Early Pleistocene uplift of the northeastern Tibetan Plateau: Evidence from the Dunhuang Basin, NW China

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S1367-9120(19)30482-1 https://doi.org/10.1016/j.jseaes.2019.104130 JAES 104130

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Journal of Asian Earth Sciences

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Please cite this article as: Liu, Y., Ren, S., Liu, Y., Genser, J., Neubauer, F., Early Pleistocene uplift of the northeastern Tibetan Plateau: Evidence from the Dunhuang Basin, NW China, Journal of Asian Earth Sciences (2019), doi: https://doi.org/10.1016/j.jseaes.2019.104130

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Early Pleistocene uplift of the northeastern Tibetan Plateau: Evidence from the Dunhuang Basin, NW China Yimin Liu1,2, Shoumai Ren3*, Yongjiang Liu4, Johann Genser5, Franz Neubauer5 1

Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth

Sciences and Engineering, Sun Yat-sen University, Guangzhou, China 2

Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai,

China 3

China Geological Survey, Beijing, China

4

Key Lab of Submarine Geosciences and Prospecting Techniques, MOE, Institute of

Advanced Ocean Study, College of Marine Geology, Ocean University of China, Qingdao, China 5

Department of Geography and Geology, Paris-Lodron-University of Salzburg,

Salzburg, Austria

*Corresponding author: Shoumai Ren Address: No. 45 Fuwai Street, Xicheng District, Beijing 100037, P. R. China E-mail address: [email protected]

ABSTRACT The Cenozoic uplift of the Tibetan Plateau plays an important role in global climate change, basin-mountain geomorphology formation and desertification in western China. As an important component, the Early Pleistocene uplift process and its influence on the northeastern Tibetan Plateau has been controversial for many years. Quaternary synorogenic sediments within the Dunhuang Basin on the northeastern Tibetan Plateau record the details of plateau uplift. Detailed grain size analysis, rock magnetic properties, mudstone 36Cl dating and 40Ar/39Ar detrital mica dating were conducted on Quaternary alluvial-fluvial-lacustrine-aeolian sediments of the Dunhuang Basin. The Aksay section in the southern Dunhuang Basin is dominated by conglomerate, sandstone, siltstone and mudstone. Detrital mica

40

Ar/39Ar ages show major age

populations of 160–200 Ma, 200–400 Ma and 430–510 Ma from the northeastern Altyn Mountains. The results of 36Cl ages and rock magnetic properties show that the Altyn Mountains rapidly uplifted at ~1.16 Ma. From 1.16 to 0.80 Ma, the sedimentary environment was stable with two small-scale uplift pulses at ~1.03 Ma and 0.98 Ma. After 0.80 Ma, the climate became arid, and the Kumtag Desert formed in the Dunhuang Basin. These multistage uplifts are also widely found in the northeastern Tibetan Plateau. The Early Pleistocene uplift of the Altyn Mountains, corresponding to the Kunhuang Movement, resulted in the northeastern margin of the Tibetan Plateau reaching its present height and climate change towards drought in the region. Keywords: northeastern Tibetan Plateau; Dunhuang Basin; Early Pleistocene; tectonic uplift; Cenozoic climate; sedimentary records

1. Introduction The Tibetan Plateau is a key location to study tectonic uplift and environmental evolution (Botsyun et al., 2019; David and Carmala, 2007; Hong et al., 2010; Li et al., 2015; Liu-Zeng et al., 2018). The Cenozoic uplift of the Tibetan Plateau has not only affected the landscape and natural environments of western China but also had a profound impact on the Asian monsoon, inland aridification and global climate change (e.g., Guo et al., 2002; Li et al., 2011; Liu and Dong, 2013; Rieser et al., 2009; Sun et al., 2010; Sun and Wang, 2005; Wang et al., 2008). Although many scholars have completed numerous studies on the Cenozoic uplift of the Tibetan Plateau over the last several decades, there has been no consensus on the time of the basic formation of the Tibetan Plateau and the influence of later uplift on the surrounding environments (An et al., 2001; Ge et al., 2006; Li et al., 2017; Molnar, 2005; Murphy et al., 1997; Shi et al., 1995; Spicer et al., 2003; Sun and Liu, 2000; Tapponnier et al., 1990; Turner et al., 1993; Wang et al., 2014). Many basins have appeared and developed surrounding the Tibetan Plateau, and these basins record the details of plateau uplift (Bush et al., 2016; Mishra et al., 2013; Ritts et al., 2004; Sun et al., 2005; Tian et al., 2018; Yin et al., 2002; Zhao et al., 2017; Zhuang et al., 2011). On the northeastern (NE) Tibetan Plateau, recent studies indicate that later episodic rapid uplift has occurred since the late Miocene (Fang et al., 2013; Li et al., 2014b; Rea et al., 1998; Zhou et al., 2006). These multistage uplift processes can be divided into three stages: the Qingzang Movement (between 3.6 and 1.7 Ma; Li et al., 1996), Kunhuang Movement (between 1.1 and 0.6 Ma; Cui et al., 1998), and Gonghe Movement (after 0.15 Ma; Li et al., 1996).

