Evolution of the late Cenozoic tectonic stress regime in the Shanxi Rift, central North China Plate inferred from new fault kinematic analysis

Abstract

The Shanxi Rift, an intracontinental belt along the eastern margin of the Ordos Block, North China Plate, has undergone multi-stage extensional deformation during the late Cenozoic. In this study, new fault kinematic analysis of boundary faults in the Shanxi Rift, constrained by geochronological data, defines a three-stage tectonic stress regime since the late Miocene, providing new structural evidence for deciphering the northeastward growth of the Tibetan Plateau. The earliest stage involved a transtensional stress regime of NW-SE extension and NE-SW compression in the late Miocene-early Pleistocene (ca. 10-1.8Ma) and characterized by mean principal stress axes of σ1 at 344.7°/87.2°, σ2 at 217.6°/01.1°, and σ3 at 128.1°/01.0°. The early transtensional stress regime was responsible for the opening of the Shanxi Rift and was very likely associated with intensive right-lateral pull-apart activity in the eastern Ordos Block due to the northeastward growth of the Tibetan Plateau. During the second stage, the stress regime changed to less intense NE-SW extension, with mean stress orientations of 323.3°/85.2° for σ1, 127.5°/02.9° for σ2, and 214.9°/02.6° for σ3 in the early late Pleistocene (ca. 1.8-0.11Ma). This stage is marked by a distinct shift from fluvio-lacustrine to fluvio-piedmont sedimentary facies at the end of the early Pleistocene, and the widespread eruption of basalt in the Datong Basin north of the Shanxi Rift. This short-lived extension appears to be the result of relaxation in the midst of crustal shortening during growth of the Tibetan Plateau. The third stage was transtensional, characterized by NNW-SSE extension and WNW-ESE compression (σ1 at 060°/88.9°, σ2 at 074.9°/03.9°, and σ3 at 164°/00°) since the late Pleistocene (ca. 0.11Ma), causing dextral shear deformation in the Shanxi Rift and the disappearance of its paleo-lake. This stage resulted from regional ENE-WSW shortening due to northeastward growth of the Tibetan Plateau.