New Insights Into the Heterogeneity of the Lithosphere‐Asthenosphere System Beneath South China From Teleseismic Body‐Wave Attenuation

Abstract

The long tectonic history of South China includes Precambrian amalgamation and several Phanerozoic episodes of lithospheric modification. It formed via the collision of the Yangtze and Cathaysia blocks (Figure 1a) along the Jiangshan-Shaoxing fault in the Neoproterozoic (e.g. Z. X. Li et al., 2002). After amalgamation, three important tectonothermal events occurred in South China, namely the Wuyi-Yunkai (Early Paleozoic), Indosinian (Triassic), and Yanshanian (Jurassic-Cretaceous) events (Y. Wang et al., 2013b), often called "movements" in Chinese literature. Each event led to extensive deformation and magmatism across South China. The lingering effects of these events on lithospheric structure have been investigated by many geophysical studies, including models of P wave velocity structure from active seismic profiles (Y.

Evidence for Stress Localization Caused by Lithospheric Heterogeneity From Seismic Attenuation

“…Byrnes and Bezada (2020) observed a high Δt* anomaly in the Salton Trough, a low‐lying and flat basin, while Deng et al. (2021) observed a local minimum in Δt* in the rugged mountainous ranges of the Chuan‐Dian Block in southwestern China.…”

“…The hypothesis that deformation is localized in part by variations in the strength of the upper mantle predicts that this pattern of apparent attenuation could be extrapolated to much of the Rocky Mountains, where the Laramide style deformation is ubiquitous, and other areas showing Laramide-style deformation such as the Sierras Pampeanas (e.g., Ramos et al, 1986). Patterns of this sort have been observed with seismic attenuation in the Iberian Pennsiula (Bezada, 2017) and in Southern China (Deng et al, 2021) where basins have remained undeformed during diffuse deformation, but such a pattern has not to our knowledge been previously observed within a recent oregony. If pre-existing crustal structure alone can localize deformation, then one would not expect the observed correlation between uplift and lithospheric thickness in these regions.…”

Variable Depths of Magma Genesis in the North China Craton and Central Asian Orogenic Belt Inferred From Teleseismic P Wave Attenuation

“…We showed above that Qp values beneath this region are approximately the same as in globally average asthenosphere. In contrast, lower Qp values are observed beneath volcanic regions where small‐scale convection or subduction driven melting occurs (e.g., Abers et al., 2014; Byrnes & Bezada, 2020; Byrnes et al., 2019; Pozgay et al., 2009; Wei & Wiens, 2020), and markedly lower Qp values are inferred near the Hainan plume in South China (Y. F. Deng et al., 2021). We show Section 4 in Supporting Information S1 that while lower Qp values in the HA regions are estimated if a t * reference value in LA1 of −0.1 s is assumed, a value at the lower end of the uncertainty of the observations, the estimated Qp values are lower but still similar to the globally average asthenosphere (Figure S4 in Supporting Information S1).…”

“…Since the 2-D 𝐴𝐴 Δ𝑡𝑡 * model only gives the path-integrated attenuation, and given that our data are not sufficient to constrain a 3-D tomographic model for Qp, we explore several hypothetical scenarios to estimate plausible values of Qp using a procedure similar to that applied in Byrnes et al (2019) and Y. F. Deng et al (2021). Qp values are estimated assuming a vertically propagating P wave from 200 km depth to the surface.…”

Teleseismic Attenuation, Temperature, and Melt of the Upper Mantle in the Alaska Subduction Zone

“…However, the attenuation is not just low in the basins but also slightly lower than on either side (e.g., Figures 3 and 4), suggesting additional factors. In China and Iberia‐Morocco, very low attenuation has been attributed to cold and rigid lithosphere underlying basins, a potential factor for basins that form atop undeforming continental blocks (Bezada, 2017; Deng et al., 2021). However, in our case the apparent attenuation is markedly less (more negative Δt* ) than adjacent parts of the cold subducting plate to the southeast, with no lithospheric boundary in between, and the sharpness of the horizontal gradient in observed Δt * over <20 km (Figure 8) makes it unlikely that deep‐seated lithospheric structure can be responsible for this phenomenon.…”