HR: 1340h
AN: T33C-1476    [Abstracts]
TI: The Role of Transverse Faults in Accommodating Lateral Propagation of Faults and Folds: Evidence From Geomorphic and Structural Analysis of Active Folding in the Camarillo Fold Belt, Ventura County, California
AU: * DeVecchio, D E
EM: duaned@umail.ucsb.edu
AF: University of California Santa Barbara, Department of Earth Science, Santa Barbara, CA 93106, United States
AU: Keller, E A
EM: keller@geol.ucsb.edu
AF: University of California Santa Barbara, Department of Earth Science, Santa Barbara, CA 93106, United States
AB: Length of faults and fault propagation folds in contractional environments are generally thought to increases with displacement in response to fault tip migration. However, only a few studies have documented fault tip migration and lateral growth of hangingwall anticlines. Here, we present several examples in which the interplay of discrete structural domains and transverse faults leads to punctuated fault growth and lateral propagation of hangingwall folds. Folds of the Camarillo Fold Belt, including the South Mountain anticline, are the topographic expression of north-south shortening in the western Transverse Ranges. The inception of tectonic uplift and folding is likely no older than 500 ka and may have begun as recent as 50 ky on the westernmost folds in the belt. Folds are developed above discrete fault segments that strike east-west and range in length from 4 to 50 km with displacement from 100's to 1000's of meters. Fault segment boundaries are characterized by north-south oriented transverse faults that are either exposed at the surface or inferred from subsurface data. At least one of the transverse faults is inherited from an earlier Miocene extensional phase in which it appears to have limited the growth of the ancestral normal dip-slip Simi fault. Adjacent structural domains are separated by transverse faults, and characterized by plunging folds at their margins, distinct changes in the topographic expression and structural geometry of folds, and the relative timing of deformation. Topographic and structural analysis of folding suggests anticlines within discrete structural domains developed as doubly-plunging fault propagation folds that amplified with time. However, fold and fault lengths were constrained by the presence of transverse faults and remained constant through time. Following a period of amplification, new faults and folds become active in the adjacent domain to the west and begin accumulating strain, resulting in composite folds that young to the west. Structural domains along composite fault zones all young to the west and typically step southward with time. These observations suggest that transverse faults initially impede fault tip migration until a critical strain gradient across the transverse fault is achieved. At which time the main fault breaches the transverse fault, resulting in westward lengthening of the main fault and lateral propagation of the fold(s) into the adjacent structural domain.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8108 Continental tectonics: compressional
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting