{"title":"专题社论“造山带、蛇绿岩和海洋:地球构造演化的快照”","authors":"Yasufumi Iryu, Tatsuki Tsujimori, Naoto Hirano, Yuji Ichiyama","doi":"10.1111/iar.12468","DOIUrl":null,"url":null,"abstract":"<p>Integrated studies of orogens, ophiolites, and oceans (OOO) provide a snapshot of Earth's dynamic evolution. As a key proxy of lithospheric plate underflow, the rocks in orogenic belts and oceans have been intensively studied from various scientific viewpoints and at different spatial–temporal scales. The rock record in OOO helps to better understand past plate-tectonic processes and thereby to interpret ongoing geodynamic processes in Earth's outer shell where we dwell. However, challenges remain with respect to obtaining a more comprehensive understanding of such processes through interdisciplinary exchange.</p><p>This thematic issue contains presentations given at the international symposium “Orogens, Ophiolites, and Oceans: A Snapshot of Earth's Tectonic Evolution” held in Sendai, Japan, in late February 2020. This thematic issue also honors Dr. Akira Ishiwatari for his important contribution to ophiolite studies. Dr. Ishiwatari played a pioneering and pivotal role in developing ophiolite studies in Japan based on field geology and petrology. The 2-day international symposium, miraculously held in person just before the coronavirus outbreak, focused on recent progress in petrochemical–tectonic studies of orogens, ophiolites, and oceans (oceanic crusts and oceanic deposits), especially in the vicinity of the Japanese Islands. Participants and presenters (including Dr. Ishiwatari) at the symposium were geoscience professionals and students in the areas of petrology, geochemistry, geochronology, and marine geology related to OOO (Figure 1). We trust that this thematic issue will serve as a worthy tribute to the research and contribution of Dr. Akira Ishiwatari.</p><p>We dedicate this thematic issue to Dr. Akira Ishiwatari for his important contribution to our understanding of ophiolites, especially the petrological classification of worldwide ophiolites and the geological features of Japanese ophiolites. His early studies in the late 1970s and early 1980s focused on the geology of the so-called “Yakuno Intrusive Rocks” in SW Japan, leading to the first recognized ophiolite sequence in Japan (Ishiwatari, <span>1978</span>). The “Yakuno Ophiolite” identified by Dr. Ishiwatari has been internationally recognized as an ophiolite with an unusually thick oceanic crust (Ishiwatari, <span>1985a</span>, <span>1985b</span>; Ishiwatari, <span>1991</span>). As a skilled field geologist with a strong background in petrology, Dr. Ishiwatari worked not only on the Yakuno Ophiolite but also on ophiolites in the French Alps (Ishiwatari, <span>1985c</span>) and Russian Far East (Ishiwatari et al., <span>2003</span>; Ishiwatari & Ichiyama, <span>2004</span>), as well as on plume-related accreted ocean-island basalts (Ichiyama et al., <span>2008</span>), and Miocene volcanic rocks formed during the opening of the Japan Sea (Ayalew & Ishiwatari, <span>2011</span>; Ishiwatari & Imasaka, <span>2002</span>). He also studied deep-sea igneous rocks as a modern ophiolite analog (Ishiwatari, <span>1992</span>; Ishiwatari et al., <span>2006</span>). Throughout his career, Dr. Ishiwatari made numerous cooperative academic exchanges with Chinese and Russian geoscientists (Figure 2). His international networking led to the success of the ophiolite session at the 29th IGC in Kyoto, Japan, in 1992, the key presentations in the session were collated in a book entitled “Circum-Pacific Ophiolites” (Ishiwatari et al., <span>1994</span>). His collaborative works on coesite-bearing ultrahigh-pressure metamorphic rocks in eastern China, blueschist–ophiolite associations in the Sikhote-Alin (Russian Far East), and the Japanese Hida Belt resulted in a novel proposal termed the “Yaeyama Promontory Hypothesis” (Ishiwatari & Tsujimori, <span>2003</span>).</p><p>Dr. Ishiwatari served as Editor-in-Chief of the journal <i>Island Arc</i> during 2004–2007 and as a co-chair of the Scientific Planning and Evaluation Panel of the Integrated Ocean Drilling Program during 2008–2010. He also served as the president of the Geological Society of Japan from 2012 to 2014. He increased his profile in Japan as a Commissioner of the Nuclear Regulation Authority, Japan, from 2014 to the present.</p><p>This thematic issue contains 11 papers on studies of OOO from different perspectives. The papers focus on past geodynamic processes, as recorded in on-land and submarine rocks at different scales from mineral-equilibrium to plate-tectonic levels.