AGE OF THE WICHITA IGNEOUS PROVINCE: INTEGRATING ZIRCON GEOCHRONOLOGICAL AND GEOCHEMICAL CONSTRAINTS ON VOLUMINOUS CAMBRIAN MAGMATISM IN THE SOUTHERN OKLAHOMA AULACOGEN

The Wichita Igneous Province (WIP) was emplaced within the Southern Oklahoma Aulacogen during rifting along the southern Laurentian margin preceding Cambrian opening of the southern Iapetus Ocean. Despite its tectonic significance, the WIP lacks the robust geochronological framework needed to evaluate the duration of its emplacement and crystallization history. We present the first high-precision CA-ID-TIMS U-Pb zircon geochronological constraints for several of the main igneous units in the WIP and integrate these dates with in situ trace element variations in zircon using LA-ICP-MS. Based on Ti-in-zircon thermometry, zircon crystallized over a large temperature range (mafic rocks = 930-875°C, felsic rocks = 850-750°C). Anorthositic gabbro in the Glen Mountains Layered Complex (GMLC), which is the oldest main igneous unit exposed in the Wichita Mtns., yields an age of 532.49 ± 0.15 Ma. The GMLC was tilted and its upper, more differentiated parts along with an unknown thickness of roof rock were eroded away prior to eruption of A-type rhyolites ≥ 2 km thick. 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. The Cache and Quanah Granites yield weighted mean ²⁰⁶Pb/²³⁸U dates of 530.61 ± 0.13 Ma and 530.23 ± 0.14 Ma, respectively. These data show 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 Arbuckle Mtns. ~100 km to the east has an age of 539.20 ± 0.15 Ma, raising the possibility that magmatism was diachronous along strike in the aulacogen. Zircon trace elements from the GMLC indicate that it was derived largely from continental lithosphere previously modified by subduction, whereas the felsic units reflect an OIB-type component. Contrasting zircon chemistry between the GMLC and the felsic rocks can be explained by uprise of a mantle plume that initially caused melting of subcontinental mantle lithosphere, which gave way to increased involvement of asthenospheric melts with time.