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EXTENDED ABSTRACTS: 19TH HIMALAYA-KARAKORAM-TIBET WORKSHOP, 2004, NISEKO, JAPAN
Cenozoic tectonics and geodynamic evolution of the Tien Shan mountain
belt as response to India-Eurasia convergence
Michael M Buslov†‡*, Johan De Grave§¶ and Elena A Bataleva#
† United Institute of Geology, Geophysics & Mineralogy, Siberian Branch-Russian Academy of Science, Novosibirsk, RUSSIA
‡ Hokkaido University, Sapporo, JAPAN
§ Department of Mineralogy & Petrology, University of Gent, Gent, BELGIUM
¶ Department of Geological & Environmental Sciences, Stanford University, Stanford, USA
# United Institute of High Temperatures RAS, Bishkek, KYRGYZSTAN
* To whom correspondence should be addressed. E-mail: [email protected]
....................................................................................................................................................................................................................................................................
The present-day structure of the Tien Shan mountains consists
out of roughly E-W trending, high mountain ranges (exceeding
7000 m), alternating with (near) parallel sedimentary basins. The
Tien Shan is situated in Central Asia at the boundary between
the active orogenic structures of the northern Tarim plate and
the stable Kazakhstan platform (Figure 1). The structural pattern
of the Tien Shan indicates a complex Cenozoic deformational
history with a current N-S shortening rate of 10-15 mm/yr in
the southern Tien Shan and 2-6 mm/yr in the northern Tien
Shan. Moreover, shortening vectors from the northern and
southern Tien Shan are oriented along different directions. These
different shortening rates and orientations can be explained by
the presence of the Precambrian Issyk-Kul microcontinent
embedded in the northern Tien Shan region. The mosaic-block
structure of the Tien Shan mountains is shaped by isometrically
outlined Precambrian microcontinents (Tarim and Issyk-Kul)
surrounded by Paleozoic island arcs and accretionary prisms that
are dissected by Late Paleozoic-Early Mesozoic strike-slip faults.
This complex structure of the Central Asian crust has a strong
impact on the distribution of strain induced by the ongoing
India-Eurasia convergence. In this study we investigate the
relationships between the Cenozoic structure of the Tien Shan,
reactivation of inherited faults, and interaction of rigid
Precambrian microcontinents in the relatively mobile
accretionary-collision belts (Buslov et al. 2003).
Northward propagation of the deformation front away
from the Himalayan collision zone towards intracontinental
Central Asia is suggested by systematic northward rejuvenation
of mountain ranges and intramontane basins (Dobretsov et al.
1995). The model for this northward propagation may be
described as follows: (1) India thrusting under Tibet, resulting
in the uplift and rotation of the latter (35 to 20 Ma); (2) subsidence
of the Tarim depression, Tarim under-thrusting the Tien Shan,
rise of the southern Tien Shan (20 to 11 Ma); (3) reactivation of
pre-existing structures around and within the Issyk-Kul
microcontinent (10 to 3 Ma); (4) rise of the northern Tien Shan
(peak at 3-2 Ma).
Apatite fission track thermochronology performed on
crystalline basement rocks from the western and northern IssykKul basin showed that a first acceleration of rock uplift and
denudation affected the northern Tien Shan starting between
20 and 10 Ma ago, and a second acceleration occurred after 3
Ma ago. The latter is also expressed in the stratigraphy by a
marked change in sedimentary environment in the Late
Pliocene-Early Pleistocene, by thick sequences of coarse
conglomerates, sedimentary gaps and tectonic unconformities.
In the Paleogene, more than 3 km of lacustrine sediments were
deposited in the subsiding basin. The onset of uplift of the
southern Tien Shan started in the Neogene, when clastic and
proluvial sediments, transported from the rising southern ranges
106
were deposited in the basin. In this stage, the basin was much
larger and more elongated than at present. It was probably
controlled by ENE trending faults.
The thrusting of the Tarim plate under the southern Tien
Shan results in the shortening of the upper crust at rates of <1015 mm/yr, whereas India moves northward at 50 mm/yr
(Abdrakhmatov et al. 2001). A part of the strain may have been
accommodated within viscoelastic layers in the middle crust of
the Tien Shan. Seismic and magneto-telluric studies show clear
tectonic layering of the Tien Shan lithosphere, with several nearly
horizontal viscoelastic layers. The lower layer is underthrust
northward underneath the northern Tien Shan as indicated by
seismic data (Figure 1b). Tectonic layering of the lithosphere
beneath the southern Tien Shan is possibly related to the rotation
and underplating of the Tarim plate and indentation of its
basement into the middle crust of the southern Tien Shan. This
caused high-rate slip and failure in the upper crust to depths of
20-30 km (Sabitova and Adamova 2001). Wave-guide lenses are
found in the upper crust at a depth of 10-20 km north of the
Pamir thrust sheets. Oblique wave-guide layers connect the
horizontal layers. A clear change of the wave-guide is present
along an EW profile at 42°N (profile II-II in Figure 1): its southern
extremity is located 15 km shallower than the northern one.
