Leveraging data from multidisciplinary studies to produce submarine geologic maps: the Mid-Atlantic Ridge Rainbow region and the Eastern Lau Backarc Basin

Abstract:

While the vast majority of Earth’s volcanism occurs in submarine environments, underwater eruptive units are significantly under-observed and under-sampled compared to their subaerial counterparts due to their relative inaccessibility. As a result, a number of basic features (e.g., eruption frequency, volume, duration, eruptive style) remain unknown for most submarine volcanic systems. Addressing some of these first-order questions requires geologic mapping and sampling of eruptive units on local to regional scales, as successfully done in case studies along the Galápagos Spreading Center and East Pacific Rise. In this study, we present preliminary mapping efforts that leverage existing data from multidisciplinary study sites on the Mid-Atlantic Ridge (MAR) and Lau backarc spreading centers. We combine geophysical mapping with bottom observations and petrologic analyses to examine how inferred properties of the magmatic system (e.g., time-averaged magma supply, composition and storage depth) correspond to differences in volcanic construction (e.g., relative frequency and size of eruptions, vent distribution and evolution, effusion rate and lava morphology). Consistent with previous findings, regions of the MAR site with lower magma supply are associated with larger volcanic flow fields that are more distinct in backscatter amplitudes from their surroundings, likely due to longer recurrence intervals as compared to regions with higher magma supply. Low supply areas also produce more eruptions from single, focused vents, as opposed to elongate fissures or series of vents. Results from the Lau spreading centers indicate that magmatic water content has significant effects on magma evolution, eruptive style and resulting volcanic construction. Water-rich segments exhibit elongate, sharply peaked volcanic ridges, with evidence of explosive eruptions that produce volcaniclastic debris produced in water depths of ~1500-2000 m. Compared to mid-ocean ridges, backarc lavas exhibit a broader range in physical properties (e.g., density, viscosity, and explosivity) and generate more variable volcanic terrain. Comprehensive studies are needed to target the effects of magmatic water on submarine eruption dynamics and crustal construction in these poorly understood backarc settings.