IF 1 4区地球科学

Island Arc Pub Date : 2025-05-26 DOI: 10.1111/iar.70017

Sakurako Yabuta, Makoto Takeuchi, Yoshihiro Asahara, Qi Li

{"title":"Origin of the Sandstone Dikes Intruding Into the Miocene Shidara Group, Southwest Japan Based on Sandstone Composition and Detrital Zircon U–Pb Ages","authors":"Sakurako Yabuta, Makoto Takeuchi, Yoshihiro Asahara, Qi Li","doi":"10.1111/iar.70017","DOIUrl":"https://doi.org/10.1111/iar.70017","url":null,"abstract":"<p>Geological conditions and fluid migration records that lead to the formation of sandstone injectites, including sandstone dikes, are attracting attention from various perspectives, including resource development. It is crucial to know the direction of intrusion from the parent sand body and the type of dike to understand the formation mechanism of sandstone dikes, while the location of the parent sand body is often unknown. Although the parent sand body of sandstone dikes intruding the Miocene Hokusetsu Subgroup of the Shidara Group in Southwest Japan is also unknown, this study has identified its parent sand body by comparing the sandstone composition and detrital zircon U–Pb age spectra of the sandstone dikes with those of each formation of the Hokusetsu Subgroup. The sandstone of the sandstone dikes are feldspathic sandstones similar to those of the lower part of the Hokusetsu Subgroup. Furthermore, the detrital zircon U–Pb ages of the sandstone dikes, which are characterized by a major cluster at about 95 Ma and minor clusters at 73–72 Ma, constrain its parent sand body among the lower Hokusetsu Subgroup. It resembles the zircon age spectrum of the lower Umedaira Sandstone Member, the uppermost horizon of the lower part of the Hokusetsu Subgroup. This means that the sandstone dikes originated from the lower part of the Umedaira Sandstone Member. This fact suggests that comparing the sandstone properties, such as sandstone composition and detrital zircon U–Pb age spectra of sandstone dikes with those of the host rock, is an effective method for identifying the parent sand body.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70017","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140343","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}

引用次数: 0

Holocene Terraces Along the Tsailiao River, Western Foothills, Southwest Taiwan: Lithofacies, Chronology, Fossil Assemblages, and Neotectonic Implications 台湾西南西麓柴辽河全新世阶地：岩相、年代学、化石组合及其新构造意义

IF 1 4区地球科学

Island Arc Pub Date : 2025-05-16 DOI: 10.1111/iar.70016

Kodai Iwasaki, Ai Kawamura, Haengyoong Kim, Yoshinari Kawamura, Chun-Hsiang Chang, Muneki Mitamura

{"title":"Holocene Terraces Along the Tsailiao River, Western Foothills, Southwest Taiwan: Lithofacies, Chronology, Fossil Assemblages, and Neotectonic Implications","authors":"Kodai Iwasaki, Ai Kawamura, Haengyoong Kim, Yoshinari Kawamura, Chun-Hsiang Chang, Muneki Mitamura","doi":"10.1111/iar.70016","DOIUrl":"https://doi.org/10.1111/iar.70016","url":null,"abstract":"<p>Understanding the geohistory of fossil-bearing strata is essential for paleontological research. The Tsailiao area in the Tsochen District of Tainan City is one of the most important terrestrial fossil sites for Quaternary mammalian paleontology in Taiwan because it has yielded the most abundant and diverse mammalian fossils. However, the stratigraphy and depositional processes of the fossil-bearing terrace deposits in the area have not been well understood because previous research is insufficient for the precise distribution of the terraces and lithological and chronological descriptions of their representative deposits. Therefore, we studied terrace deposits, focusing on their distribution and the fossils they contain, from geomorphological, stratigraphic, chronological, and sedimentological perspectives. The terraces in the study area were grouped into three different heights, T1, T2, and T3, in descending order. Meandering rivers formed the T1, T2, and T3 terraces during the early, middle-late, and late Holocene, respectively. Each terrace deposit contained a basal gravel bed that yielded diverse fossils. However, most invertebrate fossils are inconsistent with a freshwater river environment and show signs of abrasion. Thus, they are considered derived fossils from underlying basement rocks. The mammalian fossils, including those of extinct species, were also found in the terrace deposits. Since the ages of the fossils do not correspond to those of the deposits, these fossils are likewise considered derived fossils. The results of our study contribute to the understanding of the terraces in the area. Our study of the terraces is expected to provide additional knowledge for geomorphological and tectonic studies in and around the area.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70016","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144074517","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}

