Tectonic evolution of the Indio Hills segment of the San Andreas fault in southern California, southwestern USA

Abstract

Abstract. Transpressional uplift domains of inverted Pliocene–Pleistocene basin fill along the San Andreas fault zone in Coachella Valley, southern California (USA), are characterized by fault linkage and segmentation and deformation partitioning. The Indio Hills wedge-shaped uplift block is located in between two boundary fault strands, the Indio Hills fault to the northeast and the main San Andreas fault to the southwest, which merge to the southeast. Uplift commenced about or later than 0.76 million years ago and involved progressive fold and faulting stages caused by a change from distributed strain to partly partitioned right-slip and reverse/thrust displacement on the bounding faults when approaching the fault junction. Major fold structures in the study area include oblique, right-stepping, partly overturned en echelon macro-folds that tighten and bend into parallelism with the Indio Hills fault to the east and become more open towards the main San Andreas fault to the west, indicating an early and close relationship of the macro-folds with the Indio Hills fault and a late initiation of the main San Andreas fault. Sets of strike-slip to reverse step-over and right- and left-lateral cross faults and conjugate kink bands affect the entire uplifted area, and locally offset the en echelon macro-folds. Comparison with the Mecca Hills and Durmid Hills uplifts farther southeast along strike in Coachella Valley reveals notable similarities, but also differences in fault architectures, spatial and temporal evolution, and deformation mechanisms. The present work contributes to better understand the structure and tectonic history of a major fault system along a transform plate boundary.