UC Santa Barbara

As soon as a fold begins to grow above base level, it becomes subject to erosion. A numerical model of simultaneous fold growth and river erosion captures the early stages of channel formation and delineates the evolution of longitudinal channel profiles. This numerical exploration suggests that the patterns of channel incision into growing folds can be used to guide kinematic interpretations of fold growth. Four types of fold limb growth are modeled: limb lengthening through (1) the fold crest or (2) the fold toe, (3) limb rotation, and (4) curved fold limbs due to trishear folding. Initially, the pattern of channel incision is sensitive to the kinematics of surface deformation. Subsequently, more mature streams evolve toward similar incision patterns with deepest incision near the midpoint of the longitudinal channel profile. We compare these model predictions to Rough Ridge on New Zealand's South Island, where high-resolution topographic data reveal the multitude of channels incised into the flanks of these folds. Because the opposing limbs of these folds have followed distinct deformation pathways, the early sensitivity of channel incision to deformation pathway can be examined. Furthermore, the lateral propagation of the fold through time allows for an approximate space-for-time substitution, such that the evolution of these incision patterns can be examined from early through more mature stages. This analysis indicates that the west limb of Rough Ridge has grown by limb lengthening through the toe and the east limb has grown primarily by lengthening through the crest. Copyright 2011 by the American Geophysical Union.