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

The 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. Plain Language Summary: Understanding the Earth's third pole necessitates knowing the onset of the India‐Asia collision. The Lhasa Block (LB) stood the southern extremity of Asia, and its pre‐collisional paleolatitude is thus crucial for dating the commencement of the collision. Our paleomagnetic and 40Ar/39Ar geochronologic investigation herein indicates a paleolatitude of ∼31.4°N for the LB around ∼53 Ma. Combined with the revised Late Cretaceous paleolatitude estimates, the LB was inferred at a paleolatitude of ∼24°N in the Late Cretaceous and then reached a present‐like location at ca. 53 Ma. This is supported by geologic records. Incorporating a reasonable estimate (∼1,000 km) for the northward extension of Greater India, our paleomagnetic reconstruction of the Neo‐Tethyan tectonic realm strongly supports a two‐stage collision scenario consisting of the ∼55 Ma intrao‐ceanic arc‐India collision followed by the final collision between the India‐arc assemblage and Asia at ∼36 and 31 Ma. Key Points: An updated primary thermal magnetic remanence in the ca. 53 Ma Pana Formation volcanic rocks was acquiredThe paleolatitude of the Lhasa Block ca. 53 Ma is indistinguishable with that expected from stable Eurasia, suggesting minimal crustal shortening since the early EoceneThe arc‐continental collision model is strongly suggested based on restoration on the northern extension of the Greater India [ABSTRACT FROM AUTHOR]