Island Arc最新文献

{"title":"Zircon U–Pb Ages of Granitoids in Northern Kyushu, Southwest Japan: Implications for the Transition of Cretaceous Igneous Activity Along the Eastern Margin of the Asian Continent","authors":"Yukiyasu Tsutsumi,&nbsp;Kenichiro Tani","doi":"10.1111/iar.70056","DOIUrl":"https://doi.org/10.1111/iar.70056","url":null,"abstract":"<div>\u0000 \u0000 <p>Age determination of the Cretaceous granitoids in Japan is important for understanding igneous activities caused by subduction of the Izanagi–Kula–Pacific plates beneath the eastern margin of the Asian continent. New zircon U–Pb age data for 51 rock samples from 49 localities were obtained from northern Kyushu to build chronological evidence for further discussion of East Asian tectonics. The granitoids are divided into two parts across the Kokura–Tagawa Tectonic Line (KTTL); the Western Granitoids are classified as magnetite series, whereas the Eastern Granitoids are classified as ilmenite series. The Western Granitoids become younger toward the south, that is, toward the trench, from ca. 112 to 95 Ma, while the Eastern Granitoids become younger toward the north, that is, toward the continent, from ca. 107 to 99 Ma. Their age trends and overlapping age ranges demonstrate that two igneous zones existed in parallel and simultaneously during the Cretaceous and became closer to each other with time. The traces of the igneous zones on the continental and oceanic sides would correspond to the Korean Peninsula and the San-yo Province of Southwest Japan, respectively, and Kyushu, which had features of both, was situated at the junction of the two igneous zones. Considering only the ages of granitoids, the original position of Southwest Japan before the formation of the Sea of Japan would have been located more to the southwest than previously thought.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2026-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148848808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermobaric Structure of the Sefuri Metamorphic Rocks in the Itoshima Area, Tsukushi Complex, Northern Kyushu, Southwest Japan: A Possible Western Extension of the Ryoke Arc","authors":"K. Miyazaki,&nbsp;Y. Muraoka,&nbsp;T. Ikeda,&nbsp;T. Nishiyama","doi":"10.1111/iar.70055","DOIUrl":"https://doi.org/10.1111/iar.70055","url":null,"abstract":"<div>\u0000 \u0000 <p>This article presents the pressure–temperature (<i>P</i>–<i>T</i>) structure of the high-<i>T</i> Sefuri Metamorphic Rocks in the Itoshima area, northern Kyushu, Southwest Japan, together with zircon U–Pb ages of the metamorphic and plutonic rocks in the area. These rocks were previously interpreted as contact metamorphic rocks formed by the intrusion of Cretaceous granitic bodies. However, they exhibit features commonly attributed to regional metamorphism, such as penetrative schistosity. The development of schistosity can be explained by deformation above the temperature of the brittle-ductile transition. Our numerical simulations suggest that such high-<i>T</i> conditions in regions consisting of numerous granitic bodies are generated by the superposition of heat from short-period pulses of granitic magma intrusions. The <i>P</i>–<i>T</i> structure of the Sefuri Metamorphic Rocks around Mt. Raizan indicates that significant ductile thinning occurred along the roof of the diapirically ascending middle and southern domains of the Itoshima Granodiorite. Schistosity-developed high-<i>T</i> metamorphic rocks associated with Cretaceous granitic intrusions are common in northern Kyushu. We define the Tsukushi Complex as comprising these metamorphic rocks and closely associated Cretaceous plutonic rocks. The compilation of zircon U–Pb ages from the Tsukushi Complex indicates that pulsed metamorphism occurred synchronously with long-period pulses of granitic plutonism. The synchronous metamorphism and plutonism that formed the Tsukushi Complex, together with contemporaneous volcanism, are comparable to the synchronous high-<i>T</i> metamorphism and plutonism that formed the Ryoke Complex and the associated Cretaceous volcanism in Southwest Japan. In both complexes, the isolated large (&gt; 1000 km²) domains composed of the high-grade metamorphic rocks and granodiorite plutons may represent the deeper roots of coeval volcanic clusters at the surface. These observations suggest that the Tsukushi Complex may be an eroded remnant of a western extension of the Ryoke Arc, which comprises the Ryoke Complex and coeval surface volcanic clusters.