Geochemistry Geophysics Geosystems最新文献

{"title":"Reconstruction of Core-Surface Flows During the Last 3,300 Years","authors":"Pablo Rivera,&nbsp;F. J. Pavón-Carrasco,&nbsp;M. L. Osete","doi":"10.1029/2025GC012475","DOIUrl":"https://doi.org/10.1029/2025GC012475","url":null,"abstract":"<p>Understanding the Earth's magnetic field evolution requires examining the fluid flow at the core-mantle boundary that drives the changes over different timescales. The inversion process to derive core-surface flow velocities from secular variation data encounters non-uniqueness issues, necessitating a priori assumptions that yield different flow solutions. In this work, we investigate the Earth's core-surface flows over the last 3,300 years using the SHAWQ-family archeomagnetic model (Campuzano et al., 2019, https://doi.org/10.1016/j.epsl.2019.01.050; Osete et al., 2020, https://doi.org/10.1016/j.epsl.2019.116047) to invert for time-dependent purely toroidal and tangentially geostrophic solutions. We apply the constraints as regularization terms that let us reproduce different large-scale flows at the core surface. We evaluate the frozen-flux hypothesis and we show that the temporal averaging range in archeomagnetic models reliably captures the long-term behavior of core-surface flows over time. Then, we use these core flow models to analyze different global phenomena, such as the episodes of large-scale eastward and westward flow and the exchange of angular momentum between the fluid core and the mantle that contributes to the Length of the Day variations at millennial timescales.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012475","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565938","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 Analysis of Diachronous V-Shaped Ridges and Troughs That Flank the Reykjanes Ridge South of Iceland","authors":"Nicky White,&nbsp;Chia-Yu Tien,&nbsp;Callum Pearman,&nbsp;John Maclennan,&nbsp;Bramley Murton,&nbsp;Expedition 395 Scientists","doi":"10.1029/2025GC012729","DOIUrl":"10.1029/2025GC012729","url":null,"abstract":"<p>It is recognized that mantle plumes play a direct role in generating regional uplift and producing immense volumes of basaltic magmatism, both of which can influence paleoclimate. The Icelandic Plume, beneath the North Atlantic Ocean, is of particular importance due to its size and position at a significant paleoceanographic gateway. It is transected by a mid-oceanic ridge system, which has generated a series of V-shaped ridges and troughs that flank the Reykjanes Ridge south of Iceland. The origin of these diachronous features is debated—do they reflect thermal fluctuations within the plume head or have they formed as a result of compositional variations within the buoyant convecting mantle? To address these and other hypotheses, the International Ocean Discovery Program (IODP) carried out three drilling expeditions, which recovered basalt cores from a sequence of V-shaped ridges and troughs. Here, we show that the petrology and geochemistry of fifty whole-rock samples taken from boreholes that penetrate different ridges and troughs reveal systematic differences in major, trace and rare earth element concentrations. By combining forward and inverse modeling based upon polybaric fractional melting, we show that these geochemical variations can be explained by varying melt fraction as a function of depth for plausible mantle source compositions. Our results suggest that temperature differences of 25–30<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>°</mo>\u0000 </mrow>\u0000 <annotation> ${}^{circ}$</annotation>\u0000 </semantics></math>C between cooler troughs and hotter ridges play a dominant role. We conclude that the drilled basaltic rocks reveal a chronology of resolvable temperature perturbations that should help to elucidate the fluid dynamics of flow within this major plume.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012729","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565778","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 Analysis of Diachronous V-Shaped Ridges and Troughs That Flank the Reykjanes Ridge South of Iceland","authors":"Nicky White,&nbsp;Chia-Yu Tien,&nbsp;Callum Pearman,&nbsp;John Maclennan,&nbsp;Bramley Murton,&nbsp;Expedition 395 Scientists","doi":"10.1029/2025GC012729","DOIUrl":"https://doi.org/10.1029/2025GC012729","url":null,"abstract":"<p>It is recognized that mantle plumes play a direct role in generating regional uplift and producing immense volumes of basaltic magmatism, both of which can influence paleoclimate. The Icelandic Plume, beneath the North Atlantic Ocean, is of particular