The Dunhuang Basin is along the northeastern end of the Altyn Mountains and adjacent to the northeastern margin of the Tibetan Plateau (Fig. 1). Cenozoic synorogenic sediments within the Dunhuang Basin enable reconstruction of the tectonic uplift and climatic environmental change history of the NE Tibetan Plateau (Gilder et al., 2001; Kent-Corson et al., 2009; Li et al., 2014a; Lin et al., 2015; Lu et al., 2006; Ritts et al., 2004; Sun et al., 2005; Van der Woerd et al., 2001; Wang et al., 2003; Yin et al., 2002; Zhuang et al., 2011). In this study, we investigated Quaternary sediments in the Dunhuang Basin (Fig. 1b). Here, we present detailed sedimentological observations, grain size analysis, rock magnetic properties, mudstone

36

Cl age

determinations, and detrital mica 40Ar/39Ar age determinations of the Aksay section to understand the uplift processes and climatic evolution on the NE Tibetan Plateau during the Pleistocene. 2. Geological setting and samples The Dunhuang Basin, at the western end of Hexi Corridor, occupies an area of approximately 40, 000 km2 (Fig. 1b; ~400 km in the W-E direction and 80–120 km in the N-S direction). The altitude ranges between 1150 and 1200 m, with an annual mean precipitation of 39.9 mm. The Dunhuang Basin is surrounded by the Beishan Mountains to the north, the Altyn-Qilian Mountains to the south, and the Mazong Mountains to the east and is directly connected to the Tarim Basin to the west. The Dunhuang Basin can be divided into the Andun and Aksay sub-basins from the northwest to the southeast by the Sanwei uplift. The Dunhuang Basin basement rocks are composed of Archean-Proterozoic

orthogneisses (tonalite-trondhjemite-granodiorite gneisses) and amphibolite (metamafic rocks) and Paleozoic metasedimentary rocks (He et al., 2013; Zhao et al., 2015). Jurassic stratigraphy is only distributed in the proximity to the Sanwei and Altyn mountains. The stratigraphy consists of the Lower Jurassic Dashankou Formation of coarse clastic rock, Middle Jurassic Zhongjiangou and Xinhe formations of mudstone intercalated with coal and basalt, and Upper Jurassic Boluo Formation of brown and purple pebbly sandstone, sandstone and mudstone (Guo and Zhang, 1998). Early Cretaceous and Paleogene stratigraphy are absent, with only a small amount of Lower Cretaceous continental clasts deposited in intermontane areas. An angular unconformity exists between the Cretaceous and Neogene stratigraphy. The Neogene Tiejianggou Formation consists of red and gray conglomerate, sandstone and mudstone interpreted as lacustrine, fluvial and alluvial environments (Gilder et al., 2001; Sun and Wang, 2005; Wang et al., 2003; Zhuang et al., 2011). The Quaternary rocks are characterized by alluvial-fluvial-lacustrine-aeolian deposits (Ma et al., 2013). The Aksay section (94°21′24.0″E, 39°40′17.2″N) on the southern Dunhuang Basin was chosen for detailed measurements and sampling. All rocks are semi-consolidated, and we used the terms for those not fully lithified, such as mud and sand. The Aksay section is 18 m in thickness and exposes three major Quaternary sedimentary units (Fig. 2). Among them, the oldest unit consists of conglomerate intercalated with mudstone and siltstone. The middle unit rests conformably on the conglomerate and is characterized by sandstone, siltstone and mudstone. The youngest unit consists of an Aeolian sandstone, termed the Kumtag Desert, which directly overlies fine-grained sediments.

Here, we collected 148 sediment samples for grain size analysis, 142 sediment samples for analysis of rock magnetic properties, 4 mudstone samples for

36

Cl dating and 3

sandstone samples for detrital mica 40Ar/39Ar dating. 3. Methods The details for grain size analysis, rock magnetic properties,36Cl dating,40Ar/39Ar mineral dating are as follows. The particle size distribution of the samples was measured using a SALD-3001 laser diffraction particle size analyzer at the Institute of Geology and Geophysics, Chinese Academy of Sciences. The samples first received ultrasonic treatment in a 20% (NaPO3)6 solution, which was used to disperse the particles. The grain-size analytical procedures were as detailed by Ding et al. (1999) and Liu and Deng (2014). Recorded grain-size fractions were entered into GRADISTAT v8 (Blott and Pye, 2001), and the average grain-size values presented herein were determined using the Folk and Ward (1957) graphical measure based on a log-normal distribution of metric size values. When plotting the grain-size distribution and cumulative curves, we deleted the data corresponding to particles smaller than 0.595 μm because the minor mode between 0.5 and 0.25 μm is a peculiar artifact of the SALD-3001 laser particle analyzer itself, as suggested by Yang and Ding (2004). All magnetic measurements were completed at the Paleomagnetism and Geochronology Laboratory at the Institute of Geology and Geophysics, Chinese Academy of Sciences. Mass-specific magnetic susceptibility (χ) at 470 Hz (i.e. χlf) and 4700 Hz (i.e. χhf) was carried out using a Bartington MS2 susceptibility meter. The

