Island Arc最新文献

{"title":"P–T Evolution of Paleoproterozoic Dangoli Pelitic Gneisses, Baijnath Klippe, NW Himalaya: Insights From the Geochemistry and Zircon U–Pb Geochronology","authors":"Mallickarjun Joshi,&nbsp;Shubham Patel,&nbsp;Biraja P. Das,&nbsp;Govind Oinam,&nbsp;Tanya Srivastava,&nbsp;Alok Kumar","doi":"10.1111/iar.70008","DOIUrl":"https://doi.org/10.1111/iar.70008","url":null,"abstract":"<div>\u0000 \u0000 <p>The Cenozoic Himalayan orogeny resulted from the continental collision between the Tibetan block and the northern Indian Precambrian shield. The latter, replete with evidence of Columbian supercontinent assembly, likely comprised the north Indian continental margin that was reworked mechanically and thermally during the Himalayan orogeny, and still survives as Precambrian vestiges in the Himalaya. Parts of this Paleoproterozoic crust, which now occur as nappes and klippen, were tectonically transported by the Main Central Thrust southwards over the Lesser Himalayan sedimentaries during the orogeny. The Absence of Columbian metamorphic signatures in these thrust sheets has intrigued geologists for long. We present evidence for a Middle Orosirian metamorphic event from the pelitic gneisses of the Almora Group in the Baijnath Klippe from NW Himalaya. The physical conditions of metamorphism have been inferred using mineral chemistry, bulk-rock chemistry, and phase section modeling using Perple_X software in the MnNKCFMASHT model system. Zircon U–Pb geochronology for the Dangoli pelitic gneisses yielded a robust upper intercept at 1891 ± 12.82 Ma. The P–T phase diagram indicates that the peak mineral assemblage stabilized in the P–T range of 0.41–0.46 GPa and 675°C–700°C suggesting upper amphibolite facies metamorphism. Integrated metamorphic and geochronological results indicate that the Dangoli pelitic gneisses were derived by muscovite dehydration melting of metasediments during the peak metamorphism related to syn-collisional setting broadly coeval with the Paleoproterozoic magmatism during the Columbia supercontinent assembly. The evidence for definite involvement of Paleoproterozoic high-grade metamorphic rocks of the northern Indian shield in the Himalayan orogeny is being documented.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143466157","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":"Non-Uniform Stress Field of the Forearc Region in Middle Miocene Southwestern Japan Inferred From the Orientations of Clastic Dikes and Mineral Veins in the Tanabe Group","authors":"Noriaki Abe,&nbsp;Katsushi Sato","doi":"10.1111/iar.70007","DOIUrl":"https://doi.org/10.1111/iar.70007","url":null,"abstract":"<div>\u0000 \u0000 <p>The Middle Miocene was a period of tectonic transition in the southwest Japan arc. The cessation of backarc spreading at 15 Ma has been thought to have caused a pronounced change in the overall stress state from tension to compression in the arc-perpendicular direction. However, the spatial variation in stress throughout the arc, especially in the forearc, which reflects the characteristics of plate subduction, has yet to be delineated. This study investigates the stress field of the forearc region and its temporal change by applying a stress tensor inversion technique to outcrop-scale dilatant fractures. We measured the attitudes of clastic dikes and mineral veins in the Lower–Middle Miocene Tanabe Group, the paleo-forearc basin deposits in the southwestern Kii Peninsula. Results of paleostress analyses show that the Tanabe Group was influenced by (i) stress with an E–W minimum compressional axis before 15 Ma and (ii) stress with a NW–SE maximum horizontal compressional axis after 15 Ma. In contrast to conventional interpretations, we find that the former stress differed from arc-perpendicular tension in the backarc region before 16 Ma. The latter stress differed from trench-parallel tension on the southernmost Kii Peninsula. Such spatial non-uniformity of the forearc stress can be explained by the occurrence of a dynamic backstop, such as a landward area of the out-of-sequence thrust, beneath the Tanabe Group.