引用次数: 0

Geotectonic Identity of Cretaceous-Paleogene Granitoids in the Tsukuba Igneous Complex, Japan: A New Multi-Proxy Reassessment 日本筑波火成岩杂岩白垩系-古近系花岗岩类大地构造特征：一种新的多代理重新评价

IF 1 4区地球科学

Island Arc Pub Date : 2025-05-12 DOI: 10.1111/iar.70015

Wataru Fujisaki, Kanta Sato, Kazuma Iwata, Mariko Abe, Hisashi Asanuma, Masahiko Sato, Yusuke Sawaki, Kaoru Sugihara

{"title":"Geotectonic Identity of Cretaceous-Paleogene Granitoids in the Tsukuba Igneous Complex, Japan: A New Multi-Proxy Reassessment","authors":"Wataru Fujisaki, Kanta Sato, Kazuma Iwata, Mariko Abe, Hisashi Asanuma, Masahiko Sato, Yusuke Sawaki, Kaoru Sugihara","doi":"10.1111/iar.70015","DOIUrl":"https://doi.org/10.1111/iar.70015","url":null,"abstract":"<div>\u0000 \u0000 <p>To reassess the geotectonic identity of the Tsukuba Igneous Complex (TIC) granitoids, we compiled a comprehensive data set of the granitoids and associated microgranular enclaves (MGEs) using zircon U–Pb geochronology, magnetic susceptibility (MS) analysis, and whole-rock geochemistry. The TIC granitoids comprised high-K, calcic to calc-alkaline, and peraluminous I-type granite. SiO<sub>2</sub> values were relatively high, and enrichment in Pb was observed while Ti and Nb were both depleted. The trace element signatures are diagnostic indicators for rocks formed in subduction-related settings. The MGEs in the Kabasan granitoid body were almost coeval with the host granitoids at ca. 79–76 Ma. Taking into consideration the mineral and geochemical compositions between the MGEs and the host granitoids, it was concluded that the MGEs originated from diorite xenoliths. Moreover, our new zircon U–Pb dating of TIC granitoids and MGEs showed that the TIC emplacement ages are divided into two groups; that is, ca. 80–76 Ma and ca. 70–61 Ma. This fact clearly demonstrates that TIC magmatism occurred two times during the Late Cretaceous to Early Paleogene. On the other hand, the data of TIC MS is two or three orders of magnitude lower than that of San-in granitoids MS, and the TIC granitoids belong to the ilmenite-series. The MS differences between the TIC and San-in granitoids can be explained by the amount of involved sediment, indicating that the zircon U–Pb dating is the most appropriate proxy for the reassessment of the geological identity of TIC granitoids. Accordingly, we propose that the TIC granitoids have two separate origins based on the emplacement age: that is, the Late Cretaceous TIC granitoids belong to those of the Ryoke or San-yo belts, whereas the Early Paleogene TIC granitoids are considered as the eastern extension of the San-in belt.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143939124","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}

引用次数: 0

Emplacement and Cooling History of a Pluton With Evident Laminated Structure Constrained by Field Anatomy of the Kinpusan Pluton, Central Japan 日本中部金山岩体的场解剖约束下具有明显层状结构的岩体就位和冷却历史

IF 1 4区地球科学

Island Arc Pub Date : 2025-05-07 DOI: 10.1111/iar.70014

Ken Yamaoka, Daichi Murakami, Hiroshi Mori, Tokiyuki Morohoshi, Hideki Iwano, Tohru Danhara, Takafumi Hirata

{"title":"Emplacement and Cooling History of a Pluton With Evident Laminated Structure Constrained by Field Anatomy of the Kinpusan Pluton, Central Japan","authors":"Ken Yamaoka, Daichi Murakami, Hiroshi Mori, Tokiyuki Morohoshi, Hideki Iwano, Tohru Danhara, Takafumi Hirata","doi":"10.1111/iar.70014","DOIUrl":"https://doi.org/10.1111/iar.70014","url":null,"abstract":"<div>\u0000 \u0000 <p>There are limited examples of incremental emplacement models of pluton that can be demonstrated through field observations. Comprehensive field investigations identified the existence of magmatic structures of alternating layers of multiple magmatic enclave-rich and enclave-free granite sheets in the Kinpusan pluton in central Japan, which geologically constrains the geometry and duration of the intrusion time interval of the incremental magmatic unit. Most layer boundaries are inferred by the presence or absence of enclaves, and the microstructure of the granites comprising the different layers is hardly distinguishable. However, several outcrops that show clear subhorizontal structures due to grain size contrast in the host granite exist. The emplacement history consists of repetitive downward accretion of 20–200 m thick subhorizontal magma sheets with relatively high magma flux, and is a good candidate for comparison with thermal models used by many researchers in recent years. The observed grain size, aplite, and miarolitic cavities show a tendency to increase in the lower center of the body, indicating a longer period of high-temperature preservation than the pluton margin. Spatial patterns at this map scale were consistent with the predictions of the intrusion thermal model and the results of the zircon U–Pb dating together with a zircon saturation modeling, supporting the validity of the modeling.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143919520","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}

