Regional Flow in the Lower Crust and Upper Mantle under the Southeastern Tibetan Plateau

Zhi Wang, Runqiu Huang, Jian Wang, Shunping Pei, Wenli Huang

.

DOI: 10.4236/ijg.2011.24064                

Abstract

Seismic tomography reveals an “R-shape” regional flow constrained between the depths of 50 to 80 km in the Southeastern Tibetan Plateau (STP) which demonstrates some of the differences revealed by the magnetotelluric (MT) soundings in some areas. The “R-shape” flow could be present in both the lower crust and uppermost mantle, but not in the lower crust above the Moho discontinuity. Lateral flow has been imaged under the Qiangtang and Songpan-Ganzi blocks while two channel flows have been revealed beneath the south part of the STP with the eastward lateral flow from the Qiangtang block separating into two channel flows. One branch turns southwards at the south Qiangtang block, along the Bangong-Nujiang fault reaching to the Indochina block, and another is across the Songpan-Ganzi block (fold system) which then separates into northward and southward parts. The northward branch is along the edge of the north Sichuan basin reaching to the Qingling fault and the southward channel turns south along the Anninghe fault, then turns eastward along the margins of the south Sichuan basin. Our study suggests that the crustal deformation along the deep, large sutures (such as the Longmen Shan fault zone) is maintained by dynamic pressure from the regional flow intermingled with the hot upwelling asthenosphere. The material in the lower crust and uppermost mantle flowing outward from the center of the plateau is buttressed by the old, strong lithosphere that underlies the Sichuan basin, pushing up on the crust above and maintaining steep topography through dynamic pressure. We therefore consider that the “R-shape” regional flow played a key role in the crustal deformation along the deep suture zones of the Bangong-Nujiang, the Longmen-Shan faults, and other local heavily faulted zones.

