Processes of faulting in jointed rocks of Canyonlands National Park, Utah

Detailed studies of 11 segmented normal faults from five grabens in the Nee dles District of Canyonlands National Park, Utah, demonstrate key processes in the growth, linkage, and evolution of grabens, Field observations and s tereophotogrammetry reveal a ubiquitous asymmetry in cross-sectional geomet ry, based on distinct map patterns of graben-bounding faults, rollover anti clines with attendant joint dilation. footwall uplift with joint closure, a nd spoon-shaped graben floors. Master and antithetic faults across Devils L ane and several other grabens are defined quantitatively by the displacemen t distributions along the faults. Two-dimensional shape parameters that cha racterize the displacement profiles indicate that inelastic processes such as changes in fault frictional strength influence strain accumulation along the faults. The degree of graben asymmetry increases systematically with d istance from the Colorado River; greater symmetry is associated with locall y greater age and/or strain of grabens nearer the river. Scatter in plots o f maximum displacement vs. fault length was attributed previously to linkag e of fault segments alone but is here shown to correlate additionally with distance from the Colorado River and, therefore, to spatial strain gradient s within the graben array. Extensional strain across the fault array, accum ulating at rates of perhaps 1.5 to 2 cm/yr or 10(-14) to 10(-13) s(-1), is accommodated at depth by salt flow and formation of reactive salt diapirs b eneath the grabens and was probably initiated when the Colorado River had c ut sufficiently deep into the section for active salt diapirism to commence .