importance due to its size and position at a significant paleoceanographic gateway. It is transected by a mid-oceanic ridge system, which has generated a series of V-shaped ridges and troughs that flank the Reykjanes Ridge south of Iceland. The origin of these diachronous features is debated—do they reflect thermal fluctuations within the plume head or have they formed as a result of compositional variations within the buoyant convecting mantle? To address these and other hypotheses, the International Ocean Discovery Program (IODP) carried out three drilling expeditions, which recovered basalt cores from a sequence of V-shaped ridges and troughs. Here, we show that the petrology and geochemistry of fifty whole-rock samples taken from boreholes that penetrate different ridges and troughs reveal systematic differences in major, trace and rare earth element concentrations. By combining forward and inverse modeling based upon polybaric fractional melting, we show that these geochemical variations can be explained by varying melt fraction as a function of depth for plausible mantle source compositions. Our results suggest that temperature differences of 25–30<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>°</mo>\u0000 </mrow>\u0000 <annotation> ${}^{circ}$</annotation>\u0000 </semantics></math>C between cooler troughs and hotter ridges play a dominant role. We conclude that the drilled basaltic rocks reveal a chronology of resolvable temperature perturbations that should help to elucidate the fluid dynamics of flow within this major plume.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012729","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565779","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":"Laboratory Measurements of Rise Velocity for Individual, Hydrate-Free and Hydrate-Coated Gas Bubbles in Water","authors":"Alexandra M. Padilla,&nbsp;William F. Waite","doi":"10.1029/2024GC011919","DOIUrl":"10.1029/2024GC011919","url":null,"abstract":"<p>Tracking methane transport becomes more complicated in the deep ocean where seafloor release of methane gas bubbles occurs at the high pressures and low temperatures conducive to hydrate formation on bubble surfaces. Gas hydrate formation can make the bubble surface rigid, preventing the dynamic interplay between bubble size, shape and rise velocity that gas-transport models commonly rely upon when using bubble size to predict bubble rise velocity. To better constrain gas-transport model predictions, we conducted controlled laboratory measurements of rise velocity, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>u</mi>\u0000 <mi>z</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${u}_{z}$</annotation>\u0000 </semantics></math>, for hydrate-free air, methane, and xenon bubbles and hydrate-coated xenon bubbles. Experimental results for <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>u</mi>\u0000 <mi>z</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${u}_{z}$</annotation>\u0000 </semantics></math> were compared to predicted <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>u</mi>\u0000 <mi>z</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${u}_{z}$</annotation>\u0000 </semantics></math> values from several published parameterizations used to study dissolution of gas bubbles rising in the ocean. For both hydrate-free and hydrate-coated gas bubbles, the McGinnis et al. (2006), https://doi.org/10.1029/2005jc003183 parameterization provides the most accurate <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>u</mi>\u0000 <mi>z</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${u}_{z}$</annotation>\u0000 </semantics></math> predictions.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011919","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147643216","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":"Geodynamic Controls on Mantle Differentiation and Preservation of Long-Term Geochemical Heterogeneity: Focus on the Primitive Undegassed Mantle","authors":"Nicolas Récalde,&nbsp;J. Huw Davies,&nbsp;James Panton,&nbsp;Don Porcelli,&nbsp;Morten Andersen","doi":"10.1029/2025GC012516","DOIUrl":"https://doi.org/10.1029/2025GC012516","url":null,"abstract":"<p>The compositional evolution of the Earth's mantle is the result of mantle differentiation and thermal evolution. Partial melting of mantle materials produces geochemical heterogeneities, allows for degassing and depends on the thermal state of the mantle, itself governed by convection. Helium and argon constraints suggest that the Earth's mantle is not fully degassed, implying the preservation of long-term heterogeneities, including the