Architectural and kinematic analysis of mesoscopic normal faults: Chenque Formation (Lower-Middle Miocene) in the Eastern Sector of the Golfo San Jorge basin, central Patagonia

Abstract

The Chenque Formation (Lower to Middle Miocene) in the Golfo San Jorge Basin represents the deposits of an Atlantic transgressive event with mesoscopic evidences of extensional tectonics. We present the results of the kinematical analysis of 276 non-rotational, planar mesoscopic normal faults identified in the unit, and the determination of paleostrain tensors. Rake values vary around 85-90°. The damage zones present joints and secondary faults oriented parallel, normal, conjugate, or oblique to the main faults. Generally, the core zone presents gypsum crystals growing perpendicular to the fault planes, but could contain deeply weathered claystones, calcite, and dilatational jogs infilled by silica. In the analyzed field localities (n= 12), we recognize one or two families of main faults with wide variation in their fault strikes, and a subordinate third fault family which is oriented oblique-to-transverse to the formers. The regional extension direction is oriented toward N 349.5°. Calculations of the strain ellipsoid indicate average extension direction values that are arranged at high-angle compared to previous megascopic normal faults. The Lower to Middle Miocene strain field in the Eastern Sector of the Golfo San Jorge Basin is conditioned by the orientation of megascopic discontinuities that distorted the strain field.