Geochemistry Geophysics Geosystems最新文献

{"title":"Recycling Subducted Organic Carbon as Diamonds: An Example From the New Caledonia Forearc Ophiolite","authors":"Jonathan C. Aitchison,&nbsp;Daniel Patias,&nbsp;Dominique Cluzel,&nbsp;Trevor R. Ireland,&nbsp;Renjie Zhou,&nbsp;Dongyang Lian,&nbsp;Jingsui Yang,&nbsp;Zhen Yan","doi":"10.1029/2025GC012250","DOIUrl":"https://doi.org/10.1029/2025GC012250","url":null,"abstract":"<p>Micro-diamonds and moissanite (SiC) have been identified in ophiolitic mantle harzburgites and chromitites of the New Caledonian Peridotite Nappe. The pale yellow (100–250 μm) micro-diamonds and light blue moissanite (mean −26.5‰, range −33.5‰ to −23.8‰ and mean −26.9‰, range −31.8‰ to −25.6‰ respectively) exhibit consistently strong negative <i>δ</i>¹³C values consistent with vegetal (C3) photosynthesis. Preservation of U-Pb ages amongst co-occurring rutile xenocrysts, with a closure temperature of 620 ± 20°C, constrains the maximum thermal conditions experienced by these rocks. These temperatures indicate that the New Caledonian diamonds did not form under the deep mantle conditions typical of conventional diamond genesis but instead within a distinct supra-subduction zone (SSZ) forearc setting. The association with moissanite suggests formation within anoxic, organic carbon-rich sediments at the top of the subducting slab or within the subduction channel under localized super-reducing conditions. In light of mantle heterogeneity, extension of the known distribution of ophiolitic diamonds to the Southern Hemisphere supports interpretation of their formation in relation to an SSZ process rather than a deep mantle source. It also highlights a previously unrecognized aspect of the global carbon cycle, underscoring the significance of SSZ forearc ophiolites in deep carbon transport and transformation.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012250","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143861813","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 Continuous 150-kyr Record of Geomagnetic Field Variations From Lake Chala, Eastern Equatorial Africa","authors":"Anita Di Chiara,&nbsp;Vassil Karloukovski,&nbsp;Barbara A. Maher,&nbsp;Maarten Van Daele,&nbsp;Thijs Van der Meeren,&nbsp;Dirk Verschuren","doi":"10.1029/2024GC011933","DOIUrl":"https://doi.org/10.1029/2024GC011933","url":null,"abstract":"<p>Records of geomagnetic field variations from continental Africa are sparse yet provide a key dating tool for low-latitude paleoclimatic changes. Long-lived tectonic and crater lakes in eastern tropical Africa potentially provide important, long (&gt;100,000 years, kyrs) and continuous sedimentary records of African monsoonal climate over past glacial and interglacial stages; the environmental backdrop to human evolution and dispersion. Here, notwithstanding its low latitude location, we present a detailed paleomagnetic record from eastern equatorial Africa extracted from the upper ∼129 m of a continuous sediment sequence drilled in Lake Chala (3°S; 37°E), a permanently stratified crater lake near Mt. Kilimanjaro. The high and stable sedimentation rate (∼0.85 m/kyr), lack of compaction and reliable paleomagnetic signal (assessed by paleo- and rock magnetic analyses) enabled the production of a new virtual geomagnetic pole (VGP) record for the last ∼150 ka for equatorial Africa. Six magnetic excursions are recorded: Blake 1 and 2, Post-Blake, Laschamp, Mono Lake and Hilina Pali. This exceptional record provides key information on the recurrence and duration of intervals of Quaternary geomagnetic instability, and independently-obtained constraints on the Hilina Pali excursion. Our new paleomagnetic record thus provides a reference data set for late-Quaternary geomagnetic excursions from African sites and a basis for better understanding of the temporal and spatial evolution of Earth's magnetic field. Finally, correlated with a revised geomagnetic instability timescale, these excursions provide a robust, independent age model for the Lake Chala sediment record, critical for correlating its paleoclimate and environmental proxy records to global reference records.