Island Arc最新文献

{"title":"Zircon U–Pb geochronology and geochemistry of the Late Jurassic granite porphyries from central-eastern Jilin Province, NE China: Petrogenesis and tectonic implications","authors":"Xiqing Ye,&nbsp;Zhitao Xu,&nbsp;Mengmeng Li,&nbsp;Liying Sun,&nbsp;Zhongwei Li,&nbsp;Donghan Yan,&nbsp;Jingqiao Feng","doi":"10.1111/iar.12464","DOIUrl":"10.1111/iar.12464","url":null,"abstract":"<p>The recently discovered Yizuoying Mo deposit is located in central-eastern Jilin Province, NE China. The molybdenum (Mo) mineralization, mainly hosted in granite porphyry, is considered to be granite-related. Zircon U–Pb dating of the granite porphyry yielded concordant ages of 160.81 ± 0.62 Ma, which is consistent with the weighted mean U–Pb age of 160.53 ± 0.65 Ma, indicating that the emplacement of granitic plutons occurred in the Late Jurassic. The granite porphyry samples are peraluminous, high-K calc-alkaline and show an A-type geochemical signature with high Na₂O + K₂O and Zr + Nb + Ce + Y content, K₂O/MgO, Fe₂O₃^T/(Fe₂O₃^T + MgO), REEs (rare earth elements) and 10 000 Ga/Al ratios. Based on the trace element content of zircons, they have high Th, U, Zr, Hf, and Pb abundance and obvious La and Eu anomalies, and their distribution pattern is similar to that of A-type granites. The zircon εHf(<i>t</i>) values range from 4.5 to 10.5 with Neoproterozoic <i>T</i>_DM2 ages (536–922 Ma) for Hf isotopes, and they have relatively high values of εNd(<i>t</i>) (3.14 to 3.49; <i>T</i>_DM2 = 665–693 Ma) and initial ⁸⁷Sr/⁸⁶Sr (0.723260–0.734669). Detailed elemental and isotopic data suggest that the Yizuoying granite porphyry belongs to the A₂-subtype and was formed by partial melting of a crustal source with a neoproterozoic overall residence age. Integrating new data on the oxygen fugacity of zircons and published data on the tectonic evolution, we suggest that the granite porphyry and associated Mo mineralization in the Yizuoying deposit formed in an extensional environment at ~160 Ma, related to the subduction of the Paleo-Pacific plate. The evolution of granitic magma in this period contributed to Mo mineralization.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45479695","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":"Solidification pressures and ages recorded in mafic microgranular enclaves and their host granite: An example of the world's youngest Kurobegawa granite","authors":"Kota Suzuki,&nbsp;Tetsuo Kawakami,&nbsp;Shigeru Sueoka,&nbsp;Ayu Yamazaki,&nbsp;Saya Kagami,&nbsp;Tatsunori Yokoyama,&nbsp;Takahiro Tagami","doi":"10.1111/iar.12462","DOIUrl":"10.1111/iar.12462","url":null,"abstract":"<p>Solidification pressures and ages of mafic microgranular enclaves (MMEs) and their host granite were determined and compared based on Al-in-hornblende geobarometry and U–Pb zircon dating in two sample localities in the Kurobegawa Granite. In sample KRG19-A03 from the middle unit of the pluton, the MME and the host granite yielded 0.18 ± 0.03 to 0.24 ± 0.04 GPa and 0.16 ± 0.03 to 0.23 ± 0.04 GPa, respectively. The MME and the host granite of sample KRG19-B08b from the lower unit, respectively, yielded 0.12 ± 0.02 to 0.21 ± 0.03 GPa and 0.13 ± 0.02 to 0.18 ± 0.03 GPa. In each sample locality, the estimated solidification pressures of the MME and its host granite overlap. The weighted mean ages were calculated as 0.775 ± 0.045 Ma and 0.831 ± 0.055 Ma for the MME and the host granite of KRG19-A03, respectively. The MME and the host granite of KRG19-B08b, respectively, yielded 0.672 ± 0.033 Ma and 0.735 ± 0.042 Ma. The ages for MMEs tend to be younger than the host granites, although they overlap within uncertainty. Zircon commonly occurs as the matrix minerals in both lithologies, meanwhile, zircon also occurs as early phases in plagioclase cores only in the host granites. Such differences in mode of occurrence of zircon suggest that the age variation reflects the differences in timing of zircon crystallization between the lithologies. Therefore, the MMEs record the same solidification pressures as the host granites and better represent the final solidification timing of the pluton. From these data of the MMEs, an average exhumation rate of each sample locality was estimated as 7.1–14.5 mm/year (KRG19-A03) and 5.5–14.4 mm/year (KRG19-B08b). These exhumation rates are much larger than that of the ca. 5.6–5.2 Ma Shiaidani Granodiorite (0.93–2.5 mm/year), implying that drastic change of the exhumation rate took place between ca. 5.2 Ma and ca. 0.83 Ma.