OVERVIEW: Late Cenozoic tectonics of the central and southern Coast Ranges of California

Abstract

The central and southern Coast Ranges of California coincide with the broad Pacific-North American plate boundary. The ranges formed during the transform regime, but show little direct mechanical relation to strike-slip faulting. After late Miocene deformation, two recent generations of range building occurred: (1) folding and thrusting, beginning ca. 3.5 Ma and increasing at 0.4 Ma, and (2) subsequent late Quaternary uplift of the ranges. The ranges rose synchronously along the central California margin and are still rising; their long axes are quasiparallel to the plate boundary and strike-slip faults. The upper crustal internal and marginal structures of the ranges are contractional, dominated by folds and thrusts resulting from the convergent component of plate motion. Newly constructed transects using seismic reflection and refraction, plus gravity and magnetic studies, reveal lower crustal basement(s) at depths of 10-22 km. The upper surface of the basement and Moho show no effect of the folding and thrusting observed in the upper crust. We conclude that horizontal shortening is accommodated at depth by slip on subhorizontal detachments, and by ductile shear and thickening. The ranges are marked by high heat flow; weak rocks of the Franciscan subduction complex; high fluid pressure; bounding high-angle reverse, strike-slip, or thrust faults; and uplift at a rate of 1 mm/yr beginning about 0.40 Ma. Transverse compression manifested in folding within the Coast Ranges is ascribed in large part to the well-established change in plate motions at about 3.5 Ma.

Development of schistosity by dissolution–crystallization in a Californian serpentinite gouge

“…Among the various lithologies, kilometre-scale serpentinite units are exposed in different locations along the San Andreas Fault system. These bodies are remnants of Mesozoïc oceanic crust and altered mantle (Bailey et al, 1970;Page, 1972;Page et al, 1998) and are locally crosscut by active faults.…”

Tectonic underplating of trench sediments beneath magmatic arcs: the central California example

“…However, we believe that this tectonic classification is a simplifying one -it is based on the observation that most of the separate blocks of the Coast Ranges were locked together possibly by the latest Cretaceous or during the Early Cenozoic, and the 'out-of-place' nature of these rocks is fundamentally related to the San Andreas fault system (Graham et al 1989), not cryptic and/or poorly defined pre-Cenozoic structures. The Monterey terrane was translated 310-350 km to the north by the San Andreas fault with respect to its origin in southern California (Page et al 1998). The San Andreas is unambiguously the eastern boundary of this block ( Figure 2); however no obvious fault uniquely separates the block's large-scale fabric from outboard geologic domains to the west.…”

“…A standard palinspastic restoration to the pre-San Andreas configuration shows that the Monterey terrane can be correlated with southern California geology (Barbeau et al 2005;James 1992;Kidder et al 2003;Kistler and Champion 2001;Page et al 1998). Some have argued that a robust tie to southern California geology requires an additional 200-300 km of right lateral displacement along an Early Cenozoic, proto-San Andreas fault (e.g.…”

“…(Almgren and Reay 1977;Howell et al 1977Howell et al , 1978Poore et al 1977;Taliaferro 1944). The Coast Ranges are segmented by numerous Late Cenozoic strike-slip and highangle reverse faults associated with the San Andreas system (Page et al 1998). Formation of the modern Coast Ranges ended with an episode of latest MioceneQuaternary transpressional uplift (Compton 1966;Ducea et al 2003a).…”

Strain partitioning of active transpression within the Lebanese restraining bend of the Dead Sea Fault (Lebanon and SW Syria)

“…Becker et al 2005), as well as along the central San Andreas Fault (e.g. Molnar 1992;Page et al 1998), which is also oriented oblique to the relative plate motion. Both cases, as well as the Lebanese restraining bend, involve transform systems with significant total displacement and regionally distributed strain.…”