Transcript Presentation

Geophysical study of the crust and upper mantle in
the Qinghai-Tibet Plateau, China:
Broadband seismic observations and
tomography imaging of the
lithosphere in southern and
central Tibetan
He Rizheng, Gao Rui, Zheng Hongwei (CAGS, Cnina)
Zhao Dapeng (Northeastern University, Japan )
USA,2008-11-11
Since Paleozoic, Multiple collisions in diferent geological eras
have sequentially produced near E-W tendings structures,
such as sutures, thrust and folds, thrust and normal faults.
Since ～17Ma, strong E-W extending took place in the Tibet, as
some sequence of collision of India plate with Eurasian
plate( Armijo et al,1989; Yin An et al，2000).
（Kapp and Guynn，2004）
Typical Models for Tibet uplifting
(Argand, 1924)
(Zhao and Morgan, 1987)
The Key question was deep
structure under the central Tibet
needed to be known.
(Dewey and Burke, 1973)
(Hamburger et al., 1992)
(England and Houseman, 1989)
(Tapponnier et al., 1982)
http://www.geo.arizona.edu/~ozacar/models~1.html
05-06
To understand those key questions, hundreds of
broadband stations deployed in Tibet in past two decades
05-06
04-05
07-09
08-09
03-04
03-04
To understand above-mentioned questions, we collect the
datasets of several projects, such as INDEPTH-I,II,III, HIMNT,
305 Stations
in Tibet.
ISC etc, which had been carried
out in theused
central
this study
All of stations used sum up to 305 stations.
3-D Tomography method used was from Zhao Dapeng
(1992,1994, 2001) .
P-wave
images
at
various
depths:
From 0
km
to 100
km
1. Low P-velocity under
Tethyan Himalaya is
shallower than Moho
depth.
2. Velocity structure of
Lhasa Terrane was more
complicated.
3. Low-velocity anomaly
boday located beneath
YGR, which is the most
scale rift in the Central
Tibet.
4. As a whole, the strike of
velocity anomaly body is
similar to suface tectonic
trend.
P-wave
images
at
various
depths:
From
150 km
to 400
km
1. The trending of Pvelocity anomalous
bodies had varied
from E-W in the crust
to nearly S-N.
2. low P-velocity
anomalous body
beneath Tethyan
Himalaya disappered.
Comparing with the
existing results
（He et al.,2006）
(Tilmann et al., 2003)
Comparision between the profile along Tibetan Highway from our group and
the result of Owens and Zandt（1997）.The above one is from Owens and
Zandt（1997),the below one is from this study.
（Zheng et al.,2006)
Tomographic images of E-W
profiles along 25°N show
that Indian Lithosphere had a
bend.
（Zheng et al.,2006）
Tomographic images of the Indian
Lithosphere can be continuously
traced from N24°to N34° under
E88° profile.
（Zheng et al.,2007）
The frontier of subducted Indian Lithospheric Mantle
White solid-lines show the location of the frontier of subducted
ILM projected to the surface. Black dash-lines denote the location
needing to be confirmed. The dash-line contour shows a low Pn
and high Sn attenuation zone (McNamara, 1994 ).
（He et al.,2006）
Our Conclusions
1. The frontier of ILM presently located
beneath the central Qiangtang Terrane,
about N34°.
2. ILM deformed, which was similar to that of
the SCOOP , with about NE strike. The
deformation of ILM resulted of Extending in
the region.
3. The partial melting materials beneath
Tethyan Himalaya maybe resulted of
lecuogranites in the High Himalaya and
Tethyan Himalaya.
Vocanism in Northern
Tibet is hard to
understand
The zone of
uneffect Sn-Low Pn
Is similar to the
potassic vocanic
zone
Cenozoic Potassic magmatism in the central Tibetan happened
during Tibetan uplifting (Hacker et al., 2000; Ding et al., 2003William et al,2004;
Chung et al，2004; Guo et al., 2006).
Seismicity Map (Mb>3.0) from USGS
Hotan
JSS
Ando
Nyma
Zongba
Dangxiong
From 01,Jan to 08, Nov
05-06
09-10
05-06
07-09
04-05
08-09
10-11
03-04
So, we make a plan that we will deploy hundreds
of BB
03-04
stations with ~10km space along the
S-N profile along
E88.5 ° from JSS to KLS, and E-W profile along N34°
or N35°from E83° to E95°to cross the Lavas zone in
Northern Tibet to capture some images of deep structure
under the zone.
2008-09-18
Cartoon of ILM under central Tibet (E85° to E90°)
(Yin & Harrison, 2000 )
(Tilmann et al., 2003)
(He et al.,2006)