Keywords

Regional Flow, Channel Flow, Crustal Deformation, Deep and Large Suture

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	P. Molnar and P. Tapponnier, “Active Tectonics of Tibet,” Journal of Geophysical Researches, Vol. 83, No. B11, 1978, pp. 5361-5376. doi:10.1029/JB083iB11p05361
[2]	L. H. Royden, B. C. Burchfiel, R. W. King, E. Wang, Z. Chen, F. Shen and Y. Liu, “Surface Deformation and Lower Crustal Flow in Eastern Tibet,” Science, Vol. 276, No. 5313, 1997, pp. 788-790. doi:10.1126/science.276.5313.788
[3]	L. H. Royden, B. C. Burchfiel and R. D. van der Hilst, “The Geological Evolution of the Tibetan Plateau,” Science, Vol. 321, No. 5892, 2008, pp. 1054-1958. doi:10.1126/science.1155371
[4]	M. K. Clark, J. W. M. Bush and L. H. Royden, “Dynamic Topography Produced by Lower Crustal Flow against Reheological Strength Heterogeneities Bordering the Tibetan Plateau,” Geophysical Journal Interiors, Vol. 162, No. 2, 2005, pp. 575-590. doi:10.1111/j.1365-246X.2005.02580.x
[5]	Z. Wang, Y. Fukao and S. Pei, “Structural Control of Rupturing of the Mw7.9 2008 Wenchuan Earthquake, China,” Earth and Planetary Science Letters, Vol. 279, No. 1-2, 2009, pp. 131-138. doi:10.1016/j.epsl.2008.12.038
[6]	Z. Wang, D. Zhao and J. Wang, “Deep Structures and Seismogenesis under the North-South Seismic Zone in Southwest China,” Journal of Geophysical Researches, Vol. 115, 2010, B12334. doi:10.1029/2010JB007797
[7]	Z. Chen, B. C. Burchfiel, Y. Liu, R. W. King, L. H. Royden, W. Tang, E. Wang, J. Zhao and X. Zhang, “Global Positioning System Measurements from Eastern Tibet and Their Implications for India/Eurasia Intercontinental Deformation,” Journal of Geophysical Researches, Vol. 105, No. B7, 2000, pp. 16215-16227. doi:10.1029/2000JB900092
[8]	C. Wang, W. Chan and W. D. Mooney, “Three-Dimensional Velocity Structure of Crust and Upper Mantle in Southwestern China and Its Tectonic Implications,” Journal of Geophysical Researches, Vol. 108, No. B9, 2003, pp. 2442-2459. doi:10.1029/2002/JB001973
[9]	P. Zhang, Z. Shen, M. Wang, W. Gan, R. Burgmann, P. Molnar, Q. Wang, Z. Niu, J. Sun, J. Wu, H. Sun and X. You, “Continuous Deformation of the Tibetan Plateau from Global Positioning System Data,” Geology, Vol. 32, No. 9, 2004, pp. 809-812. doi:10.1130/G20554.1
[10]	Z. Niu, M. Wang, H. Sun, J. Sun, X. You, W. Gan, G. Xue, J. Hao, S. Xin, Y. Wang, Y. Wang and L. Bai, “Contemporary Velocity Field of Crustal Movement of Chinese Mainland from Global Positioning System Measurements,” Chinese Science Bulletin, Vol. 50, No. 9, 2005, pp. 939-941. doi:10.1360/982005-220
[11]	W. Gan, P. Zhang, Z. K. Shen, Z. Niu, M. Wang, Y. Wan, D. Zhou and J. Cheng, “Present-Day Crustal Motion within the Tibetan Plateau Inferred from GPS Measurements,” Journal of Geophysical Researches, Vol. 112, 2007, B08416. doi:10.1020/2005JB004120
[12]	J. Huang, D. Zhao and S. Zheng, “Lithospheric Structure and Its Relationship to Seismic and Volcano Activity in Southwest China,” Journal of Geophysical Researches, Vol. 107, 2002, B102255.
[13]	C. Li, R. D. van der Hilst and M. N. Toksoz, “Constraining P-Wave Velocity Variations in the Upper Mantle beneath Southeast Asia,” Physics of the Earth and Planetary Interiors, Vol. 154, No. 2, 2006, pp.180-195. doi:10.1016/j.pepi.2005.09.008
[14]	C. Li, R. D. van der Hilst, A. S. Meltzer and E. R. Engdahl, “Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma,” Earth and Planetary Science Letters, Vol. 274, No. 1-2, 2008, pp. 157-168. doi:10.1016/j.epsl.2008.07.016
[15]	D. Bai, M. Unsworth, M. Meju, X. Ma, J, Teng, X. Kong, Y. Sun, J. Sun, L. Wang, C. Jiang, C. Zhao, P. Xiao and M. Liu, “Crustal Deformation of the Eastern Tibetan Plateau Revealed by Mannetotelluric Imaging,” Nature Geoscience, Vol. 3, 2010, pp. 358-362. doi:10.1038/ngeo830
