Geochemistry Geophysics Geosystems最新文献

{"title":"The Addition of Felsic Sediments to the Lower Continental Crust During the Variscan Orogeny","authors":"M. F. Ringwood,&nbsp;S. E. Ortner,&nbsp;R. L. Rudnick","doi":"10.1029/2024GC011843","DOIUrl":"https://doi.org/10.1029/2024GC011843","url":null,"abstract":"<p>Lower crustal metasedimentary xenoliths (garnet-sillimanite granulites) from the Bournac breccia pipe in the Massif Central, France, provide a robust example of sediments transported to depth and incorporated into stable lower continental crust during a collisional orogeny. Dates for detrital igneous zircon range from the Archean (up to 3,300 Ma) to the Devonian and record sedimentation prior to the onset of the collisional phase of the Variscan orogeny. Metamorphic zircon and monazite document the presence of the metasediments in the lower crust by ca. 330 Ma during the later phase of Variscan collision. Zircon and monazite crystallization continued within the lower crust until ca. 265 Ma, corresponding to a period of slow cooling following an episode of ultra-high temperature (UHT) metamorphism that peaked at 313 Ma. Zr-in-rutile thermometry and GASP barometry applied to these samples record conditions of 0.63–0.77 GPa and 830–910°C, which correspond to Ti-in-zircon temperatures from the latter part of the Variscan orogeny and geotherms in excess of typical continent-continent collisions. Rutile in these samples remained open to Pb loss until their eruption at ca. 11.6 Ma, providing an indirect date of the Bournac eruption. These rocks record the incorporation of felsic sedimentary material into the stable deep continental crust during a collisional orogen and their residence there for over 300 Ma. More broadly, the addition of sediments to stable lower crust contributes to changes in crustal composition and has significant implications for the heterogeneity of the deep continental crust, as well as overall crustal heat production and mantle heat flow.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011843","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143115028","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":"Nanolite Crystallization in Volcanic Glasses: Insights From High-Temperature Raman Spectroscopy and Low-Temperature Rock-Magnetic Analysis","authors":"Dmitry Bondar,&nbsp;Aurèlien Canizarès,&nbsp;Dario Bilardello,&nbsp;Pedro Valdivia,&nbsp;Alessio Zandonà,&nbsp;Claudia Romano,&nbsp;Mathieu Allix,&nbsp;Danilo Di Genova","doi":"10.1029/2024GC011846","DOIUrl":"https://doi.org/10.1029/2024GC011846","url":null,"abstract":"<p>High-temperature Raman spectroscopy offers a cost-effective alternative to extensive infrastructure and sensitive instrumentation for investigating nanolite crystallization in undercooled volcanic melts, a key area of interest in volcanology. This study examined nanolite formation in anhydrous andesite melts in situ at high temperatures, identifying distinct Raman peaks at 310 and 670 cm⁻¹ appearing above the glass transition temperature. The initial amorphous glass remained stable up to 655°C, beyond which Fe-Ti-oxide nanolites progressively formed at higher temperatures, as also confirmed by complementary XRD analysis. The evolution of the 310 cm⁻¹ peak depends only on the magnitude of nanolite crystallization, while the intensity of the 670 cm⁻¹ peak is temperature-dependent and challenging to observe above 500°C. Complementary low-temperature rock-magnetic analyses confirmed Fe-Ti-oxide nanocrystallization with nanolites around 20 nm in diameter. The study tested lasers of different wavelengths (from 355 to 514 nm) and found the green laser to be the most effective for collecting spectra at both room and high temperature. However, above 720°C, black body radiation significantly hinders Raman observation with the green laser when using a non-confocal setup and analyzing poorly transparent samples. If higher temperature measurements are desired, switching to a confocal setup and using lower wavelength lasers should be considered. This research offers a protocol for studying nanolite formation and melt dynamics at high temperatures, providing a foundation for future studies of volcanic processes.