Pub Date : 2025-12-15Epub Date: 2025-10-22DOI: 10.1016/j.lithos.2025.108297
Yanjie Li , Yan Liu
<div><div>Granitoids surrounding the Bayan Obo giant rare earth element (REE) deposit in Inner Mongolia, which is the largest REE deposit in the world, have been identified as important wall rocks that may have influenced REE mineralization. However, this hypothesis remains debated, and the classification and petrogenesis of these granitoids are still poorly constrained, which hinders a clear understanding of the local tectonic evolution. To address these issues, we conducted integrated zircon and monazite U<img>Pb geochronology, petrography, whole-rock geochemistry, and Sr–Nd–Pb and zircon Hf<img>O isotopic studies of granitoids in the northern, southwestern, and eastern sectors of the Bayan Obo deposit. These granitoids comprise granites and quartz monzonites that are peraluminous, have high alkali contents and A/CNK values, and are enriched in light REEs and depleted in heavy REEs. Moreover, there is an evolutionary trend from quartz monzonite to granite based on their geochemical compositions. The zircon U<img>Pb ages range from 267.2 to 262.1 Ma, and monazite U–Th–Pb dating yields an age of 270 ± 1.6 Ma, ca. 100 Myr younger than the most recent Caledonian REE mineralization event in the Bayan Obo deposit (∼400 Ma). Petrographic observations and geochemical data suggest that both the granites and quartz monzonites are moderately evolved I-type granites and had a similar source. The quartz monzonites most likely represent early, more mafic products of the magma, whereas the granites formed through subsequent magmatic differentiation. Whole-rock Sr–Nd–Pb and zircon Hf<img>O isotopic compositions suggest derivation mainly from partial melting of ancient mafic lower crust, with an estimated ∼25 % contribution from subduction-related materials (marine sediments and altered oceanic crust). The formation of these granitoids is attributed to the southward subduction of the Paleo-Asian oceanic lithosphere beneath the North China Craton (NCC). Extensive arc magmatism along the northern margin of the NCC during the Permian likely reactivated Proterozoic crustal components, leading to partial melting and the formation of these granitoid intrusions at ca. 265 Ma. Regional comparisons suggest that the continental arc origin of these granitoids provides evidence for southward subduction of Paleo-Asian oceanic lithosphere during the Permian. The occurrence of granitoids around the Bayan Obo REE deposit and their geological relations indicate that such subduction beneath the NCC persisted in this region until ca. 265 Ma. Although very fine-grained monazite and bastnäsite occur locally within the granitoids, these minor REE minerals were most likely produced by hydrothermal reactivation of the Bayan Obo deposit during granitoid emplacement. In general, granitoid magmatism induced localized hydrothermal alteration, causing partial destruction of pre-existing dolomite and limited REE dissolution–transport–reprecipitation, but did not provide additional REE mater
{"title":"Zircon UPb geochronology and Sr–Nd–Pb–Hf–O isotope geochemistry of granitoids around the Bayan Obo rare earth element deposit at the northern margin of the North China Craton: Implications for their petrogenesis and tectonic setting","authors":"Yanjie Li , Yan Liu","doi":"10.1016/j.lithos.2025.108297","DOIUrl":"10.1016/j.lithos.2025.108297","url":null,"abstract":"<div><div>Granitoids surrounding the Bayan Obo giant rare earth element (REE) deposit in Inner Mongolia, which is the largest REE deposit in the world, have been identified as important wall rocks that may have influenced REE mineralization. However, this hypothesis remains debated, and the classification and petrogenesis of these granitoids are still poorly constrained, which hinders a clear understanding of the local tectonic evolution. To address these issues, we conducted integrated zircon and monazite U<img>Pb geochronology, petrography, whole-rock geochemistry, and Sr–Nd–Pb and zircon Hf<img>O isotopic studies of granitoids in the northern, southwestern, and eastern sectors of the Bayan Obo deposit. These granitoids comprise granites and quartz monzonites that are peraluminous, have high alkali contents and A/CNK values, and are enriched in light REEs and depleted in heavy REEs. Moreover, there is an evolutionary trend from quartz monzonite to granite based on their geochemical compositions. The zircon U<img>Pb ages range from 267.2 to 262.1 Ma, and monazite U–Th–Pb dating yields an age of 270 ± 1.6 Ma, ca. 100 Myr younger than the most recent Caledonian REE mineralization event in the Bayan Obo deposit (∼400 Ma). Petrographic observations and geochemical data suggest that both the granites and quartz monzonites are moderately evolved I-type granites and had a similar source. The quartz monzonites most likely represent early, more mafic products of the magma, whereas the granites formed through subsequent magmatic differentiation. Whole-rock Sr–Nd–Pb and zircon Hf<img>O isotopic compositions suggest derivation mainly from partial melting of ancient mafic lower crust, with an estimated ∼25 % contribution from subduction-related materials (marine sediments and altered oceanic crust). The formation of these granitoids is attributed to the southward subduction of the Paleo-Asian oceanic lithosphere beneath the North China Craton (NCC). Extensive arc magmatism along the northern margin of the NCC during the Permian likely reactivated Proterozoic crustal components, leading to partial melting and the formation of these granitoid intrusions at ca. 265 Ma. Regional comparisons suggest that the continental arc origin of these granitoids provides evidence for southward subduction of Paleo-Asian oceanic lithosphere during the Permian. The occurrence of granitoids around the Bayan Obo REE deposit and their geological relations indicate that such subduction beneath the NCC persisted in this region until ca. 265 Ma. Although very fine-grained monazite and bastnäsite occur locally within the granitoids, these minor REE minerals were most likely produced by hydrothermal reactivation of the Bayan Obo deposit during granitoid emplacement. In general, granitoid magmatism induced localized hydrothermal alteration, causing partial destruction of pre-existing dolomite and limited REE dissolution–transport–reprecipitation, but did not provide additional REE mater","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108297"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418538","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}
