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Stoffers, P., Botz, R., Cheminee, J.L., Devey, C.W., Froger, V., Glasby, G.P., Hartmann, M., Hekinian, R., Koegler, F., Laschek, D., Larque, P., Michaelis, W., Muehe, R.K., Puteanus, D. and Richnow, H.H. (1989). Geology of the Macdonald Seamount region, Austral Islands; recent hotspot volcanism in the South Pacific. Marine Geophysical Researches 11(2): 101-112. |
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The southeastern extension of the Austral Islands volcanic chain terminates near 29 degrees S, 140 degrees W at the active Macdonald Seamount. The 'hotspot' region near Macdonald consists of at least five other volcanic edifices each more than 500 m high, included in an area about 50-100 km in diameter. On the basis of the sea-floor topography, the southeastern limit of the hotspot area is located about 20 km east of the base of Macdonald, where it is defined by the 3950 m isobath. At the edge of the hotspot area, there is a marked deepening of the seafloor from c.3900 m down to 4000-4300 m. The deeper sea-floor is faulted and heavily sedimented. The Macdonald volcano itself stands 3760 m above the surrounding seafloor, and has a basal diameter of 45 km. Its summit in Jan 1987 was 39 m below sea level, and it seems likely that Macdonald will emerge at the surface in the near future. Recent (Mar. and Nov. 1986) phreatic explosions on Macdonald Seamount erupted fragments of ultramafic and mafic plutonic blocks together with basic lapilli (volcaniclastic sand). The plutonic blocks have been variably altered and metamorphosed, and in some cases show signs of mineralisation (disseminated sulphides). The blocks presumably come from deeper levels in the volcanic system. The volcanics so far dredged from Macdonald consist of olivine and clinopyroxene cumulus-enriched basalts, evolved basalts, and mugearite. On the basis of incompatible element variations, simple crystal fractionation seems to be controlling the chemical evolution of Macdonald magmas. |
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Keywords
alkaline earth metals; areal geology; Austral Islands; basalts;, cores; East Pacific; East Pacific Ocean Islands; ejecta;, fractional crystallization; French Polynesia; Geisha Seamount;, geophysical methods; geophysical surveys; Hawaii; hot spots;, igneous rocks; isotopes; lava flows; lithosphere; Loihi Seamount;, Macdonald Seamount; magnetic anomalies; magnetic methods; mantle;, metals; mineralization; Nd-144/Nd-143; neodymium; North Pacific;, Northeast Pacific; Oceania; Pacific Ocean; Pacific Plate;, petrology; Polynesia; Ra Seamount; rare earths; Samoa; Seabeam;, South Pacific; Sr-87/Sr-86; stable isotopes; strontium; surveys;, Teahitia-Mehetia; United States; volcanic rocks; volcanism;, volcanology, 05A, Igneous and metamorphic petrology |
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Journal
Marine Geophysical Researches |
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