COOLING HISTORY OF A SHALLOW PLUTON AS SEEN IN THE MOUNT SCOTT GRANITE OF THE SOUTHERN OKLAHOMA AULACOGEN
The Mount Scott Granite is porphyritic, preserving evidence of a pre-ascent and emplacement crystal assemblage. Pre-ascent crystals include the cores of quartz, feldspar, and zircon. The feldspar cores demonstrably crystalized from the magma prior to ascent, but examples of anomalously low Ti in quartz and high Ti in zircon potentially implicate more complicated origins for some of these cores. Emplacment phases include rim growth on the pre-ascent cores, individual crystals of titanite, as well as matrix quartz and potassic feldspar that variably exhibit granophyric texture. Several geothermometers applied to the emplacement assemblage illuminate the cooling pathway for the pluton, assuming emplacement pressures of 50 MPa, roughly corresponding to a maximum intrusion depth of 2 km. Zircon rims produce average Ti-in-zircon temperatures ranging from 757-815 °C, sphene crystals indicate Zr-in-titanite temperatures of 744-766 °C, quartz rims and matrix grains yield TitaniQ estimates of 700-750 °C, and two-feldspar thermometry on rims and matrix crystals produce temperatures that average 633°C. In addition to these estimates of crystallization temperatures, a preliminary evaluation of magnetite records exsolution temperatures averaging 610 °C, and feldspar records exsolution temperatures averaging 550 °C.
Subsequent granitic magmas, followed by subvolcanic rhyolite and basalt (diabase) magmas, intruded adjacent to and into the Mount Scott Granite. Despite the proximal magmatism, multiple lines of evidence, including simple heat conduction models and diffusion models on chemical zoning in quartz and titanite, point to rapid cooling of the pluton with only limited localized thermal perturbation.