primitive undegassed mantle. While previous research has shown that the preservation of old heterogeneities can be improved by increasing the material's density or viscosity, the role of mantle dynamics in controlling mantle differentiation remains unclear. Therefore, using 3D spherical mantle convection simulations tracking bulk composition and degassing, we investigate the influence of mantle viscosity, heat-producing elements (HPEs) enrichment and initial temperature on mantle differentiation. The resulting preservation of primitive undegassed material is systematically analyzed. Results show that thermal evolution (i.e., the cooling history of the mantle) is the main control of the processing history. The ability of the mantle to release its heat, also determined by shallow conditions, governs the processing rates and the types of material processed within melting zones. Models testing the influence of HPEs concentration and initial temperature all reach Earth's current processing rate estimates but primitive undegassed material preservation varies between <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>≈</mo>\u0000 <mn>1</mn>\u0000 <mi>%</mi>\u0000 <mo>−</mo>\u0000 <mn>30</mn>\u0000 <mi>%</mi>\u0000 </mrow>\u0000 <annotation> ${approx} 1%-30%$</annotation>\u0000 </semantics></math> after <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>5</mn>\u0000 <mspace></mspace>\u0000 <mi>G</mi>\u0000 <mi>y</mi>\u0000 <mi>r</mi>\u0000 </mrow>\u0000 <annotation> $5 mathrm{G}mathrm{y}mathrm{r}$</annotation>\u0000 </semantics></math>. Therefore, the processing history is crucial when studying preservation of long-term heterogeneities. The dispersal of the unsampled primitive material by convection allows its temperature to converge to that of the average mantle, promoting its preservation.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012516","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565225","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":"Geodynamic Controls on Mantle Differentiation and Preservation of Long-Term Geochemical Heterogeneity: Focus on the Primitive Undegassed Mantle","authors":"Nicolas Récalde,&nbsp;J. Huw Davies,&nbsp;James Panton,&nbsp;Don Porcelli,&nbsp;Morten Andersen","doi":"10.1029/2025GC012516","DOIUrl":"10.1029/2025GC012516","url":null,"abstract":"<p>The compositional evolution of the Earth's mantle is the result of mantle differentiation and thermal evolution. Partial melting of mantle materials produces geochemical heterogeneities, allows for degassing and depends on the thermal state of the mantle, itself governed by convection. Helium and argon constraints suggest that the Earth's mantle is not fully degassed, implying the preservation of long-term heterogeneities, including the primitive undegassed mantle. While previous research has shown that the preservation of old heterogeneities can be improved by increasing the material's density or viscosity, the role of mantle dynamics in controlling mantle differentiation remains unclear. Therefore, using 3D spherical mantle convection simulations tracking bulk composition and degassing, we investigate the influence of mantle viscosity, heat-producing elements (HPEs) enrichment and initial temperature on mantle differentiation. The resulting preservation of primitive undegassed material is systematically analyzed. Results show that thermal evolution (i.e., the cooling history of the mantle) is the main control of the processing history. The ability of the mantle to release its heat, also determined by shallow conditions, governs the processing rates and the types of material processed within melting zones. Models testing the influence of HPEs concentration and initial temperature all reach Earth's current processing rate estimates but primitive undegassed material preservation varies between <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>≈</mo>\u0000 <mn>1</mn>\u0000 <mi>%</mi>\u0000 <mo>−</mo>\u0000 <mn>30</mn>\u0000 <mi>%</mi>\u0000 </mrow>\u0000 <annotation> ${approx} 1%-30%$</annotation>\u0000 </semantics></math> after <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>5</mn>\u0000 <mspace></mspace>\u0000 <mi>G</mi>\u0000 <mi>y</mi>\u0000 <mi>r</mi>\u0000 </mrow>\u0000 <annotation> $5 mathrm{G}mathrm{y}mathrm{r}$</annotation>\u0000 </semantics></math>. Therefore, the processing history is crucial when studying preservation of long-term heterogeneities. The dispersal of the unsampled primitive material by convection allows its temperature to converge to that of the average mantle, promoting its preservation.