Mesozoic–Cenozoic Uplift/Exhumation History of the Qilian Shan, NE Tibetan Plateau: Constraints From Low-Temperature Thermochronology

Abstract

The Qilian Shan, which is located along the northeastern margin of the Tibetan Plateau, plays a key role in understanding the dynamics of the outward and upward growth of the plateau. However, when and how tectonic deformation evolved into the geographic pattern which is currently observed in the Qilian Shan are still ambiguous. Here, apatite fission track (AFT) thermochronology and sedimentology were conducted to interpret the low-temperature tectonic deformation/exhumation events in well-dated Late Miocene synorogenic sediment sequences in the Xining Basin, which is adjacent to the southern flank of the Qilian Shan. These new low-temperature thermochronological results suggest that the Qilian Shan experienced four stages of tectonic exhumation during the late Mesozoic–Cenozoic. The Late Cretaceous exhumation events in the Qilian Shan were caused by the diachronous Mesozoic convergence of the Asian Plate and Lhasa Block. In the early Cenozoic (ca. 68–48 Ma), the Qilian Shan quasi-synchronously responded to the Indian–Asian plate collision. Subsequently, the mountain range experienced a two-phase deformation during the Eocene–Early Miocene due to the distal effects of ongoing India–Asia plate convergence. At ca. 8 ± 1 Ma, the Qilian Shan underwent dramatic geomorphological deformation, which marked a change in subsidence along the northeastern margin of the Tibetan Plateau at that time. Our findings suggest that the paleogeographic pattern in the northeastern Tibetan Plateau was affected by the pervasive suture zones in the entire Qilian Shan, in which the pre-Cenozoic and Indian–Asian plate motions reactivated the transpressional faults which strongly modulated the multiperiodic tectonic deformation in northern Tibet during the Cenozoic. These observations provide new evidence for understanding the dynamic mechanisms of the uplift and expansion of the Tibetan Plateau.

Full text

Mesozoic–Cenozoic Uplift/
Exhumation History of the Qilian Shan,
NE Tibetan Plateau: Constraints From
Low-Temperature Thermochronology
Lihao Chen
1
, Chunhui Song
1
*, Yadong Wang
2
,
3
, Xiaomin Fang
2
,
4
, Yihu Zhang
1
, Jing Zhang
1
,
Yongfa Chen
1
and Pengju He
1
1
School of Earth Sciences and Key Laboratory of Mineral Resources in Western China (Gans u Province), Lanzhou University,
Lanzhou, China,
2
Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences and Key Laboratory of
Petroleum Resources, Gansu Province, Lanzhou, China,
3
Rock-Mineral Preparation and Fission Track Dating Laboratory of
Geochemical Analysis and Testing Center, Northwest Institute of Eco-Environment and Resources, Chinese Academy of
Sciences (CAS), Lanzhou, China,
4
Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau
Research, Chinese Academy of Sciences, Beijing, China
The Qilian Shan, which is located along the northeastern margin of the Tibetan Plateau,
plays a key role in understanding the dynamics of the outward and upward growth of the
plateau. However, when and how tectonic deformation evolved into the geographic
pattern which is currently observed in the Qilian Shan are still ambiguous. Here, apatite
fission track (AFT) thermochronology and sedimentology were conducted to interpret the
low-temperature tectonic deformation/exhumation events in well-dated Late Miocene
synorogenic sediment sequences in the Xining Basin, which is adjacent to the
southern flank of the Qilian Shan. These new low-temperature thermochronological
results suggest that the Qilian Shan experienced four stages of tectonic exhumation
during the late Mesozoic–Cenozoic. The Late Cretaceous exhumation events in the Qilian
Shan were caused by the diachronous Mesozoic convergence of the Asian Plate and
Lhasa Block. In the early Cenozoic (ca. 68–48 Ma), the Qilian Shan quasi-synchronously
responded to the Indian–Asian plate collision. Subsequently, the mountain range
experienced a two-phase deformation during the Eocene–Early Miocene due to the
distal effects of ongoing India–Asia plate convergence. At ca. 8 ±1 Ma, the Qilian
Shan underwent dramatic geomorphological deformation, which marked a change in
subsidence along the northeastern margin of the Tibetan Plateau at that time. Our findings
suggest that the paleogeographic pattern in the northeastern Tibetan Plateau was affected
by the pervasive suture zones in the entire Qilian Shan, in which the pre-Cenozoic and
Indian–Asian plate motions reactivated the transpressional faults which strongly
modulated the multiperiodic tectonic deformation in northern Tibet during the
Cenozoic. These observations provide new evidence for understanding the dynamic
mechanisms of the uplift and expansion of the Tibetan Plateau.
Keywords: Apatite fission track, Northern Tibetan Plateau, Xining Basin, Qilian Shan, Tectonic exhumation,
Geomorphological, NE Tibetan Plateau
Edited by:
Tara N. Jonell,
University of Glasgow,
United Kingdom
Reviewed by:
Andrew V. Zuza,
University of Nevada, Reno,
United States
Xing Jian,
Xiamen University, China
Bangshen Qi,
Chinese Academy of Geological
Sciences, China
*Correspondence:
Chunhui Song
songchh@lzu.edu.cn
Specialty section:
This article was submitted to
Quaternary Science, Geomorphology,
and Paleoenvironment,
a section of the journal
Frontiers in Earth Science
Received: 17 August 2021
Accepted: 26 October 2021
Published: 13 December 2021
Citation:
Chen L, Song C, Wang Y, Fang X,
Zhang Y, Zhang J, Chen Y and He P
(2021) Mesozoic–Cenozoic Uplift/
Exhumation History of the Qilian Shan,
NE Tibetan Plateau: Constraints From
Low-Temperature Thermochronology.
Front. Earth Sci. 9:760100.
doi: 10.3389/feart.2021.760100
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 7601001
ORIGINAL RESEARCH
published: 13 December 2021
doi: 10.3389/feart.2021.760100

