DETRITAL ZIRCON AND METATUFF AGE CONSTRAINTS ON THE TIMING OF MESOPROTEROZOIC DEPOSITION AND OROGENESIS CA. 1.50-1.40 GA ACROSS THE SOUTHWESTERN UNITED STATES AND POSSIBLE CONNECTIONS WITH THE GEOLOGIC EVOLUTION OF THE BELT SUPERGROUP

U-Pb zircon ages from newly recognized metatuff layers in Arizona and New Mexico challenge our understanding about the timing of Proterozoic deposition and orogenesis in the southwestern United States. Similarities in depositional age and distinctive 1.61–1.50 Ga detrital zircon populations between the southwestern United States and the Belt Supergroup suggest sedimentary and tectonic linkages both within western Laurentia and between Laurentia and one or more cratons including North Australia, South Australia, and/or East Antarctica.

Four metatuff layers from the lower-to middle Yankee Joe Formation, Salt River Canyon, Arizona yield crystallization/depositional ages between ca. 1500 Ma and 1483 Ma. We tentatively correlate these metatuffs with previously reported ca. 1500–1480 Ma metatuffs from the Pilar Formation, exposed 540 km to the northeast, in the Picuris Mountains, New Mexico. In Arizona, metatuffs are interbedded with ca. 1.50–1.44 Ga metasedimentary rocks that contain globally uncommon, non-Laurentian ca. 1.60-1.48 Ga detrital zircon. In northern New Mexico, the ca. 1.48–1.45 Ga Piedra Lumbre Formation also contains abundant ca. 1.60–1.54 Ga detrital zircon. These similarities suggest a northeast-striking series of basins formed ca. 1.48–1.45 Ga in southwestern Laurentia with sediment derived, in part, from non-Laurentian cratonic sources. The lower Belt Supergroup was deposited during the same time interval and was also sourced from exotic cratons to the west. At ca. 1.45 Ga, sedimentary successions in both AZ and NM were buried 8-15 km into the middle crust and experienced greenschist to amphibolite facies regional metamorphism and ductile deformation attributed to the Picuris Orogeny. Syn-orogenic metasedimentary rocks deposited after 1.45 Ga show an absence of non-Laurentian detrital zircon and a predominance of local sources. Coeval strata of the upper Belt Supergroup also show an absence of ca. 1.60–1.50 Ga detrital zircon and a shift to Laurentian sources beginning 1.45 Ga. We suggest that prominent Paleoproterozoic detrital zircon populations in upper Belt strata were largely sourced from the exhumed foreland region and, possibly, the orogenic highlands of the Picuris Orogeny in the southwest.