QUATERNARY ACTIVITY OF THE RANGE FRONT BLIND THRUST AND ITS SPLAY FAULTS IN THE LONGMEN SHAN PIEDMONT, REVEALED BY SEISMIC IMAGING AND GROWTH STRATA RECORDS

Reliable estimates of upper crustal shortening during the Quaternary or Cenozoic in the Longmen Shan fault system are rare. It requires preservation of sedimentary records and high-resolution near-surface imaging, which are not easily available. In this paper, we present a case that high-resolution petroleum, shallow seismic reflection profiles, and borehole data combined provide an excellent opportunity to study the geometry, and active faulting and fault-related folding across the Pengzhou thrust fault, a splay fault of the Range Front blind thrust, in the Longmen Shan piedmont. Near- and sub-surface deformation indicates that the Pengzhou thrust fault is best described as a structural wedge mechanism with a ~19 m thrust scarp observable in the surface. Growth strata analysis reveals that the activity of the Range Front blind thrust and its splay faults during Early Pleistocene to present, which are estimated to be 0.43-0.66 and 0.82-1.25 mm/yr as the minimum uplift and fault slip rates since the mid-Pleistocene, respectively. The synchronicity of uplift and sedimentation rates found in the LMS piedmont suggests that a causal relationship, probably because the uplift and growing topography of the Longmen Shan fault system may have contributed to trapping sediments in the Chengdu Plain. Our results also highlight the Quaternary near-synchronous growth and propagation in accord with the development of active mountain ranges at the margin of the Tibetan Plateau.