DYNAMICS OF MAGMA RECHARGE AND MIXING AT MOUNT HOOD, OREGON - INSIGHTS FROM ENCLAVE-BEARING LAVAS

Magma recharge events and the subsequent mixing processes are widely recognized to precede volcanic eruptions. Enclaves are evidence of magma mixing processes, recording the intrusion of hot, mafic magma into a cooler, sometimes rheologically locked silicic system. The eruptive products from Mount Hood, Oregon are compositionally restricted, predominantly andesite, and contain enclaves that are mineralogically similar, yet slightly more mafic in composition. Petrologic evidence suggests that the injection and formation of these enclaves shortly precedes eruptions. Here, we use existing bulk chemical analyses of host lavas and enclaves from Main Stage (>30 ka), Polallie (30-12 ka), Timberline (1.5 ka), and Old Maid (~230 years ago) eruptive periods, optical petrography, and new field measurements of enclave abundance, shape, size distributions, and vesicularity to constrain the factors influencing mixing dynamics of the pre-eruptive magmatic system. We will combine the field and laboratory analyses with preliminary numerical models of enclave deformation and breakup, with material properties constrained by the field and laboratory measurements to determine the driving mechanism influencing enclave formation, and provide timescales of enclave cooling preceding eruption.