Pub Date : 2025-01-28DOI: 10.1016/j.lithos.2025.107971
Tianxing Bai, Xin Qian, Chengshi Gan, Yuejun Wang
The South China Block is predominantly influenced by the Paleo-Pacific dynamic domain during the Late Mesozoic, resulting in the formation of volcanic-intrusive complexes along the interior and coastal regions, which provide significant insights into magmatic evolution and geodynamic processes. This paper presents new zircon ages and geochemical data for the Late Jurassic granites in Zhuhai and its surrounding islands. The inland granites from Zhuhai (163–159 Ma) consist of biotite granites and two-mica granites with (87Sr/86Sr)i ratios of 0.70901–0.70993, εNd (t) values from −10.1 to −8.9, and εHf (t) values from −12.5 to −4.2. In contrast, the island biotite granites form Wanshan and Dong'ao islands (155–150 Ma) exhibit lower (87Sr/86Sr)i ratios of 0.70418–0.70722, higher εNd (t) values from −7.0 to −6.1, and εHf (t) values from −8.5 to −2.0 than inland granites. The two groups share similar (206Pb/204Pb)i ratios of 17.95–18.96, (207Pb/204Pb)i ratios of 15.72–15.76, and (208Pb/204Pb)i ratios of 38.53–39.16. Geochemical characteristics indicate that the inland granites formed from the partial melting of Paleoproterozoic crustal metasedimentary rocks, while the island granites were derived from a mixed source region of ancient metaigneous rocks with a juvenile crustal component. Subsequent extreme crystallization and amalgamation formed granitic plutons. Our study, together with geological observations and previous data, suggests that the Late Jurassic magmatism in the interior and coastal regions of the southeastern South China Block likely corresponds to western and eastern sides of Cathaysia and formed in response to the far-field effects of the subduction of the Paleo-Pacific Plate beneath the Eurasia.
{"title":"Late Jurassic high-silica granites in the interior and coastal South China and their tectonic implication","authors":"Tianxing Bai, Xin Qian, Chengshi Gan, Yuejun Wang","doi":"10.1016/j.lithos.2025.107971","DOIUrl":"10.1016/j.lithos.2025.107971","url":null,"abstract":"<div><div>The South China Block is predominantly influenced by the Paleo-Pacific dynamic domain during the Late Mesozoic, resulting in the formation of volcanic-intrusive complexes along the interior and coastal regions, which provide significant insights into magmatic evolution and geodynamic processes. This paper presents new zircon ages and geochemical data for the Late Jurassic granites in Zhuhai and its surrounding islands. The inland granites from Zhuhai (163–159 Ma) consist of biotite granites and two-mica granites with (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> ratios of 0.70901–0.70993, ε<sub>Nd</sub> (t) values from −10.1 to −8.9, and ε<sub>Hf</sub> (t) values from −12.5 to −4.2. In contrast, the island biotite granites form Wanshan and Dong'ao islands (155–150 Ma) exhibit lower (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> ratios of 0.70418–0.70722, higher ε<sub>Nd</sub> (t) values from −7.0 to −6.1, and ε<sub>Hf</sub> (t) values from −8.5 to −2.0 than inland granites. The two groups share similar (<sup>206</sup>Pb/<sup>204</sup>Pb)<sub>i</sub> ratios of 17.95–18.96, (<sup>207</sup>Pb/<sup>204</sup>Pb)<sub>i</sub> ratios of 15.72–15.76, and (<sup>208</sup>Pb/<sup>204</sup>Pb)<sub>i</sub> ratios of 38.53–39.16. Geochemical characteristics indicate that the inland granites formed from the partial melting of Paleoproterozoic crustal metasedimentary rocks, while the island granites were derived from a mixed source region of ancient metaigneous rocks with a juvenile crustal component. Subsequent extreme crystallization and amalgamation formed granitic plutons. Our study, together with geological observations and previous data, suggests that the Late Jurassic magmatism in the interior and coastal regions of the southeastern South China Block likely corresponds to western and eastern sides of Cathaysia and formed in response to the far-field effects of the subduction of the Paleo-Pacific Plate beneath the Eurasia.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107971"},"PeriodicalIF":2.9,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377377","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 : 2025-01-28DOI: 10.1016/j.lithos.2025.107973
Clarisse Monteiro Fernandes , Julio Cezar Mendes , Patrícia Anselmo Duffles Teixeira