引用次数: 0

The Late Silurian Langmuri Cu-Ni Deposit in East Kunlun Orogenic Belt: An Example of Magmatic Sulfide Deposit in a Post-Collisional Extensional Setting 东昆仑造山带晚志留世Langmuri铜镍矿床：碰撞后伸展环境下岩浆硫化物矿床的一个例子

IF 1 4区地球科学

Island Arc Pub Date : 2025-04-28 DOI: 10.1111/iar.70013

Namkha Norbu, Jinchao Li, Zhouyuan Zhang, Wenjing Zhang

{"title":"The Late Silurian Langmuri Cu-Ni Deposit in East Kunlun Orogenic Belt: An Example of Magmatic Sulfide Deposit in a Post-Collisional Extensional Setting","authors":"Namkha Norbu, Jinchao Li, Zhouyuan Zhang, Wenjing Zhang","doi":"10.1111/iar.70013","DOIUrl":"https://doi.org/10.1111/iar.70013","url":null,"abstract":"<div>\u0000 \u0000 <p>The East Kunlun orogenic belt (EKOB), located in the northeastern part of the Qinghai-Tibet Plateau, is a significant Cu-Ni mineralization region associated with the geological evolution of the Paleo-Tethys and Proto-Tethys stages. Orogenic environments in this region exhibit considerable metallogenic potential, with two distinct metallogenic models: the subduction-related island arc model and the post-collisional extensional model. This study investigates the petrology, zircon U–Pb chronology, and geochemistry of ore-bearing intrusions in the Langmuri Cu-Ni deposit. The results reveal that the wehrlite yields a zircon U–Pb age of 420.0 ± 1.4 Ma, with an average ε<sub>Hf</sub>(<i>t</i>) value of −5.5 and significant Nb-Ta negative anomalies. These features suggest that the parental magma was likely derived from the partial melting of a metasomatized continental lithospheric mantle. Additionally, crustal contamination during magma ascent triggered significant crustal sulfur assimilation. The Langmuri deposit represents a mineralization event formed during the final tectonic stage of the Proto-Tethys Ocean in a post-collisional extensional setting. Slab breakoff released hydrous fluids and melts that metasomatically enriched the lithospheric mantle, thereby providing the material basis for magmatic sulfide segregation.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143884039","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}

引用次数: 0

Metamorphic History of the Yoshimi Metamorphic Rocks, Kanto Mountains, Japan: Implication From Rutile Exsolution Textures 日本关东山吉岛变质岩的变质史：来自金红石外露构造的启示

IF 1 4区地球科学

Island Arc Pub Date : 2025-04-14 DOI: 10.1111/iar.70012

Tatsuro Adachi, Ichiro Iwasaki

{"title":"Metamorphic History of the Yoshimi Metamorphic Rocks, Kanto Mountains, Japan: Implication From Rutile Exsolution Textures","authors":"Tatsuro Adachi, Ichiro Iwasaki","doi":"10.1111/iar.70012","DOIUrl":"https://doi.org/10.1111/iar.70012","url":null,"abstract":"<div>\u0000 \u0000 <p>The Yoshimi Metamorphic Rocks are composed mainly of mafic metamorphic rocks (e.g., garnet-amphibolite, garnet-clinopyroxenite, and orthopyroxene-clinopyroxene granulite) and fault-bounded pelitic gneiss. Peak metamorphic temperatures of mafic metamorphic rocks are estimated to have been approximately 800°C, based on garnet-clinopyroxene, garnet-hornblende, and orthopyroxene-clinopyroxene thermometers. Subsequently, the rocks were retrogressed and hydrated under the amphibolite facies at 0.6–0.8 GPa and around 600°C using a combination of several geothermobarometers. In mafic metamorphic rocks, exsolved rutile is found in garnet, orthopyroxene, and clinopyroxene. Such rutile probably formed during cooling from granulite to amphibolite facies. On the other hand, rutile exsolution is not observed in garnet from the pelitic gneisses, which only record a single stage of amphibolite facies metamorphism at 600°C–700°C and 1.1–1.5 GPa, as determined by garnet-biotite geothermometers and a garnet-biotite-muscovite-plagioclase-quartz geobarometer. Dating of zircon in garnet-amphibolite indicates that the protolith formed at <i>ca</i>. 120 Ma, with retrogressive amphibolite facies metamorphism at <i>ca</i>. 68 Ma. Zircons in the pelitic gneisses yield ages of <i>ca</i>. 66 Ma as an upper limit on the timing of original sedimentation and 63 Ma for metamorphism. The differences in the ages and metamorphism between the mafic metamorphic rocks and the pelitic gneisses clearly indicate they experienced different metamorphic histories, and that they were brought together during the exhumation process.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143826762","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}

