Data for: Ductile and brittle Rio Grande rift deformation in Oligocene granite records a two-stage rift history in southern Colorado

These datasets include structural data and K-feldspar 40Ar/39Ar data from the ~30 Ma granite of Chokecherry Canyon in southern Colorado, and form the basis of the paper by the same authors in the journal Tectonics (Malavarca et al., in review). This study identifies mylonitic deformation in the 30.0 ± 0.5 Ma Chokecherry granite which records the earliest extension in the northern Rio Grande Rift. Mylonitic fabrics formed during rapid postmagmatic cooling at ~540–420° C and record WSW-ENE extension. These data support a two-stage rift history. Stage I (30–20 Ma) records ENE–WSW extension localized in low-angle mylonitic shear zones associated with mid-crustal intrusions; Stage II (≤20 Ma) reflects brittle high-angle normal faulting, focused exhumation, and rift narrowing.