Two-station measurement of Rayleigh-wave phase velocities for the Huatung basin, the westernmost Philippine Sea, with OBS: implications for regional tectonics

Abstract

S U M M A R YA broad-band ocean-bottom seismometer (OBS) deployed ∼180 km east of Taiwan provides a first glimpse into the upper mantle beneath the westernmost section of the Philippine Sea or the Huatung basin (HB). We measured interstation phase velocities of Rayleigh waves between the OBS and stations on the eastern coast of Taiwan. The phase velocities show smooth variations from 3.8 to 3.9 km s −1 for periods of 25-40 s. In this short period range, phase velocities are comparable to those characterizing the 15-30 Ma Parece-Vela basin of the Philippine Sea. Modelling of the finite-frequency effect proves the validity of the measurement for the average HB. The shear-wave velocity models inverted from the 25 to 40 s dispersion show a velocity at lithospheric depths about 0.1 km s −1 lower than that of the west Philippine Sea, which agrees with the age effect derived from the Pacific pure-path model. Inversions incorporating the less reliable data above 40 s yield a shear velocity <4.0 km s −1 below 150 km, an unrealistic value even for a hotspot plume environment. The seismological evidence, together with the correlation in seafloor depth, suggests that the HB and the Parece-Vela basin may have a similar age. This is at odds with the previous geochronological study suggesting an early-Cretaceous age for the HB. Thermal rejuvenation of the lithosphere was examined as a potential solution to reconciling the two age models.

Philippine Sea Plate inception, evolution, and consumption with special emphasis on the early stages of Izu-Bonin-Mariana subduction

“…The age of this small basin is highly controversial. Estimates vary from 131 to 119 Ma (Deschamps et al 2000) to 52-43 Ma for the northern part and Early Cretaceous for the southern part (Sibuet et al 2002), to 44-33 Ma (Hilde and Lee, 1984), 42-33 Ma (Doo et al 2015), or even ∼ 30-15 Ma (Kuo et al 2009). Further details and an interesting discussion about this controversy are available in Eakin et al (2015).…”

Age and tectonic evolution of the northwest corner of the West Philippine Basin

“…Using the same approach, Sibuet et al (2002) suggested that the HB was formed between C20 and C23 (51-43 Ma). Kuo et al (2009) measured phase velocities of Rayleigh-wave between OBS (broad-band ocean-bottom seismometer) and stations on the eastern coast of Taiwan and proposed that the characteristic of the phase velocities of the HB is comparable to the 15-30 Ma Parece-Vela basin. Hsu et al (1998) also suggests the oceanic crust west of the GR is younger than in the east.…”

Strain modes within the forearc, arc and back-arc domains in the Izu (Japan) and Taiwan arc-continent collisional settings

“…Regarding the origin of the Huatung Basin situated in the backside of the arc, many interpretations have been given including an Eocene part of the West Philippine Basin (Hilde and Lee, 1984), an Early Cretaceous trapped piece of an old oceanic basin (Deschamps et al, 2000), a composite back-arc basin with an old (Mesozoic ?) part in the south and an Eocene part in the north (Sibuet et al, 2002) or an Oligo-Miocene oceanic basin (Kuo et al, 2009). Since Hickey-Vargas et al (2008) found an Indian MORB-OIB Hf-Nd isotopic signature and Pb isotope ratios intermediate between Indian and Pacific MORB in the mantle source of the gabbros dredged in the Huatung Basin, it likely corresponds to a trapped piece of early Cretaceous oceanic crust produced at a ridge overlying an Indian-type mantle as proposed by Deschamps et al (2000).…”