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7480707 
Journal Article 
[High-K tholeiitic volcanic rocks of Yoneyama Formation from the northern Fossa Magna, central Japan: Derivative from high water content magma] 
Aizawa, M; Okamura, S; Shinshiro, R; Takahashi, T 
2019 
Yes 
Ganseki Kobutsu Kagaku / Japanese Magazine of Mineralogical and Petrological Sciences
ISSN: 1345-630X
EISSN: 1349-7979 
48 
1 
1-24 
Japanese 
Late Pliocene-Early Pleistocene igneous rocks of Yoneyama Formation from the northern Fossa Magna region, central Japan, consist of basaltic to andesitic rocks and small intrusive rocks; they contain frequently hornblende (Hbl) gabbroic xenoliths and Hbl xenocrysts. Based on field data, together with petrographic, geochemical, and geochlonological descriptions, the volcanism comprised 5 stages. The rocks at the Ogamidake, the 1st and 3rd stages are tholeiitic rock series (TH), whereas calc-alkalic rock series (CA) are dominated at the 2nd and 4th stages. All rocks are characterized by high-K content and contain pargasitic Hbl phenocrysts in both rock series. Estimation using Ca-amphibole geobarometer suggests that Hbls have crystallized at depths of lower crust. Existence of Hbl and high An content of plagioclase (～ An90) in both rock series imply that both magmas are rich in H2O. Estimated H2O contents are ～ 5 wt％ for both TH and CA magmas. Based on mineral texture, P-T estimation and major-trace elements modeling, we infer that cryptic fractionation of Hbl can produce the TH magma trend. Our model is incompatible with general model that TH magma originate from anhydrous or low H2O content magma. 
Northern Fossa Magna; Yoneyama; High-K series; Tholeiitic rock series; H 2 O contents; Ca-amphibole; Cryptic hornblende fractionation; Hornblende gabbro; Lower crust