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Abstract:
How the Tibetan Plateau grew farther north from the India-Asia collision boundary has profound implications on the mechanics of continental deformation and accretion. The Hoh-Xil Basin in the northern Tibetan Plateau was once a foreland basin adjacent to the high-elevation proto-plateau until the Early Miocene and was rapidly uplifted since then. Here we collected 363 broadband seismic stations operated from 2007 to 2020, including 226 stations from five linear arrays mainly deployed in two north-south profiles across the core of the Hoh-Xil Basin with an average interstation distance of ~15 km. Based on Rayleigh wave signals extracted from ambient noise cross-correlations, we obtained more than 13000 dispersion curves and constructed a 3-D S-wave velocity (VS) model using measurements in 6–65 s periods by the direct inversion method. Our model shows significant lateral variations of VS in the crust and uppermost mantle from the southern to the northern Tibetan Plateau, which should reflect different melt fractions according to the theoretical seismic velocity-melt fraction relationship. We observe widespread partially molten crust in the northern Tibetan Plateau but only isolated pockets in the south manifested as low-VS anomalies in the middle-lower crust. The spatial correlation of these low-VS anomalies with strong uppermost mantle low-VS anomalies and young crust-/mantle-derived magmatism in the Hoh-Xil Basin suggests that the plateau grew through magmatic intrusion and accretion induced by the asthenospheric upwelling due to lithospheric mantle removal. These findings lead to implications for the role of delamination-driven magmatism in the continental crust growth in collision orogens.