<div><div>The Pan-African/Brasiliano orogeny, the result of the West-Gondwana assembly from the Neoproterozoic to the Early Paleozoic, culminated in a widespread, long-lived Ediacaran to Cambro-Ordovician granite production event at the Araçuaí-Ribeira Orogenic System. Collisional granitoids were emplaced along an interval wider than 100 m.y., following three subduction-accretion episodes. The Serra dos Órgãos batholith is the main granitoid intrusion emplaced during the <em>syn</em>-collisional episode at the Central Ribeira belt, southeastern Brazil. The integration of Nd–Sr–Hf isotopes and mineral chemistry data were employed to constrain the physical-chemical conditions concerning this intrusion and host rocks, along with potential sources. For this purpose, sensu stricto granites from Serra dos Órgãos batholith and the surrounding Sumidouro Leucogneiss were examined. Zircon and whole-rock isotopic signatures reveal distinct multi-component inheritance in both the intrusion and the country rocks. The Sumidouro Leucogneiss recorded diverse zircon populations of igneous origin, with juvenile to crustal Nd–Sr–Hf isotopic signatures in a large range of geochronological ages (200 m.y. interval), an evidence of zircon preservation in disequilibrium melting situations. The Sumidouro Leucogneiss must be the result of partial melting of multiple sources, behaving as a temporal archive of past events preceding the collision. Conversely, the Serra dos Órgãos batholith records a more mature, crustal signature, presenting a main zircon population interpreted as autocrystic (ca. 590 Ma), and minor inheritance given by an antecrystic population (ca. 610–620 Ma). The less spanned geochronological ages, more homogeneous Nd–Sr–Hf isotopic signatures, and the discrete preservation of an antecrystic zircon population are evidence of early zircon crystallization from a homogeneous source undergoing disequilibrium melting. An even older, ca. 1.9 Ga inherited/xenocrystic zircon population recorded in both the intrusion and the surrounding leucogneisses is also a piece of evidence of zircon preservation in disequilibrium melting situations. Zircon saturation and Ti-in-zircon temperatures strongly suggest thermal disequilibrium between relict zircon and magmas, consistent with the presence of antecrystic and inherited/xenocrystic zircon populations, previously distinguished by isotopic and U<img>Pb criteria. Ti-in-zircon thermometry suggests early crystallization temperatures for zircon precipitation, while biotite geothermometry yields near-<em>solidus</em>, late crystallization temperatures for the Serra dos Órgãos batholith. REE-in-zircon oxybarometry suggests <em>f</em>O<sub>2</sub> around FMQ conditions for the intrusion, contrasting with more oxidized <em>f</em>O<sub>2</sub> conditions for the country rocks. The evidence indicates that the studied sensu stricto granites were formed by water-undersaturated melting of crustal protoliths at temperatures up to 840
{"title":"An appraisal on crustal growth and reworking in collisional high-temperature granites: The Neoproterozoic Serra dos Órgãos batholith, Central Ribeira belt, SE Brazil","authors":"Clarisse Monteiro Fernandes , Julio Cezar Mendes , Patrícia Anselmo Duffles Teixeira","doi":"10.1016/j.lithos.2025.107973","DOIUrl":"10.1016/j.lithos.2025.107973","url":null,"abstract":"<div><div>The Pan-African/Brasiliano orogeny, the result of the West-Gondwana assembly from the Neoproterozoic to the Early Paleozoic, culminated in a widespread, long-lived Ediacaran to Cambro-Ordovician granite production event at the Araçuaí-Ribeira Orogenic System. Collisional granitoids were emplaced along an interval wider than 100 m.y., following three subduction-accretion episodes. The Serra dos Órgãos batholith is the main granitoid intrusion emplaced during the <em>syn</em>-collisional episode at the Central Ribeira belt, southeastern Brazil. The integration of Nd–Sr–Hf isotopes and mineral chemistry data were employed to constrain the physical-chemical conditions concerning this intrusion and host rocks, along with potential sources. For this purpose, sensu stricto granites from Serra dos Órgãos batholith and the surrounding Sumidouro Leucogneiss were examined. Zircon and whole-rock isotopic signatures reveal distinct multi-component inheritance in both the intrusion and the country rocks. The Sumidouro Leucogneiss recorded diverse zircon populations of igneous origin, with juvenile to crustal Nd–Sr–Hf isotopic signatures in a large range of geochronological ages (200 m.y. interval), an evidence of zircon preservation in disequilibrium melting situations. The Sumidouro Leucogneiss must be the result of partial melting of multiple sources, behaving as a temporal archive of past events preceding the collision. Conversely, the Serra dos Órgãos batholith records a more mature, crustal signature, presenting a main zircon