Radiolarian-based stratigraphic reconstruction along the western Yarlung-Tsangpo suture zone, southern Tibet, and its implication for Neo-Tethyan late-stage evolution

Mélange complexes and continental marginal deposits along suture zones can provide crucial insights into the subduction-accretion processes of oceanic lithosphere and continent-continent collisions. Herein, moderately to well-preserved Late Jurassic−Early Cretaceous and late Paleocene radiolarian assemblages, including 86 species within 52 genera, were identified in the Jiangmuna mélange and the adjacent Tethyan Himalayan sedimentary strata along the western Yarlung-Tsangpo suture zone, southern Tibet. Reconstruction of the ocean plate stratigraphy revealed that the Jiangmuna mélange represents the products of fragmentation and mixing of Early Jurassic−Late Cretaceous ocean plate materials originally accumulated in different portions of the central Neo-Tethyan domain. The bottom-up lithological transition and the southward-younger seamount system indicate that the Neo-Tethyan oceanic lithosphere was subducted northward beneath the Zhongba microterrane, and then the Jiangmuna mélange was accreted one unit after another along the southern margin of the Zhongba microterrane during the Late Cretaceous. The adjacent Tethyan Himalayan sedimentary strata were originally deposited in a continental slope-basin environment along the northern margin of the Indian plate since the Middle Jurassic. The occurrence of Selandian−Thanetian radiolarian assemblages implies that deep-water sedimentation persisted along the northern margin of the Indian plate until at least the late Paleocene. Our findings, combined with previously published data, indicate that the Neo-Tethys Ocean existed at least from the Early Jurassic to late Paleocene, and the Neo-Tethyan late-stage evolution involved at least two subduction-accretion systems along the southern margins of the Lhasa block and the Zhongba microterrane, respectively, prior to the two-stage India-Eurasia collision.