40Ar/39Ar ages and bulk-rock chemistry of the lower submarine units of the central and western Aleutian Arc

In order to further constrain the timing of Aleutian Arc initiation as well its early evolution, an extensive 40Ar/39Ar dating and geochemical (major selected trace elements) campaign (40 samples) lower units ridge has been carried out on samples dredged from deep fore-arc canyons rear-arc tectonic structures. The new dataset slightly increases minimum inception age for system, with two oldest dated at 46.1 ± 3.3 Ma 47.80 0.57 Ma. Both mid Eocene ages were obtained tholeiitic mafic volcanic rocks western section arc. data also support occurrence three distinct periods enhanced magmatic activity (magmatic pulses) during pre-Quaternary evolution arc (at 38–27, 16–11 6–0 Ma), previously suggested based a more limited dominantly subaerial dataset. Moreover, refine duration first pulse activity, which ended 2 later than previous estimates. last pulses may be associated rotations subducting plates while second might result regional changes. significant overlap between distribution submarine suggests that much earlier parts have uplifted subaerially exposed. expected crustal growth is unlikely significantly impacted residence times, since no variation in degree differentiation can observed or after pulses. On other hand, type magmas erupted changed evolution. Prior pulse, appears tholeiitic. was characterized by coeval tholeiitic, transitional calc-alkaline magmas, increasing ~3 Subsequently, period occurred 29 8 Ma, followed progressive return activity. These temporal changes magma types correspond likely variations thickness beneath active front, could therefore response physical overriding plate.