引用次数: 0

Outcrop-Scale, Ring Structures Discovered in Northwestern Kyushu, Japan 日本九州西北部发现的露头规模环状结构

IF 1 4区地球科学

Island Arc Pub Date : 2025-04-06 DOI: 10.1111/iar.70011

Atsushi Yamaji

{"title":"Outcrop-Scale, Ring Structures Discovered in Northwestern Kyushu, Japan","authors":"Atsushi Yamaji","doi":"10.1111/iar.70011","DOIUrl":"https://doi.org/10.1111/iar.70011","url":null,"abstract":"<div>\u0000 \u0000 <p>Two, outcrop-scale, basaltic, ring structures were discovered in Oligocene sandstone on an abrasion platform in northwestern Kyushu, Japan. This paper aims to report their occurrence and discuss their formation mechanisms. When viewed from above, they were shaped like a teardrop and an oval with diameters of ~16 and ~6 m, respectively; and were emplaced 5.5 m apart. There were neither radial nor concentric fractures in the country rock. The smaller structure had a ring dike and is underwater for most of the time, so its observational data are much less than those of the larger structure. The latter had a cone sheet with an intrusive contact with the host rock. The structures were probably feeder pipes of the Pliocene Higashi-Matsuura Basalts which cap hills around the structures at an altitude of ~140 m. The structures provide a rare opportunity with their small sizes to gain a panoramic view of volcanic conduits in relation to their host rocks, offering valuable insights into magma processes. Basaltic breccia and intrusions with lingulate shapes were surrounded by the cone sheet. Flow banding of this sheet indicated that the sheet was formed by repeated intrusion and destruction events, and that magma's ascent through a few-decimeter-thick annular spaces formed the cone sheet. The angular projections of the outer wall of this sheet and fractures in the country rock suggest that the structures expanded their diameters by stoping. Gusts of granular flow above the level of magma fragmentation likely smoothed the originally rugged wall of arcuate openings, in which parts of the sheet were formed. There were systematic joints around the structures, and the curvatures of some of the joints suggest that the ring structures were formed simultaneously with the jointing under weak, far-field, extensional stress with roughly north–south trending, minimum horizontal stress.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143787151","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}

引用次数: 0

Weathering Effects on Luminescence Dating—An Example of the Toya Tephra in Japan— 风化作用对发光年代测定的影响——以日本托雅Tephra为例