population interpreted as autocrystic (ca. 590 Ma), and minor inheritance given by an antecrystic population (ca. 610–620 Ma). The less spanned geochronological ages, more homogeneous Nd–Sr–Hf isotopic signatures, and the discrete preservation of an antecrystic zircon population are evidence of early zircon crystallization from a homogeneous source undergoing disequilibrium melting. An even older, ca. 1.9 Ga inherited/xenocrystic zircon population recorded in both the intrusion and the surrounding leucogneisses is also a piece of evidence of zircon preservation in disequilibrium melting situations. Zircon saturation and Ti-in-zircon temperatures strongly suggest thermal disequilibrium between relict zircon and magmas, consistent with the presence of antecrystic and inherited/xenocrystic zircon populations, previously distinguished by isotopic and U<img>Pb criteria. Ti-in-zircon thermometry suggests early crystallization temperatures for zircon precipitation, while biotite geothermometry yields near-<em>solidus</em>, late crystallization temperatures for the Serra dos Órgãos batholith. REE-in-zircon oxybarometry suggests <em>f</em>O<sub>2</sub> around FMQ conditions for the intrusion, contrasting with more oxidized <em>f</em>O<sub>2</sub> conditions for the country rocks. The evidence indicates that the studied sensu stricto granites were formed by water-undersaturated melting of crustal protoliths at temperatures up to 840 ","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107973"},"PeriodicalIF":2.9,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143207830","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 : 2025-01-28DOI: 10.1016/j.lithos.2025.107972
Ji Wan Jeong , Nobuhiko Nakano , Tatsuro Adachi , Kenta Kawaguchi
The tectonic evolution of the Korean Peninsula during the Middle to Late Paleozoic remains a subject of debate due to sparse evidence. The Guryong Group—a metamorphosed sedimentary formation located in the Odesan area of the Gyeonggi Massif—is reported to have been deposited during the Middle Paleozoic and subsequently underwent Permo–Triassic collision-related metamorphism. Therefore, the Guryong Group is crucial for understanding the Paleozoic tectono-thermal history of the region. In this study, we performed comprehensive zircon U-Pb dating and Lu-Hf isotope analysis coupled with geochemical investigations of the metasedimentary rocks of the Guryong Group and its surrounding rocks of the Gyeonggi Massif. Our aim is to determine the timing of deposition and tectonic settings, thereby elucidating the Paleozoic tectono-thermal evolution of the Korean Peninsula. The detrital zircon age distributions in the metasedimentary rocks from the western Guryong Group include clusters of ca. 1899–1616 Ma (8 %), 998–723 Ma (11 %), 537–419 Ma (10 %), and 418–307 Ma (56 %), with the youngest detrital zircons dating between 344 and 307 Ma. In contrast, calc-silicate rocks from the eastern Guryong Group exhibit different age patterns of ca. 1958–1830 Ma (20 %), 1522–1427 Ma (8 %), 1398–1200 Ma (17 %), 1194–1001 Ma (17 %), and 850–720 Ma (23 %), and a main age peak of ca. 749 Ma. Additionally, three biotite gneisses and one quartzite from the eastern Guryong Group show age clusters of ca. 3361–3187 Ma (7 %), 2778–2500 Ma (19 %), 2494–2414 Ma (24 %), 2382–2200 Ma (24 %), 2186–2002 Ma (15 %), and 1927–1826 Ma (6 %), with no Paleozoic detrital zircons. These results suggest that parts of the Guryong Group were deposited at different times from the western part, similar to paragneisses in the Gyeonggi Massif. The newly identified Carboniferous metasedimentary rocks, with the youngest detrital zircons dated to 344–307 Ma, contain 56 % of detrital zircons aged between 418 and 307 Ma. This suggests that Devonian to Carboniferous magmatic rocks were the major source to form the Carboniferous sedimentary rocks of the Guryong Group. The whole-rock chemical analyses of metasedimentary rocks in the western Guryong Group reveal a consistent pattern characterized by enrichment in light rare-earth elements (REEs) and notable depletion in Nb-Ta. The εHf(t) values of zircon grains dated to the Devonian are negative (ranging from −6.67 to −18.13), suggesting that these Devonian magmatic rocks originated from the reworking of the Precambrian basement of the Gyeonggi Massif. This study supports the hypothesis that extensive arc magmatism occurred in the Odesan area during the Devonian to Carboniferous periods prior to the Permo–Triassic continental collision, possibly representing the easternmost extension of Paleozoic arc magmatism occurring along the southern margin of the North China Craton.