</p><p>The two papers by Hiroi et al. (<span>2020</span>) and Harada et al. (<span>2021</span>) present new observations concerning middle-crustal metamorphic processes in or near zones of continent–continent convergence. Hiroi et al. (<span>2020</span>) report felsite inclusions within granulite-facies garnets from continental-collision orogens (Sri Lanka, East Antarctica, Canada, and India). Those authors focus on euhedral quartz phenocrysts in the felsite inclusions. Zoning of cathodoluminescence (CL) emission attributed to trace amounts of titanium indicates crystal growth in supercooled felsic melt. The CL zoning of quartz phenocrysts in felsite inclusions implies that the cooling rates of studied granulites from collision orogens are one to two orders of magnitude higher than presumed to date. Harada et al. (<span>2021</span>) document a C<span></span>O<span></span>Sr isotope geochemical investigation into upper-amphibolite-facies marble and carbonate–silicate rock from the Hida Belt, which was once part of the crustal basement of the East Asian continental margin. The calcite C<span></span>O isotopic compositions show wide variation in δ<sup>13</sup>C [VPDB] and δ<sup>18</sup>O [VSMOW] values (from −4.4‰ to +4.2‰ and from +1.6‰ to +20.8 ‰, respectively). In particular, the carbonate–silicate rock shows low δ<sup>13</sup>C values (from −4.4‰ to −2.9‰). Those authors conclude that the low δ<sup>13</sup>C values can be explained by decarbonation (CO<sub>2</sub>-releasing) reactions.</p><p>Metamorphic processes at convergent plate margins are also discussed in the following two papers. Nishiyama et al. (<span>2021</span>) investigate gneiss-hosted metaperidotite bodies with spinifex-like texture from the Higo Metamorphic Rocks (HMR), Kyushu, Japan, and propose a new petrogenetic mechanism. According to their new results, the metaperidotites might have formed by high-pressure dehydration of antigorite-dominant serpentinite, possibly in a relatively deep root of mantle wedge under metamorphic conditions of <i>P</i> = ~1.6 GPa and <i>T</i> = ~740–750°C. The exotic occurrences of small bodies of high-pressure metaperidotites within the medium-pressure HMR gneisses suggest a tectonic juxtaposition of these two contrasting lithologies at a convergent plate margin. Fukushima et al. (<span>2021</span>) present a study on trace-element zoning patterns in prograde-zoned garnets in Group-C, low-temperature eclogites from Syros (Greece) and South Motagua Mélange (Guatemala). Analysis of Y + HREE profiles of the garnet porphyroblasts enables to discuss porphyroblast growth rates and cation diffusivities in the eclogitic matrices. Those authors also modify a previous diffusion-limited rare-earth element uptake model. Their new garnet porphyroblast growth model should contribute to unraveling cation-diffusion processes and thus lead to a better understanding of the geochemical kinetics in subduction zones.</p><p>Two pieces of research in NE Japan by Uchino (<span>2021</span>) and Okamoto et al. (<span>2021</span>) provide new insights into the tectonic evolution of Japanese Paleozoic oceanic plate convergence. Uchino (<span>2021</span>) use detrital zircon U–Pb ages to newly recognize an Early Triassic accretionary complex in the Nedamo Belt. This recognition is used as a basis for a new subdivision of the Nedamo Belt, namely, the Early Triassic Takinosawa and early Carboniferous Tsunatori units. The study also establishes a northeastward-younging trend of accretionary-orogen growth in the Kitakami Mountains. The detrital age spectra suggest that the Takinosawa Unit is comparable to Early Triassic fragments in the Kurosegawa Belt in Shikoku, which supports a pre-Jurassic geotectonic correlation between SW and NE Japan. Okamoto et al. (<span>2021</span>) investigate the petrological and geochemical natures of the early Paleozoic Motai serpentinites in the South Kitakami Mountains. The study finds that the geochemical characteristics of primary mantle minerals and secondary hydrous minerals are similar to those of serpentinites from the Mariana forearc. Those authors conclude that the protoliths of the Motai serpentinites were depleted-mantle peridotites that developed beneath the forearc region of a subduction zone located in a convergent margin of the early Paleozoic proto-East Asian continent.</p><p>The remaining papers focus on ophiolites and oceans, including modern sea floors and seamounts. The papers by Tamura et al. (<span>2022</span>) and Machida et al. (<span>2021</span>) deal with the crustal structure and surface environment of the Pacific Plate. Tamura et al. (<span>2022</span>) present an overview of the relationship between crustal thickness and seismic survey Moho reflection structure in a broad area of the Pacific Plate (the western–northwestern part and the East Pacific Rise) and examine several crust formation processes, as inferred from geochemical variation in magmas at mid-oceanic ridges. Those authors conclude that a relatively thick oceanic crust with thick dunite layers is plausibly caused by hydrous melting below mid-oceanic ridges, implying that seawater penetrates to the mantle along faults that develop as the crust forms. Machida et al. (<span>2021</span>) investigate ferromanganese nodules from the western North Pacific seafloor around Minamitorishima Island. The lack of some growth layers in ferromanganese nodules is interpreted as being due to a delayed supply of the nucleus material of nodules or a growth hiatus of Fe–Mn layer(s); in addition, missing sublayers in the ferromanganese nodules are inferred to regulate nodule size. This study demonstrates that multidimensional compositional mapping of ferromanganese nodules is a highly effective approach for reconstructing the submarine environment.