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011846","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143115027","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":"Particle Sedimentation in a Fluid at Low Reynolds Number: A Generalization of Hindered Settling Described by a Two-Phase Continuum Model","authors":"C. Huber,&nbsp;E. M. Parmentier,&nbsp;D. Florez","doi":"10.1029/2024GC011820","DOIUrl":"https://doi.org/10.1029/2024GC011820","url":null,"abstract":"<p>Particle-fluid separation by settling is a ubiquitous process in Earth and Planetary Sciences. The settling velocity of particles is controlled by a balance between buoyancy and drag forces. Since the seminal work of George Gabriel Stokes, parameterizations for the reduction of particle velocities caused by viscous dissipation due to mutual interactions have been described by a non-linear mapping between particle volume fraction and separation velocity. We argue that these parameterizations neglect important physical behavior at high particle volume fractions (&gt;80% of the maximum packing) and are only appropriate when considering suspensions where the particle volume fraction does not evolve in space or time. We introduce a more general model that accounts for the energy dissipation caused by changes in local particle volume fraction, which introduces a new term similar to the compaction term at higher particle volume fraction. This term depends on a consolidation/compaction viscosity that measures the resistance to changes in solid volume fraction. We derive closure equations for this compaction viscosity under dilute and concentrated particle volume fraction limits. Numerical simulations show that the extended hindered settling model predicts two significant differences compared to traditional hindered settling. First, while the steepening of particle volume fraction fronts remains, a dynamic instability is also generated at the front. Second, the rate of growth and structure of a cumulate layer growing above a no-flux boundary is affected by the compaction-like term and predicts the trapping of a higher volume fraction of interstitial melt in a correspondingly thicker cumulate layer.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011820","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143114342","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":"Geochemistry and Geochronology of A-Type Intermediate-Felsic Rocks in NW Himalaya, Pakistan: Implications for Petrogenesis and Tectonic Evolution of Northern Gondwana","authors":"Musa Khan,&nbsp;Huan Li,&nbsp;Thomas J. Algeo,&nbsp;Asad Khan,&nbsp;Michael W. Förster,&nbsp;Zaheen Ullah","doi":"10.1029/2024GC011802","DOIUrl":"https://doi.org/10.1029/2024GC011802","url":null,"abstract":"<p>Igneous intrusives in northern Pakistan can provide valuable insights into pre-Himalayan metaluminous to peraluminous magmatism along the northern boundary of the supercontinent Gondwana and its potential tectonic significance. This study generates new geochronologic, petrographic and geochemical data for intermediate (monzonite, syenite, and foid syenite) and felsic (granite and quartz monzonite) rocks within the NW Himalayan region of Pakistan. Both the intermediate and felsic rocks have values of A/NK &gt; 1.1, implying a metaluminous to peraluminous composition, and are distinguished by high FeO_T/(MgO + FeO_T) (0.81–1.0), high 10,000 × Ga/Al ratio (2.1–5.1), elevated Nb + Zr + Y + Ce contents (122–1,204 ppm), and negative anomalies of P and Ti, consistent with aluminous A-type magmatic affinity. These rocks are classified as A₁-type, which is linked to anorogenic intraplate extensional setting. Both rock groups yield high calculated average whole-rock Zr saturation temperatures (i.e., T_Zr; 790–823°C), which suggests formation from high-temperature magmas. Whole-rock geochemistry, including variable (⁸⁷Sr/⁸⁶Sr)_i values (0.7034–0.7086), positive εNd(<i>t</i>) (+0.1 to +3.9), high Pb isotopic values (that is, (²⁰⁶Pb/²⁰⁴Pb)_i = 18.68 to 19.31, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.64 to 15.74, and (²⁰⁸Pb/²⁰⁴Pb)_i = 38.93 to 39.78), and variation in zircon εHf(<i>t</i>) values (+0.8 to +7.0), indicates diverse magma sources for the intermediate-felsic rocks and provide evidence of partial melting of metasomatized lithospheric mantle, producing a primary magma of foid to quartz syenitic composition. Subsequently, this magma was responsible for the partial melting of the overlying juvenile crust, producing granitic, quartz monzonitic and monzonitic magmas. During the magma evolution process of these rocks, this process was primarily determined by partial melting that followed fractionation of K-feldspar, ilmenite and apatite. T_DM2 ages indicate that the parent materials of intermediate-felsic rocks were generated during the Mesoproterozoic-Neoproterozoic. LA-ICP–MS U-Pb dating of magmatic zircons documents their formation in the Late Paleozoic at ∼278-268 Ma. The intermediate-felsic rocks are correlatable with alkaline igneous rocks of the Peshawar Plain, which record the breakup of the supercontinent Gondwana and the subsequent opening of Neo-Tethys during a Late Paleozoic rifting event. The nepheline syenite records a younger episode during the Cenozoic (37 Ma), corresponding to the collision of the Indian-Eurasian tectonic plates.