{"title":"Detrital zircon chronology of the Guryong Group, the eastern part of the Gyeonggi Massif, Korea: Implication for the Late Paleozoic pre-collisional evolution in the Korean Peninsula","authors":"Ji Wan Jeong , Nobuhiko Nakano , Tatsuro Adachi , Kenta Kawaguchi","doi":"10.1016/j.lithos.2025.107972","DOIUrl":"10.1016/j.lithos.2025.107972","url":null,"abstract":"<div><div>The tectonic evolution of the Korean Peninsula during the Middle to Late Paleozoic remains a subject of debate due to sparse evidence. The Guryong Group—a metamorphosed sedimentary formation located in the Odesan area of the Gyeonggi Massif—is reported to have been deposited during the Middle Paleozoic and subsequently underwent Permo–Triassic collision-related metamorphism. Therefore, the Guryong Group is crucial for understanding the Paleozoic tectono-thermal history of the region. In this study, we performed comprehensive zircon U-Pb dating and Lu-Hf isotope analysis coupled with geochemical investigations of the metasedimentary rocks of the Guryong Group and its surrounding rocks of the Gyeonggi Massif. Our aim is to determine the timing of deposition and tectonic settings, thereby elucidating the Paleozoic tectono-thermal evolution of the Korean Peninsula. The detrital zircon age distributions in the metasedimentary rocks from the western Guryong Group include clusters of ca. 1899–1616 Ma (8 %), 998–723 Ma (11 %), 537–419 Ma (10 %), and 418–307 Ma (56 %), with the youngest detrital zircons dating between 344 and 307 Ma. In contrast, calc-silicate rocks from the eastern Guryong Group exhibit different age patterns of ca. 1958–1830 Ma (20 %), 1522–1427 Ma (8 %), 1398–1200 Ma (17 %), 1194–1001 Ma (17 %), and 850–720 Ma (23 %), and a main age peak of ca. 749 Ma. Additionally, three biotite gneisses and one quartzite from the eastern Guryong Group show age clusters of ca. 3361–3187 Ma (7 %), 2778–2500 Ma (19 %), 2494–2414 Ma (24 %), 2382–2200 Ma (24 %), 2186–2002 Ma (15 %), and 1927–1826 Ma (6 %), with no Paleozoic detrital zircons. These results suggest that parts of the Guryong Group were deposited at different times from the western part, similar to paragneisses in the Gyeonggi Massif. The newly identified Carboniferous metasedimentary rocks, with the youngest detrital zircons dated to 344–307 Ma, contain 56 % of detrital zircons aged between 418 and 307 Ma. This suggests that Devonian to Carboniferous magmatic rocks were the major source to form the Carboniferous sedimentary rocks of the Guryong Group. The whole-rock chemical analyses of metasedimentary rocks in the western Guryong Group reveal a consistent pattern characterized by enrichment in light rare-earth elements (REEs) and notable depletion in Nb-Ta. The ε<sub>Hf</sub>(t) values of zircon grains dated to the Devonian are negative (ranging from −6.67 to −18.13), suggesting that these Devonian magmatic rocks originated from the reworking of the Precambrian basement of the Gyeonggi Massif. This study supports the hypothesis that extensive arc magmatism occurred in the Odesan area during the Devonian to Carboniferous periods prior to the Permo–Triassic continental collision, possibly representing the easternmost extension of Paleozoic arc magmatism occurring along the southern margin of the North China Craton.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107972"},"PeriodicalIF":2.9,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143321011","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 : 2025-01-27DOI: 10.1016/j.lithos.2025.107966
Miao-Yan Zhang , Lu-Lu Hao , Yue Qi , Qiang Wang , Andrew C. Kerr , Lin Ma , Cheng-Cheng Huang , Gang-Jian Wei , Jie Li , Jin-Long Ma , Qi-Wei Li , Zi-Long Wang , Tong-Yu Huang , Yu-Chen Yang
At continental collisional zones, the continental crust is known to subduct, penetrating the deep lithospheric mantle and undergoing partial melting. However, the extent to which these melts can effectively alter, or metasomatize, the overlying mantle remains a contentious issue. This debate is especially pronounced in the Cenozoic Himalayan-southern Tibet collisional orogen. The complexity arises from the fact that previous research has predominantly concentrated on the post-collisional intermediate ultrapotassic rocks. However, these rocks could have originated either from the subducted Indian continental crust through a process of mantle assimilation or from mélange rocks, thereby primarily reflecting crustal recycling rather than mantle metasomatism by subducted continental crust. In this study, we shift our focus to the less-well-studied post-collisional basaltic ultrapotassic rocks (BUPRs) from the Sailipu region in the Lhasa block of southern Tibet. Our aim is to evaluate the characteristics of the orogenic mantle and the dynamics of crust-mantle interactions. In this study we report major and trace elements and Sr-Nd-Pb-Mo-B isotopes for these Miocene post-collisional BUPRs. The rocks are typically characterized by alkaline affinity, arc-like trace element distribution patterns, and enriched Sr-Nd-Pb isotopes, which point to their derivation from an enriched mantle source. Moreover, the MoB isotope ratios of these BUPRs - δ98/95Mo ranging from −0.85 ‰ to −0.27 ‰ and δ11B from −20.2 ‰ to −14.4 ‰ - are notably lower than those found in Mid-Ocean Ridge Basalts (MORBs) and arc lavas. Instead, they are similar to the isotopic compositions of basalts associated with continental subduction, as well as intermediate ultrapotassic rocks from western Anatolia and the Lhasa block, and the gneisses and schists of the Himalayas. These similarities strongly suggest the input of subducted Indian continental crust to the mantle source for these rocks. In conclusion, our study supports the metasomatism of the mantle beneath southern Tibet by subducted Indian continental crust. These results show that continental subduction zones, much like their oceanic counterparts, are key regions for mantle metasomatism, and thus expands our understanding of the geological processes at work in these dynamic areas.
