Evidence for basement type distribution from zircon U/Pb age spectra from Jurassic and Cretaceous sandstones, greater Monterrey area, Mexico

Detrital zircon U-Pb ages from sandstones derived directly from basement rocks delineate the distribution of basement ages and provide constraints on major basement offsets in NE Mexico. We recognize five discrete age populations in our samples. Population (1) constitutes Paleoproterozoic and Mesoproterozoic grains ranging ca. 1980-1560 Ma and 1450 and 1380 Ma. These grains are of North American provenance. They dominate Upper Cretaceous and younger strata and were transported to the foreland by river systems headed in the southwestern US. Population (2), Neoproterozoic (Grenville) grains ranging ca. 1280-880 Ma, is present in the Huizachal Group, the La Joya Formation, and the Menchaca Formation. These sandstones were derived from the Coahuila block and Peregrina Canyon basement. Population (3), younger Neoproterozoic grains ranging ca. 700-550 Ma, is present in the San Marcos Formation, the La Joya Formation, and Huizachal Group, and as xenocrysts in Eocene intrusions near Monclova. This age range is Pan-African and indicates Gondwanan crust. It also occurs in Yucatan and Florida. Population (4) consists of early Paleozoic grains ranging ca. 440-320 Ma. It dominates the Menchaca Formation, is prominent in the San Marcos Formation and present in the Huizachal Group sample. It is also present in xenocrysts in the Eocene intrusions. This group crystallized during late Paleozoic peri-Gondwanan arc magmatism prior to Gondwana – Laurentia collision. Population (5) contains Permo-Triassic and subordinate Early Jurassic grains ranging ca. 280-180 Ma. This population is the only age group in the Carbonera Formation and is dominant in the San Marcos Formation, La Joya Formation, and Huizachal Group. These ages have been attributed to arc magmatism along the western Gondwanan margin following its collision with Laurentia. This age distribution argues for Gondwanan crustal affinity for most of eastern Mexico, and little offset along the hypothetical Mojave-Sonora megashear.