Full text of DOI:10.1007/BF03183555

thrust fault-anticline belt in front of Chinese northern
Tianshan by surveying and dating the deformed terraces
Surveying of the deformed
terraces and crust shortening
rate in the northwestern
Tarim Basin
[
10,11]
.
In 1998, we surveyed the deformed terraces of the
Boguzi River across the Artushi anticline belt with the
level. In 1999, we surveyed again with the differential
GPS in the same area. The two results are similar. We also
collected TL dating samples on every terrace, processed
them in the Institute of Geology of China Seismologic
Bureau and got the ages of each terrace. Therefore, we
calculated the crust shortening rate since late Pleistocene
in the northwestern Tarim Basin.
1
,2
2,3
SHEN Jun , WANG Yipeng, ZHAO Ruibing ,
3
4
4
LI Jun , D. Burbank & K. Share
1
. Institute of Geology and Geophysics, Chinese Academy of Sciences,
Beijing 100029, China;
2
. Institute of Geology of China Seismological Bureau, Beijing 100029,
China;
1
Tectonic site of the deformed terraces
3
4
. Xinjiang Seismological Bureau, Urumqi 830011, China;
. Department of Geosciences of Pennsylvania State University, PA
1
The northwestern Tarim Basin is a younger com-
pressive tectonic area between Pamir-west Kunlun arcu-
ate tectonic belt and the southwestern Tianshan. Its thou-
sands meter thick Cenozoic layers have been intensively
folded. On the northeastern piedmont of western Kunlun
Mountains, the cover layers of the Tarim Basin con-
6802-2714, USA;
Correspondence should be addressed to Shen Jun (e-mail: shenjuneq
263.net)
@
Abstract Relief surveying and chronology study were
carried out on the deformed river terraces across the Artushi
anticline belt in the northwestern Tarim Basin. The crust
shortening rate of this anticline belt since late Pleistocene
was calculated to be up to 5ü6 mm/a. The total crust short-
ening rate from the northwestern Tarim Basin to southwest-
ern Tianshan since late Pleistocene was estimated to be over
[
4]
structed the external Pamir arcuate structure , and on the
southern piedmont of southwestern Tianshan they con-
[5,6,12]
structed the Keping thrust belt
. Since Middle Qua-
ternary, two nascent thrust fault-anticline belts, the Artushi
thrust fault-anticline belt and Lashi thrust fault-anti- cline
belt, have been formed between the external Pamir arcuate
structure and the Keping thrust belt in the cover layers of
the basin (fig. 1).
1
0 mm/a.
Keywords: Tarim Basin, deformed river terrace, crust shortening.
The Artushi thrust fault-anticline belt is composed of
several lateral thrust fault-anticlines in the northwestern
Tarim Basin (fig. 1). The folded layers of Artushi thrust
fault-anticline are of Upper Tertiary and Lower Pleisto-
In Cenozoic, the intensive tectonic deformation has
occurred in the inland of Asia due to the collision between
India and Asia. The area from Pamir to the Tarim Basin
and southern Tianshan is one of the most deformed prov-
cene. Dipping angles are gentler (20eü30e) in the south
flank and steeper in the north flank (erect or even re-
versed). A south dipping low angle thrust fault developed
in the core of the anticline. Most part of the northern flank
has been under thrust and concealed (profiles A and B in
fig. 1). Attitude in the outcrop of the thrust fault is 150eğ
[
1ü6]
inces
. The principle deforming style in this area is
characterized as the crust shortening due to the northward
indenting of the western syntaxis of the Himalayan Moun-
tains. A series of strong earthquakes have occurred in the
west of the Tarim Basin, such as the 1902 Artushi M 8.3
[
8]
earthquake, the 1985 Wuqia M 7.4 earthquake and the
4
0e. Very fresh fault scarp of Paleoearthquakes developed
[10]
1
997 ü 1998 strong earthquake swarm of 9 M>6
along the fault . This anticline belt was been very active
since Middle Quaternary. There have been 5 strong earth-
quakes with M 6ü6.5 occurring along this anticline belt,
according to the historical earthquake record.
earthquakes. These strong earthquakes indicate very in-
tensive present tectonic movement. The GPS results show
that the crust shortening rate of northwestern Tianshan in
Kykistan and Kazkhstan is around 13 mm/a. According to
geological deformation and earthquake moments, the crust
shortening rate of southwestern Tianshan is around 6
mm/a. The total shortening rate of Tianshan is almost 20
The river terraces across the Artushi anticline belt
[
13]
have been warped up . Those of the Boguzi River per-
pendicularly across the Artushi anticline are well reserved.
They have typical deformed features. It is an ideal site to
carry out quantitative study of the deformed terraces to
acquire the crust shortening rate in present thousands of
years.