Pub Date : 2025-12-15Epub Date: 2025-10-22DOI: 10.1016/j.lithos.2025.108299
Xue-Li Li , Jia-Le Xu , Yi-Xiang Chen , Jaime D. Barnes , Sergei Skuzovatov , Tatsuki Tsujimori
Serpentinite-derived fluids are pivotal for fluid mobility and mass transfer in subduction zones. However, the redox state of these fluids and their effects on the composition of continental crust remain unclear. Here, we investigated the Fe3+/ΣFe ratios and Fe isotope compositions of high-pressure fluid-metasomatized schists and blackwall zones surrounding serpentinites from the Tauern Window, Eastern Alps. Relative to the surrounding granodiorite protolith (δ56Fe: −0.14 to 0.66 ‰), schists in the Stillup Tal shear zone exhibit significantly lower δ56Fe values (−0.25 to −0.11 ‰), higher Fe − Mg contents and lower concentrations of large ion lithophile elements. These observations are consistent with the chlorite blackwall rimming a nearby serpentinite body in the Pfitsch area, both of which can be ascribed to the metasomatism by serpentinite-derived fluids. Furthermore, the schists display substantially lower Fe3+/ΣFe ratios than granitoid protoliths. A strong positive correlation between Fe3+/ΣFe and V/Sc ratios of the schists suggests that serpentinite dehydration released reduced fluids. Considering the mineralogical and geochemical differences between the central chlorite-rich schist and other schists in the Stillup Tal shear zone, we propose a fluid metasomatism model for the formation of metasomatic rocks. Initially, serpentinite-derived fluids migrated along a major shear zone, metasomatizing granitoids to form central chlorite-rich schists with extremely high Fe contents and low δ56Fe values (−0.25 ‰) under the condition of high fluid/rock ratios. Subsequently, the evolved serpentinite-derived fluids continued their migration along secondary fractures, generating schists with moderately low δ56Fe values (−0.24 to −0.11 ‰) under the condition of lower fluid/rock ratios. Our results provide geochemical evidence for the reducing nature of serpentinite-derived fluids and their impact on the redox state and Fe isotope composition of rocks with which they interact.
{"title":"Iron isotope evidence for the metasomatism of continental crust by serpentinite-derived reduced fluid in the subduction zone","authors":"Xue-Li Li , Jia-Le Xu , Yi-Xiang Chen , Jaime D. Barnes , Sergei Skuzovatov , Tatsuki Tsujimori","doi":"10.1016/j.lithos.2025.108299","DOIUrl":"10.1016/j.lithos.2025.108299","url":null,"abstract":"<div><div>Serpentinite-derived fluids are pivotal for fluid mobility and mass transfer in subduction zones. However, the redox state of these fluids and their effects on the composition of continental crust remain unclear. Here, we investigated the Fe<sup>3+</sup>/ΣFe ratios and Fe isotope compositions of high-pressure fluid-metasomatized schists and blackwall zones surrounding serpentinites from the Tauern Window, Eastern Alps. Relative to the surrounding granodiorite protolith (δ<sup>56</sup>Fe: −0.14 to 0.66 ‰), schists in the Stillup Tal shear zone exhibit significantly lower δ<sup>56</sup>Fe values (−0.25 to −0.11 ‰), higher Fe − Mg contents and lower concentrations of large ion lithophile elements. These observations are consistent with the chlorite blackwall rimming a nearby serpentinite body in the Pfitsch area, both of which can be ascribed to the metasomatism by serpentinite-derived fluids. Furthermore, the schists display substantially lower Fe<sup>3+</sup>/ΣFe ratios than granitoid protoliths. A strong positive correlation between Fe<sup>3+</sup>/ΣFe and V/Sc ratios of the schists suggests that serpentinite dehydration released reduced fluids. Considering the mineralogical and geochemical differences between the central chlorite-rich schist and other schists in the Stillup Tal shear zone, we propose a fluid metasomatism model for the formation of metasomatic rocks. Initially, serpentinite-derived fluids migrated along a major shear zone, metasomatizing granitoids to form central chlorite-rich schists with extremely high Fe contents and low δ<sup>56</sup>Fe values (−0.25 ‰) under the condition of high fluid/rock ratios. Subsequently, the evolved serpentinite-derived fluids continued their migration along secondary fractures, generating schists with moderately low δ<sup>56</sup>Fe values (−0.24 to −0.11 ‰) under the condition of lower fluid/rock ratios. Our results provide geochemical evidence for the reducing nature of serpentinite-derived fluids and their impact on the redox state and Fe isotope composition of rocks with which they interact.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108299"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145425017","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}
Pub Date : 2025-12-15Epub Date: 2025-11-13DOI: 10.1016/j.lithos.2025.108320
Abdolnaser Fazlnia , Kwan-Nang Pang
The southwestern segment of the Late Paleocene intrusive-subvolcanic adakites in eastern Saqqez (Yazi-Bolaghi), Iran, comprises monzodiorite, monzonite, quartz monzonite, tonalite, granodiorite, and syenogranite, exhibiting granular, porphyroid, rapakivi, inequigranular (seriate), and mylonitic textures. This intrusion affected the Late Neoproterozoic basement within the northern Sanandaj-Sirjan Zone (SaSZ), resulting from the cessation of Neo-Tethys subduction beneath western Central Iran and the onset of collision between the Arabian and Eurasian plates (Zagros orogeny) in northwest Iran. In the Yazi-Bolaghi intrusion, trace and rare earth element (REE) concentrations decrease from mafic to felsic samples. Comparisons of Sr-Nd isotopic ratios between these rocks and Late Neoproterozoic tonalite-granodiorite-granite suites in northwestern Iran reveal significant assimilation-fractional crystallization (AFC) processes, where mantle-derived mafic melts interacted with Late Neoproterozoic calc-alkaline middle-to-upper continental crust. Additionally, plagioclase and amphibole fractionation contributed to compositional diversity. These findings indicate that amphibole fractionation alone cannot sufficiently enhance silica, alkali elements, and light REE (LREE) contents to produce high-K adakitic magmas. Instead, plagioclase and amphibole fractionation in mantle melts, coupled with crustal assimilation (AFC processes), generated the felsic components of this intrusion.
