Integrating zircon trace-element geochemistry and high-precision U-Pb zircon geochronology to resolve the timing and petrogenesis of the late Ediacaran–Cambrian Wichita igneous province, Southern Oklahoma Aulacogen, USA

Abstract

AbstractThe bimodal Wichita igneous province (WIP) represents the only exposed Ediacaran to Cambrian anorogenic magmatic assemblage present along the buried southern margin of Laurentia and was emplaced during rifting in the Southern Oklahoma Aulacogen prior to Cambrian opening of the southern Iapetus Ocean. Here, we establish the first high-precision U-Pb zircon geochronological framework for the province. Weighted mean 206Pb/238U dates from mafic and felsic rocks in the Wichita Mountains indicate emplacement in a narrow time frame from 532.49 ± 0.12 Ma to 530.23 ± 0.14 Ma. Rhyolite lavas in the Arbuckle Mountains farther east yield weighted mean 206Pb/238U dates of 539.20 ± 0.15 Ma and 539.46 ± 0.13 Ma. These dates for the WIP indicate that magmatism in the Southern Oklahoma Aulacogen postdated the ca. 540 Ma rift-drift transition along the Appalachian margin to the east. Whole-rock trace-element and isotopic geochemistry, supplemented by trace elements in zircon, tracks the evolution of magma sources during WIP petrogenesis. These data indicate that initial melting and assimilation of subcontinental mantle lithosphere by an uprising mantle plume were followed by increasing involvement of asthenospheric melts with time. We suggest that upwelling of this plume in the area of the Southern Oklahoma Aulacogen triggered an inboard jump of the spreading center active along the eastern margin of Laurentia, which led to separation of the Precordillera terrane (now located in Argentina) from the Ouachita embayment present in the southern Laurentian margin.