Lithos最新文献

{"title":"The old central igneous complexes of Sal, Boa Vista and Maio islands: Implications for 17 Ma of isotopic evolution of the Cape Verde archipelago","authors":"Carlos Villaseca ,&nbsp;David Orejana ,&nbsp;María J. Huertas ,&nbsp;Eumenio Ancochea ,&nbsp;Cristina de Ignacio ,&nbsp;Joao Mata ,&nbsp;Rita Caldeira ,&nbsp;María García-Rodríguez ,&nbsp;Juan A. Moreno ,&nbsp;Cecilia Pérez-Soba","doi":"10.1016/j.lithos.2025.107975","DOIUrl":"10.1016/j.lithos.2025.107975","url":null,"abstract":"<div><div>The central igneous complexes of the easternmost islands (Sal, Boa Vista and Maio) preserve some of the most ancient outcropping rocks of the Cape Verde (CV) archipelago. These Early to Middle Miocene (about 25 to 12 Ma) complexes show marked isotopic differences between mafic rocks from the northern (Sal and Boa Vista) and the southern Maio Island, the latter showing lower ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and higher ⁸⁷Sr/⁸⁶Sr ratios. The main mantle plume composition beneath Cape Verde is here considered to be dominated by the FOZO component. Our data supports previous models suggesting the incorporation to plume components of minor DMM mantle sources in the northern CV island alignment, whereas mixing with the EM1 pole is prevalent on the southern CV islands. These isotopic differences are evident since the early stages of Cape Verde magmatism. The Late Miocene to Holocene time period (7 to 1.7 Ma) is characterized by the irruption of silica-undersaturated and carbonatite magmas with a relatively homogeneous isotopic composition and highly radiogenic Pb signatures (²⁰⁶Pb/²⁰⁴Pb up to 20.6 in carbonatitic rocks and 20.2 in silicate rocks) throughout most of the Cape Verde archipelago. During this transitional stage, the input of this new HIMU mantle component overprinted the previous mixing of the main FOZO plume component with shallow mantle members (DMM, EM1) of minor contribution.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107975"},"PeriodicalIF":2.9,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143378750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chalcophile element fractionation processes in the oceanic crust: Evidence from trace elements in magmatic sulphides","authors":"Wiebke Lehmann ,&nbsp;Manuel Keith ,&nbsp;Marcel Regelous ,&nbsp;Reiner Klemd ,&nbsp;Martin Kutzschbach","doi":"10.1016/j.lithos.2025.107978","DOIUrl":"10.1016/j.lithos.2025.107978","url":null,"abstract":"<div><div>Important insights into the behaviour of chalcophile elements in magmatic systems can be obtained from the study of immiscible sulphide liquids (SL) and crystalline monosulphide solid solutions (MSS) that are preserved as magmatic sulphides. Here, we report on the trace element compositions of &gt;100 magmatic sulphides and the host volcanic glass from mid-ocean ridges, back-arc basins and intra-oceanic arcs. Most chalcophile elements (e.g., Cu, Zn, Se, Pb, Tl) are enriched in MSS hosted by mafic silicate melts from intra-oceanic arcs compared to those from back-arc basins and mid-ocean ridges, suggesting a contribution of these elements by subduction input. Partition coefficients of SL (D^SL/SM) and MSS (D^MSS/SM) relative to mafic silicate melts (SM) from mid-ocean ridges and back-arc basins are similar to previously published values (e.g., Ni, Cu, Zn, Se, Mo, Ag, Cd, In, Sn, Bi), thereby indicating equilibrium conditions. The new partition coefficients obtained in this study suggest that mid-ocean ridge and back-arc basin magmas typically segregate minor amounts of SL and MSS relative to the silicate melt portion (0.001–1 %), which nevertheless significantly modifies the concentrations of strongly chalcophile elements (D^SL-MSS/SM &gt; 100) of mantle melts during cooling and crystallisation. In contrast, SL and MSS from more evolved subduction zone magmas (&gt;51 wt% SiO₂) typically do not reach equilibrium conditions due to higher melt viscosity and a complex sulphide segregation history. This results in unrealistically low D^SL-MSS/SM values for moderately to strongly chalcophile elements (e.g., Co, Ni, Mo, Sn), which cannot be explained by silicate and oxide fractionation accompanying the sulphide segregation. Therefore, we conclude that sulphide saturation in subduction environments commonly reflects a continuous or multistage process that involves the remelting or resorption of early formed MSS during magma ascent, which liberates chalcophile elements (e.g., Cu, Au, Zn, Sn, Cd, Bi, Te, Ag) into the silicate melt. Accompanied fluid release from such magmas provides a potential mechanism supporting the formation of magmatic-hydrothermal ore deposits. Consequently, a simple single-stage sulphide segregation model at equilibrium conditions, as suggested for mafic mid-ocean ridge magmas, cannot explain the chalcophile element evolution of more evolved silicate melts and genetically related magmatic sulphides in subduction environments.