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011933","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143861812","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":"Exploring Mid-to-Lower Crustal Magma Plumbing of Santorini and Kolumbo Volcanoes Using PmP Tomography","authors":"Kaisa R. Autumn,&nbsp;Emilie E. E. Hooft,&nbsp;Douglas R. Toomey","doi":"10.1029/2025GC012170","DOIUrl":"https://doi.org/10.1029/2025GC012170","url":null,"abstract":"<p>Deep-crustal magma plumbing at arc volcanoes controls the volume, frequency, and composition of magma being transported to and stored in the upper crust. However, the mid-to-lower crust remains a challenging region to image. We explore the mid-to-lower crustal velocity structure beneath the Christiana-Santorini-Kolumbo Volcanic Field (CSKVF) to better understand how an established stratovolcano and flanking volcano (Santorini and Kolumbo) are fed through the mid-to-lower crust. We use active-source seismic data to obtain a P-wave velocity model of the crust below the CSKVF. We invert direct and reflected P phases to cover the entire depth extent of the crust and solve for the Moho interface depth. Our model requires a curved Moho interface representative of crustal thickening via underplating. Results show a high <i>V</i>_<i>p</i> anomaly in the lower crust under Santorini and a mid-crustal low <i>V</i>_<i>p</i> anomaly offset from both Santorini and Kolumbo. We find that accumulation of magma is located under the local extensional basin in the upper mid-crust (&lt;10 km) but is offset at deeper depths. We find evidence for melt storage at 11–13 km depth feeding volcanism at the Kolumbo volcanic chain. This melt is also a plausible source for the 2025 seismic swarm and dike intrusion. Resolution is limited in the mid-crust below the Santorini caldera, leaving Santorini's mid-crustal magma plumbing unconstrained. We think it likely that Santorini and Kolumbo have entirely separate crustal plumbing systems and mantle sources, but allow the possibility of a connection in the mid or lower crust.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012170","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143856910","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":"Deciphering Degassing Mechanisms of He and \u0000 \u0000 \u0000 \u0000 H\u0000 2\u0000 \u0000 \u0000 ${mathbf{H}}_{mathbf{2}}$\u0000 at the Sedimentary Basin-Basement Interface by Surface Geophysics and Gas Geochemistry","authors":"E. Léger,&nbsp;P. Sarda,&nbsp;C. Bailly,&nbsp;H. Zeyen,&nbsp;M. Pessel,&nbsp;E. Portier,&nbsp;G. Dupuy,&nbsp;R. Lambert,&nbsp;A. Courtin,&nbsp;D. Guinoiseau,&nbsp;D. Calmels,&nbsp;V. Durand,&nbsp;G. Monvoisin,&nbsp;A. Battani,&nbsp;M. Moreira,&nbsp;F. Stuart,&nbsp;J. Barbarand,&nbsp;B. Brigaud","doi":"10.1029/2024GC012021","DOIUrl":"https://doi.org/10.1029/2024GC012021","url":null,"abstract":"&lt;p&gt;With the increasing importance of the carbon footprint of transport, new sources, closer to consumers, of &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; and He are explored. Within this context, we present a combined near-surface geophysical imaging, soil gas sampling, and bubbling well gas sampling approach to study fluid and gas pathways near a fault system in the Morvan massif, part of the French Massif Central, in the south-east of the Paris Basin. Electrical resistivity and seismic refraction tomography profiles allowed identifying a fault network. The co-located soil gas sampling shows a He hot-spot clearly linked to a section of one fault, suggesting a preferential pathway via water advection. Very high He concentrations, are also measured in &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{N}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;-dominated free gas from two bubbling wells very close to the soil He hot-spot. Evidence for a water reservoir with high &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{N}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;-He gas bubbles in the very shallow basement-sediment cover interface is obtained through our geophysical data. In contrast, &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; spreads more widely, pointing to biological production and consumption coupled to soil aeration, as well as a possible geological seep with diffusion processes controlled by clay/marls. The very distinct spatial