{"title":"Origin and geochemistry of the adakitic magmatism from the southwest Yazi-Bolaghi intrusion (East Saqqez, NW Iran)","authors":"Abdolnaser Fazlnia , Kwan-Nang Pang","doi":"10.1016/j.lithos.2025.108320","DOIUrl":"10.1016/j.lithos.2025.108320","url":null,"abstract":"<div><div>The southwestern segment of the Late Paleocene intrusive-subvolcanic adakites in eastern Saqqez (Yazi-Bolaghi), Iran, comprises monzodiorite, monzonite, quartz monzonite, tonalite, granodiorite, and syenogranite, exhibiting granular, porphyroid, rapakivi, inequigranular (seriate), and mylonitic textures. This intrusion affected the Late Neoproterozoic basement within the northern Sanandaj-Sirjan Zone (SaSZ), resulting from the cessation of Neo-Tethys subduction beneath western Central Iran and the onset of collision between the Arabian and Eurasian plates (Zagros orogeny) in northwest Iran. In the Yazi-Bolaghi intrusion, trace and rare earth element (REE) concentrations decrease from mafic to felsic samples. Comparisons of Sr-Nd isotopic ratios between these rocks and Late Neoproterozoic tonalite-granodiorite-granite suites in northwestern Iran reveal significant assimilation-fractional crystallization (AFC) processes, where mantle-derived mafic melts interacted with Late Neoproterozoic calc-alkaline middle-to-upper continental crust. Additionally, plagioclase and amphibole fractionation contributed to compositional diversity. These findings indicate that amphibole fractionation alone cannot sufficiently enhance silica, alkali elements, and light REE (LREE) contents to produce high-K adakitic magmas. Instead, plagioclase and amphibole fractionation in mantle melts, coupled with crustal assimilation (AFC processes), generated the felsic components of this intrusion.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108320"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576543","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}
Pub Date : 2025-12-15Epub Date: 2025-11-13DOI: 10.1016/j.lithos.2025.108319
Fan Yang , Xiao-Long Huang , Yi-Gang Xu , Yang Yu , Peng-Li He , Le Zhang , Ze-Xian Cui
The upper mantle shows a hybrid composition, predominantly consisting of peridotite with pyroxenite veins. The contribution of pyroxenite derived from recycled oceanic crust (ROC) to trace element enrichment in mid-ocean ridge basalts (MORBs) remains debated. This study explores a critical yet often overlooked factor: the melting behavior of pyroxenite beneath ridges, which is pivotal for the origin of enriched-MORBs. We identified two groups of MORBs from the International Ocean Discovery Program (IODP) site Hole U1433B in the South China Sea. The early-erupted MORBs exhibit enriched incompatible trace elements and contain olivine phenocrysts with typical MORB-type δ18O values (5.08 ± 0.68 ‰). In contrast, the later-erupted MORBs, which are more depleted in incompatible trace elements, contain high Fo olivine phenocrysts characterized by elevated Ni and Al contents, low Zn/FeO ratios, and notably higher δ18O values (6.50 ± 0.40 ‰) compared to mantle values. This chemical variability suggests that melts with a greater contribution from ROC-derived pyroxenite are relatively depleted in trace elements, as further supported by thermodynamic modeling results. The modeling also indicates that pyroxenite generates trace-element-enriched melts beneath ridges only when it is itself enriched in trace elements. Therefore, we suggest ROC-derived pyroxenite mainly contributes trace-element-depleted melts to MORBs. This expands the explanatory framework for the chemcial diversity of MORBs.
{"title":"Recycled oceanic crust restricting trace element enrichment in mid-ocean ridge basalts","authors":"Fan Yang , Xiao-Long Huang , Yi-Gang Xu , Yang Yu , Peng-Li He , Le Zhang , Ze-Xian Cui","doi":"10.1016/j.lithos.2025.108319","DOIUrl":"10.1016/j.lithos.2025.108319","url":null,"abstract":"<div><div>The upper mantle shows a hybrid composition, predominantly consisting of peridotite with pyroxenite veins. The contribution of pyroxenite derived from recycled oceanic crust (ROC) to trace element enrichment in mid-ocean ridge basalts (MORBs) remains debated. This study explores a critical yet often overlooked factor: the melting behavior of pyroxenite beneath ridges, which is pivotal for the origin of enriched-MORBs. We identified two groups of MORBs from the International Ocean Discovery Program (IODP) site Hole U1433B in the South China Sea. The early-erupted MORBs exhibit enriched incompatible trace elements and contain olivine phenocrysts with typical MORB-type δ<sup>18</sup>O values (5.08 ± 0.68 ‰). In contrast, the later-erupted MORBs, which are more depleted in incompatible trace elements, contain high Fo olivine phenocrysts characterized by elevated Ni and Al contents, low Zn/FeO ratios, and notably higher δ<sup>18</sup>O values (6.50 ± 0.40 ‰) compared to mantle values. This chemical variability suggests that melts with a greater contribution from ROC-derived pyroxenite are relatively depleted in trace elements, as further supported by thermodynamic modeling results. The modeling also indicates that pyroxenite generates trace-element-enriched melts beneath ridges only when it is itself enriched in trace elements. Therefore, we suggest ROC-derived pyroxenite mainly contributes trace-element-depleted melts to MORBs. This expands the explanatory framework for the chemcial diversity of MORBs.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108319"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576547","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}
The Sonapahar granite gneiss within the Meghalaya Gneissic Complex of northeastern India provides a rare record of Mesoproterozoic low-δ18O A-type felsic magmatism formed by partial melting of a hydrothermally altered lower crust. Field relationships reveal that the Sonapahar granite gneiss occurs as concordant, lensoidal bodies in gradational contact with surrounding metapelites, suggesting a genetic link to the melt source. Microstructural features, including aligned oxide-rich bands, poikilitic texture, and interstitial quartz, indicate in situ melt generation under high-temperature, fluid-absent granulite-facies conditions. SIMS UPb dating of zircons yields a crystallization age of 1629 ± 5.2 Ma, synchronous with regional granulite metamorphism. Concordant domains within zircons preserve low δ18O values (3.1 ‰ to 4.8 ‰), suggesting anatexis of a metapelitic protolith that had been previously altered by 18O-depleted fluids. Field and map relationships suggest generation of ∼15 % partial melting, and trace element modeling supports derivation from fertile cordierite gneiss with elevated Zr, Th, and Y contents. These isotopic data collectively indicate the intracrustal reworking of isotopically modified crust under high heat flow, likely associated with post-orogenic tectonothermal activity during the evolution of the Columbia supercontinent. Comparisons with low-δ18O systems from the Talbot sub-basin, Australia, and North Dabie, China, highlight the broader significance of the Sonapahar granite gneiss in preserving deep crustal isotopic signatures in high-grade metamorphic terrane.