IF 1 4区地球科学

Island Arc Pub Date : 2025-04-02 DOI: 10.1111/iar.70010

Yoshihiro Ganzawa, Naoya Katsumi, Hisatoshi Ito, Gaku Mitsuzawa, Mayuko Shimizu

{"title":"Weathering Effects on Luminescence Dating—An Example of the Toya Tephra in Japan—","authors":"Yoshihiro Ganzawa, Naoya Katsumi, Hisatoshi Ito, Gaku Mitsuzawa, Mayuko Shimizu","doi":"10.1111/iar.70010","DOIUrl":"https://doi.org/10.1111/iar.70010","url":null,"abstract":"<div>\u0000 \u0000 <p>The dating of volcanic quartz from the same volcanic source, namely the Toya pyroclastic flow deposits and the ash-fall deposits, was conducted using the red thermoluminescence method (RTL). The results yielded the anticipated ages for the pyroclastic flow deposit (99–103 ka) and considerably older ages for the ash-fall deposits (51%–83% older, 150–188 ka). This discordance is attributed to changes in the annual dose rate due to elemental migration resulting from the weathering of the ash-fall deposit. X-ray diffraction (XRD) and solid <sup>29</sup>Si nuclear magnetic resonance (NMR) analysis of the ash-fall deposits indicate that allophane/imogolite was newly generated. Furthermore, solid <sup>27</sup>Al NMR measurements indicate that the fresh glass with tetrahedral Al has undergone a transformation to the octahedral Al of allophane/imogolite. A comparison of the Ti-normalized values of elements between the pyroclastic flow deposit and the ash-fall deposit, conducted using LA-ICP-MS measurements, revealed a significant reduction in alkali and rare earth elements (REEs) and an enlargement in aluminum in the ash-fall deposit. However, the Ti-normalized values of uranium (U) and thorium (Th) showed different migration trends depending on the sample. The following weathering factors are correlated with elemental migration: (1) The release of positive ions by the weathering of volcanic glass, (2) The adsorption and desorption of ions on the surface functional groups of clay (allophane/imogolite) and iron hydroxide, (3) The high hydrophilicity of the allophane/imogolite, and (4) Non-equilibration of the U and Th decay series due to Rn release. The annual dose rate of the ash-fall deposit has been subject to fluctuations as a consequence of the weathering process. Consequently, the adoption of the present annual dose rate for the dating may result in an unexpected age. It is therefore crucial to select sediments that can ensure a closed system of element transfer.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143762085","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}

引用次数: 0

Diatom and Radiolarian Biostratigraphy in the Vicinity of the 2011 Tohoku Earthquake Source Fault in IODP Hole 343-C0019E of JFAST JFAST IODP 343-C0019E孔2011年东北震源断裂带附近硅藻和放射虫生物地层

IF 1 4区地球科学

Island Arc Pub Date : 2025-03-11 DOI: 10.1111/iar.70009

Masao Iwai, Isao Motoyama, Weiren Lin, Reishi Takashima, Yasuhiro Yamada, Nobuhisa Eguchi

{"title":"Diatom and Radiolarian Biostratigraphy in the Vicinity of the 2011 Tohoku Earthquake Source Fault in IODP Hole 343-C0019E of JFAST","authors":"Masao Iwai, Isao Motoyama, Weiren Lin, Reishi Takashima, Yasuhiro Yamada, Nobuhisa Eguchi","doi":"10.1111/iar.70009","DOIUrl":"https://doi.org/10.1111/iar.70009","url":null,"abstract":"<p>The frontal prism in the Japan Trench on the 2011 Tohoku-Oki earthquake (Mw 9.0, March 11, 2011) rupture zone had been drilled during the Integrated Ocean Drilling Program (IODP) Expeditions 343 and 343 T. We investigated fossil diatoms and radiolarians to determine age constraints on the cored sediments and reveal the behavior of sediment deformation history. Although diatoms and radiolarians abundances are varied in samples from common to rare with poor to moderate preservation in studied sediments, general biostratigraphic schemes in the North Pacific are applicable and well constrain the age of those sediments, except for samples from fault clay in which fossils were barren. These results suggest that there are three large stratigraphic gaps at ~830 mbsf between the Cretaceous chert and the upper Miocene pelagic clay, at ~820 mbsf between the upper Miocene and the Pliocene –Quaternary, and at ~670 mbsf between the upper Miocene and the Pliocene –Quaternary. The former likely represents a hiatus or unconformity derived from tectonic erosion just above the incoming Pacific Plate, and the latter two correspond to an injection of late Quaternary material above the plate boundary fault due to an increase in volcanic activity in the NE Japan arc after 8 Ma. The Upper Miocene pelagic sequence below the plate boundary décollement comprises reversed stratigraphy, suggesting deformation by thrusting, slumping, folding, etc., indicating structural complexity in the frontal prism of the subduction zone most likely due to the subduction of horst-and-graben.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70009","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143595022","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}

引用次数: 0

P–T Evolution of Paleoproterozoic Dangoli Pelitic Gneisses, Baijnath Klippe, NW Himalaya: Insights From the Geochemistry and Zircon U–Pb Geochronology 西北喜马拉雅Baijnath Klippe古元古代Dangoli泥质片麻岩P-T演化：地球化学和锆石U-Pb年代学的启示

IF 1 4区地球科学

Island Arc Pub Date : 2025-02-22 DOI: 10.1111/iar.70008

Mallickarjun Joshi, Shubham Patel, Biraja P. Das, Govind Oinam, Tanya Srivastava, Alok Kumar

{"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, Shubham Patel, Biraja P. Das, Govind Oinam, Tanya Srivastava, 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}

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