Two-stage formation of Death Valley

Abstract

Extension in Death Valley is usually interpreted as a combination of low-angle Basin and Range-style extension and strike slip associated with the developing Pacifi c-NorthAmerica plate boundary in western North America, with these two tectonic regimes operating synchronously in Death Valley. Examination of structural, stratigraphic, and timing relationships in the region suggests that this interpretation needs revision. Evolution of Death Valley is best described as a two-stage process. In the fi rst stage, lasting from ca. 18 to 5 Ma, low-angle Basin and Range extension transported allochthons consisting of Late Proterozoic through Early Paleozoic miogeoclinal section along detachment surfaces that, as extension continued, were exhumed from mid-lower crustal levels to the surface. Near the end of this extensional phase and lasting until ca. 3 Ma, deposition of a thick sequence of volcanics, clastics, and some lacustrine carbonates signaled a period of relative tectonic quiescence, with sediments in some areas covering the exhumed detachment surfaces. At ca. 3 Ma, initiation of the East California Shear Zone started development of the present-day topographic depression of Death Valley, formed as a pull-apart basin associated with this strike slip. Faulting broke the older, inactive, Basin and Range detachment surfaces, with high-angle transtensional faulting along the Black Mountains front. The Black Mountains were elevated as a result of footwall uplift, with the well-known turtleback structures being megamullions along these bounding faults. These megamullions are similar to those seen at oceanic spreading centers. The Panamint Range has previously been interpreted as an extensional allochthon, with the entire range transported from on top of or east of the Black Mountains. A new interpretation presented here is that the range is a large core complex similar to the core complex at Tucki Mountain, at the northern end of the range. The Basin and Range extensional detachment tracks over the top of the range, with extensional allochthons perched on the eastern fl anks of the range. This modifi ed model for evolution of Death Valley suggests a strong link between timing and style of deformation in the basin with the developing Pacifi c-North America plate boundary, particularly eastward propagation of this boundary.For permission to copy, contact editing@geosociety.org

A 3D model for the formation of turtleback surfaces: the Horzum Turtleback of western Turkey as a case study

“…To create turtleback surfaces there is no need for a strikeslip setting as previously suggested by some researchers in the Basin and Range Province (Wright et al, 1974;Norton, 2011). After reconstruction of a clockwise rotation (Holm et al, 1993) in Death Valley, it is interesting to see that the original positions of the Badwater, Copper Canyon, and Mormon Point turtlebacks are located on the possible relay ramps between the normal fault segments.…”

“…However, researchers in the Black Mountain area have to consider the influence of the strike-slip faulting on the formation mechanism of turtleback surfaces. A recently published paper by Norton (2011) suggests a close link between strike-slip systems and the Death Valley turtleback surfaces. Holm et al (1993) documented 50°-80° clockwise vertical axis rotations that are considered to be due to right lateral strike-slip system.…”

“…Miller and Pavlis (2005) gave an outstanding review of the earlier works and concluded that multiple faults, rather than a single detachment fault, play an important role in the development of the turtlebacks. Most recently, Norton (2011) suggested that the turtlebacks are megamullions formed by the strike-slip faulting in the Death Valley area and that these structures are unique to the western North America extensional province. Most earlier attempts to explain the turtleback formation are 2D models drawn on a cross-sectional view.…”

“…For this reason, this 3D model could also be useful in the evaluation of the Death Valley turtlebacks that have a relatively more complex structural history (i.e. Basin and Range extension plus strike-slip shearing; see Norton, 2011).…”

CVM-S4.26

“…Several hypotheses about the formation of the Death Valley and the Panamint Range have been discussed in the literature and they often involve low-angle detachment faulting (e.g., Stewart 1983;Wernicke et al 1988;Snow and Wernicke 2000) and/or strike-slip pull-apart mechanisms (e.g., Burchfiel and Stewart 1966;Topping 1993;Serpa and Pavlis 1996;Miller and Prave 2002;Norton 2011). In the low-angle detachment faulting models, the Panamint Range was originally located on top or to the east of the Black Mountains, which is presently on the east of the Death Valley.…”