Reconstruction of the structure of Ordovician-Devonian arc system and its evolution processes: Hayachine - Miyamori ophiolite and Motai high-pressure metamorphic rocks in Iwate Prefecture

一仁, 小沢; 寛和, 前川; 明, 石渡

doi:10.5575/geosoc.2013.0025

Cited by 6 publications

(21 citation statements)

References 46 publications

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“…), which were either unaffected by or weakly suffered from contact metamorphism of Cretaceous granite bodies, are mostly lherzolite with abundant primary clinopyroxene and Al‐rich spinel (Ozawa ; Ozawa et al . ; Fig. and Table ).…”

Section: Supplementary New Datamentioning

confidence: 85%

“…This is particularly the case in the Hayachine Complex, the main part of which was extensively overprinted by contact metamorphism of the Cretaceous Tono granite (Figs ; Asai ; Fujimaki & Yomogida , b; Ozawa et al . ). Peridotites distributed in the western part of the Hayachine Complex were either unaffected by or weakly suffered from contact metamorphism of the Cretaceous granite bodies and are mostly lherzolite (Ozawa , ).…”

Section: Discussionmentioning

confidence: 97%

“…It is thus concluded that the peridotite from the Hayachine Complex is clinopyroxene‐bearing and classified as lherzolite or clinopyroxene‐bearing harzburgite, being consistent with the abundance of clinopyroxene pseudomorphs as pointed out by Ozawa et al . ().…”

Section: Discussionmentioning

confidence: 97%

“…This diagram is modified age histogram after O zawa et al . (). Data sources for (a) are HM ophiolite hornblende K – A r ages from O zawa et al .…”

Section: A Review On the Hayachine–miyamori Ophiolite And The Kitakammentioning

confidence: 97%

“…The lithologic variation is systematic; it varies from hornblende gabbro to cortlandite through porphyritic plagioclase‐bearing clinopyroxene hornblendite/hornblende clinopyroxenite and olivine clinopyroxene hornblendite (Ozawa ; Ozawa et al . ).…”

Section: A Review On the Hayachine–miyamori Ophiolite And The Kitakammentioning

confidence: 97%

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Evolution processes of Ordovician–Devonian arc system in the South‐Kitakami Massif and its relevance to the Ordovician ophiolite pulse

et al. 2015

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The South Kitakami Massif is one of the oldest geological domains in Japan having Silurian strata with acidic pyroclastic rocks and Ordovician–Silurian granodiorite–tonalite basement, suggesting that it was matured enough to develop acidic volcanisms in the Silurian period. On the northern and western margin of the South Kitakami Massif, an Ordovician arc ophiolite (Hayachine–Miyamori Ophiolite) and high‐pressure and low‐temperature metamorphic rocks (Motai metamorphic rocks) exhumed sometime in the Ordovician–Devonian periods are distributed. Chronological, geological, and petrochemical studies on the Hayachine–Miyamori Ophiolite, Motai metamorphic rocks, and other early Paleozoic geological units of the South Kitakami Massif are reviewed for reconstruction of the South Kitakami arc system during Ordovician to Devonian times with supplementary new data. The reconstruction suggests a change in the convergence polarity from eastward‐ to westward‐dipping subduction sometime before the Late Devonian period. The Hayachine–Miyamori Ophiolite was developed above the eastward‐dipping subduction through three distinctive stages. Two separate stages of overriding plate extension inducing decompressional melting with minor involvement of slab‐derived fluid occurred before and after a stage of melting under strong influence of slab‐derived fluids. The first overriding plate extension took place in the back‐arc side forming a back‐arc basin. The second one took place immediately before the ophiolite exhumation and near the fore‐arc region. We postulate that the second decompressional melting was triggered by slab breakoff, which was preceded by slab rollback inducing trench‐parallel wedge mantle flow and non‐steady fluid and heat transport leaving exceptionally hydrous residual mantle. The formation history of the Hayachine–Miyamori Ophiolite implies that weaker plate coupling may provide preferential conditions for exhumation of very hydrous mantle. Very hydrous peridotites involved in arc magmatism have not yet been discovered except for in the Cambrian–Ordovician periods, suggesting its implications for global geodynamics, such as the thermal state and water circulation in the mantle.