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107978"},"PeriodicalIF":2.9,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143438078","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 evolution of the south Tianshan orogen: Geochronological and geochemical constraints from granitic and mafic dikes","authors":"Tuo Jiang ,&nbsp;Jun Gao ,&nbsp;Reiner Klemd ,&nbsp;Xinshui Wang ,&nbsp;Jilei Li ,&nbsp;Xirun Tong","doi":"10.1016/j.lithos.2025.107983","DOIUrl":"10.1016/j.lithos.2025.107983","url":null,"abstract":"<div><div>Giant mafic and granitic dike swarms can provide invaluable insight into the paleo-geographic reconstruction of supercontinents and the identification of mantle plumes. Although some case studies of orogeny-related dikes have been undertaken, rare systematic information is available concerning the relationship between the formation mechanism of the dikes and orogenesis. In this study, we conducted a detailed geological, geochronological and geochemical study on recently identified granitic and mafic dikes close to the Wuwamen ophiolite complex in the Chinese South Tianshan, aiming to reveal the link between the formation of the dikes and the orogenic evolution. A dike swarm comprising 456 Ma biotite granite dikes, 423 Ma alkali feldspar granite dikes and a 301 Ma diabase dike crosscuts the Xieliwancaikai gneissic diorite with a zircon U<img>Pb age of 475 Ma. In addition, a 301 Ma granite porphyry dike extends across the middle Devonian meta-sedimentary strata in the Tianqiao area. The geochemical characteristics of the biotite granite and the alkali feldspar granite dikes and their gneissic diorite host suggest that the granitic magma was produced by lower crustal melting. However, the granite porphyry dike has chemical characteristics resembling those of S-type granites commonly produced by partial melting of overthickened crust in collisional orogenic belts. Furthermore, the mafic magma source of the diabase dike resulted from low-degree partial melting of a fertilized sub-continental lithospheric mantle. In conjunction with previously published data on the Wuwamen ophiolite Complex, we propose that the 456 Ma metaluminous granite dike reflects the subduction onset of the South Tianshan Ocean, while the 423 Ma metaluminous granite dike represents the felsic arc melts generated during the subsequent subduction. The 321–313 Ma peraluminous mica granite dikes are thought to have formed during the collision between the Tarim and Kazakhstan–Yili–Central Tianshan blocks. In addition, the peraluminous granite, the strongly peraluminous granite porphyry and the diabase dikes that formed between 307 and 301 Ma were generated in a post-collisional extensional environment. Therefore, bimodal dike swarms provide crucial constraints on the geodynamic evolution of orogens.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107983"},"PeriodicalIF":2.9,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143422098","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Filling the gap in the UHP metamorphic record of the Liguro-Piemont Lower unit: Insights on fluid-mediated formation of atoll garnets","authors":"A. Maffeis ,&nbsp;A. Petroccia ,&nbsp;S. Nerone ,&nbsp;F. Caso ,&nbsp;A. Corno ,&nbsp;M. Bonazzi ,&nbsp;F. Boero ,&nbsp;S. Corvò ,&nbsp;S. Ghignone ,&nbsp;C. Groppo","doi":"10.1016/j.lithos.2025.107981","DOIUrl":"10.1016/j.lithos.2025.107981","url":null,"abstract":"<div><div>This contribution investigates the petrologic evolution of a coesite-glaucophane-bearing eclogite belonging to the Liguro-Piemont Lower unit of the Western Alps and explores the formation mechanisms of atoll garnets by integrating petrographic, mineral-chemical, and thermodynamic analyses. The studied eclogite underwent a complex metamorphic history