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42082670","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":"Autogenic and allogenic controls on the temporal palaeographic evolution of the Himalayan foreland basin: Insights from facies analysis of the lower Siwalik succession, Kumaun Himalaya, India","authors":"Pradeep K. Goswami,&nbsp;Karuna Singh","doi":"10.1111/iar.12461","DOIUrl":"10.1111/iar.12461","url":null,"abstract":"<p>The lower Siwalik succession in the south-central Kumaun Himalaya records Middle Miocene fluvial sedimentation in the Himalayan foreland basin, the largest foreland basin of the world. Detailed facies analysis reveals three distinct facies associations, one of which is sand dominated channel deposits, and the other two are mudstone-sandstone, and mudstone dominated overbank deposits. The initial sedimentation in the region was in channels and frequently/extensively flooded overbank areas of a meandering/anastomosing river system. Activities along basement structures sometimes caused upheaval of the basin so that the streams got incised, and overbank areas rose up beyond the reach of flood waters. As a result, the fluvial sedimentation in these upland areas ceased, the sediments that had already deposited there were subjected to extensive pedogenesis, and occasionally reworked and redistributed by sheet flows and shallow channels. The channel pattern in the region gradually changed to braided type due to channel adjustments in response to rejuvenated tectonic activities and monsoon intensification in the hinterland. These factors caused increased influx of coarser sediments in the channels, which led to gradual steepening of the channel, and once the steepening crossed the threshold, the channel changed from meandering to braided type. Interpretation of our results is contrary to the general belief that Siwalik fluvial system changed from meandering streams to braided streams during the Middle Siwalik times, and the fluvial system in the studied part of the Siwalik basin underwent this change much earlier, during the sedimentation of Lower Siwalik.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44024482","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":"Origin and evolution of the Paleo-Kuril arc inferred from detrital zircon U–Pb chronology in eastern Hokkaido, NE Asia","authors":"Futoshi Nanayama,&nbsp;Toru Yamasaki,&nbsp;Toshiya Kanamatsu,&nbsp;Hideki Iwano,&nbsp;Tohru Danhara,&nbsp;Takafumi Hirata","doi":"10.1111/iar.12458","DOIUrl":"10.1111/iar.12458","url":null,"abstract":"<p>The Nemuro and Saroma Groups and Yusenkyo Formation occur in eastern Hokkaido and are considered to be forearc or intra-arc basin sediments of the Paleo-Kuril arc (PKA) deposited during the Late Cretaceous to middle Eocene. To further clarify the origin of the PKA, we examined the U–Pb ages of detrital zircons within these sandstones and acidic tuff beds; based on our results, we drew the following conclusions. (1) The PKA originated from an oceanic island arc on the oceanic Izanagi Plate around 85 Ma, to which the Nikoro Group greenstone complex was accreted between 81–80 Ma; the Lowest Unit of the Saroma Group covered the surface of the Nikoro accretional greenstone complex. (2) The PKA then first collided with NE Asia around the beginning of the deposition of the Hamanaka Formation (~70 Ma) and transitioned to a continental arc adjacent to NE Asia. This collision generated giant slump beds during deposition of the Akkeshi Formation. During deposition of the Kiritappu Formation, the entire Nemuro Peninsula was uplifted, supplying large volumes of clastic sediments. (3) Although we do not have data directly bearing on why the North American Plate was established in the edge of NE Asia, we speculate that it separated from the Eurasian continent around ~70 Ma when NE Asia first collided with the PKA. Subsequently, the PKA has behaved as part of the North American Plate. The Paleo-Japan arc (or East Sikhote–Alin arc) and the PKA became joined via the Hidaka Belt. Around 40 Ma, during the deposition of coarse conglomerate beds of the Urahoro Group, the PKA was uplifted and bent clockwise due to a second collision with NE Asia. (4) The modern Kuril arc was established around 36 Ma (late Eocene–early Oligocene), and the Kuril backarc basin opened into the present tectonic setting in the late Oligocene–early Miocene.