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faults_part2 - I Normal Faults A Characteristics 1 Defined...

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61 I. Normal Faults A. Characteristics 1. Defined a. Inclined dip-slip faults in which hanging wall has moved down relative to footwall (1) younger rocks placed on older rocks by fault (2) Crustal extension = driving process 2. Separation and Normal Faulting a. Relative stratigraphic offset of normal fault a function of: (1) strike and dip of fault plane (2) strike and dip of bedding (a) controls outcrop and cross-section rock patterns 3. Folds Associated with Normal Faults a. Drag Folds b. Listric normal faults and roll-over anticlines (1) listric fault: angle of dip decreases with increasing depth (a) concave upward normal fault (2) Roll-over Anticline (a) As hanging wall block downdrops, beds deform to maintain contact with footwall 4. Associated Deformation a. drag folds b. slickensides c. cataclastites d. ducile shear at deeper levels B. Shape and Displacement of Normal Faults 1. Surface Trace a. Sinuous vs. straight fault trace b. Mountain front geomorphology
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62 2. Shape at Depth a. listric normal b. high-angle normal faults: constant dip at depths c. Detachment faults: major fault surface of "rock detachment" (1) commonly low angle d. Imbricate Faults: parallel fault sets e. rotational vs. non-rotational normal faults C. Structural Associations 1. small scale vs. large scale faulting a. outcrop vs. mountain front size faults 2. synthetic vs. antithetic faults a. synthetic: smaller scale faults parallel to major faults b. antithetic: smaller scale faults oriented with dip in opposite direction of major faults 3. Horsts and Grabens (fault bounded blocks) a. Horsts: uptrown fault-bounded blocks b. Grabens: down-thrown fault-bounded blocks (1)
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