Lateral Variations of Moho Depth and Average Crustal Properties Across the Taiwan Orogen From H‐V Stacking of P and S Receiver Functions

Abstract

AbstractThe complexity of the young Taiwan orogen mainly resulting from arc‐continent collision is manifold. As the Moho and crustal properties are crucial to unravel the still‐debated orogenic models, we adopt a H‐V stacking method jointly utilizing P and S receiver functions for simultaneously reliable determination of crustal thickness and average P‐ and S‐wave velocity, their ratio (Vp/Vs), and bulk sound speed (Vb) beneath 50 stations in Taiwan and offshore islands. Results indicate the Moho is inclined from ∼20 km in the north and west coastal areas to ∼47 km in the midwest of the Central Range (CR), and abruptly elevated >25 km at the eastern edge of the CR and adjacent collision suture zone. The uplifted Moho along with exclusively high Vp/Vs (2.1) suggest the subducted Eurasian crust may have been exhumed and compositionally modified by the accreted ophiolite complex of oceanic affinity during forearc basin closure. Our Moho mostly lies in the depths of the sharpest positive velocity gradient, a few to a dozen kilometers shallower than the Vp = 7.5 km/s isosurface assumed in the tomographic models. The unusually thin crust (∼20 km) with high Vp/Vs (1.9–2.0) is observed in the northern Taiwan volcanic zone, plausibly attributed to the post‐orogenic extensional thinning and induced melting in the sublithospheric mantle producing magmatic fluids trapped in the crust. Moreover, Vb apparently decreases from the coasts to the middle CR coinciding with the thickest crust, implying the crust under the central mountain range is more compressible and easily deformed/thickened by ongoing collisional compression.