Less‐Well‐Developed Crustal Channel‐Flow in the Central Tibetan Plateau Revealed by Receiver Function and Surface Wave Joint Inversion

Abstract

A crustal channel‐flow model has been previously used to explain the formation of crustal extensional structures in the Tibetan Plateau. However, the existence of massive crustal channel‐flow in the central plateau is still controversial. To reveal the crustal S‐wave velocity structure with high vertical resolution, we conducted a joint inversion of receiver functions and surface wave dispersions from the 2‐D broadband seismic array SANDWICH deployed in the central plateau. Our results show a low‐velocity layer (LVL) in the middle‐lower crust beneath all stations. The minimum S‐wave velocity in each LVL is mostly within 3.0–3.4 km/s, which result in the maximum velocity reductions are less than 17.5%. It deduces a melt volume percentage (MVP) less than 7% even attributing all velocity reduction to partial melting of rocks. Our study suggests that there is not a high enough melt volume in central Tibet to develop crustal channel‐flow, which requires a larger MVP to decrease rock strength more than an order of magnitude. The formation of extensional structures in the central plateau may contribute to ductile deformation in the middle‐lower crust but not crustal channel‐flow.

Isolated Crustal Partial Melting in the Southern Tibetan Plateau From H‐κ‐c Method

“…These zones could potentially impede the development of crustal flow. In a word, we suggest a limited north-south present-day crustal flow across the LB within our study region, compatible with the inference by Dong et al (2020) and Nie et al (2023).…”

Different Formation Modes of the North–South‐Trending Rifts in Southern Tibet: Implications From Ambient Noise Tomography

“…For the average low Vs (3.2 km/s), we calculated that Vs/Vs0 is ∼0.94–0.86 within the LVL, which corresponds to melt fractions of ∼2.1%–5.4% (Caldwell et al., 2009; Watanabe, 1993), respectively. This means that ideal “crustal flow,” which requires a melt fraction greater than 7%, would have difficulty occurring beneath the PXR and TYR (Caldwell et al., 2009; Nie et al., 2023; Rosenberg & Handy, 2005). Recent seismic anisotropic studies (Bao et al., 2020; B. Zhang et al., 2023) also questioned the large scale crustal flow beneath Tibet.…”

“…Considering that large‐scale crustal flow is difficult to achieve (Bao et al., 2020; Nie et al., 2023; B. Zhang et al., 2023) and that the N–S‐trending rifts are perpendicular to the orogenic belt, the ideal crustal flow model and gravity collapse model may not explain the formation of the TYR and PXR. Nevertheless, the lower viscosity of the middle crust is likely to promote rifting within an extensional background (Bischoff & Flesch, 2018; Pang et al., 2018).…”

Fault Networks in Triaxial Tectonic Settings: Analog Modeling of Distributed Continental Extension With Lateral Shortening

“…Tapponnier & Molnar, 1976;Tapponnier et al, 1982). Geophysical studies suggest that in such settings, basal shearing can be induced by underthrusting of lithospheric mantle and viscous flow in the lower crust, generating shortening and extension (i.e., constriction) within the upper plate (Ellis, 1996;Merry et al, 2021;Nie et al, 2023;Tikoff et al, 2022;Yin & Taylor, 2011). The structural inventory in these regions is a manifold ranging from evenly-spaced conjugate strike-slip fault networks in central Tibet (Bendick & Flesch, 2007;Taylor et al, 2003; Yin & Taylor, 2011;Zuza et al, 2017) and central Anatolia (Emre et al, 2016) to more regular horst-and-graben systems in southern Tibet (Tapponnier et al, 1981;Woodruff et al, 2012) and western Anatolia (Figures 8a and 8b) (Emre et al, 2016;Jolivet et al, 2013).…”