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Volatile abundances in mafic arc magmas provide information on slab devolatilization processes, and thus give insight into fluid recycling in subduction zones. In order to investigate both magmatic and mantle volatile (H2O, CO2, S, Cl) variations in a subduction zone, we have analyzed olivine-hosted melt inclusions from nine basaltic centers located at varying distances from the trench in the Michoacan-Guanajuato Volcanic Field (MGVF), Mexico. Additionally, we have used trace element data to assess the variability in mantle source compositions across the arc. By sampling mainly primitive basaltic centers (many contain Fo88-91 olivine), we can compare magmatic volatile contents of near-primary magmas across the arc. Our data show that magmatic H2O is high (3.0-5.0 wt%) from the volcanic front to 160 km behind the front. Other volatiles (CO2, S, and Cl) also show high concentrations across the arc. We used …