Earth and Planetary Science Letters最新文献

{"title":"Carboniferous, not Paleoproterozoic, eclogite-facies metamorphism in the northern North China Craton as revealed by in situ garnet Lu-Hf and U-Pb geochronology","authors":"Yao-Qi Yan , Hao Wang , Jin-Hui Yang , Shi-Tou Wu , Jing Ran , Bao-Quan Zhou , Ya-Dong Wu","doi":"10.1016/j.epsl.2025.119207","DOIUrl":"10.1016/j.epsl.2025.119207","url":null,"abstract":"<div><div>Eclogites exposed within orogenic belts or cratonic margins provide critical records of oceanic subduction, continental collision, and supercontinent assembly. Understanding the timing and processes of Precambrian eclogite facies metamorphism is essential for elucidating the onset of modern-style plate tectonics on Earth. The eclogite in the northern margin of the North China Craton (NMNCC) has been regarded by some as key petrological evidence supporting the operation of modern-style plate tectonics during the Paleoproterozoic. However, there is significant controversy regarding the timing (Paleoproterozoic versus Carboniferous) of the peak eclogite-facies metamorphism in the NMNCC, primarily due to the presence of at least two generations of metamorphic zircons within the eclogites and their associated paragneisses. Here we conduct a comprehensive in situ Lu-Hf and U-Pb dating analysis of garnet, the principal mineral for recovering peak eclogite-facies P-T conditions, combined with zircon U-Pb isotopic and mineral inclusion analyses. This approach provides direct and precise geochronological constraints on the peak eclogite-facies metamorphism in the NMNCC. One paragneiss sample yields many Paleoproterozoic (ca. 1.85 Ga) zircon grains with metamorphic characteristics, while metamorphic zircons from other studied eclogite and paragneiss samples yield SIMS U-Pb ages ranging from 325.5 ± 2.0 Ma to 308.9 ± 3.4 Ma. In contrast, the garnets from all eclogite and paragneiss samples do not indicate Paleoproterozoic age and yield consistent in situ Lu-Hf ages of 354 ± 91 Ma to 369 ± 89 Ma and in situ U-Pb ages of 245 ± 180 Ma to 335 ± 27 Ma. The diffusivity of Lu, Hf, U, and Pb ions is substantially slower than that of major elemental cations (i.e., Ca<sup>2+</sup>, Mg<sup>2+</sup>, and Fe<sup>2+</sup>) in garnet. Therefore, the consistent Carboniferous garnet Lu-Hf and U-Pb ages cannot be ascribed to retrograde metamorphism or post-eclogite facies metamorphic overprint. Despite large analytical uncertainties, these ages provide definitive evidence that the eclogite facies metamorphism occurred during the Carboniferous, rather than the Paleoproterozoic. Considering the presence of garnet, rutile, and phengite inclusions within Carboniferous zircons, the obtained zircon U-Pb ages of 326–309 Ma are regarded as the best estimate for the timing of the eclogite facies metamorphism in the NMNCC. The Paleoproterozoic zircons in the paragneiss sample are likely of detrital origin, despite showing some metamorphic characteristics in CL images. The eclogite facies metamorphism likely recorded a collision event between the NMNCC and an island arc within the Paleo-Asian Ocean during the Carboniferous, rather than the onset of modern-style plate tectonics during the Paleoproterozoic. This study underscores the ability of in situ Lu-Hf and U-Pb dating of garnet in distinguishing various potential metamorphic episodes within individual samples and advocates","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"653 ","pages":"Article 119207"},"PeriodicalIF":4.8,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143355410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Decoding the end-Devonian Hangenberg oceanic anoxia event: Insights from ironstones in South China","authors":"Yuanjun Jonathan Lyu ,&nbsp;Mei-Fu Zhou ,&nbsp;Ying Cui ,&nbsp;Rui-Zhong Hu ,&nbsp;Zerui Ray Liu ,&nbsp;Xiyao Li","doi":"10.1016/j.epsl.2025.119203","DOIUrl":"10.1016/j.epsl.2025.119203","url":null,"abstract":"<div><div>The Devonian-Carboniferous Hangenberg event (HBE) was a global oceanic anoxia event. The HBE had profound impacts on the surface environments and caused the sixth biggest bio-extinction in Phanerozoic, with ending the long-lasting greenhouse climate in the Devonian. However, possible mechanisms that triggered the HBE have long been a matter of debate. Enhanced continental weathering or oceanic upwelling has been proposed to be responsible for the HBE. Here, valuable information about the HBE is offered from chamosite and siderite ironstones with structures indicative of paleo-storms