Interpretive Structural Cross Section from the Central Diablo Range to the San Joaquin Valley, California

Abstract

Abstract An interpretation of the structure of the Central Diablo Range and its relation to the northern San Joaquin Valley is presented. The interpretation recognizes the need to separate in time and space at least three tectonic events: (1) formation of the basin of deposition of the Great Valley Sequence (GVS), (2) Paleogene convergence to produce the Diablo Range antiform, and (3) Late Cenozoic convergence to produce the present topography of the Range. The basin of deposition for the GVS was formed on two separate portions of the Foothills Terrane Arc. The Jurassic and Lower Cretaceous portion of the GVS, which has only been recognized in the Range, was deposited on oceanic crust on the west side of the Foothills Terrane Arc in a distal setting. The proximal Upper Cretaceous portion of the GVS was deposited on Foothills Terrane Arc after ductile deformation of the Arc substrate and tectonic stripping of the Arc superstructure. The ductile deformation within the Arc occurred synchronously with deposition of the distal portion of the GVS. It is suggested that the Arc superstructure detached in the Lower Cretaceous, slid slowly southwestward during the late Lower Cretaceous and Upper Cretaceous, and now forms the tectonic wedge beneath the Diablo Range, which has been interpreted by Wentworth and others (1984) from reflection seismic data. The Central Diablo Range is an anticline expressed by GVS and younger sedimentary rocks dipping "radially" away from a core of Franciscan Formation. Everywhere the GVS is separated from the Franciscan core by a complex fault zone (Jayko and others, 1987) called the "Coast Range Thrust." This "thrust" was initiated by gravity driven slumping of the GVS into the Franciscan trench, perhaps during the Late Cretaceous as a part of the detachment of the arc superstructure. The anticline was created in essentially its present form by Paleogene thrusting of the distal GVS and Franciscan package northeastward over the proximal GVS in the northern San Joaquin Valley on a gentle southwestward dipping thrust plane. Thrusting continued, perhaps intermittently, on the same thrust structures through the middle Miocene. The present elevation of the range is due to a reactivation of these same structures after deposition of the Plio-Pleistocene Tulare Formation. More than 2,600 feet of structural relief developed on the base of the Tulare Formation between the San Joaquin Valley and the Diablo Range during the latest Cenozoic at the latitude of the Panoche Hills. The interpretation is presented on a conceptually balanced cross section constructed along Garzas Creek. Potential hydrocarbon traps are indicated.