</p><p>The three papers by Miyata et al. (<span>2020</span>), Aftabuzzaman et al. (<span>2021</span>), and Hirano et al. (<span>2021</span>) address the topic of seamounts. Miyata et al. (<span>2020</span>) examine shallow-water carbonates collected from the eastern slope of Hahajima Seamount, located at the junction between the Izu–Bonin and Mariana forearc slopes. Despite numerous previous studies, the origin of the Hahajima Seamount remains uncertain. On the basis of sedimentological and chronological analyses of the Hahajima carbonates, which are dominated by floatstone with numerous mollusks, those authors report lithological similarities and similar Sr isotope ages (Cretaceous) of carbonates between the Hahajima Seamount and the Ogasawara Plateau located east of the former and on the opposite side of the Izu–Bonin Trench (Pacific Plate). This study indicates that shallow-water carbonates of the Hahajima Seamount were not deposited in situ but instead originated from the Ogasawara Plateau. Thus, the eastern section of this seamount is interpreted as an accretionary wedge. Aftabuzzaman et al. (<span>2021</span>) present sedimentological, geochemical, and chronological analyses on carbonate rock samples collected from the western slope of Minamitorishima (Marcus Island) and determine the history of this seamount as follows. After deposition of the Cretaceous shallow-water carbonates, including the mollusk-rich limestone, Minamitorishima was inundated, and its top was covered with a pelagic cap. Late Eocene–early Oligocene volcanism caused episodic uplift and returned the top of Minamitorishima to a shallow-water environment. After the early Oligocene phosphatization of the pelagic cap, coral reefs flourished on the top of this island. The reef limestone was dolomitized during the Tortonian–Messinian. Hirano et al. (<span>2021</span>) report an investigation into the basement basalts of the Minamitorishima volcanic edifice. Those authors report a Paleogene volcanic edifice with an ocean-island-basalt-like geochemical affinity. The Paleogene volcanic activity might have locally overprinted Early to mid-Cretaceous volcanic edifices, at least on the Ogasawara Plateau and the Minamitorishima volcanic edifice. The presence of Cretaceous reefal limestone reported by Aftabuzzaman et al. (<span>2021</span>) strongly supports this scenario. As reported by Miyata et al. (<span>2020</span>), such seamount-capping carbonates that were deposited on the Pacific Plate prior to its subduction can provide highly valuable records that allow comprehensive geological interpretations to be made of the Izu–Bonin–Mariana forearcs.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":null,"pages":null},"PeriodicalIF":1.0000,"publicationDate":"2022-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12468","citationCount":"0","resultStr":"{\"title\":\"Editorial for the thematic issue, “Orogens, ophiolites, and oceans: A snapshot of Earth's tectonic evolution”\",\"authors\":\"Yasufumi Iryu, Tatsuki Tsujimori, Naoto Hirano, Yuji Ichiyama\",\"doi\":\"10.1111/iar.12468\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>Integrated studies of orogens, ophiolites, and oceans (OOO) provide a snapshot of Earth's dynamic evolution. As a key proxy of lithospheric plate underflow, the rocks in orogenic belts and oceans have been intensively studied from various scientific viewpoints and at different spatial–temporal scales. The rock record in OOO helps to better understand past plate-tectonic processes and thereby to interpret ongoing geodynamic processes in Earth's outer shell where we dwell. However, challenges remain with respect to obtaining a more comprehensive understanding of such processes through interdisciplinary exchange.</p><p>This thematic issue contains presentations given at the international symposium “Orogens, Ophiolites, and Oceans: A Snapshot of Earth's Tectonic Evolution” held in Sendai, Japan, in late February 2020. This thematic issue also honors Dr. Akira Ishiwatari for his important contribution to ophiolite studies. Dr. Ishiwatari played a pioneering and pivotal role in developing ophiolite studies in Japan based on field geology and petrology. The 2-day international symposium, miraculously held in person just before the coronavirus outbreak, focused on recent progress in petrochemical–tectonic studies of orogens, ophiolites, and oceans (oceanic crusts and oceanic deposits), especially in the vicinity of the Japanese Islands. Participants and presenters (including Dr. Ishiwatari) at the symposium were geoscience professionals and students in the areas of petrology, geochemistry, geochronology, and marine geology related to OOO (Figure 1). We trust that this thematic issue will serve as a worthy tribute to the research and contribution of Dr. Akira Ishiwatari.