Seamount Calderas and Craters- Keys to Submarine Magmatic and Volcanic Processes

Abstract:

Near-ridge axis seamounts are ubiquitous features in all global ocean basins. Processes that give rise to these volcanoes provide important insights into magmatic processes in Earth’s mantle associated with crustal accretion at an adjacent mid-ocean ridge (MOR) segment. Many seamounts have craters and calderas implying well-established magmatic storage systems that supply lavas to build edifices over time spans that range from tens to hundreds of thousands of years. High-resolution AUV-based mapping and in situ sampling using Alvin or ROVs carried out recently at seamounts provide important morphostructural data that can be used to better understand eruptive history and volcano evolution. Geochemical studies of near-axis seamounts reveal that the lavas contain evidence for more variable mantle sources than those associated with generation of adjacent MOR axial basalts. Recent studies of a ~300km seamount chain near 8°20’N, west of the East Pacific Rise and parallel to the northern margin of the Western Siqueiros Fracture Zone, may provide critical observations needed to assess the relative contribution of axial and off-axis melts to seamount volcanism. These studies inform our understanding of seamount formation at greater distances (~>50 km) from the ridge axis and the implications of fracture zone processes on melt delivery from the upper mantle to storage reservoirs in the crust. Data collected during the OASIS Expedition at the 8°20’N Seamount Chain will be compared with other seamount lineaments from well-studied chains including the Lamont Seamounts at 9°50’N on the EPR, and the Vance Seamounts at 45°20’N on the Juan de Fuca Ridge. Targeted sampling with deep submergence ROVs as well as HOVs and geochemical analysis of lavas from seamount calderas and craters provides critical constraints on the evolution of these systems. We will discuss the development of a manipulator-based submersible- and ROV rock drill that can be used to collect suites of oriented samples from vertical walls such as those found commonly in seamount calderas and craters, as well as MOR rift valley walls. The advancement of collection techniques for spatially correlated and oriented suites of rock will drastically increase our ability to investigate the temporal evolution of seamount magma systems and their mantle sources.