Boninite
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Boninite is an
Boninite is considered to be a primitive andesite derived from melting of metasomatised mantle.
Similar
Petrology
Boninite typically consists of phenocrysts of pyroxenes and olivine in a crystallite-rich glassy matrix.
Geochemistry
Boninite is defined by
- high magnesium content (MgO= >8%)
- low titanium (TiO2 < 0.5%)
- silicacontent is 52–63%
- high Mg/(Mg + Fe) (0.55–0.83)
- Mantle-normal compatible elements Ni = 70–450 parts per million, Cr = 200–1800 ppm
- Ba, Sr, LREE enrichments compared to tholeiite
- Characteristic Ti/Zr ratios (23–63) and La/Yb ratios (0.6–4.7)
Genesis
Most boninite
Boninite attains its high magnesium and very low titanium content via high degrees of partial melting within the convecting mantle wedge. The high degrees of partial melting are caused by the high water content of the mantle. With the addition of slab-derived volatiles, and incompatible elements derived from the release of low-volume partial melts of the subducted slab, the depleted mantle in the mantle wedge undergoes melting.
Evidence for variable enrichment or depletion of incompatible elements suggests that boninites are derived from refractory peridotite which has been metasomatically enriched in
Boninites can be derived from the peridotite residue of earlier arc tholeiite generation which is metasomatically enriched in LREE before boninite volcanism, or arc tholeiites and boninites can be derived from a variably depleted peridotite source which has been variably metasomatised in LREE.
Areas of fertile peridotite would yield tholeiites, and refractory areas would yield boninites.
Examples
Name | Location | Age | Comments |
---|---|---|---|
Bonin Islands | Pacific Ocean | Eocene | mostly volcanic breccias and pillow lava flows[2] |
Zambales ophiolite | western Luzon | Eocene | upper volcanic unit: high silica boninite, low silica boninite, boninitic basalt.
lower volcanic unit: low silica boninite series volcanics[3] |
Cape Vogel | Papua New Guinea | Paleocene | [2] |
Troodos | Cyprus | Cretaceous | upper pillow lavas of ophiolite complex[2] |
Guam | Pacific Ocean | Paleogene | late Eocene to early Oligocene[2] |
Setouchi | Japan | Miocene | sanukitoids, 13 million years old[2] |
Baja California | Mexico | Miocene | 14 to 12 million years old, includes bajaite[2] |
New Caledonia | Pacific Ocean | Mesozoic | Permian-Triassic and Cretaceous age[2] |
Mariana Trench | Pacific Ocean | Eocene | [2] |
North-east Lau Basin | Pacific Ocean | Modern | Eruption of boninite lava was observed in 2009 at West Mata volcano in the Lau Basin by scientists using a remotely-operated submersible. Previously, boninite had been found only near extinct volcanoes more than one million years old.[4] |
References
- .
- ^ ISBN 978-0-04-445003-0.
- ISSN 1869-9529.
- ^ "Marine Scientists Discover Deepest Undersea Erupting Volcano". News Release 09-243. National Science Foundation. 17 December 2009. Retrieved 20 February 2016.
- Anthony J. Crawford and W. E. Cameron, 1985. Petrology and geochemistry of Cambrian boninites and low-Ti andesites from Heathcote, Victoria Contributions to Mineralogy and Petrology, vol 91 no. 1. Abstract
- Dobson, P.F., Blank, J.G., Maruyama, S., and Liou, J.G. (2006) Petrology and geochemistry of boninite series volcanic rocks, Chichi-jima, Bonin Islands, Japan. International Geology Review 48, 669–701 (LBNL #57671)
- Dobson, P.F., Skogby, H, and Rossman, G.R. (1995) Water in boninite glass and coexisting orthopyroxene: concentration and partitioning. Contrib. Mineral. Petrol. 118,414-419.
- Le Maitre, R. W. and others (Editors), 2002, Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks, Cambridge University Press, 2nd, ISBN 0-521-66215-X
- Blatt, Harvey and Robert Tracy, 1995, Petrology, Second Edition: Igneous, Sedimentary, and Metamorphic, W. H. Freeman, 2nd, p. 176 ISBN 0-7167-2438-3
- Hickey, Rosemary L.; Frey, Frederick A. (1982) Geochemical characteristics of boninite series volcanics: implications for their source. Geochimica et Cosmochimica Acta, vol. 46, Issue 11, pp. 2099–2115
- Resing, J. A., K.H. Rubin, R. Embley, J. Lupton, E. Baker, R. Dziak, T. Baumberger, M. Lilley, J. Huber, T.M. Shank, D. Butterfield, D. Clague, N. Keller, S. Merle, N.J. Buck, P. Michael, A. Soule, D. Caress, S. Walker, R. Davis, J. Cowen, A-L. Reysenbach, and H. Thomas, (2011): Active Submarine Eruption of Boninite at West Mata Volcano in the Extensional NE Lau Basin, Nature Geosciences, 10.1038/ngeo1275.
Petrology