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012516","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565260","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":"Eocene Lamproitic Magmatism in Gangdese: Melting Sub-Arc Lithospheric Mantle and Implications for the Early Cenozoic Magmatic “Flare Up” in Southern Tibet","authors":"Y. H. Tian,&nbsp;L. S. Zeng,&nbsp;L. H. Zhao,&nbsp;L. L. Yan,&nbsp;G. X. Li","doi":"10.1029/2025GC012634","DOIUrl":"https://doi.org/10.1029/2025GC012634","url":null,"abstract":"<p>The role of sub-arc mantle lithosphere in the build-up of a batholith is an outstanding issue that is still not well resolved. Lamproite is a mantle-derived magmatic rock that provides a window to learn the composition and the enrichment processes of subcontinental lithospheric mantle (SCLM). Zircon and titanite U-Pb age data on a dike of lamproite from the Gangdese batholith indicate that this dike was generated at ∼44 Ma. These lamproitic samples are ultrapotassic with high K₂O contents and high Sr and Ba concentrations. They show strong enrichment in light rare earth elements (LREE), depletion in heavy rare earth elements (HREE) and substantial negative anomalies in Ti, Nb, and Ta. These lamproitic rocks are characterized by radiogenic ⁸⁷Sr/⁸⁶Sr and unradiogenic ɛ_Nd(t) (−11.6 to −12.5), elevated ²⁰⁶Pb/²⁰⁴Pb(t) (18.71–18.73), ²⁰⁷Pb/²⁰⁴Pb(t) (15.75–15.76) and ²⁰⁸Pb/²⁰⁴Pb(t) (39.62–39.73) isotope compositions, suggesting that the lamproite was derived from a fluid-metasomatized sub-arc lithospheric mantle. Monte Carlo modeling indicates that this metasomatic event occurred at 174 Ma during the subduction of the Tethyan oceanic lithosphere. The ∼44 Ma Tunba lamproitic magmatism represents a magmatic response to the early Cenozoic slab breakoff of the Neo-Tethyan oceanic lithosphere. During the early Cenozoic magmatic “flare up,” melting of a metasomatized sub-arc lithospheric mantle could increase the magma production in addition to the magmas from the asthenospheric mantle. This process could be another important factor that enhances the magmatic “flare up” in the Gangdese batholith in particular and other batholith worldwide.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012634","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565435","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":"Changes in Shell and Crystal Structure From Life to Sediments: An EBSD Characterization of Subantarctic Planktic Foraminifera","authors":"S. M. Smart,&nbsp;S. E. Fawcett,&nbsp;H. Stowell,&nbsp;A. Pérez-Huerta","doi":"10.1029/2025GC012330","DOIUrl":"https://doi.org/10.1029/2025GC012330","url":null,"abstract":"<p>Fossil foraminifera store a wealth of information about past climates and ecosystems in their shell chemistry. However, these element and isotope signals may be affected by post-mortem diagenesis (i.e., alteration). Here, we use Electron Backscatter Diffraction (EBSD; crystal orientation mapping) to evaluate the structural integrity of sub-fossil (core-top) <i>Globorotalia inflata</i> and <i>truncatulinoides</i> shells versus live-caught (net-tow) specimens from the Subantarctic. All shells have smaller, less crystalline grains in the inner wall compared to the outer wall, with more extreme inner- versus outer-wall differences in crystallinity for core-tops. In tow-shells, larger outer-wall grains are elongated, whereas in core-tops, they vary from elongated to polygonal. Sectioning geometry contributes to more polygonal shapes in some maps, and the addition of gametogenic calcite (not yet present in tow-shells) explains the thicker, double-layer structure in core-tops. Weaker diffraction from the inner/ontogenetic layer likely implicates partial dissolution. Crystal orientations in tow-caught shells are strictly radial, with the <i>c</i>-axis normal to and following the curvature of the shell wall. The dominant misorientation (i.e., difference in orientation between neighboring grains) is 60° driven by extensive <i>c</i>-axis twinning. In core-tops, crystal orientations are less strictly radial and sometimes exhibit fanning, which are possible indicators of recrystallization. In <i>G. inflata</i>, particularly those without a veneer, <i>c</i>-axis twinning is weak. We propose a combination of originally less-twinned gametogenic calcite and greater diagenetic loss of twin boundaries than <i>G. truncatulinoides</i>. Variable preservation of inner versus outer layers and potentially different shells/chambers from the same sediments highlights the challenge of selecting appropriate targets for paleo-reconstructions.