Geochemistry Geophysics Geosystems最新文献

{"title":"Elemental Geochemistry of Tidal Marsh Sediment and Its Potential as an Indicator of Sea-Level Change in Cascadia","authors":"Anthony Giang,&nbsp;Jessica E. Pilarczyk,&nbsp;Isabel Hong,&nbsp;Louise Riou,&nbsp;David Huntley,&nbsp;Roger MacLeod,&nbsp;Owen G. Ward,&nbsp;John J. Clague,&nbsp;Peter Bobrowsky,&nbsp;Andrea D. Hawkes,&nbsp;Simon E. Engelhart,&nbsp;Benjamin P. Horton","doi":"10.1029/2024GC012129","DOIUrl":"https://doi.org/10.1029/2024GC012129","url":null,"abstract":"<p>Holocene sea-level reconstructions from tidal marshes are commonly derived from proxy indicators that have a consistent and quantifiable relationship with tidal elevation. While microfossils are most commonly employed, using multiple indicators leads to more robust reconstructions. We explore the utility of elemental geochemistry obtained through x-ray fluorescence as a proxy indicator in tidal marshes at Port Alberni, British Columbia, Canada and Willapa Bay, Washington, United States. The elemental composition of bulk surface sediment collected from 141 stations along 10 transects was determined using an ITRAX Core Scanner. Partitioning Around Medoids cluster analysis on the elemental data distinguished between tidal flat, low marsh, and high marsh zones at both locations, similar to zones established from previously published microfossil (foraminifera, diatoms) data sets on the same samples. The elemental composition of low elevation samples from the tidal flat is dominated by lithogenic (Si, K, Ti, Fe) and biogenic (Sr) elements, whereas higher elevation samples have high proportions of organic content (Br, incoherent and coherent scattering ratio). Principal Component Analysis points to differences in organic versus inorganic content, a function of tidal elevation, as the main driver of geochemistry-derived zones. Approximately 70% of the elemental variability within both marshes is controlled by the inorganic content, as indicated by lithogenic and biogenic elements versus organic content. The elemental composition of bulk surface sediment from two regions spaced ∼300 km apart shows a promising relationship with tidal elevation over a wider spatial scale and highlights the potential of this proxy for use in sea-level reconstructions.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012129","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143925788","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":"How Do Passive Margins Convert to Active Margins?","authors":"Timothy M. Kusky,&nbsp;Junpeng Wang","doi":"10.1029/2025GC012394","DOIUrl":"https://doi.org/10.1029/2025GC012394","url":null,"abstract":"<p>There has been a long debate about how passive (Atlantic-type) margins can convert to active (Andean) margins, particularly if they can do so directly, or some other process such as an arc-continent collision must intervene (Burke et al., 1984; Dewey, 1969, https://doi.org/10.1016/0012-821x(69)90089-2; Kusky &amp; Kidd, 1985). Most numerical models have long-suggested that only very young passive margins can be sites of subduction initiation since old margins become stronger as they cool and develop thick sedimentary piles during thermal subsidence (e.g., Cloetingh et al., 1982, https://doi.org/10.1038/297139a0, 1989, https://doi.org/10.1007/bf00874622; 1996; Zhong &amp; Li, 2019, https://doi.org/10.1029/2019gl084022), whereas other analog and numerical models have suggested that old passive margins may spontaneously convert to subduction zones (e.g., Bercovici &amp; Mulyukova, 2021, https://doi.org/10.1073/pnas.2011247118; Faccenna et al., 1999, https://doi.org/10.1029/1998jb900072; Nikolaeva et al., 2010, https://doi.org/10.1029/2009jb00654; Stern &amp; Gerya, 2018, https://doi.org/10.1016/j.tecto.2017.10.014; Zhang et al., 2023, https://doi.org/10.1029/2023gl103553).