Insights into Arc-Wide Magmatic Processes from Volcano-Seismic and Geochemical Data in Alaska

Abstract:

We combine seismic and geochemical datasets that span a 2000 km stretch of the Aleutian arc

to investigate the processes that control arc magmatism at a regional scale. We use seismic data

recorded over 10 years from 46 volcano monitoring networks to search for regional variations

in volcano seismicity. The volcanoes in the central portion of the arc—those located from

Aniakchak to Okmok—are associated with significantly more seismicity at depths below 15 km.

We compare the trends in seismicity with variations in the SiO2 compositions of the volcanoes

by compiling published geochemical data. The transition between felsic volcanism in the east

to more mafic volcanism in the west occurs in the same region where the depth distribution of

volcanic earthquakes changes. Since deep volcanic earthquakes are often thought to be generated

by the ascent of magma through the deep crust (i.e., depths greater than 15 km), our results

suggest that magma ascent is more prolific in the central part of the arc compared to the western

and eastern regions. This observation is in agreement with the location of the largest and most

historically active volcanoes in the Aleutian arc, which are found in same region that generates

abundant deep volcano seismicity. We propose two models to explain these apparent variations

in magmatic flux: (1) a stress-based model, in which subduction obliquity and the collision of the

Yakutat block affect the stress regime in the upper plate, inhibiting the rise of magma in eastern

and western regions of the arc and (2) a melt-based model, where more magma is generated

in the central region of the arc through increased H2O in the downgoing slab via water-laden

sediments and subducting fracture zones.