Mid- to Late Cretaceous ductile deformation and thermal evolution of the crust in the northern Dome Rock Mountains, Arizona

Abstract

Mid- to Late Cretaceous basement-involved deformation in the Maria Tectonic Belt of southeastern California and west-central Arizona varies in style from low-angle overthrusts to km-scale fold nappes. To establish the relationship between tectonite fabrics and thermal evolution of the rocks, structural and petrographic analysis was conducted in the northern Dome Rock Mountains, where the two different styles converge. A penetrative northeast-dipping foliation forms the most conspicuous fabric in an ∼5 km wide zone of distributed ductile deformation. Within the broader zone of ductile deformation, northeast-dipping shear zones contain evidence for both southwest- and northeast-directed deformation. Textural analysis of mylonitic rocks reveals that southwest-directed deformation occurred under prograde conditions, whereas northeast-directed deformation occurred under retrograde conditions. Southwest-directed deformation resulted in tubular (extreme sheath) fold development on a kilometer scale in the footwall of a reverse-sense shear zone. Northeast-directed deformation cuts the map-scale tubular fold and is inferred to have developed as a manifestation of gravitational collapse of rocks mechanically weakened by fluid infiltration and upper greenschist- to lower amphibolite-facies metamorphism. We propose that the mode and degree of fluid infiltration, rather than temperature or structural level alone, controlled the style of deformation in the Maria Belt.