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143389119","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":"Zircon U–Pb Dating of the Urahoro Group and Atsunai Formation in the Shiranuka Hills of Eastern Hokkaido, Northeast Japan: Implications for Tectonic Development","authors":"Toru Takeshita,&nbsp;Hisatoshi Ito,&nbsp;Hiromi Kaji","doi":"10.1111/iar.70006","DOIUrl":"https://doi.org/10.1111/iar.70006","url":null,"abstract":"<div>\u0000 \u0000 <p>Zircon U–Pb dates for detrital grains in the Shakubetsu Formation of the uppermost Eocene Urahoro Group and the Upper Miocene Atsunai Formation distributed in the eastern part of Hokkaido have been determined for the first time. Both weighted mean 48.8 ± 1.4 Ma (<i>n</i> = 80) for &lt; 70 Ma zircons and youngest grain 36.5 + 1.8, −2.5 Ma (Middle to Late Eocene) ages of the Urahoro Group are consistent with the sedimentary ages and Paleogene magmatic arc origin of the detritus clarified in the previous studies. Although the Zircon U–Pb ages (<i>n</i> = 24) of the Atsunai Formation range between 5 and ~1700 Ma, a weighted mean age of 7.05 ± 0.57 Ma (<i>n</i> = 10) for &lt; 10 Ma zircons (youngest cluster) could constrain the maximum sedimentary age, which is consistent with the previous ages from diatom biostratigraphy and K-Ar method. However, while the K-Ar age was obtained from an Ol-Cpx-Opx basalt in tuff breccia, the dated zircons were probably derived from felsic tuff including many pumice grains. Therefore, the bimodal volcanism could have occurred at <i>c.</i> 7 Ma in the present forearc region, indicating that the volcanic front at this age migrated south significantly, correlated to the one which also occurred coevally in the seaward side of the present volcanic front in the NE Japan arc. Further, it has been found that the eastern boundary of the Shiranuka Hills is characterized by an ESE verging, large-scale monocline based on the present field study and previous geological maps. Since the Atsunai Formation was involved in the formation of the large-scale monocline, the structure started to form after the sedimentation at <i>c.</i> 7 Ma. The fact implies that the ongoing collision of the Kuril forearc sliver with the NE Japan arc has propagated to this area since the latest Late Miocene.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143120005","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":"An Ordovician Assemblage of Cool Water-Adapted Paleotropical Ostracods Suggests an Early Psychrosphere","authors":"Anna McGairy,&nbsp;Phong Duc Nguyen,&nbsp;Mark Williams,&nbsp;Christopher P. Stocker,&nbsp;Thomas H. P. Harvey,&nbsp;Toshifumi Komatsu,&nbsp;Thomas W. Wong Hearing,&nbsp;C. Giles Miller,&nbsp;Chloé M. Marcilly,&nbsp;Alexandre Pohl","doi":"10.1111/iar.70001","DOIUrl":"https://doi.org/10.1111/iar.70001","url":null,"abstract":"<p>An ostracod assemblage from the Late Ordovician (Katian) Phu Ngu Formation of northern Vietnam, South China paleoplate, yields typical Baltic and Laurentian-affinity genera together with some endemic forms. Detailed paleontological and sedimentary analysis of the Phu Ngu Formation suggests it was deposited in a deeper marine forearc setting, below storm wave base, but with (at least intermittently) oxygenated sea-bottom conditions. Taphonomic assessment of the ostracod assemblage suggests it is in situ. The occurrence of globally widespread ostracod genera, including those from paleocontinents that were geographically remote from South China, is difficult to reconcile with the assumed limited dispersal capability of ostracods in shallow-shelf settings—a characteristic that has often been used to refine Ordovician paleogeographical reconstructions. Here, we present the novel approach of using paleoclimate reconstructions to assess the environmental distributions of Paleozoic ostracod genera. We show that the deep-marine depositional setting of our documented assemblage, together with general circulation model simulations of Ordovician ocean-temperatures, suggests an early radiation of benthic ostracods into the deeper, colder, and thermally uniform ocean below the thermocline. The presence of a globally-distributed psychrospheric (cool and deep marine) ostracod fauna would imply that our understanding of Ordovician ostracod dispersal is incomplete, and future paleobiogeographical studies should try to decouple the signal of shallow-shelf benthic taxa, often endemic and probably limited by sea temperature, from those that are more cosmopolitan and tolerant of cooler, deeper waters.