Geochemistry Geophysics Geosystems最新文献

{"title":"Magnetic Characterization of Sediment Source-To-Sink Processes in the Bengal Fan Since 45 ka","authors":"Rong Huang,&nbsp;Liao Chang,&nbsp;Shishun Wang,&nbsp;Pengfei Xue,&nbsp;Shengfa Liu,&nbsp;Xuefa Shi,&nbsp;Somkiat Khokiattiwong,&nbsp;Narumol Kornkanitnan","doi":"10.1029/2024GC011784","DOIUrl":"https://doi.org/10.1029/2024GC011784","url":null,"abstract":"<p>The Bengal Fan is the largest submarine fan on Earth with a complex submarine channel system. Therefore, it is challenging to understand the evolution of Bengal Fan sediment source-to-sink processes. Here we present a synthesis of high-resolution environmental magnetic records of five sediment cores from the central and lower Bengal Fan to reconstruct sedimentation history for the past 45 ka. Rock magnetic measurements and electron microscopic analyses reveal that detrital (titano)magnetites are the dominant magnetic minerals in the central fan sediments, while lower fan deposits exhibit enhanced magnetofossil contribution. During the last three marine isotope stages, glacial periods have increased detrital magnetic mineral concentration and grain size compared with interglacial periods. This increase is primarily attributed to the weakening of the Indian summer monsoon. Spatially, magnetic mineral concentration and grain size show decreasing trends from north to south and from east to west in the Bengal Fan, which may be modulated by submarine channel shifts. Deposition center migration driven by sea level fluctuations and sediment provenance variations were key factors controlling magnetic mineral concentration and grain size. Therefore, magnetic proxies serve as sensitive indicators of sedimentation patterns within the Bengal Fan. The spatiotemporal distribution of magnetic particles provides valuable insights into the source-to-sink dynamics and the dominant factors affecting sediment transportation in global submarine fans.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 2","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011784","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143370078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Petrogenesis of Plagioclase Ultraphyric Basalts (PUB) From the Northeastern (NE) Pacific Ridge System: Evidence From Mineral Textures and Geochemical Characteristics","authors":"John B. Hewitt,&nbsp;Gokce K. Ustunisik,&nbsp;Roger L. Nielsen","doi":"10.1029/2024GC011835","DOIUrl":"https://doi.org/10.1029/2024GC011835","url":null,"abstract":"<p>Plagioclase crystals in plagioclase ultraphyric basalts (PUB) record changes in the major, trace, and isotopic compositions of evolving magmas. Those changes represent the record of specific processes in the crust and upper mantle that impart distinct crystal textures onto which chemical signatures are written. The extent to which the type and abundance of plagioclase textures and chemical signatures identified in one tectonic setting are found in others is still unclear. Here we report on the textural and compositional characteristics of PUB lavas from the Northeastern (NE) Pacific Ridge system (Juan de Fuca Ridge, Blanco Fracture Zone, and Gorda Ridge). The NE Pacific Ridge system exhibits a variety of populations of plagioclase megacrysts. The distribution of textural and compositional characteristics (e.g., single mode, bimodal, or trimodal distribution) are consistent with the presence of more than one parental magma in some samples. In PUB lava from the NE Pacific, we found that the populations of different textural types of plagioclase megacrysts are not compositionally distinct. Specifically, in any individual sample, there is no correlation of texture with major and trace element composition. We interpret the disconnect between texture and composition to be indicative of a system characterized by mixing of similar batches of magma resulting in populations of plagioclase megacrysts dominated by homogeneity or small degrees of normal/reverse zoning in most but not all cases. Furthermore, the populations of megacrysts and glomerocrysts are distinct in each sample and not correlated with their setting (on-axis, off-axis, or intra-transform basin).