The Mesozoic stratigraphic record of the southern Qiangtang basin in central Tibet records the evolution and closure of the Bangong‐Nujiang ocean to the south. The Jurassic succession includes Toarcian‐Aalenian shallow‐marine limestones (Quse Formation), Aalenian‐Bajocian feldspatho‐litho‐quartzose to feldspatho‐quartzo‐lithic sandstones (shallow‐marine Sewa Formation and deep‐sea Gaaco Formation), and Bathonian outer platform to shoal limestones (Buqu Formation). This succession is truncated by an angular unconformity, overlain by upper Bathonian to lower Callovian fan‐delta conglomerates and litho‐quartzose to quartzo‐lithic sandstones (Biluoco Formation) and Callovian shoal to outer platform limestones (Suowa Formation). Sandstone petrography coupled with detrital‐zircon U‐Pb and Hf isotope analysis indicate that the Sewa and Gaaco formations contain intermediate to felsic volcanic detritus and youngest detrital zircons (183–170 Ma) with εHf(t) ranging widely from +13 to −25, pointing to continental‐arc provenance from igneous rocks with mixed mantle and continental‐crust contributions. An arc‐trench system thus developed toward the end of the Early Jurassic, with the southern Qiangtang basin representing the fore‐arc basin. Above the angular unconformity, the Biluoco Formation documents a change to dominant sedimentary detritus including old detrital zircons (mainly >500 Ma ages in the lower part of the unit) with age spectra similar to those from Paleozoic strata in the central Qiangtang area. A major tectonic event with intense folding and thrusting thus took place in late Bathonian time (166 ± 1 Ma), when the Qiangtang block collided with another microcontinental block possibly the Lhasa block.

Located between the Bangong-Nujiang suture zone and the Qiangtang Block in central Tibet, the Najiangco area (~5 km to the north of Nima-Selingco) contains an Upper Jurassic-Lower Cretaceous sedimentary succession deposited during a period of marine regression. The youngest marine sedimentary unit in the Najiangco area is the Upper Jurassic Shamuluo Formation, which consists of sandstone, limestone, siltstone, and shale. Sedimentary facies analysis shows that tidal flat and subtidal lagoonal facies characterized the northern margin of the basin, while delta front and prodelta facies dominated the middle part, and carbonate shoal and patch reef facies prevailed along the southern margin. Provenance analysis, including petrographic modal analysis of sandstones and U-Pb dating of detrital zircons, shows that a recycled orogen in the central Qiangtang to the north of Najiangco area was the source of the sandstones in the Shamuluo Formation. Biostratigraphy and U-Pb zircon dating of a porphyritic granitoid dike (150.8 ± 1.9 Ma) indicate that the Shamuluo Formation was deposited during the Late Jurassic (Oxfordian to Kimmeridgian). During Middle Jurassic time, the southern Qiangtang Basin was dominated by shallow-marine environments. Later, during the Late Jurassic (Oxfordian to Kimmeridgian), the shallow-marine facies retreated to the southern margin of the basin. Combined with regional paleogeographic data from central Tibet, two 2 / 38 stages of southward retreat of the Qiangtang remnant sea, and three stages of topographic uplift of the Qiangtang Block can be recognized during late Middle Jurassic to Early Cretaceous time.

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Constraining the stepwise growth of the Tibetan Plateau in time and space is critical to test geodynamic models of subduction and continental collision, as well as environmental and climatic changes at the regional and global scale. The Lhasa block is a key region to unravel the early stages of Tibetan Plateau growth before the India-Asia collision. Stratigraphic, sedimentological, geochronological, and provenance analysis of the Jingzhushan Formation in the northern Lhasa block and of the Daxiong Formation in the central Lhasa block provide new information to reconstruct the paleogeographic evolution of the central part of the Tibetan Plateau during the Cretaceous. Sharply distinct from the underlying shallow-marine limestones, the over 1000-m-thick Jingzhushan and Daxiong formations mainly consist of conglomerates and coarse-grained sandstones deposited in alluvial-fan and braided-river systems. Both units were deposited during the early Late Cretaceous between ca. 93 and 87 Ma, as determined by geochronology of interstratified tuff layers, youngest ages of detrital zircons, and micropaleontological data from limestone pebbles. Clast composition, U-Pb ages and Hf isotopic signatures of detrital zircons, and paleocurrent data indicate that the Jingzhushan and Daxiong formations were derived from the same elevated source area located in the central-northern Lhasa block. These two parallel belts of coeval conglomerates record a major change in topography of the source region from a shallow seaway to a continental highland, implying initial topographic growth of an area over 80,000 km 2 wide named here the Northern Lhasaplano. Early Late Cretaceous topographic growth of the Northern Lhasaplano was associated with demise of seaways, development of thrust belts, and thickening of the lower crust. The same paleogeographic and paleotectonic changes were recorded earlier in the Northern Lhasaplano than in the Southern Lhasaplano, indicating progressive topographic growth from north to south across the Bangong-Nujiang suture zone and Lhasa tectonic domain during the Cretaceous.