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Section: Supplementary New Datamentioning

confidence: 85%

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 97%

“…This diagram is modified age histogram after O zawa et al . (). Data sources for (a) are HM ophiolite hornblende K – A r ages from O zawa et al .…”

Section: A Review On the Hayachine–miyamori Ophiolite And The Kitakammentioning

confidence: 97%

Section: A Review On the Hayachine–miyamori Ophiolite And The Kitakammentioning

confidence: 97%

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Evolution processes of Ordovician–Devonian arc system in the South‐Kitakami Massif and its relevance to the Ordovician ophiolite pulse

et al. 2015

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Ordovician backarc‐basin metadolerite and metabasalt of the South Kitakami Terrane, Northeast Japan

Uchino

Kawamura

2016

Island Arc

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Basement rocks that occur along the northern margin of the South Kitakami Terrane in Japan consist of Ordovician ultramafic rocks (Hayachine ultramafic complex), gneissose amphibolite (Kuromoriyama amphibolite), and mafic rocks (Kagura igneous rocks, KIR). The KIR are composed of metagabbro, metadolerite, metabasalt, and minor felsic-intermediate dikes. Although the KIR contain green hornblende due to metamorphism of greenschist to epidote-amphibolite facies, they rarely retain primary brown hornblende. Approximately 30% of the metabasalt shows porphyritic textures, with phenocrysts of saussuritized plagioclase and/or altered mafic minerals. The geochemistry of the common metadolerite and metabasalt of the KIR shows a tholeiite trend, a low TiO 2 content, and high Th/Nb and Ti/V ratios. The KIR are therefore indicative of a suprasubduction zone tectonic setting, which implies a backarc origin (as also indicated by discrimination diagrams). Trace element patterns of the KIR resemble those of the backarc-basin basalt of the Japan and Yamato basins in the Japan Sea. We propose that the KIR formed during backarc spreading from the Ordovician to Early Silurian. This view is supported by the geochemical data, the tectonic setting of the Hayachine ultramafic rocks, and the provenance of clastics within Silurian sedimentary rocks.

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Complex factors contribute to the chemical composition of clastic sediments traveling from rivers to the ocean along island arcs: A case study of the Otsuchi area, Northeast Japan

Sugiura,

Sawada,

Iizuka

et al. 2023

Island Arc

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The chemical composition of coastal sediments and river sediments is influenced by the geological constitution of provenance and fractionation of clastic particles during sedimentary processes. The intricate nature of the geology in active subduction zones has complicated the comprehension of detrital sediments. More geochemical case studies in such areas are necessary to enhance the understanding of the coastal detrital sediments. This study presents the results of a geochemical and particle size analysis of sediment samples from the Sanriku coastal area of Northeast Japan, including inside and outside of Otsuchi Bay and the three rivers that flow into the bay. Otsuchi Bay area is known to have been severely affected by the 2011 off the Pacific coast of the Tohoku Earthquake and tsunami, and tsunami deposits on its seabed have been reported. The present geochemical analysis indicates that the sediments along those three rivers are well explained by the mixing of rocks occurring in their respective provenance. The chemical composition and particle size distribution of the sediments within Otsuchi Bay suggested the removal of coarse‐grained quartz. They increased the abundance of fine‐grained mafic minerals from Unosumai River having the largest catchment area among the three rivers. During shell debris in the seabed sediment outside of the bay made interpretation of the results was difficult; the sediments collected closer to the bay mouth contained more coarse‐grained material with a composition closer to granitoid and sandstone in the provenance. In contrast, offshore sediments consisted of finer grains with a composition closer to mudstone. Notably, the sediments within Otsuchi Bay did not exhibit the characteristic compositional fractionation or particle size distribution associated with tsunami deposits. These findings underscore the importance of considering the geological diversity of provenances and the particle size distribution of minerals in understanding coastal sediments in subduction zones, including tsunami deposits.

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Reconstruction of the structure of Ordovician-Devonian arc system and its evolution processes: Hayachine - Miyamori ophiolite and Motai high-pressure metamorphic rocks in Iwate Prefecture

Cited by 6 publications

References 46 publications

Evolution processes of Ordovician–Devonian arc system in the South‐Kitakami Massif and its relevance to the Ordovician ophiolite pulse

Evolution processes of Ordovician–Devonian arc system in the South‐Kitakami Massif and its relevance to the Ordovician ophiolite pulse

Ordovician backarc‐basin metadolerite and metabasalt of the South Kitakami Terrane, Northeast Japan

Complex factors contribute to the chemical composition of clastic sediments traveling from rivers to the ocean along island arcs: A case study of the Otsuchi area, Northeast Japan

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