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Multiple mantle plume components involved in the petrogenesis of subduction-related lavas from the northern termination of the Tonga Arc and northern Lau Basin: Evidence from the geochemistry of arc and backarc submarine volcanics Public Deposited

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  • New seafloor mapping and sampling demonstrates that the eruption of the high-Ca boninites is clearly associated with rifting of the northern Tonga ridge and the northern Lau Basin at the northern termination of the Tonga Trench. There is very strong evidence for OIB plume related mantle sources involved in the petrogenesis of lavas erupted in the northern Lau Basin and at the termination of north Tonga ridge. Evidence comes from 1) geophysics, which indicates there is a deep flow of mantle across the ’slab window’ formed by the trench- transform fault transition 2) geochemistry of boninites and associated rift related lavas which display strongly LREE enriched patterns, enrichment in HFSE such as Nb and Ta and low 143Nd/144Nd isotope values and 3) petrogenetic conditions of Tongan boninites, whose primary magmas have ~24 wt% MgO, require refractory lherzolite-harzburgite sources and temperates of at least ~1480°C at 1.5 Gpa. The presence of abnormally hot mantle at relatively shallow depths at the northern Tonga ridge, results from intrusion of a hot refractory OIB Samoan plume mantle source into the mantle wedge. The isotope results from this study supports the view that mantle mixing between Samoan plume mantle and an Indian-type mantle source beneath northern Lau Basin is the dominant influence on isotope compositions of lavas erupted in the northern Lau Basin, including the island of Niua Fo’ou. However the source mantle of the active Tofua Arc is more consistent with mixing between a Pacifictype mantle source and material derived from the Society Island plume. It is speculated that mantle flow through the slab ‘window’ at the northern termination of the Tonga Trench is relatively long-lived (at least as old as the earliest of Lau Basin opening) which has allowed a range of source components to mix with mantle sources involved in Lau back-arc magma genesis.
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  • Falloon, T.J., Danyushevsky, L.V., Crawford, T.J., Maas, R., Woodhead, J.D., Eggins, S.M., Bloomer, S.H., Wright, D.J., Zlobin, S.K., and Stacey, A.R., Multiple mantle plume components involved in the petrogenesis of subduction-related lavas from the northern termination of the Tonga Arc and northern Lau Basin: Evidence from the geochemistry of arc and backarc submarine volcanics, Geochemistry, Geophysics, Geosystems (G3), 8, Q09003, doi:10.1029/2007GC001619.
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