LATE TRIASSIC SUPRA-SUBDUCTION ZONE OPHIOLITE BASEMENT UNDERPINNING OF THE GUERRERO COMPOSITE TERRANE OF WESTERN MEXICO AND ITS LINKAGE TO THE ARTEAGA COMPLEX ACCRETIONARY PRISM; SUPPORT FOR ANDEAN-STYLE SUBDUCTION SINCE 220 Ma ALONG THE NORTH AMERICAN MARGIN

Prior work indicates that a convergent margin existed along the North America Cordillera from British Columbia to SW Mexico during the Permo-Triassic. However, contradictory views of terrane accretion have clouded understanding of how key rocks along the margin are related. Late Triassic and Jurassic supra-subduction zone ophiolite-arc rocks in the Vizcaino-Cedros area of Baja California are broadly correlative to the ophiolitic terranes of the western Sierra-Klamath belt and Coast Ranges of California and Oregon. The relationship between the Vizcaino-Cedros region and the Peninsular Ranges of Baja California to the east is obscured by the Quaternary Vizcaino desert. The Camalli ophiolite, a small ophiolite exposure at the southern termination of the Peninsular Ranges is located 140 km NE of the Vizcaino-Cedros region. Here we report new zircon U/Pb ages, petrologic, and geochemical data that indicate the Camalli ophiolite is correlative with the 220 Ma Vizcaino Ophiolite. This implies that Late Triassic ophiolite basement underlies Guerrero composite terrane rocks in Baja California. The Triassic Baja California ophiolite basement may further correlate with the Arteaga accretionary complex in SW mainland Mexico. The latter underlies supracrustal Jurassic-Cretaceous arc strata that are also ascribed to the Guerrero terrane. The Arteaga complex has a quartzose turbidite matrix, Late Triassic fossils, as well as Grenville, Pan-African and Permian detrital zircon suites that match the Potosi fan of mainland Mexico. This Gondwanan provenance signature also occurs in the Vizcaino region along with detrital suites that have distinct Laurentian provenance. Given these ties, the simplest interpretation is that Vizcaino-Camalli ophiolite and Arteaga accretionary complex collectively formed due to east-directed subduction beneath amalgamated Laurentian and Gondwanan rocks that became the SW North America margin. The juvenile basaltic rocks of the Guerrero terrane formed during Triassic to Early Cretaceous slab rollback, forearc extension, and backarc spreading. This is consistent with prior work (Centeno-García et al., 2011; Boschman et al., 2018) indicating the Vizcaino-Cedros-Guerrero forearc basement formed in place as an Andean margin along SW North America.