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011802","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143113925","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":"Inner Forearc Stress State and Plate Coupling","authors":"Viven Sharma,&nbsp;Ikuko Wada,&nbsp;Joe Rippke","doi":"10.1029/2024GC011812","DOIUrl":"https://doi.org/10.1029/2024GC011812","url":null,"abstract":"<p>The long-term state of stress in the subduction forearc depends on the balance between margin-normal compression due to the plate-coupling force and the margin-normal tension due to the gravitational force on the margin topography. In most subduction margins, the outer forearc is largely in margin-normal compression due to the dominance of the plate-coupling force. The inner forearc's state of stress varies within and among subduction zones, but what gives rise to this variation is unclear. We examine the state of stress in the forearc region of nine subduction zones by inverting focal mechanism solutions for shallow forearc crustal earthquakes for five zones and inferring the previous inversion results for the other four. The results indicate that the inner forearc stress state is characterized by margin-normal horizontal deviatoric tension in parts of Nankai, Hikurangi, and southern Mexico. The vertical and margin-normal horizontal stresses are similar in magnitudes in northern Cascadia as previously reported and are in a neutral stress state. The inner forearc stress state in the rest of the study regions is characterized by margin-normal horizontal deviatoric compression. Tension in the inner forearc tends to occur where plate coupling is shallow. A larger width of the forearc also promotes inner-forearc tension. However, regional tectonics may overshadow or accentuate the background stress state in the inner forearc, such as in Hikurangi.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011812","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143111595","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":"Potassium Isotope Evidence for Origin of Archean TTG Rocks From Seawater-Hydrothermally Altered Oceanic Crust","authors":"D.-Y. Xiong,&nbsp;X.-L. Wang,&nbsp;W. Li,&nbsp;Y.-F. Zheng,&nbsp;C. R. Anhaeusser,&nbsp;A. Hofmann,&nbsp;D. Wang,&nbsp;J.-Y. Li","doi":"10.1029/2024GC011892","DOIUrl":"https://doi.org/10.1029/2024GC011892","url":null,"abstract":"<p>Tonalite-trondhjemite-granodiorite (TTG) rocks constitute a crucial part of the Archean continental crust, yet their origins remain contentious. It is critical to decipher their source nature and hydration mechanism. This paper presents a study of whole-rock K stable isotopes in well-preserved ca. 3.51–3.42 Ga TTG rocks and associated mafic rocks from the Barberton granitoid-greenstone terrane (BGGT) in the Kaapvaal Craton, South Africa. The results show for the first time a substantial δ⁴¹K variation from −0.69 ± 0.07‰ to −0.32 ± 0.05‰ (2SD) for the Paleoarchean mafic rocks, exceeding the present mantle δ⁴¹K range from −0.6 to −0.3‰. This variation can be well explained by the seawater-hydrothermal alteration at different temperatures. Similarly, the Paleoarchean TTGs exhibit a wide δ⁴¹K range from −0.55 ± 0.04‰ to 0.07 ± 0.08‰ (2SD). In combination with available zircon δ¹⁸O values of 5.07–6.02‰, it is evident that Archean TTGs would be derived from partial melting of the seawater-hydrothermally altered oceanic crust (AOC). The distinct K-O isotope signatures demonstrate that the hydration of Archean mafic crust is caused by the hydrothermal alteration at mid-ocean ridges during seafloor spreading. The variable K-O isotope compositions in the Archean TTGs signify a series of processes that are dominated by the seawater-hydrothermally altered AOC in a Wilson cycle from divergence through convergence to rifting of Archean oceanic plates. This offers a viable mechanism for TTG petrogenesis and the growth of continental crust in the Archean.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011892","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143111269","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":"Distinct Hadean Mantle Sources of Felsic and Mafic Terranes Juxtaposed in the Paleoarchean","authors":"Arathy Ravindran,&nbsp;Bradley J. Peters,&nbsp;Klaus Mezger,&nbsp;Eric Hasenstab-Dübeler,&nbsp;Maya J. M.,&nbsp;Maria Schönbächler","doi":"10.1029/2024GC011834","DOIUrl":"https://doi.org/10.1029/2024GC011834","url":null,"abstract":"&lt;p&gt;The short-lived radionuclide system &lt;sup&gt;146&lt;/sup&gt;Sm-&lt;sup&gt;142&lt;/sup&gt;Nd can provide direct information about geological differentiation events in the terrestrial Hadean (&gt;4.0 Ga) mantle. The spatiotemporal formation and evolution of crustal material that formed from different mantle domains can constrain the existing