SGER AWARD: A Potential Example of Fold Growth Due to Kink-Band Migration on Near Earthquake-Cycle Timescales

Oregon State University, Corvallis OR

Investigators

Abstract

One of the most active debates in structural geology over the last 20 years has focused on the existence of folds formed due to kink-band migration (e.g. the fault-bend (FBF) and fault-propagation (FPF) folds).A suite of folded geomorphic surfaces in western Argentina have been identified that apparently display the essential geometrical characteristics of folding due to kink-band migration. Because the folded surfaces are closely associated with flexural slip surface faulting in an earthquake in 1944,this site may contain the first evidence of kink- band migration on near earthquake cycle time scales. The primary purpose of this exploratory research is to establish whether the structural geometry of a suite of folded geomorphic surfaces is consistent with fundamental predictions of kink-band migration fold growth. The present knowledge of their structural characteristics is limited, however, which precludes clear definition of their potential for providing new insight into kink-band migration and folding mechanisms in general. Thus, an exploratory grant is sought to develop an initial data set from these unique, superbly exposed surfaces to define more clearly the potential and direction for future investigation. Key objectives of this initial investigation include:(1)understanding the geometrical evolution of folds at the spatial and temporal scale of successively younger geomorphic surfaces;(2)detailed characterization of the geomorphology of the surface of an actively growing emergent fold in which fold growth and erosion/deposition are out-of-phase; and (3)determination of the extent to which kink-band migration folding is the mechanism by which this fold is growing. These data and analyses will help to frame more explicitly questions regarding the structural and geomorphic evolution of this and other growing folds in the region, the interplay between fold growth and intervening periods of erosion and deposition, and the incremental growth of folds at near-earthquake time scales. Increased knowledge of fold growth on this time scale has potential impacts for understanding the earthquake hazard associated with active blind faults, the interpretation of fold growth history from syntectonic strata, petroleum exploration in basins characterized by syntectonic sedimentation and in regions of basement-involved thrusting, and fault-related fold models.