Displacement Along the San Andreas Fault, California

Abstract

A p o s t -e a r l i e s t Miocene displacement of about 160 miles (260 km) on the San Andreas fault system in southern California is suggested by the occurrence of similar rocks and geologic histories in three terranes-the Tejon, Soledad, and Orocopia. These three terranes are interpreted as parts of an original east-west trending belt now displaced with right slip of about 130 miles (210 km) on the San Andreas fault and 30 miles (50 km) on the San Gabriel fault. Augen gneiss and blue-quartz gneiss of the amphibolite facies, in truded by a complex of gabbro, diorite, anorthosite, and syenite, and all intruded again by granitic rocks, constitute basement terranes of similar compositions and histories that are offset about 130 miles along the San Andreas fault. Other distinctive rocks on both sides of the fault include basic dikes and mafic bodies rich in ilmenite, magnetite, and apatite in the anorthosite and blue-quartz granite, quartz-bearing syenite, granophyre, and pegmatite in the syenite. Greenschist, marine Eocene strata, and Oligocene nonmarine beds and included volcanic rocks are associated. Similar terranes, but lacking the anorthosite-syenite complex, are apparently separated by about 30 miles on the San Gabriel fault, a displacement com patible with evidence from Upper Tertiary sedimentary units that suggest later right slip of as much as 2 0 miles. Post early Miocene displacement on the San Andreas fault in central California is probably about 175 miles (Hill and Dibblee, 1953). This displacement is based on the offset of unusual associations of lower Miocene volcanic works (with remarkable similarities in petrography), red beds, and marine lower Miocene and Oligocene strata. Younger and smaller displacements, although still in completely described, appear acceptable, because they are geomet rically sound and are concerned with slip and not with separation alone. Displacements of older features in California, which form the basis for statements that perhaps the San Andreas has a right slip of more than 300 miles, rest on arguments of a different order of accept ability. Available information suggests that the fault system origi nated in the earliest Tertiary. Progress in the study of the major California faults, although in separable from the complex geology along the continental margin, can be accelerated through the geometric analysis of geological ter-rains. Trace slip has displaced some low-dipping, sedimentary, volcanic, and metamorphic units; intensive studies of these and other units are required to discover gross linear features, such as basin-margin lines and lines of facies change that form the basis for finding net slip. within this zone are older than the presently active fault, but there is widespread controversy as to definition and significance. T h e term, rift, is applied to the belt o f topographic features along the fault zone (Lawson and others, 1908, p. 2 5 ); it is generally a shallow trench up to several miles wide that has resulted both from erosion in shattered and weathered ...

Structure of the continental shelf west of San Francisco, California

“…The importance of the San Andreas fault as a major strike-slip feature is well documented from the field work of Gilbert(1908), Hill andDibblee(1953), and more recently in reviews by Crowell(1962), Dickinson and Grantz(1968), Suppe(1970), and others. In the San…”

Paleotectonics of a complex Miocene half graben formed above a detachment fault: The Diligencia basin, Orocopia Mountains, southern California

“…Spittler and Arthur (1982; their fi g. 3) inexplicably denoted the base of the Diligencia Formation along the northern exposure, where it sits unconformably on the Maniobra Formation, as Qoa (Quaternary terrace gravels and sands) in spite of the fact that Williams (1956), Crowell and Susuki (1959), Crowell (1962Crowell ( , 1975b correctly mapped the angular unconformity between the Maniobra and Diligencia formations. Spittler and Arthur's (1982) mistake was retained by Law et al (2001;their fi g. 3), in spite of the fact that one of the coauthors (Davisson et al, 1992;Davisson, 1993) studied these same deposits and correctly mapped them as basal Diligencia.…”

“…1 and 2). Beginning with Crowell's (1960Crowell's ( , 1962Crowell's ( , 1975a suggestion of more than 300 km of dextral slip along the combined San Andreas/San Gabriel fault system, the Orocopia Mountains have been one of the primary areas used to test this hypothesis. The Orocopia Mountains have also been the focus of research on deposition, deformation, metamorphism, uplift and exposure of the Orocopia Schist, which resulted from fl atslab subduction during the latest Cretaceous/ Paleogene Laramide orogeny (e.g., Jacobson et al, 2000Jacobson et al, , 2002Jacobson et al, , 2007Jacobson et al, , 2011Grove et al, 2003).…”

The Tooth of Time: The North American Cordillera from Tanya Atwater to Karin Sigloch

“…This is because the proto-San Andreas transform fault was situated near the continental margin until 5-6 Ma, when it 'jumped' to its present position along the Coast Ranges and Gulf of California (Atwater 1970). Accordingly, the present San Andreas Fault system only expresses the lion's share of Pacific-North America plate motion (6 cm/yr) for the past 5-6 Myr, consistent with geologically estimated displacements of <320 km since early Miocene time (Crowell 1962;Addicott 1968;Matthews 1976).…”

“…Arc magmatism in the Sierra Nevada shut down around 80 Ma (Hamilton 1969a) but mounting evidence suggested that San Andreas displacement was much younger, starting after 30 Ma (Crowell 1962;Addicott 1968;Matthews 1976). Late Cretaceous shut-down of the arc implied slower spreading rates in the past, while a Neogene origin for the San Andreas Fault was consistent with uniform spreading.…”