{"title":"In situ melting of hydrothermally altered crust in the Meghalaya Gneissic Complex, India: A Mesoproterozoic record of low-δ18O felsic magmatism","authors":"Susobhan Neogi , Ritesh Kumar Mishra , Tapan Pal , Sandip Nandy","doi":"10.1016/j.lithos.2025.108324","DOIUrl":"10.1016/j.lithos.2025.108324","url":null,"abstract":"<div><div>The Sonapahar granite gneiss within the Meghalaya Gneissic Complex of northeastern India provides a rare record of Mesoproterozoic low-δ<sup>18</sup>O A-type felsic magmatism formed by partial melting of a hydrothermally altered lower crust. Field relationships reveal that the Sonapahar granite gneiss occurs as concordant, lensoidal bodies in gradational contact with surrounding metapelites, suggesting a genetic link to the melt source. Microstructural features, including aligned oxide-rich bands, poikilitic texture, and interstitial quartz, indicate in situ melt generation under high-temperature, fluid-absent granulite-facies conditions. SIMS U<img>Pb dating of zircons yields a crystallization age of 1629 ± 5.2 Ma, synchronous with regional granulite metamorphism. Concordant domains within zircons preserve low δ<sup>18</sup>O values (3.1 ‰ to 4.8 ‰), suggesting anatexis of a metapelitic protolith that had been previously altered by <sup>18</sup>O-depleted fluids. Field and map relationships suggest generation of ∼15 % partial melting, and trace element modeling supports derivation from fertile cordierite gneiss with elevated Zr, Th, and Y contents. These isotopic data collectively indicate the intracrustal reworking of isotopically modified crust under high heat flow, likely associated with post-orogenic tectonothermal activity during the evolution of the Columbia supercontinent. Comparisons with low-δ<sup>18</sup>O systems from the Talbot sub-basin, Australia, and North Dabie, China, highlight the broader significance of the Sonapahar granite gneiss in preserving deep crustal isotopic signatures in high-grade metamorphic terrane.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108324"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576648","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}
Widespread polygonal serpentine (PS) veins occur in the ultramafics of the Rocciavrè meta-ophiolite, which consists of alternating metadunite and antigorite-serpentinite bands. The PS veins exhibit a complex polyphasic history that includes three PS domains (Dom 1, Dom 2 and Dom 3), porphyroblasts of aluminian-lizardite (Al-Lz) and minor brucite. Four steps of vein dilation have been recognized. The microstructure indicates that Dom 1 is constituted by a PS pseudomorph after the original olivine, the first mineral that heterogeneously nucleated on the fracture wall. Al-Lz and brucite porphyroblasts developed near the wall-rock overgrowing olivine. Dom 2 is constituted by an aggregate of PS + brucite that completely seals the vein. Dom 3 is constituted by the last generation of PS that grew as coarser-grained fiber bundles partially replacing Dom 2.
Chemical analyses showed that PS of Dom 1 and Dom 2 have a similar, very low Fe-content, whereas PS of Dom 3 have systematically slightly higher Fe, which is possibly responsible for the rusty color typical of weathered surfaces. Porphyroblastic Al-Lz has high Al and minor Fe contents. Late barite sealed fractures opened in correspondence of Al-Lz cleavage planes. X-ray powder diffraction and μ-Raman revealed the presence of both PS polytypes, PS-15, with 15 sectors, and PS-30, with 30 sectors, respectively, and minor brucite. TEM images showed the presence of both PS-15 and PS-30, locally associated with brucite and rare chrysotile. μ-Raman maps confirmed that all domains contain the same submicroscopic association of PS-15, PS-30 and brucite, in highly variable ratios from point to point.
Each PS vein is bounded by two reaction zones, where the host metadunite is altered to an aggregate of lizardite + magnetite + brucite + minor chlorite with accessory awaruite and heazlewoodite. Therefore, the close relationship between metadunite and PS veins supports a local origin for vein feeding elements. The vein mineralogy indicates genetic conditions characterized by CO2-free aqueous fluid, slightly silica-undersaturated bulk composition, and low fO2 compatible with magnetite, Fe=Ni alloys and Ni sulphides. The PS veins are crossed by later chrysotile veinlets, in turn cut by very thin veins of euhedral brucite included in a fine-grained carbonate aggregate, identified by μ-Raman spectroscopy as a mixture of artinite and hydromagnesite.
The coeval development of PS in the vein and lizardite in the reaction zone of the host metadunite suggests that these two phases must have, at least in part, a superposed stability field and that other factors, including kinetics factors, must be responsible for the fibrous habit of serpentine – either chrysotile or PS, since the latter derives from the former – in the vein.