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143117790","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":"Sedimentary Records of the Upper Cretaceous Yetang Formation: Compression Tectonic Setting in the Xingning Basin, Southeastern Edge of the South China Block","authors":"Dazhi Xu,&nbsp;Zhongjie Xu,&nbsp;Kunning Cui,&nbsp;Ningchen Sun","doi":"10.1111/iar.70005","DOIUrl":"https://doi.org/10.1111/iar.70005","url":null,"abstract":"<div>\u0000 \u0000 <p>The southeastern edge of the South China Block (SCB) experienced the subduction of the Paleo-Pacific Block, resulting in varying tectonic settings across different regions of the SCB during the subduction. To explore the tectonic settings during sediment deposition in the southeastern edge of the SCB in the early Late Cretaceous, we analyzed the Jiao Yangjing-Yetang section of the Xingning Basin, Guangdong province. This section contains a sedimentary sequence of the Upper Cretaceous Yetang Formation, facilitating lithofacies analysis, U–Pb zircon chronology, trace elements analysis, crustal thickness estimation, Hf isotopes analysis, and age distribution comparison of detrital zircons. Our findings indicate that the Late Cretaceous Yetang Formation was deposited during the early Late Cretaceous Cenomanian stage (99.6 ± 1.9 Ma), and identifies five groups of detrital zircon U–Pb ages: 2320–1810, 1100–670, 500–400, 230–160, and 130–96 Ma. The early Late Cretaceous ℇ_Hf (t) values ranged from −7.4 to 0.6, suggesting that the debris originated from the southwestern Fujian and northern Guangdong regions. Trace elements analysis of detrital zircons indicates increasing crustal thickness during the early Late Cretaceous. The Xingning Basin was in a compressive environment during the late Early Cretaceous, and the compressive condition continued until the early Late Cretaceous period (99.6 ± 1.9 Ma).</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143112413","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":"First Constraints on the Pressure–Temperature–Time Evolution of the Vijayan Complex, Sri Lanka: Implications for Its Position in Gondwana","authors":"Ruwanthika Kumari,&nbsp;P. L. Dharmapriya,&nbsp;Xiaofang He,&nbsp;S. P. K. Malaviarachchi,&nbsp;Pahan Abewardana,&nbsp;Lei Zhao","doi":"10.1111/iar.70003","DOIUrl":"https://doi.org/10.1111/iar.70003","url":null,"abstract":"<div>\u0000 \u0000 <p>Sri Lanka occupies a pivotal geological position within East Gondwana, featuring four prominent high-grade Precambrian lithotectonic units: the Highland Complex (HC), the Wanni Complex, the Vijayan Complex (VC) and the Kadugannawa Complex. Despite reasonable geochemical and geochronological investigations into rocks in the VC, a comprehensive understanding of their petrological characteristics, particularly their pressure–temperature–time evolution, remains limited, impeding accurate terrane correlations. In this study, a detailed analysis of mineral assemblages, reaction textures, and U–Pb zircon ages in samples collected from the eastern margin of the HC to the eastern coast, in the VC were conducted. Results indicate that the VC preserved textural evidence for prograde dehydration reactions indicating upper amphibolite to granulite facies transition. The peak metamorphism is followed by a stage of near isobaric cooling stage. Conventional geothermobarometric analysis coupled with phase equilibria modeling of VC gneisses reveal peak metamorphic P–T conditions of 790°C–830°C and 7–8 kbar. Retrograde metamorphism has occurred until the temperature decreased to 740°C. The U–Pb zircon dates at ca. 1010–960 Ma suggest protolith ages of the VC coinciding with Rodinia amalgamation and dispersal, aligning metamorphic thermal peaks at ca. 575–545 Ma with the Kuunga orogeny during Gondwana amalgamation. Our data signifies connections between the VC and both the Lurio foreland in Mozambique and the Innhovde Suite and Yamato-Belgica Complex in East Antarctica, however, the differences in metamorphic conditions and geochronological signatures necessitate further investigation into its tectonic history and paleogeographic evolution.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143112414","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":"Greetings From the New Editors-In-Chief","authors":"Takashi Hasegawa,&nbsp;Yuji Ichiyama","doi":"10.1111/iar.70004","DOIUrl":"https://doi.org/10.1111/iar.70004","url":null,"abstract":"&lt;p&gt;After the 5 years of the editorial services of Akihiro Kano and Tatsuki Tsujimori from 2020 to 2024, it is an honor and privilege for us to take over the roles of Editor-in-Chief of &lt;i&gt;Island Arc&lt;/i&gt; from January 2025. On behalf of the new editorial board, we would like to express our deepest gratitude to the previous editorial team for their exceptional contributions to the journal.