The crustal shortening /thickening within high Tibet and its tectonic ...

Hotine-Marussi Symposium of Theoretical and Computational Geodesy, Wuhan, China, May 29, 2006
Area : ~ 1,000,000 km 2
Elevation : 4000-5000 m
The crustal shortening /thickening within high
Tibet and its tectonic implication
Wang Qi 1,2 Tan Kai 1 and Yang Shaomin 1
1 Institute of Seismology, CEA Wuhan
2 Chinese University of Geoscience , Wuhan
From Burchfiel , GSA Today , 14( 2), 4–10, 2004

Tibetan Plateau : Tectonic Setting
1) India and Asia collide each other along
Himalayas at 40-60 Ma
2) Since then, India, subcontinent is moving
northward at 40-55 mm/a
3) Tibet is deforming in the Cenozoic era ,
associated with various styles of tectonic
features in continent
faulting, metamorphism, sedimentation,
magmatism, earthquake, so on
As summaried by Molnar & Tapponnier,
Science,189, 419, 1975
Features of recent continental tectonics in Asia
can be interpreted as results of the India-
Eurasia collision.
.
Tapponnier et al., Science ,
294,1671, 2001

Telling Feature : Raised Tibet with Striking Flatness
South
North
Tibet
Seismic sounding profile
India
Vertical Stretching
Horizontal N-S Shortening
E-W Extending
1 Crustal shortening is taking place
in the direction of Indian northward
movement path.
2 Crust and/or upper mantle beneath Tibet
are thickened to double mean thickness of
continental crust
3 The Tibet is uplift, standing as the
highest plateau in the world
Question : How is the crust thickened
Kind et al., Science, 298, 1219,2003

Uplift mode in Tibet I
Subduction Model : Indian plate is underthrusting
entirely into Tibet, proposed by Argand, 1924
1 The Indian plate plunged at
Himalayas and extended
northerly beneath the Tibetan
crust
North
South
2 Tibet is raised to the present
topography progressively from
south to north.
Boosting in part, initiated in
south and migrating to north
Himalayas
Tarim

Uplift mode in Tibet II
Indentor ( Bulldoser ) Model : the crust is thickened by pure shear as with India
indenting , proposed by Dewey & Bird , 1973
Pre-collision
South
North
Backstop
Indentor
Himalaya
Tibet is raising steadily and
uniformly
Tarim
1 ) Tibet is deforming
homogeneously
throughout the lithosphere
as viscous sheet
Post-collision
2) Tibet is uniformly
raised to the present
height

Uplift mode in Tibet III
Injection “ Lift” Model: India lower crust is injecting
into middle layer of Tibet crust , proposed by Zhao &
Morgan 1987
1 The India upper mantle
is detached from overlying
crust and sinking into
asthenosphere
North
South
2 The Indian crust is
injecting into weak layer
of Tibet crust and
weakening with reheating
Upper crust is lifted
up step by step
Injecting, then
steadily heating
3 Tibet on wholesale is
lifted hydrostatically and
reach ultimately to the
maximum elevation
Himalayas
the weakened crust is
flowing horizontally in the
channel

Approaches for Model Constraint
1 These models are originally proposed to
interpret features observed geologically and
geophysically
Wang et al. Science, 249, 574 2001
2 No single approach alone(geology , seismology,
geomagnetism, palaeontology …) could yield all
insights into the fundamental problem
3 Geodesy can provide very useful constraints
on present-day crustal deformation.
4 GPS inferred velocity field is leading to better
understanding of kinematics of tectonics and
ultimately geodynamics of continental lithosphere.
Zhang et al., Geology,32, 809, 2004

Kinematic Description of Asian Tectonics :
Rigid block motion vs Viscous continuous deformation
Molnar et al., Science 286, 516, 1999
A
B
Royden et al., Science, 276, 788, 1997.
Avouac & Tapponnier, Geophys Res Lett, 20, 895, 1993
Royden et al., Science, 276, 788, 1997.

Velocity Pattern for rigid blocks :
1 Localized deformation on weaken crustal zone
2 Velocity leap in narrow belt by slip on active fault
3 Stepwise velocity curve
San Andreas
GPS profile
Deformation across the San Andreas fault,
California, Prescott et al., JGR, 106, 6673, 2001
GPS across Basin and Range Province, North
America Thatcher Int Geol Rev, 45, 191, 2003.