{"title":"Mantle metasomatism by subducted Indian continental crust: Evidence from post-collisional basaltic ultrapotassic rocks in southern Tibetan plateau","authors":"Miao-Yan Zhang , Lu-Lu Hao , Yue Qi , Qiang Wang , Andrew C. Kerr , Lin Ma , Cheng-Cheng Huang , Gang-Jian Wei , Jie Li , Jin-Long Ma , Qi-Wei Li , Zi-Long Wang , Tong-Yu Huang , Yu-Chen Yang","doi":"10.1016/j.lithos.2025.107966","DOIUrl":"10.1016/j.lithos.2025.107966","url":null,"abstract":"<div><div>At continental collisional zones, the continental crust is known to subduct, penetrating the deep lithospheric mantle and undergoing partial melting. However, the extent to which these melts can effectively alter, or metasomatize, the overlying mantle remains a contentious issue. This debate is especially pronounced in the Cenozoic Himalayan-southern Tibet collisional orogen. The complexity arises from the fact that previous research has predominantly concentrated on the post-collisional intermediate ultrapotassic rocks. However, these rocks could have originated either from the subducted Indian continental crust through a process of mantle assimilation or from mélange rocks, thereby primarily reflecting crustal recycling rather than mantle metasomatism by subducted continental crust. In this study, we shift our focus to the less-well-studied post-collisional basaltic ultrapotassic rocks (BUPRs) from the Sailipu region in the Lhasa block of southern Tibet. Our aim is to evaluate the characteristics of the orogenic mantle and the dynamics of crust-mantle interactions. In this study we report major and trace elements and Sr-Nd-Pb-Mo-B isotopes for these Miocene post-collisional BUPRs. The rocks are typically characterized by alkaline affinity, arc-like trace element distribution patterns, and enriched Sr-Nd-Pb isotopes, which point to their derivation from an enriched mantle source. Moreover, the Mo<img>B isotope ratios of these BUPRs - δ<sup>98/95</sup>Mo ranging from −0.85 ‰ to −0.27 ‰ and δ<sup>11</sup>B from −20.2 ‰ to −14.4 ‰ - are notably lower than those found in Mid-Ocean Ridge Basalts (MORBs) and arc lavas. Instead, they are similar to the isotopic compositions of basalts associated with continental subduction, as well as intermediate ultrapotassic rocks from western Anatolia and the Lhasa block, and the gneisses and schists of the Himalayas. These similarities strongly suggest the input of subducted Indian continental crust to the mantle source for these rocks. In conclusion, our study supports the metasomatism of the mantle beneath southern Tibet by subducted Indian continental crust. These results show that continental subduction zones, much like their oceanic counterparts, are key regions for mantle metasomatism, and thus expands our understanding of the geological processes at work in these dynamic areas.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107966"},"PeriodicalIF":2.9,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143360222","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 : 2025-01-27DOI: 10.1016/j.lithos.2025.107952
I. Novo-Fernández , R. Albert , R. Arenas , J.I. Gil Ibarguchi , S. Sánchez Martínez , A. Gerdes , R. Díez Fernández , A. Beranoaguirre , A. Garcia-Casco
In the Cabo Ortegal Complex (NW Iberian Massif), a 20 km long and 700 m thick layer of eclogites constitutes one of the world's largest outcrops of this type of rocks. It belongs to the Upper Allochthon, a terrane that represents the remnants of a Cambrian peri-Gondwanan fore-arc basin that was involved in the Variscan collision. In this layer, three types of eclogites are differentiated according to their mineralogy and bulk composition: the common, the ferrotitaniferous, and the Al-Mg-rich eclogites. This work studies the three types of eclogites via thermodynamic modelling. The ferric content of the bulk composition during the metamorphic peak is analyzed, the results demonstrating a strong influence on the metamorphic paragenesis in two of the three types. Isochemical equilibrium phase diagrams in the MnNCKFMASTHO system indicate metamorphic peak conditions of c. 23–25 kbar at c. 750–800 °C prior to a decompression up to c. 16–20 kbar. UPb dating in zircon crystals (LA-ICP-MS) from an eclogite yields an age of c. 390 Ma for the high-P metamorphism. All this indicates deep subduction of the peri-Gondwanan realm at the onset of the Variscan Orogeny during Early Devonian. The results are used to discuss the stacking of units that constitute the Upper Allochthon and envisage the processes that contributed to their exhumation.
