PRECISE U-PB ZIRCON GEOCHRONOLOGICAL CONSTRAINTS ON VOLUMINOUS CAMBRIAN MAGMATISM IN THE SOUTHERN OKLAHOMA AULACOGEN
We present the first high-precision CA-ID-TIMS U-Pb zircon geochronological constraints for the WIP. Our data reveal an age of 532.49 ± 0.15 Ma for anorthositic gabbro in the Glen Mountains Layered Complex (GMLC), which is the oldest main igneous unit exposed in the Wichitas. The GMLC was tilted during an early phase of extension, and its upper, more differentiated parts along with an unknown thickness of roof rock were eroded away prior to eruption of A-type rhyolites, which have an exposed thickness of 2 km. Lava flows from the base and top of this sequence yield ages of 530.98 ± 0.15 and 530.70 ± 0.12 Ma, respectively, and the extensive Mt. Scott sheet granite, which intruded along the unconformity between the layered complex and the rhyolites has an age of 530.45 ± 0.14 Ma. These data suggest that significant parts of the WIP were emplaced in a narrow time frame (~2 m.y.) within a tectonically active, rapidly evolving rift setting, possibly in association with a mantle plume that triggered opening of the southern portion of the Iapetus Ocean. Rhyolite exposed in the Arbuckles has an age of 539.20 ± 0.15 Ma, raising the possibility that magmatism was diachronous along strike in the aulacogen, although this needs to be tested by further isotopic dating.