[
9]
mm/a . However, for lack of quantitative studies on the
0 ka time scale crust shortening rate of Chinese south-
1
western Tianshan, the shortening rate of Tianshan is only
a rough estimation.
In the compressive areas, the late Quaternary crust
shortening rate can be reliably estimated by accurate relief
surveying and dating on deformed river terraces. Avouc et
al. and Yang et al. estimated the crust shortening rate of
2 Surveying of deformed terraces and calculation of
deformation magnitude
(ν) Surveying of deformed terraces. In 1998, we
surveyed the T2, T3 and T4 terraces with level and range
Chinese Science Bulletin Vol. 46 No. 12 June 2001
1043

NOTES
Fig. 1. The principal tectonic belt in the northwestern Tarim Basin. 1, Late Paleozoic; 2, Tertiary; 3, Upper Tertiary; 4, early Pleistocene;
, middle Pleistocene; 6ü8, Holocene active fault; 6, strike slip fault; 7, concealed fault; 8, thrust fault; 9, anticline; 10, seriel number of
5
tectonic belt;ĉ, western Kunlun tectonic belt;Ċ, external Pamir (Wupar) arcuate structure belt; ċ, Kashi thrust fault-anticline belt; Č,
Artushi thrust fault-anticline belt; č, Keping thrust belt; Ď, east of southwestern Tianshan; ď, west of southwestern Tianshan. In the
geological profile, all faults are Holocene active. The Tuotegongbaizi-Arpaleike fault is active in N and Q. The north Artushi fault and
2
north Kashi fault are active since Q .
finder, combining with the 1Ή10000 relief map (fig. 2).
In 1999, we resurveyed the most intensively deformed
northern parts of T3 and T4 terraces with differential GPS.
Our equipment is GPS system 500 made by Leica-Geo-
system Company. The GPS receiver is Leica SR530.
Based on the reference, which is an unmoving GPS re-
ceiver and the rover, which is a moving GPS receiver, the
system can reduce the error and improve the resolution.
The vertical resolution is about 5 mm+1 ppm. Our sur-
veying profiles are less than 5 km. Theoretically, the ver-
tical error is no more than 1 cm. It is accurate enough for
the quantitative study on the thousands time scale tectonic
deformation. The results of 1999 differential GPS survey-
ing and 1998 level surveying are very close to each other
to finish the relief profiles across the whole anticline (fig.
3).
(ξ) Estimation of crust shortening. Normally, the
magnitude of crust shortening is calculated by the bal-
anced tectonic layers. In our work, the deformed terraces
are formed in about 20000 years. Relative to the kilome-
ters deformation formed in nearly one million years, it is a
small deformation issue. It cannot be calculated with the
balanced layers. The surveyed profiles of the terraces
show that the terraces are warped up around an axis and
only curved down near the northern ends. The corridor
geological mapping of the anticline shows that it is a
typical kink band and the deformation is relative to the
thrust fault. The character of the deformed terraces coor-
dinates with the kinetics of the kink band. Therefore, we
use the following simple equation to calculate the crust
shortening of the small deformation issue:
(
fig. 3(a), (b)).
To improve the efficiency, we got the data for the
slightly deformed south part of higher terraces, the lower
terraces and the flood bed from the 1Ή10000 relief map
1044
Chinese Science Bulletin Vol. 46 No. 12 June 2001

'
LĬtanTꢀ˜+ꢀ Ą( here T is the dipping angle of the thrust
fault).
The dipping angle of the thrust fault is around 40r
e, which is got from the trenches we excavated along the
thrust fault. The calculated crust shortening is 90 m for T4,
0 m for T3 and 21 m for T2 (table 1).
We collected the TL samples in the deposits of T2ü
T4 terraces and processed them at the TL Laboratory of
the Institute of Geology of China Seismological Bureau.
The samples have high signals. The dating results are re-
liable. The ages of T2, T3 and T4 terraces are (6.08f0.47)
ka, (11.7f0.9) ka and (16.9f1.3) ka, respectively. We
calculated the warping up rate and crust shortening rate of
each terrace from the deformation magnitudes and the
ages of terraces. The average crust shortening rate is
around 5.3 mm/a since late Pleistocene, 6 mm/a since
early Holocene and 3.5 mm/a since middle Holocene (ta-
ble 1).
2
7
(
ξ) Error estimation. There are errors in the sur-
veying of deformed terraces, the calculation of the defor-
mation, the collection and procession of dating samples.
The error of the procession dating samples is about 8%.
The site of the samples and the condition of the samples
also make a little error, up to 10%ü20%. Considering the
errors in the relief surveying and calculation in the crust
shorting, the total error may reach 30%. Therefore, the
average crust shortening rate is about (5.3f1.6) mm/a
since late Pleistocene, (6.0f1.8) mm/a since early Holo-
cene and (3.5f1.0) mm/a since middle Holocene. Obvi-
ously, the rate was higher in late Pleistocene and early
Holocene, but it slowed down since middle Holocene.