variability observed for He and &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; results from these different transport processes. A simple geochemical model is proposed to explain the geochemical signature of bubble gas, rich in &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;s","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012021","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143856911","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":"Comparative Properties of Saponitic Fault Gouge and Serpentinite Muds Cored From Mud Volcanoes of the Mariana Subduction Zone","authors":"D. E. Moore,&nbsp;C. A. Morrow,&nbsp;D. A. Lockner,&nbsp;B. A. Bekins","doi":"10.1029/2024GC012100","DOIUrl":"https://doi.org/10.1029/2024GC012100","url":null,"abstract":"<p>We obtained 12 core samples for physical and chemical characterization from three serpentinite mud volcanoes (Yinazao, Asùt Tesoru, and Fantangisña) located on the forearc of the Mariana subduction system, that were drilled during International Ocean Discovery Program Expedition 366. Two samples from the Fantangisña mud volcano are interpreted to be clay-rich fault gouges derived from the subduction channel. Their bulk compositions are intermediate between the serpentinites and oceanic basalts. The oceanic crustal materials in the gouges have been thoroughly metasomatized and the serpentinites extensively altered to the trioctahedral, Mg-rich smectite clays saponite and corrensite. The only relict phases in clasts of crustal rock are accessory Ti- and P-bearing minerals. The two fault gouge samples have lower frictional strengths (<i>μ</i> &lt; 0.2) than the serpentinites (<i>μ</i> = 0.2–0.4), and their measured permeabilities are also somewhat lower. Their physical and compositional properties correspond to saponitic gouges from other faults that juxtapose serpentinite against crustal rocks, in particular gouges from the two creeping traces of the San Andreas Fault recovered in the core from the San Andreas Fault Observatory at Depth. The décollement beneath Fantangisña mud volcano is thus expected to be very weak and likely characterized by stable slip.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012100","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143856806","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":"Geochemical—Mineralogical Constraints on the Provenance of Sediment Supplied From South African River Catchments Draining Into the Southwestern Indian Ocean","authors":"E. J. Pryor,&nbsp;I. R. Hall,&nbsp;M. H. Simon,&nbsp;M. Andersen,&nbsp;D. Babin,&nbsp;A. Starr,&nbsp;A. Lipp,&nbsp;H. J. L. van der Lubbe","doi":"10.1029/2024GC011869","DOIUrl":"https://doi.org/10.1029/2024GC011869","url":null,"abstract":"<p>This study utilizes the radiogenic isotopes of neodymium (Nd) and strontium (Sr) measured in river mud —which serves as a proxy for the suspended load—to examine how source-rock lithology and weathering intensity impact the composition of material delivered to marine sediments along the Southeast African continental margin. Sediments were sampled from 22 river catchments between Durban and Cape Town in South Africa. Two distinct endmembers (i.e., geographical source areas) characterizing the regional river systems were identified. According to endmember modeling, rivers of the Eastern Cape drain soils weathered of the Karoo Supergroup and Drakensberg basalts (⁸⁷Sr/⁸⁶Sr of 0.74049 and εNd of −8.53), whereas rivers of the Southern Cape drain the Cape Supergroup, exhibiting more radiogenic ⁸⁷Sr/⁸⁶Sr ratios (0.74596) and unradiogenic εNd values (−10.09). River sediments from the Karoo Supergroup are finer-grained compared to those from the Cape Supergroup. We analyzed clay mineralogy and two grain size fractions (&lt;2 μm; 2–32 μm) from co-registered samples, and the results suggest that the spatial variability in the ⁸⁷Sr/⁸⁶Sr values is due to the lower degree of chemical weathering of silicate rocks and increased illite abundances toward the south, which a simple mixing model can explain. Kaolinite abundance decreased from Northeast to Southwest within South African coastal river catchments. In contrast, illite abundances increased due to diminished chemical weathering in the southern regions driven by the weaker rainfall regime. As demonstrated in this study, combining geochemical tools provides a reliable foundation for provenance studies of offshore marine sediment studies.