High-Mg andesites and basalts in the southern Nishisonogi Peninsula, Nagasaki Prefecture

<研究報告>長崎県西彼杵半島南部の高Mg安山岩と玄武岩

High-Mg andesites and basalts in the southern Nishisonogi Peninsula, Nagasaki Prefecture

Creators Shiraki Keiichi

Creators Miyamoto Mitsutaka

Creators Matsuo Hiroaki

Creators Ueki Yuko

Creators Azuma Takateru

Creators Nagao Takashi

Creators Matsumoto Yukio

Creators Tajima Toshihiko

The late Cenozoic volcanic rocks in the southern Nishisonogi Peninsula, which are characterized by dominance of undifferentiated, primitive rocks, show a large variation in chemical composition ranging from high-Mg andesite (HMA) through tholeiitic basalt to alkali basalt and from high-Mg basalt to rhyolite. Most HMA is cpx-HMA crystallized clinopyroxene with the highest Mg# and Cr_2O_3 of 87.4 and 1.24%, respectively, following olivine with the highest Fo of 92.1 and NiO of 0.48%. An orthopyroxene andesite containing bronzite with Mg# and Cr_2O_3 as high as 89.5 and 1.06%, respectively, was found at Ebisu-zaki, the second opx-HMA occurrence in this area. Many of the pyroxene andesites reveal high Cr (>100ppm)

[NCID]AN1046804X