Tectonic contact between the Franciscan Mélange and the Great Valley Sequence-Crustal expression of a Late Mesozoic Benioff Zone

Abstract

Late Mesozoic Franciscan rocks of the California Coast Ranges, chaotically deformed and consisting of graywacke, micrograywacke, shale, chert, and mafic pillow lava, are considered to have been deposited in and adjacent to a northwest‐trending oceanic trench. Principally on the east, contemporaneous, well‐bedded conglomerate, lithic sandstone, siltstone, and shale of the Great Valley sequence evidently were laid down on a continental shelf, slope, and sea floor environment. The junction between these two sequences, one the ensimatic eugeosynclinal mélange of Franciscan rocks, the other the more orderly Great Valley miogeosynclinal strata overlying chiefly sialic‐type basement, is marked by the South Fork Mountain‐Stoney Creek‐Ortigalita (–Sur‐Nacimiento) fault system. This structural break is interpreted as the crustal expression of a Late Mesozoic Benioff zone. Episodic or relatively continuous underthrusting of the trench mélange beneath this former seismic shear zone is held responsible for the contrasting characteristics of the Franciscan rocks and the simultaneously deposited Great Valley sequence, as well as for their ubiquitous tectonic juxaposition. A speculative four‐state tectonic model is proposed that involves: (1) rapid Late Jurassic relative northeastward or eastward spreading of the Pacific Ocean floor, coupled with westward or southwestward encroachment by the continental lithospheric plate; (2) mid‐Cretaceous buoyant uplift of portions of the eugeosynclinal prism during a period of less intense spreading; (3) accelerated post‐Cretaceous convergence between oceanic and continental lithospheric plates; and (4) Miocene‐Pleistocene diapiric uplift of the Franciscan mélange related to northwestward seafloor spreading.

Journal of Research of the U. S. Geological Survey, 1978, volume 6, issue 3

“…5) and on a very nearly direct path toward the Oligocene pole at 78° N., 146° E., reported by Gromme and McKee (1971), a fact strongly suggesting that the pole determined for the Great Valley sequence is indeed Cretaceous in age. This interpretation is in excellent agreement with suggestions by Irwin (1964), Blake, Irwin, and Coleman (1967), and Ernst (1970) that thrust faulting along the Great Valley province boundary occurred during the Late Cretaceous. However, this faulting may represent only the beginning of deformation in this region, because data presented by Hackel (1966) suggest that uplift of the sequence at the south end of the Sacramento Valley did not occur until after the early Eocene.…”

The Middle America Trench in the Geological Framework of Central America

“…Schematic cross section of the Californian-Cordilleran edifice in Baja California and Sonora (Cordoba et al, 1980 mentary (eastern Sierra Madre) and volcanic-plutonic (western Sierra Madre) units. The whole picture is that of a tectonic edifice connected to the Pacific (paleo)subduction during the Mesozoic and the Tertiary (see for comparison Ernst, 1970;Coney and Reynolds, 1977), with the oceanic Baja California Franciscan series subducted beneath a distorted continental margin of the Sierra Madre Mexican series and all run through by plutons and calc-alkaline volcanoes of Baja California and the western Sierra Madre.…”

Facies architecture and provenance of a boulder-conglomerate submarine channel system, Panoche Formation, Great Valley Group: A forearc basin response to middle Cretaceous tectonism in the California convergent margin

“…From east to west, the major tectonic elements include the volcanic arcs of the Sierra NevadaKlamath mountains, the forearc basin of the Great Valley (represented by the Great Valley Group [GVG]), and the accretionary prism of the Franciscan Complex ( Fig. 1; Hamilton, 1969;Dickinson, 1970Dickinson, , 1976Ernst, 1970;Hsü, 1971;Maxwell, 1974;Schweickert and Cowan, 1975). Numerous studies of each tectonic element have helped resolve the details of the margin that involves changes in magmatism, accretionary tectonics, and basin subsidence (Ingersoll, 1978(Ingersoll, , 1979(Ingersoll, , 1982Dickinson and Seely, 1979;Ingersoll and Dickinson, 1981;Moxon and Graham, 1987;DeGraaff-Surpless et al, 2002;Williams and Graham, 2013;Surpless, 2014;Sharman et al, 2015;Wakabayashi, 2015;and many others).…”