DOES THE ARRIVAL OF MAFIC RECHARGE TRIGGER VOLCANIC ERUPTIONS? NEW INSIGHTS FROM FELDSPAR THERMOMETRY

Injection of mafic magma into the base of crustal reservoirs has long been proposed a mechanism for triggering intermediate to felsic volcanic eruptions (Kent et al, 2010; de Silva et al, 2008; Tepley et al, 2000); however recent work at Augustine and Merapi (Putirka, 2016) identifies thermobarometric evidence for pronounced cooling between the final recharge event and eruption. We test the extrapolability of these findings by using plagioclase thermometry (Putirka, 2008) to reconstruct the magmatic processes active in the lead-up to eruptions at the Brokeoff Volcano member of the Lassen Volcanic Center. We reconstruct the thermal histories of twenty-nine feldspar transects from eight separate eruptive units. Preliminary results indicate that twenty-four of the feldspar transects from Brokeoff Volcano preserve evidence of cooling between the final thermal input and the crystal rim, with an average cooling of 43°C and a maximum cooling of 108°C. The occurrence of substantial cooling suggesting that some mechanism other than the arrival of mafic recharge must serve as the ultimate trigger mechanism for eruption.