From sea level to high elevation in 15 million years:Uplift history of the northern Tibetan Plateau margin in the Altun Shan

Abstract

Approximately 1300 m of Oligocene-Miocene clastic strata are exposed along the Miran River in the southeastern Tarim basin, where the adjacent Altun Shan form the topographic escarpment of the northern Tibetan Plateau. The sedimentary section is faulted against Proterozoic rocks of the Altun Shan in the footwall of the south-dipping, oblique reverse Northern Altyn Tagh fault. Oligocene-Lower Miocene strata consist of fine-grained rocks that record low-gradient depositional systems. Mid-Miocene and younger rocks consist of coarse conglomerate, derived from the Altun Shan and deposited by high-gradient depositional systems. The change to coarse, high-gradient depositional systems with detrital source areas coincident with the modern Miran River drainage is interpreted to mark the onset of uplift of the Altun Shan on the Northern Altyn Tagh fault and its erosional exhumation. The age of the change from pre-orogenic to synorogenic sedimentation is constrained by a foraminifera assemblage at the base of the conglomeratic section that includes Early-Middle Miocene planktonic foraminifera. This interpretation is also supported by apatite fission track and (U-Th)/He ages and thermal models that indicate rapid Miocene cooling, and hence, rapid exhumation of the Altun Shan. In addition to defining the age of the synorogenic section, the foraminifera assemblage contains planktonic taxa, indicating a connection to open marine waters, and benthic assemblages typical of brackish to near-sea level paleobathymetry. Thus, micropaleontologic evidence demonstrates that the Miran River locality, now at ϳ1400 m elevation, was at sea level approximately 15 million years ago. Thus, in addition to constraining the age of surface uplift and exhumation of the Altun Shan, the principal mountain range of the Tibetan Plateau in this region, as ϳ15 to 16 Ma, the foraminifera assemblage indicates that the SE Tarim basin, off the northern edge of the plateau, had an average surface uplift rate of nearly 100 m/m.y. for the past 15 million years. These results suggest that shortening in the Altun Shan and uplift of the range significantly post-dated the initiation of large-scale strike-slip on the Altyn Tagh fault, and that regional surface uplift mechanisms operated in the Tarim basin, beyond the margins of the Tibetan Plateau.

Seismic reflection data support episodic and simultaneous growth of the Tibetan Plateau since 25 Myr

“…The intensity contrast between the two episodes likely indicates that, during the first episode, the front of the proto-West Kunlun orogen at the edge of the plateau was further south from its present position, and it only propagated to its present position during the second episode. Our results therefore suggest that the northwestern edge of the Tibetan Plateau underwent two major episodes of propagation since B23 Myr: one at B23-12 Myr and the other since 5 Myr, leading to the region being uplifted from near sea-level 10 to the present height of 46,000 m (B5,000 m relative to the Tarim foreland basin). Such a two-episode uplift history is comparable to the two episodes of rapid cooling events recorded along the eastern margin of the Tibetan Plateau 3 .…”

“…The Tarim Block to the north has an Archaean to Proterozoic crystalline basement. Shallow-marine limestone and calcareous shale were deposited for much of the time from the Cambrian until at least B25 Myr, and could be as late as B15 Myr 10,21 . Sequence stratigraphic boundaries and their ages within the study region are based on the fossil record and lateral correlations with type sections of the Tarim basin 22,23 .…”

“…Work along the West Kunlun Range at the northwest margin of the Tibetan Plateau, however, has led to diverse conclusions, ranging from three-episode uplift 4 to a single post-4.5 Myr uplift 5 . Estimations for the initiation of uplift range from B46 Myr to B3 Myr (refs 4-13) based on a variety of approaches: B46 Myr based on stratigraphic and sedimentary analysis 6 ; B37 À 30 Myr based on chronology and lithostratigraphy 2,7,8 ; B25-15 Myr based on fission track dating 9 , thermochronological results 10 and Nd isotopic analysis of dust 11 and B4.5 Myr or younger based on magnetostratigraphic and palaeo-environmental analyses 4,5,12,13 . No previous attempt has been made to constrain the uplift history using the subsurface stratigraphic record in the desert-covered Tarim Basin apart from a mentioning in a regional overview 14 .…”

Cyprininae phylogeny revealed independent origins of the Tibetan Plateau endemic polyploid cyprinids and their diversifications related to the Neogene uplift of the plateau

“…The closely nested diversification rate shifts during the Late Miocene to Early Pleistocene (~12-1 Mya) (shifts 4, 5, and 7-15) occurred only in two characteristically Tibetan lineages of polyploidy cyprinids, with one (shifts 7-15) composed entirely of the cleft breast cyprinids in the genus Schizothorax and the other (shifts 4 and 5) the highly specialized schizothoracine fishes except the Schizothorax (clade SCH and SPE, respectively, Figure 3). Although the southern Tibetan Plateau underwent its main stage of fast uplift in the Early Miocene and the elevation probably remained unchanged over the past 15 million years (Harris, 2006;Spicer et al, 2003), further significant uplifts (with possible intervening deformation) of the east and north of Tibet took place within recent 15 million years (Lu et al, 2004;Ritts et al, 2008). Geological evidence suggested that rapid uplift might take place in Eastern Tibet since about 15 Mya because an cessation of rapid Pacific trench migration during the Early to Middle Miocene (~20-15 Mya) probably contributed to the onset of rapid surface uplift and crustal thickening in Eastern Tibet (Royden et al, 2008).…”

Crustal–lithospheric structure and continental extrusion of Tibet

“…However, this requires an accelerated slip rate between 25 and 17 Ma of 300 km offset (c. 40 mm a À1 ). Therefore a two-stage evolution in fault kinematics has been suggested with fast slip and extrusion during the Late Oligocene-Early Miocene changing to slow slip and crustal thickening up to the present (Yue & Liou 1999;Yue et al 2003;Ritts et al 2008). …”