CAMBRIAN DETRITAL ZIRCONS OF SOUTHWEST LAURENTIA: REFINING EARLY CAMBRIAN STRATIGRAPHIC RELATIONSHIPS, PALAEOGEOGRAPHY, AND MAGMATISM

Tandem U-Pb geochronology (LA-ICPMS and CA-ID-TIMS) coupled with LA-ICPMS trace- and rare-earth-element (TREE) concentrations on detrital zircons from early Cambrian units in the southwest United States reveal a ~40 m.y. record of magmatism in Laurentia, from the Ediacaran-Cambrian boundary to the Miaolingian Epoch. Expanding on this dataset, we present new and compiled CA-ID-TIMS and TREE detrital zircon analyses from the Bolsa Quartzite and Abrigo Formation of southern AZ, the Tonto Group of the Grand Canyon, AZ (inclusive of the Sixtymile Formation), and the Wood Canyon Formation of southeastern CA. Maximum depositional ages (MDA) limit on-craton deposition of the Wood Canyon Formation to ≤7 m.y. between 526 and 519 Ma. Deposition of the Bolsa Quartzite occurred over ≤3 m.y. between 503 Ma and ~500 Ma, at least 3 m.y. later than deposition of the Tapeats Sandstone, thus further constraining the rate of marine transgression across the Laurentian craton.

In addition to updating MDAs, the results construct a geochronological and geochemical signature of the Cambrian detrital zircon populations in southwestern Laurentia that allows assignment to source rocks. Age and geochemical groupings indicate sourcing from igneous rocks of the 511–513 Ma Florida Mountains syenite, NM, the 517–528 Ma McClure Mountain syenite, CO, and the 531–539 Ma Wichita Igneous Province and Arbuckle Mountains rhyolite, OK. Younger Cambrian zircon age groupings (~503–507 Ma) have no constrained proximal intrusive sources but display geochemical traits that align with rift-related granitoids or syenites, suggesting that aulacogenic magmatic activity in southern Laurentia, related to inboard propagation of the Ouachita and Texas Transforms, continued until at least the early Miaolingian Epoch. Given the relative abundance of Cambrian detrital zircon of unknown provenance in the Laurentian sedimentary record, further characterization of plausible igneous sources is necessary to refine current paleogeographic reconstructions and landscape evolution interpretations.