</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012394","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143925789","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 Cenozoic Rise in Seawater δ11B Not Driven by Increasing Boron Adsorption","authors":"Simon J. Ring,&nbsp;Michael J. Henehan,&nbsp;Patrick J. Frings,&nbsp;Roberts Blukis,&nbsp;Friedhelm von Blanckenburg","doi":"10.1029/2024GC011911","DOIUrl":"https://doi.org/10.1029/2024GC011911","url":null,"abstract":"<p>The boron isotopic value of ancient seawater (δ¹¹B_sw) is a prerequisite for the reconstruction of seawater pH and atmospheric CO₂ concentrations. Available models and some proxy records suggest that δ¹¹B_sw underwent a large increase during the last 45 million years. This increase has been attributed to an acceleration in sediment discharge into the ocean and the enhanced adsorption of boron on particle surfaces. However, whether global sedimentation rates have increased in the late Cenozoic is contested. Additionally, adsorption efficiency was likely modulated by secondary factors related to seawater chemistry and the sedimentary mineral content, that could have counteracted changes in sedimentation rates. Here we revisit the controls on boron adsorption over the last 100 million years. We found that changes in the seawater concentration of dissolved inorganic carbon (HCO₃⁻, CO₃²⁻) and major ions (Ca²⁺, Mg²⁺, SO₄²⁻) had a negligible impact on boron adsorption. Instead, the sedimentary mineral assemblage and the acidity of seawater were important subordinate factors. By considering several possible sediment production scenarios, we propose that the ability of sediment to adsorb boron was lower in the Cretaceous but has remained similar to the present-day since the Eocene. When these results are incorporated into a seawater model, δ¹¹B_sw exhibits a step-wise enrichment over the Cenozoic, that is, at times, 2‰ above previous model results. Our analysis precludes a dominant role of adsorption in the boron isotope cycle of the late Cenozoic, but nevertheless supports the view that δ¹¹B_sw was lower than today for the last 60 million years.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011911","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143925790","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":"Continuous Real-Time Detection of H2, He, and 222Rn While Drilling DIVE-1 Boreholes (ICDP) Indicates Deep Fracture Fluid Migration in Crystalline Rocks","authors":"H. Dutoit,&nbsp;L. Truche,&nbsp;F. V. Donzé,&nbsp;T. Wiersberg,&nbsp;M. L. Doan,&nbsp;J. Li,&nbsp;A. Greenwood,&nbsp;E. Caspari,&nbsp;N. Lefeuvre,&nbsp;J. Dominique,&nbsp;S. Auclair,&nbsp;L. Masci,&nbsp;G. Hetényi,&nbsp;M. Venier,&nbsp;O. Müntener,&nbsp;ICDP DIVE Science Team","doi":"10.1029/2025GC012168","DOIUrl":"https://doi.org/10.1029/2025GC012168","url":null,"abstract":"<p>The identification and real-time monitoring of geofluids during drilling is crucial for safe drilling operations and can provide valuable insights into reservoir properties and fluid migration. While mud gas logging is well established in oil and gas exploration, recent interest in natural hydrogen (H₂) and helium (He) exploration has prompted the need for improved mud gas logging techniques for continuous wireline coring in crystalline bedrock. The detection of both H₂ and He is particularly useful when exploring these two commodities but also for identifying deep fluid migration notably in crystalline bedrock. This study presents the results of mud gas logging of O₂, N₂, ⁴⁰Ar, ³⁸Ar, ³⁶Ar, CO₂, CH₄, H₂, He, and ²²²Rn from two boreholes (909.5 and 578.5 m deep) drilled in the Ivrea-Verbano Zone (Northern Italy) as part of the DIVE-ICDP project. Comparison with data from geophysical logging showed that gas peaks correlate well with variations in the physical characteristics of the well fluid, indicating zones of fluid inflow. Real-time gas monitoring proved to be valuable for identifying deep gas migration and aiding decision-making. Despite its potential, this technique faces challenges, such as distinguishing between formation-derived and drilling-induced gases. Complementary analyses, including isotopic studies, are recommended to refine source identification. Nevertheless, the correlation of He and H₂ with CH₄ and CO₂ provides initial insights into their possible origins, making this method a promising tool for exploring H₂ and He gases in deep geological formations.