parameter χfd% was defined as 100%*(χlf − χhf)/χlf. χ alone also refers to χlf. Anhysteretic remanent magnetization (ARM) was imparted in a GSD-1 Demagnetizer with an alternating peak field of 90 mT, superimposed by a direct bias field of 0.05 mT. After normalization by the bias field this parameter is expressed as anhysteretic susceptibility (χARM). Isothermal remanent magnetization (IRM) was induced using a 2G660 pulse magnetizer in a 0.1, 0.3 and 1.0 T steady field in one direction, regarded here as IRM100mT, IRM300mT and Saturation IRM (SIRM). The “hard” isothermal remanent magnetization (HIRM) parameter was defined as (SIRM − IRM300mT)/2. Measurements of all magnetic remanences were performed using a JR-5A Spinner Magnetometer. The 36Cl measurements were performed on purified AgCl obtained from mudstone samples. Following the traditional method for preparation of 36Cl (Jiang et al., 2004), a cation-exchange-column method was improved for preparation of the natural environment sample in the accelerator mass spectrometry (AMS) measurement of 36Cl at the Tianjin Institute of Geology and Mineral Resources, China. Four mudstone samples were collected and treated using this new method step-by-step. The purified and dried AgCl was analyzed for the Atomic Energy.

36

36

Cl/Cl ratio via AMS at the China Institute of

Cl ages were determined using the radiometric decay equation as

follows: 𝑡=

−1 𝐼𝑚 𝑙𝑛⁡[ ] 𝜆 (𝐼0 + 𝐼𝐿 )

where Im is the measured ratio for the sample, I0| is the initial ratio produced in the atmosphere by the interaction of cosmic rays with argon atoms, IL is the initial ratio for ordinary atmospheric chloride (mostly derived from the ocean; considered constant

since 3.0 Ma B.P.), and λ is the decay constant of 36Cl. The 36Cl deposition is directly proportional to the 36Cl/Cl ratio on the land surface (Zreda et al., 1991). The 36Cl production rate and measured I0 in the datum point (4°18’ N) is 4.2 atoms m-2 s-1 and 0.966×10-13, respectively. The

36

Cl production rate is

between 59 and 60 atoms m-2·s-1 in the north between 38° to 40° (Hainsworth et al., 1994; Knies et al., 1994). The 36Cl production rate in the Aksay section is 59.836 atoms m-2 s-1 as determined using the linear interpolation method. Therefore, I0 in the Aksay section is 13.762 ×10-13. IL in the southern Dunhuang Basin is 1.10 ×10-13, referred by rainwater at the same latitude. Details regarding calculations are also illustrated in Ren et al. (2006). White mica concentrates of three samples were analyzed as single grains (200–350 µm, subordinately 125–200 µm) using standard laser-fusion 40Ar/39Ar techniques at the Isotopic Dating Laboratory at the Department of Geography and Geology, ParisLodron-University Salzburg, Austria. Analytical techniques follow those described in Liu et al. (2003) and Rieser et al. (2006a). Probability density plots were visualized using the DensityPlotter 8.4 (Vermeesch, 2012). 4. Results 4.1. Grain size analysis Sampled sediments from the Aksay section range from very poorly sorted, medium silt to moderately well sorted, very fine sandstone. Median particle diameters (Md) for these sediments range from 2.13 to 8.00 µm (Fig. 3). The samples show a standard deviation of 0.58 to 2.80. The skewness values of the samples range from -0.23 to 0.67.

The range of kurtosis is between 0.85 and 3.45. Most of the samples are characterized by grain-size distribution discontinuity (Fig. 4a). Probability plots of the samples show arch cumulative curves and are mainly characterized by two sand populations reflecting a fluvial environment (Fig. 4b). 4.2. Rock magnetic properties The values of χ vary from 1.45 ×10-7 to 3.61 ×10-6 m3 kg-1. The sandstone samples have higher χ values than those of the neighboring mudstone samples (Fig. 3). In addition, sandstone samples at a depth of 279 cm and 565-575 cm show the highest χ values. χfd is generally less variable and lower and varies between 0.8 and 6.4% (mean 3.1%). There is no obvious relationship between Χfd and χ (Fig. 3), suggesting that samples have not undergone stronger chemical weathering. χARM values vary between 1.50 ×10-7 and 2.20 ×10-6 m3/kg and show a high linear correlation with χ values (Fig. 3), indicating that the magnetite/maghemite particles are mainly pseudo-single domain (PSD) to multidomain (MD) grains (King et al., 1982). SIRM values generally range from 2.11 ×10-3 to 1.79 ×10-3 Am2/kg and show a similar variation pattern as that of the χ values (Fig. 3), suggesting that the χ values are mainly influenced by the magnetite/maghemite concentration. HIRM varies between 9.90 ×10-5 and 7.09 ×10-5 Am2/kg, showing a pattern not completely agreeing with that of χ (Fig. 3). The highfrequency fluctuations of HIRM might be related to pedogenesis or the evolution of the source material (Liu et al., 2007a). In summary, the magnetic concentration values (i.e. χ, χARM and SIRM) and grain-size of samples show a strong positive linear correlation (Fig. 3), suggesting the variations in the magnetic parameters in the Aksay section