INTRODUCTION
With continuous Cenozoic compression and convergence
between the Indian and Asian plates, the uplift and expansion
of the Tibetan Plateau has profoundly influenced the climatic and
paleogeographical evolution in Asia (England and Houseman,
1986;Harrison et al., 1992;Dupont-Nivet et al., 2008;Fang et al.,
2019;Spicer et al., 2020). Several tectonic geodynamic evolution
models present different interpretations of the topographic
spatial–temporal deformation mechanism of the Tibetan
Plateau. For example, some studies suggest that growth on the
northeastern margin of the plateau was driven by continuous
lithospheric shortening and monotonic deformation induced by
propagation of stresses from south to north during the
Pliocene–Quaternary (Meyer et al., 1998;Tapponnier et al.,
1990;Tapponnier et al., 2001;Hu et al., 2019). However,
recent deforming mantle models suggest that the deformation
initiated quasi-synchronously in the early Cenozoic throughout
the whole Tibetan Plateau (for example, Yin and Harrison, 2000;
Yin et al., 2008;Dayem et al., 2009;Clark, 2012;Clark et al., 2010).
The northeastern margin of the plateau developed multiple
orogenic belts, which significantly constrains the timing of the
far-field effects of plate collision and the mechanism of plateau
expansion (Tapponnier et al., 2001;Lease et al., 2012). The Qilian
Shan trends in the northwest direction between the Alxa and
Qaidam Blocks, which comprise the northeastern margin of the
Tibetan Plateau (Figure 1A). As a frontier tectonic belt that
formed in response to the plateau-related collision, the Qilian
Shan is a key to test deformation events, and the growth model of
the plateau edge has garnered significant attention. Recent studies
have revealed the Cenozoic tectonic history of the Qilian Shan,
but the initial timing of tectonism and the growth evolution of the
mountain range have remained elusive. Two consensuses have
emerged regarding the timing of prominent deformation in the
Qilian Shan, namely, the early Cenozoic (Yin et al., 2002;Yin
et al., 2008;He et al., 2017;He et al., 2020a;He et al., 2020b) and
the late Cenozoic (Wang et al., 2017;Pang et al., 2019a;Wang
et al., 2020), and these models yield distinctly different
predictions of the mechanism of the plateau growth.
Moreover, Cretaceous tectonic signals have also been found in
the Qilian Shan (Jolivet et al., 2001;Qi et al., 2016;Li et al., 2019),
but research regarding the Mesozoic tectonic evolution of the
southern, central, and northern Qilian Shan is relatively scarce
(Vincent and Allen 1999;Chen et al., 2002;Cheng et al., 2019).
The Xining Basin (XB) is adjacent to the convergence zone of
the southern, central and northern Qilian orogenic belts
(Figure 1B). This basin developed a thick and continuous late
Cenozoic sediment sequence, and the depositional age of this
sequence has been constrained by fine-scale paleomagnetism and
mammalian fossil chronology (Yang et al., 2017;Zhang et al.,
2017). Therefore, the XB is an ideal site to constrain the temporal
evolution of basin–mountain coupling. Detrital apatite fission
track (AFT) thermochronology research is a significant means to
invert the tectonic evolution of orogenic belts and basin
formation and to recover paleogeography during
basin–mountain coupling (Bernet and Spiegel, 2004). Previous
studies have provided large amounts of low-temperature
thermochronological information on the sedimentary strata
and nearby bedrock in the XB, but the interpretation of AFT
ages of sediments deposited after the Late Miocene is still unclear
(Wang et al., 2015b;Wang et al., 2016;Lease et al., 2011). In this
study, we present detrital AFT and sedimentological evidence
from two well-dated late Cenozoic synorogenic sections in the
XB, which constrain the linkages to the Mesozoic–Cenozoic
tectonic evolution of the Qilian Shan. Our observations
provide further insight into the involvement of per-Cenozoic
plate motions and the Cenozoic multiepisodic tectonic
exhumation history of the Qilian Shan. Although the timing of
the initial Indian–Asian plate collision remains controversial,
most current studies suggest that the plates initially collided at
approximately 55 ±10 Ma (Najman et al., 2010;Ding et al., 2017).
Notably, no extensive Cenozoic volcanic activity occurred near
the XB, from which it can be deduced that the exhumation/
cooling events in this study of the Qilian Shan were caused by
tectonically driven local terrain deformation rather than by
magmatic cooling and eruption (Gansu Geologic Bureau, 1989;
Gehrels et al., 2003;He et al., 2020a). Hence, the early Cenozoic
cooling signals indicate that the Qilian Shan quasi-synchronously
responded to the Indian–Asian plate collision, which is also
consistent with previous research in other parts of the
northeastern margin of the Tibetan Plateau (Dupont-Nivetet
et al., 2004;Dai et al., 2005;Jian et al., 2013;Jian et al., 2018;
Fan et al., 2019; Cheng et al., 2019;Fang et al., 2019;Hong et al.,
2020). These results enrich the knowledge of the Late
Cretaceous–Cenozoic paleogeomorphological growth history of
the northeastern Plateau.
GEOLOGICAL SETTING
The Qilian Shan is located in the northernmost portion of the
Tibetan Plateau and is divided into multiple basin–mountain
units by a series of subparallel NW-SE striking thrusts, folds, and
strike-slip faults (Meyer et al., 1998)(Figure 1B). The main
basins around the Qilian Shan, including the Qaidam Basin, Hexi
Corridor Basin, and XB, have thick and extensive Cenozoic
sediments (Figure 1B). The XB is adjacent to the eastern part
of the Qilian Shan and is in the transition zone between the
Tibetan Plateau and the Loess Plateau. This NW-oriented
quadrilateral inland Cenozoic basin is related to a dome
structure composed of Proterozoic, early Proterozoic, and
Mesoproterozoic orogenic belts (Fang et al., 2019). The basin
is bound by the Laji Shan, Daban Shan, and Riyueshan faults to
the south, north, and west, respectively (QBGM, 1991). The
mountains around the basin are situated in the Central Qilian
orogenic belt, in which the Huangshui River cuts through the
Cenozoic strata providing good natural sections for researchers to
trace the tectonism history of the Qilian Shan and the adjacent
basins on the northeastern margin of the Tibetan Plateau.
Previous studies on the tectonic history of the northeastern
Tibetan Plateau have obtained a series of important
achievements (Meyer et al., 1998;Tapponnier et al., 2001;Yin
et al., 2002;Yin et al., 2008;Lease et al., 2011;Jian et al., 2013;
Yuan et al., 2013;Allen et al., 2017;Jian et al., 2018;Fang et al.,
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 7601002
Chen et al. AFT Data in Xining Basin

FIGURE 1 | Geologic survey of the study area on the Tibetan Plateau. (A) Digital topographic elevation model of the northeastern Tibetan Plateau mainly indicates
the location of the Qilian Shan geomorphology and adjacent basins. (B) Topography of the major faults in the TP and Qilian Shan in the northeastern region and the
periphery. (C) Distribution of the Cenozoic stratigraphy of the XB and locations of the CJB (Caojiabao) and MJZ (Mojiazhuang) sections (modified from Dai et al., 2005).
(D) Sections a–b show the relationships between the Cenozoic stratigraphy and the CJB and MJZ sections for the top sequences (modified from Zhang et al.,
2017).
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Chen et al. AFT Data in Xining Basin