{"title":"P-T evolution and refined UPb geochronology of the giant eclogite layer of the Cabo Ortegal Complex (NW Iberian Massif)","authors":"I. Novo-Fernández , R. Albert , R. Arenas , J.I. Gil Ibarguchi , S. Sánchez Martínez , A. Gerdes , R. Díez Fernández , A. Beranoaguirre , A. Garcia-Casco","doi":"10.1016/j.lithos.2025.107952","DOIUrl":"10.1016/j.lithos.2025.107952","url":null,"abstract":"<div><div>In the Cabo Ortegal Complex (NW Iberian Massif), a 20 km long and 700 m thick layer of eclogites constitutes one of the world's largest outcrops of this type of rocks. It belongs to the Upper Allochthon, a terrane that represents the remnants of a Cambrian peri-Gondwanan fore-arc basin that was involved in the Variscan collision. In this layer, three types of eclogites are differentiated according to their mineralogy and bulk composition: the common, the ferrotitaniferous, and the Al-Mg-rich eclogites. This work studies the three types of eclogites via thermodynamic modelling. The ferric content of the bulk composition during the metamorphic peak is analyzed, the results demonstrating a strong influence on the metamorphic paragenesis in two of the three types. Isochemical equilibrium phase diagrams in the MnNCKFMASTHO system indicate metamorphic peak conditions of c. 23–25 kbar at c. 750–800 °C prior to a decompression up to c. 16–20 kbar. U<img>Pb dating in zircon crystals (LA-ICP-MS) from an eclogite yields an age of c. 390 Ma for the high-P metamorphism. All this indicates deep subduction of the peri-Gondwanan realm at the onset of the Variscan Orogeny during Early Devonian. The results are used to discuss the stacking of units that constitute the Upper Allochthon and envisage the processes that contributed to their exhumation.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107952"},"PeriodicalIF":2.9,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143319886","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 : 2025-01-27DOI: 10.1016/j.lithos.2025.107970
Katsuyoshi Michibayashi , Yuki Kakihata , Itsuki Natsume , Takeo Okuwaki , Marguerite Godard , Peter Kelemen , The Oman Drilling Project Science Team
Crystallographic preferred orientations (CPO) of olivine within natural peridotites are commonly expressed by pole figures for the [100], [010], and [001] axes, and they can be categorized into six well-known crystal fabric types: A, B, C, D, E, and AG. In this paper, we have studied olivine crystal fabrics preserved within serpentinized peridotites in Hole BA3A cores from the Wadi Tayin mantle section of the Samail ophiolite in the Sultanate of Oman, drilled by the ICDP Oman Drilling Project (OmanDP) as part of the Multi-Borehole Observatory (MBO). Hole BA3A cores mostly consist of serpentinized harzburgites with small proportions of thin serpentinized dunitic and mafic layers. Quarter slabs were obtained from Hole BA3A cores, from parts of the core in which the degree of serpentinization was slightly lower than the range of the average through the whole core (70–96 %). The mineral phases and crystal orientations in each polished thin section were analyzed using a scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) system. EBSD mapping and data processing were then performed to reveal the original CPO of mantle olivine, based on the orientation of relict grains of olivine in surrounding serpentine that retain the legacy of mantle fabrics. As a result, we found that olivine CPOs in Hole BA3A cores were mostly characterized by A to D type fabrics typical of steeply oriented, late, relatively low temperature mantle shear zones in the Samail ophiolite, as opposed to A to AG type fabrics typical of high-T asthenospheric mantle textures. However, Hole BA3A cores preserve foliations subparallel to the crust-mantle boundary like some of the high temperature fabrics. This implies that the olivine fabric transition could have occurred during continued deformation at progressively lower temperature until mantle flow ceased within the lithospheric mantle.
