A 500 ka Record of Volcanism and Paleoenvironment in the northern Garibaldi Volcanic Belt, British Columbia.

The Mount Meager Volcanic complex (MMVC) is one of eight major calc-alkaline volcanic centres within the Garibaldi volcanic belt, Canada. MMVC volcanism spans ~2 Ma and has been mainly intermediate to felsic in composition. However, small volume mafic centres are located around the periphery of the Mount Meager massif and have been collectively referred to as the Mosaic Assemblage or Mount Meager basalts. Here we present new 40Ar/39Ar ages and expanded chemical datasets for the MMVC mafic rocks. We show that mafic eruptive ages are both older and longer-lived than previously interpreted, spanning the last ~450 ka, and occurring in four episodes at, ~440, 200, 106, and 17 ka. We also find that chemical signatures for the MMVC mafic rocks have evolved across the four periods, fluctuating from ‘OIB’-like melt characteristics, to more typical slab-influenced, calc-alkaline, before returning to ‘OIB’-like in the youngest phase. These findings provide the first evidence of a temporal-chemical evolution of melt sourcing for the Garibaldi belt volcanism. Lastly, field mapping has identified edifices and deposits that are glaciovolcanic in origin (vs. non-glaciovolcanic) which are used in conjunction with our new 40Ar/39Ar age estimates to document the presence or absence of Coast Mountain sectors of earlier Cordilleran ice sheets in SW British Columbia over the last 500 ka.