geodynamic environment in which continental crust formed and plate tectonics was initiated. The coupled &lt;sup&gt;146,147&lt;/sup&gt;Sm-&lt;sup&gt;142,143&lt;/sup&gt;Nd isotope systematics of contemporaneous felsic and mafic-ultramafic igneous rock suites emplaced in the western Dharwar Craton (India) at ∼3.6 Ga record distinct Hadean mantle differentiation events in their source. The older mantle differentiation at &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mn&gt;4.38&lt;/mn&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;0.48&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;+&lt;/mo&gt;\u0000 &lt;mn&gt;0.12&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${4.38}_{-0.48}^{+0.12}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; Ga ago is recorded in the felsic rock suites. The most primitive crustal representatives alone yield a differentiation age of &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mn&gt;4.45&lt;/mn&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;0.18&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;+&lt;/mo&gt;\u0000 &lt;mn&gt;0.08&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${4.45}_{-0.18}^{+0.08}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; Ga. This early Hadean event is contemporaneous with the large silicate differentiation event recorded globally by Archean rocks. In contrast, the contemporaneous mafic-ultramafic suites from the Dharwar Craton record a later mantle differentiation event at &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mn&gt;4.15&lt;/mn&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;0.13&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;+&lt;/mo&gt;\u0000 &lt;mn&gt;0.07&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${4.15}_{-0.13}^{+0.07}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; Ga. Thus, distinct Hadean mantle differentiation events are preserved in coeval Archean felsic and mafic-ultramafic igneous rock suites ","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011834","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143118889","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":"Trace Element Emissions Vary With Lava Flow Age and Thermal Evolution During the Fagradalsfjall 2021–2023 Eruptions, Iceland","authors":"L. Wainman,&nbsp;E. Ilyinskaya,&nbsp;M. Pfeffer,&nbsp;C. Mandon,&nbsp;E. Bali,&nbsp;B. A. Edwards,&nbsp;B. I. Kleine-Marshall,&nbsp;S. R. Gudjonsdottir,&nbsp;A. Cotterill,&nbsp;S. W. Scott,&nbsp;P. Wieser,&nbsp;A. Stefánsson,&nbsp;E. J. Nicholson,&nbsp;J. Sepulveda-Araya,&nbsp;S. J. Hammond,&nbsp;B. E. Kunz,&nbsp;F. Jenner,&nbsp;J. R. Gunnarsson,&nbsp;A. Aiuppa,&nbsp;M. Burton,&nbsp;T. A. Mather","doi":"10.1029/2024GC011822","DOIUrl":"https://doi.org/10.1029/2024GC011822","url":null,"abstract":"<p>Basaltic fissure eruptions emit volatile and environmentally reactive gases and particulate matter (PM) into the lower troposphere (e.g., SO₂, HCl, and HF in the gas phase; Se, As, Pb as complexes in the PM phase). Lava flows from fissure eruptions can be spatially extensive, but the composition and fluxes of their emissions are poorly characterized compared to those from main vent(s). Using uncrewed aircraft systems-mounted (drone) samplers and ground-based remote Fourier Transform Infrared Spectroscopy, we investigated the down-flow compositional evolution of emissions from active lava flows during the Fagradalsfjall 2021–2023 eruptions. The calculated fluxes of volatile trace metals from lava flows are considerable relative to both main vent degassing and anthropogenic fluxes in Iceland. We demonstrate a fractionation in major gas emissions with decreasing S/halogen ratio down-flow. This S-Cl fractionation is reflected in the trace element degassing profile, where the abundance of predominantly sulfur-complexing elements (e.g., Se, Te, As, Pb) decreases more rapidly in down-flow emissions relative to elements complexing as chlorides (e.g., Cu, Rb, Cs), oxides (e.g., La, Ce) and hydroxides (e.g., Fe, Mg, Al, Ti). Using thermochemical modeling, we explain this relationship through temperature and composition dependent element speciation as the lava flow ages and cools. As a result, some chloride-complexing elements (such as Cu) become relatively more abundant in emissions further down-flow, compared to emissions from the main vent or more proximal lava flows. This variability in down-flow element fluxes suggests that the output of metals to the environment may change depending on lava flow age and thermal evolution.