Igneous Activity and Structural Development of the Mianhua Terrace, Offshore North Taiwan

Abstract

Using bathymetric and multichannel seismic (MCS) data, we explored the volcanic influence on the bathymetric and stratigraphic features of the Mianhua Terrace. The Mianhua Terrace occupies the marine counterpart of the Northern Taiwan Volcanic Zone (NTVZ) along the collapsed Taiwan orogenic wedge and is dominated by post-collisional magmatism and extensional structures. The bathymetric data showed several semicircular-shaped features near the shelf break. The MCS profiles showed that the Pleistocene unconformity buried beneath the Mianhua Terrace is partly difficult to observe due to seafloor multiples, suggesting that the seafloor is dominated by physically hard lithology, probably volcanic lavas. We interpreted the high-amplitude reflectors and their projected seafloor relief as intrusive sills and associated extrusive edifice. Similarly, we interpreted high-amplitude reflectors in the vicinity of normal faults as intrusive sills emplaced and facilitated by fault structures. A volcanic or hydrothermal mound was also recognized. We propose that the Mianhua Terrace is a breached ramp in a transfer zone between the tips of two successive normal faults along the shelf break. Once the fault tips reactivate and extend toward each other, the Mianhua Terrace may continue to collapse, leading to catastrophic volcanic or associated hydrothermal events.

Post-collisional and volcanic features of the Late Miocene-Pleistocene foreland area, northern offshore Taiwan

“…the Pengjia Islet, Mianhu Islet, and Huaping Islet (Wang et al 1999). Additionally, the identified submarine volcanic features are currently increasing (Hsiao et al, 1998;Tsai et al, 2017;Chang et al, 2021). It began to form at 2.8 Ma, and was previously considered as the westernmost branch of the Ryukyu volcanic arc for it is calc-alkalie andesite similar to those observed in convergent setting (Chen 1990).…”

“…Among these submarine valley and canyons, Keelung Sea Valley runs parallel to the coastline off northern Taiwan and defines the Keelung Shelf to the north. The western branch of the Mianhua Canyon (Hereafter MHCWB; Chang et al, 2021) around the Mianhua Islet and Huaping Islet indented about 120 km into the shelfbreak, showing a great distance of indention far beyond other canyons and could be considered as the most striking bathymetry feature on the shelf area (Fig 1 and 2; Song et al 2000).…”

The Huapinghsu Channel/Mienhua Canyon System as a Sediment Conduit Transporting Sediments From Offshore North Taiwan to the Southern Okinawa Trough

“…The areas surrounding the SOT are characterized not only by active tectonics but also by frequent typhoons and earthquakes (Hsu et al, 2004;Huh et al, 2004;Liang et al, 2019). Submarine slides and mass-wasting features are also observed in this region (Tsai et al, 2018;Chang et al, 2021).…”

“…Submarine sea valleys, channels, and canyons offshore northeastern Taiwan have been known for more than 40 years (Wang and Hilde, 1973;Boggs et al, 1979;Kimura, 1983;Marsset et al, 1987;Song and Chang, 1993;Yu and Hong, 1993;Song et al, 2000;Chang et al, 2021), but their morphologies, sedimentary processes, sediment dispersals, and evolution have not been fully investigated. Few are well understood as data acquired by modern marine geophysical and geological techniques have been insufficient.…”