mainly depend on the clastic sediment supply. The sandstones with high χ-values in the Dunhuang basin are closely related to the surrounding mountains’ uplift (Sun et al., 2005). In addition, because only normal polarity was observed in the Paleomagnetic analyses, it is difficult to determinate the ages of the Aksay section via magnetostratigraphy. 4.3. 36Cl dating Chlorine-36 has a half-life of 302,000 years and is produced, both in the atmosphere and at the Earth's surface, by cosmic radiation action (Phillips, 2013). It is suitable for dating late Pleistocene deposits (Phillips et al., 1983). The measured 36Cl/Cl ratios and calculated 36Cl ages are provided in Table 1. Sedimentation rates have fallen from 10.1 to 1.0 cm/ka from bottom to top of the Aksay section (Fig. 3), which are similarly with those of fluvial deposits (Pan et al., 2016) and much lower than those of alluvial sediments (Fang et al., 2013; Zhao et al., 2017) draining the Qilian Mountains in the Hexi Corridor. Table 1 Cl/Cl in the Aksay section. The uncertainties given are 1σ.

36

Sample

Depth (cm)

s20

20

s165

165

s850

s1620

850

1620

36 36

Cl Raw Counts

Cl/Cl -13

(×10 )

254

2.42

175

2.28

169

1.61

70

1.71

87

1.32

85

1.20

90

1.23

132

1.10

38

1.00

4.4. 40Ar/39Ar mineral dating

Mean 36Cl/Cl 13

Age

(×10- )

(Ma)

2.35 ± 0.14

0.80 ± 0.03 (3%)

1.66 ± 0.15

0.96 ± 0.04 (4%)

1.25 ± 0.10

1.08 ± 0.04 (3%)

1.05 ± 0.09

1.16 ± 0.04 (3%)

The results of 40Ar/39Ar total-fusion isotopic and age data of 57 single white mica grains are provided in the supplementary material. Sample S1030 from the bottom of the Aksay section shows a wide scatter in age distribution. Three age groups dominate: 170–190 Ma, 240–310 Ma and 460–510 Ma, respectively. Some grains display age ranges from 350 to 410 Ma, and one at 87 Ma (Fig. 5). Sample S946 from the bottom of the Aksay section can be separated into two groups at 160–200 Ma and 430–470 Ma. Only one grain displays an age at 250 Ma (Fig. 5). Sample S195 from the top of the Aksay section shows a similar age pattern. It contains grains of two different age groups (170–230 Ma and 430–500 Ma), with one at 325 Ma (Fig. 5). 5. Discussion 5.1. Provenance analysis Samples from the Aksay section yielded Mesozoic and early Paleozoic

40

Ar/39Ar

mica ages similar to the age distribution of rocks at Dangjinshan Pass in the northeastern Altyn Mountains (Figs. 5 and 6). Notably, some micas with ages ranging from 400 to 200 Ma are observed from the Aksay section, particularly the bottom sample S1030. Although these ages are less common in the Dangjinshan Pass area (Fig. 5), numerous detrital white micas with ages between 200 and 400 Ma are reported in the western and northern Qaidam Basin (Fig. 6). These detrital micas are considered to have probably been transported from the Altyn and Qilian mountains (Rieser et al., 2006a; Rieser et al., 2006b; Rieser et al., 2007). This extraordinary discrepancy in the age distribution patterns between the rocks in the source area and the corresponding sedimentary rocks in the basin have also been reported in South Tibet (Wu et al., 2010).

Thus, the main provenance of the southern Dunhuang Basin was from the northeast part of the Altyn Mountains and no obvious change occurred in the source during deposition. 5.2. Tectonics and climate of the northeastern Tibetan Plateau during the Pleistocene Combined with field sedimentary investigations, our

36

Cl ages suggest that the

sediments of the Aksay section span the period from 1.16 to 0.80 Ma. The molassestype sediments in the southern Dunhuang Basin, at a sedimentary age of 1.16 Ma, were interpreted to represent rapid uplift and exhumation of the northeast Altyn Mountains. The mudstone and siltstone intercalation should be interpreted as overflow deposits, rather than sedimentary discontinuity. During the period 1.16–0.80 Ma, the southern Dunhuang Basin was filled by fluvial and lacustrine sandstone and mudstone with a sedimentation rate decreasing from 10.1 to 1.0 cm/ka. Although the NE Tibetan Plateau was stable during this phase, two magnetic susceptibility peaks occur at ~1.03 and 0.98 Ma, caused by episodic uplift of the northeastern Altyn Mountains (Fig. 3; Sun et al., 2005). After 0.80 Ma, the southern Dunhuang Basin changed from a former lacustrine system to the aeolian system-Kumtag Desert. Interbedding of aeolian and lacustrine deposits is not found in the upper part of the Aksay section. Grain size parameters of clastic sediments (sand and muddy sand) from the same part are different from aeolian sands (Sahu, 1964). Therefore, the transformation of sedimentary environment from lacustrine to aeolian is the result of climate drying, rather than migration of desert. During nearly the same interval, many similar geological activities occurred elsewhere on the NE Tibetan Plateau (Fig. 7). The youngest apatite fission track age in