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41767861","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":"Middle Devonian ostracods from the Naidaijin Formation, Kurosegawa belt, Kyushu, Japan: Paleoecological and paleogeographical significance","authors":"Gengo Tanaka","doi":"10.1111/iar.12459","DOIUrl":"10.1111/iar.12459","url":null,"abstract":"<p>This study reports five ostracod taxa from the Middle Devonian Naidaijin Formation, Kumamoto Prefecture, Kyushu, Japan comprising shelf-nearshore beyrichiid and bairdiocypridoid species, and two species of <i>Bairdia</i>. This is the first report of ostracod fossils from the Devonian strata in the Kurosegawa belt. Most analyzed fossils are the same species as those found in the Middle Devonian strata of Yunnan and Guangxi provinces in South China, indicating that the Kurosegawa belt of Kyushu shared biogeographical affinities with the palaeo-equatorial South China paleocontinent.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43398121","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":"Age, petrogenesis, and tectonic implications of the late Permian magmatic rocks in the Middle Gobi volcanoplutonic Belt, Mongolia","authors":"Ariuntsetseg Ganbat,&nbsp;Tatsuki Tsujimori,&nbsp;Laicheng Miao,&nbsp;Inna Safonova,&nbsp;Daniel Pastor-Galán,&nbsp;Chimedtseren Anaad,&nbsp;Shogo Aoki,&nbsp;Kazumasa Aoki,&nbsp;Munkhnasan Chimedsuren","doi":"10.1111/iar.12457","DOIUrl":"10.1111/iar.12457","url":null,"abstract":"<p>The Mongol–Okhotsk Belt, the youngest segment of Central Asian Orogenic Belt, was formed by the evolution and closure of the Mongol–Okhotsk Ocean. The oceanic closure formed two volcanoplutonic belts: Selenge Belt in the north and the Middle Gobi Belt in the south (in present day coordinates). However, the origin and tectonic evolution of the Mongol–Okhotsk Belt in general, and the origin and formation age of the Middle Gobi Belt in particular, remain enigmatic. To better understand the history of the magmatic activity in the Middle Gobi Belt, we conducted geochemical, U–Pb geochronological, zircon Hf, and whole-rock Nd isotopic analyses of samples from the Mandalgovi volcanoplutonic suite, the major component of the Middle Gobi Belt. Our results show that the plutonic rock consists of ~285 Ma gabbro, ~265 Ma biotite-granite and ~250 Ma hornblende-granodiorite. The volcanic counterpart is represented by a Permian Sahalyn gol rhyolite and ~247 Ma Ikh khad andesite. The geochemical compositions of biotite-granite and hornblende-granodiorite indicate that their precursors were metagraywacke and amphibolite, respectively. They are characterized by positive whole-rock ε_Nd(<i>t</i>) and zircon ε_Hf(<i>t</i>) values, indicating juvenile protoliths. The gabbro was derived by partial melting of a metasomatized lithospheric mantle source in a supra-subduction setting. The biotite-granite and Sahalyn gol rhyolite are formed by remelting of sediments in an inter-arc extension setting. Later the hornblende-granite and Ikh khad volcanic were emplaced at a volcanic arc formed by the subduction of the Mongol–Okhotsk Ocean. We conclude that the magmatic rocks of the Middle Gobi Belt formed in an active continental margin setting. Considering the consistent distribution of coeval arc-derived magmatic formations along the southern margin of the Mongol–Okhotsk Belt, the oceanic basin was closed in a relatively simultaneous manner.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45224460","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":"Stratigraphic reconstruction of the lower–middle Miocene Goto Group, Nagasaki Prefecture, Japan","authors":"Shoichi Kiyokawa,&nbsp;Masaru Yasunaga,&nbsp;Takanori Hasegawa,&nbsp;Ayako Yamamoto,&nbsp;Daisaku Kaneko,&nbsp;Yuta Ikebata,&nbsp;Noriko Hasebe,&nbsp;Yukiyasu Tsutsumi,&nbsp;Mami Takehara,&nbsp;Kenji Horie","doi":"10.1111/iar.12456","DOIUrl":"10.1111/iar.12456","url":null,"abstract":"<p>The Goto Islands are located at the westernmost tip of the Japan archipelago, and preserve a lower–middle Miocene sedimentary sequence deposited during rifting of the continental margin and opening of the Sea of Japan. The stratigraphy of the Goto Group and new K–Ar, fission-track, and U–Pb age data were used to determine the initial conditions of rifting in southwest Japan. The thickness of the Goto Group is 2000–3000 m. The lower unit (ca. 22–17.6 Ma) consists of thick, greenish, volcaniclastic rocks with basaltic volcanic material, representing the initial stages of continental rifting. The middle unit (ca. −17.6 Ma) consists of alternating sandstones and shales deposited in lacustrine and meandering fluvial environments in a syn-rift sedimentary basin during a period of volcanic activity. The