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[SCG47-P16] Occurrences of ultramafic xenoliths in basalt from Yobuko area, Saga Prefecture
Keywords:ultramafic xenoliths, Yobuko area, Basalt
Arai et al. (2018) reported occurrence of ultramafic xenoliths from several area such as Kurose, Fukuoka Prefecture, Takashima, Saga Prefecture and Fukuejima, Nagasaki Prefecture. In addition, we newly found the ultramafic xenoliths from a part of basaltic lava in the Yobuko area, Saga Prefecture. Basaltic lava is aphyric one, and unconformably overlies Neogene sedimentary rocks. In this study, we investigated that the petrographic features and constituent minerals of the ultramafic xenoliths from the Yobuko area for their petrologic characterization. The petrographic types and their abundance ratio of the Yobuko xenoliths are compared to those from Takashima and Kurose.
The collected xenoliths samples contain dunite of 11.6 %, wehrlite of 6.0 %, green clinopyroxenite of 45.4 %, green olivine-clinopyroxenite of 31.2 %, websterite of 0.1 %, black clinopyroxenite of 1.4 %, black olivine-clinopyroxenite of 0.03 %, granulite of 2.5 % and crustal materials of 1.7 %, where the ratio is percentage of each rock volume.
Kobayashi and Arai (1981) and Arai et al. (2005) classified ultramafic xenoliths into Group I and Group II. According to their classification, dunite, wehrlite, green clinopyroxenite, and green olivine-clinopyroxenite are classified into Group I xenoliths, and websterite, black clinopyroxenite and black olivine-clinopyroxenite into Group II. The total number of xenoliths belonging to Group I attains 94.2% of the total number of samples, and that of Group II is 4.2 %.
It is noted that lherzolite and harzburgite xenoliths were not recognized in the present study. The rock species and their abundance ratio of the xenoliths from the Yobuko area are similar to those from the Takashima, and are different to those from Kurose. The harzburgite and lherzolite in the Kurose are present, and the ratios of Group I and Group II are different from that of the Yobuko and the Takashima xenoliths.
The collected xenoliths samples contain dunite of 11.6 %, wehrlite of 6.0 %, green clinopyroxenite of 45.4 %, green olivine-clinopyroxenite of 31.2 %, websterite of 0.1 %, black clinopyroxenite of 1.4 %, black olivine-clinopyroxenite of 0.03 %, granulite of 2.5 % and crustal materials of 1.7 %, where the ratio is percentage of each rock volume.
Kobayashi and Arai (1981) and Arai et al. (2005) classified ultramafic xenoliths into Group I and Group II. According to their classification, dunite, wehrlite, green clinopyroxenite, and green olivine-clinopyroxenite are classified into Group I xenoliths, and websterite, black clinopyroxenite and black olivine-clinopyroxenite into Group II. The total number of xenoliths belonging to Group I attains 94.2% of the total number of samples, and that of Group II is 4.2 %.
It is noted that lherzolite and harzburgite xenoliths were not recognized in the present study. The rock species and their abundance ratio of the xenoliths from the Yobuko area are similar to those from the Takashima, and are different to those from Kurose. The harzburgite and lherzolite in the Kurose are present, and the ratios of Group I and Group II are different from that of the Yobuko and the Takashima xenoliths.