associated with five distinct metamorphic stages: an early greenschist facies stage (&lt;400 °C, &lt;0.6 GPa), two prograde high-pressure stages (early pre-Dp: 450–480 °C, 1.9–2.6 GPa; late pre-Dp: 420–510 °C, 2.3–2.9 GPa), a peak-pressure stage (syn-Dp: 480–580 °C, 2.8–2.9 GPa), and an exhumation stage (post-Dp: 600–630 °C, 1.3–1.5 GPa). The coesite finding links the UH<em>P</em> localities already known northward (Cignana) and southward (Monviso and Val di Susa) in the Liguro-Piemont Lower unit, corroborating the coherence of metamorphic evolution across the Western Alps and filling the gap in the UH<em>P</em> (Ultra-High Pressure) metamorphic record of this sector of the Liguro-Piemont Lower unit. Mineral inclusion patterns and microstructural features support the involvement of aqueous fluids during atoll garnet formation. Electrolytic fluid modelling suggests a dilute aqueous fluid characterized by dissolved Si and Na, capable of selectively dissolving garnet cores and precipitating secondary garnet and omphacite. The garnet fracturing and exposure of its core is attributed to increasing fluid pressure induced by volume changes (up to 40 % increase of the inclusions' volume) related to the breakdown of the lawsonite included in the garnet mantle and to the associated dehydration reactions. These findings contribute to our understanding of fluid-mediated processes during rock exhumation and highlight the role of aqueous fluids in metamorphic reactions and mineral replacement. Also, our results call for further research to explore the link between atoll garnet formation, fluid-rock interactions, and deep paleo-seismicity.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107981"},"PeriodicalIF":2.9,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143387847","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":"Coupled U-Pb, Lu-Hf and trace element geochemistry of apatite reveals complex magmatic-hydrothermal Nb-REE remobilization of the Neoproterozoic Saint-Honoré carbonatite deposit (Quebec, Canada)","authors":"Hélène Legros ,&nbsp;Nils Van Weelderen ,&nbsp;Sarah Dare ,&nbsp;Stijn Glorie ,&nbsp;Michael Higgins ,&nbsp;Dany Savard ,&nbsp;L. Paul Bédard","doi":"10.1016/j.lithos.2025.107980","DOIUrl":"10.1016/j.lithos.2025.107980","url":null,"abstract":"<div><div>Niobium and REE are critical resources that are predominantly associated with carbonatite and alkaline complexes. The Saint-Honoré ore deposit, located in Québec, is a major producer of Nb (7 % of world production) with reserves of 630 thousand tons Nb and major REE resources (1058 thousand tons inferred). This deposit is composed of an outer syenite, inner syenite enclaves, multiple Nb-rich carbonatite intrusions and, a central REE-rich carbonatite. The carbonatites exhibit several generations of apatite (Ca₅(PO₄)₃(F,OH,Cl)) including a magmatic ‘white’ apatite associated with pyrochlore ((Na,Ca)₂Nb₂O₆(OH,F)) and a late hydrothermal ‘red’ apatite. Trace element geochemistry of apatite reveals a very distinct chemistry for both apatite types. The magmatic carbonatite stage is associated with the main Nb mineralization and is dated at 577 ± 14 Ma (U-Pb) and 580 ± 13 Ma (Lu-Hf), with a typical magmatic carbonatite signature whereas the hydrothermal stage has a mixed signature between carbonatite and external fluids which remobilized Nb-(REE) mineralization at 564 ± 16 Ma (Lu-Hf). While the magmatic and hydrothermal stage ages overlap and are also coeval to our lamprophyre apatite age of 569 ± 29 Ma (U-Pb), the late hydrothermal stage is distinctively marked by higher U, Cl, Ba, Fe, Nb and K concentrations in apatite. The late hydrothermal event is linked to a carbonatite fluid mixed with crustal fluids which may have contributed to the emplacement of the REE mineralization in the late stage of the carbonatite complex. This study also highlights the first detailed data on apatite geochemistry from lamprophyre.