The Death Valley Turtlebacks Reinterpreted as Miocene-Pliocene Folds of a Major Detachment Surface

Daniel Holm, Kent State University - Kent Campus
Robert J. Fleck, Kent State University - Kent Campus
Daniel R. Lux, Kent State University - Kent Campus

Copyright 1994 University of Chicago Press. Available on publisher's site at http://www.jstor.org/stable/30065646.

Abstract

Determining the origin of extension parallel folds in metamorphic core complexes is fundamental to understanding the development of detachment faults. An excellent example of such a feature occurs in the Death Valley region of California where a major, undulatory, detachment fault is exposed along the well-known turtleback (antiformal) surfaces of the Black Mountains. In the hanging wall of this detachment fault are deformed strata of the Copper Canyon Formation. New age constraints indicate that the Copper Canyon Formation was deposited from ~6 to 3 Ma. The formation was folded during deposition into a SE-plunging syncline with an axial surface coplanar with that of a synform in the underlying detachment. This relation suggests the turtlebacks are a folded detachment surface formed during large-scale extension in an overall constrictional strain field. The present, more planar, Black Mountains frontal fault system may be the result of out-stepping of a normal fault system away from an older detachment fault that was deactivated by folding.