NEW FINDINGS FROM DETRITAL ZIRCON STUDIES IN NORTH-CENTRAL NEW MEXICO, USA: REVISED REGIONAL CORRELATIONS AND EVIDENCE FOR MESOPROTEROZOIC SEDIMENTATION AND INTRACRATONIC REACTIVATION

Detrital zircon age data from quartzites and meta-conglomerates in the Tusas and Picuris Mountains, northern New Mexico reveal new information about age and provenance trends within a >1000 km2 Proterozoic sedimentary basin, and provide a critical test of regional correlations and evidence for the reactivation of continental lithosphere in the southwest US.

Samples from the Paleoproterozoic Vadito and Hondo Groups are dominated by a single detrital zircon population with peak ages that range from 1765 to 1704 Ma. Minor Archean and ca. 1850 Ma age peaks were also recognized in some samples. Close correspondence between detrital zircon ages and the age of surrounding basement rocks indicates predominately local sources, and we interpret systematic shifts in peak ages with stratigraphic position to represent local changes in sources through time. Similarities of age spectra and peak ages confirm previous correlation of stratigraphic units between discontinuous exposures of the Hondo Group. We interpret that these supracrustal rocks were deposited in a single basin that we informally refer to as the Pilar basin.

Our results require the reconsideration of the Marqueñas Formation as part of the Vadito Group. Samples from the middle and upper Marqueñas Formation in the Picuris Mountains both contained Mesoproterozoic detrital zircon, and meta-conglomerate from the upper Marqueñas Formation yielded a statistically significant population with a peak age of 1459 Ma interpreted to represent the maximum depositional age of the Marqueñas Formation. These data represent the first evidence of sedimentation directly associated with ca. 1450 Ma regional metamorphism, plutonism, and deformation in the southwestern United States and provide an important new constraint on the tectonic evolution of southern Laurentia during this time.

Mesoproterozoic basin development may in part be controlled by normal displacement across the east striking, south-dipping Plomo-Pecos fault zone followed by basin inversion due to thrusting across these faults. Alternatively, the Marquenas Formation may indicate syn-orogenic deposition during thrusting. Either case indicates the reactivation of intracratonic lithosphere in the southwestern US.