2019;Hong et al., 2020;Cheng et al., 2021). Current
sedimentological and low-temperature thermochronological
evidence suggests that the region quasi-synchronously
responded to the Indian–Asian Plate collision during the early
Cenozoic, and then it entered a period of relative quiescence
(Duvall et al., 2013;Pan et al., 2013;Wang et al., 2016;Zhang
et al., 2016;An et al., 2020). Subsequently, widespread faulting
and orogenic belt deformation occurred at ∼15 Ma (Zheng et al.,
2017;Pang et al., 2019b;Yu et al., 2019). Along with the continued
northward compression of the plateau and eastward propagation
of the Haiyuan faults, the bedrock and basin sediments recorded
many rapid exhumation/deposition events during 8–10 Ma (Fang
et al., 2005;Zheng et al., 2010;Fang et al., 2012;Wang et al., 2016;
Zhuang et al., 2018). The large amounts of low-temperature
thermochronological data published in recent years show that
the Qilian Shan has experienced four stages of cooling history:
Late Triassic–Early Cretaceous (Jolivet et al., 2001;Qi et al., 2016);
Late Cretaceous–Eocene (Jian et al., 2013;Li et al., 2013;Pan et al.,
2013;Wang et al., 2016;Jian et al., 2018); Oligocene–Middle
Miocene (Li et al., 2013;Yu et al., 2017) and Late Miocene (Zheng
et al., 2017;Pang et al., 2019a;Wang et al., 2020). Most of the
bedrock data focus on the Oligocene–Early Miocene and Late
Miocene (Zheng et al., 2010;Zheng et al., 2017;Meng et al., 2020;
Wang et al., 2020), while detrital data in the basin cover all the
stages of cooling ages (Pan et al., 2013;He et al., 2017;He et al.,
2018;He et al., 2020b).
In this study, we selected two Late Miocene–Pliocene
sequences in the Caojiabao (CJB) (12.4–2.6 Ma) (36°42′55.8″
N, 101°49′42″E; elevation: 2,740 m) and Mojiazhuang (MJZ)
(12.7–4.8 Ma) (36°41′07.08″N, 102°04′15.78″E; Elevations:
2,840 m) sections within the XB and collected samples for
detailed low-temperature thermochronological research. The
CJB and MJZ sections are the uppermost sequences of the
Cenozoic basin strata and are located at the center and
FIGURE 2 | Magnetostratigraphy, stratigraphic column, paleocurrent directions (from Zhang et al., 2017 except the new data marked by red arrows), sampling
sites, and low-temperature thermochronology results for the Caojiabao (CJB) section. (A–D) Photographs showing the representative stratigraphy for the section. The
detrital AFT grain ages of CJB-1, CJB-2, and modern river samples were statistically decomposed into components (with modeled component peak ages and
proportions) and chi-square tests through RadialPlotter and DensityPlotter (Vermeesch, 2012).
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Chen et al. AFT Data in Xining Basin

FIGURE 3 | Magnetostratigraphy, stratigraphic column, paleocurrent directions (all from Yang et al., 2017), sampling sites, and low-temp erature thermochronology
results for the Mojiazhuang (MJZ) section. The detrital AFT grain ages of the samples were statistically analyzed using RadialPlotter and DensityPlotter (Vermeesch,
2012). (A–F) Photographs of representative stratigraphy in the section.
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Chen et al. AFT Data in Xining Basin