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011869","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143852661","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":"Multiple Seamount Subduction and Lithological Variability Possibly Control Pore Fluid Pressure and Shallow Slow Earthquake Activity in Nankai Trough off Muroto","authors":"Paul Caesar M. Flores,&nbsp;Shuichi Kodaira,&nbsp;Gaku Kimura,&nbsp;Kazuya Shiraishi,&nbsp;Yasuyuki Nakamura,&nbsp;Gou Fujie,&nbsp;Tetsuo No,&nbsp;Yuka Kaiho","doi":"10.1029/2024GC011926","DOIUrl":"https://doi.org/10.1029/2024GC011926","url":null,"abstract":"<p>The clustered distribution of shallow slow earthquakes in the Nankai Trough has been attributed to different factors such as seamount subduction, pore fluid pressure, fluid migration, and sediment input. However, there is still a lack of comprehensive understanding of how these factors interact to generate slow earthquakes. We examined the seismic reflection profiles crossing four subducted seamounts off Muroto to understand how they deform the accretionary wedge. Along-trough seismic reflection profiles within the accretionary wedge were also used to infer the lithology of the underthrusted sediments. The seamounts are at different stages of subduction and their associated underplated sediments were identified. Comparison with published sandbox models indicates that the underplated sediments comprise fluid-rich trench fill sediments. Negative polarity decollement and transparent underthrust are observed off Muroto. The transparent underthrust is interpreted as mudstone, while stratified underthrust sediments in other regions are interpreted as turbidites. Comparing with previous numerical simulations, we propose the following deformational history: (a) subduction of the first seamount resulted in underplating of a large volume of fluid-rich trench fill sediments, (b) the underplated sediments are undergoing horizontal compression from subsequent subduction of the three seamounts resulting in high pore pressure consistent with previously reported low velocity zones, and (c) the horizontal compression may also result in fluid expulsion and these fluids migrate updip and get trapped because the mudstones serve as an impermeable cap. This mechanism accounts the aforementioned factors associated with slow earthquakes and likely controls the clustered distribution off Muroto.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011926","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143849077","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":"Assessment of Seawater Nd Isotope Signatures Extracted From Foraminiferal Shells and Authigenic Phases From Volcanogenic Sediments of the Adriatic Sea","authors":"Guohui Gao,&nbsp;Christophe Colin,&nbsp;Giuseppe Siani,&nbsp;Sophie Sepulcre,&nbsp;Rosella Pinna-Jamme,&nbsp;Frederic Haurine,&nbsp;Arnaud Dapoigny","doi":"10.1029/2024GC011992","DOIUrl":"https://doi.org/10.1029/2024GC011992","url":null,"abstract":"<p>The neodymium isotope signatures (<i>ε</i>Nd) of the authigenic fraction have been extensively used to reconstruct past seawater <i>ε</i>Nd and hydrological circulation. Among the various methods, sequential extraction of hydrogenic ferromanganese oxyhydroxides from bulk sediments represents a rapid and straightforward approach that may potentially induce artifacts due to the potential release of non-seawater-derived Nd during the extraction procedure. Here we investigated different methods for extracting past seawater Nd isotope compositions from a core collected in the Adriatic Sea whose tephra layers have been previously well documented. We analyzed <i>ε</i>Nd in planktonic foraminifera samples and in non-decarbonated sediment leachates obtained with three solutions commonly used in the context of the Mediterranean Sea: (a) 0.02 M hydroxylamine hydrochloride (HH) solution, (b) 1N HCl, and (b) a 25% (v/v) acetic acid (AA). Our results show that (a) the foraminiferal <i>ε</i>Nd remains unaffected by the diagenesis of tephra content; (b) all three methods indicate significantly more radiogenic <i>ε</i>Nd values in tephra levels (up to 1.5 <i>ε</i>Nd unit), which is attributed to tephra dissolution accounting for 2.7% of extracted Nd; (c) of the three leaching methods applied to samples with low tephra content, hydroxylamine hydrochloride (HH) yields <i>ε</i>Nd values that are more consistent with those obtained on planktonic foraminifera; (d) the <i>ε</i>Nd values of planktonic foraminifera in core MD90-917 remained constant indicating that the Adriatic deep water primarily reflects the local Nd isotope composition over the last 20 kyr.