</p><p>We dedicate this thematic issue to Dr. Akira Ishiwatari for his important contribution to our understanding of ophiolites, especially the petrological classification of worldwide ophiolites and the geological features of Japanese ophiolites. His early studies in the late 1970s and early 1980s focused on the geology of the so-called “Yakuno Intrusive Rocks” in SW Japan, leading to the first recognized ophiolite sequence in Japan (Ishiwatari, <span>1978</span>). The “Yakuno Ophiolite” identified by Dr. Ishiwatari has been internationally recognized as an ophiolite with an unusually thick oceanic crust (Ishiwatari, <span>1985a</span>, <span>1985b</span>; Ishiwatari, <span>1991</span>). As a skilled field geologist with a strong background in petrology, Dr. Ishiwatari worked not only on the Yakuno Ophiolite but also on ophiolites in the French Alps (Ishiwatari, <span>1985c</span>) and Russian Far East (Ishiwatari et al., <span>2003</span>; Ishiwatari & Ichiyama, <span>2004</span>), as well as on plume-related accreted ocean-island basalts (Ichiyama et al., <span>2008</span>), and Miocene volcanic rocks formed during the opening of the Japan Sea (Ayalew & Ishiwatari, <span>2011</span>; Ishiwatari & Imasaka, <span>2002</span>). He also studied deep-sea igneous rocks as a modern ophiolite analog (Ishiwatari, <span>1992</span>; Ishiwatari et al., <span>2006</span>). Throughout his career, Dr. Ishiwatari made numerous cooperative academic exchanges with Chinese and Russian geoscientists (Figure 2). His international networking led to the success of the ophiolite session at the 29th IGC in Kyoto, Japan, in 1992, the key presentations in the session were collated in a book entitled “Circum-Pacific Ophiolites” (Ishiwatari et al., <span>1994</span>). His collaborative works on coesite-bearing ultrahigh-pressure metamorphic rocks in eastern China, blueschist–ophiolite associations in the Sikhote-Alin (Russian Far East), and the Japanese Hida Belt resulted in a novel proposal termed the “Yaeyama Promontory Hypothesis” (Ishiwatari & Tsujimori, <span>2003</span>).</p><p>Dr. Ishiwatari served as Editor-in-Chief of the journal <i>Island Arc</i> during 2004–2007 and as a co-chair of the Scientific Planning and Evaluation Panel of the Integrated Ocean Drilling Program during 2008–2010. He also served as the president of the Geological Society of Japan from 2012 to 2014. He increased his profile in Japan as a Commissioner of the Nuclear Regulation Authority, Japan, from 2014 to the present.</p><p>This thematic issue contains 11 papers on studies of OOO from different perspectives. The papers focus on past geodynamic processes, as recorded in on-land and submarine rocks at different scales from mineral-equilibrium to plate-tectonic levels.</p><p>The two papers by Hiroi et al. (<span>2020</span>) and Harada et al. (<span>2021</span>) present new observations concerning middle-crustal metamorphic processes in or near zones of continent–continent convergence. Hiroi et al. (<span>2020</span>) report felsite inclusions within granulite-facies garnets from continental-collision orogens (Sri Lanka, East Antarctica, Canada, and India). Those authors focus on euhedral quartz phenocrysts in the felsite inclusions. Zoning of cathodoluminescence (CL) emission attributed to trace amounts of titanium indicates crystal growth in supercooled felsic melt. The CL zoning of quartz phenocrysts in felsite inclusions implies that the cooling rates of studied granulites from collision orogens are one to two orders of magnitude higher than presumed to date. Harada et al. (<span>2021</span>) document a C<span></span>O<span></span>Sr isotope geochemical investigation into upper-amphibolite-facies marble and carbonate–silicate rock from the Hida Belt, which was once part of the crustal basement of the East Asian continental margin. The calcite C<span></span>O isotopic compositions show wide variation in δ<sup>13</sup>C [VPDB] and δ<sup>18</sup>O [VSMOW] values (from −4.4‰ to +4.2‰ and from +1.6‰ to +20.8 ‰, respectively). In particular, the carbonate–silicate rock shows low δ<sup>13</sup>C values (from −4.4‰ to −2.9‰). Those authors conclude that the low δ<sup>13</sup>C values can be explained by decarbonation (CO<sub>2</sub>-releasing) reactions.</p><p>Metamorphic processes at convergent plate margins are also discussed in the following two papers. Nishiyama et al. (<span>2021</span>) investigate gneiss-hosted metaperidotite bodies with spinifex-like texture from the Higo Metamorphic Rocks (HMR), Kyushu, Japan, and propose a new petrogenetic mechanism. According to their new results, the metaperidotites might have formed by high-pressure dehydration of antigorite-dominant serpentinite, possibly in a relatively deep root of mantle wedge under metamorphic conditions of <i>P</i> = ~1.6 GPa and <i>T</i> = ~740–750°C. The exotic occurrences of small bodies of high-pressure metaperidotites within the medium-pressure HMR gneisses suggest a tectonic juxtaposition of these two contrasting lithologies at a convergent plate margin. Fukushima et al. (<span>2021</span>) present a study on trace-element zoning patterns in prograde-zoned garnets in Group-C, low-temperature eclogites from Syros (Greece) and South Motagua Mélange (Guatemala). Analysis of Y + HREE profiles of the garnet porphyroblasts enables to discuss porphyroblast growth rates and cation diffusivities in the eclogitic matrices. Those authors also modify a previous diffusion-limited rare-earth element uptake model. Their new garnet porphyroblast growth model should contribute to unraveling cation-diffusion processes and thus lead to a better understanding of the geochemical kinetics in subduction zones.