{"title":"Polyphase polygonal serpentine veins in the Rocciavrè meta-ophiolite (Western Alps, NW Italy)","authors":"Luca Barale , Giancarlo Capitani , Roberto Compagnoni , Roberto Conconi , Roberto Cossio , Linda Pastero , Marcello Mellini","doi":"10.1016/j.lithos.2025.108326","DOIUrl":"10.1016/j.lithos.2025.108326","url":null,"abstract":"<div><div>Widespread polygonal serpentine (PS) veins occur in the ultramafics of the Rocciavrè meta-ophiolite, which consists of alternating metadunite and antigorite-serpentinite bands. The PS veins exhibit a complex polyphasic history that includes three PS domains (Dom 1, Dom 2 and Dom 3), porphyroblasts of aluminian-lizardite (Al-Lz) and minor brucite. Four steps of vein dilation have been recognized. The microstructure indicates that Dom 1 is constituted by a PS pseudomorph after the original olivine, the first mineral that heterogeneously nucleated on the fracture wall. Al-Lz and brucite porphyroblasts developed near the wall-rock overgrowing olivine. Dom 2 is constituted by an aggregate of PS + brucite that completely seals the vein. Dom 3 is constituted by the last generation of PS that grew as coarser-grained fiber bundles partially replacing Dom 2.</div><div>Chemical analyses showed that PS of Dom 1 and Dom 2 have a similar, very low Fe-content, whereas PS of Dom 3 have systematically slightly higher Fe, which is possibly responsible for the rusty color typical of weathered surfaces. Porphyroblastic Al-Lz has high Al and minor Fe contents. Late barite sealed fractures opened in correspondence of Al-Lz cleavage planes. X-ray powder diffraction and μ-Raman revealed the presence of both PS polytypes, PS-15, with 15 sectors, and PS-30, with 30 sectors, respectively, and minor brucite. TEM images showed the presence of both PS-15 and PS-30, locally associated with brucite and rare chrysotile. μ-Raman maps confirmed that all domains contain the same submicroscopic association of PS-15, PS-30 and brucite, in highly variable ratios from point to point.</div><div>Each PS vein is bounded by two reaction zones, where the host metadunite is altered to an aggregate of lizardite + magnetite + brucite + minor chlorite with accessory awaruite and heazlewoodite. Therefore, the close relationship between metadunite and PS veins supports a local origin for vein feeding elements. The vein mineralogy indicates genetic conditions characterized by CO<sub>2</sub>-free aqueous fluid, slightly silica-undersaturated bulk composition, and low <em>f</em><sub>O2</sub> compatible with magnetite, Fe=Ni alloys and Ni sulphides. The PS veins are crossed by later chrysotile veinlets, in turn cut by very thin veins of euhedral brucite included in a fine-grained carbonate aggregate, identified by μ-Raman spectroscopy as a mixture of artinite and hydromagnesite.</div><div>The coeval development of PS in the vein and lizardite in the reaction zone of the host metadunite suggests that these two phases must have, at least in part, a superposed stability field and that other factors, including kinetics factors, must be responsible for the fibrous habit of serpentine – either chrysotile or PS, since the latter derives from the former – in the vein.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108326"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576652","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}
Pub Date : 2025-12-15Epub Date: 2025-11-19DOI: 10.1016/j.lithos.2025.108331
L.M. Saper , G. Bromiley , R. Cao , M. Brounce , E.C. Hughes , D. Woelki
Sulfur cycling in the vicinity of subduction zones is an important control on chalcophile element mobility and the formation of massive sulfide ore deposits such as those exposed in the Cretaceous-aged Troodos Ophiolite in Cyprus. Here, we assess the sources and fates of magmatic S in the Troodos Ophiolite using in-situ S isotope measurements of quenched volcanic glasses along with petrographic and geochemical evidence for sulfide saturation in both primitive and evolved melts. Primitive glasses (MgO ≥ 8 wt%) define the primary S isotope composition of the ophiolite: δ34S = +0.14 ± 0.56 ‰ (1 s.d., V-CDT, n = 12), which overlaps with mid-ocean ridge basalts and is low compared to bulk δ34S values measured in altered rocks and sulfide ore deposits in the ophiolite that interacted with 34S-enriched seawater. The Troodos glasses have geochemical and isotopic evidence for slab influence, however these parameters (e.g., H2O, oxygen fugacity, Ba/La, 87Sr/86Sr) do not correlate with δ34S values, suggesting that the flux of slab-derived S was low. Magmatic pyrrhotite inclusions in Mg-rich olivine and chromite phenocrysts indicate that some primitive Troodos mantle melts were reduced and saturated with an immiscible Ni-rich sulfide liquid. During ascent, melt aggregation and decompression resulted in sulfide-undersaturation and a wide range of dissolved S contents in lavas. The S contents of lavas require a heterogeneous mantle source and cannot be explained solely by magmatic S degassing. In evolved magmas, saturation of Cu-rich sulfide accompanied exsolution of a fluid phase and Fe–Ti oxide saturation, and in some cases this may have occurred during rapid cooling upon eruption at the seafloor. Collectively, these observations confirm that magmatic S in the Troodos Ophiolite was derived from a reduced, depleted and variably sulfide-saturated mantle and that slab fluids involved in flux melting were sulfur-poor.
