Late Cretaceous to Late Eocene Exhumation in the Nima Area, Central Tibet: Implications for Development of Low Relief Topography of the Tibetan Plateau

Abstract

Much of the interior of the Tibetan Plateau is characterized by internal drainage, low relief topography, and high altitude. How and when this landscape formed is controversial. In this study, we use new zircon U‐Pb data and low‐temperature thermochronological data (apatite and zircon [U‐Th/He], apatite fission track [AFT]) from the Late Cretaceous to Cenozoic Nima Basin sedimentary rocks and Xiabie granite in the adjacent Muggar Thrust hanging wall (part of the regional Shiquanhe‐Gaize‐Amdo thrust system), to determine the paleodrainage and timing of exhumation in the region. Individual AHe and ZHe cooling ages range from 9 to 60 Ma and 58 to 118 Ma, and the AFT ages range from 30 to 90 Ma. The thermal history derived from the Northern Nima Basin sediments and Xiabie granite require a period of exhumation between 70 and 40 Ma in the thrust fault hanging wall, and 40 and 30 Ma in the Nima Basin. Across the region, this event was followed by low rates of exhumation and the deposition of locally sourced sediment, lacustrine, and evaporitic deposits that are indicative of an internal drainage system. We suggest that the exhumation event is associated with development of thrust‐elevated relief that may have disrupted the drainage network favoring the development of an endorheic system. This system, sediment accumulation, and/or post‐30 Ma tectonic quiescence led to the generation of low relief topography.

Cenozoic low temperature cooling history of the eastern Lhasa terrane: Implications for high-relief topography of external drainage area in the southern Tibetan Plateau

“…Although LTT studies suggest that the interior plateau (the northern Lhasa terrane) has experienced intense uplift and exhumation during $80-45 Ma (Hetzel et al, 2011;Rohrmann et al 2012;Haider et al, 2013), it was still a topographic depression in the Paleogene, and did not reach its present elevation (>4 km) until $29-26 Ma as revealed by paleoaltimetry evidence (Rowley and Currie, 2006;DeCelles et al, 2007;Fang et al, 2020;Xiong et al, 2022). The low-relief surface was established at the same time as the northern Lhasa terrane reached its high elevation (Han et al, 2019;Li et al, 2022;Xue et al, 2022). In contrast, the southern Lhasa terrane reached its present elevation (>4 km) around 58-47 Ma ago, much earlier than the northern Lhasa terrane (Ding et al, 2014;Ingalls et al, 2018).…”

“…The significant change in the Lhasa terrane is that the northern Lhasa terrane uplifted to the same elevation as the southern Lhasa terrane, and the lowrelief landscape was developed as well (Fig. 6b; Han et al, 2019;Ding et al, 2022;Li et al, 2022;Xue et al, 2022). Since then, the northern Lhasa terrane has resided in an arid environment and experienced long-term tectonic quiescence.…”

“…Thus, it makes sense that the >30 Ma LTT ages are widely preserved in the internal drainage area (Fig. 5; Han et al, 2019;Li et al, 2022;Xue et al, 2022).…”

“…Except for the difference in present precipitation, the internal drainage area has been in an arid climatic condition since the late Oligocene ($26 Ma), estimated by the evaporitic lacustrine and eolian dune-field deposits and their carbon and oxygen isotopic data (DeCelles et al, 2007). An arid environment is usually characterized by less intensive chemical weathering and surface erosion, which tends to facilitate the development of a low-relief topography (Fielding et al, 1994;Xue et al, 2022). Whereas in the external drainage areas, the environment is relatively humid and several large rivers developed, causing rapid incision of the southern and eastern Tibetan Plateau (Fig.…”

“…The surface of this depression was uplifted to its present elevation (>4.0 km) around $29-26 Ma ago, resulting in the formation of the regional protoplateau (Rowley and Currie, 2006;DeCelles et al, 2007;Fang et al, 2020;Su et al, 2020;Ding et al, 2022;Xiong et al, 2022). Contemporaneously, the low-relief landscape of the depression also developed as indicated by low-temperature thermochronological data and sedimentary provenance analyses, due to mantle flow or tectonic quiescence in an arid environment (Han et al, 2019;Li et al, 2022;Xue et al, 2022).…”