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011822","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142868934","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":"Episodic Seafloor Hydrothermal Alteration as a Source of Stable Remagnetizations in Archean Volcanic Rocks","authors":"A. R. Brenner,&nbsp;R. R. Fu,&nbsp;A. J. Brown,&nbsp;E. B. Hodgin,&nbsp;D. T. Flannery,&nbsp;Mark D. Schmitz","doi":"10.1029/2024GC011799","DOIUrl":"https://doi.org/10.1029/2024GC011799","url":null,"abstract":"<p>Interpreting the paleomagnetic records of altered rocks, especially those from Earth's earliest history, is complicated by metamorphic overprints and recrystallization of ferromagnetic minerals. However, these records may be as valuable as a primary signal if the timing and mechanism of alteration-related remagnetizations can be ascertained. We illustrate the success of this approach in the case of seafloor hydrothermal alteration by integrating simple rock magnetic and magnetic microscopy data with petrography, hyperspectral imagery, aeromagnetic surveys, field mapping, and geochronology of Paleoarchean basalts from North Pole Dome located in the East Pilbara Craton, Western Australia. We identify 12 hydrothermal episodes during the deposition of the stratigraphy between ∼3490 and 3350 Ma. These episodes produced stratabound zones of hydrothermal alteration with predictable facies successions of mineral assemblages reflecting sub-seafloor gradients in fluid temperature, pH, composition, and water/rock ratios. Rock magnetic data and magnetic microscopy pinpoint the secondary ferromagnetic minerals within each alteration assemblage, revealing a specific single-domain magnetite population within leucoxenes (titanite and anatase after primary titanomagnetites) that always accompanies low-water/rock alteration in fluids buffered to pH equilibrium with the host basalts. Highly uniform magnetic properties indicate that once formed, these magnetites remain unchanged upon further exposure to rock buffered fluids, stabilizing them against later alteration events and making them durable paleofield recorders. The altered basalts hosting this magnetite have unique and consistent appearances, mineralogy, IR absorption features, aeromagnetic signatures, and magnetic properties across all hydrothermal systems studied here, highlighting how integrating these data sets can identify and interpret this alteration style in future paleomagnetic investigations.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011799","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142868933","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":"Integrated Rock Mass Characterization of the Lower Continental Crust Along the ICDP-DIVE 5071_1_B Borehole in the Ivrea-Verbano Zone","authors":"J. Li,&nbsp;E. Caspari,&nbsp;A. Greenwood,&nbsp;S. Pierdominici,&nbsp;K. Lemke,&nbsp;M. Venier,&nbsp;J. Kück,&nbsp;L. Baron,&nbsp;M. Pistone,&nbsp;B. Petri,&nbsp;L. Ziberna,&nbsp;G. Hetényi","doi":"10.1029/2024GC011707","DOIUrl":"https://doi.org/10.1029/2024GC011707","url":null,"abstract":"<p>The first borehole 5071_1_B of the ICDP-Drilling the Ivrea-Verbano zonE (DIVE) project in Italy, which intersects the Massone antiform, provides a unique opportunity to integrate downhole geophysical measurements with observations from 100% recovered drill core in rarely drilled lithologies. The objective of this study is to petrophysically and structurally characterize the rock mass and constrain factors influencing the seismic velocity in the lower continental crust. A comprehensive data set, comprising core, well log and vertical seismic profiling data, was collected. The structural analysis indicates that the axial plane of the intersected tightly folded antiform is slightly tilted at the borehole location and thus the borehole intersects the hinge zone at the top and its limb in the lower part of 5071_1_B. Numerous open natural fractures with variable dips and two dominant dip azimuthal orientations are identified along the borehole, which affect the electrical and acoustic properties. The velocities at the core, well log and seismic scale are consistent but lower than intrinsic seismic velocities of the lower continental crust, since they are not only affected by fractures but also by micro cracks at the 5071_1_B in situ conditions. A systematic lithology correlation is not evident for these properties. However, a cluster analysis of gamma ray and magnetic susceptibility logs shows an excellent agreement with the logged core lithologies in the presence of remarkable spatial variability. Furthermore, the main lithologies are grouped into three distinct clusters, suggesting two types of kinzigites with distinct magnetic and radiogenic properties.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"25 12","pages":""},"PeriodicalIF":2.9,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011707","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142851558","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}