northeast of the XB, respectively (Zhang et al., 2017;Yang et al.,
2017;Fang et al., 2019)(Figure 1C,D). The strata exposed in
these two sections are divided into the Guanjiashan Fm. (formerly
the Xianshuihe Fm.) and Mojiazhuang Fm. from bottom to top
according to regional stratigraphic correlation (Figures 2,3).
Limited high-resolution magnetostratigraphy and in situ
mammalian fossils indicate that the Guanjiashan Fm. is
140–64 m thick and 12–7 Ma in age in the CJB section and
336–137 m thick and 12.7–7 Ma in age in the MJZ section (Fang
et al., 2019)(Figures 2,3). Based on the lithologic assemblage and
mammalian fossils, the Guanjiashan Fm. is divided into two units
(Yang et al., 2017). The upper unit is mainly composed of thick
brown-yellow massive mudstone/siltstone, which is interbedded
with blue-gray thin-layered sandstone and coarse conglomerate.
The conglomerate is mainly composed of metamorphic
sandstone and quartzite with a southward zonal structure
(Figures 2B,D, and 3E). In the stratum, there are many
mudstone layers and thin layers of gray-green massive or
horizontally bedded marl containing mammalian fossils
(Figures 3C and D). The lower unit contains thin grayish
sandstone layers and fine-grained conglomerate but lacks a
paleosol layer. The conglomerate is mainly composed of
metamorphic sandstone, quartzite, and schist (Yang et al.,
2017)(Figures 2C and 3E).
The characteristics of the Mojiazhuang Fm. differ between two
sections, as the exposure of the formation is only 20 m thick in the
CJB section but more complete and thicker in the MJZ section
(7–4.8 Ma, 137–0m) (Yang et al., 2017;Zhang et al., 2017)
TABLE 1 | Detrital AFT data from sediment samples.
Sample nTrack density (×10
5
) U (ppm) p
(χ
2
)
Central
age (Ma)
Average
Dpar
(range)
(μm)
Mean
track
length ±
SD (μm)
No.
lengths
Fossil
(N
s
)(×10
5
cm
−2
)
Induced
(N
i
)(×10
5
cm
−2
)
Dosimeter
(N
d
)(×10
6
cm
−2
)
Modern river sample 108 1.63 (2023) 8.28 (10,308) 1.68 (17,656) 7.43 0 44 ±2.4 2.56 (1.9–3.56) 13.01 ±1.52 60
CJB-1 112 2.04 (2,198) 5.86 (6,301) 1.37 (13,301) 6.6 0 69.4 ±3.3 1.92 (1.22–3.43) 13.58 ±1.62 80
MJZ15 82 1.69 (450) 16.14 (4,280) 1.45 (13,301) 14.93 0 24.1 ±1.4 2.54 (1.12–3.46) 13.24 ±1.62 72
MJZ45 82 2.3 (618) 16.32 (4,389) 1.44 (13,301) 16.32 0 28.6 ±1.6 1.83 (1.12–3.03) 14.03 ±1.54 61
MJZ95 71 1.6 (529) 14.65 (4,844) 1.42 (13,301) 14.45 0 28.1 ±2.4 1.67 (1.03–2.74) 13.19 ±1.42 53
MJZ195 96 1.88 (845) 11.13 (4,999) 1.43 (13,301) 11.5 0 25.5 ±1.4 1.73 (0.92–2.82) 13.56 ±1.18 54
MJZ240 113 3.85 (3,111) 8.8 (7,123) 1.41 (13,301) 9.06 0 81.4 ±2.8 2.68 (1.83–3.98) 13.27 ±1.24 51
CJB-2 105 1.18 (1702) 3.69 (5,311) 1.38 (13,301) 4.21 0 59.9 ±2.7 2.54 (1.64–3.5) 13.95 ±1.67 80
MJZ320 73 1.53 (664) 4.25 (1848) 1.42 (13,301) 4.62 0 83.4 ±6.6 2.23 (1.42–3.19) 13.14 ±1.74 46
Note: ρs: spontaneous track densities measured in internal mineral surfaces; ρi and ρd: induced and dosimeter track densities on external mica detector; in bracket is the number of tracks
and radiation flux; p(χ
2
): probability of obtaining χ
2
value for single-grain ages degrees of freedom; Dpar is the fission tracks etch pit measurements.
TABLE 2 | Detrital AFT peak-fitting data.
Sample Depositional
Age (Ma)
nAge range
(Ma)
P
1
P
2
P
3
P
4
Modern river sample 0 108 9.49–181 23 ±1.7 —47.9 ±2.9 93.5 ±6.9
37.3 ±6.5% 46.4 ±6.9% 16.3 ±9.5%
CJB-1 3.6 118 13.52–173.08 20.8 ±2.3 —52 ±4.7 93.1 ±9.5
9.4 ±3% 34 ±11% 57 ±11%
MJZ15 4.8 82 8.59–95 19.4 ±1.5 39 ±4.4 ——
75.3 ±9.8% 24.7 ±9.8%
MJZ45 6 82 6.4–94 18.9 ±2.1 39 ±4.1 ——
48 ±12% 52 ±12%
MJZ95 7 71 5.97–159.97 16.1 ±1.3 —53.7 ±5.8 —
63.7 ±8.1% 36.3 ±8.1%
MJZ195 8.5 96 5.4–138 —26 ±1.4 —81.9 ±8.3
80 ±4.8% 20 ±4.8%
MJZ240 9.2 113 25.18–198.61 ——55.8 ±4.7 97.3 ±5.1
35.2 ±10% 64.8 ±10%
CJB-2 10 105 14.2–151.38 —39.2 ±3.5 67.6 ±4.4 —
25 ±12% 75 ±12%
MJZ320 12 81 12.28–184.83 24.7 ±2.7 ——111.7 ±7.3
22.6 ±5.4% 77.4 ±5.4%
Note: The binomial peak-fitting ages are given in 1 Ma ±1 SE. The percentage of grains in a specific peak is also given. Ntotal number of analyzed grains; “—” is no data. The depositional
ages of the XB are determined by magnetostratigraphy, and their errors are lower than 0.1 Ma. Sample single-grain ages are statistically decomposed into age components (P1–P4) by
Density Plotter (Vermeesch, 2012). The modeled peak ages (with estimated standard deviations) and proportions of age components are given. Depositional ages of samples from the
Mojiazhuang and Caojiabao sections are correlated to the magnetostratigraphic ages from Zhang et al. (2016) and Yang et al. (2017).
Frontiers in Earth Science | www.frontiersin.org December 2021 | Volume 9 | Article 7601006
Chen et al. AFT Data in Xining Basin

(Figures 2,3). In the MJZ section, this formation is mainly
composed of a very thick gray conglomerate with a thin layer of
light brown gravelly siltstone, and the conglomerate features a
massive structure, poor sorting, and miscellaneous basal support
(Figure 2A,3A, and B). The Mojiazhuang Fm. in the CJB
section mainly consists of fluvial to lacustrine red beds and
contains gravel sediments from terraces (Zhang et al., 2017)
(Figure 2). The gravel composition, paleocurrent direction,
and sedimentary facies and structure in the CJB section are
similar to those of the MJZ section, which is mainly composed
of conglomerate, sandstone, mudstone, and siltstone (Figures
3A–C), lending support to the regional stratigraphic correlation.
The gravel composition of the Mojiazhuang Fm. is mainly
metamorphic sandstone, siltstone, quartz, and schist (Yang
et al., 2017).
SAMPLING AND MEASURING
We collected nine ∼3- to 6-kg sandstone samples from the
modern Huangshui River and the sedimentary sections.
Meanwhile, to identify the main source areas of the sections,
researchers used paleocurrent orientations to constrain the
provenance change in the sediments transported by flows.
Previous paleocurrent measurements of the Mojiazhuang Fm.
at the top of the CJB section suggest that flows were directed to
the south or southwest (Zhang et al., 2017), whereas the
Guanjiashan Fm. lacks paleocurrent direction indicators. In
this study, the paleocurrent direction was supplementarily
measured from the pebble–cobble imbrications in the
conglomerates in the lower part of the CJB section (80 m).
The data are plotted as rose diagrams to identify the source
direction (Figure 2C). The external detector method was used for
AFT dating in this study, and the detrital apatite age was
calculated by the Zeta calibration method (Hurford and
Green, 1983). This work was completed in the Rock-Mineral
Preparation and Fission Track Dating Laboratory of the
Geochemical Analysis and Testing Center, Northwest Institute
of Eco-Environment and Resources, Chinese Academy of
Sciences. The neutron flux was monitored with IRMM540R
standard U glass. The Zeta calibration factor of 264.09 ±6.88
was used in age dating (the Zeta calibration standards used were
the Durango, Mt. Dromedary, and Fish Canyon Tuff standards).
Spontaneous fission tracks in apatite were etched with 5% HNO
3
at 21°C for 20 s (Ketcham et al., 2009;Sobel and Seward, 2010).
Induced fission tracks in the muscovite external detectors were
etched with 40% HF at 20°C for 40 min. Fission tracks and track
length measurements were counted on a Zeiss microscope at
1,000×magnification under a dry objective. We performed a
p(χ
2
) test of the AFT ages for each sample using the Radial Plotter
program (Vermeesch, 2012;Sundell and Saylor, 2017). A p(χ
2
)
probability value of less than 5% is evidence that AFT ages
represent a mixed age population (Galbraith and Laslett,
2005). Under that condition, the peak age of the apatite
single-grain age component of each sample was determined by
the Density Plotter program (Vermeesch, 2012).
RESULTS
Detrital AFT ages of all the samples are presented in Tables 1 and
2, and the apatite single-grain ages range from 198.61 to 5.4 Ma
(Table 1)(Supplementary Table S1 in the supporting
information). All samples failed the p(χ
2
) test, which means
that the sample cooling ages were dispersed and derived from
multiple sediment sources (Figures 2,3). To distinguish the
stable satisfactory age populations of different sources, 113–-71
apatite grains from each sample were dated, and all samples were
decomposed into 2–4 best fit peak ages (Table 2). Figures 2,3
show each sample’s age–density histogram and the peak age value
of the mixture model of multiage components for kernel density
estimation. Whether the sample was annealed post depositionally
must be evaluated before interpreting the detrital AFT ages. The
strata in the two sections in this study are approximately
horizontal, and the thickness is much less than the annealing
depth of the apatite samples (<3 km) (Bernet and Spiegel, 2004).
FIGURE 4 | Lag time plot of detrital AFT ages in the XB. Black symbols (P1–P4) are component ages from this study. Dashed lines are the lag time contours with
corresponding lag times labeled. The peak age trend shift (peak ages progressively decrease and then increase) occurred at ∼8±1 Ma for P1, P2, P3, and P4, where
each are considered to represent the time of a significant sediment recycling event.
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Chen et al. AFT Data in Xining Basin