in South China. Based on sedimentology, stratigraphy and calcite U-Pb dating, we confirm that the chamosite ironstones and siderite ironstones were formed before and during the main anoxia interval of the HBE, respectively. The concentrations of rare earth elements, U and Mo, V/Cr ratio and Fe and C isotopes of the ironstones are collectively indicative of a redox-stratified ocean under a greenhouse climate at the beginning of the HBE. Subsequently, storm-induced upwelling likely led to surface water eutrophication and the expansion of the oxygen minimum zone, resulting in severe shelf anoxia. The genetic model proposed for the HBE may have implications for the trigger mechanisms of other OAEs in the context of greenhouse climates.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"653 ","pages":"Article 119203"},"PeriodicalIF":4.8,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143313284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mantle wedge serpentinites as a potential nitrogen reservoir regulating subduction-zone nitrogen recycling and mantle heterogeneity","authors":"Kan Li ,&nbsp;Kai Wu ,&nbsp;Amber Jie Yu ,&nbsp;Yi-Fan Du ,&nbsp;Weidong Sun ,&nbsp;Long Li","doi":"10.1016/j.epsl.2025.119211","DOIUrl":"10.1016/j.epsl.2025.119211","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Subduction zone is a unique channel on Earth regulating the long-term exchange of nitrogen (N) between Earth's surface and its interior. Increasing evidence has implied that the serpentinized forearc mantle wedge could be an overlooked sink for slab-derived N that potentially regulates the subduction-zone N cycle but has been poorly studied so far. Here we report the N concentrations and isotope compositions of a suite of lizardite serpentinites, lizardite-antigorite serpentinites, and antigorite serpentinites from the Mianlue tectonic mélange in the Qinling Orogen. These samples cover the serpentine phase variations in serpentinized forearc mantle wedge overlain the subducting slab down to a depth of ∼30 km, and thus provide a unique opportunity to unravel the role of the forearc mantle wedge serpentinization in subduction-zone N cycle. The results show that these serpentinites have significantly higher N concentrations (19.7 to 37.4 ppm) than seafloor serpentinites (3 to 19 ppm), indicating more efficient N uptake during fluid-rock interactions inside the subduction zone. The combined N concentrations and δ&lt;sup&gt;15&lt;/sup&gt;N values suggest that the N added into these serpentinites was mainly mobilized directly from subducted sediments (with a δ&lt;sup&gt;15&lt;/sup&gt;N range of -1 ‰ to +10 ‰) with a small portion possibly derived from abiotic N&lt;sub&gt;2&lt;/sub&gt; reduction (with δ&lt;sup&gt;15&lt;/sup&gt;N value down to -13 ‰). Despite the prograde phase change from lizardite to antigorite, these serpentinites display comparable N concentrations and no sign of metamorphic N devolatilization. The Mianlue serpentinites also show comparable N concentrations with the forearc serpentinized peridotites (dominated by lizardite/chrysotile) from the Mariana mud volcanoes and forearc antigorite serpentinites from the Tso Morari ultrahigh pressure unit exhumed from &gt;100 km depth. These observations suggest strong N retention in the mantle wedge serpentinites during prograde metamorphism. If such N enrichment is typical in the serpentinized forearc mantle wedge, it means that up to 1.4&lt;sup&gt;±0.6&lt;/sup&gt; × 10&lt;sup&gt;9&lt;/sup&gt; mol·yr&lt;sup&gt;-1&lt;/sup&gt; slab N can be incorporated into global forearc mantle wedge. Although this amount only accounts for ∼4 % of the sedimentary N input flux, it may account for a significant portion of the small amount of slab N released during early subduction. This implies that forearc serpentinites may play an unprecedentedly recognized role in subduction-zone N cycle. This role may be even more important in hot subduction zones. If N loss from Catalina Schist (i.e., ∼70 % N loss in the forearc) is employed to represent hot subduction zones, our estimation shows that up to ∼25 % of the lost sedimentary N could be re-fixed in forearc serpentinites. The strong N retention in forearc serpentinites as well as in the minerals after antigorite breakdown (e.g., chlorite, amphibole, clinopyroxene and garnet) facilitates deep recycling of slab N (even in the early Earth","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"653 ","pages":"Article 