Poster session abstract GU2018-1639, European Geosciences Union (EGU) General Assembly 2018 (8-13 April, 2018, Vienna, Austria

HAUFF, Folkmar

HIRAI, Yasuhiro

HOERNLE, Kaj

MIYAZAKI, Takashi

TAMURA, Yoshihiko

TIMM, Christian

VAGLAROV, Bogdan Stefanov

WERNER, Reinhard

宮崎, 隆

平井, 康裕

田村, 芳彦

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Geophysical Research AbstractsVol. 20, EGU2018-1639, 2018EGU General Assembly 2018© Author(s) 2017. CC Attribution 4.0 license.Geochemical variations in primitive lavas from the Kibblewhite volcano,Kermadec arcYasuhiro Hirai (1,2), Yoshihiko Tamura (1), Kaj Hoernle (3), Reinhard Werner (3), Folkmar Hauff (3), ChristianTimm (4), Takashi Miyazaki (1), and Bogdan Vaglarov (1)(1) Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Kanagawa, Japan(hiraiy@jamstec.go.jp), (2) Division of Natural System, Kanazawa University, Kanazawa, Ishikawa, Japan, (3) GEOMARHelmholtz Centre for Ocean Research, Wischhofstrasse, Kiel, Germany, (4) GNS Science, Lower Hutt, New ZealandKibblewhite is one of the submarine volcanoes in the volcanic front of the southern segment of the Kermadec arc.Samples were collected from this volcano by dredging during the RV SONNE Vitiaz (SO-255) cruise in March-April 2017. The recovered lavas range from basalt to rhyolite (SiO2 = 49.9-70.9 wt.%; Mg# = 78.2-28.8) andbelong to the Low-K to Medium-K series of Gill (1981), consistent with previous observations (Wright et al.,2006). Here, we focus on mafic lavas with Mg# >55, and those geochemical compositions are consistent with thepresence of at least three types of primary magmas beneath the Kibblewhite volcano.The primitive lavas (Mg# >55) can be divided into ankaramites, rift-type basalts, and magnesian andesites.Ankaramites contain abundant (∼40 vol.%), centimeter-sized clinopyroxene (cpx) and olivine phenocrysts andshow high CaO/Al2O3 ratio (0.9 to 1.4), which is similar to “island arc ankaramite” of Vanuatu Arc (Barsdell andBerry, 1990). Rift-type basalts (containing∼3 vol.% olivines and∼1 vol.% plagioclase and cpx) have higher wt.%TiO2, Al2O3, and lower FeO* and Ba/Nb values (∼20.8) compared with the other types (Ba/Nb = 155-570) andare similar to basalts from Havre Trough (Todd et al., 2011), suggesting smaller contributions from subductioncomponents. Magnesian andesites (SiO2 = 57.4-58.8 wt.%; MgO = 5.3-5.7 wt.%; Mg# = 56-58) are aphyric withskeletal olivine and cpx microphenocrysts and sometimes contain olivine xenocrysts.Olivines in the ankaramites are forsteritic (Fo = ∼92), but have unusually low NiO contents (∼0.15 wt.%), andare not in equilibrium with mantle peridotite. On the other hand, olivines in the rift-type basalts show positivecorrelation between NiO (0.11-0.28 wt.%) and Fo contents (85-89). This trend is consistent with olivine maximumfractionation model, which suggests that ∼12% olivine should have been fractionated from the primary meltsin equilibrium with MORB residual mantle (Fo = ∼91; Warren et al., 2016). Olivine microphenocrysts in themagnesian andesites have restricted compositions (Fo = 84-85; NiO = 0.13-0.17), which are in equilibrium withhost rocks. The olivine xenocrysts extend to more forsteritic compositions (Fo = 86-93) and have higher NiOcontents (0.19-0.35 wt.%) that can be in equilibrium with residual arc mantle (Ishii et al., 1992). Fractionationof 15% olivine with the same amount of cpx from the primary melts explains the continuous trends in major andcompatible trace element composition.The high CaO/Al2O3 of the ankaramites and the unusually low NiO contents in their olivines cannot be explainedby partial melting of a peridotite source, however, experimental studies suggest that olivine-clinopyroxene cu-mulate could have been the source. Estimated primary melt of the magnesian andesite is also andesitic (SiO2 =54.8 wt.%) with 12.7 wt.% MgO, and its normative composition is consistent with melting experiment of hydrouslherzolite at 1 GPa (Hirose and Kawamoto, 1995). All three types of lavas have a very restricted range of Nd andPb isotopic compositions (e.g. 143Nd/144Nd = 0.51295-0.51300; 206Pb/204Pb = 18.84-18.89), suggesting that theyhave been derived from a similar source.

Geochemical variations in primitive lavas from the Kibblewhite volcano, Kermadec arc

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Geochemical variations in primitive lavas from the Kibblewhite volcano, Kermadec arc

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