PROVENANCE ANALYSIS FROM DETRITAL ZIRCONS IN UPPER CRETACEOUS SANDSTONES IN THE ARIVECHI REGION, EASTERN SONORA, MEXICO

The Upper Cretaceous rocks in the Arivechi region, eastern Sonora, consist of a thick sequence of conglomerate, andesite, rhyolitic tuff, sandstone, siltstone, and shale. Characteristically the sequence contains a series of sedimentary and intrusive sliding blocks derived from Paleozoic and Early Cretaceous rocks. They developed successively along the flanks of a back-arc extensional basin, called San Antonio basin, as part of a magmatic arc system developed during Late Cretaceous time. The San Antonio basin is located along eastern Sonora. The Upper Cretaceous rocks rest unconformably on Proterozoic, Paleozoic, Jurassic, and Early Cretaceous rocks in northern and eastern Sonora, regions that are critical to understand the Cretaceous tectonic evolution.

U-Pb ages of detrital zircon from three sandstone samples exhibit these features: the lower most sample of the Upper Cretaceous strata reveals occurrences of Paleoproterozoic, mainly Mesoproterozoic, and Paleozoic ages with primary peaks between 1602-1688, 1400-1487, 1341-1399, and 247-274 Ma. The middle sample exhibit peaks occurrences between 90-99 (Upper Cretaceous), and 100-105 Ma. The upper sample shows peaks between 71-79 (Campanian, Upper Cretaceous) and 80-89 Ma.

Occurrences of Mesoproterozoic zircons are interpreted to reflect detrital contributions from a plutonic suite of 1400 Ma well exposed in northern Sonora associated to older country rocks of +/-1600, the Pinal Schist. The Paleozoic suite can be derived from Permian granitoids. Recently, in northwestern Sonora have been identified plutonic rocks of these affinities. The younger suites are derived from a Cretaceous magmatic arc, but detrital zircon ages are different from ages reported in previous studies. Detrital zircons in Upper Cretaceous sandstones in the Arivechi region reflect an introduction of detritus from different magmatic arcs with structural reactivation during Late Cretaceous time.