119211"},"PeriodicalIF":4.8,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143314154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 Oligocene formation of the Qaidam Basin revealed by calcite U-Pb dating: Insights into the northward growth of Tibetan Plateau","authors":"Mengjia Ge ,&nbsp;Lei Wu ,&nbsp;Shitou Wu ,&nbsp;Xuhang Li ,&nbsp;Renjie Zhou ,&nbsp;Xiubin Lin ,&nbsp;Ancheng Xiao ,&nbsp;Shufeng Yang ,&nbsp;Hanlin Chen","doi":"10.1016/j.epsl.2025.119208","DOIUrl":"10.1016/j.epsl.2025.119208","url":null,"abstract":"<div><div>The Qaidam Basin, nestled within the Tibetan Plateau, serves as a vital geological archive documenting the history of plateau growth. However, uncertainties regarding the Cenozoic chronostratigraphy have persisted due to challenges in dating techniques. Here, we presented <em>in situ</em> U-Pb dating on diagenetic calcite cements from lacustrine limestone interbeds in the Xichagou section, western Qaidam Basin. Our work reveals robust and consistent ages of ∼19.6 Ma and ∼13.5 Ma for the upper Xiaganchaigou and lower Xiayoushashan formations, respectively, representing the first radiometric ages for the Cenozoic sediments in the Qaidam Basin. Using these U-Pb ages as chronological anchors, we relocated the correlation of the recognized magnetic polarities with the reference geomagnetic polarity timescale, and further refined the Cenozoic chronostratigraphy together with borehole logging data and correlation with other adjacent sections. Our work revised the onset of deposition of the lowermost Lulehe Formation from the early Eocene to the late Oligocene (∼27.4 Ma) in the western Qaidam Basin. In conjunction with previously published data from the northeastern Qaidam Basin, our findings emphasize that Cenozoic sediment accumulation began almost simultaneously across the entire Qaidam Basin in the late Oligocene, likely caused by synchronous tectonic-driven basin subsidence and uplift of neighboring mountain in response to the India-Eurasian collision. Comparative analysis with the nearby Hoh Xil, Jiuquan and Yin'E basins highlights a progressive northward expansion of the Tibetan Plateau since the late Oligocene, characterized by concurrent basin formation and mountain building processes, rather than uniform plateau-wide elevation gain. The findings underscore the importance of integrating radiometric dating techniques with magnetostratigraphy and structural data to refine regional chronostratigraphic frameworks and understand the dynamic processes shaping the evolution of the Tibetan Plateau.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"653 ","pages":"Article 119208"},"PeriodicalIF":4.8,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143313282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A two-phase two-component slurry model of the F-layer at the base of Earth's core","authors":"Fryderyk Wilczyński ,&nbsp;Christopher J. Davies ,&nbsp;Christopher A. Jones","doi":"10.1016/j.epsl.2024.119196","DOIUrl":"10.1016/j.epsl.2024.119196","url":null,"abstract":"<div><div>We present a new two-phase two-component slurry model of the F-layer at the base of Earth's liquid outer core. Seismic observations indicate that the F-layer is stably stratified, which challenges conventional models of core dynamics that assume outer core convection and dynamo action are powered by heat and light element release at the inner core boundary (ICB). Previous work (<span><span>Wong et al., 2021</span></span>) has shown that an F-layer comprising a “snow” of solid iron particles falling through an iron-oxygen liquid can account for the inferred thickness, density and velocity anomaly of the F-layer; however, the model prescribed simplified fluid dynamical descriptions of the solid and liquid phases. Here we build on the work of <span><span>Wong et al. (2021)</span></span> by incorporating a self-consistent description of two-phase fluid dynamics. Analysing a suite of 1D time-independent solutions reveals that the solid fraction <span><math><msup><mrow><mi>ϕ</mi></mrow><mrow><mi>s</mi></mrow></msup></math></span> and liquid velocity <span><math><msup><mrow><mi>u</mi></mrow><mrow><mi>l</mi></mrow></msup></math></span> decrease with increasing bulk oxygen concentration and buoyancy number <em>B</em>, while <span><math><msup><mrow><mi>ϕ</mi></mrow><mrow><mi>s</mi></mrow></msup></math></span> and <span><math><msup><mrow><mi>u</mi></mrow><mrow><mi>l</mi></mrow></msup></math></span> increase with increasing ICB heat flux and solid/liquid viscosity ratio <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mi>η</mi></mrow></msub></math></span>. Extrapolating to core conditions suggests that <span><math><msup><mrow><mi>ϕ</mi></mrow><mrow><mi>s</mi></mrow></msup><mo>,</mo><msup><mrow><mi>u</mi></mrow><mrow><mi>l</mi></mrow></msup><mo>≪</mo><mn>1</mn></math></span> while the solid velocity <span><math><msup><mrow><mi>u</mi></mrow><mrow><mi>s</mi></mrow></msup></math></span> is comparable to velocities at the top of the liquid core inferred from geomagnetic secular variation. Our results suggest that stable stratification in the F-layer arises from compositional variations maintained by outward barodiffusion and flux of light element that balance the inward flux of solid.