Ponyalou, O.L.; Petterson, M.G.; Espi, J.O. The Petrology and Geochemistry of REE-Enriched, Alkaline Volcanic Rocks of Ambitle Island, Feni Island Group, Papua New Guinea. Geosciences2023, 13, 339.
Ponyalou, O.L.; Petterson, M.G.; Espi, J.O. The Petrology and Geochemistry of REE-Enriched, Alkaline Volcanic Rocks of Ambitle Island, Feni Island Group, Papua New Guinea. Geosciences 2023, 13, 339.
Ponyalou, O.L.; Petterson, M.G.; Espi, J.O. The Petrology and Geochemistry of REE-Enriched, Alkaline Volcanic Rocks of Ambitle Island, Feni Island Group, Papua New Guinea. Geosciences2023, 13, 339.
Ponyalou, O.L.; Petterson, M.G.; Espi, J.O. The Petrology and Geochemistry of REE-Enriched, Alkaline Volcanic Rocks of Ambitle Island, Feni Island Group, Papua New Guinea. Geosciences 2023, 13, 339.
Abstract
Ambitle in the Feni Island group is located at the southeastern end of the NW trending Ta-bar-Lihir-Tanga-Feni (TLTF) island chain, northeastern Papua New Guinea. This island chain is known for the presence of alkaline magmas, geothermal activity, copper-gold mineralization, and mining. The purpose of this study is to present and interpret the petrographic, mineralogical, and geochemical data of the subaerial volcanic rocks from Feni within the context of the tectonic evolution of the TLTF. The TLTF arc is a younger arc situated within the Greater Melanesian Arc, specifically the New Ireland Basin bounded by New Ireland and the extinct Kilinailau Trench. The formation of the TLTF is attributed to post-subduction extensional tectonics relating to the opening of the Manus Basin and the magma is potentially sourced from subduction-modified upper mantle. The main rock types sampled in this study are alkalic and include feldspath-oid-bearing basalt, trachybasalt, phonotephrite, trachyandesite, and trachydacite or quartz-trachyte. Minerals identified include forsteritic olivine, diopside, augite, andesine, anor-thitic plagioclase, nepheline and leucite in the primitive mafic suites whereas the more evolved intermediate and felsic hypabyssal suites contain amphibole, albite, orthoclase, biotite, and either rare quartz or feldspathoids. Amphibole composition is primarily magnesiohastingsite with minor pargasite formed under polybaric conditions. Accessory minerals include apatite, ti-tanite, and Ti-magnetite. Feni magmas are highly enriched in REEs relative to neighboring arcs. Fractional crystallization is the dominant process in the geochemical evolution of the Ambitle lavas. Pyroxene fractionation is dominant in the mafic lavas whereas hornblende fractionation is a major petrologic process within the intermediate suites proven by the presence of LREE enrichment and depletions in MREE and HREE.
Environmental and Earth Sciences, Geochemistry and Petrology
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