The AFT peak age component of each sample is older than the
corresponding sedimentary age and changes vertically within the
sections, which is not consistent with the annealing
characteristics caused by post–depositional burial heating (Van
der Beek et al., 2006). However, a few detrital AFT grain ages are
always younger than or equal to their depositional ages. These
younger AFT grain ages may indicate that the sediments may
have experienced some degree of reheating or even total
annealing. The track length distribution in detrital sample
mixtures of differentiated lengths has been probably modified
by annealing due to burial/reworking during the post
depositional period. Most of our samples yielded tens of
measured confined track lengths, and the c-axis–corrected
mean track lengths of all samples ranged from 13.58 ±
1.62 μm (CJB-1) to 14.03 ±1.54 μm (MJZ45) (Table 1).
However, it is difficult to identify the degree of sample
annealing before and after deposition based on these track
lengths. The relative track length (>13 μm) distribution has
ruled out significant annealing in both periods (Gallagher
et al., 1998). The average measured Dpar range of the sample
grains is 3.01–2.16 μm(Table 1). These parameters suggest that
the AFT peak ages are not affected by the chemical composition
or burial annealing of the grains (Gleadow et al., 1986;Donelick
et al., 1990). Therefore, we rule out the possibility of thermal
resetting of the detrital AFT ages by burial heating, and the single-
grain and peak ages could represent exhumation information
related to their provenance.
The paleocurrent direction results show that similar to the
overlying Mojiazhuang Fm., the Guanjiashan Fm. presents a
southward paleocurrent direction in the lower part of the CJB
section. Based on the previous paleocurrent data, the
Mojiazhuang Fm. and Guanjiashan Fm. in the MJZ section
also have analogous southward flow directions (Yang et al.,
2017), which indicate a northerly source, i.e., the Daban Shan
(Figures 1B,3). In addition, when evaluating the sedimentary
ages of the detrital AFT samples, the samples in the section need
to interpolate the error in the depositional ages of each sample,
which is thought to be less than 1.0 Ma based on the
magnetostratigraphic data published by Zhang et al. (2017)
and Yang et al. (2017). Furthermore, we set the sedimentary
age of modern fluvial clastic sediments originating from the
Daban Shan through the CJB section to 0 Ma. The plot of
detrital AFT peak ages versus depositional age yields the
following peaks (Figure 4): P1 (24.7–16.1 Ma), P2
(39.2–27.7 Ma), P3 (67.6–47.9 Ma), and P4 (111.7–82.8 Ma)
(Table 2). The above peaks have an obvious trend from
24.7 ±2.7 Ma, 39.2 ±3.5 Ma, 67.6 ±4.4 Ma, and 111.7 ±
7.3 Ma at the bottom of the section to 16.1 ±1.3 Ma, 27.7 ±
3.7 Ma, 53.7 ±5.8 Ma, and 82.8 ±8.5 Ma at 8 ±1 Ma. For
samples with depositional ages of less than 7 Ma, a massive P1
peak appears at the top of the sections, and the P2 and P4 peak
ages increase to 23 ±1.7 Ma, 39.9 ±4.4 Ma, and 93.5 ±6.9 Ma at
the top of the sections. By contrast, the AFT peak age at the top of
the sequence tends to be more stable than those of the samples
deposited before 8 ±1 Ma. The 8.5–7Mafluctuation in the AFT
peak age in the sections suggests that preexisting deposited
sediments were recycled in the CJB and MJZ sections. In
addition, the lag time is significantly shortened to 9.1 ±1Ma
during the 8 ±1 Ma sedimentary interval, indicating that strong
tectonic deformation occurred on the northern margin of the XB
during that period (Figure 4). The AFT peak age trends in the
succession stratigraphy of the CJB and MJZ sections can provide
evidence of recycled sediments on the northern margin of the XB
(Malusà and Fitzgerald., 2020).
DISCUSSION
Sedimentary Provenance of the CJB and
MJZ Sections
The basin sediments transported from the peripheral mountains
record information on the cooling/exhumation evolution of the
basement in the source area (Coutand et al., 2006). Hence, the
unannealed AFT data in sediments can be interpreted by
identifying the source area and by investigating the
provenance of the sediment in the CJB and MJZ sections. The
sediment accumulation in the XB since the Cenozoic has been
influenced by multistage tectonic exhumation of the East Kunlun
orogenic belt and the West Qinling and Qilian Shan orogenic
belts. Previous studies have suggested that the aforementioned
tectonic units acted as provenances supplying the basin with
sediment during the early Cenozoic (Horton et al., 2004;Zhang
et al., 2016;He et al., 2019). The source area of the basin after the
Miocene shifted to the Qilian Shan (Daban Shan) or Laji Shan
(Zhang et al., 2016)(Figure 1C). Furthermore, the MJZ and CJB
sections comprise the uppermost horizontal sedimentary strata of
the uppermost Cenozoic sequence in the XB. Their lithology and
sedimentary structure characteristics are very similar, and the
stratigraphic lithology has been divided into three sedimentary
facies from bottom to top: floodplain, braided river, and alluvial
fan (Yang et al., 2017;Zhang et al., 2017). Floodplain deposits
dominate the bottom of both sections and consist of interbedded
mudstone and siltstone with numerous paleosol complexes and
occasional thin marl or thin sandstone beds. In the middle
sequence of the section, the braided river intrusion with strong
hydrodynamic forces increases the interbedding of sandstone and
fine conglomerate layers. The upper part of both sections is
dominated by coarse-grained alluvial fan sediments which
were deposited under stronger hydrodynamic forces, forming
thick pebble–pebble conglomerate beds with occasional
sandstones and siltstones (Zhang et al., 2017). All the
measured paleocurrent results are characterized by a dominant
southerly current direction, and the sedimentary facies and
stratigraphic lithology are similar, allowing correlation between
the two sections. These findings suggest that the sediments from
the Precambrian basement strata in the south are bounded by the
Daban Shan in the eastern part of the Qilian Shan and were the
main source area supplying the basin during the Late
Miocene–Early Pliocene (Yang et al., 2017;Zhang et al., 2017).
The generally large-diameter gravel clasts in the thick
conglomerates of the sections attest to high-intensity fluid flow
transport, from which it is speculated that the mountains to the
north of the basin may have been greatly uplifted during this
period (Yang et al., 2017). In addition, Zhang et al. (2016) argued
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Chen et al. AFT Data in Xining Basin