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"653 ","pages":"Article 119196"},"PeriodicalIF":4.8,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143313217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Development of arc curvature by asymmetric migration: Evidence from Permian–Triassic granitoids in the New England Orogen (eastern Australia)","authors":"Gideon Rosenbaum ,&nbsp;Abbas Babaahmadi ,&nbsp;Stijn Glorie ,&nbsp;Wouter P. Schellart","doi":"10.1016/j.epsl.2025.119209","DOIUrl":"10.1016/j.epsl.2025.119209","url":null,"abstract":"<div><div>Magmatic arcs commonly display curved and segmented map-view geometry and their temporal evolution involves migration across strike and episodic magmatism. To investigate relationships between arc curvature and slab geometry in an evolving orogen, we studied the spatio-temporal evolution of a Permian–Triassic arc in eastern Australia. New and compiled U-Pb zircon dates reveal that arc magmatism was episodic, with peak activity at ∼252 Ma, followed by a ∼7 Myr magmatic lull. The onset of contractional deformation (Hunter-Bowen orogeny), at 269–252 Ma, was accompanied by landward arc migration, but the rates of arc advance varied along strike. This created a prominent curve in the arc. A subsequent phase of subduction rollback and/or slab steepening, at 240–235 Ma, was accompanied by trenchward arc migration and the development of a new non-curved arc. We suggest that arc curvature was likely the consequence of along-strike changes in the slab dip angle, with arc advance occurring in response to flattening of the subducting slab. The immobile portion of this arc coincides with an area where the underlying lithosphere is anomalously thick, indicating that arc migration was directly influenced by overriding-plate heterogeneities, whereby the presence of a thicker overriding lithosphere inhibited slab flattening. We conclude that interactions between slab geometry and overriding-plate thickness may control arc behaviour globally and may explain kinks and curvatures in other arc systems, such as in the Bolivian Orocline.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"653 ","pages":"Article 119209"},"PeriodicalIF":4.8,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143313212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Phosphorus-to-calcium ratios in benthic foraminiferal shells as a proxy for coastal seawater phosphate concentrations","authors":"Han Zhang ,&nbsp;Bochao Xu ,&nbsp;Zhiqing Lai ,&nbsp;Adina Paytan ,&nbsp;William C. Burnett ,&nbsp;Xiaoyi Guo ,&nbsp;Lihui Ren ,&nbsp;Yuan Lu ,&nbsp;Jianing Zhang ,&nbsp;Huamao Yuan ,&nbsp;Qingzhen Yao ,&nbsp;Zhigang Yu","doi":"10.1016/j.epsl.2025.119210","DOIUrl":"10.1016/j.epsl.2025.119210","url":null,"abstract":"<div><div>Establishing a reliable proxy for seawater phosphate concentrations is important for understanding phosphorus (P) biogeochemistry in the ocean and its change over geological time. P/Ca ratios in benthic foraminiferal shells were examined as a potential proxy for seawater dissolved inorganic phosphate (DIP) concentrations. We developed a method for analyzing benthic foraminiferal P/Ca ratios using Electron Probe Microanalysis (EPMA). We first examined the effect of two different cleaning protocols on P/Ca ratios in foraminiferal shells. Average P/Ca ratios only after physical were over 50 % higher than those after physical and oxidative cleaning, indicating that oxidative cleaning efficiently removed P associated with organic matter. Our results also showed that P concentrations were high in the pore-rich regions of foraminiferal shells, which may be related to higher concentration of organic matter. We collected P/Ca ratios in non-pore regions of oxidative cleaned shells of the benthic foraminifera species <em>Florilus decorus</em> (<em>F. decorus</em>) from the Changjiang Estuary. Results show a significant positive relationship between the average P/Ca ratios of these samples and DIP concentrations in bottom seawater. We therefore propose that P/Ca ratios in non-pore regions of oxidative cleaned foraminiferal shells hold potential as a proxy for DIP concentrations in marine environment. Further exploration into phosphorus phases and the role of organics within foraminiferal shells is needed to advance this proxy and enable its quantitative application in reconstructing ancient ocean DIP history.