Geology and Petrology of Musa volcano, east Hokkaido.
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Abstract:
Musa volcano is situated at the central part of the Akan-Shiretoko volcanic chain, which belongs to the Kurile arc, eastern Hokkaido. In this region, Pliocene subaqueous volcanism (Yunosawa, 574m highland, and 626m-peak volcanoes) has changed to terrestrial one (Musa volcano) in early Pleistocene. Musa volcano is composed of a cluster of several stratovolcanoes and lava domes, and is topographically divided into two stages, older and younger. K-Ar age of the andesite from the younger stage has been obtained to be 0.48 ± 0.19 Ma. The eruptive rocks of Musa volcano ranges from basaltic andesite to dacite, and are defined as low-K series of Gill (1981). K2O content of the rocks increases from the volcanic front (Musa and Mashu volcanoes) to the back arc side (Shari, Shiretoko-Iwo volcanoes). The zonal distribution of lava chemistry (eg. K2O) in the southern part of the Kurile arc transverses the echelon arrangement of the volcanoes.Keywords:
Stratovolcano
Dacite
Lava dome
Basaltic andesite
Stratovolcano
Dacite
Phreatomagmatic eruption
Caldera
Basaltic andesite
Peléan eruption
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Dacite
Basaltic andesite
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We found high-Mg andesite (56.5 wt.% SiO2 and 7.2 wt.% MgO) from Mikasayama in Wassamu town, northern Hokkaido. Its K-Ar age is 11.1±0.8 Ma. The high-Mg andesite is characterized by co-existence of Fo-rich olivine (Fo90-85) and An-poor plagioclase (An64-38) phenocrysts. The mineralogical evidence suggests that the high-Mg andesite from Mikasayama was produced by mixing of primitive basalt magma, containing Mg-rich olivine and clinopyroxene phenocrysts, and hornblende dacite magma.
Phenocryst
Dacite
Basaltic andesite
Igneous differentiation
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Dacite
Basaltic andesite
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Mount Ijo is a Tertiarry vocano located in Kulonprogo, Yogyakarta Province. Andesite and dacite are the two volcanic rock units in Mount Ijo and around Kulonprogo. Dacite intruded andesite unit in Middle Miocene period. The two volcanic rock units are tried to be correlated based on geochemistry perspective. XRF were applied on major oxides measurements of selected eight samples while ICP-MS on trace and rare earth elements. Major oxides data of volcanic rocks arround Kulonprogo from previous studies are selected for additional data.The studied rocks are classified as basalt, basaltic andesite, andesite, and dacite based on their geochemistry contents. The studied samples show high degree of correlation in the Harker's Diagrams. Olivine and pyroxene fractionation together with ilmenite oxidation are most probably took place along magma differentiation. Alike patterns were also shown both in extended REE and REE spider diagrams. The comagmatic andesite and dacite is evidenced more by constant Rb/Sr ratio escalation through differentiation. Keyword: andesite, dacite, geochemistry, magma differentiation, Kulonprogo
Dacite
Basaltic andesite
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Dacite
Basaltic andesite
Igneous differentiation
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The Quaternary Zao volcano is situated on the Tohoku Backbone Ranges, Northeast Japan. It is known that activity of the volcano started about 1 Ma and continues to the present. The volcanic history of the Zao volcano can be divided into four stages as follows. Stage 1: A relatively small-scale volcano was formed. It is composed predominantly of pyroclastic materials of basalt and basaltic andesite. Stage 2: A stratovolcano was constructed by lavas and pyroclastic materials of andesite and dacite. The stage 2 is further subdivided into two substages, 2 a and 2 b. Stage 3: Lavas and pyroclastic materials from two vents situated near the summit widely distributed around the flank of the volcano. Rocks consist of basaltic andesite and andesite with a small amount of basalt. Stage 4: After formation of caldera, Goshikidake pyroclastic cone was formed in the caldera. The eruptive products comprise pyroclastic materials and lavas of basaltic andesite. The rocks of stage 1 belong to low-K series, and all the others to medium-K series. The medium-K rocks from different stages show contrasting trends; the rocks of stage 3 have slightly higher K 2O than those of stage 2 and stage 4 at the same SiO2 content. The basalt of stage 3 is medium-K and a contrast to the low-K basalts of stage 1.
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Dacite
Basaltic andesite
Igneous differentiation
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Musa volcano is situated at the central part of the Akan-Shiretoko volcanic chain, which belongs to the Kurile arc, eastern Hokkaido. In this region, Pliocene subaqueous volcanism (Yunosawa, 574m highland, and 626m-peak volcanoes) has changed to terrestrial one (Musa volcano) in early Pleistocene. Musa volcano is composed of a cluster of several stratovolcanoes and lava domes, and is topographically divided into two stages, older and younger. K-Ar age of the andesite from the younger stage has been obtained to be 0.48 ± 0.19 Ma. The eruptive rocks of Musa volcano ranges from basaltic andesite to dacite, and are defined as low-K series of Gill (1981). K2O content of the rocks increases from the volcanic front (Musa and Mashu volcanoes) to the back arc side (Shari, Shiretoko-Iwo volcanoes). The zonal distribution of lava chemistry (eg. K2O) in the southern part of the Kurile arc transverses the echelon arrangement of the volcanoes.
Stratovolcano
Dacite
Lava dome
Basaltic andesite
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Stratovolcano
Dacite
Lava dome
Phreatic eruption
Dome (geology)
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