</p><p>Two pieces of research in NE Japan by Uchino (<span>2021</span>) and Okamoto et al. (<span>2021</span>) provide new insights into the tectonic evolution of Japanese Paleozoic oceanic plate convergence. Uchino (<span>2021</span>) use detrital zircon U–Pb ages to newly recognize an Early Triassic accretionary complex in the Nedamo Belt. This recognition is used as a basis for a new subdivision of the Nedamo Belt, namely, the Early Triassic Takinosawa and early Carboniferous Tsunatori units. The study also establishes a northeastward-younging trend of accretionary-orogen growth in the Kitakami Mountains. The detrital age spectra suggest that the Takinosawa Unit is comparable to Early Triassic fragments in the Kurosegawa Belt in Shikoku, which supports a pre-Jurassic geotectonic correlation between SW and NE Japan. Okamoto et al. (<span>2021</span>) investigate the petrological and geochemical natures of the early Paleozoic Motai serpentinites in the South Kitakami Mountains. The study finds that the geochemical characteristics of primary mantle minerals and secondary hydrous minerals are similar to those of serpentinites from the Mariana forearc. Those authors conclude that the protoliths of the Motai serpentinites were depleted-mantle peridotites that developed beneath the forearc region of a subduction zone located in a convergent margin of the early Paleozoic proto-East Asian continent.</p><p>The remaining papers focus on ophiolites and oceans, including modern sea floors and seamounts. The papers by Tamura et al. (<span>2022</span>) and Machida et al. (<span>2021</span>) deal with the crustal structure and surface environment of the Pacific Plate. Tamura et al. (<span>2022</span>) present an overview of the relationship between crustal thickness and seismic survey Moho reflection structure in a broad area of the Pacific Plate (the western–northwestern part and the East Pacific Rise) and examine several crust formation processes, as inferred from geochemical variation in magmas at mid-oceanic ridges. Those authors conclude that a relatively thick oceanic crust with thick dunite layers is plausibly caused by hydrous melting below mid-oceanic ridges, implying that seawater penetrates to the mantle along faults that develop as the crust forms. Machida et al. (<span>2021</span>) investigate ferromanganese nodules from the western North Pacific seafloor around Minamitorishima Island. The lack of some growth layers in ferromanganese nodules is interpreted as being due to a delayed supply of the nucleus material of nodules or a growth hiatus of Fe–Mn layer(s); in addition, missing sublayers in the ferromanganese nodules are inferred to regulate nodule size. This study demonstrates that multidimensional compositional mapping of ferromanganese nodules is a highly effective approach for reconstructing the submarine environment.</p><p>The three papers by Miyata et al. (<span>2020</span>), Aftabuzzaman et al. (<span>2021</span>), and Hirano et al. (<span>2021</span>) address the topic of seamounts. Miyata et al. (<span>2020</span>) examine shallow-water carbonates collected from the eastern slope of Hahajima Seamount, located at the junction between the Izu–Bonin and Mariana forearc slopes. Despite numerous previous studies, the origin of the Hahajima Seamount remains uncertain. On the basis of sedimentological and chronological analyses of the Hahajima carbonates, which are dominated by floatstone with numerous mollusks, those authors report lithological similarities and similar Sr isotope ages (Cretaceous) of carbonates between the Hahajima Seamount and the Ogasawara Plateau located east of the former and on the opposite side of the Izu–Bonin Trench (Pacific Plate). This study indicates that shallow-water carbonates of the Hahajima Seamount were not deposited in situ but instead originated from the Ogasawara Plateau. Thus, the eastern section of this seamount is interpreted as an accretionary wedge. Aftabuzzaman et al. (<span>2021</span>) present sedimentological, geochemical, and chronological analyses on carbonate rock samples collected from the western slope of Minamitorishima (Marcus Island) and determine the history of this seamount as follows. After deposition of the Cretaceous shallow-water carbonates, including the mollusk-rich limestone, Minamitorishima was inundated, and its top was covered with a pelagic cap. Late Eocene–early Oligocene volcanism caused episodic uplift and returned the top of Minamitorishima to a shallow-water environment. After the early Oligocene phosphatization of the pelagic cap, coral reefs flourished on the top of this island. The reef limestone was dolomitized during the Tortonian–Messinian. Hirano et al. (<span>2021</span>) report an investigation into the basement basalts of the Minamitorishima volcanic edifice. Those authors report a Paleogene volcanic edifice with an ocean-island-basalt-like geochemical affinity. The Paleogene volcanic activity might have locally overprinted Early to mid-Cretaceous volcanic edifices, at least on the Ogasawara Plateau and the Minamitorishima volcanic edifice. The presence of Cretaceous reefal limestone reported by Aftabuzzaman et al. (<span>2021</span>) strongly supports this scenario. As reported by Miyata et al. (<span>2020</span>), such seamount-capping carbonates that were deposited on the Pacific Plate prior to its subduction can provide highly valuable records that allow comprehensive geological interpretations to be made of the Izu–Bonin–Mariana forearcs.</p>\",\"PeriodicalId\":14791,\"journal\":{\"name\":\"Island Arc\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":1.0000,\"publicationDate\":\"2022-11-04\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12468\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Island Arc\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1111/iar.12468\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"GEOSCIENCES, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Island Arc","FirstCategoryId":"89","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1111/iar.12468","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
