High-resolution lithospheric V s structure of the Ordos Block from dense-array ambient noise tomography: implications for reactivation

SUMMARY The far-field impact of Tibetan Plateau (TP) expansion on cratonic blocks remains enigmatic. We address this for the Ordos Block (OB) by constructing a high-resolution 3-D shear-wave velocity model using ambient noise tomography from an unprecedented dense seismic array (461 stations). Our model reveals: (1) NE-trending high-velocity anomalies at 10–25 km depth correlating with crustal magnetic signatures, providing seismic evidence for late Archean amalgamation of microblocks (Jining, Ordos, Xuchang, Xuhuai); (2) TP-induced reactivation manifesting as southwestern OB crustal thickening (50 km) with a high-velocity lower crustal layer (≥4.0 km s−1; 100 km wide, 10 km thick), attributed to TP lower crustal underthrusting beyond the plateau margin (35.5°–37.5°N), facilitating >200 km strain transfer into the OB interior; (3) Incipient rifting dynamics in the Daihai Rift, where upper-crustal high-Vs (preserved rigidity) overlies mid-lower crust/uppermost mantle low-Vs anomalies (mantle-sourced thermal modification), indicating early-stage rifting driven by combined Pacific plate retreat and TP far-field stresses; (4) Craton-wide segmentation across a fundamental 37.5°N lithospheric boundary demarcating mantle upwelling/crust–mantle interaction (north) from passive TP push-dominated deformation (south). These findings redefine the OB as a strain-partitioned system, where lithospheric heritage controls differential response to plate-boundary forces.