the Tengchong volcano is directly driven by the active subduction of the Indian plate, resulting from slab dehydration and induced mantle convection, like many volcanoes in subduction zones as well as the Changbai intraplate volcano in northeast China (Huang et al, , Huang, Wang, Xu, Wang, et al, ; Lei et al, , ; Zhao & Tian, ; Lei & Zhao, ). Another mechanism argues for the contribution of mantle flow from beneath the subducting Indian slab (Zhang et al, ); a slab window created by slab break‐off is necessary in this case. However, the present results show a continuous Indian slab in the upper mantle (Figure S7).…”

“…Beneath the eastern Himalayan syntaxis and Burma, high‐velocity bodies, with active seismicity in the top 200‐km depth (Engdahl et al, ; Ni et al, ), extend down to 400‐km depth (Huang, Zhao, et al, ; Li et al, ; Pesicek et al, ; Wei et al, ), representing the subducting Indian plate. The depressed 660‐km velocity discontinuity (D660) implies that cold material has probably sunk into the mantle transition zone (MTZ; Xu et al, ; Yu et al, ; Zhang et al, ). Beneath the Sichuan basin, the core of the stable Yangtze craton, high‐velocity anomalies are also predominant in the upper mantle (Huang & Zhao, ; Huang, Wang, Xu, Wang, et al, ; Lei & Zhao, ; Tao et al, ; Wei et al, ; Zhang et al, ).…”

“…The Tengchong volcano is an active volcano; its last eruption occurred in 1609. The origin of the Cenozoic volcano is still in debate (Lei et al, ; Zhang et al, ). Shear‐wave splitting measurements argue for significant asthenospheric deformation there (Huang, Wang, Xu, Ding, et al, ), resulting from the extruded asthenospheric flow from the high plateau (Huang, Zhao, et al, ).…”

Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes

“…On the basis of plate tectonic reconstructions, Neo‐Tethyan Oceanic crust was subducted into the mantle beneath Tengchong in the Cretaceous (Hafkenscheid et al, ; Van der Voo et al, ). Recently, high‐resolution seismic and tomographic data showed that a broad low‐velocity zone extends down to the 410 km discontinuity with a high‐velocity anomaly region at ~660 km (e.g., Lei et al, , ; R. Zhang et al, ; Wei et al, ). The high‐velocity region might represent a cold and stagnant slab, probably the Neo‐Tethyan Oceanic slab (Figure ; Zhou et al, ).…”