Initial growth of the Northern Lhasaplano, Tibetan Plateau in the early Late Cretaceous (ca. 92 Ma)

Abstract

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.

Paleomagnetism of the Late Cretaceous Red Beds From the Far Western Lhasa Terrane: Inclination Discrepancy and Tectonic Implications

“…Furthermore, the Electron Spin Resonance (ESR) results and magnetostratigraphical dating show that the bottom ages of the Jingzhushan Formation in the Ritu area are ~92.0 ± 9.0 Ma and ~96 Ma, respectively (Li et al, 2016). This age is generally consistent with the age of the Jingzhushan Formation (~92 Ma) in the central northern LT as constrained by detrital zircon geochronology and micropaleontological data (Lai et al, 2019). Besides, according to the presence of sporopollen assemblage (such as Coptosporites, Leavigatosporites, Doltoidospora sp., Polypodiaceaesporites sp., Polypodiisporites sp., and Lygodiumsporites sp.…”

“…), the Jingzhushan Formation in the Nima area was assigned to the Late Cretaceous (Jia et al, 2007). Lithofacies and sedimentary features suggest that the Jingzhushan Formation was deposited in an alluvial‐fan and braided‐river environment (Lai et al, 2019).…”

Recognition of trench basins in collisional orogens: Insights from the Yarlung Zangbo suture zone in southern Tibet

“…During the Early Cretaceous, the Xigaze forearc basin was underfilled and detritus could not reach the trench. Only since~92 Ma, the uplift of the Lhasa block (Lai et al, 2019;Wang et al, 2020) generated larger volumes of sediments that rapidly filled the Xigaze forearc basin and could thus bypass the trench-slope break and eventually reach the trench where the Jiachala, Rongmawa, and Luogangcuo formations accumulated.…”

Quantitatively Tracking the Elevation of the Tibetan Plateau Since the Cretaceous: Insights From Whole‐Rock Sr/Y and La/Yb Ratios

“…Several models have been proposed for the Cenozoic uplift history of the TP, including synchronous uplift, northward stepwise uplift, incremental northward uplift, and differential uplift (England & Houseman, 1989; Law & Allen, 2020; Liu et al, 2016; Tapponnier et al, 2001). The pre‐Cenozoic uplift history of the TP has only been described qualitatively and there is little information available outside of the Lhasa terrane (DeCelles et al, 2007; Kapp, DeCelles, Gehrels, et al, 2007; Lai, Hu, Garzanti, Sun, et al, 2019). The Gangdese arc region was thought to be at a relatively low elevation during the Early Cretaceous and become the Lhasaplano during the late Late Cretaceous to Paleocene (Ding et al, 2014; Kapp, DeCelles, Leier, et al, 2007).…”

“…The Gangdese arc region was thought to be at a relatively low elevation during the Early Cretaceous and become the Lhasaplano during the late Late Cretaceous to Paleocene (Ding et al, 2014; Kapp, DeCelles, Leier, et al, 2007). Another protoplateau (Northern Lhasaplano) was proposed to be formed in the Northern and Central Lhasa terranes with a width >160 km during the early Late Cretaceous (Lai, Hu, Garzanti, Sun, et al, 2019).…”