摘要
造山带、蛇绿岩和海洋(OOO)的综合研究提供了地球动态演化的快照。造山带和海洋中的岩石作为岩石圈板块底流的重要代表,从不同的科学观点和不同的时空尺度上进行了深入的研究。OOO的岩石记录有助于更好地理解过去的板块构造过程,从而解释我们居住的地球外壳中正在进行的地球动力学过程。然而,在通过跨学科交流对这些过程获得更全面的了解方面仍然存在挑战。本期专题刊包含2020年2月下旬在日本仙台举行的“造山带、蛇绿岩和海洋:地球构造演化的快照”国际研讨会上发表的演讲。这期专题还表彰了石塔明博士对蛇绿岩研究的重要贡献。Ishiwatari博士在基于野外地质和岩石学的日本蛇绿岩研究中发挥了开创性和关键作用。这次为期两天的国际研讨会奇迹般地在冠状病毒爆发前亲自举行,重点讨论了造山带、蛇绿岩和海洋(海洋地壳和海洋沉积物)的石化构造研究的最新进展,特别是在日本列岛附近。研讨会的参与者和演讲者(包括Ishiwatari博士)都是与OOO相关的岩石学、地球化学、地质年代学和海洋地质学领域的地球科学专业人士和学生(图1)。我们相信这个专题问题将是对Ishiwatari博士的研究和贡献的值得致敬。我们将此专题特刊献给Ishiwatari博士,他对我们理解蛇绿岩,特别是世界蛇绿岩的岩石学分类和日本蛇绿岩的地质特征做出了重要贡献。他在20世纪70年代末和80年代初的早期研究集中在日本西南部所谓的“Yakuno侵入岩”的地质上,导致了日本第一个公认的蛇绿岩序列(Ishiwatari, 1978)。Ishiwatari博士鉴定的“Yakuno蛇绿岩”是国际公认的具有异常厚的海洋地壳的蛇绿岩(Ishiwatari, 1985a, 1985b;Ishiwatari, 1991)。作为一名在岩石学方面有着深厚背景的熟练的野外地质学家,Ishiwatari博士不仅研究Yakuno蛇绿岩,还研究法国阿尔卑斯山(Ishiwatari, 1985)和俄罗斯远东地区(Ishiwatari et al., 2003)的蛇绿岩。Ishiwatari,Ichiyama, 2004),以及与羽状体相关的海洋-岛屿玄武岩(Ichiyama et al., 2008),以及在日本海开放期间形成的中新世火山岩(Ayalew &Ishiwatari, 2011;Ishiwatari,Imasaka, 2002)。他还研究了深海火成岩作为现代蛇绿岩的类比物(Ishiwatari, 1992;Ishiwatari et al., 2006)。在他的职业生涯中,Ishiwatari博士与中国和俄罗斯地球科学家进行了多次合作学术交流(图2)。他的国际网络使1992年在日本京都举行的第29届IGC蛇绿岩会议取得了成功,会议上的主要报告被整理成一本名为“环太平洋蛇绿岩”的书(Ishiwatari et al., 1994)。他对中国东部含钙岩的超高压变质岩、俄罗斯远东地区锡霍特-阿林的蓝片岩-蛇绿岩组合以及日本飞驒带的合作研究产生了一个被称为“八山海岬假说”的新建议。Tsujimori, 2003)运作。Ishiwatari在2004年至2007年期间担任《Island Arc》杂志的主编,并在2008年至2010年期间担任综合海洋钻探计划的科学规划和评估小组的联合主席。2012年至2014年,他还担任日本地质学会会长。从2014年到现在,他在日本担任日本核监管局(Nuclear Regulation Authority)专员,提高了他在日本的形象。本期专题收录了11篇从不同角度研究OOO的论文。论文的重点是过去的地球动力学过程,作为记录在陆地和海底岩石在不同尺度从矿物平衡到板块构造水平。Hiroi et al.(2020)和Harada et al.(2021)的两篇论文提出了关于大陆-大陆汇聚带或其附近的中地壳变质过程的新观测结果。Hiroi等人(2020)报道了来自大陆碰撞造山带(斯里兰卡、东南极洲、加拿大和印度)的麻粒岩相石榴石中的felsite内含物。这些作者主要研究了长石包裹体中的自体石英斑晶。微量钛的阴极发光(CL)分带表明过冷石英熔体中晶体生长。 长石包裹体中石英斑晶的CL分带表明,碰撞造山带麻粒岩的冷却速率比目前推测的要高一到两个数量级。Harada et al.(2021)对曾经是东亚大陆边缘地壳基底一部分的飞驒带的上角闪岩相大理岩和碳酸盐-硅酸盐岩进行了C - O - Sr同位素地球化学研究。方解石C - O同位素组成δ13C [VPDB]和δ18O [VSMOW]值变化较大(分别为−4.4‰~ +4.2‰和+1.6‰~ +20.8‰)。碳酸盐岩-硅酸盐岩δ13C值较低(−4.4‰~−2.9‰)。这些作者得出结论,低δ13C值可以用脱碳(co2释放)反应来解释。在接下来的两篇文章中也讨论了会聚板块边缘的变质过程。Nishiyama等(2021)研究了日本九州Higo变质岩(HMR)中具有棘状结构的片麻岩质变质橄榄岩体,并提出了一种新的岩石成因机制。根据他们的新研究结果,这些变质橄榄岩可能是由反长花岗岩为主的蛇纹岩高压脱水形成的,可能是在地幔楔的较深的根部,在P = ~1.6 GPa和T = ~740 ~ 750℃的变质条件下形成的。在中压HMR片麻岩中出现的高压偏透岩小体表明,这两种不同岩性的构造并置在一个会聚的板块边缘。福岛等人(2021)对c组的递进带石榴石、来自希腊Syros和危地马拉South Motagua msamulange的低温榴辉岩中的微量元素分区模式进行了研究。通过对石榴石成卟啉层的Y + ree谱分析,可以探讨成卟啉层在榴辉岩基质中的生长速率和阳离子扩散率。这些作者还修改了先前的扩散限制稀土元素吸收模型。他们的新石榴石卟啉母岩生长模型将有助于揭示阳离子扩散过程,从而更好地理解俯冲带的地球化学动力学。Uchino(2021)和Okamoto et al.(2021)在日本东北部的两项研究为日本古生代大洋板块辐合的构造演化提供了新的认识。Uchino(2021)利用碎屑锆石U-Pb年龄重新识别了Nedamo带早三叠世增生杂岩。这一认识为内达摩带的新细分——早三叠世Takinosawa和早石炭世Tsunatori单元的划分奠定了基础。研究还确定了北上山增生造山带向东北年轻化的趋势。岩屑年龄谱表明,竹泽组与四国黑川带早三叠世岩屑具有可比性,支持日本西南、东北早侏罗世大地构造对比。Okamoto et al.(2021)研究了南北上山早古生代Motai蛇纹岩的岩石学和地球化学性质。研究发现,地幔原生矿物和次生含水矿物的地球化学特征与马里亚纳弧前蛇纹岩相似。作者认为,Motai蛇纹岩原岩为发育于早古生代原东亚大陆辐合边缘俯冲带前弧区下方的枯竭幔脉橄榄岩。其余的论文集中在蛇绿岩和海洋,包括现代海底和海山。Tamura et al.(2022)和Machida et al.(2021)的论文研究了太平洋板块的地壳结构和表面环境。Tamura等人(2022)概述了太平洋板块广大地区(西北西部和东太平洋隆起)的地壳厚度与地震测量莫霍反射结构之间的关系,并根据大洋中脊岩浆的地球化学变化推断了几种地壳形成过程。这些作者得出的结论是,相对较厚的海洋地壳和较厚的泥质层可能是由大洋中脊以下的含水熔融造成的,这意味着海水沿着地壳形成时形成的断层渗透到地幔中。Machida等人(2021)研究了南鸟岛周围北太平洋西部海底的锰铁结核。锰铁结核中缺乏一些生长层被解释为由于结核核材料的供应延迟或铁锰层的生长中断;此外,锰铁结核中缺失的亚层可以调节结核的大小。研究表明,锰铁结核的多维成分映射是重建海底环境的有效方法。Miyata等人的三篇论文。 (2020), Aftabuzzaman等人(2021)和Hirano等人(2021)解决了海底山的问题。Miyata等人(2020)研究了从Hahajima海山东坡收集的浅水碳酸盐,该海山位于伊豆-波宁和马里亚纳前弧斜坡之间的交界处。尽管之前进行了大量的研究,但哈哈岛海山的起源仍然不确定。通过对以浮岩为主、软体动物较多的Hahajima海山碳酸盐岩的沉积学和年代学分析,认为Hahajima海山与位于Hahajima海山以东、伊豆-波宁海沟(太平洋板块)对面的Ogasawara高原碳酸盐岩具有相似的岩性和相似的Sr同位素年龄(白垩纪)。研究表明,滨岛海山的浅水碳酸盐岩不是原位沉积,而是起源于小笠原高原。因此,该海底山的东段被解释为一个增生楔。Aftabuzzaman等人(2021)对南鸟岛(马库斯岛)西坡采集的碳酸盐岩样品进行了沉积学、地球化学和年代分析,并确定了该海山的历史如下。晚始新世—早渐新世的火山作用使南鸟岛顶部幕式隆升,使南鸟岛顶部恢复到浅水环境,其中包括富含软体动物的灰岩。在早渐新世的上层冰盖磷化之后,珊瑚礁在这个岛的顶部繁盛。礁灰岩在托尔顿-墨西尼亚期白云化。Hirano et al.(2021)报告了对南鸟岛火山大厦基底玄武岩的调查。这些作者报告了一个具有海洋-岛屿-玄武岩类地球化学亲和性的古近系火山大厦。古近纪火山活动可能局部叠加了早白垩世至中白垩世的火山构造,至少在小笠原高原和南鸟岛火山构造上是如此。Aftabuzzaman等人(2021)报道的白垩纪礁灰岩的存在有力地支持了这一假设。根据Miyata等人(2020)的报道,在太平洋板块俯冲之前沉积在太平洋板块上的这种海山盖层碳酸盐岩可以提供非常有价值的记录,从而可以对伊豆-博宁-马里亚纳前弧进行全面的地质解释。
Editorial for the thematic issue, “Orogens, ophiolites, and oceans: A snapshot of Earth's tectonic evolution”
Integrated studies of orogens, ophiolites, and oceans (OOO) provide a snapshot of Earth's dynamic evolution. As a key proxy of lithospheric plate underflow, the rocks in orogenic belts and oceans have been intensively studied from various scientific viewpoints and at different spatial–temporal scales. The rock record in OOO helps to better understand past plate-tectonic processes and thereby to interpret ongoing geodynamic processes in Earth's outer shell where we dwell. However, challenges remain with respect to obtaining a more comprehensive understanding of such processes through interdisciplinary exchange.