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"654 ","pages":"Article 119210"},"PeriodicalIF":4.8,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143300335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Large burial flux of modern organic carbon in the St. Lawrence estuarine system indicates a substantial atmospheric carbon sink","authors":"Yunfeng Wang ,&nbsp;Jason M.E. Ahad ,&nbsp;Alfonso O. Mucci ,&nbsp;Yves Gélinas ,&nbsp;Peter M.J. Douglas","doi":"10.1016/j.epsl.2025.119204","DOIUrl":"10.1016/j.epsl.2025.119204","url":null,"abstract":"<div><div>Estuarine and fjord systems host large amounts of buried organic carbon with highly heterogeneous sources in their sediments. The age of this buried carbon is important because it determines to what extent it represents a short-term atmospheric carbon sink on decadal to centennial timescales. Here, we utilized molecular (fatty acids and <em>n</em>-alkanes) and bulk radiocarbon (¹⁴C), stable isotope, and elemental analyses and a mixing model to apportion the source of organic carbon buried in the Lower St. Lawrence Estuary, the world's largest estuary, and the linked Saguenay Fjord, differentiating between modern, millennial aged, and fossil carbon sources. The ¹⁴C ages of long-chain (C₂₄₊₂₆) fatty acids indicate an average terrestrial storage time of ∼1700 ± 284 yr (before present) for soil organic carbon prior to re-deposition in these sediments. A three-tracer source model for bulk organic carbon indicates that 64 ± 0.8 % of organic carbon buried in the Saguenay Fjord and Lower St. Lawrence Estuary was modern marine- and terrestrially-derived carbon, representing direct atmospheric carbon sinks, while 36 ± 4 % was pre-aged soil and fossil petrogenic organic carbon. Comparison with a similar dataset from the subtropical Pearl River Estuary in China indicates that burial of soil and petrogenic organic carbon is significantly lower in the Lower St. Lawrence Estuary on both a fractional and flux basis, probably as a result of greater topographic relief and human land use in the Pearl River catchment, which generates greater erosional inputs of soil and petrogenic carbon.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"652 ","pages":"Article 119204"},"PeriodicalIF":4.8,"publicationDate":"2025-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143307416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Evidence for the role of tropical plumes in driving mid-Holocene north-west Sahara rainfall","authors":"Hamish O. Couper ,&nbsp;Christopher C. Day ,&nbsp;Julia J. Barrott ,&nbsp;Samuel J. Hollowood ,&nbsp;Stacy A. Carolin ,&nbsp;Ben Lovett ,&nbsp;Abdeljalil Bouzouggar ,&nbsp;Nick Barton ,&nbsp;Gideon M. Henderson","doi":"10.1016/j.epsl.2024.119195","DOIUrl":"10.1016/j.epsl.2024.119195","url":null,"abstract":"<div><div>The West African Monsoon (WAM), Atlantic north-westerlies and Mediterranean cyclones are significant sources of rainfall in north-west Africa, supplying moisture to the fringes of the Sahara. Rainfall patterns and the extent of the desert vary through time with strong evidence of a wetter Sahara during the early- to mid-Holocene (widely referred to as the African Humid Period). North of 28°N there is a particular lack of palaeorainfall reconstructions, with higher spatial- and temporal-resolution required to constrain the mechanisms responsible for past sub-tropical climate change, and the impacts of environmental change on human developments. We provide palaeorainfall reconstructions from stalagmites from today's arid north-west Sahara, inland from the coast and south of the Atlas Mountains in Morocco (30–32°N). The records show increased rainfall between 8.7–4.3 kyr BP. The timing, and oxygen isotopes of the speleothem growth, in comparison with other records, strongly suggest that South-of-Atlas rainfall continued after the decline of the West African Monsoon in the mid-Holocene. We propose that additional rainfall was supplied by increased tropical-plume rainfall in the South-of-Atlas region. We suggest that an increased North-South inter-hemispheric temperature anomaly, shifting the ITCZ northwards, increased the supply of tropical-moisture to tropical-plumes. For the first time this study provides evidence supporting tropical-plumes as an additional source of past-rainfall, helping to reconcile palaeo-archives and modelling studies. Increased South-of-Atlas rainfall improved habitability and increased recharge to rivers flowing south into the Sahara, which likely facilitated connectivity through the Sahara, during a key period in the development of land use and animal production.