Paleomagnetic assessment of oroflexural deformation in west‐central Nevada and significance for emplacement of allochthonous assemblages

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Abstract
Abrupt westerly deflections of north‐south trending facies boundaries, the isopleth of (87sr/86Sr)° = 0.076, and arcuate structural trends of Paleozoic, Mesozoic, and Cenozoic age in the west‐central Basin and Range Province, have been explained by (1) post‐Early Jurassic oroflexural folding and shear, (2) the existence of a pre‐Late Jurassic resistant block along the western continental margin, possibly representing late Precambrian breakup, and (3) regional flexure (“Mina deflection”) prior to intrusion of Late Cretaceous plutons which crosscut flexure‐related structural trends. Paleomagnetic data gathered from Late Cretaceous plutons and remagnetized metasedimentary rocks along and north of the northern margin of the zone of east‐west structural trends are not in support of significant oroflexural folding (and attending major clockwise rotation) since Late Cretaceous time. The data (Water Canyon pluton: D = 1°, I = 57°, α95 = 4°, k = 9, N= 132; Gunmetal pluton: D = 354, I = 60, α95 = 6, k = 21, N = 29; East Garfield Hills pluton: D = 349, I = 74, α95 = 11, k = 14, N = 12; La Panta pluton: D = 22, I = 66, α95 = 10, k = 16, N = 13; Gillis Canyon pluton: D = 354, I = 50, α95 = 4, k = 20, N = 50; and folded units of the Excelsior Mountains: D = 309, I = 79, α95 = 7, k = 12, N = 37) are dispersed from expected Cretaceous directions for the Mina deflection region, but they do not conform to a model of major systematic regional clockwise rotation. The generally small deflections of unit means from expected directions could be explained by irregular components of Late Cenozoic tilting and/or rotation. The paleomagnetic data do not deny the possibility of pre‐Late Cretaceous oroclinal bending. Nevertheless, regional structural analysis complimented by the paleomagnetic results indicate that the Mina deflection is in all likelihood a primary feature whose geometry reflects the late Precambrian fragmentation of western North America. Structures related to the accretion of allochthonous assemblages between Middle Devonian and Cretaceous time in this part of the Cordillera also reflect the primary nature of this feature.