CONFIRMATION OF TEMPORALLY DISTINCT MAGMATIC EVENTS IN THE WICHITA MOUNTAINS, OKLAHOMA

We report new LAICPMS U/Pb ages on magmatic titanite and zircon from mafic and silicic igneous rocks from the Wichita Mountains that confirms Ham et al., (1964) in describing older mafic igneous rocks separated in time, as represented by and angular unconformity, from younger, dominantly felsic igneous rocks. Titanite from the Mount Sheridan Gabbro yielded a weighted mean age of 577 ± 2 Ma (n=30; all errors 2σ; maximum errors could be 2% or ~11 Ma). Zircons from one of several large pegmatitic granite dikes that intrude the Mount Sheridan Gabbro yield a weighted mean age of 535 ± 2 Ma (n=32). The Mount Scott Granite at Rush Lake yield a weighted mean zircon age of 538 ± 6 Ma (n=21). An unnamed flow-banded rhyolite, that lies unconformably beneath the Pratt Hill Quartzite, yield a weighted mean zircon age of 534 ± 5 Ma (n=31). The “rhyolite-dike” at Medicine Park, interpreted as one of the youngest felsic intrusions in this locale, yield a weighted mean zircon age of 536 ± 6 Ma (n=19).

The U/Pb crystallization age for Mount Sheridan Gabbro firmly establishes the Roosevelt Gabbro Group were intruded, crystallized, uplifted, and eroded well before emplacement of the Carlton Rhyolite and Wichita Granite Groups. This mafic magmatism is similar in age to the 568 ± 4 Ma Catoctin flood basalt (Southworth et. al., 2009) further establishing the existence of a Large Igneous Province associated with rifting along the margins of Laurentia at this time. Younger ⁴⁰Ar/³⁹Ar ages of 533 ± Ma on amphibole and biotite from the Mount Sheridan Gabbro are contemporaneous with crystallization ages of the distinctly younger silicic igneous rocks and record a complete and rapid thermal resetting of this isotopic system. The narrow range in crystallization ages for rhyolite–granite–rhyolite dike cycle indicates a second voluminous felsic (and mafic at depth) magmatic flare-up occurred penecontemporaneously with the continued break-up of the southern margin of Laurentia.