&lt;/p&gt;&lt;p&gt;&lt;i&gt;Island Arc&lt;/i&gt;, the official international journal of the &lt;i&gt;Geological Society of Japan&lt;/i&gt;, was established in 1992. Over the past three decades, &lt;i&gt;Island Arc&lt;/i&gt; has served as a vital platform for discussions among the international earth science community and advancing our understanding of the diverse geological processes involved in plate convergent margins in circum-Pacific regions. The dedication of the previous editorial board resulted in the drastic enhancement of the Journal Impact Factor (JIF) by Clarivate Analytics from 2019 to 2022 (up to 2.442). However, despite their efforts, the value unfortunately declined to 1.0 in 2023, partly due to changes in the JIF calculation methodology. Similarly, Elsevier's CiteScore dropped from 3.5 in 2022 to 2.9 in 2023, although these values remain higher than those recorded during the 2016–2019 period (1.6–2.6). Please note that journals with a low annual article count, such as &lt;i&gt;Island Arc&lt;/i&gt;, are more susceptible to significant fluctuations in their journal-level metrics. Furthermore, citations from the &lt;i&gt;Journal of the Geological Society of Japan&lt;/i&gt; are not factored into the JIF calculation. Nevertheless, it is clear that maintaining the journal's high quality and enhancing its reputation remain key responsibilities. To this end, we encourage the community to submit exciting and high-impact manuscripts to &lt;i&gt;Island Arc&lt;/i&gt;. Our editorial team is committed to ensuring professional, efficient, and fair manuscript handling and strives for swift publication.&lt;/p&gt;&lt;p&gt;The previous editorial team implemented several significant changes, including renewing journal's cover art, and transitioning to a “one issue per year” format following the cessation of print editions to move entirely to online publication. They also made considerable efforts to accelerate the peer-review process, particularly through the recent transition from ScholarOne Manuscripts to Wiley's brand-new Research Exchange (ReX) platform. While the new ReX platform still requires further refinement, this modern web-based system benefits not only authors but also reviewers. In parallel with these efforts, &lt;i&gt;Island Arc&lt;/i&gt; continues to provide significant value by not requiring an article processing charge (APC) for publication. Additionally, if an author's institution has an open-access publishing agreement with Wiley, articles can be published as open-access at no cost (or with a substantial discount) to the authors. In recent years, &lt;i&gt;Island Arc&lt;/i&gt; has notably increased international readership, particularly from the U.S. and China, in rec","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70004","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143112415","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":"Holocene Temperature Trend Inferred From Oxygen and Carbonate Clumped Isotope Profiles of a Stalagmite Collected From a Maritime Area of Central Honshu, Japan","authors":"Akira Murata,&nbsp;Taiki Mori,&nbsp;Hirokazu Kato,&nbsp;Hsun-Ming Hu,&nbsp;Chuan-Chou Shen,&nbsp;Ryoko Senda,&nbsp;Kenji Kashiwagi,&nbsp;Akihiro Kano","doi":"10.1111/iar.70002","DOIUrl":"https://doi.org/10.1111/iar.70002","url":null,"abstract":"<p>The Holocene has been extensively researched concerning past climates, and various proxy records have provided information on temperature changes during this period. Many studies have found a period of elevated temperatures during the Middle Holocene, known as the Holocene Thermal Maximum (HTM). However, the exact timing of this warm period varies depending on the region. Here, we investigate a stalagmite collected from Kiriana Cave, which covers two intervals: 13.7–12.4 and 10.4–1.16 thousand years ago (ka before 1950 AD). In previous studies at this cave site, the meteoric water δ¹⁸O is not sensitive to the precipitation amount and the seasonality of precipitation but follows the seawater δ¹⁸O. By using these assumptions of the meteoric water δ¹⁸O, the paleo-temperature was quantitatively reconstructed from the stalagmite δ¹⁸O and the carbonate clumped isotopes. These paleoclimatic proxies indicated that the temperature at the cave site significantly changed during the Holocene. Based on the records of the stalagmite δ¹⁸O, the HTM occurred between 10.9 and 6.7 ka, reaching its peak temperature (15.0°C) around 7.0 ka. At this time, temperatures were approximately 3°C warmer than present. The timing of the warm interval aligns closely with marine temperature records but is notably earlier than terrestrial records from Europe and North America. Cooling began at 6.5 ka, and the decreased temperature stabilized in an interval between 6.0 and 4.5 ka. The temperature decreased further to the lowest value (~10.0°C) at 3.0 ka. After this cooling maximum, the climate gradually became warm until the stalagmite stopped growing at 1.16 ka. Our Holocene temperature reconstruction is consistent with the temperature and palaeoceanographic records obtained from reef corals and marine sediments in and around the Japanese Islands in terms of the amplitude of change, warm middle Holocene, and cool late Holocene.