俯冲带附近的硫循环是亲铜元素流动和块状硫化物矿床形成的重要控制因素，如塞浦路斯白垩纪Troodos蛇绿岩中暴露的硫化物矿床。本文利用淬火火山玻璃的原位S同位素测量以及原始和演化熔体硫化物饱和度的岩石学和地球化学证据，评估了Troodos蛇绿岩中岩浆S的来源和流向。原始玻璃（MgO≥8 wt%）定义了蛇绿岩的主要S同位素组成：δ34S = +0.14±0.56‰（1 s.d, V-CDT, n = 12），与洋中脊玄武岩重叠，与蛇绿岩中蚀变岩和硫化物矿床测量的整体δ34S值相比较低，蛇绿岩与富34s海水相互作用。Troodos玻璃具有板坯影响的地球化学和同位素证据，但这些参数（如H2O、氧度、Ba/La、87Sr/86Sr）与δ34S值无关，表明板坯衍生S的通量很低。富镁橄榄石和铬铁矿斑晶中的岩浆磁黄铁矿包裹体表明，一些原始的Troodos地幔熔体被还原并被不混溶的富镍硫化物液体饱和。在上升过程中，熔体聚集和减压导致熔岩硫化物欠饱和，溶解S含量范围较大。熔岩的S含量需要非均质地幔源，不能仅仅用岩浆S脱气来解释。在演化的岩浆中，富cu硫化物的饱和伴随着流体相的析出和Fe-Ti氧化物的饱和，在某些情况下，这可能发生在海底喷发后的快速冷却过程中。总的来说，这些观察结果证实，Troodos蛇绿岩中的岩浆S来自一个还原的、耗尽的、硫化物饱和的地幔，而参与熔剂熔化的板块流体是缺硫的。
{"title":"The primary magmatic δ34S of the Troodos Ophiolite and evidence for early and late sulfide saturation","authors":"L.M. Saper , G. Bromiley , R. Cao , M. Brounce , E.C. Hughes , D. Woelki","doi":"10.1016/j.lithos.2025.108331","DOIUrl":"10.1016/j.lithos.2025.108331","url":null,"abstract":"<div><div>Sulfur cycling in the vicinity of subduction zones is an important control on chalcophile element mobility and the formation of massive sulfide ore deposits such as those exposed in the Cretaceous-aged Troodos Ophiolite in Cyprus. Here, we assess the sources and fates of magmatic S in the Troodos Ophiolite using in-situ S isotope measurements of quenched volcanic glasses along with petrographic and geochemical evidence for sulfide saturation in both primitive and evolved melts. Primitive glasses (MgO ≥ 8 wt%) define the primary S isotope composition of the ophiolite: δ<sup>34</sup>S = +0.14 ± 0.56 ‰ (1 s.d., V-CDT, <em>n</em> = 12), which overlaps with mid-ocean ridge basalts and is low compared to bulk δ<sup>34</sup>S values measured in altered rocks and sulfide ore deposits in the ophiolite that interacted with <sup>34</sup>S-enriched seawater. The Troodos glasses have geochemical and isotopic evidence for slab influence, however these parameters (e.g., H<sub>2</sub>O, oxygen fugacity, Ba/La, <sup>87</sup>Sr/<sup>86</sup>Sr) do not correlate with δ<sup>34</sup>S values, suggesting that the flux of slab-derived S was low. Magmatic pyrrhotite inclusions in Mg-rich olivine and chromite phenocrysts indicate that some primitive Troodos mantle melts were reduced and saturated with an immiscible Ni-rich sulfide liquid. During ascent, melt aggregation and decompression resulted in sulfide-undersaturation and a wide range of dissolved S contents in lavas. The S contents of lavas require a heterogeneous mantle source and cannot be explained solely by magmatic S degassing. In evolved magmas, saturation of Cu-rich sulfide accompanied exsolution of a fluid phase and Fe–Ti oxide saturation, and in some cases this may have occurred during rapid cooling upon eruption at the seafloor. Collectively, these observations confirm that magmatic S in the Troodos Ophiolite was derived from a reduced, depleted and variably sulfide-saturated mantle and that slab fluids involved in flux melting were sulfur-poor.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108331"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576653","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}
Pub Date : 2025-12-15Epub Date: 2025-11-20DOI: 10.1016/j.lithos.2025.108339
İrfan Temizel , Mehmet Arslan , Sarah Sherlock
In this study, we investigate the petrology, age, whole-rock geochemistry, and Sr-Nd isotopic compositions of post-collisional andesitic suites from the İkizce and Ulubey (Ordu) areas of the Eastern Pontides Orogenic Belt (EPOB) to elucidate their magma source characteristics and the region's geodynamic evolution. The 40Ar-39Ar dating of the İkizce and Ulubey andesitic suites yielded cooling ages of ∼51–49 Ma and ∼ 49–46 Ma (Middle Eocene), respectively. Both İkizce and Ulubey andesite suites have adakitic geochemistry, displaying medium to high-K, high LaN/YbN (∼17.8–23.1 and 8.9–23.3, respectively) and Sr/Y (79–138 and 62–143, respectively) ratios. Besides, the adakitic suites show similar LREE-enriched and HREE-flattened patterns (LaN/LuN = 11.3–23.7 and 8.8–28.2, respectively) with insignificant Eu anomalies (EuN/Eu* =0.90–1.08 and 0.82–1.11, respectively). The İkizce and Ulubey adakitic suites have 87Sr/86Sr(i) (0.703861–0.703973 and 0.704347–0.704437), and 143Nd/144Nd(i) (0.512810–0.512846 and 0.512662–0.512748) with positive ɛNd(i) values (4.57–5.27 and 1.06–3.39), respectively. Combining the whole-rock geochemical and Sr-Nd isotope dataset of the studied adakitic andesitic suites suggests two different melt sources, whereby the İkizce adakitic suite was generated from slab-derived melts and the Ulubey adakitic suite originated from delaminated lower crust-derived melts, each of which also interacted with the lithospheric mantle components in a post-collisional tectonic setting during the Middle Eocene period.
