LAUSR

Detailed geologic mapping and structural investigation of the footwall of the northern Snake Range (NSR) metamorphic core complex reveal km‐scale Late Cretaceous fold and thrust relationships of the northern Snake Range Fold and Thrust System (NSRFTS) that are broadly coeval with the deep burial and amphibolite facies metamorphism of Eocambrian strata. The O'Neill Peak Recumbent Syncline (OPRS) ‐ an NNW‐trending, non‐cylindrical, eastward‐opening, inclined to recumbent syncline and its overlying anticlinal closure, the O'Neill Peak Anticline, affect the entire Middle to Upper Cambrian stratigraphy, effectively doubling its structural thickness from ∼3.5 to ∼8 km. West of the OPRS, pervasive isoclinal folding in lower Cambrian schistose units and local thrust duplication of lower and middle Cambrian units of the Eightmile Thrust System record layer‐parallel shear and shortening. Detailed cross sections are used to create an interpretive pre‐extensional reconstruction of the NSR that integrates the NSRFTS with associated supracrustal shortening structures now exposed in the Confusion Range to the east. We conclude that the NSRFTS and overlying structures accommodated ≥10 km of horizontal shortening, resulting in ≥7 km of structural burial of the deepest structural levels in the NSR footwall, thus explaining the localized kyanite‐grade metamorphism and elevated thermobarometric P‐T estimates. This burial was apparently quite localized as evidenced by decreasing metamorphism to the north and south. The highest magnitude of subsequent extensional exhumation of the NSR footwall appears to coincides with the area of deepest burial, suggesting that Mesozoic crustal thickening influenced both the magnitudes and geometry of subsequent Cenozoic extensional exhumation.