Deciphering the Sources of Fine-Grained, Late Miocene Volcaniclastic Density Current Deposits in the Manji-Enpo Volcano-Bound Basin (Unit V, IODP Expedition 350 Site U1437 - Izu-Bonin Rear Arc): Insights from Shard and Crystal Geochemistry, SEM Petrography, XRF Core Scanning, and Shipboard Data.
We sampled three representative volcaniclastic density current deposits from lithological Unit V (1120.11–1312.21 mbsf). Unit V is characterized by monomict, thinly bedded (<1 m) felsic tuffs intercalated with thick intervals of tuffaceous mudstone. The intervals sampled preserved erosional basal contacts and upon visual inspection were minimally altered. We are (SEM-BSE imaging) and collecting LA-ICP-MS, EMP, and SEM-EDX analyses of shards and crystals in serial thin sections of each interval. These analyses are complemented by shipboard data and new XRF core scans for whole-rock multi-element composition. With these data we will determine textural and compositional gradients and grain size variations, and attempt to constrain the degree of in-mixing of hemipelagic sediment. These data will help us constrain the tephra source or sources. Understanding these volcaniclastic intervals in Unit V is important for constraining the different sources and material inputs into the other lithological units at U1437, a topic of extensive study by other Expedition 350 participants, and to characterize an alternative stratigraphic architecture around a seamount.