Mechanisms for accommodation of Miocene extension: Low‐angle normal faulting, magmatism, and secondary breakaway faulting in the southern Sacramento Mountains, southeastern California

Abstract

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Late-stage evolution of the Chemehuevi and Sacramento detachment faults from apatite (U-Th)/He thermochronometry--Evidence for mid-Miocene accelerated slip

“…These correlations are based on the fact that many features in the low-angle detachment faults of these ranges are similar (e.g., movement direction, timing of activity, fault rock types, progressive change in the fault rocks with increasing paleodepth, and multiple splays of low-angle detachment faults; Howard and John, 1987;Anderson, 1988). Detailed mapping of the detachment faults between the ranges also supports this correlation (Campbell-Stone et al, 2000).…”

“…4) (Foster et al, 1996;Campbell-Stone et al, 2000). The Sacram suite cuts across well-developed mylonitic fabrics and folds of the Miocene Eagle Wash intrusive complex toward the northwest (see following) and mylonitic fabric within the Whale Mountain sequence to the southeast (CampbellStone, 1997).…”

“…The younger splay is primarily distinguished from the older by a difference in associated fault rocks and mineral alteration assemblages (Campbell-Stone, 1997;Campbell-Stone et al, 2000). Later movement on the secondary fault is suggested by crosscutting relationships between the two detachments in the northeast of the range, and by truncation of the older splay by high-angle faults thought to be related to doming of the footwall.…”

“…Large-magnitude extension in these ranges occurred between ca. 23 and 12 Ma, based on thermochronologic estimates of rapid footwall cooling (Foster et al, 1990John and Foster, 1993;Foster and John, 1999;Campbell-Stone et al, 2000), crystallization ages of synextensional plutons (Anderson, 1988;Foster et al, 1996), and constraints from adjacent sedimentary basins (Howard and John, 1987;Nielson and Beratan, 1990;Dorsey and Becker, 1995;Nielson and Beratan, 1995;Miller et al, 1998;Miller and John, 1999).…”

Synextensional dike emplacement across the footwall of a continental core complex, Chemehuevi Mountains, southeastern California

“…Extrusive magmatism in the CREC also records an evolution in composition during extension; the oldest volcanic deposits comprise a heterogeneous suite of basaltic, intermediate, and minor felsic rocks, whereas the youngest volcanism is basaltic or bimodal in composition (Gans et al, 1989;Gans and Bohrson, 1998;Foster and John, 1999). Although a significant volume of the documented syntectonic magmatism in the CREC is extrusive, plutons and dikes were also emplaced prior to, during, and after peak slip on low-angle normal faults associated with the core complexes (Davis et al, 1982;Campbell and John, 1996;Campbell-Stone et al, 2000;Campbell-Stone and John, 2002;Singleton and Mosher, 2012). Dikes characteristic of the early syntectonic magmatism in the CREC are exposed in the Whipple, Mohave, Chemehuevi, and Sacramento mountains (Howard and John, 1987;John, 1987b;Lister and Davis, 1989;Nielson and Beratan, 1995;Sherrod and Nielson, 1993).…”