that the detrital zircon ages and depositional environment
changes present in the Shuiwan section indicate that rapid
uplift of the Qilian Shan occurred after ca. 20 Ma. However,
Lease et al. (2011,2012) used detrital zircon ages and low-
thermochronology methods to constrain the start of the
accelerated growth of the WNW-trending eastern Laji Shan to
ca. 24–22 Ma and north-directed Jishi Shan to ca. 13 Ma. This
kinematic shift near our study area corresponds to changes in
sedimentary facies present only in the Xunhua basin (located to
the south of the Laji Shan), while the sedimentary environment
and provenance changes in the XB experienced no significant
shift during the corresponding time. Recently, Nd and Pb isotope
analyses of the Cenozoic strata in the XB have provided robust
evidence showing that the proportion of sediment input from the
Qilian Shan increased and represented ∼70–35% after the Early
Miocene (He et al., 2019). In summary, the unannealed AFT ages
of the sediments in the CJB and MJZ sections effectively
document the exhumation and deformation of the Qilian Shan.
Pre-Cenozoic Exhumation Events
The new AFT data present multistage Mesozoic–Cenozoic
tectonic dynamic evolution events based on material sourced
from the Qilian Shan. The oldest Late Cretaceous signal P4
(111.7–82.8 Ma), which was also identified in the AFT analysis
by Wang et al. (2016), formed prior to the Late Miocene sediment
sequence in the XB. Similar bedrock thermal simulation AFT age
FIGURE 5 | (A) Colored dots from thermochronology and sedimentology compilation studies on the South, Central, and North Qilian Shan; the ages are denoted
by points of different colors ranging from Cretaceous to Early Pliocene. The dashed white lines separate South, Central, and North Qilian Shan areas (modified from Feng
and He, 1996). (B) Temporal distribution of the late Mesozoic–Cenozoic tectonic events recorded in the Qilian Shan, as cons trained by thermochronology (squares) and
sedimentology (diamonds).
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Chen et al. AFT Data in Xining Basin

