Tomographic evidence for a slab tear induced by fossil ridge subduction at Manila Trench, South China Sea

Abstract

A tomographic travel-time inversion has been applied to trace the subducted slab of the South China Sea (SCS) beneath the Manila Trench. The dataset, taken from the International Seismological Centre , is composed of 13,087 P-wave arrival times from 1401 regional earthquakes and 8834 from 1350 teleseismic events. The results image the different morphology of the subducted SCS slab as a high-velocity zone. The subducting angle of the slab varies along the trench: at 16°N and 16.5°N, the slab dips at a low angle (24°~32°) for 20-250 km depth and at a moderate angle (50°) for~250-400 km depth. At 17°N, the slab dips at a low angle (32°) to near 400 km depth, and at 17.5°N and 18°N the slabs are near vertical from 70~700 km depth, while at 20°N the high-velocity anomalies exhibit features from horizontal abruptly to near vertical, extending to 500 km depth. The dramatic steepening of the slab between 17°N and 17.5°N may indicate a slab tear, which is coincident with the axis of a fossil ridge within the SCS slab at around 17°N. In addition, low-velocity zones in the three profiles above 300 km depth may represent the formation of the slab window, induced by ridge subduction and slab tear, initiating upward mantle flow and resulting in the partial melting of the edge of the slab. The slab tear could explain the volcanic gap and geochemical difference between the extinct Miocene and Quaternary volcanoes in the Luzon Arc, the much higher heat flow around the fossil ridge, and the distribution of most of the adakites and the related porphyry Cu-Au deposits in the Luzon area. Based on the geometry and morphology of the subducted slab and certain assumptions, we calculate the initial time of ridge subduction, which implies that ridge subduction and slab tear possibly started at~8 Ma.

Western Northern Luzon Isotopic Evidence of Transition From Proto‐South China Sea to South China Sea Fossil Ridge Subduction

“…Fluids/melts derived from the subducted South China Sea terrigenous/pelagic sediments will not generate the Sr-Nd isotopic characteristics of the late Miocene-Pleistocene western Northern Luzon samples, which delineate a nearly vertical trend with the Amorong basalts overlapping with the Scarborough seamount basalts. This suggests contribution of Scarborough seamount basalts to the source, which is consistent with the geophysical observation that the Scarborough Seamount Chain is currently being subducted beneath western Northern Luzon-northern Bataan (~16 o N, Figure 1a; Pautot & Rangin, 1989;Fan et al, 2014;Li et al, 2004). This interpretation is supported by independent geochemical studies of the Black Mountain Complex, Baguio District.…”

Subduction of a buoyant plateau at the Manila Trench: Tomographic evidence and geodynamic implications

“…At 20°N (Figure c), the Eurasian Plate subducts initially along the Manila Trench to ∼250 km depth at a low angle of ∼25°, and then changes to a higher dip angle (∼75°) to ∼500 km depth, which is slightly different from the tomographic results by Fan et al . [], whose images show that the subducted Eurasian Plate exhibits a horizontal feature above 100 km depth, which may be caused by the poorer hypocentral locations of local earthquakes in that study. At 19°N (Figure d), the subducted Eurasian Plate extends down to ∼250 km depth with a dip angle of ∼25°.…”

“…At 17°N (Figure f), the image shows that the Eurasian Plate subducts to a depth of ∼350 km with a low angle of ∼32°. The low‐V zones in the two sections (the patch outlined in red in Figures e and f) possibly indicate a tear in the subducted Eurasian Plate along the axis of the fossil ridge within the South China Sea and the formation of a slab window [ Fan and Wu , ; Fan et al ., ].…”

“…One conspicuous feature in the bathymetric map is the collision between the trench with two bathymetric highs, including a fossil ridge and a buoyant plateau southwest of Taiwan (Figure ). The subduction of the fossil ridge in the South China Sea has been demonstrated by seismic tomography [ Fan et al ., ], whereas the subduction of the buoyant plateau, comprised of an extended to hyperextended continental crust, was revealed by seismic reflection and wide‐angle seismic data obtained by the TAIGER (Taiwan Integrated Geodynamics Research) project [e.g., Lester et al ., ; McIntosh et al ., ; Eakin et al ., ]. The subduction of the buoyant plateau is considered to be the origin of the Central Ranges in Taiwan [ McIntosh et al ., ].…”

Rates of Deep Continental Burial From Lu‐Hf Garnet Chronology and Zr‐in‐Rutile Thermometry on (Ultra)high‐Pressure Rocks

“…Subduction angle and convergence rates for the India‐Asia Collision Zone (IACZ) from Mencin et al (), Nábělek et al (), Steckler et al (), and van Hinsbergen et al (), and those for the Dabie‐Sulu Orogen (DSO) from Liu et al (). Slab angles and convergence velocities for modern subduction zones are from Brothers (), McCaffrey (), Schellart (), Gardi et al (), Green et al (), Reilinger et al (), Garcia et al (), Lange et al (), Contreras‐Reyes et al (), Fan et al (), and are summarized in the supporting information.…”