PROVENANCE TIES LINKING THE MESOZOIC VIZCAÍNO-CEDROS FOREARC REGION OF WEST-CENTRAL BAJA CALIFORNIA TO THE SOUTHWESTERN NORTH AMERICAN MARGIN: IMPLICATIONS FOR THE ALISITOS ARC AND GUERRERO TERRANE OF MAINLAND MEXICO

The origin of the Jura-Cretaceous Guerrero-Alisitos arc terrane of western Mexico and its relation to native North American cratonal basement-cover sequences is a longstanding issue that bears on first order questions related plate tectonic assembly of the southwestern Cordilleran margin. Here we report detrital zircon U-Pb age distributions from continentally derived, Late Jurassic to Early Cretaceous age sandstones (n=25), quartzose clasts/olistromal blocks (n=15), and igneous cobbles (n=19) from the Vizcaíno Peninsula-Cedros Island region of west-central Mexico. In addition, new U-Pb crystallization ages and geochemistry from volcanic tuffs (n=21) and plutons crystallization ages (n=15) help clarify stratigraphic and provenance relationships in the west-central Baja region. This includes correlation of the Late Triassic Vizcaino ophiolite with the Late Triassic El Arco-Camalli ophiolite that occurs farther east as prebatholithic framework rock to the Peninsular Ranges batholith.

The Vizcaíno Peninsula-Cedros Island strata and underlying basement provides the most complete representation of forearc strata and basement present anywhere along a continuous 750 km exposure of the dominantly mid-Cretaceous Peninsular Ranges batholith (PRB) of southern and Baja California. The sandstones and larger clasts exhibit clear provenance ties to the PRB as well as pre-Cordilleran basement that sourced both Laurentian (SW and NW North America) and Gondwanan (Mainland Mexico) prebatholithic wallrocks of the PRB. The Late Triassic-Eocene Vizcaíno Peninsula-Cedros Island strata were deposited upon Late Triassic and Middle Jurassic ophiolite basement sequences that have clear correlatives to basement rocks of the Alisitos arc directly across strike, as well as to Triassic-Jurassic Guerrero terrane basement of mainland Mexico. The new evidence and correlations proposed here support an Aleutian-type arc model for the Guerrero-Alisitos arc. The arc formed adjacent to the mid-Cretaceous continental arc in the north and existed as a fringing oceanic arc in the south that was close enough to the continental margin to receive coarse sediment from it.