The lower Mesozoic record of detrital zircon U-Pb geochronology of Sonora, Mexico, and its paleogeographic implications

detrital zircon u-pb geochronology from each of the formations of the triassic-lower jurassic barranca and el antimonio groups of central and northwestern sonora and from the lower jurassic basomari and middle jurassic lily formations of northern sonora indicate they contain distinctive zircon populations. a proterozoic population has peak ages near 1.8, 1.7, 1.6, 1.4, and 1.1 ga. a population of permo-triassic grains with important peak ages near 269, 254, 245, 234 and 227 ma. a third population of early jurassic age (~190 ma) is only present in the middle member of the lower jurassic sierra de santa rosa formation and in the basomari formation. the fourth population of middle jurassic zircons with age peaks near 168 and 162 ma is only present in the lily formation. a fifth population of neoproterozoic and paleozoic zircons, present only in the basomari and lily formations, has silurian and devonian grains (~430 - 380 ma) and neoproterozoic grains (590 - 547 ma). possible source areas for these populations are proterozoic igneous and metamorphic basement and/or neoproterozoic and paleozoic sandstones of southwestern usa and sonora, the mostly triassic magmatic arc of the mojave desert in california and the permo-triassic arc of northern mexico, the jurassic continental magmatic arc of southwestern north america, and the jurassic eolian sand seas in arizona. regional lithofacies, fossils, and paleocurrents indicate that the barranca group records a large fluvio-deltaic system on the margin of the el antimonio marine basin, and proterozoic and permo-triassic zircon populations common to the barranca and el antimonio groups indicate that detritus was derived from the same source areas to the north. lithofacies, age, and detrital zircon populations of the basomari and lily formations indicate that they were deposited within the jurassic magmatic arc of north america. the basomari and lilly formations contain abundant early jurassic zircon grains, as does the middle mem