Geochemistry Geophysics Geosystems最新文献

{"title":"Cascading Earthquake Swarms in the Northern Taupō Volcanic Zone, New Zealand","authors":"S. Aber,&nbsp;C. J. Ebinger,&nbsp;A. C. Gase,&nbsp;C. Kalugana,&nbsp;F. Illsley-Kemp,&nbsp;I. Hamling,&nbsp;S. Sabir,&nbsp;M. K. Savage,&nbsp;J. Eccles,&nbsp;S. Hreinsdottir,&nbsp;J. Ristau,&nbsp;J. James-Le","doi":"10.1029/2024GC012079","DOIUrl":"https://doi.org/10.1029/2024GC012079","url":null,"abstract":"<p>The spatiotemporal characteristics of infrequent back-arc rifting events and their relationships to volcanic unrest as well as other transient processes within the subduction system are not well known. We report 10 spatio-temporal swarms of earthquakes that occurred along ∼175 km of the northern and central Taupō Volcanic Zone (TVZ) March–September 2019. The swarms lack clear mainshock-aftershock distributions, suggesting involvement of pressurized fluids. The most energetic swarms occurred beneath the southwestern flank of Whakaari/White Island volcano (WI) and were accompanied by elevated SO₂ emissions and ∼8 mm southwest displacement of the edifice. Focal mechanisms of the WI swarms suggest horizontal dilation in the direction of tectonic extension achieved by slip along networks of closely spaced, NE-striking normal faults linked by oblique-slip to strike-slip faults. Given the small GNSS displacements and upward-migrating swarms, we favor the interpretation that magmatic volatiles were released along faults in response to changes in crustal stress. Based on the punctuated, cascading nature of swarms along the northern TVZ, we hypothesize that faults and magmatic systems are fluid-rich, experiencing aseismic creep, and critically stressed, raising the possibility that small changes in crustal stress from slow slip along the Hikurangi subduction zone caused a reduction in the minimum horizontal stress. This change occurred along the entire northern TVZ over ∼5 months, potentially contributing to widespread volcanic unrest. The probable release of magmatic fluids from shallow magma bodies in the vicinity of WI between May and June argues against a causal relation to the 9 December 2019 WI eruption.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012079","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143875658","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":"Seismic Structure of the Mid to Upper Crust at the Santorini-Kolumbo Magma System From Joint Earthquake and Active Source Vp-Vs Tomography","authors":"R. S. Hufstetler,&nbsp;E. E. E. Hooft,&nbsp;D. R. Toomey,&nbsp;B. P. VanderBeek,&nbsp;C. B. Papazachos,&nbsp;N. Chatzis","doi":"10.1029/2024GC012022","DOIUrl":"https://doi.org/10.1029/2024GC012022","url":null,"abstract":"<p>Santorini volcano has a history of caldera-forming eruptions, most recently in the Late Bronze Age, at 3.4 kya, and remains volcanically active. The Kolumbo submarine volcano, located 7 km to the northeast of Santorini, erupted in 1650 AD in a deadly phreatomagmatic eruption. Ongoing seismic activity and active hydrothermal venting at Kolumbo indicate this volcano is a significant hazard to the Santorini region. The magma source for Santorini and the Kolumbo edifice are considered separate in the shallow crust, though their deeper magma distribution is not yet constrained. In this study, we improve constraints on the mid-crustal magma system of Santorini caldera and the nearby Kolumbo volcano using local earthquake tomography. We use 1515 P-wave and 1435 S-wave arrival times from 63 local earthquakes with magnitudes from 0.5 to 3.0 that occurred between 5 and 15 km depth together with an existing data set of active source Pg arrivals. The upper crustal magma system beneath Santorini is imaged to at least 6 km depth, and to 12 km depth beneath Kolumbo. We recover a high P-wave velocity layer (∼6–8 km) under the Kolumbo magma reservoir that we infer is a rheologically strong seismogenic layer. We also recover a mid-crustal magma body below 8 km depth located to the NE of Santorini and Kolumbo.