New hydrothermal activity and alkalic volcanism in the backarc Coriolis Troughs, Vanuatu

• Published in: Geology (Boulder) 2005-01, Vol.33 (1), p.61-64
• Main Authors: McConachy, Timothy F, Arculus, Richard J, Yeats, Christopher J, Binns, Raymond A, Barriga, Fernando J. A. S, McInnes, Brent I. A, Sestak, Stephen, Sharpe, Robina, Rakau, Brooks, Tevi, Tony
• Format: Article
• Language: English
• Subjects: aliphatic hydrocarbons; alkalic composition; alkanes; back-arc basins; basins; biota; Coriolis Troughs; deep-sea environment; dredged samples; electron probe data; Erromango Trough; experimental studies; Futuna Trough; geochemistry; Geology; glasses; hydrocarbons; hydrochemistry; hydrothermal conditions; hydrothermal vents; hydroxides; ICP mass spectra; igneous and metamorphic rocks; igneous rocks; iron hydroxides; laser ablation; laser methods; Lava; major elements; manganese; Marine; marine environment; mass spectra; Melanesia; metals; methane; Nifonea hydrothermal field; ocean floors; Oceania; organic compounds; oxides; oxyhydroxides; Petrology; plate tectonics; rifting; sea water; solutes; spectra; Thermal energy; trace elements; trachyandesites; troughs; Vanuatu; Vate Trough; volcanic glass; volcanic rocks; volcanism; Volcanoes
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G20870.1

The Vanuatu Australia Vents Expedition (VAVE) to the Coriolis Troughs in southern Vanuatu during September 2001 aboard the RV Franklin discovered a new hydrothermal vent field-herein informally named Nifonea-and recent alkalic volcanic activity. The Nifonea field in the central Vate Trough was located by coincident light transmission and CH4 anomalies in a hydrothermal plume of ∼60 km2 extent, best developed between 1600 and 1750 m depth at ∼150 m above the seafloor. Extensive hydrothermal fauna and yellow-brown crusts and mounds cover an area of ∼1 km2. Very fresh, glassy, variably vesicular, sparsely phyric and aphyric basalt, trachybasalt, and basaltic trachyandesite (with ∼5-6 wt% combined alkalies at ∼51%-53% SiO2 and enriched light rare earth elements, Nb, and Zr) samples were dredged from youthful curtain, tube, and sheet flows, plus iron oxyhydroxide deposits. The alkalic composition of lavas in this tectonic setting is unique and attributed to thin ocean crust being developed in an incipient rifting phase involving a relatively low percentage of source-mantle melting. The Coriolis Troughs are among Earth's most youthful backarc basins and thus provide valuable insights to incipient rifting and hydrothermal processes.