{"title":"Post-collisional adakitic andesite suites originated from remnant slab- and delaminated lower crust-derived melts modified by mantle components: Constraints for petrogenesis of Cenozoic adakitic magmas in NE Türkiye","authors":"İrfan Temizel , Mehmet Arslan , Sarah Sherlock","doi":"10.1016/j.lithos.2025.108339","DOIUrl":"10.1016/j.lithos.2025.108339","url":null,"abstract":"<div><div>In this study, we investigate the petrology, age, whole-rock geochemistry, and Sr-Nd isotopic compositions of post-collisional andesitic suites from the İkizce and Ulubey (Ordu) areas of the Eastern Pontides Orogenic Belt (EPOB) to elucidate their magma source characteristics and the region's geodynamic evolution. The <sup>40</sup>Ar-<sup>39</sup>Ar dating of the İkizce and Ulubey andesitic suites yielded cooling ages of ∼51–49 Ma and ∼ 49–46 Ma (Middle Eocene), respectively. Both İkizce and Ulubey andesite suites have adakitic geochemistry, displaying medium to high-K, high La<sub>N</sub>/Yb<sub>N</sub> (∼17.8–23.1 and 8.9–23.3, respectively) and Sr/Y (79–138 and 62–143, respectively) ratios. Besides, the adakitic suites show similar LREE-enriched and HREE-flattened patterns (La<sub>N</sub>/Lu<sub>N</sub> = 11.3–23.7 and 8.8–28.2, respectively) with insignificant Eu anomalies (Eu<sub>N</sub>/Eu* =0.90–1.08 and 0.82–1.11, respectively). The İkizce and Ulubey adakitic suites have <sup>87</sup>Sr/<sup>86</sup>Sr<sub>(i)</sub> (0.703861–0.703973 and 0.704347–0.704437), and <sup>143</sup>Nd/<sup>144</sup>Nd<sub>(i)</sub> (0.512810–0.512846 and 0.512662–0.512748) with positive ɛNd<sub>(i)</sub> values (4.57–5.27 and 1.06–3.39), respectively. Combining the whole-rock geochemical and Sr-Nd isotope dataset of the studied adakitic andesitic suites suggests two different melt sources, whereby the İkizce adakitic suite was generated from slab-derived melts and the Ulubey adakitic suite originated from delaminated lower crust-derived melts, each of which also interacted with the lithospheric mantle components in a post-collisional tectonic setting during the Middle Eocene period.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108339"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145620229","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}
Pub Date : 2025-12-15Epub Date: 2025-11-19DOI: 10.1016/j.lithos.2025.108332
Zhongzhou Li , Yijun Wang , Mengxi Wang , Ting Liang
<div><div>Development processes (construction and following solidification) of crystal mush have been considered as a fundamental issue for investigating the cooling process of layered intrusions. However, the magma processes related to the development of crystal mush and their roles are still enigmatic. In this study, we collected samples from the cyclic unit (CU) III in the upper part of Middle Zone (MZb) of the Wangjiangshan layered intrusion in Central China, in order to examine the development of crystal mush in a basaltic magma chamber. We carried out a comprehensive analysis on high-resolution elemental mapping, <em>in situ</em> major and trace elemental and Sr isotopic compositions for plagioclase of the CU III, which is mainly composed of olivine gabbro, oxide gabbro and minor biotite gabbro. Plagioclase crystals can be divided into five types based on distinct textures and compositions, <em>i.e.,</em> skeletal texture (Type 1), patchy zoning texture (Type 2), reverse zoning texture (Type 3), normal zoning texture (Type 4) and unzoned (Type 5). Type 1 plagioclase of olivine gabbro and biotite gabbro have skeletal cores in a boxy or geometric shape, indicating a moderate- to high-degree undercooling (−∆T = 30–70 °C) during cooling. Resorbed cores of Type 2 and some Type 3 plagioclase in olivine gabbro have high (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub><em>i</em></sub> (0.70409–0.70428), indicating that they may crystallize from the boundary layers contaminated by country rocks at the roof of magma chamber and then be entrained downward to the bottom of main magma body by magma convection. Convective melts from the roof would travel downwards and then contact with the hotter main magma at the bottom, resulting in a moderate- to high-degree undercooling. Thus, we propose that magma convection is crucial for the rapid construction of crystal mush. The rims of Type 4 plagioclase in biotite gabbro have distinct lower (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub><em>i</em></sub> (0.70337–0.70354) but higher REE (17.7–30.7 μg/g) than those for resorbed cores, suggesting that they may be formed by the replenishment of an evolved magma during solidification of crystal mush. Thus, the moderate- to high-degree undercooling of biotite gabbro may be ascribed to magma replenishment, which promotes the solidification of crystal mush. On the other hand, the solidification timescales of crystal mush in olivine gabbro and biotite gabbro are ∼ 6.1 kyr and ∼ 4.7 kyr, respectively, distinctly shorter than that of ∼ 15.4 kyr for oxide gabbro, indicating a rapid solidification of crystal mush by magma convection and replenishment. In contrast, the absence of Type 1 to Type 3 plagioclase in oxide gabbro indicates the stagnation of magma convection and absence of magma replenishment, resulting in a decrease of undercooling degree and a slow construction and solidification of crystal mush. Furthermore, the invariable An for rims of some Type 1 to Type 4 plagioclase in olivi
{"title":"The development process of crystal mush in mafic magma chambers: Insights from the texture and composition of plagioclase in the Wangjiangshan layered intrusion, Central China","authors":"Zhongzhou Li , Yijun Wang , Mengxi Wang , Ting Liang","doi":"10.1016/j.lithos.2025.108332","DOIUrl":"10.1016/j.lithos.2025.108332","url":null,"abstract":"<div><div>Development processes (construction and following solidification) of crystal mush have been considered as a fundamental issue for investigating the cooling process of layered intrusions. However, the magma processes related to the development of crystal mush and their roles are still enigmatic. In this study, we collected samples from the cyclic unit (CU) III in the upper part of Middle Zone (MZb) of the Wangjiangshan layered intrusion in Central China, in order to examine the development of crystal mush in a basaltic magma chamber. We carried out a comprehensive analysis on high-resolution elemental mapping, <em>in situ</em> major and trace elemental and Sr isotopic compositions for plagioclase of the CU III, which is mainly composed of olivine gabbro, oxide gabbro and minor biotite gabbro. Plagioclase crystals can be divided into five types based on distinct textures and compositions, <em>i.e.,</em> skeletal texture (Type 1), patchy zoning texture (Type 2), reverse zoning texture (Type 3), normal zoning texture (Type 4) and unzoned (Type 5). Type 1 plagioclase of olivine gabbro and biotite gabbro have skeletal cores in a boxy or geometric shape, indicating a moderate- to high-degree undercooling (−∆T = 30–70 °C) during cooling. Resorbed cores of Type 2 and some Type 3 plagioclase in olivine gabbro have high (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub><em>i</em></sub> (0.70409–0.70428), indicating that they may crystallize from the boundary layers contaminated by country rocks at the