Late Cenozoic long-distance eastward growth of the Tibetan Plateau: Insights from underappreciated layer-parallel shortening strain in the Central Sichuan Basin, South China

The extent of eastward growth of the Tibetan Plateau and deformation of the Sichuan Basin remain controversial, primarily due to the lack of direct evidence for Cenozoic deformation within the Central Sichuan Basin. This study presents anisotropy of magnetic susceptibility (AMS) data from an ∼210-km-long transect across the Central Sichuan Basin to unravel penetrative layer-parallel shortening (LPS) strain. Our results delineate a distinct structural zonation where an ∼110-km-wide western incipient deformational belt with NW-SE LPS is separated from an ∼10-km-wide eastern belt with both NW-SE and NE-SW LPS by an ∼74-km-wide central undeformed belt. This zonation reveals that late Cenozoic eastward plateau growth has propagated far beyond the frontal Longquan Shan fault, penetrating ∼110 km into the Central Sichuan Basin as widespread LPS. Conversely, the narrow eastern belt likely records late Mesozoic orogenic events. We attribute this long-distance propagation to enhanced slip along a shallow Triassic décollement, driven by substantial topographic and sedimentary loading coupled with a low strain rate in the Longmen Shan. This penetrative strain accommodates an estimated ∼24 km of previously unrecognized upper-crustal shortening, confirming LPS as a major contributor to Cenozoic basin deformation. The central undeformed belt defines the eastern limit of this upper-crustal shortening, signifying that late Cenozoic rapid exhumation of the Eastern Sichuan Basin likely resulted from tectonic uplift via strain accumulation along a midcrustal décollement and enhanced climate-driven erosion. Our findings highlight the crucial roles of upper-crustal penetrative strain, midcrustal strain transfer, and surface processes in shaping the eastern Tibetan Plateau and Sichuan Basin.