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2026-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148617179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Upper Cretaceous Yüksekova Complex (Type Area), Easternmost Türkiye: Formation and Emplacement of a Proximal Back-Arc Segment of a Tethyan Intra-Oceanic Arc","authors":"Alastair H. F. Robertson,&nbsp;Osman Parlak,&nbsp;Kemal Taslı","doi":"10.1111/iar.70054","DOIUrl":"https://doi.org/10.1111/iar.70054","url":null,"abstract":"<p>We provide the first comprehensive information and interpretation of the type area of the regionally important Upper Cretaceous oceanic arc, known as the Yüksekova Complex. Here, the arc's development is investigated using field observations, igneous and sedimentary petrography, micropaleontology of planktic foraminifera, x-ray diffraction of fine-grained sediments, igneous and sedimentary geochemistry, structural relations, and regional comparisons. The complex in its type area is a folded and faulted but otherwise intact succession of massive lavas, pillow lavas, and fragmental pyroclastic and epiclastic rocks, interbedded with volcaniclastic and bioclastic turbidites, volcanogenic mudrocks (hemipelagites), Maastrichtian <i>Globotruncana</i>-bearing pelagic carbonates, and sparse felsic airfall tuffs. Intrusive rocks are mainly localized multiple granitic-aplitic dikes, minor basic- to intermediate-composition dikes, and small gabbroic bodies. Geochemical evidence indicates two lava trends, the first tholeiitic to calc-alkaline; i.e., basaltic-andesitic-felsic, and the second alkaline (OIB) with minor but variable subduction influence. Mainly basic- to intermediate-composition detritus was derived from associated basaltic-andesitic volcanics, whereas generally more felsic-composition sediments, which include shallow-water bioclasts, were derived from a contemporaneous, evolved arc volcano and an associated carbonate platform (now not exposed). Comparisons with the Yüksekova Complex farther west (Kovancılar–Elazığ–Maden areas), and with both modern and ancient oceanic arc settings (e.g., W Pacific; Himalayas), suggest that the Yüksekova Complex (type area) represents the proximal segment of a back-arc rift. The alkaline lavas could represent extrusion of deep-sourced, enriched magma along a crustal rupture, or simply be a consequence of mantle heterogeneity. The Yüksekova Complex underwent compressional deformation and low-grade metamorphism related to latest Cretaceous and Eocene emplacement, followed by final, Early Miocene emplacement onto the Arabian continental margin to the south during advanced continental collision. The Yüksekova oceanic arc restores to a Mesozoic ocean basin in southeast Anatolia (Berit ocean), between the Mesozoic Malatya–Keban platform to the north and the Pütürge and Bitlis continental units to the south (and eastward potential extensions).</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2026-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70054","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148616149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Field Mapping and Zircon U–Pb Dating of the Early Paleozoic Amphibolite-Facies Paragneiss in the South Kitakami Belt, NE Japan: Implications for the Sedimentary and Metamorphic History of Proto-Japan","authors":"Takayuki Uchino,&nbsp;Tetsuya Tokiwa,&nbsp;Hayato Takenouchi","doi":"10.1111/iar.70053","DOIUrl":"https://doi.org/10.1111/iar.70053","url":null,"abstract":"<p>The early Paleozoic tectonic setting of proto-Japan remains poorly constrained. In the South Kitakami Belt in Northeast Japan, Ordovician–early Silurian basement rocks and overlying Silurian–Cretaceous shallow marine sediments are widely distributed. The basement rocks include the Hikami Granitoids and the associated Tsubonosawa Metamorphic Rock (TMR), which experienced high-temperature and low-pressure (high-<i>T/P</i>) metamorphism. The TMR comprises biotite gneiss and migmatite derived from a terrigenous clastic protolith. Previously reported radiometric ages of the TMR vary widely, ranging from 450 to 180 Ma. To better understand the origin of the TMR, we produced a detailed geological map and obtained zircon U–Pb ages from biotite gneiss