roof of magma chamber and then be entrained downward to the bottom of main magma body by magma convection. Convective melts from the roof would travel downwards and then contact with the hotter main magma at the bottom, resulting in a moderate- to high-degree undercooling. Thus, we propose that magma convection is crucial for the rapid construction of crystal mush. The rims of Type 4 plagioclase in biotite gabbro have distinct lower (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub><em>i</em></sub> (0.70337–0.70354) but higher REE (17.7–30.7 μg/g) than those for resorbed cores, suggesting that they may be formed by the replenishment of an evolved magma during solidification of crystal mush. Thus, the moderate- to high-degree undercooling of biotite gabbro may be ascribed to magma replenishment, which promotes the solidification of crystal mush. On the other hand, the solidification timescales of crystal mush in olivine gabbro and biotite gabbro are ∼ 6.1 kyr and ∼ 4.7 kyr, respectively, distinctly shorter than that of ∼ 15.4 kyr for oxide gabbro, indicating a rapid solidification of crystal mush by magma convection and replenishment. In contrast, the absence of Type 1 to Type 3 plagioclase in oxide gabbro indicates the stagnation of magma convection and absence of magma replenishment, resulting in a decrease of undercooling degree and a slow construction and solidification of crystal mush. Furthermore, the invariable An for rims of some Type 1 to Type 4 plagioclase in olivi","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108332"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145620227","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}
The Precambrian Ingul-Bryansk granulite belt forms part of the western margin of the Sarmatian segment of the East European Craton where the dominant rock types belonging to the Bryansk (khondalite) Series are aluminous gneisses and granulites, porphyroblastic biotite-garnet schists and gneisses (kinzigites) and moderately aluminous biotite gneisses, amphibolites. Here we present zircon UPb geochronological data obtained using SIMS that indicate that the sedimentary protoliths of the Bryansk Series rocks mainly come from Meso-Neoarchean (3.24–2.50 Ga) and Paleoproterozoic (2.2–2.1 Ga) provenances. Minimum ages of detrital zircons and ages of early metamorphic zircons constrain the sedimentation time of the protoliths of the Bryansk Group rocks to be 2.1–2.04 Ga. The Bryansk domain rocks underwent two metamorphic events at 2036 Ma and before 1983 Ma. Petrographic observations and major and trace element geochemical data suggest that the protoliths of this Paleoproterozoic metavolcanic-sedimentary series are composed partly of a sandy-clay suite (kinzigite) that was probably derived entirely from the Mesoarchean Sarmatia province, mafic volcanic rocks (amphibolites) that were erupted subsynchronously with the metasedimentary rocks, and members of moderate- to high-alumina clay-graywacke metasedimentary rocks (gneisses, granulites) from a mixed Archean-Paleoproterozoic province. Geochemical data for the mafic metavolcanic rocks indicate an intraplate tectonic setting. The metasedimentary units are thought to have been deposited in a variable landscape (from subaqueous to subaerial) under tropical climate conditions, which provided low to high sediment maturity and premetamorphic chemical weathering of the protolith. The dominant provenance composition corresponded to felsic rocks with varying proportions of mafic material admixture. We propose that the Ingul-Bryansk belt developed independently on the western margin of Sarmatia as a passive margin before the Columbia supercontinent formation. Juvenile materials of about 2.2–2.1 Ga were added to the source area of the Bryansk metasedimentary units, which may indicate an important activity associated with the formation of an unknown ocean and an active margin on the opposite side of the Sarmatia. The collision of these active margins with the passive margin of Sarmatia occurred at approximately 2.04 to after 1.98 Ga ago, which marked the peak of orogeny and led to two-stage metamorphism - first granulite and then associated with exhumation of the region, respectively.
{"title":"Paleoproterozoic geodynamics of the western margin of Sarmatia, East European Craton","authors":"R.A. Terentiev , K.A. Savko , E.H. Korish , M. Santosh","doi":"10.1016/j.lithos.2025.108305","DOIUrl":"10.1016/j.lithos.2025.108305","url":null,"abstract":"<div><div>The Precambrian Ingul-Bryansk granulite belt forms part of the western margin of the Sarmatian segment of the East European Craton where the dominant rock types belonging to the Bryansk (khondalite) Series are aluminous gneisses and granulites, porphyroblastic biotite-garnet schists and gneisses (kinzigites) and moderately aluminous biotite gneisses, amphibolites. Here we present zircon U<img>Pb geochronological data obtained using SIMS that indicate that the sedimentary protoliths of the Bryansk Series rocks mainly come from Meso-Neoarchean (3.24–2.50 Ga) and Paleoproterozoic (2.2–2.1 Ga) provenances. Minimum ages of detrital zircons and ages of early metamorphic zircons constrain the sedimentation time of the protoliths of the Bryansk Group rocks to be 2.1–2.04 Ga. The Bryansk domain rocks underwent two metamorphic events at 2036 Ma and before 1983 Ma. Petrographic observations and major and trace element geochemical data suggest that the protoliths of this Paleoproterozoic metavolcanic-sedimentary series are composed partly of a sandy-clay suite (kinzigite) that was probably derived entirely from the Mesoarchean Sarmatia province, mafic volcanic rocks (amphibolites) that were erupted subsynchronously with the metasedimentary rocks, and members of moderate- to high-alumina clay-graywacke metasedimentary rocks (gneisses, granulites) from a mixed Archean-Paleoproterozoic province. Geochemical data for the mafic metavolcanic rocks indicate an intraplate tectonic setting. The metasedimentary units are thought to have been deposited in a variable landscape (from subaqueous to subaerial) under tropical climate conditions, which provided low to high sediment maturity and premetamorphic chemical weathering of the protolith. The dominant provenance composition corresponded to felsic rocks with varying proportions of mafic material admixture. We propose that the Ingul-Bryansk belt developed independently on the western margin of Sarmatia as a passive margin before the Columbia supercontinent formation. Juvenile materials of about 2.2–2.1 Ga were added to the source area of <!--> <!-->the Bryansk metasedimentary units, which may indicate an important activity associated with the formation of an unknown ocean and an active margin on the opposite side of the Sarmatia. The collision of these active margins with the passive margin of Sarmatia occurred at approximately 2.04 to after 1.98 Ga ago, which marked the peak of orogeny and led to two-stage metamorphism - first granulite and then associated with exhumation of the region, respectively.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108305"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145474836","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}
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