[16]	D. Zhao, A. Hasegawa and H. Kanamori, “Deep Structure of Japan Subduction Zones as Derived from Local, Regional, and Teleseismic Events,” Journal of Geophysical Researches, Vol. 99, No. B11, 1994, pp. 22313-22329. doi:10.1029/94JB01149
[17]	Z. Wang, J. Wang, Z. Chen, Y. Liu, R. Huang, S. Pei, Q. Zhang and W. Tang, “Seismic Imaging, Crustal Stress and GPS Data Analyses: Implications for the Generation of the 2008 Wenchuan Earthquake (M7.9), China,” Go- ndwana Researches, Vol. 19, No. 1, 2011, pp. 202-212. doi:10.1016/j.gr.2010.05.004
[18]	F. Pollitz, M. Vergnolle and E. Calais, “Fault Interaction and Stress Triggering of Twentieth Century Earthquakes in Mongolia,” Journal of Geophysical Researches, Vol. 108, 2003, B102503. doi:10.1029/2002JB002375
[19]	M. Kennedy and M. C. van Soest, “Flow of Mantle Fluids through the Ductile Lower Crust: Helium Isotope Trends,” Science, No. 5855, Vol. 318, 2007, pp. 1433- 1436. doi:10.1126/science.1147537
[20]	R. Armijo, P. Tapponnier, J. L. Mercier and H. Tonglin, “Quaternary Extension in Southern Tibet,” Journal of Geophysical Researches, Vol. 91, No. B14, 1986, pp. 13803-13872. doi:10.1029/JB091iB14p13803
[21]	P. Tapponnier, Z. Xu, F. Roger, B. Meyer, N. Arnaud, G. Wittlinger and J. Yang, “Oblique Stepwise Rise and Growth of the Tibet Plateau,” Science, Vol. 294, No. 5547, 2011, pp. 1671-1677. doi:10.1126/science.105978
[22]	W. Wei, M. Unsworth, A. Jones, J. Booker, H. Tan, D. Nelson, L. Chen, S. Li, K. Solon, P. Bedrosian, S. Jin, M. Deng, J. Ledo, D. Kay and B. Roberts, “Detection of Widespread Fluids in the Tibetan Crust by Magnetotelluric Studies,” Science, Vol. 292, No. 5517, 2001, pp. 716- 718. doi:10.1126/science.1010580
[23]	M. K. Clark and L. H. Royden, “Topographic Ooze: Building the Eastern Margin of Tibet by Lower Crustal Flow,” Geology, Vol. 28, No. 8, 2000, pp. 703-724. doi:10.1130/0091-7613(2000)28<703:TOBTEM>2.0.CO;2
[24]	M. K. Clark, L. M. Schoenbohm, L. H. Royden, K. X. Whipple, B. C. Burchfiel, X. Zhang, W. Tang, E. Wang and L. Chen, “Surface Uplift, Tectonics, and Erosion of Eastern Tibet from Large-Scale Drainage Patterns,” Tectonics, Vol. 23, 2004, TC1006. doi:10.1029/2002TC001402
[25]	M. Roy and L. H. Royden, “Crustal Rheology and Faulting at Strike-Slip Plate Boundaries. 1. An Analytic Model,” Journal of Geophysical Researches, Vol. 105, No. B3, 2000, pp. 5583-5597. doi:10.1029/1999JB900339
[26]	E. Enkelmann, L. Ratschbacher, R. Jonckheere, R. Nestler, M. Fleischer, R. G. Bradley, R. Hacker, Y. Q. Zhang and Y. Ma, “Cenozoic Exhumation and Deformation of Northeastern Tibet and the Qinling: Is Tibetan Lower Crustal Flow Diverging around the Sichuan Basin?” GSA Bulletin, Vol. 118, No. 5-6, 2006, pp. 651-671. doi:10.1130/B25805.1
[27]	R. Huang, Z. Wang, S. Pei and Y. Wang, “Crustal Ductile Flow and Its Contribution to Tectonic Stress in Southwest China,” Tectonophysics, Vol. 473, No. 3-4, 2009, pp. 476-489. doi:10.1016/j.tecto.2009.04.001
[28]	W. Wei, S. Jin, G. F. Ye, M. Deng, H. D. Tan, M. Unsworth, J. Booker, A. G. Jones and S. H. Li, “Features of Faults in the Central and Northern Tibetan Plateau Based on Results of INDEPTH (III)-MT,” Frontier Earth Science of China, Vol. 1, No. 1, 2007, pp. 121-128. doi:10.1007/s11707-007-0016-3
[29]	J. Sun, G. Jin, D. Bai and L. Wang, “Sounding of Electrical Structure of the Crust and Upper Mantle along the Eastern Border of Qinghai-Tibet Plateau and Its Tectonic Significance,” Science of China D, Vol. 46, 2003, p. 243.
[30]	D. Alsdorf and D. Nelson, “The Tibetan Satellite Magnetic Low: Evidence for Widespread the Tibetan Crust?” Geology, Vol. 27, No. 10, 1999, pp. 943-946. doi:10.1130/0091-7613(1999)027<0943:TSMLEF>2.3.CO;2
[31]	J.K., He and S.J. Lu, “Lower Friction of the Xianshuihe– Xiaojiang Fault System and Its Effect on Active Deformation around the South-Eastern Tibetan Margin,” Terra Nova, Vol. 19, No. 3, 2007, pp. 204-210. doi:10.1111/j.1365-3121.2007.00735.x