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143119490","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":"Geological and Geomorphological Causes of Two Historical Deep-Seated Catastrophic Landslides Induced by the 1892 Heavy Rainfall Event in the Shimanto Accretionary Complex, Tokushima, Japan","authors":"Noriyuki Arai","doi":"10.1111/iar.70000","DOIUrl":"https://doi.org/10.1111/iar.70000","url":null,"abstract":"<div>\u0000 \u0000 <p>The catastrophic Hose and Ogawatuetui landslides occurred coincidentally in 1892 following heavy rainfall in the upper reaches of the Kaifu River, Tokushima, Japan. The area is underlain by a steeply dipping coherent formation with many faults, and lies in the Shimanto Belt where deep-seated catastrophic landslides are known to occur following heavy rainfall and large subduction zone earthquakes. The main geological and geomorphological causes of the landslides were found to include local relief ≥ 350 m (1200-m-diameter analysis windows); knickpoints and slope breaks at 90–150 m above sea level, competent massive and thick-bedded sandstone with open fractures on the upper slope, and alternating thin beds of incompetent fine sandstone and shale beds of high deformability and low permeability on the lower slope.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"33 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142724235","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":"Distribution of Stable and Radioactive Iodine Dissolved in Interstitial Waters Within the Subduction Input Sediment Offshore Sumatra Subduction Zone","authors":"Satoko Owari,&nbsp;Hitoshi Tomaru,&nbsp;Hiroyuki Matsuzaki","doi":"10.1111/iar.12542","DOIUrl":"https://doi.org/10.1111/iar.12542","url":null,"abstract":"<p>Subduction input (sediment before subduction)-located seaward of the trench is one of the largest iodine budgets on the earth's surface. It is responsible for the deep iodine source in the landward of the trench where the iodine flux is significantly high. However, the distribution in the subduction input is poorly understood, contrary to the subducted sediment (sediment after subduction) landward of the trench. We determined iodine concentration and ¹²⁹I/¹²⁷I ratio of the interstitial water from the seafloor to the basement continuously at a subduction input site ~250 km southwest of the Sunda Trench for the first time to understand the iodine distribution. In the study site, the iodine concentration increased with depth linearly to ~100 μM at 1400 mbsf. Iodine isotope ratios (¹²⁹I/¹²⁷I) remained constant as low as ~400 × 10⁻¹⁵ from 400 to 1400 mbsf, suggesting that the iodine distribution was mainly controlled by old iodine-rich fluid (low ¹²⁹I/¹²⁷I ratio and high iodine concentration) supplied along the basement and by mixing with seawater (high ¹²⁹I/¹²⁷I ratio and low iodine concentration). The linear iodine gradient was changed at ~200 and ~1200 mbsf, where the methane concentration rapidly increased and total organic carbon decreased. This indicates that young iodine (low ¹²⁹I/¹²⁷I ratio) was released from the organic materials in the sediment into the interstitial water at these depths. This is the first observation of in situ iodine/methane addition to the interstitial water associated with the organic decomposition. The iodine concentration and ¹²⁹I/¹²⁷I ratio indicated that iodine in the subduction input was either derived from the in situ sediment or allochthonous fluid transported from subducted sediment due to differences in physical properties and permeability. This allochthonous iodine transportation to the subduction input may broaden the concept of the iodine cycling in the subduction system, including the sediments after and before subduction.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"33 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12542","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142724259","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}