Abstract

Transpressional uplift domains of inverted Miocene–Pliocene basin fill along the San Andreas fault zone in Coachella Valley, southern California, 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 Banning fault to the southwest, which merge to the southeast. Uplift commenced about 2.2–0.76 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 Banning 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 Banning 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 in Coachella Valley reveals notable similarities, but also differences in fault architectures, spatial and temporal evolution, and deformation mechanisms.

Highlights

  • Indio Hills is structurally different by consisting of a sub-horizontal, NW–SE-trending, open, upright anticline, which trends parallel to the Indio Hills fault (Fig. 2)

  • 1) The Indio Hills segment of the San Andreas Fault Zone (SAFZ) in Coachella Valley, southern California evolved as a wedge-shaped uplift block between two major SAFZ-related fault strands, the

  • Indio Hills and Banning faults, which merge in a dextral freeway junction of a transitional nature to the southeast

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Summary

Introduction

The variable fault and fold architectures and associated ongoing seismic activity in these uplift areas underline the need for persistent along-strike studies of the SAFZ to characterize the fundamental geometry, resolve the kinematic development, and correlate regionally major fault strands (cf Janecke et al, 2018). Such studies are essential to explain the observed lateral variations in fold and fault architectures and to resolve mechanisms of transpression, fault linkage, and areal segmentation in continental transform settings

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