Velocity Pattern for Viscous medium
1 Distributed deformation throughout crust
2 Velocity changes little across active fault
3 Smooth velocity curve, decrease monotonically or
linearly with respect to fixed point
Visco-elastic Medium
Driving Force
Velocity
fault
Fixed point
O
Length
Continuously
Deforming
Extension
GPS Profile across boundary zone between the
Australian and Pacific Plate, New Zealand,
Bourne et al, Nature, 391, 655,1998

GPS across Tibetan Plateau
Conclusion I :
In general, Conclusion GPS across I :
Tibet shows a linearly
In general, GPS across
decreased velocity rates
Tibet shows a linearly
respect to Siberia from
decreased velocity rates
40 mm/yr to zero
respect to Siberia from
40 mm/yr to zero
Wang et al. Science, 249, 574, 2001
Conclusion II :
Faults in Tibet slip at rates no more than 10 mm/yr except Himalayas,
Perhaps the deformation is continuous and homogeneous
Zhang et al., Geology,32, 809, 2004
Problem : Sparse dataset does not rule out
the discontinuous mode

~ 2000 site velocities from 1991 to 2004,

GPS Profile across Tibet
mm/yr
Zanbo
Nujiang
Jinsha
1 Thrust Slip Rates
Zangbo : 6.2 ±1.4 mm/yr
Nujiang : 7.4 ± 1.0 mm/yr
Jinsha : 8.4 ± 1.3 mm/yr
N15°E component
Lhasa
Velocity Profile based on
elastic dislocation model
Qiangtang
Songpang
2 The stepwise velocity in
N15°E component across
the High Tibet
3 Intervening blocks (Lhasa,
Qiangtang, Songpan )
Zangbo
Nujiang
Jinsha
deform less than 2-3 mm/yr
Zhang et al., Geology,32, 809, 2004

Himalayan-Tibetan Orogen
Suture and Tertiary Fault:
underthrusting was dominating in the high Tibet
Tertiary Shortening 10-20 Ma
Hacker et al. , Science ,
287, 2463, 2000
Jinsha (Fenghuo Shan
Thrust)
60 - 80 km
Bangong Nujiang
(Amdo-Gaze Thrust)
~250 km
Yarlung Zangbo (Gangdes
Thrust )
> 60 km
Tapponnier et al., Science ,
294, 1671, 2001
Fenghuo
Shan Thrust
Amdo-Gaze Thrust
Gangdes Thrust,
Yin et al., Annu Rev Earth Sci. 28,
211,2 000.

Fault Plane Solution of Earthquake :
No reverse fault in the
interior of Tibet is identified
Molnar & Lyon-Caen ,
Geophys. J. int. , 99, 123, 1989
From Chen et al., J.Geophys.Res. 109, 2002JB002151, 2004
Quaternary Faults in Tibet
Yin et al., Annu Rev Earth Sci. 28, 211,2 000.
No thrusting events M>6 in the
interior of Tibet was recorded
美 国 地 质 调 查 局
Normal and striking-slip
faulting is prevailing at
present

Discussion
• Have these thrusting structures be active since the collision or be
reactivated during late Quaternary (100 kyr) , (10 kyr) Holocene ,
even recent several years
• The thrusting events may occur on the blind reverse faults, producing
no rupture on surface instead of folding growth smeared by
unroofing erosion.
• Thrusting earthquake overcome harder friction on the larger interface
than striking-slip events, thus requires long repeat time and
corresponding large earthquake
• Localized elastic strain is absorbed by aseismic slip-event
Tapponnier et al., Science ,294, 1671, 2001

Summary
• New GPS show a pattern of discontinuous deformation from south to
north across Tibet.
• The thrusting slip rates on Gangdes, Banggong-Nujiang and Jinsha
Suture are 6-8 mm/yr
• Intra-crustal subduction along the sutures has thickened the uppermiddle
crust under Tibet.
• This is facilitated by continuous insertion of the Indian lower crust into the
Tibetan lower curst, raising Tibet

Conceptional Model Modified after DeCelles et al, Tectonics, 21, 1062, 2002
A variant of subduction model propsed
by Argand 1924
Elevation History :
Northerly migrating the 4000-meter front of Tibetan plateau,
constrained by isotope-based palaeo-altimetry
Rowley & Currie, Nature, 439,677 2006

Hotine-Marussi Symposium of Theoretical and Computational Geodesy, Wuhan, China, May 29, 2006
Area : ~ 1,000,000 km 2
Elevation : 4000-5000 m
The crustal shortening /thickening within high Tibet and its tectonic implication
Thank your attention
Wang Qi 1,2 Tan Kai 1 and Yang Shaomin 1
1 Institute of Seismology, CEA Wuhan
2 Chinese University of Geoscience , Wuhan
From Burchfiel , GSA Today , 14( 2), 4–10, 2004