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107980"},"PeriodicalIF":2.9,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143348780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mechanisms of shear zone development in Krossøy, the Bergen Arcs, Norway","authors":"Lorena H. Filiberto ,&nbsp;Håkon Austrheim ,&nbsp;Andrew Putnis ,&nbsp;José Alberto Padrón-Navarta ,&nbsp;Steven Reddy ,&nbsp;Christine V. Putnis","doi":"10.1016/j.lithos.2025.107977","DOIUrl":"10.1016/j.lithos.2025.107977","url":null,"abstract":"<div><div>The island of Krossøy in the Bergen Arcs, southwestern Norway, provides an ideal geological setting to study the mechanisms of grain size reduction in plagioclase during shear zone development. The transition from a granulite facies anorthosite to mylonitic textures under amphibolite facies conditions is investigated through field observations, petrographic analysis, electron microprobe analysis, and electron backscattered diffraction (EBSD) techniques. Initial ductile deformation, evidenced by complex twinning and intragrain misorientation, leads to strain hardening and subsequent brittle fracturing. This results in grain size reduction primarily through fragmentation, forming a bimodal grain size distribution. Syntectonic recrystallization produces compositionally similar neoblasts. Subsequent interactions with fluids induce compositional recrystallization, leading to further grain size reduction and the formation of zoned plagioclase grains. These processes highlight the critical role of fluid-mediated recrystallization in shear zone development and strain localization. The spatial variation in deformation and hydration stages across Krossøy is attributed to both mechanical anisotropy and chemical reequilibration driven by fluid pathways. These findings enhance our understanding of the interplay between mechanical anisotropy, brittle failure and fluid infiltration in the lower crust, providing insights into the conditions that facilitate the formation and evolution of shear zones in the Bergen Arcs.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107977"},"PeriodicalIF":2.9,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143372526","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":"Partial melting of hydrated harzburgite at shallow pressures: An option to produce melts with boninitic characteristics","authors":"Jürgen Koepke ,&nbsp;Sandrin T. Feig ,&nbsp;Jasper Berndt ,&nbsp;Renat R. Almeev","doi":"10.1016/j.lithos.2025.107979","DOIUrl":"10.1016/j.lithos.2025.107979","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Water-saturated partial melting experiments were carried out using a refractory harzburgite from the Oman Ophiolite as starting material. The experiments were performed at pressures of 100, 200 and 500 MPa using both reducing (corresponding to the FMQ buffer) and oxidizing (FMQ + 3) conditions. Specially designed internally heated pressure vessels were used to control oxygen fugacity and allow rapid quenching. Temperatures varied between 980 and 1220 °C, and run durations were up to 82 h. The solidus and clinopyroxene-out curve show significant variation with pressure. As expected, the melts produced were generally SiO&lt;sub&gt;2&lt;/sub&gt;-rich, with SiO&lt;sub&gt;2&lt;/sub&gt; concentrations ranging between 55 and 65 wt%. These melts exhibit boninitic characteristics. Due to the refractory character of the starting material, the experimental melts are highly depleted in incompatible trace elements, showing chondrite-normalized REE patterns with a characteristic concave-upward shape. Calcium and sodium in the system are mainly derived from the clinopyroxene in the starting harzburgite, resulting in extremely high Ca/Na ratios in the experimental melts. Fractionation of such melts could potentially yield highly depleted gabbronorites as cumulate rocks, with anorthite (An) contents of plagioclase generally in excess of 90 mol%. At temperatures above the clinopyroxene breakdown, the residual mineral paragenesis exhibits characteristics similar to extremely refractory harzburgites, with Cr# in Cr-spinel (Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; /(Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; + Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;), molar) reaching up to 86, reminiscent of ophiolites formed under supra-subduction zone conditions.