</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 2","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011835","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143370077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Chemical Weathering and Erosional Response of Northern New Guinea to Orbital-Scale Climate Variability","authors":"Yifan Du,&nbsp;Peter D. Clift,&nbsp;Andrew Carter","doi":"10.1029/2024GC011883","DOIUrl":"https://doi.org/10.1029/2024GC011883","url":null,"abstract":"<p>The island of New Guinea comprises arc-ophiolite units tectonically imbricated with continental rocks offscraped from the colliding Australian plate and contributes large amounts of sediment to the ocean. A sequence deposited close to the north shore and sampled at International Ocean Discovery Program (IODP) Site U1485 is largely formed from sediment delivered by the Sepik River. We reconstruct changing intensities of chemical weathering and source bedrock contributions for 330 ka to assess how they are influenced by orbitally driven climate change. Higher smectite/kaolinite ratios indicate a more seasonal chemical weathering during glacial times, with interglacial periods marked by more tropical weathering. Nd and Sr isotopes show that erosion of continental bedrock is at its maximum during interglacial periods when rainfall was more intense and penetrated deeper into the Highlands, where silicic units are preferentially exposed. During colder/drier time, erosion is more focused in arc-ophiolite lowland regions. The Chemical Index of Alteration (CIA) and several other major element proxies imply a gradual increase in the alteration intensity of sediments due to chemical weathering. Comparing the bulk sediment and source rock compositions shows long-term variability in the consumption rates of CO₂. Weathering is most effective at removing atmospheric CO₂ during glacial times when ΔCO₂ values (mol/kg) reach around three times those seen in major mainland Asian river systems. Conversely, CO₂ consumption is reduced during interglacial maxima, implying that weathering in New Guinea, controlled by orbital cycles, may amplify global climate variations.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 2","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011883","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143248734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Constraining Soil Hydrothermal CO2 Degassing Across the Changbaishan Volcanic Area: Insights From 13C-14C Perspective","authors":"Linan Wang,&nbsp;Jun Zhong,&nbsp;Mao-Liang Zhang,&nbsp;Guo-Ming Liu,&nbsp;Si-Liang Li,&nbsp;Sheng Xu","doi":"10.1029/2024GC011914","DOIUrl":"https://doi.org/10.1029/2024GC011914","url":null,"abstract":"<p>Soil hydrothermal CO₂ represents important forms of diffuse degassing in volcanic areas, but the corresponding CO₂ output remains unclear. Herein, we investigated geochemical features of soil gas, that is, soil gas components, carbon isotopic compositions of soil CO₂ (δ¹³C-CO₂ and Δ¹⁴C-CO₂), and soil CO₂ fluxes in the Changbaishan volcanic area (CHV). The geochemical characteristics of soil gas in diffuse degassing structures differed significantly from those in volcano-affected structures. Specifically, soil CO₂ concentrations were up to 2.5 × 10⁵ ppm, with δ¹³C-CO₂ values ranging from −6.2‰ to −1.6‰ and Δ¹⁴C-CO₂ values spanning from −996‰ to −845‰, showing significant hydrothermal CO₂ signatures. The isotopic mixing model was constructed to estimate the contribution of hydrothermal, biogenic, and atmospheric CO₂ to soil CO₂. The results showed that soil CO₂ in diffuse degassing structures was predominantly derived from hydrothermal CO₂, while soil CO₂ in the volcano-affected structures was mainly derived from biogenic CO₂. Combined with the soil CO₂ fluxes, it was concluded that the hydrothermal CO₂ output through soil degassing was 5.83 × 10⁴ t yr⁻¹ in CHV, significantly lower than previous estimates. We found that hydrothermal CO₂ release in CHV exceeded the CO₂ consumption through silicate weathering, thereby acting as the carbon source. We also estimated the hydrothermal soil CO₂ output from global volcanoes based on literature-published values from 80-degassing volcanoes, which was ∼150 Mt yr⁻¹. Our results highlighted the importance of conducting ¹³C-¹⁴C investigations in global volcanic areas to replenish the database of hydrothermal CO₂ output in different forms and subsequently evaluate their climatic implications.