Island Arc最新文献

{"title":"Reexamination of the Neogene Paleostress Field Using Fault-Slip Data From Jogashima, Miura Peninsula, Central Japan","authors":"Toru Sakai,&nbsp;Hideo Takagi","doi":"10.1111/iar.70038","DOIUrl":"https://doi.org/10.1111/iar.70038","url":null,"abstract":"<div>\u0000 \u0000 <p>The Neogene Misaki Formation, which occurs on the southwestern part of Jogashima Island at the southern tip of Miura Peninsula, Japan, is cut by numerous minor faults. Using fault-slip data, we reconstructed the paleostress field by stress inversion analysis. Two significant stresses, A and B, were detected. Stress A is an E–W tensional (normal-faulting) stress that is close to axial compression, and Stress B is an E–W compressional (reverse-faulting) stress that is close to axial extension. These stresses occurred after the formation of large-scale geological structures, such as the Kenzaki Anticline and Jogashima Syncline. In addition, the dip-slip faults are cut by a large dextral fault that is subvertical and strikes WNW–ESE. Therefore, this dextral fault has been active in a stress field similar to that of the present day (i.e., <i>σ</i>₁-axis oriented NNW–SSE and <i>σ</i>₃-axis oriented ENE–WSW). (143 words).</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"35 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2026-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146007808","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":"Timing of Mylonitization Based on Zircon U–Pb Ages of the Ryoke Plutonic Rocks in the Akaiwadani and Taraki Areas, Eastern Kii Peninsula, Southwest Japan: Implications for Uplifting of a Late Cretaceous Volcanic Arc on the Asian Continental Margin","authors":"Makoto Takeuchi,&nbsp;Sakurako Yabuta,&nbsp;Qi Li,&nbsp;Yoshihiro Asahara","doi":"10.1111/iar.70036","DOIUrl":"https://doi.org/10.1111/iar.70036","url":null,"abstract":"<p>The timing of mylonitization of the Ryoke Plutonic Rocks in the Tsukide area, eastern Kii Peninsula, Southwest Japan, which is part of a Late Cretaceous volcanic arc on the Asian continental margin, was investigated based on geological relationships and zircon U–Pb dating. The mylonite zone is located north of the Median Tectonic Line (MTL) and has accommodated a large displacement between the low-<i>P</i>/<i>T</i>-type Ryoke Metamorphic Complex, including the Ryoke Plutonic Rocks, and the high-<i>P</i>/<i>T</i>-type Sanbagawa Metamorphic Rocks. The mylonitization in this area was previously dated to 74–67 Ma, as determined from the K–Ar cooling ages of hornblende, biotite, and alkali feldspar. However, these ages might represent the most recent cooling ages that reflect thermal resetting by later intrusions. In this study, the timing of mylonitization was constrained by zircon U–Pb ages of a deformed granitoid and undeformed granitoid that intrudes it. Three stages of mylonitization, M1–M3, were recognized in this area. M1 is high-<i>T</i>-type mylonitization that occurred between 87.5 ± 1.7 and 83.2 ± 1.2 Ma. M2 and M3 are medium- to low-<i>T</i>-type mylonitization that occurred at ca. 77.5 Ma and after ca. 70 Ma, respectively. Top-to-the-west sense shearing occurred after M2 along shear zones that converge obliquely with the present-day MTL. The shear zone became narrower than that of M1, due to uplift and cooling, and eventually transitioned into discrete faults. M1 coincided with the change in the subducting plate beneath proto-Japan from the Izanagi Plate to the Kula Plate at 85 Ma, and M2 occurred during subduction of the Kula Plate.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70036","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145625942","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":"Correction to “Origin of Amphibole Cumulates at the Base of an Exposed Arc Crustal Section: Perspectives From Fiordland, New Zealand”","authors":"","doi":"10.1111/iar.70035","DOIUrl":"https://doi.org/10.1111/iar.70035","url":null,"abstract":"<p>Manselle, P., S. Foley, and N. Daczko. 2025. “Origin of Amphibole Cumulates at the Base of an Exposed Arc Crustal Section: Perspectives From Fiordland, New Zealand.” <i>Island Arc</i> 34, no. 1: e70030. https://doi.org/10.1111/iar.70030.