کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4715202 | 1638430 | 2009 | 11 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Genesis of high-magnesium andesites and associated basalts from Saga–Futagoyama, northwest Kyushu, southwest Japan Genesis of high-magnesium andesites and associated basalts from Saga–Futagoyama, northwest Kyushu, southwest Japan](/preview/png/4715202.png)
High-magnesium andesites associated with basalts erupted after the opening of the Sea of Japan are present at Saga–Futagoyama in northwest Kyushu, southwest Japan. High Mg/(Mg + Fe) [=0.84] of orthopyroxene phenocrysts and bulk rock Mg–Fe–Ni compositions suggest that these high-magnesium andesites were originally primitive melts insignificantly modified in crustal magma chambers. KDCa–Na [= (Ca/Na)pl/(Ca/Na)bulk rock] ranges from 1.21 to 0.97 and suggests that the high-magnesium andesite magmas would originally have contained H2O less than 1.8 wt.%. Nb/La does not show a negative correlation with respect to SiO2. These lines of evidence indicate that hydrous components derived from the subducting slab would not have played a significant role in the genesis of the high-magnesium andesite magmas. Instead, the normative olivine − quartz − [CaTs + Jd] compositions and a negative correlation between Sr/Nd and SiO2 indicate that the basalt-high-magnesium andesite association would have been formed by multi-stage partial melting of relatively anhydrous source at pressure ranging from 1.5 to 0.5 GPa.
Journal: Journal of Volcanology and Geothermal Research - Volume 187, Issues 1–2, 30 October 2009, Pages 106–116