TEXTURE AND COMPOSITION OF OLIVINE AND PLAGIOCLASE CRYSTALS FROM THE 2011 ERUPTION OF AXIAL SEAMOUNT: IMPLICATIONS FOR MAGMATIC PROCESSES AT A MID-OCEAN RIDGE VOLCANO

Axial Seamount is an active submarine volcano located at the intersection between the Juan de Fuca spreading center and the Cobb hotspot in the northeast Pacific, roughly 490 km off the coast of Oregon. Since the 1998 eruption, Axial volcano has been closely observed using state of the art ocean bottom pressure and tilt sensors and seismic hydrophones to monitor seafloor deformation and seismic activity associated with pre-eruptive magmatic dynamics. On 6 April 2011 Axial erupted along the southern rift zone just west of the international district. The eruption emplaced a volume of 99 x 1­­0⁶ m³ of lava consisting of both high-eruptive-rate sheet and lobate flows and low-eruptive-rate pillow mounds, determined by bathymetric remapping and Remotely Operated Vehicle (ROV) observation. Pillow lava samples were collected from the 2011 eruption site from 2 locations roughly 290 meters from each other using the ROV Jason during an expedition affiliated with the Woods Hole Oceanographic Institution and the University of Washington in July 2017. In this study, we examine the textures and chemistry of olivine and plagioclase crystals from the pillow basalts using backscattered electron images, X-ray mapping and point analyses in energy dispersive spectroscopy mode on an electron probe microanalyzer (EPMA). Initial results show that the five investigated olivine crystals are completely homogeneous in major and trace element composition and do not display zoning, indicating a very simple equilibrium growth history for these olivines. The information stored in crystals forms an archive for magmatic processes prior to eruption providing important constraints for a better understanding of Axial’s magmatic system.