signals are widely exposed in the northern XB and northwestern
Qilian Shan (George et al., 2001;Jolivet et al., 2001;Pan et al.,
2013;Wang et al., 2015a;Qi et al., 2016;Wang et al., 2020). In
addition, the XB, Qaidam Basin, and Hexi Corridor Basin have
received Qilian Shan sediments, and the abundant clastic material
with Late Cretaceous cooling ages and the widespread angular
and parallel unconformities between the Cenozoic and Late
Cretaceous strata indicate that a significant tectonic event
occurred during the Late Cretaceous to Early Cenozoic
(Bureau of Geological and Mineral Resources of Qinghai
Province (BGMRQP); Gansu Geological Bureau, 1989; Abels
et al., 2001;Pullen et al., 2008;Wan et al., 2010;Li et al.,
2013;Ding et al., 2017;Zuza et al., 2018;Chen et al., 2019;
Lin et al., 2019;Pang et al., 2019b;He et al., 2020a;He et al.,
2020b)(Figure 5). These characteristics in the Qilian Shan have
also been observed elsewhere in northern Tibet, and low-
temperature thermochronological evidence indicates that Late
Cretaceous to early Eocene exhumation events were widespread
regional events (Jian et al., 2018). Thermochronological evidence
and paleoelevation estimates also suggest rapid to moderate
cooling and substantial surface elevation gain in central Tibet
during the Cretaceous to Eocene (Kapp et al., 2003;Wang et al.,
2008;Rowley and Currie, 2006;Ding et al., 2017). This situation
implies that the Andean-type northward subduction of the Neo-
Tethys oceanic plate during the Cretaceous led to thickening of
the north Tibet lithosphere (Staisch et al., 2016;Allen et al., 2017;
Ding et al., 2017;Lippert et al., 2014). These events may have been
caused by the closure of the Mesozoic Tethys in the southern
Qaidam Basin, which acted as the force driving Cretaceous
tectonic activity on the northern plateau (Vincent & Allen,
1999;Yin and Harrison, 2000;Jolivet et al., 2001;Pullen et al.,
2008;Duvall et al., 2013;Jian et al., 2018). The north-directed
Lhasa–Asian Plate collision triggered northeastward sinistral
strike-slip activity on the Altyn and Kunlun faults in the
Jurassic–Late Cretaceous (Murphy et al., 1997; Liu et al., 2000;
Ritts and Biffi, 2000;Yin and Harrison, 2000;Jolivet et al., 2001;
Sobel et al., 2001;Kapp et al., 2005;Liu et al., 2005;Tian et al.,
2014;Kapp et al., 2015). Although the amount of crustal
thickening and pervasive suture zones in the northeastern
Tibetan Plateau prior to the collision remain unclear, the new
detrital AFT analysis results in this study indicate that the
widespread pre-collisional deformation region may have
influenced the tectonics of the current northern margin of the
Tibetan Plateau.
Cenozoic Multistage Tectonism
Exhumation Events
Evidence of Cenozoic deformation in the Qilian Shan is
concentrated in the suture zone of the ancient block, and this
zone has inherited the tectonic activity properties of the pre-
Cenozoic structures (Zuza et al., 2016,2018). Based on dated
unannealed detrital AFT ages and previous thermochronological
and sedimentological studies, we infer that the CJB and MJZ
sections record three exhumation stages representing the Qilian
Shan tectonic evolution during the Cenozoic. The detrital AFT
peak age P3 (67.7–47.9 Ma) reveals that the first stage of
Paleocene–Early Eocene tectonic reactivation in the Qilian
Shan occurred almost synchronously with the initial
India–Asia collision (An et al., 2020;He et al., 2020a). At this
time, the detrital accumulation rate accelerated in the Qijiachuan
Fm. (54–51.8 Ma), and the XB experienced clockwise vertical axis
block rotation (Horton et al., 2004), both of which reflect the
growth of the Qilian Shan during the early Cenozoic (Fang et al.,
2019). Similar scenarios are observed in the Qilian Shan and
northern Qaidam basins, in which contemporaneous tectonic
exhumation events were associated with exhumation, the onset of
coarse sediment deposition, sedimentation rate acceleration, and
unconformity development (Horton et al., 2004;Yin et al., 2002;
Meng and Fang, 2008;Yin et al., 2008;Bush et al., 2016;Qi et al.,
2016;He et al., 2017;Jian et al., 2018;Zhuang et al., 2018;Cheng
et al., 2019;An et al., 2020;He et al., 2020a;He et al., 2020b;
Cheng et al., 2021)(Figure 5), but none received large quantities
of clasts from the Qilian Shan deposited on the Hexi Corridor
during the corresponding time (Dai et al., 2005;Bovet et al.,
2009). Accompanying the initial Indian–Asian Plate collision, the
early Cenozoic deformation was also roughly stratigraphically
consistent with cooling events in the northeastern part of the
plateau, such as the Jiuquan basin (He et al., 2018;Lin et al., 2019),
Lanzhou basin (Yue et al., 2000;Fang et al., 2007), East Kunlun
Shan (Duvall et al., 2011;Duvall et al., 2013), Altyn fault (Mock
et al., 1999;Jolivet et al., 2001), Haiyuan-Liupan Shan (Lin et al.,
2011), and West Qinling (Clark et al., 2010).
The second-stage age populations with peaks at P2
(39.2–27.7 Ma) and P1 (24.7–16.1 Ma) indicate that the Qilian
Shan was subjected to a series of exhumation events that occurred
in the Late Eocene–Oligocene and Early Miocene.
Thermochronological studies identifying Eocene–Early Miocene
tectonic events havealso been based on detrital and in situ AFT age
signals in the Qaidam Basin, Hexi Corridor Basin, Qilian Basin,
and Qilian Shan (Jolivet et al., 2001;Zheng et al., 2010;Qi et al.,
2016;He et al., 2017;Zhang et al., 2018;Zhuang et al., 2018;Yu
et al., 2019;An et al., 2020;He et al., 2020a;He et al., 2020b)
(Figure 5). In addition, sedimentological studies have emphasized
that in the Eocene–Oligocene, thrusting continued to progress in
the Qilian Shan (Yin et al., 2002;Yin et al., 2008;Cheng et al., 2019).
As a result, the sedimentary environment changed from a dry salt
lake to a floodplain from the Mahalagou Fm. to the Xiejia Fm., and
a growth strata relationship formed between the two groups at the
edge of the XB (Fang et al., 2019). An analysis of the Early Miocene
provenance also suggests that the primary provenance of the XB
was the Qilian orogenic belt, while the Laji Shan represented a
secondary provenance, indicating that the Qilian Shan experienced
tectonic exhumation during this episode (Lease et al., 2011;Xiao
et al., 2012;Wang et al., 2016;Zhang et al., 2016;Wang et al., 2017).
The corresponding episodes of bedrock exhumation in the Qilian
Shan are also confirmed by the marked increase in the
accumulation rate and sediment flux in the Qaidam Basin and
Hexi Corridor Basin (Jian et al., 2013;Wang et al., 2017;Jian et al.,
2018;Zhuang et al., 2018;Zhuang et al., 2019)(Figure 5). The
oldest Cenozoic sediments in the Hexi Corridor is the Huoshaogou
Fm., where the sequence presence of the thick alluvial fan
conglomeration at the bottom of the foreland basin may
indicate the initial deformation and uplift of the northern
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Chen et al. AFT Data in Xining Basin

