Paper No. 89
Presentation Time: 9:00 AM-6:00 PM
THE PETROGENESIS OF PERALKALINE RHYOLITE VIA BOTH OPEN- AND CLOSED-SYSTEM PROCESSES: A CASE STUDY FROM BIG BEND NATIONAL PARK, TEXAS
The Bee Mountain Basalt (BMB) Formation consists of a complex suite of Eo-Oligocene mafic to intermediate lavas ranging in composition from basalt to trachyandesite. These lavas erupted between 34 and 29 Ma, during the post-orogenic phase of the Trans Pecos Magmatic Province (TPMP), an alkali/alkali-calcic igneous province active from 48 to 17 Ma. The BMB has been proposed to have provided the source of heat and volatiles for nearly all peralkaline felsic volcanism in the Big Bend area of the TPMP, including the Pine Canyon Caldera suite (via AFC processes), the Emory Peak Rhyolite (via volatile-induced partial melting), and the Burro Mesa Rhyolite (via FC processes). In this study we present the results of thermodynamic (MELTS) modeling of the several proposed series within the BMB to test these multiple models for the origin of peralkaline magmas.