upper unit (ca. 17.6–16.8 Ma) consists of thick sandstones of fluvial–deltaic facies that were deposited during rapid subsidence at the continental margin. This unit was deposited by a large fluvial system that flowed into the Sea of Japan. These sequences contain relatively cooler to warmer flora (Daijima-type) and record the warm period of the Miocene Climatic Optimum. The Goto felsic volcanic rocks (16.8 ~ 15.4 Ma) unconformably overlie the Goto Group, and granitic magmatism (ca. 16–14.5 Ma) occurred after sedimentation of the Goto Group. The widespread lacustrine, meandering–braided fluvial, and vast deltaic systems of the Goto Group, and felsic volcanism, were formed due to rapid subsidence that produced a horst-and-graben basin during the early stages of rifting of a volcanic arc along the eastern margin of Eurasia. These events occurred from 22.0 to 16.8 Ma before and during the formation of the Sea of Japan.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12456","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45043680","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":"2022 Island Arc Award","authors":"","doi":"10.1111/iar.12451","DOIUrl":"10.1111/iar.12451","url":null,"abstract":"&lt;p&gt;&lt;b&gt;Title: A visage of early Paleozoic Japan: Geotectonic and paleobiogeographical significance of Greater South China&lt;/b&gt;&lt;/p&gt;&lt;p&gt;&lt;b&gt;Author: Yukio Isozaki&lt;/b&gt;&lt;/p&gt;&lt;p&gt;&lt;b&gt;Reference: &lt;i&gt;Island Arc&lt;/i&gt; (2019), &lt;i&gt;28&lt;/i&gt;, e12296&lt;/b&gt;&lt;/p&gt;&lt;p&gt;Tectonic evolution of Great South China (GSC) during early Paleozoic is fundamental for considering the origin of the Japanese Islands, but has not been fully understood. Nevertheless, zircon U–Pb ages from Paleozoic granitoids and sandstones have provided critical information on the continental margin along which proto-Japan began to grow. Based on currently available dataset of the dating as well as paleogeographic data, Isozaki (2019) reconstructed the early Paleozoic evolution of Japan. He suggested that the tectonic setting changed from a passive continental margin (Stage I) to an active margin (Stage II) during Cambrian when the oldest arc granitoid, high-P/T blueschist, and clastic sediments were formed. The predominant occurrence of Neoproterozoic zircons in Paleozoic rocks indicates that the relevant continental block was a part of South China, which probably formed a northeastern segment of GSC. He estimated that GSC was probably twice as large as the present conterminous South China. In addition, he summarized the faunal characteristics of the Permian marine fauna in Japan, which are in good accordance with the relative position of GSC with respect to the North China block during the late Paleozoic. This extensive summary and novel reconstruction provided clear pictures of the geological history of the Japanese Islands and prospective for future researches to the readers of Island Arc. Therefore, we identified that the paper by Isozaki is suitable for Island Arc Award in 2022.&lt;/p&gt;&lt;p&gt;&lt;/p&gt;&lt;p&gt;Yukio Isozaki, the Professor Emeritus of the University of Tokyo, has broad expertise in histrorical geology, tectonics, and paleontology. He received his Ph.D from Osaka City University in Geology in 1986. He has worked as an Associate Professor and Professor in Yamaguchi University, Tokyo Institute of Technology, and the University of Tokyo until his retirement in last year. His research started in the analysis of ancient accretionary complexes using microfossils and geochronological dating. By proposing and utilizing the concept/scheme of ocean plate stratigraphy (OPS), he clarified the overall piled nappe structure of Southwest Japan, and synthesized the geological history of the Japanese Islands. His interest expands into the history of life, in particular, on mass extinction events in the past and relevant rapid biodiversification. His main targets include the biggest extinction in history across the Paleozoic-Mesozoic boundary and Cambrian-Ordovician biodiversification. He coined the term “superanoxia” for the long-term oxygen depletion in the Permo-Triassic superocean, a unique C-isotope episode named “Kamura event”, and proposed a possible scenario named “plume winter” for the mass extinction. Considering his ex","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.12451","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"62641153","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":"Multistage zircon growth recording