{"title":"Legacy of mantle fabrics preserved within heavily serpentinized peridotites in Hole BA3A cores of the Oman Drilling Project","authors":"Katsuyoshi Michibayashi , Yuki Kakihata , Itsuki Natsume , Takeo Okuwaki , Marguerite Godard , Peter Kelemen , The Oman Drilling Project Science Team","doi":"10.1016/j.lithos.2025.107970","DOIUrl":"10.1016/j.lithos.2025.107970","url":null,"abstract":"<div><div>Crystallographic preferred orientations (CPO) of olivine within natural peridotites are commonly expressed by pole figures for the [100], [010], and [001] axes, and they can be categorized into six well-known crystal fabric types: A, B, C, D, E, and AG. In this paper, we have studied olivine crystal fabrics preserved within serpentinized peridotites in Hole BA3A cores from the Wadi Tayin mantle section of the Samail ophiolite in the Sultanate of Oman, drilled by the ICDP Oman Drilling Project (OmanDP) as part of the Multi-Borehole Observatory (MBO). Hole BA3A cores mostly consist of serpentinized harzburgites with small proportions of thin serpentinized dunitic and mafic layers. Quarter slabs were obtained from Hole BA3A cores, from parts of the core in which the degree of serpentinization was slightly lower than the range of the average through the whole core (70–96 %). The mineral phases and crystal orientations in each polished thin section were analyzed using a scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) system. EBSD mapping and data processing were then performed to reveal the original CPO of mantle olivine, based on the orientation of relict grains of olivine in surrounding serpentine that retain the legacy of mantle fabrics. As a result, we found that olivine CPOs in Hole BA3A cores were mostly characterized by A to D type fabrics typical of steeply oriented, late, relatively low temperature mantle shear zones in the Samail ophiolite, as opposed to A to AG type fabrics typical of high-T asthenospheric mantle textures. However, Hole BA3A cores preserve foliations subparallel to the crust-mantle boundary like some of the high temperature fabrics. This implies that the olivine fabric transition could have occurred during continued deformation at progressively lower temperature until mantle flow ceased within the lithospheric mantle.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107970"},"PeriodicalIF":2.9,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143320469","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}
The India–Eurasia collision during Cenozoic era has led to large-scale uplift and lithospheric extrusion of the central Tibetan Plateau. As a vital boundary for accommodating the compressive stress in the interior of the plateau, the Diancangshan–Ailaoshan tectonic zone (DATZ) in Yunnan Province has witnessed to this evolutionary history and documented the tectonic processes. As the indication of the collisional process at depth, the Cenozoic potassic magmatic rocks that developed along the DATZ are the critical lithological probe for elucidating the deep dynamic mechanisms underlying the India–Eurasia collision and their connection with the plateau's lithospheric extrusion. In this paper, we present new zircon U-Pb, Hf and O isotopic data, along with whole-rock major and trace elemental compositions, and whole-rock Sr-Nd isotopic data of Eocene porphyries located at the junction of the Diancangshan and Ailaoshan metamorphic massifs in Yunnan Province. Zircon U-Pb dating results indicate that they were emplaced at 37–35 Ma. Geochemically, all the studied porphyries exhibit an affinity to potassic adakitic rocks with the enrichment in K2O (K2O = 3.88–5.69 wt%), high Sr contents (mostly >400 ppm), elevated Sr/Y ratios (30–106), and low Y and Yb contents, indicating an origin from the partial melting of the thickened mafic continental lower crust which is garnet-bearing amphibolite. However, the disparity in zircon Hf and O isotopic compositions between the Binchuan–Midu and Weishan granitic porphyries reflects their different sources. They are the Neoproterozoic and Late Paleozoic mafic lower crust that formed during the Neoproterozoic and Paleo-Tethyan subduction, respectively. By integrating regional data, including structural feature, metamorphism, sedimentation and magmatism patterns, we propose that the generation of the late Eocene (37–35 Ma) potassic rocks along the Jinshajiang–Ailaoshan tectonic zone in Yunnan Province was a consequence of the southeastward extrusion of the central Tibetan Plateau lithosphere, coupled with the left-lateral shearing of the DATZ and the rotating of the Lanping–Simao and Yangtze blocks.
{"title":"Origin of Eocene adakitic porphyries in the Binchuan–Weishan area, southeastern Tibetan Plateau: Constraints on the initial left-lateral strike slip of the Diancangshan–Ailaoshan tectonic zone","authors":"Xiaohan Dong , Guochun Zhao , Bingbing Liu , Limin Wu , Jianfeng Gao , Lifeng Zhong , Touping Peng","doi":"10.1016/j.lithos.2025.107967","DOIUrl":"10.1016/j.lithos.2025.107967","url":null,"abstract":"<div><div>The India–Eurasia collision during Cenozoic era has led to large-scale uplift and lithospheric extrusion of the central Tibetan Plateau. As a vital boundary for accommodating the compressive stress in the interior of the plateau, the Diancangshan–Ailaoshan tectonic zone (DATZ) in Yunnan Province has witnessed to this evolutionary history and documented the tectonic processes. As the indication of the collisional process at depth, the Cenozoic potassic magmatic rocks that developed along the DATZ are the critical lithological probe for elucidating the deep dynamic mechanisms underlying the India–Eurasia collision and their connection with the plateau's lithospheric extrusion. In this paper, we present new zircon U-Pb, Hf and O isotopic data, along with whole-rock major and trace elemental compositions, and whole-rock Sr-Nd isotopic data of Eocene porphyries located at the junction of the Diancangshan and Ailaoshan metamorphic massifs in Yunnan Province. Zircon U-Pb dating results indicate that they were emplaced at 37–35 Ma. Geochemically, all