Recognizing the effects of a small scale extensional stepover along the Central break of the Ocotillo Badlands contractional stepover, southern California, U.S.A.
Advisor: Gary Girty
Friday, December 20, 2019
CSL – 422 10am
Previous investigators successfully mapped the general structure of the contractional stepover characteristic of the Ocotillo Badlands. This stepover formed as the North break of the Coyote Mountains fault stepped NE to the Central break. Though these early investigators recognized a small extensional stepover in the Central break of the Coyote Mountains fault, none commented on its effects on the earlier contractional structures characteristic of the badlands. During this study, through the use of a smart phone GPS application, and Google Earth Pro satellite imagery, the finer details of the fault-fold structural fabric exposed within the SE part of the Ocotillo Badlands contractional stepover was documented. Resulting observations and data are consistent with the following series of events. First, ~NS contraction initiated folding as the North break stepped NE to the Central break of the Coyote Creek fault. As folds tightened, a series of NW dextral and NE sinistral faults formed. Within this same time frame, the Central break stepped ~305 m to the SW to the secondary Central break, forming an extensional stepover, and , and a series of en echelon tear faults began to form. Folds to the NE of the series of en echelon tear faults continued tightening while those to the SW were locked and behaved more passively to continuing deformation. The alignment of the secondary Central break, a series of small dextral faults, and the NW most segment of the series of dextral tear faults implies that slip may be attempting to break through this region. Hence, mapping at a 1:6000 scale along with the use of GPS and Google Earth Pro imagery, revealed for the first time, the effects of the development of a small extensional stepover along the Central break of the long recognized and classical Borrego Badlands contractional stepover.