In-situ chemistry of plagioclase and amphibole phenocrysts of Mt. Lamington volcano in Papua New Guinea: Evidence for influence of Woodlark spreading ridge to Papuan arc

Mt. Lamington is a Quaternary volcano located on the Papuan Peninsula, SE Pacific. Texture studies and in-situ chemistry analyses on mineral phenocrysts are performed on andesite and its enclaves and pre-erupted shoshonite to better understand the petrogenesis and tectonic settings of the volcano. Both amphibole and plagioclase phenocrysts have variable zoning textures in the three major lithologies. Although the andesite and enclaves have similar bulk Sr-87/Sr-86 ratios (similar to 0.7039), their plagioclase phenocrysts show varied in-situ Sr-87/Sr-86: nging from 0.70360 to 0.70519 in andesite (An(26-58)) and from 0.70373 to 0.70393 in enclaves (An(31-61)). The shoshonite shows a bulk Sr-87/Sr-86 ratio of-0.7037, and plagioclase phenocrysts in it show in-situ Sr-87/Sr-86 ratios ranging from 0.70386 to 0.70409 (An(27-57)). A synthetic analysis of in-situ plagioclase strontium isotopes of the volcano, as well as bulk strontium and neodymium isotopes data from adjacent areas indicates three components: one high-Nd-143/Nd-144 and low-Sr-87/Sr-86 depleted mantle source represented by the most depleted samples of the Woodlark oceanic crust, one low-Nd-143/Nd-144 and medium-Sr-87/Sr-86 enriched mantle source represented by arc-type volcanics, and a third relatively low-Nd-143/Nd-144 and high-Sr-87/Sr-86 source represented by melts from arc crustal precursors. A spatial negative correlation of Nd-143/Nd-144 ratios of volcanics from east (Woodlark Basin) to west (Mt. Lamington) indicates that the magma sources have changed from depleted mantle to recently enriched lithospheric mantle plus contamination of the Papuan arc crust. This relationship agrees with a hypothesis that Mt. Lamington volcano represents the west extension of the Woodlark spreading ridge onto the Papuan arc, which in turn was a result of subduction from north. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study on Mt. Lamington volcano uses texture studies and in-situ chemistry analyses on mineral phenocrysts to reveal the petrogenesis and tectonic settings. The research indicates three components in the volcano, including depleted mantle, enriched mantle, and melts from arc crustal precursors. The spatial negative correlation of Nd-143/Nd-144 ratios from east to west suggests a change in magma sources from depleted mantle to enriched lithospheric mantle with contamination of the Papuan arc crust.