The Rincon Mountains metamorphic core complex, located east of Tucson, Arizona, consists of an arched footwall of foliated crystalline rocks bounded above by the generally outward dipping, Oligocene‐Miocene San Pedro extensional detachment fault. The southwest trending axes of corrugations in the detachment fault, and in footwall foliation and lithologic layering, parallel mylonitic lineation, and inferred top‐southwest displacement on the fault. An upper plate fault block within a synformal fault groove on the west side of the Rincon Mountains contains a thrust fault that is interpreted as displaced 34‐38 km westward from an original position adjacent to a similar thrust in the footwall of the San Pedro detachment fault. Much of the footwall of the detachment fault in the eastern Rincon Mountains consists of metasedimentary tectonites derived largely from Paleozoic carbonates that were buried beneath Proterozoic crystalline rocks forming the hanging wall of the Laramide Wildhorse Mountain thrust. These tectonites were later exhumed by displacement on the San Pedro detachment fault. Structural reconstruction supports the interpretation that the carbonate tectonites localized extensional faulting along the San Pedro detachment fault at crustal depths where carbonates would be weak and deform by crystal plasticity while quartzo‐feldspathic rocks would be strong and brittle. This weak zone is located adjacent to the greatest width of exposed extension‐parallel mylonitic fabrics in southeastern Arizona and may have been associated with the earliest initiation of extension in the region. Domains of low‐strength carbonates may be an underappreciated influence on extensional tectonics in cratonic southwestern North America.

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The use of structural restorations as a tool to investigate structural evolution, fault and horizon relationships, and validity of interpretation has been widespread for more than four decades. The first efforts relied on hand-drafted bed-length measurements of commonly constant thickness stratigraphic units and were typically applied to fold-and-thrust belt settings. The advent of computer-assisted section construction and restoration software allowed for the assessment of more complicated structural interpretations by applying several new methods for forward and inverse strain transformation. Although quicker and more accurate than hand-drafted, the results of computer-aided structural modeling still need to be interrogated. We have reviewed the different strain transformation (restoration) methods available and their implications for bed length and area conservation: (1) fundamental simple shear and its two basic modes (flexural slip and inclined shear inversions), (2) fault-related folding techniques, and (3) the effects of mechanical stratigraphy and compaction. The assessment of the restoration methods was illustrated by examining two examples: the Mount Crandell Duplex Structure in southern Alberta and the Virgin River Extensional Basin in the southeast of Nevada. For both examples, we developed tables listing and confirming the deformed/restored state line lengths and areas. We believe that such tables should be provided for any strain transformation exercise, along with the restoration results as parameters for quality control, to prevent over- and underestimations that deviate more than 5% from the initial interpretation.

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