</p><p>In Table 3 on page 12, the column header “<i>P</i>(kbar)” is incorrect as it indicates that pressures are given in kbar. This should be corrected to “<i>P</i>(GPa).”</p><p>Below is the correct Table 3.\u0000 </p><p>We apologize for this error.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70035","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145572294","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":"The Significant Role of the Mafic Lower Crust in the Chemical Diversity of Arc Magmas","authors":"Masao Ban,&nbsp;Jun-Ichi Kimura,&nbsp;Toshiro Takahashi,&nbsp;Yuka Hirahara,&nbsp;Tsukasa Ohba,&nbsp;Akihiko Fujinawa,&nbsp;Shintaro Hayashi,&nbsp;Takeyoshi Yoshida,&nbsp;Takashi Miyazaki,&nbsp;Nobutaka Tsuchiya,&nbsp;Shin-ichi Kagashima,&nbsp;Qing Chang,&nbsp;Ryoko Senda,&nbsp;Bogdan Stefanov Vaglarov,&nbsp;Yoshiyuki Tatsumi","doi":"10.1111/iar.70033","DOIUrl":"https://doi.org/10.1111/iar.70033","url":null,"abstract":"<p>The origin of extremely diverse arc magmas erupted along the 600-km-long Quaternary frontal arc of NE Japan was examined using Sr–Nd–Hf–Pb isotopic and major/trace elemental compositions. The major/trace element chemistry of the magmas varied with the various combinations of low-K to medium-K and calc-alkaline to tholeiitic rock suites, even within a single volcano. Nevertheless, magmas from individual volcanoes showed quasi-linear isotopic variations in the Pb–Pb and Nd–Pb isotope spaces irrespective of their complex rock suites. The isotope data indicate a binary mixing origin of the magmas derived from a mostly homogeneous mantle source and the others from an isotopically diverse crust represented by Cretaceous to Paleogene basement granitoids. Assimilation-fractional-crystallization (AFC) and melting-assimilation-storage-hybridization (MASH) processes formed the tholeiitic and calc-alkaline series, respectively. These would have occurred in the amphibolitic lower crust that constitutes the roots of the basement granitoids. This study demonstrates that the mafic lower crust extensively contributes to the chemical diversity of arc magmas, even for relatively undifferentiated basaltic andesites.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70033","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145317489","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":"Thermal Structure Around the Shibukawa Ultramafic Body of the Mikabu Greenstones in the Low-Grade Sanbagawa Schists, Northwest Shizuoka, Central Japan","authors":"Seira Katagiri,&nbsp;Yui Kouketsu,&nbsp;Katsuyoshi Michibayashi","doi":"10.1111/iar.70034","DOIUrl":"https://doi.org/10.1111/iar.70034","url":null,"abstract":"<p>The Cretaceous high-P/T metamorphic complex such as Sanbagawa schists and Mikabu greenstones is located in the outer zone of the Median Tectonic Line in the Shibukawa area, northwestern Shizuoka Prefecture, central Japan. In this area, a 2 × 1 km Shibukawa ultramafic body, a member of the Mikabu greenstones, occurs within the chlorite zone of the low-grade Sanbagawa schists. The upper part of this ultramafic body is covered by pelitic schists (classified as the Upper unit). The peak temperatures estimated from the Raman spectra of carbonaceous material (CM) in the pelitic schists were 277°C–354°C. The temperatures of the Upper unit range from 277°C to 293°C, which are lower than those of the surrounding Sanbagawa schists, ranging from 295°C to 354°C. Considering the elevation and large-scale structures of the body, the Upper unit is inferred to be a shallow, lower-grade Sanbagawa schist unit preserved in the ultramafic body, as it has a geological structure similar to that of the surrounding schists. This suggests that although the occurrence of the Shibukawa ultramafic body has complicated the geological structure of the Sanbagawa schists, the metamorphic temperature increases toward apparently lower structural levels. In addition to constraining metamorphic temperatures, it shows that the Raman CM geothermometer is a powerful tool for revealing structural characteristics based on geological and thermal relationships within low-grade metamorphic rocks in shallow subduction zones.