New geological and geochronological data of the Placer de Guadalupe uplift, Mexico: a new piece of the Late Triassic-Jurassic Nazas Arc?

摘要

Basement exposed in the Placer de Guadalupe-Plomosas uplift in northern Mexico provides important clues for the geologic evolution of the region. The stratigraphic units form stacked thrust sheets of psammitic and calcareous formations, interlayered with magmatic rock. The eastern calcareous and quartzite formations exhibit structures associated with ductile deformation, whereas the upper stratigraphic units only contain structures formed via younger brittle deformation. Porphyry interlayered in the upper Plomosas Formation has a U-Pb zircon age of 171 +/- 1Ma. This age is consistent with its stratigraphic position, interbedded quartzarenites with a maximum depositional age of ~168Ma. Granite flakes within the Horquilla Formation are dated at 209 +/- 3Ma, and the La Vinata quartzite exhibits a maximum age of ~193Ma. The Upper Plomosas Formation correlates well with the arc-related Middle Jurassic Nazas Formation of northeastern Mexico, constituting the first report of a Jurassic continental margin arc outcrop in the 'Central Mexican Gap zone'. We document Late Norian to Bajocian ages for the stratigraphic units cropping out in the Placer de Guadalupe area. The Jurassic age cluster indicates that the Nazas Arc magmatism in the region occurred during the Late Triassic and ended in the Middle Jurassic times. Permian ages previously assigned to these rocks and the occurrence of a Permo-Triassic deformation event have to be dismissed.