the Altyn Mountains is 1.8 Ma, indicating rapid exhumation of the southwestern Altyn Mountains during the Early Pleistocene (Chen et al., 2006). The average sediment accumulation rate along SG-1 and 15YZK01 core and field profiles in the western Qaidam Basin increased at ~0.8 Ma (Chen et al., 2017; Zhang et al., 2012; Zhang et al., 2013). The Late Cenozoic stratigraphy in the Kunlun Pass Basin implicates that tectonic uplift of the East Kunlun Mountains occurred at 1.77, 1.20, 0.87 and 0.78 Ma (Song et al., 2005). Thermochronological data in East Kunlun Mountains provides further support for rapid uplift at 1.0–0.9 Ma (Chen et al., 2011; McRivette et al., 2019). 36Cl dating of downside and upside mudstone layers of the unconformity in the Altyn, Qimantag and East Kunlun mountains shows that angular unconformities occurred at ~1.54–0.28 Ma, 1.39–1.24 Ma and 1.23–1.20 Ma, respectively (unpublished data). The Cenozoic magnetostratigraphy in the Hexi Corridor suggests that uplifts of the Qilian Mountains occurred at ~2.5–2.2 Ma, 1.7–1.2 Ma, 0.9–0.8 Ma and 0.1 Ma, resulting in the range’s present height (Fang et al., 2013; Fang et al., 2005; Liu et al., 2010; Zhao et al., 2017). All these findings strongly suggest that a major tectonic event, corresponding to the Kunhuang Movement, occurred during the Early Pleistocene and affected the entire NE Tibetan Plateau (Fig. 7; Cui et al., 1998; Li et al., 2014b). During the Kunhuang Movement, the average elevation of the NE Tibetan Plateau reached 3000 m, with mountain peaks rising above 4000 m (Fang et al., 1999; Liu et al., 2010; Shi et al., 1995; Thompson et al., 1997). In addition to the Kunhuang movement, climatic changes on the NE Tibetan Plateau began during the Early Pleistocene. Around the NE Tibetan Plateau, widespread

sediments effectively documented the paleoenvironment variability (Fig. 7). The initial present day Kumtag Desert located in the Dunhuang Basin appeared in ~0.80 Ma, which is similar to the formation of the deserts in the Northwest Arid Area of China at about 0.88–0.80 Ma (Guan et al., 2011). The palynologic compositions in the SG-3 core from the western Qaidam Basin indicate rapid drying events began at ~2.6 Ma, 1.2 Ma, 0.9 Ma and 0.6 Ma (Cai et al., 2012). The study of the Gypsum in the SG-1 core from the western Qaidam Basin demonstrates that a notable long-term and stepwise drying occurred after ~2.2 Ma, with two cold and dry events at ~1.0 Ma and ~0.6 Ma (Li et al., 2017). Gypsum and salt deposits in drilling core 15YZK01 from the western Qaidam Basin began to form at 2.10 Ma and 0.73 Ma or 0.75 Ma, respectively (Chen et al., 2017). Sedimentary characteristics and the faunal and floral evolution of the Kunlun Pass Basin show that the environment became dry and cold at 1.1 Ma (Wu et al., 2001). Although researches on climatic change of the northeastern Tibetan Plateau during the Pleistocene is less, almost all of studies show that the environment became dry after tectonic uplifts in the northeastern Tibetan Plateau. Especially after the Kunhuang Movement (1.1-0.6 Ma), the last drying events occurred (Fig. 7). Therefore, the climatic change may have been caused by uplift of the NE Tibetan Plateau. However, many studies suggest that global cooling (Mid-Pleistocene Transition, MPT), not uplift of the Tibetan Plateau, was the major driving mechanism of the climatic changes (Li et al., 2017; Li et al., 2014b). However, increasingly more evidence supports that the uplift of the Tibetan Plateau has driven global climate change and the MPT has occurred during or has slightly lagged behind this tectonic uplift (Clark et al., 2006; Dupont-Nivet et al.,

2008; Lisiecki and Raymo, 2005; Liu et al., 2010; Raymo et al., 1997; Sun et al., 2019). According to the aforementioned discussion, the uplift of the Altyn Mountains during the Early Pleistocene is among of the most important events of the Kunhuang Movement. During the Kunhuang movement, tectonic uplift, an increased sediment accumulation rate and an angular unconformity occurred on the NE Tibetan Plateau. By the end of the Kunhuang Movement, the NE Tibetan Plateau had reached its present height, and the regional climate had greatly changed. 6. Conclusions Based on new data from field observations, grain size analysis, rock magnetic properties, mudstone

36

Cl ages and detrital mica

40

Ar/39Ar ages from the southern

Dunhuang Basin, NE Tibetan Plateau, the following are key results and conclusions: (1) The Aksay section in the southern Dunhuang Basin is dominated by alluvialfluvial-lacustrine-aeolian sediments and deposits accumulated between 1.16 and 0.80 Ma. Detrital mica 40Ar/39Ar ages show major age populations of 160–200 Ma, 200–400 Ma and 430–510 Ma, recorded in the northeastern Altyn Mountains. Therefore, this study suggests that the source rocks of the Quaternary sediments in the southern Dunhuang basin are mainly from the Altyn Mountains, and no obvious change in the source occurred during deposition. (2) This study suggests that samples from the Aksay section recorded a rapid uplift event of the northeastern Altyn Mountains at ~1.16 Ma with two small-scale pulses of uplift at ~1.03 Ma and ~0.98 Ma. The multistage uplift, corresponding to the Kunhuang Movement, shows that the northeastern margin of the Tibetan Plateau had reached its

