New 40Ar/39Ar Dating and Paleomagnetism of the Pana Formation Rocks From the Linzhou Basin, Lhasa Block: Implications for the India‐Asia Collision

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AbstractThe India‐Asia collision onset and cessation of the Neo‐Tethyan oceanic subduction are pivotal for understanding the collision processes, Tibetan Plateau uplift and global climate change, yet they remain hotly debated. The mostly cited ∼60–50 Ma initial collision age would require a ca. 20 Ma delay of the orogenic responses in Asia. Besides, the majority of the Cretaceous and Paleogene paleomagnetic data from the Lhasa Block (LB) indicates a “Greater” and “Quiescent” Asia prior to the India‐Asia collision, conflicting with the widely observed latest Cretaceous intense deformation within the block. To address these paradoxes, we present new paleomagnetic results on the Pana Formation volcanic rocks from the Linzhou basin, southern LB, with 40Ar/39Ar dating results indicating emplacement around ∼53 Ma. Combined with previous paleomagnetic results, the updated mean ChRM direction indicates the LB at 31.4°N (28.9–33.9°N) in the early Eocene. This indicates a minimal amount of crustal shortening (1.2 ± 3.8° or 0.9 ± 3.8°) in the northern Plateau since the early Eocene, and a substantial N‐S distance of 1,880 ± 420 km between the Indian and Asian leading margins at that time. Reassessed paleomagnetic data from LB, in conjunction with current knowledge on the original size of Greater India, fit well with a two‐stage collision model. This model suggests a ∼55 Ma collision between India and an intra‐oceanic arc, followed by a ∼34 Ma final collision between India and Asia, aligning well with the collision‐related responses in the plateau.