SHALLOW EMPLACEMENT OF CONSANGUINEOUS PLUTONIC BODIES AS EXAMPLED IN THE MOUNT SCOTT INTRUSIVE SUITE, OKLAHOMA, USA

Continental rift magmatism, like other settings, may include volcanic eruptions and shallow intrusions that are sourced from a common parental magma. Cambrian extension within the Southern Oklahoma Aulacogen produced extensive A-type felsic magmatism, now exposed in the Wichita Mountains. Four separately mapped lithodemic units, the Mount Scott, Rush Lake, Medicine Park, and Saddle Mountain granites, each a shallow tabular intrusion with distinctive chemical and textural characteristics, exhibit compositional relationships consistent with an origin from a common reservoir. Together these form the Mount Scott Intrusive Suite.

Using the voluminous Mount Scott Granite as the parent composition, the other three granite bodies are reasonably modeled as products of crystal fractionation. Mass-balance modeling indicates that two daughter liquids formed through plagioclase and hornblende crystallization, a process consistent with the distribution of these minerals in the suite. One daughter fraction produced the magma that gave rise to the Medicine Park Granite and part of the Rush Lake Granite; the second daughter fraction produced the remainder of the Rush Lake Granite. Compositional parameters indicate these two fractionation events occurred at depths 7 to 8 km below the surface. Contact relationships indicate that these liquids ascended to intrude a shallow horizon of 1 to 2 km. These early fractions were followed by the parental magma, the Mount Scott Granite, also emplaced at the same horizon. The relatively brief interval separating emplacement of these similar magma batches produced a unique thermal regime that resulted in their distinctive textures. Following emplacement, the Mount Scott Granite magma underwent further hornblende and alkali feldspar fractionation to produce a liquid that gave rise to the hypabyssal Saddle Mountain Granite.