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012022","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143875634","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":"Pore Fluid Origins, Circulation, and Links With Methane Hydrate on the South-Central Chilean Margin","authors":"Vincent J. Clementi,&nbsp;Wei-Li Hong,&nbsp;Yair Rosenthal,&nbsp;Samantha C. Bova,&nbsp;Laurel B. Childress","doi":"10.1029/2025GC012195","DOIUrl":"https://doi.org/10.1029/2025GC012195","url":null,"abstract":"<p>The chemical composition of marine sedimentary pore waters, notably freshening signals inferred from decreases in dissolved Cl⁻, have demonstrated a link between methane hydrate accumulation and the circulation of fluids and gases in convergent margin systems. However, the south-central Chilean Margin (32–46°S) lacks geochemical evidence for this relationship. In 2019, D/V <i>JOIDES Resolution</i> Expedition 379T drilled two sites (J1005 and J1006) near legacy site ODP 1233 (41°S) and recovered 120 m sediment cores from a seafloor venting structure. The sites are less than 10 km apart but exhibit differences in pore water chemistry and methane hydrate occurrence. The extent of Cl⁻ decrease is a function of distance from the venting structure, with the greatest freshening (and only recovery of methane hydrate) occurring at the closest site. Methane fluxes follow the same pattern, suggesting a common influence. Increasing oxygen and decreasing hydrogen isotopes point to mineral bound water originating ∼2.5 km below the seafloor as the primary source of pore water freshening. In contrast, marine silicate weathering coupled to methanogenesis, authigenic carbonate formation, and the alteration of oceanic crust regulate Sr systematics. These spatial heterogeneities indicate that fluid migration is attributable to regional overpressures in the accretionary complex and flows along narrow fault structures. We suggest that the focused migration of deep, gas-charged fluids serves as a model for regional methane hydrate accumulation, reconciling model estimates and field observations. Collectively, our results highlight an important link between regional hydrogeology, diagenetic processes, and methane hydrate formation on the south-central Chilean Margin.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012195","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143875637","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":"Quantitative Microstructural Analysis of Exhumed Epidote-Amphibolites and Plate Interface Rheology in Warm Subduction Zones","authors":"Laurens H. Kleijbeuker,&nbsp;Hamed Amiri,&nbsp;Maartje F. Hamers,&nbsp;Alissa J. Kotowski","doi":"10.1029/2024GC011886","DOIUrl":"https://doi.org/10.1029/2024GC011886","url":null,"abstract":"<p>Epidote-amphibolites form along the plate interface during subduction infancy and are stable in warm, mature subduction zones that generate slow earthquakes. Epidote-amphibolite rheology therefore likely influences plate-scale processes during plate boundary formation and grain-scale processes that give rise to slip transients. We present optical and electron microscopy of naturally deformed epidote-amphibolites from beneath the Oman ophiolite (∼7–10 kbar, 400–550°C) to characterize their deformation behavior. Epidote-amphibolites are fine-grained, strongly foliated and lineated, and exhibit polyphase fabrics in which amphiboles (grain size ∼10–50 μm) and epidotes (grain size ∼5–20 μm) are strain-accommodating phases. Two-point correlation connectivity analysis demonstrates that amphiboles are well-connected regardless of phase proportions/distributions. Chemical analysis and electron backscatter diffraction reveals amphibole syn-kinematic metamorphic zonations, strong crystallographic and shape - preferred orientations (CPOs and SPOs), subgrain geometries indicating (hk0)[001] slip, and high average Grain Orientation Spreads (GOS; ∼6°), interpreted as coupled dissolution-precipitation creep (DPC) and dislocation glide. Epidotes record weak CPOs, low intragranular misorientations, moderate SPOs, and low GOS (∼0–2°), interpreted as deformation by DPC. Depending on phase distributions, epidote-amphibolite rheology can be approximated as interconnected weak layers of amphibole dissolution creep or a composite rheology of plasticity and fluid-assisted/diffusion-accommodated creep. We estimate stress from quartz piezometry (∼30–45 MPa) and strain rates from flow laws and geologic data (6 · 10⁻¹¹ to 10⁻¹³ s⁻¹), and calculate equivalent viscosities of &lt;10¹⁸ Pa-s. On tectonic timescales, such low viscosities are consistent with epidote-amphibolites serving as strain localizing agents during subduction infancy. On seismic timescales, coupled dislocation glide and diffusion creep exemplify a strain-hardening deformation state that could culminate in creep transients.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011886","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143875636","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":"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}