Three-dimensional ambient noise tomography across the Taiwan Strait: The structure of a magma-poor rifted margin

Abstract

Rifting along southeastern Eurasia in the Late Cenozoic led to the formation of a magma-poor rifted margin facing the South China Sea to the southeast and the Philippine Sea to the east. Further rifting along the outer part of the margin during the middle to late Miocene was accompanied by an extensive episode of intraplate flood volcanism that formed the Penghu Archipelago. Previous geophysical studies in the area of the strait have focused primarily on the shallow structures of the rift basins and the depth to the Moho. In this study we present the regional-scale 3-D S wave structure of the Taiwan Strait that is derived from a joint Chinese and Taiwanese 3-D ambient noise tomography study. The S wave model shows a thinning of the crust beneath the rift basins where, locally, thin high-velocity layers suggest the presence of intrusive bodies. The rift basin and the foreland basin along the west coast of Taiwan are imaged as low-velocity zones with thicknesses between 5 and 10 km and extending eastward beneath the Taiwan mountain belt. In the upper 10 km of the crust, the basaltic rocks of the Penghu Archipelago are imaged as a high-velocity zone that, with depth, becomes a relatively low-velocity zone. We interpret this low-velocity zone in the lower crust and upper mantle beneath the Penghu Archipelago to image a thermal anomaly related to the still cooling magma feeding system and the melt reservoir area that fed the flood basalts at the surface. Penghu Archipelago and its relationship to what is otherwise defined as a magma-poor rifted margin CHEN ET AL.AMBIENT TOMO ACROSS THE TAIWAN STRAIT 1782

3‐D Crustal Shear‐Wave Velocity Structure of the Taiwan Strait and Fujian, SE China, Revealed by Ambient Noise Tomography

“…The high‐velocity zone in the upper crust along the coast of Fujian, which is conspicuously distributed between the CL‐ZA fault zone and FLF (Figures and ), is also found in the results of Cai et al () and K. X. Chen et al (). The anomalously high velocity in the upper crust coincides well with the PDMB, which predominately consists of granites and amphibolite‐facies metamorphic rocks (W. S. Chen et al, ; Liu et al, ).…”

“…In this study, we utilize 2 years (2014–2015) of continuous seismic records from 88 permanent stations in the seismic network of the Earthquake Administration of Fujian Province (Data Management Centre of China National Seismic Network, ; X. F. Zheng et al, ) and 25 stations of the Broadband Array in Taiwan for Seismology (Institute of Earth Sciences, Academia Sinica, Taiwan, ) (Figure b). In addition, a few hundred phase‐velocity dispersion curves by K. X. Chen et al () extracted from 23 stations from the Broadband Array in Taiwan for Seismology, 6 stations from the Earthquake Administration of Fujian Province, and 16 SinoProbe stations are included to produce more accurate results.…”

“…It has been well known that continuous ambient seismic noise cross‐correlation between two stations can be used to retrieve empirical Green's functions (F. C. Lin et al, ; Shapiro & Campillo, ; Y. Yang et al, ; Yao et al, ). Surface‐wave dispersion data extracted from empirical Green's functions can be further inverted for shear‐wave velocity structures of the crust and upper mantle (e.g., K. X. Chen et al, ; Yao et al, ). Each time domain cross‐correlation function is obtained by cross‐correlating two vertical‐component noise data with a sampling rate of 5 Hz.…”

“…The Moho depth has been relatively well resolved in this region. Receiver functions (Ai et al, ; He et al, ), gravity data (Hsieh et al, ), and tomography with body waves (Kuo et al, ) and surface waves (K. X. Chen et al, ; Y. C. Huang, Yao, et al, ) have all been used to determine the Moho depth. The results have generally agreed that the Moho depth in the strait is shallower than 30 km.…”

“…However, the easternmost part of the island has very thin oceanic crust. In addition, K. X. Chen et al () used ambient noise tomography to invert for the shear‐wave velocity structure of the crust and uppermost mantle of the strait and Taiwan Island and indicated there may have been a cooling magma reservoir and feeding system in the deep crust and upper mantle beneath Penghu Island.…”