ABSTRACT The tectonic deformation and state of stress are significant parameters to understand the active structure, seismic phenomenon and overall ongoing geodynamic condition of any region. In this paper, we have examined the state of stress and crustal deformation during the formation of the Beng Co pull-apart basins produced by an enéchelon strike-slip fault systems using 2D Finite Element Modelling (FEM) under plane stress condition. The numerical modelling technique used for the experiments is based on FEM which enables us to analyze the static behavior of a real and continues structures. We have used three sets of models to explore how the geometry of model (fault overlap and pre-existing weak shear zone) and applied boundary conditions (pure strike-slip, transpressional and transtensional) influence the development of state of stress and deformation during the formation of pull-apart basins. Modelling results presented here are based on five parameters: 1) distribution, orienttation, and magnitude of maximum (σH max) and minimum (σH max) horizontal compressive stress 2) magnitude and orientation of displacement vectors 3) distribution and concentration of strain 4) distribution of fault type and 5) distribution and concentration of maximum shear stress (σH max) contours. The modelling results demonstrate that the deformation pattern of the en-échelon strike-slip pull-apart formation is mainly dependent on the applied boundary conditions and amount of overlap between two master strike-slip faults. When the amount of overlap of the two master strike-slip faults increases, the surface deformation gets wider and longer but when the overlap between two master strike-slip faults is zero, block rotation observed significantly, and only narrow and small surface deform
ation obtained. These results imply that overlap between two master strike-slip faults is a significant factor in controlling the shape, size and morphology of the pull-apart basin formation. Results of numerical modelling further show that the pattern of the distribution of maximum shear stress (τmax) contours are prominently depend on the amount of overlap between two master strike-slip faults and applied boundary conditions. In case of more overlap between two masters strike-slip faults, τ max mainly concentrated at two corners of the master faults and that reduces and finally reaches zero at the centre of the pull-apart basin, whereas in case of no overlap, τmax largely concentrated at two corners and tips of the master strike-slip faults. These results imply that the distribution and concentration of the maximum shear stress is mainly governed by amount of overlap between the master strike-slip faults in the en-échelon pull-apart formation. Numerical results further highlight that the distribution patterns of the displacement vectors are mostly dependent on the amount of overlap and applied boundary conditions in the en-échelon pull-apart formation.
Cite this paper
Joshi, G. and Hayashi, D. (2010) Finite element modelling of the pull-apart formation: implication for tectonics of Bengo Co pull-apart basin, southern Tibet. Natural Science, 2, 654-666. doi: 10.4236/ns.2010.26082.
 Katzman, R., Brink, U.S. and Lin, J. (1995) Three dimension of modelling of pull-apart basins: Implications for the tectonics of the Death Sea Basins. Journal Geophysical Research, 100(B4), 6295-6312.
Petrunin, A. and Sobolev, S.V. (2006) What controls the thickness and lithospheric deformation at a pull-apart basin? Geology, 34(5), 389-392.
Burchfiel, B.C. and Stewary, J.H. (1966) Pull-apart origin of the central segment of the Death valley. Geological Society of America, 77(4), 439-442.
Sylvester, A.G. (1988) Strike-slip faults. Bulletin of Geological Society of America, 100(11), 1666-1703.
Ayden, A.A. and Nur, A. (1982) Evolation of Pull-Apart basins and their scale independence. Tectonics, 1(1), 91-105.
Gamond, J.F. (1983) Displacement feature associated with fault zone: A comparison between observed examples and experimental models. Journal of Structural Geology, 5(1), 33-45.
Bahat, D. (1983) New aspects of rhomb structures. Journal of Structural Geology, 5(6), 591-601.
Connolly, P. and Cosgrove, J. (1999) Prediction of fracture-induced permeability and fluid flow in the crust using experimental stress data. AAPG Bulletin, 83(5), 757777.
Hu, S., O’Sullivian, B.P., Raza, A. and Cona, B.P. (2001) Thermal History and tectonic subsidence of the Bohai Basin, northern China: A Cenozoic rifting and pull-apart basins. Physics of the Earth and Planetary Interiors, 126(3-4), 121-135.
Armijo, R., Meyer, B., Navarro, A., King, G. and Barkar, A. (2002) Asymmetric slip partitioning in the Sea of Marmara pull-apart: A clue to propagation processes of the North Anatolian Fault. Terra Nova, 14(2), 80-86.
Armijo, R., Tapponnier, P. and Tonglin, H. (1989) Late Cenozoic right-lateral strike-slip faulting in southern Tibet. Journal of Geophysical Research, 94(B3), 27872938.
