Petrologic characteristics of early part of the Okama-Goshikidake activity of the Zaovolcano.
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Iizuna volcano (1871m) is formed at the southern end of the Myoko volcanoes which are situated in the northern part of the Fossa Magna. It is a Quaternary stratovolcano built on an anticlinal axis of basal Neogene strata, and has a horseshoe caldera with 2.5×2.0km in diameter at its summit. The volcanic cone is considerably dissected in contrast to the Myoko and Kurohime volcanoes. At the western to northern midslope of the cone, the five domes of Kenashiyama, Nakanomine, Takadekki, Tengudake, and 1340 m-ridge are arranged in NE-SW direction (Fig. 1).The growth-history of the Iizuna volcano may be divided broadly into the Ist and IInd stages, and the latter may be subdivided into the stratovolcano, caldera, and lava dome stages (Table 1). The eruptives from this volcano are full of variety such as lavas, pyroclastic (scoria, pumice, lapilli, and others) falls, pyroclastic flows, and volcanic mud flows. The rocks consist of basalt, pyroxene andesite, and hornblende andesite (Fig. 2). Augite-hypersthene andesite is predominant in volume.During the activity of the IInd stage, the mode of eruption and rock nature generally tend to change as follows, respectively: mode of eruption; eruption of scoria fall→alternated eruption of lava flows and pyroclastics→eruption of pyroclastic flows and falls, and viscous lave flows: rock nature; basalt→pyroxene andesite→horhblende andesite. The activity of this volcano began at the middle Pleistocene, and had already closed at least 32, 000 years ago.
Stratovolcano
Lapilli
Scoria
Lava dome
Basaltic andesite
Caldera
Peléan eruption
Phreatomagmatic eruption
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1969)
Tara-dake volcano is located in Omura Peninsula, Northwestern Kyushu. This volcano forms the western end of Daisen Volcanic Zone. The basement of this volcano is consisted of early Tertiary sediments and Pliocene volcanics. The volcanic activity of Tara-dake can be devided into four stages. In the first stage, this volcano extruded alkali basalt flows principally with a little of calc-alkali andesite flows. The second stage is represented by numerous andesitic pyroclastic rocks, which directly cover the extrusives of the first stage. Most of the pyroclastic rocks are fit for the pyroclastic flow of the intermediate type (Armakai, 1957). They were formed by several eruptions of many volcanoes, constructing Tara-dake volcano. After this stage, andesitic lava flows were erupted and lava domes were formed finally. In reference to the genesis of calc-alkali rocks, it is the important fact that the alkali basalts and clac-alkali andesites were erupted successively. The successive eruption of calc-alkali rocks and tholeiite (or high-alumina basalt) is known in various volcanoes of Japan. But similar relation between alkali and calc-alkali rocks has not been found out up to this time. In this area, both series of rocks include many xenoliths and xenocrysts, and both were comparatively affected the contaimination effect. So the Tara-dake andesite might be derived from the alkali basalt which assimilated the crustal material.
Alkali basalt
Basaltic andesite
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Andesites
Pumice
Lava dome
Stratovolcano
Chronology
Volcanic arc
Volcanic hazards
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Lamongan volcano is one of the unique volcanoes in the Sunda Volcano. This volcano has side eruption centers or on the slopes of the volcano. The morphology of parasitic eruptions in this volcanoes complex includes maars and boccas. There are about 64 parasitic eruption centers consisting of 37 volcanic cones (bocca) and 27 ranu (maar).
The purpose of this research is to study the characteristics of lithology and petrogenesis of this volcano complex, especially in Ranu Pakis and surrounding areas. The analytical method used is to do geological mapping and petrographic analysis.
The lithology found in this research area consists of magmatic and phreatomagmatic eruption deposits. Genetically this lithology includes pyroclastic flow, pyroclastic fall (scoria fall and phreatomagmatic scoria fall/accretionary lapili), tuff (phreatic) and basaltic lava. In some pyroclastic deposits, especially in maar there are fragments of accretionary lapilli, while in bocca there are basaltic lavas. Other fragments present in pyroclastic deposits are basalt scoria blocks and bombs embedded in the groundmass of volcanic ash. The results of petrographic analysis indicate that the volcanic rocks in the study area are calc alkaline affinity consisting of pyroxene andesite, basalt and pyroxene basalt lava. The pyroxene basalt lava is composed by plagioclase, clinopyroxene and little olivine embedded in the volcanic glass. Lavas are structured scoria and textured porphyritic, intersertal, trachytic, aphyric and pilotaxitic. Trachytic texture is found in the basalt fragments of pyroxene from the pyroclastic fall deposits in Ranu Pakis and Ranu Wurung. While pyroxene andesite lavas composed by plagioclase, clinopyroxene embedded in the volcanic glass. Lavas are structured scoria and textured porphyritic, intergranular, pilotaxitic and aphyric.
Phreatomagmatic eruption
Cinder cone
Pyroclastic fall
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Caldera
Stratovolcano
Scoria
Andesites
Cinder cone
Silicic
Dacite
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The Jinlongdingzi active volcano erupted before 1600a,and it is the latest basaltic explosive volcano at Longgang Volcano.Its volcanic products include the Jinlongdingzi Volcanic cone(elevation 999.4m),the lava flow and the widely-spread volcanic pyroclastic sheet(sihai Pyroclastic Sheet),Jinlongdingzi volcanic rocks are trachybasalts with very similar REE patterns and incompatible element patterns,and their 87Sr/86Sr and 143Nd/144Nd ratios range from 0.704846 ot 0.704921 and from 0.512619 to 0.512646,respectively.It is revealed that the trachybasalt has the character of primary magma derived directly from mantle sources with very little evolution and crust contamination during its ascending.The younger mantle xenoliths demonstrate that the mantle source of the Jinlongdingzi Volcao is hydrous,with relatively low temperature.
Lava dome
Peléan eruption
Xenolith
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1974)
Kayo-dake volcano is located in Akita Prefecture and is one of the volcanoes of Nasu Volcanic Zone. The main stage of volcanic activity was in the Early Quaternary. The volcano consists of lavas and a small amount of pyroclastic rocks. They are basalt, mafic andesite and andesite which belong to the tholeiite series and andesite of the calc-alkali rock, series. The rocks of the tholeiite series surpass those of the calc-alkali rock series in quantity. In the beginning of volcanic activity, basalt and mafic andesite of the tholeiite series were effused, and then, andesite belonging to the same rock series was erupted. After an intermission of activity, andesite of the calc-alkali rock series forming parasitic volcanoes, lava flows from a central crater, and a central cone, was effused. It may be a distinctive feature of this volcano that a comparatively large amount of andesite of the tholeiite series is present.
Basaltic andesite
Alkali basalt
Dacite
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Abstract A buried, old volcanic body (pre‐Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre‐Komitake Volcano is characterized by hornblende‐bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine‐bearing basaltic rocks of Fuji Volcano. K‐Ar age determinations and geological analysis of drilling cores suggest that the pre‐Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre‐Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long‐term eruption rate of about 3 km 3 /ka or more for Fuji Volcano is much higher than that estimated for pre‐Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO 2 , differs from that within pre‐Komitake and other volcanoes in the northern Izu‐Bonin arc, where incompatible elements increase with increasing SiO 2 . These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven.
Dacite
Phreatic eruption
Stratovolcano
Lava dome
Shield volcano
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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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Pyroclastic fall
Phreatomagmatic eruption
Peléan eruption
Caldera
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