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012330","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565261","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":"Changes in Shell and Crystal Structure From Life to Sediments: An EBSD Characterization of Subantarctic Planktic Foraminifera","authors":"S. M. Smart,&nbsp;S. E. Fawcett,&nbsp;H. Stowell,&nbsp;A. Pérez-Huerta","doi":"10.1029/2025GC012330","DOIUrl":"10.1029/2025GC012330","url":null,"abstract":"<p>Fossil foraminifera store a wealth of information about past climates and ecosystems in their shell chemistry. However, these element and isotope signals may be affected by post-mortem diagenesis (i.e., alteration). Here, we use Electron Backscatter Diffraction (EBSD; crystal orientation mapping) to evaluate the structural integrity of sub-fossil (core-top) <i>Globorotalia inflata</i> and <i>truncatulinoides</i> shells versus live-caught (net-tow) specimens from the Subantarctic. All shells have smaller, less crystalline grains in the inner wall compared to the outer wall, with more extreme inner- versus outer-wall differences in crystallinity for core-tops. In tow-shells, larger outer-wall grains are elongated, whereas in core-tops, they vary from elongated to polygonal. Sectioning geometry contributes to more polygonal shapes in some maps, and the addition of gametogenic calcite (not yet present in tow-shells) explains the thicker, double-layer structure in core-tops. Weaker diffraction from the inner/ontogenetic layer likely implicates partial dissolution. Crystal orientations in tow-caught shells are strictly radial, with the <i>c</i>-axis normal to and following the curvature of the shell wall. The dominant misorientation (i.e., difference in orientation between neighboring grains) is 60° driven by extensive <i>c</i>-axis twinning. In core-tops, crystal orientations are less strictly radial and sometimes exhibit fanning, which are possible indicators of recrystallization. In <i>G. inflata</i>, particularly those without a veneer, <i>c</i>-axis twinning is weak. We propose a combination of originally less-twinned gametogenic calcite and greater diagenetic loss of twin boundaries than <i>G. truncatulinoides</i>. Variable preservation of inner versus outer layers and potentially different shells/chambers from the same sediments highlights the challenge of selecting appropriate targets for paleo-reconstructions.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012330","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565437","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":"Eocene Lamproitic Magmatism in Gangdese: Melting Sub-Arc Lithospheric Mantle and Implications for the Early Cenozoic Magmatic “Flare Up” in Southern Tibet","authors":"Y. H. Tian,&nbsp;L. S. Zeng,&nbsp;L. H. Zhao,&nbsp;L. L. Yan,&nbsp;G. X. Li","doi":"10.1029/2025GC012634","DOIUrl":"10.1029/2025GC012634","url":null,"abstract":"<p>The role of sub-arc mantle lithosphere in the build-up of a batholith is an outstanding issue that is still not well resolved. Lamproite is a mantle-derived magmatic rock that provides a window to learn the composition and the enrichment processes of subcontinental lithospheric mantle (SCLM). Zircon and titanite U-Pb age data on a dike of lamproite from the Gangdese batholith indicate that this dike was generated at ∼44 Ma. These lamproitic samples are ultrapotassic with high K₂O contents and high Sr and Ba concentrations. They show strong enrichment in light rare earth elements (LREE), depletion in heavy rare earth elements (HREE) and substantial negative anomalies in Ti, Nb, and Ta. These lamproitic rocks are characterized by radiogenic ⁸⁷Sr/⁸⁶Sr and unradiogenic ɛ_Nd(t) (−11.6 to −12.5), elevated ²⁰⁶Pb/²⁰⁴Pb(t) (18.71–18.73), ²⁰⁷Pb/²⁰⁴Pb(t) (15.75–15.76) and ²⁰⁸Pb/²⁰⁴Pb(t) (39.62–39.73) isotope compositions, suggesting that the lamproite was derived from a fluid-metasomatized sub-arc lithospheric mantle. Monte Carlo modeling indicates that this metasomatic event occurred at 174 Ma during the subduction of the Tethyan oceanic lithosphere. The ∼44 Ma Tunba lamproitic magmatism represents a magmatic response to the early Cenozoic slab breakoff of the Neo-Tethyan oceanic lithosphere. During the early Cenozoic magmatic “flare up,” melting of a metasomatized sub-arc lithospheric mantle could increase the magma production in addition to the magmas from the asthenospheric mantle. This process could be another important factor that enhances the magmatic “flare up” in the Gangdese batholith in particular and other batholith worldwide.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":"27 3","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GC012634","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147565434","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}