Armijo, R., Tapponnier, P., Mercier, L. and Tonglin, H. (1986) Quaternary extension in southern Tibet: field observations and tectonic implications. Journal of Geophysical Research, 91(B14), 13803-13872.
Harding, T.P. (1990) Identification of wrench faults using sub-surface structural data: Criteria and pitfalls. AAPG Bulletin, 74(10), 1590-1609.
Recherds, P.D., Boyce, A.J. and Pringle M.S. (2001) Geological evolution of the Escondida area, northern Chile: a model for spatial and temporal localization of porphyry Cu mineralization. Economic Geology, 96(2), 271-305.
Monastero, F.C., Katzenstein, A.M., Miller, J.S., Unruh, J. R., Adams, M.C. and Richerds-Dinger, K. (2005) The Coso geothermal field: A nascent metamorphic core complex. Bulletin of Geological Society of America, 117(11-12), 15341553.
Segall, P. and Pollard, D.O. (1980) Mechanics of discontinuous faults. Journal of Geophysical Research, 85(B8), 4337-4350.
Basile, C. and Brun, J.P. (1999) Transtensional faulting pattern from pull-apart basin to continental margins: An experimental investigation. Journal of Structural Geology, 21, 23-37.
Du, Y. and Aydin, A. (1993) The maximum distortion energy density criterion for shear fracture propagation with applications to the growth paths of en-échelon faults. Geophysical research Letters, 20(11), 1091-1094.
Gölke, M., Cloetingh, S. and Fuch, K. (1994) Finite element modelling of pull-apart formation. Tectanophysics, 240(1-4), 45-57.
Petrunin, A. and Sobolev, S.V. (2008) Three-dimensional numerical models of the evolution of pull-apart basins. Physics of Earth and Planatery Interiors. 171(1-4), 387-399.
Molnar, P. and Tapponier, P. (1975) Cenozoic tectonics of Asia: Effects of a continental collision. Science, 189, 419-426.
Mercier, J.L., Armijo, R., Tapponinier, P., Carey-Gailhardis, E. and Han, T.L. (1987) Change from late tertiary compression to late quaternary extension, in southern Tibet, during the India-Asia collision.
 Tectonics, 6(3), 275-304.
Torre, T.L. de la, Monsalve, G., Sheehan, A.F., Sapkota, S. and Wu, F. (2007) Earthquake processes of the Himalayan collision zone in eastern Nepal and the southern Tibetan Plateau. Geophysical Journal International, 171(2), 718-738.
Hayashi, D. (2008) Theoretical basis of FE simulation software package. Bulletin of the Faculty of Science, University of the Ryukyus, 85(), 81-95.
Joshi, G.R. and Hayashi, D. (2008a) Neotectonic deformation and shortening along the Himalayan front in the Garhwal region by finite element modelling. Bullettino di Geofisica Teorica ed Applicacate, 49, 228-233.
Joshi, G.R. and Hayashi, D. (2008b) Numerical modelling of neotectonic movements and state of stresses in the central seismic gap region, Garhwal Himalaya. Journal of Mountain Science, 5(4), 279-298.
Joshi, G.R. and Hayashi, D. (2010) Development extensional stresses in the compressional setting of the Himalayan thrust wedge: Inference from numerical modelling. Natural Science (in press).
Barton, P.J. (1986) The relationship between the seismic velocity and density in the continental crust a useful constraint? Geophysics Journal of the Royal Astronomical Society, 87(1), 195-208.
Zhao, W., Nelson, K.D. and Project INDEPTH Team (1993) Deep Seismic reflections evidence for continental underthrusting beneath south Tibet. Nature, 366, 557-559.
Cogan, M.J., Nelson, K.D., Kidd, W.S.F., Wu, C. and Project INDEPTH Team (1998). Shallow structure of the Yadong-Gulu rift, southern Tibet, from refraction analysis of Project INDEPTH common midpoint data. Tectonics, 17(1), 46-61.
Timosenko, S.P. and Goodier, J.N. (1970) Theory of elasticity. 3rd Edition, McGraw-Hill Book Company, London.
Clark, Jr., S.P. (Ed.) (1966) Handbook of Physical Constants. New York, Geological Society America, Memoir.
Molnar, P. and Chen, W.P. (1983) Focal depths and fault plane solutions of earthquakes under the Tibetan Plateau. Journal of Geophysical Research, 88, 1180-1196.