and leucosome in migmatite. The youngest cluster ages are ca. 470 Ma for the gneiss and ca. 440 Ma for the leucosome. Notably, the younger leucosome ages are derived from overgrowths on zircon rims. Since the leucosome is considered to have formed by anatexis of the TMR protolith, the ca. 440 Ma age indicates the metamorphic age of the TMR. In contrast, the ca. 470 Ma age from detrital zircons in the gneiss constrains the depositional age of the TMR protolith to the Middle Ordovician or later. Our data suggest that the protolith formed on the continental shelf during the Middle Ordovician and subsequently experienced high-<i>T/P</i> metamorphism due to intrusion of the Hikami Granitoids, resulting in formation of the gneiss during the latest Ordovician–earliest Silurian. The complex present-day distribution of the TMR reflects folding of a xenolitic TMR sheet incorporated into the Hikami Granitoids, followed by offset and displacement along strike-slip faults with minor vertical components.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70053","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148467412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Well-Constrained Middle Darriwilian Isotopic Carbon Excursion (MDICE) in South China and Its Global Implications","authors":"Shenyang Yu,&nbsp;Zhongyang Chen,&nbsp;Yutao Wang,&nbsp;Xiang Fang,&nbsp;Yao Wang,&nbsp;Shouxiang Wang,&nbsp;Yingyan Mao,&nbsp;Stephen Kershaw,&nbsp;Qijian Li","doi":"10.1111/iar.70052","DOIUrl":"https://doi.org/10.1111/iar.70052","url":null,"abstract":"<div>\u0000 \u0000 <p>The Middle Darriwilian Isotopic Carbon Excursion (MDICE) is a globally recognized Ordovician carbon isotope event, but its records in the South China Block (SCB) are commonly incomplete due to regional stratigraphic hiatus. This study presents an integrated analysis of conodont biostratigraphy, carbon isotope stratigraphy, and microfacies analysis from a stratigraphically continuous succession spanning the Kuniutan to lower Pagoda formations (Darriwilian to early Katian) at the Mayang section, Upper Yangtze Platform, SCB. Microfacies data indicate a shallowing event during the deposition of the uppermost Kuniutan to lowermost Datianba formations (upper <i>Pygodus serra</i> Biozone, late Darriwilian), yet the absence of subaerial exposure features supports continuous sedimentation. Carbon isotope data reveal a positive excursion of ~1‰ within the Kuniutan Formation, characterized by a sustained high-value interval from the <i>Eoplacognathus suecicus</i> to <i>Pygodus serra</i> biozones and a shortened falling limb, interpreted as an apparent complete record of the MDICE. A second, larger positive excursion (2‰–3‰) near the top of the section, initiating in the upper <i>Baltoniodus alobatus</i> Biozone and peaking in the lower <i>Hamarodus brevirameus</i> Biozone, is correlated with the early Katian Guttenberg Isotopic Carbon Excursion (GICE) or its regional equivalent. Global comparison confirms the MDICE as a broadly correlative perturbation of the Ordovician carbon cycle, while pronounced regional differences in its expression highlight the importance of depositional and palaeogeographic controls.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2026-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148463130","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Suitable Grain Size for Distinguishing Mainstem and Tributary Gravelly Deposits in Riverbeds and Terraces Using Roundness Image Analysis","authors":"Atsushi Taya,&nbsp;Takayuki Takahashi,&nbsp;Daisuke Ishimura,&nbsp;Masaki Yamada","doi":"10.1111/iar.70051","DOIUrl":"https://doi.org/10.1111/iar.70051","url":null,"abstract":"<p>Roundness of gravel particles is widely used as an indicator of sediment transport, yet its potential for discriminating provenance between mainstem and tributary rivers has not been fully tested. In this study, we applied an image-analysis-based roundness measurement (Rgrains) to gravel samples from mainstem and tributary deposits in the Tama and Doushi river basins in central Japan. We used both modern riverbed sediments and terrace deposits across four grain-size fractions (2–4, 4–8, 8–16, and 16–32 mm) to examine suitable grain sizes for distinguishing mainstem and tributary deposits. The results suggest that terrace gravel clasts may be distinguished between mainstem and tributary