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The lower terrace yields an exposure age of 19 kyr; the upper yields 30.5 kyr.
Topographic profiles 4 km in length give us offsets of the terraces with respect to the present-day footwall of 14.7 and 33.1
meters. The combination of these two offsets and the two ages allows a calculation of the burial of the footwall, around 8
meters.
These data yield a vertical displacement rate of ≈1.3 mm/yr, more than twice that of previous studies further northwest
(Hetzel et al., 2004). The associated shortening rate due to thrust slip calculated with end member values of the thrust dip
(30 to 60 degrees) range between 1.5 and 2.5 mm/yr. Again, this is significantly higher than the results from further northwest
(Hetzel et al., 2004). This might be explained by the in-sequence propagation of an active back thrust (north of the
Hexi Corridor) where Hetzel et al. (2004) obtained their results. At continental scale our results are consistent with GPS
studies (Zhang et al., 2004).
Depth (cm)
0 50 100 150 200 250
1e+5
2e+5
HX3-P1
10Be
/ g SiO2
3e+5
4e+5
5e+5
6e+5
7e+5
8e+5
Y = (73161 +/- 67213+ (611607+/- 65035) * exp -0.014375x
Rsqr = 0.956
Attenuation lenght: 160cm
d=2.3
scalling factor after stone (2000)
Age = 30.544 +/- 4.74 kyrs
Depth (cm)
0 50 100 150 200 250
0
1e+5
HX3-P2
10Be
/ g SiO2
2e+5
3e+5
Y = (0 +/- 974) + (347600 +/- 1411) * exp -0.014375x
Rsqr = 0.996
Attenuation lenght: 160cm
d=2.3
scalling factor after stone (2000)
Age = 19.014 +/- 0.093 kyrs
Figure 1: Concentration of cosmogenic ( [10Be] / gSiO2) with respect to depth. Scaling factor for
production rate (Stone [2000]) and consideration of inheritance yields the age of exposure begining.
Exposure ages are 30.5 kyrs (upper surface S1) and 19 kyrs (lower surface S2). Calculations
done with Cosmocalc (Vermeesch, 2007).
REFERENCES:
Hetzel, R., Tao, M., Stokes, S., Niedermann, S., Ivy-Ochs, S., Gao, B., Strecker, M.R., Kubik, P.W. 2004: Pleistocene/Holocene slip
rate of the Zhangye thrust (Qilian Shan, China) and implications for the active growth of the northeastern Tibetan
Plateau. Tectonics 23 (6), 1-17.
Stone, J. 2000: Air pressure and cosmogenic isotope production, J. Geophys. Res. 105, 23,753–23,759.
Vermeesch, P. 2007: CosmoCalc: An Excel add-in for cosmogenic nuclide calculations, Geochem. Geophys. Geosyst., 8,
Q08003, doi:10.1029/2006GC001530.
Zhang, P.-Z., Shen, Z., Wang, M., Gan, W., Burgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J., Hanrong, S., Xinzhao, Y.
2004: Continuous deformation of the Tibetan Plateau from global positioning system data Geology, 32 (9), 809-812.
4e+5
1
Symposium 1: Structural Geology, Tectonics and Geodynamics