Exhumation of serpentinized peridotite in the northern Manila subduction zone inferred from forward gravity modeling

Abstract

The Taiwan Integrated Geodynamic Research program (TAIGER) collected two wide‐angle and reflection seismic transects across the northern Manila subduction zone that provide constraints on the seismic velocity structure of the crust. Two‐dimensional gravity modeling along these two transects shows a significant, relatively high density (3.12 and 3.02 g/cm3) in the fore‐arc region, at the interface between the subducting Eurasian Plate and the accretionary prism in front of the Luzon arc on the overriding Philippine Sea Plate. The anomalous density in this zone is higher than that in the fore‐arc crust and the accretionary prism but lower than that in mantle. Numerous geophysical and geological data, together with numerical models, have indicated that serpentinization of the fore‐arc mantle is both expected and observed. Serpentinization of mantle rocks can dramatically reduce their seismic velocity and therefore their seismic velocity in a density to velocity conversion. Therefore, the source of the high‐density material could be serpentinized fore‐arc mantle, with serpentinization caused by the dehydration of the subducting Eurasian Plate. We interpret that positive buoyancy combined with weak plate coupling forces in the northern Manila subduction zone is resulting in this serpentinized fore‐arc mantle peridotite being exhumed.

Variations in the crustal structure and strength of plate coupling along the Ryukyu subduction zone

“…To determine H m , the lithospheric density model is needed. We applied a 2-D gravity modeling technique to establish the subsurface density model (e.g., Doo et al 2015b;. To reduce the nonunique problem, the seismic velocity structure is crucial and necessary for 2-D gravity modeling processing.…”

“…If the synthetic anomaly could not adequately fit the observed gravity data (Sandwell et al 2014), we slightly adjusted the densities (within a reasonable range) until the synthetic anomaly was fitted to the observed gravity anomaly. For details on the process of forward gravity modeling, readers are referred to the literature (Doo et al 2015b;. Readers may be concerned about the nonunique problem of 2-D gravity modeling, P-wave seismic velocity models could provide good constraints on subsurface structural geometry and density information that help to greatly reduce this problem.…”

Deep crustal structure in the Taiwan–Ryukyu arc–trench system junction area: New constraints from gravity modelling

“…We adjusted the densities and layer geometry until the synthetic gravity anomaly can fit the observed gravity data well. For details on the process of forward gravity modelling, readers are referred to the literatures (Doo et al., 2015, 2016). Although the results of gravity modelling are nonunique, Van Avendonk et al., (2014, 2016) provided constraints on the P‐wave velocity structure of the crust that help to reduce this problem.…”

“…Due to the resolution problems, some velocity images are not clear in deep parts in the forearc region and eastern Taiwan. Based on the P‐wave velocity models, along four transects (T1, T2, T2933 and T4A), using 2‐D forward gravity modelling, Doo et al., (2015), Doo et al., (2016) identified a significant deep structural feature, the uplifted serpentinised mantle material, at depths between 15 and 35 km. Their results indicate that this low‐density structural feature could extend northward from the northern Manila Trench to eastern Taiwan.…”