present height during the Early Pleistocene, which resulted in climate change and drought along the northeast side of the Tibetan Plateau. Acknowledgments We would like to thank Prof. Xiao-Hong Ge for comments and criticisms regarding this paper. His comments and suggestions were extremely valuable in improving our manuscript. The authors are also grateful to the two anonymous reviewers for constructive reviews. This work was financially supported by the National Natural Science Foundation of China [grant numbers 40872127, 40972148, 40572135]; and the Leader in Innovation of Qingdao city [grant number 19-3-2-19zhc]. References An, Z.S., Kutzbach, J.E., Prell, W.L., Porter, S.C., 2001. Evolution of Asian monsoons and phased uplift of the Himalaya-Tibetan plateau since Late Miocene times. Nature 411(6833), 62-66. http://doi.org/10.1038/35075035. Blott, S.J., Pye, K., 2001. GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth Surf. Processes Landforms 26(11), 1237-1248. http://doi.org/10.1002/esp.261. Botsyun, S., Sepulchre, P., Donnadieu, Y., Risi, C., Licht, A., Caves Rugenstein, J.K., 2019. Revised paleoaltimetry data show low Tibetan Plateau elevation during the Eocene. Science 363(6430). http://doi.org/10.1126/science.aaq1436. Bush, M.A., Saylor, J.E., Horton, B.K., Nie, J.S., 2016. Growth of the Qaidam Basin during Cenozoic exhumation in the northern Tibetan Plateau: Inferences from depositional patterns and multiproxy detrital provenance signatures. Lithosphere 8(1),

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Magnetostratigraphy of deep drilling core SG-1 in the western Qaidam Basin (NE Tibetan Plateau) and its tectonic implications. Quat. Res. 78(1), 139-148. http://doi.org/10.1016/j.yqres.2012.03.011. Zhang, W.L., Fang, X.M., Song, C.H., Appel, E., Yan, M.D., Wang, Y.D., 2013. Late Neogene magnetostratigraphy in the western Qaidam Basin (NE Tibetan Plateau) and its constraints on active tectonic uplift and progressive evolution of growth strata. Tectonophysics 599, 107-116. http://doi.org/10.1016/j.tecto.2013.04.010. Zhang, Z.C., Guo, Z.J., Zou, G.Q., Feng, Z.S., Li, H.F., 2009. Geochemical characteristics and SHRIMP U-Pb age of zircons from the Danghe reservoir TTG in Dunhuang, Gansu Province, and its significations. Acta Petrol. Sin. 25(3), 495-505 (in Chinese with English abstract). Zhao, Y., Sun, Y., Yan, J.H., Diwu, C.R., 2015. The Archean-Paleoproterozoic crustal evolution in the Dunhuang region, NW China: Constraints from zircon U–Pb geochronology

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an alluvial conglomerate sequence: An example from the Hexi Corridor, NE Tibetan Plateau. Quat. Geochronol. 39, 68-78. http://doi.org/10.1016/j.quageo.2017.02.007. Zheng, W.J., Zhang, P.Z., Ge, W.P., Molnar, P., Zhang, H.P., Yuan, D.Y., Liu, J.H., 2013. Late Quaternary slip rate of the South Heli Shan Fault (northern Hexi Corridor, NW China) and its implications for northeastward growth of the Tibetan Plateau. Tectonics 32(2), 271-293. http://doi.org/10.1002/tect.20022. Zhou, J.X., Xu, F.Y., Wang, T.C., Cao, A.F., Yin, C.M., 2006. Cenozoic deformation history of the Qaidam Basin, NW China: Results from cross-section restoration and implications for Qinghai–Tibet Plateau tectonics. Earth Planet. Sci. Lett. 243(1-2), 195210. http://doi.org/10.1016/j.epsl.2005.11.033. Zhuang, G.S., Hourigan, J.K., Ritts, B.D., Kent-Corson, M.L., 2011. Cenozoic multiple-phase tectonic evolution of the northern Tibetan Plateau: Constraints from sedimentary records from Qaidam basin, Hexi Corridor, and Subei basin, northwest China. Am. J. Sci. 311(2), 116-152. http://doi.org/10.2475/02.2011.02. Zreda, M.G., Phillips, F.M., Elmore, D., Kubik, P.W., Sharma, P., Dorn, R.I., 1991. Cosmogenic chlorine-36 production rates in terrestrial rocks. Earth Planet. Sci. Lett. 105(1), 94-109. http://doi.org/10.1016/0012-821X(91)90123-Y. Figure caption Fig. 1. (a) Topographic map of East Asia showing the location of the study area. (b) Geological sketch of the Dunhuang Basin. ATM: Altyn Mountains, OB: Ordos Basin, QB: Qaidam Basin, QLM: Qilian Mountains, SB: Sichuan Basin, TB: Tarim Basin. (c) Schematic diagram showing the stratigraphy of the Dunhuang Basin.