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70034","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145111248","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":"Early Miocene Fore-Arc Magmas Derived From Subcontinental Lithospheric Mantle During the Japan Sea Opening: Geochemistry of the Ishimoriyama and Iritono Volcanic Rocks in the Iwaki District, NE Japan","authors":"Takahiro Yamamoto","doi":"10.1111/iar.70032","DOIUrl":"https://doi.org/10.1111/iar.70032","url":null,"abstract":"<p>During the Miocene opening of the Japan Sea, volcanic activity expanded greatly toward the trench due to the injection of the hot asthenosphere into the mantle wedge. The Ishimoriyama and Iritono volcanic rocks, both erupted at around 17.5 Ma in the Iwaki district on the Pacific coast of NE Japan, are products of this event. Ishimoriyama is a small composite volcano comprising calc-alkaline basaltic to andesitic volcaniclastic rocks. Iritono is a monogenetic volcano composed of low-K aphyric pillow basalts with high TiO₂ contents. The Pb isotopic compositions of volcanic rocks from both volcanoes (²⁰⁶Pb/²⁰⁴Pb = 18.39–18.40, ²⁰⁷Pb/²⁰⁴Pb = 15.61–15.62, and ²⁰⁸Pb/²⁰⁴Pb = 38.53–38.57) are more radiogenic than the Indian MORB-like trend defined by other Miocene volcanic rocks in the fore-arc region of NE Japan and overlap those of the most enriched Japan Sea Miocene basalts. The variation among the Japan Sea basalts can be explained by the mixing of depleted Indian MORB-like mantle and enriched preexisting subcontinental lithospheric mantle (SCLM). Therefore, the Ishimoriyama and Iritono volcanic rocks were derived from SCLM, and the reason why magma was generated by partial melting of the SCLM, which does not normally melt spontaneously, was due to the injection of the hot asthenosphere. The trace element abundances in the Ishimoriyama volcanic rocks match those in normal arc-type volcanic rocks, but their compositional variations suggest the fractionation of large amounts of amphibole from basaltic andesite magma. Because this differentiation process requires a high pH₂O in the parental magma, the source could have been hydrous SCLM. In contrast, the Iritono volcanic rocks are depleted in fluid-mobile elements and have convex rare earth element patterns peaking at Sm. Accordingly, this magma formed when a residual SCLM domain was re-melted by the hot asthenospheric injection. These distinct geochemical differences between two nearly contemporaneous volcanic rocks only 20 km apart indicate that the SCLM was heterogeneous, with adjacent hydrous and residual domains.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70032","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144869977","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":"Slab Tear Beneath the Sunda Strait","authors":"Luhut Pardamean Siringoringo,&nbsp;Benyamin Sapiie,&nbsp;Alfend Rudyawan,&nbsp;I Gusti Bagus Eddy Sucipta","doi":"10.1111/iar.70031","DOIUrl":"https://doi.org/10.1111/iar.70031","url":null,"abstract":"<div>\u0000 \u0000 <p>Slab tearing plays a critical role in subduction zones worldwide, as it facilitates mantle upwelling, influences magma generation, and leads to the formation of tensional structures, which may create favorable conditions for geothermal potential. Understanding its mechanisms and effects is essential for interpreting the complex geodynamics of convergent margins. This research investigates geodynamic processes in the Sunda Strait, focusing on slab tearing and its geological implications. Analysis of earthquake hypocenter data (1906–2025) reveals significant differences in slab depth between Sumatra and Java, supporting the slab tearing hypothesis. These differences arise from variations in the age and density of the subducting oceanic crust, causing sharp contrasts in slab dip angles. High heat flow in the eastern and northeastern Sunda Strait indicates mantle upwelling due to vertical and horizontal slab tearing, respectively. The presence of Sukadana Basalt (OIB-like) in eastern Lampung and normal faults in the Sunda Strait, along the eastern Lampung and western Java coasts further supports this hypothesis. Additionally, shifts in volcanic arc distribution and volcanic activity discontinuities confirm the tectonic effects of slab tearing. This study highlights how slab dip angle variations influence magma genesis and volcanic behavior. It also reveals the unique geodynamics of the transition zone between orthogonal and oblique subduction. The findings enhance understanding of geological processes in the Sunda Strait and provide insights for future research on slab tearing and regional tectonics.