K–Ar ages of the Akan‐Shiretoko volcanic chain lying oblique to the Kurile trench: Implications for tectonic control of volcanism
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Abstract The Akan‐Shiretoko volcanic chain, situated in the Southwestern Kurile arc, consists mainly of nine subaerial andesitic stratovolcanoes and three calderas. The chain extends in a SW–NE direction for 200 km, situated oblique to the Kurile trench at an angle of 25 degrees. Thirty‐seven new K–Ar ages, plus previous data, suggest that volcanic activity along the Akan‐Shiretoko volcanic chain began at ca 4 Ma at Akan, at the southwestern end of the chain, and systematically progressed northeastward, resulting in the southwest‐northeast‐trending volcanic chain. This spatial and temporal distribution of volcanoes can be explained by anticline development advancing northeastward from the Akan area, accompanied by magma rising through northeast‐trending fractures that developed along the anticlinal axis. The northeastward development of the anticline caused uplifting of the Akan‐Shiretoko area and changed the area from submarine to subaerial conditions. Anticline formation was likely due to deformation of the southwestern Kurile arc, with southwestward migration of the Kurile forearc sliver caused by oblique subduction of the Pacific plate. The echelon topographic arrangement of the Shiretoko, Kunashiri, Etorofu and Urup was formed at ca 1 Ma.Keywords:
Stratovolcano
Caldera
Anticline
Forearc
Caldera
Volcanology
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Caldera
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Large calderas, or supervolcanoes, are sites of the most catastrophic and hazardous events on Earth, yet the temporal details of post-supereruption activity, or resurgence, remain largely unknown, limiting our ability to understand how supervolcanoes work and address their hazards. Toba Caldera, Indonesia, caused the greatest volcanic catastrophe of the last 100 kyr, climactically erupting ∼74 ka. Since the supereruption, Toba has been in a state of resurgence but its magmatic and uplift history has remained unclear. Here we reveal that new 14C, zircon U-Th crystallization and (U-Th)/He ages show resurgence commenced at 69.7±4.5 ka and continued until at least ∼2.7 ka, progressing westward across the caldera, as reflected by post-caldera effusive lava eruptions and uplifted lake sediment. The major stratovolcano north of Toba, Sinabung, shows strong geochemical kinship with Toba, and zircons from recent eruption products suggest Toba's climactic magma reservoir extends beneath Sinabung and is being tapped during eruptions.
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The Nasu volcano group is composed of six volcanic edifices, Kasshiasahidake, Sanbon-yaridake, Asahidake, Minamigassan, Futamatayama, and Chausudake, located in the volcanic front of the Northeast Japan arc. Kasshiasahidake (ca. 0.54-0.42 Ma), Sanbon-yaridake (ca. 0.36-0.27 Ma), Minamigassan (ca. 0.21-0.03 Ma) have similar geological sequences. Alternation of thin basaltic andesite lava flows and associated pyroclastics developed in the lower part, whereas thick andesitic or dacitic lava flows and minor pyroclastic flows developed in the upper part. Between these two stages, caldera collapse sometimes occurred. On the other hand, Asahidake (ca. 0.21-0.06 Ma), Futamatayama (ca. 0.14 Ma), and Chausudake(ca. 0.04-0 Ma) are composed of andesitic lavas, lava domes, and pyroclastic flows, lacking thin basaltic andesite sequences. From evolutionary historical point of view, Kasshiasahidake, Sanbon-yaridake, and Minamigassan (including Asahidake and Chausudake edifices) edifices construct individual stratovolcanoes, which have similar evolutionary histories. Futamatayama is distinct from these. Volume and eruption duration of the three stratovolcanoes are as follows; ca. 200 k.y., 16.2 km3 for Kasshiasahidake, ca. 150 k.y., 7.2 km3 for Sanbon-yaridake, ca. 200 k.y., 17.8 km3 for Minamigassan (including Asahidake and Chausudake). These volumes and eruption rates are less than those of large stratovolcanoes (Akagi, Haruna, Hakone volcanoes etc.) in near the triple junction of plate boundary, but are comparable to those of small stratovolcanoes (Quaternary volcanoes in Shin-etsu Highland).
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A field-based study used geologic mapping and a ground-based magnetic survey to investigate the exhumed central intrusive complex (CIC) of Summer Coon stratovolcano in Colorado. The CIC comprises a group of diorite to granodiorite stocks and sub-vertical domains of conduit-filling breccia hosted within basaltic-andesite breccia associated with cone building. The stocks serve as the focal points for 53 basaltic-andesite (mafic) and 36 andesite to rhyolite (evolved) radial dikes mapped within the CIC. The evolved dikes with outcrop lengths (strike length) of <650 m are confined to the central areas of the CIC, cut through the stocks, and have steeply plunging terminal segments. In contrast, most evolved dikes with outcrop lengths >1600 m are excluded from the central areas of the CIC, do not cut through the stocks, and have terminal segments that plunge shallowly toward their focus. Assuming the dikes are blade-shaped and that they originated directly below the CIC, the propagation direction of the evolved dikes was estimated using the plunge angles, spatial distribution, and dike outcrop lengths. The relatively long dikes may have ascended toward the level of exposure along inclined paths. These dikes remained exclusively within the basaltic-andesite breccia and, probably due to the higher relative stiffness of the stocks, were unable to propagate through the stocks as they ascended. Upon approaching the level of exposure, the same dikes encountered a stress barrier likely generated by the gravitational load of the edifice. This barrier altered the dike propagation paths from inclined to sub-horizontal, significantly increasing their outcrop lengths. In contrast, the dikes with short outcrop lengths ascended along primarily sub-vertical paths, intersecting the level of exposure within the central portions of the CIC. To propagate sub-vertically through both the relatively stiff stocks and a potential stress barrier, the magma overpressures within the shorter dikes may have been higher relative to the longer sub-horizontally propagating dikes. It is probable that at active volcanoes, only dikes with sufficiently high overpressures can ascend through the central intrusive complex of mature stratovolcanoes to feed eruptions near the summit. Perhaps more frequently, stress barriers and existing intrusions stall or deflect dikes with lower relative overpressures toward the slopes of the volcano where they may feed flank eruptions.
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Breccia
Basaltic andesite
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Dacite
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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.
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Basaltic andesite
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