Fig. 2. Field photographs of Aksay section. (a) Panoramic view of the Aksay section. (b) Conglomerate intercalated with mudstone. (c) Oblique bedding in sandstone. (d) Depositional cycles of mudstone interbedded by sandstone. Fig. 3. Stratigraphy, grain sizes, magnetic proxy records and

36

Cl age for the Aksay

section from the Dunhuang Basin. Bluish intervals show high χ-values. Fig. 4. (a) Grain-size distributions for typical samples. (b) Log-probability cumulative curves of grain-size distribution for typical samples. Fig. 5. Detrital white mica 40Ar/39Ar age probability plots. (Chen et al., 2009; Liu et al., 2003; Liu et al., 2001; Sobel and Arnaud, 1999; Wang et al., 2005) Fig. 6. Geological map showing available 40Ar/39Ar ages of mica and biotite on the NE Tibetan Plateau. Regular numbers indicate 40Ar/39Ar muscovite and biotite ages of relevant magmatic, metamorphic units, and underlined numbers mark 40Ar/39Ar muscovite ages of sedimentary units. Data sources: 1, Chen et al. (2009); 2, Liu et al. (2003); 3, Liu et al. (2007b); 4, Liu et al. (2001); 5, Rieser et al. (2006a); 6, Rieser et al. (2006b); 7, Rieser et al. (2007); 8, Sobel and Arnaud, (1999); 9, Sobel et al. (2001); 10, Wang et al. (2005); 11, Zhang et al. (2005); 12, Zhang et al. (2009) Fig. 7. Tectonic uplift events (in red) and climate aridity events (in black) along the northeastern margin of the NE Tibetan Plateau during the Pleistocene. Regular numbers indicate palaeomagnetic ages, bold are ages simulated by thermochronology, italics are ages calculated by fault slip rate, and underlined numbers mark

36

Cl/Cl ages. Data

sources: 1, this study; 2, Cai et al. (2012); 3, Cao et al. (2019); 4, Chen et al. (2017); 5, Chen et al. (2018); 6, Chen et al. (2011); 7, Fang et al. (2013); 8, Fang et al. (2005); 9,

He et al. (2018); 10, Li et al. (2017); 11, Liu et al. (2010); 12, McRivette et al. (2019); 13, Pan et al. (2016); 14, Song et al. (2005); 15, Wu et al. (2001); 16, Zhang et al. (2012); 17, Zhang et al. (2013); 18, Zhao et al. (2017); 19, Zheng et al. (2013); 20, unpublished data

Sediments within the Dunhuang Basin record uplift process of the Altyn Mountains Quaternary uplifts of the Altyn Mountains occurred at ~1.16, 1.03 and 0.98 Ma The Kumtag Desert in the southern Dunhuang Basin formed after ~0.80 Ma The Kunhuang Movement resulted in climate drought in the northeastern Tibetan Plateau

C 40.5°N

C

Dunhuang Basin

40°N 39.5°N

S AnZ

Aksay Sub-basin O

Z

Quaternary O-S

Subei O

N Neogene O

Z

O E

Q

K

Q

J

Cretaceous Paleogene Jurassic Є

OrdovicianCambrian Silurian Ordovician

Z Sinian

C

Є Q

42°N

TB

O

S O

K Q

K K

D Fig. 1b

E

S

(a)

ATM QLM QB

OB

SB

30°N India 75°E T Triassic

P

95°E C

D

Carboniferous Devonian Permian

Granite

Diorite

Fig. 1

City

River

Section location

Sandstone

1000 800

Pebbly Sandstone

600 400

Sinian

Siltstone

1200

S Silurian

AnZ Presinian

1600 1400

Q

Tibet Plateau

E

E AnZ

AnZ

Q

Z

Q Q

E

N

Mudstone

1800

J

ins

AnZ

Є

2200

N

AnZ

n Alty

Q

2400

Yumen

N

un Mo

2600

2000 Q

ta

Aksay Section

O-S

N

an

Danghe River J

Aksay

t

J

Thickness Lithology (m)

Period

Quaternary

AnZ

J

plif

iU we

Dunhuang

O

O-S

T O-S

Guazhou Shule River

Q

O-S Andun Sub-basin

AnZ

O-S

Beishan Mountains

C

P

C

C

N

C

(c)

Late

Q

P

(b)

P

Middle

C

C

N

P

O-S

96°E

Early

50 km

O-S

Neogene

95°E

N Q 0

Jurassic

Figure1

200 0

Conglomerate

Geniss

Figure2

150° (b)

(a)

150° Conglomerate

Mudstone Conglomerate (c)

160° (d)

190° Mudstone

Mudstone

Sandstone

Sandstone

Fig. 2

Figure3

Md (μm) 0 100 200

Depth (cm) 0

0

χfd (%) 5

10

SIRM (10-3 Am2 kg-1) 0 10 20

Age (Ma BP) 0.5 1 1.5 0.80

s20

1.0 cm/ka

s165 200

0.96

s195

~0.98

400

5.5 cm/ka ~1.03

600

800

1.08

s850 1000

s946 s1030 10.1 cm/ka

1200

1400

1600

1.16

s1620

10 50 χ (10-7 m3 kg-1)

1

1800

Mudstone

Silty mudstone

Siltstone

0

1.25 2.5 χARM (10-6 m3 kg-1)

Sandstone

Fig. 3

0

4 8 HIRM (10-4 Am2 kg-1)

Conglomerate 36Cl dating Detrital mica sample sample

Figure4 (a) 25

25 95-2 370 705-2 1440

Volume (%)

20 15 10 5 0 0.1

1

Probability cumulative curve (%)