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012168","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143914139","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":"B-Type Olivine Fabrics Within the Cumulate Buck Creek Ultramafic Body Emplaced During Southern Appalachian Taconic Subduction","authors":"Virginia L. Peterson,&nbsp;Jeffrey M. Rahl,&nbsp;Samuel DeYoung,&nbsp;Davis Eyth,&nbsp;Madeline Mennenga,&nbsp;Benjamin A. Pummell","doi":"10.1029/2024GC011913","DOIUrl":"https://doi.org/10.1029/2024GC011913","url":null,"abstract":"<p>The Buck Creek ultramafic complex is a fragment of oceanic cumulate emplaced into the lower Laurentian continental crust during Ordovician Taconic subduction. We document olivine fabrics in the relatively pristine dunites preserved from peak metamorphic conditions of ∼850°C and 1.0–1.4 GPa confining pressure. Mineral assemblages and microstructures indicate nearly anhydrous conditions at peak metamorphism and the activity of dislocation creep with minor evidence of grain boundary sliding. Grain size piezometry indicates stress conditions of ∼17–25 MPa. Analysis of crystallographic preferred orientations (CPO) and intracrystalline misorientations indicate the primary activity of the [001](010) slip system leading to the development of B-type olivine fabrics. We suggest that the Buck Creek dunites formed as ocean crust cumulates and were partially subducted beneath the Laurentian continental crust to deformation conditions similar to those in the shallow mantle wedge. We document that deformation at Buck Creek occurred at lower differential stress conditions and lower water content than typically associated with B-type CPOs, broadening the range of known conditions in which these fabrics may form.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011913","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143919368","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":"Role of Magma Ocean Differentiation in the Formation and Long-Term Preservation of Distinct Geochemical Domains Within the Deep Mantle","authors":"Seema Kumari,&nbsp;Ramananda Chakrabarti","doi":"10.1029/2025GC012282","DOIUrl":"https://doi.org/10.1029/2025GC012282","url":null,"abstract":"<p>We modeled the evolution of the terrestrial Magma Ocean using the short-lived ¹⁸²Hf-¹⁸²W isotope system (<i>t</i>_1/2 = 8.9 Myr) in a multi-reservoir early Earth. We start with a chondritic Earth at <i>T</i>₀ = 4.567 Ga. Core segregates and attains its present-day mass, W elemental and isotopic (¹⁸²W/¹⁸⁴W) composition by the end of core formation (<i>T</i>_CF). The duration and rate of core formation constrain the starting composition of the silicate Earth and magma ocean that formed at the last stages of the core formation. Crystallization of magma ocean results in the formation of crystals/cumulates of mass <i>M</i>_CX, leaving behind a residue with mass <i>M</i>_RES. A series of differential equations describing the changing mass and abundance of ¹⁸²Hf, ¹⁸²W, and ¹⁸⁴W nuclides in each reservoir are solved numerically at 0.1 Myr time-step for the initial 200 Myr of Earth's history. Our results constrain the depth of the early magma ocean to be ∼38–70% of the total mantle mass, corresponding to a depth of ∼770–1,600 km and the timing of magma ocean crystallization over a duration <i>T</i>_CX of ≤50 Myr after core formation, which successfully reproduces the present-day Hf and W concentrations and ¹⁸²W/¹⁸⁴W ratios in <i>M</i>_RES reservoir similar to the deep mantle sources sampled by ocean island basalts. The model-derived results suggest that leftover residual (liquid) magma ocean after magma ocean crystallization could partly or fully represent the present-day large low shear velocity provinces, LLSVPs.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012282","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143914515","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":"Horizontal Transport of Picture Gorge Basalt Magma Through the Monument Dike Swarm Determined by Magnetic Fabric","authors":"Margaret S. Avery,&nbsp;Anthony F. Pivarunas","doi":"10.1029/2024GC012078","DOIUrl":"https://doi.org/10.1029/2024GC012078","url":null,"abstract":"<p>Flood basalts of the mid-Miocene Columbia River Basalt Group (CRBG) cover 210,000 km² of Washington, Oregon, and Idaho. The source of CRBG melt is debated; widely spaced feeder dike swarms can be projected toward hypothetical sources near