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Flexural Modeling of Linxia Basin, NE Tibetan Plateau: Insights into Subsidence and Deformation Mechanisms


Flexural modeling of basin fill provides constraints on crustal properties and may also provide insight into the timing of tectonic loading and development of topographic relief. Basins located on the northeastern margin of the Tibetan Plateau share common elements possibly including a Paleogene flexurally-dominated subsidence history. Among these, Linxia basin has an unbroken late Eocene–Pleistocene sedimentary record which records this early period of shortening. Linxia basin is thought to be part of an extensive foreland basin formed by Paleogene flexural subsidence. Crustal thickening was the result of movement on the West Qinling fault possibly in response to rapid northward transmission of compressional stresses related to Indo-Asian collision. This broad foreland basin may have been dissected first by the E-W trending Laji Shan at ∼ 22 Ma and then by the N-S trending Jishi Shan at ∼ 13 Ma, isolating the Linxia basin from basins to the north and west. In order to better understand the tectonic evolution of the Linxia basin flexural profiles spanning the late Eocene–Pliocene were modeled and compared to decompacted sedimentary thicknesses for the same time intervals. These decompacted sedimentary thicknesses are based on an E-W transect of measured stratigraphic sections (perpendicular to the Jishi Shan) and a N-S transect (perpendicular to the West Qinling Shan). Modeled flexural profiles matched decompacted sedimentary thicknesses only for a crustal elastic thickness less than 10km. This unrealistically low elastic thickness suggests that the subsidence mechanism in the Linxia basin from the late Eocene–Pliocene is not flexure, but instead horizontal-axis rotation. We propose a new model for the Linxia basin in which rotation of crustal blocks in response to far-field compressive stresses is accommodated by reactivation of pre-Cenozoic crustal weaknesses. We further constrain the timing of loading by the West Qinling Shan followed by the Jishi Shan using the provenance of sediments within the basin.