sources by comparing their roundness distributions with those of modern riverbed sediments. Mainstem sediments consistently exhibited higher roundness than tributary sediments, whereas tributary deposits showed statistical characteristics biased toward specific roundness values, reflecting the restricted nature of their catchments and channels. The minimum grain size required for identification depended on the tributary gradient: in steep-gradient tributaries dominated by debris flows, clear differences were observed even in fine fractions (2–4 and 4–8 mm), whereas coarser fractions (16–32 mm) were generally required for low-gradient tributaries dominated by bedload transport. Furthermore, fluvial transport processes inferred from riverbed slopes appear to exert a stronger influence on clast roundness than lithology, which plays a relatively minor role. The roundness of terrace gravel clasts may preserve information on tributary gradients and transport modes at the time of deposition, and comparison with modern riverbed gravel clasts suggests that past tributary gradients may be reconstructed. These findings suggest that quantitative roundness analysis provides a useful approach for linking terrace gravel clasts to their provenance, offering insights into fluvial terrace development and sediment transport in mountainous rivers.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2026-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70051","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148238232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Permian Arc Cumulates and Adakitic Magmatism in the Oura Plutonic Complex, Southwest Japan: Implications for Ridge Subduction Along the Proto-East Asian Continental Margin","authors":"Yuji Ichiyama,&nbsp;Shohei Hashimoto,&nbsp;Hisatoshi Ito,&nbsp;Akihiro Tamura,&nbsp;Tomoaki Morishita","doi":"10.1111/iar.70050","DOIUrl":"https://doi.org/10.1111/iar.70050","url":null,"abstract":"<div>\u0000 \u0000 <p>Two Paleozoic ophiolites, the Ordovician Oeyama and Permian Yakuno ophiolites, juxtaposed in the inner zone of southwestern Japan, record the tectonic evolution of the proto-East Asian continental margin during the Paleozoic. The Oura plutonic complex, located in the northern part of Maizuru City, Kyoto Prefecture, consists mainly of mafic to ultramafic rocks with minor amounts of intermediate intrusive rocks. Despite its key position for understanding the geotectonic framework of the Inner Zone of southwestern Japan, the geological attribution of the Oura plutonic complex has remained controversial. Zircon U–Pb dating of metagabbro and metadiorite from the Oura plutonic complex yields Permian ages of 273 and 292–254 Ma, respectively, indicating an affinity with the Permian Yakuno ophiolite of the Maizuru belt. Whole-rock and mineral geochemical data from metagabbro and ultramafic rocks indicate formation in an oceanic island arc setting, suggesting that the Oura plutonic complex represents lower crustal cumulates beneath a Permian island arc. The metadiorite is characterized by high Sr/Y and La/Yb ratios, typical of adakitic magmas derived from the melting of subducted oceanic crust. The Oura metadiorite is therefore interpreted to have originated from adakitic magma, most likely generated during backarc spreading. Late Paleozoic adakitic rocks are distributed not only in the Maizuru belt but also in northeast Japan and the Khanka–Jiamusi massif, and plausibly provide crucial clues to deciphering the tectonic evolution along the Permian proto-East Asian continental margin.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2026-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148237786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"","authors":"","doi":"","DOIUrl":"","url":null,"abstract":"","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2026-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148092005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"","authors":"","doi":"","DOIUrl":"","url":null,"abstract":"","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2026-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148071539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"","authors":"","doi":"","DOIUrl":"","url":null,"abstract":"","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148080273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}