</p>\u0000 </div>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144869842","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 of Amphibole Cumulates at the Base of an Exposed Arc Crustal Section: Perspectives From Fiordland, New Zealand","authors":"Patrick Manselle,&nbsp;Stephen Foley,&nbsp;Nathan Daczko","doi":"10.1111/iar.70030","DOIUrl":"https://doi.org/10.1111/iar.70030","url":null,"abstract":"<p>The formation of amphibole-rich cumulates in arc settings plays a crucial role in influencing the chemistry of ascending arc magmas. However, understanding the processes of formation of these cumulates is challenging due to the subtle nature of their fractionation. This study presents new petrographic and geochemical analyses of amphibole-rich cumulate rocks from outcrops across Fiordland, New Zealand, an exposed section of the lower arc crust. Our findings show two primary styles of formation. Style 1 represents direct fractionation from a melt, and is typified by adcumulate textures, similar rare earth element concentrations, and minor mineral phases. Style 2 amphiboles show greater variations in their rare earth element contents and typically lack adcumulate textures. Our results indicate that direct igneous fractionation from a melt is the primary formation mechanism for amphibole cumulates, with minor contributions from melt–rock interaction, aligning with the amphibole sponge model. This research underscores the significance of amphibole cumulate formation in the evolution of the lower crust in arc systems and illustrates how co-crystallizing minerals and precursor assemblages can influence the chemistry of ascending magmas during metasomatism.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70030","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144833088","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":"Large Contact Aureole Overprinting the Ryoke Regional Metamorphic Zoning: Insights From the Takato–Komagane Area, Central Japan","authors":"Takuro Yoshioka,&nbsp;Hideo Takagi,&nbsp;Hiroyuki Nagahama,&nbsp;Tomoki Taguchi","doi":"10.1111/iar.70027","DOIUrl":"https://doi.org/10.1111/iar.70027","url":null,"abstract":"<p>The Ryoke metamorphic belt records the conditions of the middle–upper crust during Cretaceous crustal deformation and magmatism. To understand the development and evolution of the middle–upper crust, it is important to investigate the thermal structure of the Ryoke metamorphic belt. The Ryoke metamorphic rocks crop out widely in the Takato–Komagane area in Nagano Prefecture, central Japan. However, the spatial variations in metamorphic conditions in both areas are still unclear. We therefore investigated the metamorphic zoning and conducted Raman spectroscopy of carbonaceous material (RSCM) thermometry, chemical analyses, and pseudosection modeling of the Ryoke metamorphic rocks. The Bt, Sil–Kfs, and Grt–Crd zones in the Takato area, and the Bt, Kfs–Crd, and Grt–Crd zones in the Komagane area were redefined based on the mineral assemblages in metasedimentary rocks. The metamorphic zoning is different between the Takato and Komagane areas. We revealed that sillimanite occurs throughout both areas, although its occurrence changes gradually from in the matrix to inclusions in cordierite, between the Takato and Komagane areas. Peak <i>P</i>–<i>T</i> conditions of the Sil–Kfs zone are estimated to be 630°C–650°C and 320–380 MPa using RSCM thermometry and pseudosection modeling. Pseudosection modeling, microscopic observations, and thermometry results indicate higher temperatures in the Komagane area than in the Takato area. It is interpreted that part of the regional metamorphic belt underwent thermal overprinting induced by a late-stage pulse of the gneissose Ryoke granitoids, resulting in the formation of a metamorphic zone distinct from that in the Takato area, characterized by the occurrence of sillimanite inclusions.