Imaging magma beneath the rift zones of Axial Seamount on the Juan de Fuca Ridge

Abstract

Axial Seamount is an active submarine volcano formed by the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg hot spot. The Axial Seamount volcanic system includes the central volcano marked by a caldera and bounding northern and southern rift zones. Prior studies of the last three eruptions at Axial (Jan. 1998, Apr. 2011, Apr. 2015) indicate lava flows and earthquake swarms extending from the summit caldera and into the rift zones. These eruptions are believed to have been sourced from the well-imaged large magma reservoir found beneath the summit caldera of Axial (Arnulf et al., 2014, Carbotte et al., 2020). However, areas beyond the summit caldera have not been explored for potential magma sources that could have contributed to these events. In this study, we process and analyze multi-channel seismic (MCS) data acquired in 2002 from the Juan de Fuca Ridge to characterize the internal structure of the rift zones. The reflective profiles reveal small crustal magma bodies beneath and in the vicinity of lava flows in rift zones from the three prior eruptions. These magma bodies are less than 5km wide and are located at depths of ~1.5-5.2km beneath the seafloor. We also image wide magma bodies within the overlap regions between the rift zones and the neighboring Juan de Fuca segments. We image a 6.4km wide body under the eastern flank of the northern rift zone overlapping with the Coaxial segment and a 1km wide, ~400-500km thick magma body under the overlapping basin between the southern rift zone and Vance segment. Collectively the new observations from the MCS data reveals that, in addition to the main magma reservoir, there are also multiple small and discontinuous crustal magma bodies underlying the Axial segment. Through interpretations of the seismicity pattern and lava flow compositions, we believe that these magma bodies likely contribute the rift zone magmatism.