(b) 99.99 99.9 99.5 98 90 70 50 30 10 2 0.5 0.1 0.01

10 100 Particle size (μm)

1000

25 95-2 370 705-2 1440

0

1

2 3 Grain size (ϕ)

4

Figure5

8

S195 (n=23)

4 0

Number

2 0 S1030 (n=17)

2 1

Relative Probability

S946 (n=17)

4

0 Mica

Dangjinshan Pass Biotite

0

120

240 360 Age (Ma)

480

600

Figure6

40°N

90°E 0

N

95°E Dunhuang 150-164, 221-248, 343-370, 425-4611-3,10 1 26-36, 89, 160-178, 322-352, 428-4581-4,8,10 2271 358 4 24712 491, 5121 203, 209 3051 225, 3561 17418 2471 50

100 km

3838 4148

38°N

432

8

9 47, 98 238 4

Yumen Jiuquan

Dangjinshan Pass 3171 24611 23010

419, 4291 354, 3941 219, 250-279, 295-306, 381, 4465,7 Mangya 4538 924 40911 1 351, 395 123, 180-277, 317-500, 543, 8455,7 210, 268-388, 420-443, 477-480, 515-5226-7 Cenozoic

Precambrian

Strike-slip fault

Mesozoic

Magmatic rock

Fault

Paleozoic

Thrust fault

Aksay section

Fig. 6

352 306

40

252

40

40

Ar/39Ar white mica age (Ma) Ar/39Ar detrital white mica age (Ma) Ar/39Ar biotite age (Ma)

Figure7

N

93°E 0

100

200 km

39°N

Tarim Basin 1.2 Ma 0.9 Ma 0.6 Ma2

36°N

0.80 Ma1

1.54-0.28 Ma20 2.5 Ma s ountain 1.1 Ma Altyn M 17 0.8 Ma

1.39-1.24 Ma20

Muztag

1.16 Ma ~1.03 Ma ~0.98 Ma1

Qimantag 2.2 Ma 1.0 Ma 0.6 Ma10

99°E

<1.8-1.23 Ma

Dunhuang Basin 0.93-0.84 Ma Dunhuang 2.10 Ma 0.73 or 0.75 Ma4

0.14 Ma8

Hexi Corridor Jiayuguan

~2.5-2.2 Ma ~1.7-1.2 Ma18

Qilian Mountains

~2.1 Ma9

Kangze’gyai

~2 Ma19

1.1 Ma13

~0.9-0.8 Ma ~0.1 Ma7, 11 Zhangye 1.4-0.8 Ma3

Qaidam Basin

2.58-2.14 Ma 0.05 Ma5 ~0.78 Ma16 2.58-1.95 Ma Golmud 0.78 Ma4 1.23-1.20 Ma20 ~1.0 Ma12 1.77 Ma East Kunlun Mountains 1.20 Ma 15 1.1 Ma 0.87 Ma ~2.3-0.9 Ma ~2.7-2.0 Ma ~0.78 Ma14 ~1.3-0.7 Ma6 ~1.6 Ma6

Fig. 7

Xi’ning Dulan

Graphical Abstract

N

93°E 0

100

200 km

39°N

Tarim Basin 1.2 Ma 0.9 Ma 0.6 Ma

36°N

0.80 Ma

1.54-0.28 Ma 2.5 Ma tains n u o M 1.1 Ma Altyn 0.8 Ma

1.39-1.24 Ma

Muztag

1.16 Ma ~1.03 Ma ~0.98 Ma

Qimantag 2.2 Ma 1.0 Ma 0.6 Ma

Dunhuang Basin Dunhuang 2.10 Ma 0.73 or 0.75 Ma

<1.8-1.23 Ma 0.93-0.84 Ma 0.14 Ma

99°E

Hexi Corridor

~2.5-2.2 Ma ~1.7-1.2 Ma

Jiayuguan

Qilian Mountains

~2.1 Ma

Kangze’gyai

~2 Ma

1.1 Ma

~0.9-0.8 Ma ~0.1 Ma Zhangye

Tectonic uplift events

1.4-0.8 Ma

Qaidam Basin

2.58-2.14 Ma 0.05 Ma ~0.78 Ma 2.58-1.95 Ma Golmud 0.78 Ma 1.23-1.20 Ma ~1.0 Ma 1.77 Ma East Kunlun Mountains 1.20 Ma 1.1 Ma 0.87 Ma ~2.3-0.9 Ma ~2.7-2.0 Ma ~0.78 Ma ~1.3-0.7 Ma ~1.6 Ma

Xi’ning Dulan

Climate aridity events

Sample

Depth (cm)

s20

20

s165

165

s850

850

s1620

1620

36 36

Cl Raw Counts

Cl/Cl -13

(×10 )

254

2.42

175

2.28

169

1.61

70

1.71

87

1.32

85

1.20

90

1.23

132

1.10

38

1.00

Mean 36Cl/Cl 13

Age

(×10- )

(Ma)

2.35 ± 0.14

0.80 ± 0.03 (3%)

1.66 ± 0.15

0.96 ± 0.04 (4%)

1.25 ± 0.10

1.08 ± 0.04 (3%)

1.05 ± 0.09

1.16 ± 0.04 (3%)

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: