A Comparison of Structures in the Andean Orogen of Northern Chile and Exhumed Midcrustal Structures in Southern California, USA: An Analogy in Tectonic Style?

Salinia revisited: a crystalline nappe sequence lying above the Nacimiento fault and dispersed along the San Andreas fault system, central California

“…Gilbert 1971Gilbert , 1973Page 1981Page , 1982Dickinson 1983;Hall , 2002Hall et al 1995;Dickinson et al 2005;Ducea et al 2009;Jacobson et al 2011). Four interpretations of the nature of the boundary discussed in numbered topics below are: (i) dextral slip of (a) 2100-2500 km (1305-1554 mi) or more (Champion et al 1984) along unnamed faults or (b) 90 km (56 mi) or more of dextral slip on the Nacimiento fault (Vedder et al 1991, p. 951); (ii) sinistral strike slip of 500-600 km (311-373 mi) on the Nacimiento fault (Dickinson 1983;Seiders and Blome 1988;Dickinson et al 2005;Jacobson et al 2011, figure 10); (iii) thrusting along the K-T Nacimiento fault (Page 1967(Page , 1969(Page , 1970a(Page , 1970b(Page , 1972(Page , 1982Silver 1982Silver , 1983Page and Brocher 1993;Hall et al 1995;Barth and Schneiderman 1996;Saleeby 1997Saleeby , 2003Yin 2002;Barth et al 2003;Kidder and Ducea 2006;Ducea et al 2009;Namson and Davis 2012); and (iv) as a corollary to (iii) above, the Nacimiento fault was a low-angle subduction megathrust surface along which the Sur-Obispo Franciscan belt was subducted, and then partially extruded back out along which promoted the observed upper plate (Salinia) extension and subsidence to marine conditions in Maastrichtian time (after Grove 1993).…”

Geology and tectonics of the Baja California Peninsula and adjacent areas

“…These results and other factors led Grove et al to favor a hypothesis in which the schists formed in the shallowly dipping Laramide subduction zone, but they note that their results also are consistent with a model in which the schists formed by underthrusting of forearc-basin strata (Barth and Schneiderman, 1996).…”

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“…A slab might shallow if buoyant material is subducted, if the overriding plate accelerates, or through hydrodynamic forces in the asthenospheric wedge (slab suction) (van Hunen et al, 2004). Three specifi c events have been proposed for the Laramide: subduction of a buoyant plateau or young lithosphere (Henderson et al, 1984;Barth and Schneiderman, 1996;Livaccari et al, 1981;Saleeby, 2003), acceleration of North America (Cross and Pilger , 1978a), and changes in the velocity and/or age of the subducting slab . For our purposes, the chief difference between these is the extent and timing of the effects of fl at-slab subduction.…”

“…Despite some notable subsequent attacks (Mutschler et al, 1987;Livaccari, 1991;Maxson and Tikoff, 1996), the "fl at-slab" model has survived over the past 30 years, even if the relationship between slab angle and the distribution and style of crustal deformation, magmatism, and sedimentation remains unclear. However, geologic evidence from the southwestern United States obtained over the past few decades has suggested that Late Cretaceous to early Tertiary low-angle subduction and attendant subduction erosion only affected only a narrow (~200 km) swath of oceanic lithosphere underthrusting presentday southern California (Barth and Schneiderman, 1996;Saleeby, 2003). If so, why was the shallowly subducting lithosphere so restricted spatially, and how could such narrow "fl at-slab" produce the array of geologic features generally attributed to the Laramide orogeny throughout western North America?…”