LATE PLEISTOCENE-TO-HOLOCENE VOLCANISM AT THE EMMONS LAKE VOLCANIC CENTER (ELVC) IN THE ALEUTIAN ARC

The ELVC is one of the largest volcanic centers in the Aleutian Arc, having erupted ~ 350 km³ of basalt to rhyolite since mid-Pleistocene. ELVC hosts a 19 x 12 km set of nested calderas and six Holocene stratovolcanoes, including Pavlof, the most historically active volcano in the arc. ELVC vents define a 30 km trend oriented N55E. The Mt. Emmons, Mt. Hague, and Double Crater stratovolcanoes form the western end of the trend (inside the caldera). Little Pavlof, Pavlof, and Pavlof's Sister form the eastern end of the trend (outside the caldera).

Activity over the last 100 ka includes sub-glacial effusive eruptions of low-Si dacite to andesite, a caldera-forming plinian eruption of rhyolite, and basalt to low Si-dacite lava fountaining and strombolian eruptions. Historic basaltic lava fountains and strombolian eruptions have occurred at Pavlof, and possibly Mt. Hague, the former with > 40 eruptions in the last 216 years.

ELVC lava compositions increase in crustal (and/or subduction) contributions from east to west. The eastern lavas are olivine-controlled tholeiites. The west has both calc-alkaline and tholeiitic compositions controlled by plagioclase, pyroxene, and Fe-Ti oxide fractionation. Western lavas are enriched in fluid mobile-LILE, Th and U, and depleted in Nb relative eastern lavas.

We hypothesize two coeval, but distinct magma systems beneath ELVC. Eruptions from eastern vents are fed directly from a mafic reservoir in the lower crust, without mid- or upper-crustal storage. Present-day seismicity suggests reservoir depths of 20-40 km.

Underlying the western part of the trend is a silicic, upper crustal reservoir that was underplated (late Pleistocene) and then traversed (Holocene) by pulses of more mafic magma. Present-day seismicity and hydrothermal activity indicate that the western reservoir is still hot and leaking magmatic fluids. Gas and water samples from associated hot springs have high B and As concentrations and He and C isotope ratios indicative of magmatic sources. Frequent, hydrothermally induced earthquakes occur at depths of < 5 km.

Future basaltic eruptions of Pavlof on the eastern end of the ELVC are expected; the recurrence interval in historic time is ~ 5 years. Reactivation of the western segment is also possible, and includes the potential for more explosive and voluminous silicic eruptions.