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 2","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011914","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143248772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Terrestrial Thermometer Using Carbonate Clumped Isotopes From Gar Scales","authors":"Katelyn E. Gray,&nbsp;Mark T. Brandon","doi":"10.1029/2024GC011714","DOIUrl":"https://doi.org/10.1029/2024GC011714","url":null,"abstract":"<p>We present a new clumped isotope calibration relating temperature to the Δ₄₇ composition of the bioapatite scales of gar fish (Lepisosteidae family). Modern gars live at &lt;∼3 m depth in rivers and lakes, are non-migratory, and their scales grow continuously over their lifespan (∼8–14 years). As ectotherms, their body temperature is equivalent to ambient water temperature. These features indicate that the Δ₄₇ composition of gar scales may be useful for measuring the surface temperature in present and past terrestrial settings. Fossil gar scales are widely distributed in time (Cretaceous to modern) and location (North and South America, Europe, India, and Africa), and are highly mineralized and resistant to diagenesis. Our calibration is based on modern gars collected from eight locations in North America. We use climate data to convert the variable temperature in the gar's habitat into an effective temperature, <i>T</i>_e, to account for variable growth. For our samples, <i>T</i>_e ranges from 13.8 to 27.1°C. We report a lab protocol for measuring the Δ₄₇ composition of gar scale bioapatite with a reproducibility of 0.019‰ (1 SD). Our calibration is based on 19 samples, with ∼3 replicate measurements per sample. The result is Δ₄₇ = (0.1206 ± 0.0171) × 10⁶/<i>T</i>_e² – (0.7429 ± 0.0587) (1 SE), with <i>R</i>² = 0.75 (Δ₄₇ in ‰ and <i>T</i>_e in K). The slope of this calibration is steeper than that for the lab-controlled precipitation of inorganic carbonate. We argue that this difference is caused by kinetic isotope effects associated with hydroxyapatite biosynthesis.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 2","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011714","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143111672","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Mechanisms of Aqueous Fluid Infiltration and Redistribution in a Lower-Crustal Pseudotachylyte-Bearing Fault","authors":"Stephen Paul Michalchuk,&nbsp;Mona Lueder,&nbsp;Nils B. Gies,&nbsp;Markus Ohl,&nbsp;Jörg Hermann,&nbsp;Oliver Plümper,&nbsp;Luca Menegon","doi":"10.1029/2024GC011968","DOIUrl":"https://doi.org/10.1029/2024GC011968","url":null,"abstract":"<p>Coseismic fracturing in the strong, dry, and metastable plagioclase-rich lower-crust is an effective mechanism for creating pathways for fluids to infiltrate the host rock, kick-start metamorphism, and potentially lead to rheological weakening. In this study, we have characterized the damage zone flanking a lower-crustal pseudotachylyte (solidified frictional melt produced during seismic slip) within an anorthosite to determine the mechanisms of incipient aqueous fluid infiltration and redistribution in a lower-crustal seismogenic fault. Pulverization-style fracturing of the host anorthosite resulted in the comminution of the host plagioclase (plagioclase₁) grains and the growth of very fine (&lt;20 μm) grained secondary plagioclase neoblasts (plagioclase₂) filling the fractures. Fluid-assisted grain growth accompanied surface- and strain-energy minimization grain growth in the healing and sealing of the fractures. This process was not associated with the densification nor the creation of new reaction-induced porosity. Fourier transform infrared maps transecting the damage zones show the presence of H₂O species along the plagioclase₁ and plagioclase₂ grain boundary regions, as well as incorporated into plagioclase₂ grain interiors. Grain-size sensitive creep of fine-grained plagioclase localized along the pseudotachylyte margin where fracturing was most pervasive. In the absence of reaction-induced porosity, strain localization is determined by repeated occurrences of extreme grain-size reduction in addition to the mobilization of aqueous fluid to the grain boundary regions, to the extent in which these fine-grained wet plagioclase₂ layers are volumetrically dominant over dry, coarse plagioclase₁ fragments. This forms a layer capable of deforming by grain-size sensitive creep and sustaining the mobility of fluids.