&lt;/div&gt;&lt;div&gt;While most of the melts produced have compositions of high-Mg andesite, only a few have compositions of true boninites. It is clear, therefore, that the partial melting of hydrous harzburgite at shallow pressure is not a general model for the formation of typical boninites in subduction zone initiation environments. However, our experimental results show that the formation of distinct rock types within the paleocrust of the Oman Ophiolite such as high-Ca boninites, high-Si boninites, high-Mg andesites, depleted gabbronorite cumulate rocks, and extremely refractory harzburgites containing Cr-spinel with Cr# &gt; 80, could, in principle, be attributed to a single process of fluid-induced partial melting of harzburgite below the crust/mantle boundary of the Oman paleocrust. The temperatures for the heating process (&gt; 1040 °C) for such a model, could be provided by ascending MORB magmas. The presence of water-rich fluids at the crust/mantle boundary or within the uppermost mantle which are necessary for such a model, could be derived from seawater via deep hydrothermal fault zones. In support of this contention, we present new amphibole data from cores drilled in the lower gabbros of the Oman Ophiolite by the International Continental Scientific Drilling Program (ICD","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107979"},"PeriodicalIF":2.9,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Alkaline magmatism in the post-orogenic Triassic Predazzo complex, Dolomites, NE Italy: Ages and significance","authors":"Dario Visonà ,&nbsp;Paolo Nimis ,&nbsp;Giancarlo Cavazzini ,&nbsp;Anna M. Fioretti ,&nbsp;Marinella A. Laurenzi ,&nbsp;Matteo Massironi ,&nbsp;Igor M. Villa","doi":"10.1016/j.lithos.2024.107912","DOIUrl":"10.1016/j.lithos.2024.107912","url":null,"abstract":"<div><div>The Predazzo pluton (Predazzo–Monzoni intrusive complex, Dolomites) is a multipulse calc-alkaline–shoshonitic body, which was emplaced at 238.075 ± 0.087 Ma to 235.9 ± 1.8 Ma. On the eastern flank of the pluton, smaller-volume alkaline rocks are also found, but their relationships with the main magmatic products are not well understood. New field, petrographic, geochemical and geochronological data indicate that these alkaline rocks infilled a small volcano-tectonic trough and consist of trachytic lavas and volcanoclastic tephra (V2 unit), studded by small monzonite and syenite bodies (MS unit) in mingling-mixing relationships, yielding ages of 238.1 ± 1.8 to 230.1 ± 0.6 Ma. Phonotephrite to phonolite dykes (MF unit) crosscut the entire volcanic sequence at 215.0 ± 0.3 Ma and 203 ± 1 Ma. The alkaline cycle thus developed soon after and, possibly, during the main calc-alkaline–shoshonitic stage. Lamprophyric dykes (camptonites) were also emplaced from 234.5 ± 0.3 to 219.2 ± 0.7 Ma. Whole-rock compositions suggest that the magmas enriched in asthenospheric component that produced the lamprophyres could generate the MS–V2 and MF magmas by Assimilation-Fractional-Crystallization, involving assimilation of various carbonatic and silicic crustal components. The very rapid passage from the “post-orogenic” calc-alkaline–shoshonitic to the “anorogenic” alkaline affinity in the Middle-Late Triassic thus appears to reflect a continuous transition within the same geodynamic context, characterized by the gradual development of extensional structures, representing the prodrome of the Jurassic rifting, and progressively deeper magma sources, rather than a sudden change in the regional geodynamic regime.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107912"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161513","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":"The mobilization of trace elements in apatite during metamorphic recrystallization: A record from the Huangmailing metamorphosed phosphorite, Hubei Province, Central China","authors":"Cheng-Lai Deng,&nbsp;Shao-Yong Jiang","doi":"10.1016/j.lithos.2024.107897","DOIUrl":"10.1016/j.lithos.2024.107897","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The chemical composition of apatite provides reliable constraints on petrogenetic processes. However, the behavior of apatite and the redistribution of elements during the metamorphism of phosphorite, a unique sedimentary rock type, remain unclear. This study presents textural, in situ U&lt;img&gt;Pb geochronology, trace and rare earth elements, and Sr isotope data for apatite from the Huangmailing metamorphosed phosphorite in Hubei Province, Central China. Four distinct metamorphic phosphorite samples were collected, namely, dolomitic phosphorite, black massive phosphorite, quartz-muscovite-bearing phosphorite, and quartz-muscovite-bearing phosphorite, with different mineral assemblages. We distinguished four types of