the Oregon-Idaho border. In this study, we use anisotropy of magnetic susceptibility (AMS) to track magma flow in the Monument dike swarm (MDS), the feeder dikes of the Picture Gorge Basalt (PGB). This small formation of the main-phase CRBG eruptions allows us to explore in detail the localized dynamics of a large igneous province feeder system, with implications for the larger CRBG picture. We measured the magnetic fabric of 205 oriented paleomagnetic specimens subsampled from 97 samples collected from 15 dikes of the MDS. Thermal demagnetization and hysteresis loops show that the magnetic minerals are a mixture of single domain and multidomain sized titanomagnetites. At three dikes, the paleodepth of sampling was determined to be shallow (&lt;350 m). Magma flowing through dikes has been shown—in most cases— to acquire an anisotropic magnetic fabric with an AMS ellipsoid minimum axis perpendicular to the wall and maximum axis aligned in the direction of flow. Of 15 dikes, 12 show horizontal flow directions in the plane of the dike. Only one dike displayed imbricated fabrics, showing westward flow away from the Oregon-Idaho border. We conclude that magma flow in the MDS was sub-horizontal from a distal source.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012078","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143914020","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":"Rift-Related Low-Pressure–High-Temperature Granulite Facies Metamorphism Generates Widespread Peraluminous Crustal Melts: Evidence From the Early Jurassic Mexican Crust","authors":"Anthony Ramírez-Salazar,&nbsp;Mattia Parolari,&nbsp;Arturo Gómez-Tuena,&nbsp;Fernando Ortega-Gutiérrez,&nbsp;Mariano Elías-Herrera","doi":"10.1029/2024GC012019","DOIUrl":"https://doi.org/10.1029/2024GC012019","url":null,"abstract":"<p>High heat fluxes occurring in rift settings are expected to generate partially melted low-pressure–high-temperature granulites (LP–HTG). Therefore, studying these rocks can offer valuable insights into crustal reworking during extension. However, our interpretations are limited by the rarity of LP–HTG in the metamorphic record. To better assess the genesis of partially melted LP–HTG, it is relevant to identify their protolith and associated melt as well as to characterize their P-T evolution. We study the Tejupilco area in Mexico to present the case of the Pepechuca metapelitic xenoliths and the Tizapa metagranite, the latter belonging to the Nazas Igneous Province (NIP). This site serves as an excellent location to outline the partial melting history of the eastern and southern regions of the Mexican crust during the Jurassic. Geochemical and geochronological data, combined with thermodynamic modeling, show that the mid- to upper-crustal protoliths of the Pepechuca xenoliths—a metamorphosed portion of Triassic turbidite sequences—experienced anomalously high T/P (&gt;1700°C/GPa) regional prograde metamorphism and hydrate-breakdown partial melting during the Early Jurassic (182.2 ± 2.4 Ma). A combination of isotopic, geochronological, and modeling data demonstrates that the Tizapa metagranite originated from the melting of rocks akin to the Pepechuca xenoliths. We also show that the LP–HTG metamorphism occurred in a rift setting during the breakup of Western Pangea. Hence, our results demonstrate that rifting is a viable mechanism for crustal reworking during LP–HTG metamorphism and for the generation of peraluminous felsic igneous rocks, such as those found in the anatectic Jurassic NIP.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC012019","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901041","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":"Heterogeneous Mantle Metasomatism Controlled by Continental Subduction: Evidence From Post-Collisional Mafic Rocks in the North Qaidam Orogen","authors":"Xiangyu Gao,&nbsp;Shengyao Yu,&nbsp;Yu Qi,&nbsp;Lintao Wang,&nbsp;Chuanzhi Li,&nbsp;Xiaocong Jiang,&nbsp;Xingzhou Jiang,&nbsp;Yang Yu","doi":"10.1029/2025GC012179","DOIUrl":"https://doi.org/10.1029/2025GC012179","url":null,"abstract":"<p>Post-collisional mafic rocks not only record geodynamic processes at the end of the orogenic cycle but also retain various clues regarding preceding interactions