Constraints on the tectonics of the Mule Mountains Thrust System, southeast California and southwest Arizona

Abstract

The Mule Mountains thrust system crops out discontinuously over a 100-kin-strike length in the Blythe-Quartzsite region of southeast California and southwest Arizona. Along the thrust system, middle and upper crustal metamorphic and plutonie rocks of Proterozoie and Mesozoic age are thrust north-northeastward (015o to 035o) over a lower plate metamorphic terrane that formed part of the Proterozoie North American eraton, its Paleozoie sedimentary rock cover, overlying Mesozoic volcanic and sedimentary rocks, and the intruding Jurassic and Cretaceous granitie rocks. Stratigraphic, petrologle, and Pb isotopic ties for Jurassic granitoids and for Jurassic(?) and Cretaceous sedimentary rocks across the various parts of the thrust system indicate that related crustal blocks are superposed and preclude it from having large displacements. The thick-skinned thrust system is structurally symmetrical along its length with a central domain of synmetamorphic thrust faults that are flanked by western and eastern domains where lower plate synclines underlie the thrusts. Deformation occurred under low greenschist facies metamorphic conditions in the upper crust. Movement along the thrust system was probably limited to no more than a few tens of kilometers and occurred between 79+2 Ma and 70+4 Ma. The superposition of related rocks and the geometry of the thrust system preclude it from being a major tectonic boundary of post-Middle Jurassic age, as has been previously proposed. Rather, the thrust system forms the southern boundary of the narrow zone of Cretaceous intracratonie deformation, and it is one of the last tectonic events in the zone prior to regional cooling. (Figures 1 and 2). The 100-km-long thrust system, the youngest Mesozoic structure in the region [Tosdal, 1986], is the southern boundary of a complex deformation zone in the Cretaceous. The thrust system is also the boundary between the North American eraton toward the north and Cordilleran suspect terranes toward the south, as defined by Coney et al. [1980]. It furthermore has been proposed to be a major tectonic boundary of Late Jurassic, Late Cretaceous, or Early Tertiary age (G.J. Pelka as cited by Ehlig [1981], Dillon [1976],Vedder et al. [1982], Champion et al. [1984], and Harding and Coney [1985]). Other investigations of the Late Cretaceous Mule Mountains thrust system concluded that it can not have great displacements and thus it can not be a major terrane boundary because of stratigraphic, petrologle, and Pb isotopic ties for Jurassic and Cretaceous rocks across the structure and also because of the structural geometry of the thrust system [Tosdal, 1986, 1988]. This paper describes these ties and the structural geometry of the thrust system. In addition, K-Ax geochronologic data are presented that together with available chronologic data for rocks cut by the thrust system constrain the time of movement. Collectively, these data contravene most tectonic models for the Mule Mountains thrust system and place limits on new tectonic models. This paper is not s...

Palinspastic reconstruction of southeastern California and southwestern Arizona for the Middle Miocene

“…(? ) and Cretaceous nonmarine elastic rocks [Harding and Coney, 1985;Stone et al, 1987;Tosdal, 1988] that crops out in an areuate belt trending ENE in west-central Arizona and WNW in California [Reynolds, 1988;/ennings, 1977]. The south-dipping McCoy Mountains Formation overlies Jurassic volcanic rocks [Tosdal et al, 1989], which in turn overlie Triassic (?…”

“…The south-dipping McCoy Mountains Formation overlies Jurassic volcanic rocks [Tosdal et al, 1989], which in turn overlie Triassic (? ) and Paleozoic sedimentary rocks in the northern Palen Mountains [Stone and Kelly, 1989] [Tosdal, 1988[Tosdal, , 1990] to the south. Available data indicate the Mule Mountains thrust is latest Cretaceous in age, and that it is probably superimposed on an older Mesozoic fault zone [Tosdal, 1990].…”

Temporal and spatial trends of Late Cretaceous-early Tertiary underplating Pelona and related schist beneath southern California and southwestern Arizona

“…One of these that held that the schists formed during collision between North America and an exotic microcontinent ( Fig. 2C; "Collision" model; Haxel and Dillon, 1978;Vedder et al, 1983) quickly lost favor as it became apparent that the proposed allochthon exhibited clear North American affi nities (Haxel et al, 1985;Barth, 1990;Tosdal, 1990;Bender et al, 1993). A second interpretation has persisted, however.…”

Northward Laramide thrusting in the Quitovac region, northwestern Sonora, Mexico: Implications for the juxtaposition of Paleoproterozoic basement blocks and the Mojave-Sonora megashear hypothesis

“…The average direction and sense of displacement for the stack of thrusts in the Quitovac region is N18°W and is signifi cantly different from the wide range of directions (north, northeast, and east) proposed for different thrust systems in southeastern California, southwestern Arizona, and central Sonora (e.g., Haxel et al, 1984;De Jong et al, 1988;Tosdal, 1990;Dillon et al, 1990;Sosson and Calmus, 1990;Miller et al, 1992;Calmus and Sosson, 1995;Pubellier et al, 1995;Jacques Ayala and De Jong, 1996;Campbell and Anderson, 1998;Nourse, 2001). Despite these differences, most of the movement recorded in these thrusts systems was toward the continent.…”