Active and Recent Submarine Volcanism of the NE Lau Basin

Abstract:

The NE Lau Basin hosts a highly productive zone of submarine volcanism in the rear arc and backarc spread over a large number of volcanic centers. This is in the most rapidly opening part of Earth’s fastest opening backarc, and includes examples of both effusive and explosive volcanism. Rapid extension, microplate tectonics and slab-derived fluid fluxing of the mantle promote rapid mantle melting and migration of mantle upwelling centers, leading to near simultaneous volcanism at many different sites. Weakly developed crustal magma storage systems promote eruption of poorly mixed magmas of multiple parentage. Observations of eruptions and young eruption products demonstrate several styles of mafic volcanism across a gradient of degassing and effusion conditions spanning submarine analogs of Hawaiian to Strombolian activity, plus lower effusion rate forms common to submarine mid ocean ridges (pillow mounds) and domes at more silicic volcanic centers. Examples include the 2008-2010 West Mata summit eruption and a high mass flux rate 2008 basaltic eruption on the Northeast Lau Spreading Center. At W. Mata we observed crystal and gas rich boninite magma erupting at the summit at 1.2 km water depth in 2009. A hypothesized conduit split to feed 2 vent sites and waxing/waning magma supply to a small, open-system magma reservoir led to a range of eruption styles and deposits (e.g., cycling between lava effusion and vigorous degassing, fire fountaining, glowing lava-skinned bubble bursts, pyroclastic debris flows, and fragmentation and ejection of glowing pyroclasts). Subsequent mapping revealed roughly simultaneous eruptions along the SW rift zone and at its base, followed by summit eruption cessation and pit crater formation, all of which will be re- investigated on a late 2017 site revisit. Several styles of silicic volcanism also occur in the rear arc, including extensive dacite lava flows with a range of effusion conditions within a roughly triangular corridor between the NELSC on the west, the Mata volcano group to the northeast, the northernmost Tofua magmatic arc on the east, and Niuatahi, a silicic volcanic caldera on the south. The proximity of 4 volcanic provinces (the arc front, boninite, rear-arc silicic and back-arc spreading center) make this a great site for subduction-related volcanic process studies.