apatite based on the mineral assemblage. Type 1 apatite occurred as a layer and interbedded with kutnohorite. In contrast, type 2 apatite is associated with the crumpled K-feldspar band, and type 3 apatite is commonly associated with quartz, muscovite, and calcite. Type 4 apatite is distinct from the other three types of apatite, which is characterized by larger grain size and associated with muscovite and monazite. Precise U&lt;img&gt;Pb isotope data for type 1 and 2 apatite were obtained to constrain the metamorphic age of the sedimentary phosphorite, which ranged from 218 ± 6.4 Ma to 214.9 ± 9.6 Ma. Compared with the apatites from the unmetamorphosed phosphorite in south China, the studied apatites are commonly enriched with rare earth elements and yttrium (REY) (except type 3 apatite) but depleted in Ba. These four types of apatite have different trace and rare earth element compositions, especially their REY patterns. The lower (La/Sm)&lt;sub&gt;N&lt;/sub&gt; of type 1 apatite than that of type 2 to 3 apatite may suggest the mobilization of light rare earth element (LREE) in type 1 apatite into the metamorphic fluid. A slightly positive Eu anomaly was observed for the type 2 apatite, suggesting the contribution of dissolved K-feldspar during the metamorphic recrystallization of type 2 apatite. The REY patterns of type 3 apatite differ slightly from those of primary apatite, whereas type 4 apatite presents distinct REY patterns in comparison with the other three types of apatite, with an obvious negative Eu anomaly and the highest LREE content. These findings suggest that the enrichment of Sr and the slightly positive Eu anomalies in type 2 apatite can be linked to the breakdown of K-feldspar during metamorphic reactions. This connection is supported by the comparatively elevated Sr isotopic composition of type 2 apatite. As muscovite and monazite decomposed, the released Th, Pb, Na, and LREEs were incorporated into type 4 apatite. The newly reported data from this study prove that the composition of apatite changes during metamorphism, depending on the local mineral assemblage. The trace elements released from associated minerals may be incorporated into apatite during metamorphic recrystallization, leading to diversity in the chemical sign","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107897"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161553","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Machine learning-based identification of marine and terrestrial Volcanic Rocks in the Tibetan Plateau","authors":"Xinwei Liu ,&nbsp;Qiuming Cheng","doi":"10.1016/j.lithos.2024.107930","DOIUrl":"10.1016/j.lithos.2024.107930","url":null,"abstract":"<div><div>Distinguishing between marine and terrestrial basalts is crucial for understanding geological processes, including plate tectonics, ocean–continent transition history, and paleoenvironmental changes. However, traditional geochemical methods for tectonic setting discrimination are often limited by issues such as data overlap and the difficulty in obtaining representative samples, making it challenging to accurately differentiate tectonic environments. Machine learning provides an effective approach to address these challenges in the context of large datasets and complex geological problems. In this study, advanced machine learning techniques are applied to global basalt geochemical data to develop a model specifically tailored for regional applications. This model, designed to differentiate between oceanic and continental tectonic environments, is then applied to the Tibetan Plateau basalt data, offering insights into the tectonic background of this specific region. The results show that both oceanic and continental basalt records existed in the region up to 90 million years ago, but the oceanic basalt record subsequently disappeared. This finding suggests that, for a prolonged period before the closure of the Neo-Tethys Ocean, oceanic volcanism was no longer occurring in the Tibetan Plateau. This discovery provides new evidence for the timing of the marine–terrestrial environmental transition in the Tibetan Plateau and is significant for understanding the tectonic evolution and geodynamic processes of the Tethys tectonic domain.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107930"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}