A study of 79 chemical analyses of plutonic rocks in the northern part of the Alaska-Aleutian Range batholith shows that K2O and SiO2 in Late Cretaceous and Tertiary rocks decrease toward the Pacific margin and that Al2O3 and CaO increase. Plots for Fe2O3, FeO, MgO, and TiO2 suggest a possible increase toward the Pacific margin; Na2O, H2O+, and MnO show no significant trends across the batholith. Oxide trends for groups of plutons in the western and eastern parts of the batholith in general are opposite that of the groups combined. For the Jurassic plutonic rocks, K2O may decrease toward the Pacific margin; other oxides show considerable scatter, and meaningful trends are not readily apparent. The oxide trends across the batholith are similar to trends across the central Sierra Nevada batholith of California, with the exception of SiO2 and A12O3, which show no significant changes. In the Coast Range batholith of British Columbia, potassium also increases away from the Pacific margin. The increase in K2O toward the continent in the Alaska-Aleutian Range batholith is similar to that found across Quaternary volcanic island arcs, where K2O content increases directly with increasing depth to inclined seismic zones. This increase suggests that generation of magma may have taken place along, or above, a paleoseismic zone. Geologic evidence supports such a model for the Jurassic plutonic rocks, which represent the roots of an early Mesozoic magmatic arc that probably formed above a descending oceanic plate. However, the hypothesis that magma for Late Cretaceous and Tertiary plutonic rocks was generated along seismic zones does not fit available geologic evidence, and an anatectic model cannot be ruled out.