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 2","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011968","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143111671","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Flow- and Fracture-Driven Bubble Throat Growth Rates and Dynamic Permeability in Crystallizing Magma","authors":"P. Moitra,&nbsp;A. Albadi,&nbsp;A. Tatsch,&nbsp;P. Santra","doi":"10.1029/2024GC011932","DOIUrl":"https://doi.org/10.1029/2024GC011932","url":null,"abstract":"<p>Pyroclasts typically exhibit coalesced vesicle textures, which are the evidence of bubble coalescence and the incomplete bubble wall retraction in magma during volcanic eruptions. The sizes of bubble throats or inter-bubble apertures in permeable networks control the extent of magma outgassing, and therefore, quantifying the growth rates of the bubble throats is important but has remained poorly constrained. Using dynamically similar experiments with spontaneous bursting of a single bubble in rheologically well-characterized particulate suspensions, we investigate the growth rate of bubble throats for a range of particle volume fractions. For suspensions with <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>≲</mo>\u0000 </mrow>\u0000 <annotation> $lesssim $</annotation>\u0000 </semantics></math>0.50 particle volume fraction, a circular hole (bubble throat) forms following bubble bursting, which after an initial fast growth starts plateauing at a throat-bubble size ratio of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>≳</mo>\u0000 </mrow>\u0000 <annotation> $gtrsim $</annotation>\u0000 </semantics></math>0.20. The throat growth time scale overall increases with increasing particle volume fraction due to the increase in suspension viscosity. On the other hand, bubbles in suspensions with particle volume fraction near the maximum packing fraction (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>∼</mo>\u0000 </mrow>\u0000 <annotation> ${sim} $</annotation>\u0000 </semantics></math>0.64) exhibit a fracture-like opening. Thus, our experimental results suggest that the plateauing of the bubble throat growth in crystal-poor to crystal-rich magma likely contributes to the wide occurrence of the incompletely retracted vesicle walls in pyroclasts. The implications of the flow- to fracture-like growth of bubble throats on the development of dynamic permeability in magma are discussed.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 2","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011932","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143121221","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Origin of Ultrapotassic, Ultracalcic, Ultrabasic SiO2-Undersaturated Magmas: The Case Study of the Pleistocene Cupaello Kamafugite Monogenetic Volcano, Central Italy","authors":"Michele Lustrino,&nbsp;Lorenzo Pistocchi,&nbsp;Sara Ronca,&nbsp;Francesca Innocenzi,&nbsp;Samuele Agostini","doi":"10.1029/2024GC011683","DOIUrl":"https://doi.org/10.1029/2024GC011683","url":null,"abstract":"<p>The Pleistocene (∼0.6 Ma) Cupaello monogenetic volcano, cropping out in central Italy, belongs to the Intra Apennine Province (IAP). It is represented by a single lava flow with kamafugitic composition, associated with a volumetrically limited pyroclastic deposit and a phosphate-rich layer close to the small vent. This kamafugite is characterized by ultrapotassic (K₂O = 5.2–7.6 mass %; K₂O/Na₂O = 18.0–33.9), ultracalcic (CaO/Al₂O₃ = 2.2–2.4), ultrabasic (SiO₂ = 42.6–44.1 mass %), and SiO₂-undersaturated (∼29% CIPW normative leucite) composition, with a peculiar paragenesis (kalsilite, melilite, phlogopite, clinopyroxene, calcite, olivine and glass, plus accessory phases). Trace elements (e.g., high LILE, high LILE/HFSE, negative anomalies for Nb, Ta, Ti and Eu, and Pb peaks in primitive mantle-normalized diagrams) and isotopic constraints (e.g., strongly radiogenic ⁸⁷Sr/⁸⁶Sr, unradiogenic ¹⁴³Nd/¹⁴⁴Nd, high Δ7/4) point to subduction-modified mantle sources. Cupaello products fall within the field of the IAP volcanic products, which define, as a whole, clear negative correlations of compatible and incompatible trace elements, as well as of all the other major oxides, with CaO. These trends are here interpreted as the effect of assimilation of crustal carbonates rather than the presence of a Ca-carbonatitic component in the source, as instead commonly reported in literature. Despite this general trend, we emphasize that Cupaello rocks derive from partial melting of a subduction-modified carbonated phlogopite-peridotite source, followed by a prolonged fractional crystallization of olivine- and melilite-rich kalsilitolite assemblages. A carbonatitic component is required to explain the absence of feldspars in the ultrabasic, ultracalcic and strongly SiO₂-undersaturated magma, whose composition was possibly modified in minimal amounts by carbonate assimilation at shallow depths.