Continent-derived vitric mud and mafic-arc rocks in deep Kermadec Trench diamictons

Bimodal volcanogenic sediments dredged from depths greater than 7 km on the Kermadec Trench inner slope at latitude 31 degrees S comprise diamictons o f mudstone, basalt, and dolerite clasts enclosed in noncalcareous mud. The mud and mudstones art medium-to-high-K rhyolitic vitric mud of continentala re derivation that has been transported 900 km from New Zealand, All contai n minor shards of Kermadec are low-K rhyolitic glass. All mudstones appear to be Quaternary, but one basalt clast gave a latest Miocene K-Ar age (7.84 +/- 0.64 Ma). There have been at least three periods of deposition of mud, and two or three episodes of emplacement of diamict. The present trench sl ope is 10-24 degrees, and diamicts are interpreted to be deposits of debris flows of varying fluidity., Graded mafic volcanic sand beds are interprete d to be deposits of turbidity currents or sandy debris Boas. The degree of consolidation of mudstone clasts, along with the presence of compaction fau lts, suggests burial followed by re-exhumation, implying that redeposition processes may be deep-reaching, Shallaw-water fossils and calcareous mudsto ne clasts originating above the carbonate compensation depth (c. 4.5 km), p lus clasts of basalt and dolerite sourced locally on the crest of the Kerma dec are, reached the lower trench slope in gravity hows that bypassed the m id-slope terrace. There was extensive mixing of products from various eruptions and sources d uring multiple episodes of transportation, and during deposition and redepo sition on the lower trench slope. ri range of agencies and routes is availa ble to carry New Zealand (Taupo Volcanic Zone)-derived vitric mud to the Ke rmadec Trench-both low-level and high-level winds plus the north-flowing De ep Western Boundary Current (DWBC) of Antarctic Bottom Water. The latter wa shes the Raukumara Plain forearc basin and the western trench slope to dept hs as shallow as 2-3 km, We inter that ashfall tephra carried ol er the Rau kumara Plain by the prevailing low-level southwesterly wind is the principa l source of the muds found in the trench, The relative purity of the vitric mud in the trench might be explained by the tendency of rhyolitic material to dominate sediment dispersal systems in the aftermath of very large cald era eruptions. Confinement of the mud to the lower trench slope is probably caused by the tendency of DWBC surges of >20 cm/s to veer 10 degrees-30 de grees clockwise of the trench axis. The continent-derived volcanic ash on t he subducting slab mag influence oceanic are magma composition.