9418645 Kepezhinskas We propose to carry out two geological and geochemical transects across the volcanic arc of the Kamchatkan Peninsula. The transects are located on different basement terranes, although both are of largely oceanic affinity. Comparison of volcanic rocks of different ages at a given location will permit us to study changes in the compositions of magmas through time. Comparison between the transects will allow is to constrain the effects of lithospheric modification (contamination, etc.). Comparison along the trends will allow evaluation of subduction-related effects. The variable depth to the Benioff zone along each transect may result in variations in the nature and amount of the slab-derived component, and concomitant differences in the degree of partial melting. The occurrence of very primitive lavas and mantle xenoliths among the volcanic rocks of the region will help us to better understand source compositions and processes. This study will significantly advance our understanding of the magmatism and tectonics of the Kamchatkan arc, and of subduction-related magmatism in general.
