Tomography of the southern Taiwan subduction zone and possible emplacement of crustal rocks into the forearc mantle

Cheng, Win-Bin; Hsu, Shu Kun; Chang, Chien-Hsin

doi:10.1016/j.gloplacha.2012.01.003

Cited by 11 publications

(5 citation statements)

References 56 publications

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“…The seismically opaque zone is of a similar width (∼60 km) to the serpentinized zone in the Cascadian forearc and at most other Pacific Rim subduction zones (Bostock et al 2002;Brocher et al 2003;Hyndman & Peacock 2003). This is also in-keeping with observations from other Pacific Rim subduction zones where the Moho is either inverted, attenuated or absent due to serpentinization (Bostock et al 2002;Brocher et al 2003;Oakley et al 2008;Stern 2011;Cheng et al 2012). Serpentinization of the mantle wedge is produced by dewatering of subducted sediment and oceanic crust, and may contribute to a blurring of the boundary between crust and mantle (Brocher et al 2003) and a combined reduction in lower crust and upper mantle velocity may occur (Fig.…”

Section: Collision Zonesupporting

confidence: 81%

The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin

Prada¹,

Sallarès²,

Ranero

et al. 2015

Geophys. J. Int.

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S U M M A R YNew marine geophysical data recorded across the Tonga-Kermadec subduction zone are used to image deformation and seismic velocity structures of the forearc and Pacific Plate where the Louisville Ridge seamount chain subducts. Due to the obliquity of the Louisville Ridge to the trench and the fast 128 mm yr −1 south-southwest migration of the ridge-trench collision zone, post-, current and pre-seamount subduction deformation can be investigated between 23• S and 28• S. We combine our interpretations from the collision zone with previous results from the post-and pre-collision zones to define the along-arc variation in deformation due to seamount subduction. In the pre-collision zone the lower-trench slope is steep, the mid-trench slope has ∼3-km-thick stratified sediments and gravitational collapse of the trench slope is associated with basal erosion by subducting horst and graben structures on the Pacific Plate. This collapse indicates that tectonic erosion is a normal process affecting this generally sediment starved subduction system. In the collision zone the trench-slope decreases compared to the north and south, and rotation of the forearc is manifest as a steep plate boundary fault and arcward dipping sediment in a 12-km-wide, ∼2-km-deep mid-slope basin. A ∼3 km step increase in depth of the middle and lower crustal isovelocity contours below the basin indicates the extent of crustal deformation on the trench slope. At the leading edge of the overriding plate, upper crustal P-wave velocities are ∼4.0 km s −1 and indicate the trench fill material is of seamount origin. Osbourn Seamount on the outer rise has extensional faulting on its western slope and mass wasting of the seamount provides the low V p material to the trench. In the post-collision zone to the north, the trench slope is smooth, the trench is deep, and the crystalline crust thins at the leading edge of the overriding plate where V p is low, ∼5.5 km s −1 . These characteristics are attributed to a greater degree of extensional collapse of the forearc in the wake of seamount subduction. The northern end of a seismic gap lies at the transition from the smooth lowertrench slope of the post-collision zone, to the block faulted and elevated lower-trench slope in the collision zone, suggesting a causative link between the collapse of the forearc and seismogenesis. Along the forearc, the transient effects of a north-to-south progression of ridge subduction are preserved in the geomorphology, whereas longer-term effects may be recorded in the ∼80 km offset in trench strike at the collision zone itself.

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Section: Collision Zonesupporting

confidence: 81%

The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin

Prada¹,

Sallarès²,

Ranero

et al. 2015

Geophys. J. Int.

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“…With the density to P wave relationship of Brocher [], thus, we can then use the velocity reduction expected for serpentinized peridotite [e.g., Christensen , ] to speculate that the degree of serpentinization in these transects could be 13–17% and 23–30%, respectively. These values are in keeping with those of Cheng et al [] who use Poisson's ratio to estimate the percentage of serpentine in fore‐arc mantle in the southeastern Taiwan. Farther north, where arc‐continent collision is in progress, a tectonic mélange in eastern Taiwan contains a variety of exhumed rocks including serpentinized mantle [e.g., Liou , ], providing clear evidence that this process was active in the Manila subduction zone.…”

Section: Discussionsupporting

confidence: 86%

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

Doo

Kuo-Chen

et al. 2015

Geophysical Research Letters

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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.

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“…Some of the ~7.0 km/s P wave seismic velocities at ~30 km depth beneath the east coast of Taiwan (Figure ) could represent a portion of the Luzon Forearc mantle that is ~30% serpentinized, which would have a density of 3100 kg/m 3 [ Christensen , ]. A recent seismic tomography study of southern Taiwan shows P wave seismic velocities lower than 7.0 km/s beneath the Luzon Forearc crust here [ Cheng et al ., ], which makes it likely that the mantle wedge was hydrated farther north as well, and that serpentinites form a fraction of the crustal root of the Taiwan mountain belt beneath the suture of the Eurasian and Philippine Sea Plates.…”

Section: Discussionmentioning

confidence: 99%

Deep crustal structure of an arc‐continent collision: Constraints from seismic traveltimes in central Taiwan and the Philippine Sea

et al. 2014

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The collision of continental crust of the Eurasian Plate with the overriding Luzon Arc in centralTaiwan has led to compression, uplift, and exhumation of rocks that were originally part of the Chinese rifted margin. Though the kinematics of the fold-thrust belt on the west side of the orogen has been described in detail, the style of deformation in the lower crust beneath Taiwan is still not well understood. In addition, the fate of the Luzon Arc and Forearc in the collision is also not clear. Compressional wave arrival times from active-source and earthquake seismic data from the Taiwan Integrated Geodynamic Research program constrain the seismic velocity structure of the lithosphere along transect T5, an east-west corridor in central Taiwan. The results of our analysis indicate that the continental crust of the Eurasian margin forms a broad crustal root beneath central Taiwan, possibly with a thickness of 55 km. Compressional seismic velocities beneath the Central Range of Taiwan are as low as 5.5 km/s at 25 km depth, whereas P wave seismic velocities in the middle crust on the eastern flank of the Taiwan mountain belt average 6.5-7.0 km/s. This suggests that the incoming sediments and upper crust of the Eurasian Plate are buried to midcrustal depth in the western flank of the orogen before they are exhumed in the Central Range. To the east, the Luzon Arc and Forearc are deformed beneath the Coastal Range of central Taiwan. Fragments of the rifted margin of the South China Sea that were accreted in the early stages of the collision form a new backstop that controls the exhumation of Eurasian strata to the west in this evolving mountain belt.

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Tomography of the southern Taiwan subduction zone and possible emplacement of crustal rocks into the forearc mantle

Cited by 11 publications

References 56 publications

The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin

The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin

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

Deep crustal structure of an arc‐continent collision: Constraints from seismic traveltimes in central Taiwan and the Philippine Sea

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