Lithospheric and upper mantle structure of the northeastern Tibetan Plateau

Abstract

We use receiver functions calculated for data collected by the INDEPTH‐IV seismic array to image the three‐dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern Tibet. Our results indicate an average crustal thickness of 65 to 70 km in northern Tibet. In addition, we observe a 20 km Moho offset beneath the northern margin of the Kunlun Mountains, a 10 km Moho offset across the Jinsha River Suture and gently northward dipping Moho beneath the Qaidam Basin. A region in the central Qiangtang Terrane with higher than normal crustal Vp/Vs ratio of ∼1.83 can be the result of the Eocene magmatic event. In the Qiangtang Terrane, we observe a significant lithospheric mantle discontinuity beneath the Bangong‐Nujiang Suture at 80 km depth which dips ∼10° to the north, reaching ∼120 km depth. We interpret this feature as either a piece of Lhasa Terrane or remnant oceanic slab underthrust below northern Tibet. We detect a ∼20 km depression of the 660‐km discontinuity in the mantle transition zone beneath the northern Lhasa Terrane in central Tibet, which suggests this phase transition has been influenced by a dense and/or cold oceanic slab. A modest ∼10 km depression of the 410‐km discontinuity located beneath the northern Qiangtang Terrane may be the result of localized warm upwelling associated with small‐scale convection induced by the penetration of the sinking Indian continental lithosphere into the transition zone beneath the central Tibetan Plateau.

Collaborative Research: High-Resolution Seismic Velocity and Attenuation Models of Western China

“…Furthermore, we estimated a crustal thickness value for all 72 stations by choosing the center of the large positive velocity gradient at the base of the crust. We found that by choosing the center of the velocity gradient we obtained results roughly consistent with Han et al, 2012. If we chose the base or beginning we obtained generally unrealistic crustal thickness values.…”

“…We compared different velocity models using independent techniques to see which portions of the models are common to all of our models. We used the receiver function work of Han et al (2012) and surface wave phase velocities of Ceylan et al (2013) combined with the global group velocities from Pasyanos (2010) by applying the joint inversion method of Julia, et al (2000). We used Rayleigh wave phase velocities obtained from the two plane wave method and receiver functions calculated using the method of Liggoria and Ammon, 1999.…”

Crustal Velocity Structure of the Northeastern Tibetan Plateau from Ambient Noise Surface-Wave Tomography and Its Tectonic Implications

“…Based on their model, in the northeastern plateau margin with a gentle topography gradient, the weak mid-tolower crustal materials could escape through the SongpanGanzi terrane toward the southwestern Ordos platform. Our results show that a mid-to-lower crustal LVZ has been observed beneath the northern Qilian orogen, with the highest topography and a thickened crust (∼60 km; Yue et al, 2012) compared to its surrounding regions. However, it has not been found beneath the southern Qilian orogen.…”

“…Many studies have been performed in the Tibetan plateau, but most of the geophysical studies of the Tibetan crust and mantle structure to date have focused on the southern Kind et al, 1996;Nelson et al, 1996;Huang et al, 2000;Wei et al, 2001;Wang et al, 2003;Unsworth et al, 2005;Yao et al, 2008;Guo et al, 2009), central (Owens and Zandt, 1997;Kind et al, 2002;Tilmann et al, 2003), and eastern Tibetan plateau , with the primary objectives of understanding the continental collision process and the intrusion of the crustal and mantle materials from the Indian plate into the Eurasian plate. In comparison to other parts of the plateau, fewer seismic investigations have been done in the northeastern Tibetan plateau (e.g., Wittlinger et al, 1996;Zhu and Helmberger, 1998;Vergne et al, 2002Vergne et al, , 2003Karplus et al, 2011Karplus et al, , 2013Yue et al, 2012), which either are localized along linear profiles or focused on the velocity discontinuity structure. In our previous study (Li et al, 2012), we determined that the lowvelocity zone (LVZ) terminated around the east Kunlun fault (KLF) in the northeastern Tibetan plateau.…”

Crustal and Upper Mantle Density Structure Beneath the Qinghai-Tibet Plateau and Surrounding Areas Derived from EGM2008 Geoid Anomalies

“…The structures of the crust and the upper mantle in Tibet have obvious zonal characteristics and inhomogeneous distributions of the lower velocity in the crust and the higher velocity in upper mantle [24]. Weak zones occur in the upper crust in the Himalayas, in the middle crust in southern Lhasa, in the middle and lower crust in northern Lhasa, and in the middle and lower crust in Qiangtang and Songpan-Ganzi [25][26][27]. The Indian crust collides with the Tarim Basin at 80 • E and reaches the Bangong Nujiang Suture (BNS) belt at 88 • E (in the west at 90 • E) [11].…”