New Mexico Geological Society Annual Spring Meeting — Abstracts

Late Cretaceous (Albian–Cenomanian) strata outcrop throughout parts of northern, central, and southern New Mexico and are thought to record the final phase of sedimentation associated with normal subduction of the Farallon plate beneath western North America, and resultant deformation and volcanism linked with the Sevier fold-thrust belt and Cordilleran arc, respectively. Presented here are U-Pb detrital zircon ages from N=7 samples (n=2046 total analyses) collected from across northern New Mexico (eastern margin of the San Juan basin in the San Ysidro region and western margin of the Great Plains near the Dry Cimarron Valley and Creston regions), central New Mexico (Socorro-Carthage region), and southern New Mexico (Mescal Canyon near the Truth or Consequences region).

Detrital zircon spectra from sample localities in northern New Mexico have range of Archean–Mesozoic ages with the majority of primary and secondary peaks occurring between 1800–1600 (Yavapai-Mazatzal provinces), 1450–1350 (A-type granitoids), 1300–1000 (Grenville province) 625–595 and 430–415 (recycled Mesozoic eolianites of the Colorado plateau), as well as 190–92 Ma (Cordilleran arc). The youngest group of zircon grains from nonmarine members of the Dakota Group in northern New Mexico range from ~100–92 Ma suggesting a youngest age of early Late Cretaceous (Cenomanian–earliest Turonian). We note that there are several samples collected from established Dakota stratigraphy where occurrences of young Cretaceous-age zircon are sparse to entirely absent.

Primary and secondary peak ages from the Dakota Sandstone in central New Mexico occur primarily between 1800–1600 (Yavapai-Mazatzal provinces), 1450–1350 (A-type granitoids), 1300–1000 (Grenville province), and 240–94 Ma (Cordilleran arc and possibly older, recycled Paleozoic–Mesozoic strata). The youngest group of zircon grains from the Dakota Sandstone in central New Mexico range from ~110–94 Ma with a calculated latest Early Cretaceous (late Albian) maximum depositional age (MDA) of 102.7+/-1.1 Ma. Strata in central New Mexico have elevated occurrences of Triassic-age zircon that may reflect a combined recycled source from the underling Chinle Formation as well as from Triassic portions of the Cordilleran arc.

The Dakota Sandstone in south-central New Mexico exhibits primary and secondary peak ages very similar to the Dakota Group in northern New Mexico that occur primarily between 1800–1600, 1450–1350, 1300–1000, 625–595, 430–415, and 190–92 Ma. The youngest group of zircon grains from nonmarine portions of the Dakota in southern New Mexico range from ~107–99 Ma with a calculated Early Cretaceous (late Albian) MDA of 103.5+/-1.7 Ma. Although the sample locality in southern New Mexico is more proximal to our central New Mexico locality, there is no evidence of elevated Triassic-age zircon in this region.