EVIDENCE FOR A CONTRACTIONAL MESOPROTEROZOIC (CA. 1.45 GA) OROGENY IN THE SOUTHWESTERN UNITED STATES: THE PICURIS OROGENY

New detrital zircon and igneous zircon U–Pb ages are reported from Proterozoic metamorphic rocks in northern New Mexico. These data constrain the provenance and depositional age of a > 3-km-thick metasedimentary succession and help resolve the timing of orogenesis in a region of overlapping accretionary orogens and thermal events associated with the Proterozoic tectonic evolution of southwest Laurentia. Three samples from the Paleoproterozoic Vadito Group yield narrow, unimodal detrital zircon age spectra with peaks near 1710 Ma. Plutons that intrude parts of the Vadito Group include the Cerro Alto metadacite, the Picuris Pueblo granite, and the Peñasco quartz monzonite and yield crystallization ages of 1710 +9/-10 Ma, 1699 ± 3 Ma and 1450 +5/-10 Ma, respectively. Within the overlying Hondo Group, a metamorphosed tuff layer from the Pilar Formation yields an age of 1488 +6/-3 Ma and represents the first direct depositional age constraint for this unit. Detrital zircon from the overlying Piedra Lumbre Formation yield a minimum age peak of 1495 Ma and contain apparently non-Laurentian grains with ages between 1600 Ma and 1500 Ma, possibly sourced from Australia and/or Antarctica. Detrital zircon from the basal metaconglomerate and the middle quartzite member of the Marqueñas Formation, yield minimum age peaks of 1472 Ma and 1473 Ma, respectively. We interpret the onset of ca. 1.49–1.46 Ga deposition followed by tectonic burial, regional Al₂SiO₅ triple–point metamorphism and ductile deformation at depths of 12–18 km to reflect a Mesoproterozoic contractional orogenic event, possibly related to the suturing of the Mazatzal crustal province to the southern margin of Laurentia. We propose to call this event the Picuris Orogeny.