Qilian Shan (Dai et al., 2005;Bovet et al., 2009;Guo et al., 2009).
This process is driven by the Altyn faults and Kunlun fault that
thrust onto the Hexi Corridor Basin, Muli Basin, and Qaidam
Basin from its foreland margins (Cheng et al., 2018;Qi et al., 2013;
Qi et al., 2015;Yu et al., 2017;Zhuang et al., 2018;Zhuang et al.,
2019). The Altyn fault and East Kunlun Shan exhumation events
also indicate that the crust of the northeastern margin of the
Tibetan Plateau continued to thicken and grow outward after plate
collision (Mock et al., 1999;Ritts et al., 2004;Molnar and Stock,
2009;Clark et al., 2010;Zhuang et al., 2011).
During the last stage, the reversal of the AFT peak ages at 8 ±
1 Ma in the CJB and MJZ sections suggests that the late Miocene
sediment recycling in the XB may have been caused by tectonic
deformation (Figure 4). The detritus was eroded from the
sequence before the Mojiazhuang Fm. was deposited starting
at ca.8 Ma, and it was temporarily stored in the XB, where it was
not affected by post depositional annealing (peak age
components include P2, P3, and P4). Starting from 8.5 Ma
(MJZ195), thrust fault activity controlled the uplift and
erosion of sediment previously stored in the XB wedge-top
basin. Thus, sediment reworked from pre-8 Ma samples was
transported to the final sink and mixed with sediment derived
from erosion after 8 Ma, forming a new sedimentary unit. This
scenario suggests that long-term sediment storage and
reworking have affected the thermochronological age trends.
Detritus derived from erosion of pre-8 Ma sediment, and
temporarily stored in a wedge-top basin (for example) after
8 Ma was reworked and mixed into the final sink along with
detritus derived from the erosion of previously stored material.
As a result, the samples with sediment recycling (MJZ95,
MJZ45, MJZ15, CJB-1, and modern river samples) are
expected to include not only the peak (P1) defined by the
AFT ages measured in mineral grains but also all the major
grain-age populations inherited from the Guanjiashan Fm. Only
the smallest grain-age populations of the Guanjiashan Fm. are
prone to remain undetected in the Mojiazhuang Fm. because
they may fall below the detection limit after sediment mixing
(Vermeesch, 2012). In the Mojiazhuang Fm., the age peaks
inherited from recycled sediments are invariably older than
the age peaks derived from erosion of the Guanjiashan Fm. The
Mojiazhuang Fm. includes all the major AFT age populations
detected in the underlying late Miocene–Pliocene formations of
the CJB and MJZ succession, which is consistent with recycling
of specific intervals of a stratigraphic succession within a basin
after long-term storage and reworking (Malusà and Fitzgerald,
2020). Thermal modeling of the AFT data and analysis of the
heavy minerals in the Laji Shan bedrock also suggest that the
exhumation stage occurred in the Late Miocene (8–4Ma)
(Wang et al., 2016). In addition, the rapid increase in the
gravel diameter and coarse conglomerate content from the
Guanjiashan Fm. to the Mojiazhuang Fm. reflects a sharp
rise in the sedimentation rate during this period (Yang et al.,
2017;Fang et al., 2019). Evidence of growth strata and climate
proxies in the Jiuquan Basin and Qaidam Basin also reflects the
strike-slip thrust system activity in the Qilian Shan building
high topography from the Late Miocene to the Pliocene (Bao
et al., 2019;Yin et al., 2008;Zheng et al., 2010;Wang et al., 2017;
Zheng et al., 2017;Zhang et al., 2018;Zhuang et al., 2018;Chen
et al., 2019;Fang et al., 2019;Hu et al., 2019;Pang et al., 2019a,
Zhang et al., 2021)(Figure 5). Several previous studies also
underlined the Miocene acceleration motions of the major
strike-slip faults adjacent to the basin, which are significant
for exploring the proximal exhumation. Current evidence
suggests that the left-slip Haiyuan fault initiated at ca. 16 Ma
(e.g., Li et al., 2019, 2020; Duvall et al., 2013;Zhang et al., 2020),
but the right-slip Riyueshan and Elashan faults may also be
slightly younger, i.e., closer to ca. 10 Ma (Yuan et al., 2011;
Cheng et al., 2021). In addition, Lease et al. (2011) through
apatite (U-Th)/He dating analysis revealed that the accelerated
growth of the WNW-trending eastern Laji Shan began at ca.
24–22 Ma and that growth of the north-trending Jishi Shan did
not commence until ca. 13 Ma. Noticeably, the tectonic activity
intheLateMioceneisalsoconfirmed by the increase in the large
number of Miocene deformation tectonothermal events that
occurred on the northeastern margin of the Tibetan Plateau (ca.
15–5 Ma), as evidenced by AFT and (U-Th)/He data similar to
our data, and the reorganization of deformation along the Qilian
Shan fault (Lease et al., 2011;Yuan et al., 2011;Craddock et al.,
2012;Duvall et al., 2012;Lease et al., 2012;Yuan et al., 2013)and
the West Qinling and Eastern Kunlun faults (Clark et al., 2010;
Lin et al., 2011;Duvall et al., 2013;Wang et al., 2020).
Collectively, the scattered Early Miocene deformation in the
major left-lateral strike-slip faults was followed by widespread
late Miocene deformation associated with right-lateral slip in
the Qilian Shan (Figure 5). Therefore, we speculate that the
deformation situation related to the kinematic shift in
northeastern Tibet is compatible with west–east crustal
stretching/lateral displacement, nonrigid off-fault
deformation, and broad clockwise rotation and bookshelf
faulting, which together accommodate northeast–southwest
India–Asia convergence (Cheng et al., 2021).
In summary, the comprehensive analysis of the Qilian Shan
AFT data revealed that the mountain range experienced initial
tectonic exhumation events in the early Cenozoic in quasi-
synchronous response to the Indian–Asian Plate collision, as
supported by the previous results of sedimentological studies.
During the Oligocene–Miocene period, the combined action of
multistage deformation caused the plateau to thicken and
expand outward after plate collision. Thus, during this
period, the influence of this plate collision propagated nearly
instantaneously to different regions in the northeastern Tibetan
Plateau.IntheLateMiocene,theupliftoftheQilianShan
caused a sediment recycling event. Our findings indicate that the
Tibetan Plateau gained elevation in the Mesozoic–Early
Cenozoic, driven by the convergence of different blocks. This
plateau growth scenario seems to be incompatible with the
deforming viscous mantle lithosphere model (Clark, 2012;
Clark et al., 2010;Yin et al., 2008), which predicts that the
entire plateau has shortened at a constant strain rate over time.
An important caveat of the applicability of this model is the
pervasive suture zones in the Qilian Shan and even the Eastern
Kunlun range (Allen et al., 2017). Without these weak zones, the
NE Tibetan Plateau deformation may not have so easily
reactivated and resulted in quasi-synchronous deformation in
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Chen et al. AFT Data in Xining Basin

the early stage of the collision, which was accompanied by
region-specificamplitudes(Zuza et al., 2016;Jian et al., 2018;
Zuza et al., 2018;Cheng et al., 2021).ThelateMiocene
deformation of the plateau seriously influenced the climatic
and paleogeographic pattern evolution (Li et al., 2021;Zhang
et al., 2017).
CONCLUSION
Through AFT analysis of Late Miocene to Early Pliocene
synorogenic sediments in the XB, we discussed the
exhumation history of the Qilian Shan. Based on the AFT
dating results from these sediments, the earliest exhumation
phase occurred during the Late Cretaceous. The results reveal
both the pre-Cenozoic growth history and the Cenozoic
deformation mechanism of the Qilian Shan and other regions
along the northeastern margin of the Tibetan Plateau. The early
Cenozoic detrital AFT age group suggests that the block (as the
source of the studied sediments) responded quasi-synchronously
to the initial Indian–Asian Plate collision. The present
geomorphology in the Qilian Shan has experienced multistage
tectonic exhumation overprinting from the late Mesozoic to the
late Cenozoic. The results from this study, as well as related
findings from other regions of the northeastern Tibetan Plateau,
provide new insights into the paleogeographic pattern evolution.
DATA AVAILABILITY STATEMENT
The original contributions presented in the study are included in
the article/Supplementary Material, and further inquiries can be
directed to the corresponding author.
AUTHOR CONTRIBUTIONS
LC contributed in writing, reviewing, and editing, data curation,
writing—original draft preparation; CS and XF contributed in
supervision, project administration, and funding acquisition; YW
contributed to writing—original draft; PH contributed to formal
analysis, validation, and methodology; YZ, JZ, and YC
contributed to visualization and investigation.
FUNDING
This work was co-supported by the Second Tibetan Plateau
Scientific Expedition (STEP) program (Grant No.
2019QZKK0707), the Strategic Priority Research Program of
Chinese Academy of Sciences (Grant No. XDA200702012) and
the National Natural Science Foundation of China (Grant No.
41902223 and 41872098).
ACKNOWLEDGMENTS
We express our cordial thanks to Tao Zhang for the valuable
comments that improved the manuscript. We also thank Lijie
Yao, Pengfei Chang, and Bo Ren for their assistance in the field
and laboratory.
SUPPLEMENTARY MATERIAL
The Supplementary Material for this article can be found online at:
https://www.frontiersin.org/articles/10.3389/feart.2021.760100/
full#supplementary-material
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