These thick wave-guides are absent beneath the Fergana
depression and adjacent flats. Magneto-telluric studies in the
Tien Shan (Rybin et al. 2001) also indicate the presence of the
abovementioned layers and lenses with a high electric
conductivity. Profile II-II shows the position of the low seismic
wave area (seismic data) and high conductivity layers (magnetotelluric data). There is a good correlation between the results
obtained by the different methods. A 15-25 km thick layer is
located at a depth of 35-50 km to the north of 42°N and at a depth
of 20-35 km to the south of 42 °N. Oblique wave-guides mark
the southern border of the Issyk-Kul microcontinent (Buslov et
al. 2003).
The upper crustal strain has been mainly controlled by the
Issyk-Kul microcontinent. This lens-shaped microcontinent is
surrounded by vast shear zones that have been involved in the
tectonic activity during most of the Cenozoic. During the
Quaternary the strain has propagated as far as the central part
of the Issyk-Kul basin. Activity in the northern Tien Shan reached
its peak in the Pliocene-Early Quaternary and resulted in the
formation of the present-day topography and strong
deformation of the Issyk-Kul basement and its Cenozoic cover.
The strike of regional compression changed from NW-SE in the
Late Miocene to N-S in the Pliocene-Early Quaternary. Both the
southern and northern margins of the microcontinent were
gradually deformed and uplifted, hence reducing the area of
deposition in the basin. Due to thrusting of the northern and
southern margins, the basin morphology at both the western
HIMALAYAN JOURNAL OF SCIENCES
VOL 2 ISSUE 4 (SPECIAL ISSUE)
JULY 2004
EXTENDED ABSTRACTS: 19TH HIMALAYA-KARAKORAM-TIBET WORKSHOP, 2004, NISEKO, JAPAN
and eastern end can be described as full-ramp structures.
Underthrusting of Tarim along the southern Tien Shan resulted
in segmentation of the southern margin of the Issyk-Kul
microcontinent into several blocks separated by oblique thrusts
and strike-slip faults. Strike-slip along the Chon-Kemin fault
resulted in thrusting and reverse faulting along the northern
margin of the microcontinent. The most important active tectonic
movements affecting the Issyk-Kul region today are sinistral
strike-slip motions along the Chon-Kemin, Chon-Aksu, PredKungei, North Issyk-Kul and South Issyk-Kul faults. Strike-slip
faulting probably was responsible for the formation of a pull-apart
structure in the central part of the basin.
References
a
I
Kazakhstan platform
Almati
II
Chu basin
Bishkek
Is sy k- K
Ta
l
as
Fergana basin
-F
er
ga
na
Tadjik
basin
st
Tarim
basin
rik
e-
sl
500 km
II
ip
Pamir
Kazakhstan
platform
0
4 3 20'
km Vp
Kazakhstan
platform
Pull-apart
Cz basin
Thrust fault
Pz-Mz orogens
Strike-slip
fault
Aktyuz-Boordin
microcontinent, pC
Oblique
thrust fault
Issyk-Kul
microcontinent, pC
I
N
ul b asin
Position of
I
I profils
Profile I-I
Chu
basin
Talas-Ferghana
fault
0
0
42 4 0'
42
41 20'
0
40 40'
4 20
4 1 02 0 '
4 004 0 '
S
0
Pamir
40
0
0
39 2 0'
+
M
4 3020 '
km Vs
4 2 04 0 '
40 0
3 902 0'
0
10
20
0
10
20
35
35
50
60
75
50
M
60
75
0
20 km
N
0
Vp
0
10
20
42 40'
5.8
6.3
6.2
35
50
M
60
8.2
km
Vs
0
10
20
50
60
II
Issyk-Kul
basin
5.6
6.0
6.3
6.4
6. 0
42
3 .4
8.
6.0
6.1
4 2040 '
5 . 45 . 6
6.1
6.2
M
3. 7
3.5
6 .0
4 20
3 .3
3.7
3. 4
seismic velocities
waveguides
10
20
50
6. 5
8.
8.0
Issyk-Kul
basin
0
contour lines of
Moho
35
6.4
4 1 02 0 '
3.0
3.6
3 . 3 3.6
3 .6
S
6.3
1
3.2
0
M
5.4
6.3
75
35
6 .0
Profile II-II
km
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Thompson, D Burbank, CH Rubin,
M Miller and P Molnar. 2001.
Origin, direction, and rate of
modern compression of the
central Tien Shan (Kyrgyzstan).
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MM,
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K
Abdarakhmatov, D Delvaux, VY
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and F Salvini (eds). Intraplate
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Dobretsov NL, MM Buslov, D Delvaux,
NA Berzin and VD Ermikov. 1996.
Meso- and Cenozoic tectonics of
the Central Asian mountain belt:
effects of lithospheric plate
interaction and mantle plumes.
International Geology Review 38:
430-466
Sabitova TM and AA Adamova. 2001.
Seismic tomography study of the
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problems, and prospects). Russian
Geology and Geophysics 42(11-12):
1543-1553
Rybin AK, VY Batalev, PV Il’ichev and
GG
Shchelochkov.
2001.
Magnetotelluric
and
magnetovariational studies of the
Kyrgyz Tien Shan. Russian Geology
and Geophysics 42(11-12): 15661573
0
7. 7. 8
9
60
75
thrusts
4 0040 '
3.4 3 . 5
3.5
Tarim microcontinent
0
10
20
strike-slip faults
35
3.6
75
50
60
b
75
FIGURE 1. (a) Tectonic scheme of the Tien Shan Mountains. (b) Geophysical profiles within the
study area (see a for location)
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JULY 2004
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