This thematic issue contains presentations given at the international symposium “Orogens, Ophiolites, and Oceans: A Snapshot of Earth's Tectonic Evolution” held in Sendai, Japan, in late February 2020. This thematic issue also honors Dr. Akira Ishiwatari for his important contribution to ophiolite studies. Dr. Ishiwatari played a pioneering and pivotal role in developing ophiolite studies in Japan based on field geology and petrology. The 2-day international symposium, miraculously held in person just before the coronavirus outbreak, focused on recent progress in petrochemical–tectonic studies of orogens, ophiolites, and oceans (oceanic crusts and oceanic deposits), especially in the vicinity of the Japanese Islands. Participants and presenters (including Dr. Ishiwatari) at the symposium were geoscience professionals and students in the areas of petrology, geochemistry, geochronology, and marine geology related to OOO (Figure 1). We trust that this thematic issue will serve as a worthy tribute to the research and contribution of Dr. Akira Ishiwatari.
We dedicate this thematic issue to Dr. Akira Ishiwatari for his important contribution to our understanding of ophiolites, especially the petrological classification of worldwide ophiolites and the geological features of Japanese ophiolites. His early studies in the late 1970s and early 1980s focused on the geology of the so-called “Yakuno Intrusive Rocks” in SW Japan, leading to the first recognized ophiolite sequence in Japan (Ishiwatari, 1978). The “Yakuno Ophiolite” identified by Dr. Ishiwatari has been internationally recognized as an ophiolite with an unusually thick oceanic crust (Ishiwatari, 1985a, 1985b; Ishiwatari, 1991). As a skilled field geologist with a strong background in petrology, Dr. Ishiwatari worked not only on the Yakuno Ophiolite but also on ophiolites in the French Alps (Ishiwatari, 1985c) and Russian Far East (Ishiwatari et al., 2003; Ishiwatari & Ichiyama, 2004), as well as on plume-related accreted ocean-island basalts (Ichiyama et al., 2008), and Miocene volcanic rocks formed during the opening of the Japan Sea (Ayalew & Ishiwatari, 2011; Ishiwatari & Imasaka, 2002). He also studied deep-sea igneous rocks as a modern ophiolite analog (Ishiwatari, 1992; Ishiwatari et al., 2006). Throughout his career, Dr. Ishiwatari made numerous cooperative academic exchanges with Chinese and Russian geoscientists (Figure 2). His international networking led to the success of the ophiolite session at the 29th IGC in Kyoto, Japan, in 1992, the key presentations in the session were collated in a book entitled “Circum-Pacific Ophiolites” (Ishiwatari et al., 1994). His collaborative works on coesite-bearing ultrahigh-pressure metamorphic rocks in eastern China, blueschist–ophiolite associations in the Sikhote-Alin (Russian Far East), and the Japanese Hida Belt resulted in a novel proposal termed the “Yaeyama Promontory Hypothesis” (Ishiwatari & Tsujimori, 2003).
Dr. Ishiwatari served as Editor-in-Chief of the journal Island Arc during 2004–2007 and as a co-chair of the Scientific Planning and Evaluation Panel of the Integrated Ocean Drilling Program during 2008–2010. He also served as the president of the Geological Society of Japan from 2012 to 2014. He increased his profile in Japan as a Commissioner of the Nuclear Regulation Authority, Japan, from 2014 to the present.
This thematic issue contains 11 papers on studies of OOO from different perspectives. The papers focus on past geodynamic processes, as recorded in on-land and submarine rocks at different scales from mineral-equilibrium to plate-tectonic levels.
The two papers by Hiroi et al. (2020) and Harada et al. (2021) present new observations concerning middle-crustal metamorphic processes in or near zones of continent–continent convergence. Hiroi et al. (2020) report felsite inclusions within granulite-facies garnets from continental-collision orogens (Sri Lanka, East Antarctica, Canada, and India). Those authors focus on euhedral quartz phenocrysts in the felsite inclusions. Zoning of cathodoluminescence (CL) emission attributed to trace amounts of titanium indicates crystal growth in supercooled felsic melt. The CL zoning of quartz phenocrysts in felsite inclusions implies that the cooling rates of studied granulites from collision orogens are one to two orders of magnitude higher than presumed to date. Harada et al. (2021) document a COSr isotope geochemical investigation into upper-amphibolite-facies marble and carbonate–silicate rock from the Hida Belt, which was once part of the crustal basement of the East Asian continental margin. The calcite CO isotopic compositions show wide variation in δ13C [VPDB] and δ18O [VSMOW] values (from −4.4‰ to +4.2‰ and from +1.6‰ to +20.8 ‰, respectively). In particular, the carbonate–silicate rock shows low δ13C values (from −4.4‰ to −2.9‰). Those authors conclude that the low δ13C values can be explained by decarbonation (CO2-releasing) reactions.
Metamorphic processes at convergent plate margins are also discussed in the following two papers. Nishiyama et al. (2021) investigate gneiss-hosted metaperidotite bodies with spinifex-like texture from the Higo Metamorphic Rocks (HMR), Kyushu, Japan, and propose a new petrogenetic mechanism. According to their new results, the metaperidotites might have formed by high-pressure dehydration of antigorite-dominant serpentinite, possibly in a relatively deep root of mantle wedge under metamorphic conditions of P = ~1.6 GPa and T = ~740–750°C. The exotic occurrences of small bodies of high-pressure metaperidotites within the medium-pressure HMR gneisses suggest a tectonic juxtaposition of these two contrasting lithologies at a convergent plate margin. Fukushima et al. (2021) present a study on trace-element zoning patterns in prograde-zoned garnets in Group-C, low-temperature eclogites from Syros (Greece) and South Motagua Mélange (Guatemala). Analysis of Y + HREE profiles of the garnet porphyroblasts enables to discuss porphyroblast growth rates and cation diffusivities in the eclogitic matrices. Those authors also modify a previous diffusion-limited rare-earth element uptake model. Their new garnet porphyroblast growth model should contribute to unraveling cation-diffusion processes and thus lead to a better understanding of the geochemical kinetics in subduction zones.