</p>","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70027","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144782258","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":"Microstructural Characteristics of Sheared Gabbroic Rocks From the Mado Megamullion, Shikoku Basin, Philippine Sea","authors":"Kohei Nimura,&nbsp;Katsuyoshi Michibayashi,&nbsp;Yumiko Harigane,&nbsp;Yasuhiko Ohara","doi":"10.1111/iar.70029","DOIUrl":"https://doi.org/10.1111/iar.70029","url":null,"abstract":"&lt;p&gt;This paper investigated the deformation microstructures of gabbroic rocks from the breakaway region of the Mado Megamullion (site YK19-04S-6K-1536), Shikoku Basin, Philippine Sea to constrain the processes that contribute to the mechanical weakening of the lower oceanic crust. The deformed gabbroic rocks are characterized by porphyroclastic textures consisting mainly of coarse plagioclase + clinopyroxene ± amphibole porphyroclasts and a fine-grained matrix of plagioclase + clinopyroxene + amphibole + Fe-Ti oxides ± talc. Based on macroscopic foliation development, the samples are divided into low- and high-strain domains. The low-strain domain shows weakly developed foliations and a granoblastic texture with partially preserved magmatic textures, whereas the high-strain domain shows well-developed foliation defined by monomineralic and mixed mineral layers and porphyroclastic textures. In the low-strain domains, plagioclase grains show similar crystallographic orientations and chemical compositions between porphyroclasts and surrounding matrix, consistent with deformation predominantly via dislocation creep and subgrain rotation recrystallization. Clinopyroxene porphyroclasts and adjacent brown amphibole at porphyroclast rims share similar crystallographic orientations, suggesting topotactic replacement of clinopyroxene by amphibole associated with fluid infiltration. In the high-strain domains, fine-grained plagioclase shows distinct compositions from porphyroclasts and fabric development with [100] aligned to lineation and (001) to foliation, indicating that grain nucleation occurred during deformation via fluid-assisted reactions. It suggests that the deformation could have been accommodated by a combination of dislocation creep and dissolution–precipitation creep. Fine-grained clinopyroxene within monomineralic layers exhibits a clear (010)[001] crystallographic-preferred orientation indicative of dislocation glide. In contrast, fine-grained clinopyroxene in polymineralic layers shows weaker or nearly random orientations, suggesting enhanced grain boundary sliding at clinopyroxene–amphibole interfaces. This behavior was facilitated by grain-size reduction, abundant phase mixing, and inhibition of grain growth by Zener pinning. Brown amphibole within the high-strain matrix exhibits strong crystallographic and shape preferred orientations parallel to foliation, suggesting syn-tectonic growth and alignment. Ti-rich brown amphibole formed synchronously with deformation through clinopyroxene breakdown at temperatures of 755°C–871°C, whereas Ti-poor green amphibole formed during subsequent lower-temperature (686°C–770°C) hydrothermal alteration. A comparison with the Godzilla Megamullion suggests similar fluid-mediated deformation processes are active in megamullions throughout back-arc basin environments. Our results demonstrate that melt- and fluid-assisted reactions, coupled with grain size–sensitive deformation mechanisms, contribute signifi","PeriodicalId":14791,"journal":{"name":"Island Arc","volume":"34 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2025-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/iar.70029","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144767717","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}