The crustal structure of south central Mongolia using receiver functions

Abstract

The crustal thickness H and average crustal velocity ratio k (Vp/Vs) beneath south central Mongolia are investigated using the H-k stacking method based on teleseismic radial receiver functions. Our primary results reveal that the local crustal thickness varies from 38 to 46 km with an average value of 43 km. Thicker crust is found beneath the western Hentey Mountains, while thinner crust is located in the southern area of the Zuunbayan fault zone. The Bouguer gravity anomalies exhibit a strong correlation with the overall crustal thickness pattern throughout most of our study regime. Moreover, a new approach which integrates the Bouguer anomaly gradient and the receiver function-derived crustal thickness is adopted to calculate the density of the lower crust underneath central Mongolia. Fairly dense lower crust of approximately 3000 kg/m 3 is found in the Middle Gobi Desert. The measured crustal Vp/Vs ratio ranges from 1.68 to 1.83 with an average value of 1.74. Low Vp/Vs ratio is found beneath the western Hentey Mountains. In general, low Vp/Vs ratios correlate well with regions of quartz-rich crust and high heat flow. High Vp/Vs ratios occur in the Middle Gobi volcanic regions and the Mesozoic Southern Gobi Basin.

High‐Resolution Crustal and Uppermost Mantle Structure Beneath Central Mongolia From Rayleigh Waves and Receiver Functions

“…The estimated thickness values at this location, ∼42–44 km, are consistent with He et al. (2016)'s receiver function study.…”

Tomographic Pn Velocity and Anisotropy Structure in Mongolia and the Adjacent Regions

“…Thus, station delays larger than 1.0 s may reflect the crustal thickness variations when the mean crustal velocities in this study areas are confined between 6.2 and 6.5 km/s. Stations located in western Mongolia and China with thick crust have relatively positive station delays, while stations located in eastern Mongolia and China with thin crust have negative station delays, which are consistent with previous observations by receiver functions (He et al, ; Li et al, ).…”

“…Our results demonstrate obvious low velocities beneath Hangay Dome and the Hentey Mountains (Figure ), where there are either no or slight low velocity anomalies from the study of Wang, Niu, et al (). However, low crustal Vp / Vs ratios (He et al, ) and low Lg wave attenuation (He, Sandvol, et al, ), together with the lack of Cenozoic basalts observed beneath the western Hentey Mountains, comprehensively suggest that the crust of the western Hentey Mountains is not strongly affected by the hot mantle materials. Thus, the mechanisms of low Pn velocities observed beneath the Hentey Mountains are obviously different with those in Hangay Dome and the Sayan Range, where Cenozoic volcanism and basalts are widely scattered.…”

“…What is more, we delete the events in seismic clusters to avoid the rays traveling in one single direction. An average crustal thickness of 45 km for our initial 1D model is used (He et al, , ). The initial crustal and upper mantle velocities are set at 6.3 and 8.1 km/s, respectively.…”

“…Geodynamical evolution history of CAOB is still of great mystery. In recent years, numerous seismic tomography studies at different scales and resolutions have been carried out in Mongolia and the adjacent regions (He, Sandvol, et al, ; He et al, ; Li et al, ; Pan et al, ; Petit et al, ; Yu et al, ; Zhang, Wu, et al, ; Zhang et al, ; Zhao et al, ; Zorin et al, ). Among them, P and S wave velocity models (Bushenkova et al, ; Chen et al, ; Friederich, ; Gao, Davis, Liu, Slack, Zorin, Logatchev, et al, ; Petit et al, ; Zhang, Wu, et al, ; Zhao et al, ) and gravity models (Zorin et al, ) have revealed several low‐velocity zones in the upper mantle beneath Mongolia and the adjacent regions.…”