between subducted slabs and mantle wedges. However, the latter and related indicators have often been overlooked; in particular, how the continental crust interacts with the mantle in subduction zones and modifies its nature remains ambiguous. This study of post-collisional mafic rocks in the North Qaidam orogen provides new insights into sophisticated crust–mantle interactions via variable continental subduction. These post-collisional mafic rocks are consistent with the geochemical nature of arc lava and originated from partial melting of the antecedent metasomatic mantle. Although they possess relatively uniform whole-rock Sr–Nd isotopes, the mafic rocks from the ultrahigh-pressure metamorphic terranes present more enriched zircon Hf isotopes and remarkable signals of melt-driven mantle metasomatism than the other rocks within the non-ultrahigh-pressure metamorphic zone. This is attributed to spatially variable continental subduction and the consequent differentiated crust–mantle interactions. Trace element modeling also reveals that a greater proportion of continental component-derived metasomatic melts are needed to form mafic rocks in ultrahigh-pressure metamorphic terranes. The whole-rock magnesium isotopes are between −0.15‰ and −0.38‰, which are negatively correlated with (⁸⁷Sr/⁸⁶Sr)_<i>i</i> and positively correlated with <i>ɛ</i>_Nd(<i>t</i>) and <i>ɛ</i>_Hf(<i>t</i>). These findings indicate that these mafic rocks exhibit lighter magnesium isotopes when their mantle source is metasomatized by more continental component-derived melts enriched with radiogenic isotopes. The geochemical distinctions of the post-collisional mafic rocks verify the contributions from continental subduction to heterogeneous mantle metasomatism and magmatic diversity.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012179","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143888882","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":"Timing of Dike and Sill Emplacement in the Inner Aureole of the Alta Stock, Utah Determined by Zircon and Monazite Petrochronology","authors":"C. J. Beno,&nbsp;M. A. Stearns,&nbsp;J. R. Bowman,&nbsp;J. M. Bartley,&nbsp;D. P. Fernandez,&nbsp;A. R. C. Kylander-Clark","doi":"10.1029/2024GC011946","DOIUrl":"https://doi.org/10.1029/2024GC011946","url":null,"abstract":"<p>Detailed geochronology from two compositionally distinct generations of dikes and sills intruded into the Alta metamorphic aureole, north-central Utah, complement previous geochronologic studies from the Alta stock, providing information on the timing of magmatism and the nature of emplacement. Uranium/thorium-lead dates and chemistry were measured in zircon and monazite from these intrusions and associated reaction selvages in hornfels by split-stream laser ablation techniques. Concordant zircon U-Pb dates (<i>n</i> = 532) define a dispersed population of dates that range from ∼38 to 32 Ma. Monazite Th-Pb dates (<i>n</i> = 888) from granodioritic compositions range from ∼40 to 32 Ma. Evaluation of ²⁰⁸Pb/²³²Th and ²⁰⁷Pb/²⁰⁶Pb-corrected dates with respect to common Pb, U and Th/U values allows rigorous evaluation of the effects of excess ²⁰⁶Pb in these young monazites, yielding concordant ²⁰⁸Pb/²³²Th and ²⁰⁷Pb/²⁰⁶Pb-corrected dates in monazites from the granodiorite, consistent with zircon dates from the same thin sections. Leucogranite sills and dikes, which cross-cut the older granodiorite, have younger monazite dates from ∼33 to 28 Ma. Elevated heavy rare earth element concentrations and trends of larger negative Eu anomalies in the youngest monazites suggest crystallization from an evolved melt. Integration of these new geochronology results and field relationships with prior results from the Alta stock indicate the granodiorite represents the oldest material emplaced in the Alta system. Leucogranite aplite/pegmatite dikes and sills in the inner Alta aureole were emplaced during the final stage of Alta stock construction by injection of evolved water-rich magmas.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"26 5","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011946","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143889029","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}