polyphase metamorphic evolution caused by pulsed granitoid intrusions into a low-P/T type metamorphic belt: P–T–D–t evolution of migmatites in the Ryoke belt, southwest Japan","authors":"Tetsuo Kawakami,&nbsp;Tomoe Ichino,&nbsp;Keiichi Kazuratachi,&nbsp;Shuhei Sakata,&nbsp;Kota Takatsuka","doi":"10.1111/iar.12454","DOIUrl":"10.1111/iar.12454","url":null,"abstract":"<p>We report contrasting pressure–temperature–time (<i>P–T–t</i>) paths of migmatites developed in the highest-grade metamorphic zone (Grt–Crd zone) and the contact metamorphic zone (Crd–Kfs zone) of the Mikawa area, Ryoke belt, southwest Japan to discuss the complex <i>P–T–D–t</i> evolution of the middle crust that experienced pulsed granitoid intrusions. In the Grt–Crd zone, sillimanite-grade high-<i>T</i> metamorphic condition prevailed from ca. 97 to 87 Ma, followed by cooling to ~500 °C, ~4 kbar. The intrusion of gneissose granitoids below the Grt–Crd zone isobarically reheated the Grt–Crd zone rocks again to the sillimanite-grade high-<i>T</i> condition at ca. 84 Ma. This was followed by ca. 71–70 Ma contact metamorphism. Ductile deformation that formed and folded the foliation of migmatites started before ca. 89 Ma and continued at least until ca. 84 Ma in the Grt–Crd zone. On the other hand, ca. 74 Ma age of the Crd–Kfs zone migmatite developed around the Inagawa Granodiorite in addition to ca. 70 Ma age of a syn-tectonic pegmatite vein revealed that the intrusion of “75–69 Ma granitoids” caused partial melting and locally triggered low-strain ductile deformation in their contact aureoles. Comparison with other areas of the Ryoke belt suggests that plutono-metamorphic evolution of the Mikawa and Aoyama areas are similar with each other in that ca. 80 Ma reheating events (i.e., contact metamorphism) are observed, while absence of separate reheating event postdating peak metamorphism in the Yanai area is a rather uncommon feature in the Ryoke belt.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43734689","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":"Trace-element composition of zircon in Kofu and Tanzawa granitoids, Japan: Quantitative indicator of sediment incorporated in parent magma","authors":"Yusuke Sawaki,&nbsp;Hisashi Asanuma,&nbsp;Shuhei Sakata,&nbsp;Mariko Abe,&nbsp;Takeshi Ohno","doi":"10.1111/iar.12455","DOIUrl":"10.1111/iar.12455","url":null,"abstract":"<p>Zircon is one of the most important minerals in geochronologic research. Isotopic ratios and trace elements in zircons are expected to reflect those of their parent magmas. Many geochemical researchers have proposed various discrimination diagrams for zircon to indicate tectonic setting and to identify source rock. Because most detrital zircons accumulated at river mouths are derived primarily from granitoids, the classification of zircon within granitoids is potentially meaningful. In our research, we focused on sediment involvement during granitoid formation and tried to identify trace-element compositions in zircon that are sensitive to variation in sediment incorporation. To accomplish this, we examined trace-element compositions of both the granitoids and the included zircons in the Kofu granitic complex and the Tanzawa tonalitic plutons in Japan. Among the high-field-strength elements (Th, U, Ta, Nb, Hf, and rare earth elements), only Nb and Ta concentrations in the granitoids increased as the rate of sediment contribution increased. However, the zircon did not show such trends in Nb and Ta content. Zircon Y and P contents exhibited a positive correlation, indicating that xenotime substitution occurs to some extent. Because P exists as pentavalent ions in igneous systems, its presence likely affects the concentrations of pentads in zircon. When we divided the Nb and Ta contents by the P content, it became clear that zircon Nb/P and Ta/P ratios increase depending on sediment involvement. While some exceptions exist, we found that zircon Yb/Gd ratios also respond to sediment involvement. Our data further demonstrated that zircons in granitoids with significant sediment incorporation are characterized by low Ce/P contents, which is partly attributable to monazite crystallization before zircon saturation. This study demonstrates that combining these element ratios is useful for indicating sediment incorporation.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"31 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2022-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43120692","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}