Late Quarternary volcanic activity in the New Ireland Basin
The sedimentology, petrology, and geochemistry of volcanic ash beds in sediment cores recovered during the EDISON II Cruise (SO133) in the New Ireland Basin adjacent to the Tabar-Lihir-Tanga-Feni (TLTF) volcanic chain, east of Papua New Guinea are presented. Age determinations through AMS 14C supplemented by d18O on Globigerinoider ruber assisted the correlation of the tephra. Major and trace element compositions of numerous glass shards and minerals within the ash beds were determined using an electron microprobe and ICP-MS. The shards can be distinctly split into three compositional groups reflecting three different provenances. The first group is composed of shoshonites through phonolites to trachytes, and is characterized by a strong enrichment in K, P, Sr, LILE, LREE, with Ti and HREE depletion relative to MORB, characteristic for TLTF tephras. The second group consists of high-K dacite, rhyolite, and trachyte with similar enrichment in LILE and LREE as the TLTF lavas, but with markedly lower P and Sr concentrations, a negative Eu anomaly, and enrichment in HFSE and HREE. They closely resemble the lavas from Rabaul. The third group consists of medium to low K series andesite and rhyolite, with LILE and REE concentrations typical of island arc lavas, and have strongly depleted HFSE concentrations. They are identical to the active New Britain island arc volcanoes (excluding Rabaul). Surprisingly, only a few thin tephra beds are due to eruptions of the TLTF volcanoes. This suggests that either (i) only small, or non-explosive, eruptions have occurred during the last 333 ka B.P., or (ii) these volcanoes were largely inactive since then. There is a clear distinction, based on geochemistry, between the mantle source of the TLTF volcanoes and that of Rabaul and the other New Britain volcanoes. Glasses from Rabaul in the far northeast of New Britain have a more complicated transitional composition that may reflect a mix of both Solomon and Manus mantle components, and possibly a greater role for fractional crystallization of Ti-rich phases.