Provenance evidence for major post–early Pennsylvanian dextral slip on the Picuris-Pecos fault, northern New Mexico

Abstract

The Picuris-Pecos fault is a major strike-slip fault in northern New Mexico (USA) that exhibits ∼37 km of dextral separation of Proterozoic lithotypes and structures. The timing of dextral slip has been controversial due largely to a lack of definitive piercing points of Phanerozoic age. The Picuris-Pecos fault formed the western boundary of the late Paleozoic Taos trough. A distinctive metasedimentary terrane that shed detritus into the western Taos trough was exposed on the Uncompahgre uplift west of the fault during the early to middle Pennsylvanian. We use the distribution of metasedimentary clasts and the age of monazite grains within clasts from conglomeratic strata of the western Taos trough to determine the paleolocation of the southern boundary of this metasedimentary terrane during the middle Pennsylvanian (Desmoinesian), and thereby quantify the subsequent separation on the fault. The rematching of detrital petrofacies with source terranes in the adjacent uplift requires ∼40–50 km of dextral separation on the Picuris-Pecos fault since the early Desmoinesian. This exceeds the present ∼37 km dextral separation of Proterozoic features by the fault, and thus implies that an ∼3–13 km sinistral separation existed on the fault in the early Desmoinesian. The ∼40–50 km of post–early Desmoinesian dextral separation on the Picuris-Pecos fault is the result of slip that accumulated late in the Ancestral Rocky Mountain deformation and/or during the Laramide orogeny.