Two pieces of research in NE Japan by Uchino (2021) and Okamoto et al. (2021) provide new insights into the tectonic evolution of Japanese Paleozoic oceanic plate convergence. Uchino (2021) use detrital zircon U–Pb ages to newly recognize an Early Triassic accretionary complex in the Nedamo Belt. This recognition is used as a basis for a new subdivision of the Nedamo Belt, namely, the Early Triassic Takinosawa and early Carboniferous Tsunatori units. The study also establishes a northeastward-younging trend of accretionary-orogen growth in the Kitakami Mountains. The detrital age spectra suggest that the Takinosawa Unit is comparable to Early Triassic fragments in the Kurosegawa Belt in Shikoku, which supports a pre-Jurassic geotectonic correlation between SW and NE Japan. Okamoto et al. (2021) investigate the petrological and geochemical natures of the early Paleozoic Motai serpentinites in the South Kitakami Mountains. The study finds that the geochemical characteristics of primary mantle minerals and secondary hydrous minerals are similar to those of serpentinites from the Mariana forearc. Those authors conclude that the protoliths of the Motai serpentinites were depleted-mantle peridotites that developed beneath the forearc region of a subduction zone located in a convergent margin of the early Paleozoic proto-East Asian continent.
The remaining papers focus on ophiolites and oceans, including modern sea floors and seamounts. The papers by Tamura et al. (2022) and Machida et al. (2021) deal with the crustal structure and surface environment of the Pacific Plate. Tamura et al. (2022) present an overview of the relationship between crustal thickness and seismic survey Moho reflection structure in a broad area of the Pacific Plate (the western–northwestern part and the East Pacific Rise) and examine several crust formation processes, as inferred from geochemical variation in magmas at mid-oceanic ridges. Those authors conclude that a relatively thick oceanic crust with thick dunite layers is plausibly caused by hydrous melting below mid-oceanic ridges, implying that seawater penetrates to the mantle along faults that develop as the crust forms. Machida et al. (2021) investigate ferromanganese nodules from the western North Pacific seafloor around Minamitorishima Island. The lack of some growth layers in ferromanganese nodules is interpreted as being due to a delayed supply of the nucleus material of nodules or a growth hiatus of Fe–Mn layer(s); in addition, missing sublayers in the ferromanganese nodules are inferred to regulate nodule size. This study demonstrates that multidimensional compositional mapping of ferromanganese nodules is a highly effective approach for reconstructing the submarine environment.
The three papers by Miyata et al. (2020), Aftabuzzaman et al. (2021), and Hirano et al. (2021) address the topic of seamounts. Miyata et al. (2020) examine shallow-water carbonates collected from the eastern slope of Hahajima Seamount, located at the junction between the Izu–Bonin and Mariana forearc slopes. Despite numerous previous studies, the origin of the Hahajima Seamount remains uncertain. On the basis of sedimentological and chronological analyses of the Hahajima carbonates, which are dominated by floatstone with numerous mollusks, those authors report lithological similarities and similar Sr isotope ages (Cretaceous) of carbonates between the Hahajima Seamount and the Ogasawara Plateau located east of the former and on the opposite side of the Izu–Bonin Trench (Pacific Plate). This study indicates that shallow-water carbonates of the Hahajima Seamount were not deposited in situ but instead originated from the Ogasawara Plateau. Thus, the eastern section of this seamount is interpreted as an accretionary wedge. Aftabuzzaman et al. (2021) present sedimentological, geochemical, and chronological analyses on carbonate rock samples collected from the western slope of Minamitorishima (Marcus Island) and determine the history of this seamount as follows. After deposition of the Cretaceous shallow-water carbonates, including the mollusk-rich limestone, Minamitorishima was inundated, and its top was covered with a pelagic cap. Late Eocene–early Oligocene volcanism caused episodic uplift and returned the top of Minamitorishima to a shallow-water environment. After the early Oligocene phosphatization of the pelagic cap, coral reefs flourished on the top of this island. The reef limestone was dolomitized during the Tortonian–Messinian. Hirano et al. (2021) report an investigation into the basement basalts of the Minamitorishima volcanic edifice. Those authors report a Paleogene volcanic edifice with an ocean-island-basalt-like geochemical affinity. The Paleogene volcanic activity might have locally overprinted Early to mid-Cretaceous volcanic edifices, at least on the Ogasawara Plateau and the Minamitorishima volcanic edifice. The presence of Cretaceous reefal limestone reported by Aftabuzzaman et al. (2021) strongly supports this scenario. As reported by Miyata et al. (2020), such seamount-capping carbonates that were deposited on the Pacific Plate prior to its subduction can provide highly valuable records that allow comprehensive geological interpretations to be made of the Izu–Bonin–Mariana forearcs.
期刊介绍:
Island Arc is the official journal of the Geological Society of Japan. This journal focuses on the structure, dynamics and evolution of convergent plate boundaries, including trenches, volcanic arcs, subducting plates, and both accretionary and collisional orogens in modern and ancient settings. The Journal also opens to other key geological processes and features of broad interest such as oceanic basins, mid-ocean ridges, hot spots, continental cratons, and their surfaces and roots. Papers that discuss the interaction between solid earth, atmosphere, and bodies of water are also welcome. Articles of immediate importance to other researchers, either by virtue of their new data, results or ideas are given priority publication.
Island Arc publishes peer-reviewed articles and reviews. Original scientific articles, of a maximum length of 15 printed pages, are published promptly with a standard publication time from submission of 3 months. All articles are peer reviewed by at least two research experts in the field of the submitted paper.