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011992","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143849102","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":"Pockmark Occurrence in the Northern Gulf of Mexico Influenced by Glacial Cycles and Hydrate Stability","authors":"A. Kumar,&nbsp;A. E. Cook,&nbsp;M. A. Lawal,&nbsp;A. Portnov,&nbsp;V. Lecours","doi":"10.1029/2024GC011781","DOIUrl":"https://doi.org/10.1029/2024GC011781","url":null,"abstract":"<p>On the continental slope of the northern Gulf of Mexico, pockmarks concentrate near the estimated updip edge of the hydrate stability zone (HSZ). We identified 5,691 pockmarks in the northern Gulf of Mexico by combining existing records with manually mapped pockmarks from bathymetric data. Nearly 70 percent of the pockmarks occur within 330–600 m water depth and the number of pockmarks drops abruptly at water depths &gt;600 m. Based on hydrate stability modeling, we argue that the updip edge of the HSZ shifted downslope since the last glacial maximum. This downslope shift caused hydrate dissociation and released charged free gas resulting in pockmark formation on the seafloor. Moreover, we observe that fluctuations in the updip edge of the HSZ since the last glacial maximum (from 330 to 605 m water depth) coincide with increased pockmark abundance. On other continental margins, pockmarks have been observed within a similar water depth range, suggesting that the loss of hydrate stability during deglaciation is a worldwide phenomenon that created intense fluid emission from the seafloor.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011781","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143846164","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":"Late Paleozoic Diachronous Subduction Initiation of the SE Paleo-Asian Ocean: Implications for Tectonic Transition From Passive to Active Continental Margin Along Northern North China Craton","authors":"Hao Zeng,&nbsp;Dongfang Song,&nbsp;Wenjiao Xiao,&nbsp;Haotian Huang","doi":"10.1029/2025GC012197","DOIUrl":"https://doi.org/10.1029/2025GC012197","url":null,"abstract":"<p>Subduction initiation is fundamental to our understanding of plate tectonics. However, the mechanisms and processes of subduction initiation, especially at passive continental margins, are poorly understood due to limited geological records. Here we identify a magmatic sequence resembling the Izu-Bonin-Mariana (IBM) forearc crust in the Mandula area of Inner Mongolia that recorded the subduction initiation of the Paleo-Asian Ocean (PAO) along the northern margin of the North China Craton (NCC). Geochemical analysis indicates that basalts and sheeted diabase dikes originated from partial melting of the upwelling asthenosphere at a forearc spreading center, succeeded by incipient arc volcanic and intrusive rocks, with increasing input of subducted slab-derived hydrous fluids. Zircon U-Pb ages reveal that the magmatic events in the Mandula area have taken place in a relatively short time interval between ∼284 Ma and ~272 Ma, similar to the duration of IBM forearc magmatism. The new results integrated with available data suggest that the southward subduction initiation of the PAO along the northern NCC was diachronous from early Carboniferous to early Permian and propagated from east to west following arc-continent collision. Therefore, our study provides a four-dimensional spatiotemporal perspective for tectonic transition from passive to active continental margin along the northern NCC.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012197","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143846163","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}