Geochemistry Geophysics Geosystems最新文献

{"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}

{"title":"Mantle Source Evolution Along the South Atlantic Transect (31°S) Records a Transition From HIMU Plume Component to Depleted MORB","authors":"P. D. Kempton,&nbsp;R. M. Coggon,&nbsp;I. Millar,&nbsp;T. M. Belgrano,&nbsp;E. Albers,&nbsp;A. Michalik,&nbsp;J. A. Milton,&nbsp;A. D. Evans,&nbsp;R. N. Taylor,&nbsp;D. A. H. Teagle","doi":"10.1029/2025GC012175","DOIUrl":"https://doi.org/10.1029/2025GC012175","url":null,"abstract":"<p>Interactions between mantle plumes and mid-ocean ridges create considerable spatial variation in composition along ridge axes. What is less well known is the temporal variation in MORB compositions along single mantle flow lines. IODP Expeditions 390/393/390C/395E recovered basaltic basement from seven sites along a flow line, the South Atlantic Transect (SAT), on the western flank of the mid-Atlantic Ridge (MAR) at ∼31°S. SAT basalts ≤49 Ma are tholeiitic with isotopic compositions similar to MORBs from the MAR between 25° and 28°S. Basement from the oldest SAT site (U1556; 61.2 Ma) is more complex, consisting of three stratigraphic sequences (SSA, SSB and SSC) ranging from MORB-like at the bottom (SSC) to Ocean Island Basalt (OIB)-like at the top (SSA); their isotopic compositions are distinct relative to both younger SAT basalts and the EM1-type Tristan–Gough plume that dominates the region, being more akin to HIMU. The presence of previously unrecognized HIMU mantle in this region is due to one or more ridge jumps that occurred west of the Walvis Ridge at ∼65 Ma. These ridge jumps relocated the spreading axis over a portion of the HIMU plume that had previously given rise to late-stage, off-axis HIMU magmatism adjacent to the Walvis Ridge. Upwelling beneath the spreading center progressively tapped a variably depleted source, reproducing it in reverse in the volcanic stratigraphy at Site U1556. Continued upwelling beneath the spreading center removed most of the HIMU plume material within ∼12 Myr, the time of Site U1558 (49.2 Ma).</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012175","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143836179","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":"Compositional and Textural Variability Among Tektites From Indochina and South China: Insights Into the Impact Origin of the Australasian Tektite Strewn Field","authors":"S. Boschi,&nbsp;S. Goderis,&nbsp;S. Liao,&nbsp;W. Li","doi":"10.1029/2024GC012133","DOIUrl":"https://doi.org/10.1029/2024GC012133","url":null,"abstract":"<p>The Australasian tektite strewn field, approximately 0.8 Ma in age, covers nearly 10% of the Earth's surface, making it the largest and most recent strewn field globally. This study provides a comprehensive analysis of the elemental composition and texture of tektites recovered from various locations within the strewn field, particularly Vietnam, Thailand, and South China. These tektites exhibit a consistent major and minor element composition similar to the Upper Continental Crust characteristic of normal tektites. Notable elemental deviations in the concentrations of CaO, FeO, MgO, Pb, and Sr are observed in the Indochina Peninsula tektites, suggesting the mixing of multiple target rock components. Indochinites from Thailand and Vietnam show lower Pb and Sr levels compared to those from China, Indonesia, and Australia, potentially reflecting proximity to the hypothetical impact site on the Bolaven Plateau, Laos. The local stratigraphy of basalts over laterite and sandstone at the proposed source crater site may explain the observed decrease in Pb and Sr concentrations, primarily due to sandstone admixture, while variable MgO, CaO, and FeO suggest a basaltic contribution. The high abundance of lechatelierite inclusions and elevated SiO₂ in Indochinites compared to South China tektites underscore the role of target rock composition in tektite formation. Schlieren flow structures further confirm rock mixing during the early impact stages. Overall, the findings elucidate the relationship between tektite formation, target rock interaction, and impact processes, supporting the Indochina Peninsula as the impact area and highlighting the need for further research on elemental fractionation and target rock heterogeneity.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012133","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143831255","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}