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Structural Evolution of the J-Fold Anticline; A Multi-scalar Approach to Modeling Kinematic Fold Evolution in the Cordilleran Fold-thrust Belt, Southwest Montana

James W. Wallace and Bruce J. Douglas
Indiana University

The northeast corner of the London Hills Structural Complex, referred to herein as the Highway 2 field (HW2) area, is located on the southeastern margin of the Helena salient in Gallatin Co., southwestern Montana. The most prominent structural feature in the HW2 area is the Late-Cretaceous J-fold, a fault driven, east trending, double hinged anticline plunging to the northeast. The purpose of this study is to produce a model for the HW2 area that describes both the kinematic evolution and the mechanical behavior of the J-fold. This will be accomplished by conducting a multifaceted examination of the J-fold using highresolution terrestrial laser scanning (TLS) combined with detailed field measurements of kinematic indicators, and laboratory analysis of microstructures in thin section. Preliminary results, based on direct field measurements, suggest a 3-stage evolution of the J-fold; fault-propagation folding, followed by fault-bend folding, and ending with fixed-hinge folding. Ultimately, the HW2 study will use the light detection and ranging (LiDAR) point clouds obtained by TLS with the micro- and mesostructure distributions along the fold to produce a complete model for the evolution of the J-fold.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013