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011683","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143120051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Calculating Sedimentation Rates of Oxic Pelagic Clays Using Core Top Thorium Isotopes","authors":"Kassandra M. Costa,&nbsp;Frantz Ossa Ossa,&nbsp;Ann Dunlea,&nbsp;Frank J. Pavia,&nbsp;Logan Tegler,&nbsp;Maureen Auro,&nbsp;Morten Andersen,&nbsp;Sune G. Nielsen","doi":"10.1029/2024GC011717","DOIUrl":"https://doi.org/10.1029/2024GC011717","url":null,"abstract":"<p>Oxic pelagic clays are an important component of seafloor sediment that may hold valuable information about past ocean chemistry due to their affinity for and accumulation of biogeochemically important metals. We present a new approach to calculating site-specific sedimentation rates (SRs) by comparing authigenic sediment thorium isotope compositions (²³⁰Th/²³²Th) to seawater dissolved ²³⁰Th/²³²Th in a suite of deep (&gt;3,000 m) pelagic core sites. We extracted the authigenic sediment fraction using an HHAc leach protocol, which major element chemistry (Al, Mn, Fe, Ti) suggested was less affected by lithogenic contamination than the HCl leach. Four different methods were tested for extracting the appropriate initial ²³⁰Th/²³²Th from seawater: using either the nearest water column station (methods 1 and 2) or a regionally averaged profile (methods 3 and 4) and using either the bottommost profile measurement (methods 1 and 3) or linear regression of the profile and extrapolation to the seafloor (methods 2 and 4). Method 3 outperformed the other methods in reconstructing previously published SRs from pelagic clays in the North Pacific. The new thorium-based SRs were then combined with estimates from the total sediment thickness on ocean crust and non-lithogenic cobalt accumulation to determine the best estimates for SRs of oxic pelagic clays. The Pacific has the lowest SR (median 0.28 cm/kyr), while the Atlantic is higher (median 0.46 cm/kyr) and the Indian Ocean is highest (median 0.75 cm/kyr). These new estimates are consistent with the expected spatial patterns of sedimentation, but they revise the absolute SR values downward from available gridded SR maps.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011717","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143118854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Footwall Geology and Deformation at Flip-Flop Mid-Ocean Ridge Detachment Faults: 64°35′E Southwest Indian Ridge (SWIR)","authors":"S. Mahato,&nbsp;M. Cannat","doi":"10.1029/2024GC011769","DOIUrl":"https://doi.org/10.1029/2024GC011769","url":null,"abstract":"<p>Using bathymetry and ROV dives, we investigate two successive flip-flop detachment faults (D1 active, D2 older) in the near-amagmatic 64°35′E region of the SWIR. Kilometer-sized benches on the upper slopes of D1 footwall form the D1 degraded breakaway. Scarps at the top expose the D2 fault zone with deformed serpentinized peridotite, sigmoidal phacoids, planar fractures, and serpentinite microbreccia/gouge horizons. Two ROV sections of the D1 footwall show contrasting deformation styles, corresponding to distinct morphological domains, which relate to contrasting fault and footwall strength. One section documents corrugations, outcrops dominated by sigmoidal phacoids, and planar fractures with thin, discontinuous serpentinite microbreccia/gouge horizons. ROV dives in this corrugated domain show that NNE-trending km-spaced ridges and WNW-trending narrow benches in the shipboard bathymetry correspond, respectively, to broad undulations (mega-corrugations) of the D1 fault and to several antithetic minor normal faults (cumulated horizontal offset of ∼285 m). The other section, lacking corrugations, broad ridges, and antithetic fault, has thicker and more continuous serpentinite microbreccia/gouge horizons, indicating a weaker fault. The abundance of such weak gouges probably reflects hydrous fluid availability during deformation. We link mega-corrugations in the western domain and km-scale lobes of D1 emergence to a broad detachment damage zone with up to ∼600 m-thick mega-phacoids of less deformed serpentinized peridotite. Small antithetic normal faults in the corrugated domain are interpreted as due to bending forces in the D1 footwall. Our findings highlight the three-dimensional, non-planar structural and morphological variability of the exhumed D1 detachment fault zone along the ridge-axis.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011769","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143118855","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}