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"652 ","pages":"Article 119195"},"PeriodicalIF":4.8,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143307415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Vanadium isotope fractionation during early planetary evolution: Insights from achondrite analyses","authors":"D.V. Bekaert ,&nbsp;M. Auro ,&nbsp;K. Righter ,&nbsp;L.D. Peterson ,&nbsp;A.W. Heard ,&nbsp;D. Davis ,&nbsp;E. Füri ,&nbsp;Y. Marrocchi ,&nbsp;A.J. Irving ,&nbsp;K. Prissel ,&nbsp;K. Burton ,&nbsp;C. Fitoussi ,&nbsp;S.G. Nielsen","doi":"10.1016/j.epsl.2025.119202","DOIUrl":"10.1016/j.epsl.2025.119202","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Heavy vanadium (V) isotope compositions of bulk silicate Earth (BSE) and Mars (BSM) relative to chondrites have been suggested to result from high pressure-high temperature core segregation processes on terrestrial planets. However, an alternative possibility is that these heavy V isotope signatures could reflect inheritance from their differentiated planetary building blocks if, for instance, early formed planetesimals underwent V isotope fractionation during differentiation and/or magma ocean evaporation. To test this hypothesis, we report the first V isotope compositions of 40 achondrites (eucrites and diogenites, angrites, ureilites, and acapulcoites-lodranites) originating from four distinct parent bodies. We find that the bulk silicate portions of (4) Vesta and the Angrite Parent Body (APB) exhibit heavy V isotope signatures relative to chondrites, comparable to (or greater than) BSM, but lighter than BSE. On the contrary, the Ureilite Parent Body (UPB) and the Acapulcoite/Lodranite Parent Body (ALPB) are indistinguishable from the chondritic value. To investigate the origin of these V isotope variations, we combine V isotope data with the systematics of other elements. First, we show that differentiated planetary bodies do not exhibit clear V–Sr isotope covariations similar to those recently observed for calcium-aluminum-rich inclusions (CAIs). Only the heavy V isotope signature of (4) Vesta could have potentially resulted from accretionary and/or magma ocean volatilization processes (reflecting ∼0.6 % V and Sr loss). To account for the heavy V but chondritic Sr isotope compositions of the APB, BSM, and Moon, we suggest either (i) extremely large isotope fractionation of V during core formation, or (ii) significantly higher metal-silicate partition coefficients (i.e., more siderophile V) than expected based on experimental data and planetary body conditions. Alternatively, conditions of nebular evaporation recorded in CAIs may not apply to planetary evolution, or the volatilities of V and Sr may differ significantly under early planetary conditions. Similarly, we observe no strong correlation between V and evaporation-sensitive elements like K, likely due to K's much higher volatility compared to V. Potential correlations between V and elements such as Mg (R² = 0.98), Si (R² = 0.81), and Fe (R² = 0.46) suggest that these elements – in particular Mg – may exhibit volatilities closer to V than to K or Sr during planetary evaporation. Explaining bulk δ&lt;sup&gt;51&lt;/sup&gt;V variations through vapor–melt fractionation – rather than V partitioning into the core – would alleviate potential conflicts between our data and previous modeling based on available experimental results regarding V metal-silicate partitioning. In any case, the lack of a V isotope anomaly for the UPB and ALPB indicates that the processes responsible for the heavy V isotope compositions of (4) Vesta, the APB, and the terrestrial planets did not occur on these two bodies. ","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"652 ","pages":"Article 119202"},"PeriodicalIF":4.8,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143307359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}