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

Abstract

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.

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…Its continuation toward the Longitudinal Valley fault is not backed by any data [99]. [98] suspect a steeply dipping broken off slab of forearc oceanic crust causing the deep position of the Moho, and [111] fill the gap towards the Longitudinal Fault with a Eurasian mantle wedge. In any case the Longitudinal Fault is a deep reaching plate boundary with an important strike-slip component.…”

“…Given the large displacement along the Shuangtung thrust which splays off the Shuilikeng thrust, and the potential connection with the basal detachment in the Western Foothills, it seems likely that the Shuilikang thrust reaches deep down as indicated in Figure 11A. The area between the Shuilikeng thrust and the Lishan fault is characterized by enhanced seismic activity reaching down to a depth of 30 km [98,109,110], a fact that also points to a deep-reaching fault.…”

“…The arc-continent collision started at ~6.5 Ma [98] and resulted in a mountain belt that started growing between 5 to 4 Ma ( [99] and references therein). Recent seismicity suggests that the mountain belt is still growing at the present.…”

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…Its continuation toward the Longitudinal Valley fault is not backed by any data [106]. [105] suspect a steeply dipping broken off slab of forearc oceanic crust causing the deep position of the Moho, and [118] fill the gap towards the Longitudinal Fault with a Eurasian mantle wedge. In any case the Longitudinal Fault is a deep reaching plate boundary with an important strike-slip component.…”

“…Given the large displacement along the Shuangtung thrust which splays off the Shuilikeng thrust, and the potential connection with the basal detachment in the Western Foothills, it seems likely that the Shuilikeng thrust reaches deep down as indicated in Figure 11A. The area between the Shuilikeng thrust and the Lishan fault is characterized by enhanced seismic activity reaching down to a depth of 30 km [105,116,117], a fact that also points to a deep-reaching fault.…”