4
Results and discussion
Fig. 2. The air-photography of the terraces of the Boguzi River across the
Artushi anticline and the surveying route. 1, Boundary of terrace; 2,
position of fault; 3, surveying route.
The Artushi anticline belt we studied is only one of
the tectonic belts between the northwestern Tarim Basin
and the southwestern Tianshan. From the satellite images
and air-photographs, the field observation and the results
of other researchers on this area, the late Quaternary tec-
tonic movement of the Keketamu anticline belt and the
Tuotegongbazi-Arpaleike active fault in the north of the
Artushi anticline belt is not weaker than that of the Artu-
shi anticline belt. There occurred the 1902 Artushi M=8.3
earthquake. The terraces across the Keketamu anticline
belt and the Tuotegongbazi-Arpaleike active fault have
also warped up. However, the poor reservation of the ter-
races makes it very difficult to carry out the accurate
quantitative study. We have not extended the surveying to
this belt. Nevertheless, according to the magnitude of
geological and geomorphological deformation, we esti-
mated that the crust shortening rate in late Quaternary of
this tectonic belt is no smaller than that of the Artushi an-
ticline belt. Thus, the crust shortening rate, made by the
thrust faulting and folding, between the northwestern
Tarim Basin and southwestern Tianshan is no less than 10
mm/a.
Table 1 The results of the quantitative study on the deformed
terrace of Artushi anticline
Magni-
Crust
short-
ening/m
Age of
terrace/
kaBP
Crust
shortening
rate/mmg aꢁ
No. of tude of
terrace warping
up
Warping up
rate/mmgaꢁ
1
1
T2
T3
T4
20
61
78
21
70
90
6.08f0.47
11.7f0.9
16.9f1.3
3.5
5.2
4.7
3.5
6
5.3
3 Ages of the deformed terraces and crust shortening
rate
(
ν) Ages of the deformed terraces. Besides the
amount of the crust shortening, the ages of the deformed
terrace are also the key element to estimate the crust
shortening rates.
All terraces of the Boguzi River are substrate ter-
races. The substratum is Neogene fine sand stone, silty
clay, and the Lower Pleistocene gravel bed. The deposit is
1
ü2 m-thick gravel bed (most gravel is limestone cobble
with the radio of 2ü10 cm), inbedded partially by silt and
fine sand lens beds. No organic carbon was found. Even
though there are many methods to date the young geo-
logical or geomorphological body, the only dating method
available for these terraces is the thermal-luminoferous
The average crust shortening rate since middle
Holocene is obviously smaller than that since late Pleis-
tocene. There are two possibilities. One is that the average
crust shortening rate has been slowed down since middle
Holocene. The other is that the some elastic deformation
has not been converted to permanent deformation by the
strong earthquakes, because the observed deformation on
the surface is mostly performed by intermittent strong
(
TL), because this method can be used to date the burial
age of the fine sand and the silt to represent the age of
these terraces.
Chinese Science Bulletin Vol. 46 No. 12 June 2001
1045

NOTES
Fig. 3. The surveyed relief profiles of the deformed terraces of the Boguzi River. (a) Profiles surveyed by level and meter; (b) profiles
surveyed by differential GPS.
Soc. Am., 1993, Spec Pap 281: 1.
earthquakes. Deficiency of crust shortening indicates that
some of the elastic strain has not been released to the visi-
ble deformation by strong earthquakes. If a strong earth-
quake occurred in the near future and about 10 m crust
shortening was made, the average crust shortening rate
since middle Holocene would be the same as that since
late Pleistocene. Normally, the magnitude of the tectonic
movement does not change in a relatively short period.
The lower rate of crust shortening since middle Holocene
indicates that a large amount of elastic energy has stored,
and there is a high risk of strong earthquake in the Artushi
thrust-anticline belt.
The geophysical sounding of Jiashi project and the
petroleum prospecting reveal that the movement between
different depths of the crust of the Tarim Basin is not co-
ordinate. Under the compression from south to north, the
basement of the Tarim Basin, with high density, is sub-
duction northward into the front of Tianshan, while the
cover layers of the basin, with lower density, have formed
the two thin-skin thrust. One is the Artushi anticline belt
and Kashi anticline belt. It is thrusting northward. The
other is Keping Thrust, which is composed of 4ü5 thrust
fault-anticline belts. It is thrusting southward. Detachment
occurred between lower crust and upper crust. Neverthe-
less, the subduction rate of the Tarim Basin toward the
Tianshan should coordinate with the crust shortening rate
of the cover layers of the Tarim Basin, and the rate is no
less than 10 mm/a.
2
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8
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1
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Acknowledgements This work was supported by the National Natural
Science Foundation of China (Grant No. 49834005), the Commission of
Science and Technology of China (Grant No. 96-913-07-01) and the Key
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