PINTURA QUADRANGLE, SOUTHWESTERN UTAH - MESOZOIC SHORTENING, CENOZOIC NORMAL FAULTING, AND STRUCTURAL INHERITANCE IN THE COLORADO PLATEAU - BASIN AND RANGE TRANSITION ZONE

The Pintura quadrangle contains Late Cretaceous folds modified by Neogene and Quaternary normal faults, including the active Hurricane fault. Spatial coincidence of shortening and extensional features suggests structural inheritance, but complicates quantifying local structures. New mapping, including new geochemical and geochronological data, provide insight into this structural transition zone. The Kanarra and Pintura anticlines and an unexposed, intervening syncline formed along the southwestern margin of the Sevier thrust belt. Where these folds die out, shortening transfers southwest to the Virgin anticline. Maastrichtian-Paleocene conglomerate overlies Jurassic Navajo Sandstone along the Pintura anticline hinge, a relation that limits the fold age and documents erosion of 1,200 m of section. Miocene to early Quaternary normal faulting and reverse drag commenced before emplacement of the 21 Ma Pine Valley laccolith, then dropped the eastern laccolith margin down 1,000 m and modified the Pintura anticline. Initial movement on the Hurricane fault cut the Kanarra anticline hinge, juxtaposing Jurassic and Permian units. The Hurricane fault displaces Quaternary basalt 368 to 486 m; geochemically correlated flows on hanging wall and footwall are dated at 840-880 ka. Total stratigraphic separation, including pre-basalt displacement, is 2,000 to 3,000 m. The Hurricane fault cuts the Kanarra anticline along its entire 40 km hinge, and a major bend in the Hurricane fault coincides with the Kanarra-Virgin fold-transfer zone. These relations suggest influence of pre-existing features on the structural evolution of the Hurricane fault, including reactivation of a blind thrust ramp and localization of a geometric segment boundary by a shortening-transfer zone.