the studied porphyries exhibit an affinity to potassic adakitic rocks with the enrichment in K<sub>2</sub>O (K<sub>2</sub>O = 3.88–5.69 wt%), high Sr contents (mostly >400 ppm), elevated Sr/Y ratios (30–106), and low Y and Yb contents, indicating an origin from the partial melting of the thickened mafic continental lower crust which is garnet-bearing amphibolite. However, the disparity in zircon Hf and O isotopic compositions between the Binchuan–Midu and Weishan granitic porphyries reflects their different sources. They are the Neoproterozoic and Late Paleozoic mafic lower crust that formed during the Neoproterozoic and Paleo-Tethyan subduction, respectively. By integrating regional data, including structural feature, metamorphism, sedimentation and magmatism patterns, we propose that the generation of the late Eocene (37–35 Ma) potassic rocks along the Jinshajiang–Ailaoshan tectonic zone in Yunnan Province was a consequence of the southeastward extrusion of the central Tibetan Plateau lithosphere, coupled with the left-lateral shearing of the DATZ and the rotating of the Lanping–Simao and Yangtze blocks.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107967"},"PeriodicalIF":2.9,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143378749","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 : 2025-01-23DOI: 10.1016/j.lithos.2025.107953
Matthew M. Wincott, Simon C. Kohn, Ian J. Parkinson
We report the discovery of a diamond containing six thin, flat olivine inclusions. Cathodoluminescence (CL) imaging and X-ray tomography revealed inclusion alignment within and parallel to a single diamond growth zone. A novel application of Fourier Transform Infrared spectroscopy to diamond inclusions established that they shared a common crystallographic orientation. Whilst the olivine (100) and diamond (111) planes were parallel, the olivine b- and c-axes were not parallel to any of the diamond's major crystallographic axes. The shared morphology, spatial distribution and crystallographic orientations of the inclusions can only be explained by a single crystal origin, which has previously been used as proof of protogenesis. However, unusual CL dead zones, thought to be related to the partial dissolution and replacement of the monocrystal, are exclusively observed in the plane of the inclusions, implying that the original crystal was never equant when interacting with the diamond. As we are not aware of any mechanism resulting in olivine independently adopting such a high aspect ratio (over 60:1) in the mantle, we favour a model wherein the monocrystal grew as a thin layer on a pre-existing diamond surface before being partially dissolved and rapidly encased. We therefore conclude that the olivine inclusions are remnants of a syngenetic monocrystal, and that crystallographic orientation alignment between inclusions does not always imply a protogenetic relationship.
{"title":"Six olivine inclusions in diamond are remnants of a syngenetic monocrystal","authors":"Matthew M. Wincott, Simon C. Kohn, Ian J. Parkinson","doi":"10.1016/j.lithos.2025.107953","DOIUrl":"10.1016/j.lithos.2025.107953","url":null,"abstract":"<div><div>We report the discovery of a diamond containing six thin, flat olivine inclusions. Cathodoluminescence (CL) imaging and X-ray tomography revealed inclusion alignment within and parallel to a single diamond growth zone. A novel application of Fourier Transform Infrared spectroscopy to diamond inclusions established that they shared a common crystallographic orientation. Whilst the olivine (100) and diamond (111) planes were parallel, the olivine b- and c-axes were not parallel to any of the diamond's major crystallographic axes. The shared morphology, spatial distribution and crystallographic orientations of the inclusions can only be explained by a single crystal origin, which has previously been used as proof of protogenesis. However, unusual CL dead zones, thought to be related to the partial dissolution and replacement of the monocrystal, are exclusively observed in the plane of the inclusions, implying that the original crystal was never equant when interacting with the diamond. As we are not aware of any mechanism resulting in olivine independently adopting such a high aspect ratio (over 60:1) in the mantle, we favour a model wherein the monocrystal grew as a thin layer on a pre-existing diamond surface before being partially dissolved and rapidly encased. We therefore conclude that the olivine inclusions are remnants of a syngenetic monocrystal, and that crystallographic orientation alignment between inclusions does not always imply a protogenetic relationship.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107953"},"PeriodicalIF":2.9,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143321008","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}
Pub Date : 2025-01-22DOI: 10.1016/j.lithos.2025.107950
S. Cacciari , E. Cannaò , G. Toffol , M. Scambelluri , L.F.G. Morales , G. Pennacchioni
<div><div>In subduction zones, seismicity and rock rheology are strongly influenced by the presence of fluids. However, the mechanisms governing fluid extraction and transport along the subduction interface are still debated. The meta-peridotite of the Erro-Tobbio Unit (Ligurian Alps) records fluid-rock interaction and associated deformation that occurred at intermediate subduction depths. Fluid pathways are represented by reaction bands of metamorphic olivine (Ol<sub>2</sub>) and Ti-clinohumite, formed by the breakdown of brucite (Brc) and antigorite (Atg) at 1.8–2.5 GPa and 500–650 °C. Field and microstructural analyses allowed the role of deformation in the development of ORBs to be assessed. In-situ determination of trace elements by LA-ICP-MS allowed the scale of fluid circulation along reaction-induced channels to be constrained.</div><div>The reaction bands occur within both meta-peridotite cores and wrapping horizons of prograde antigorite mylonites. The meta-peridotite shows two main sets of reaction bands: <em>Set</em><sub><em>1</em></sub>, oriented at high angle to the bounding mylonites, and <em>Set</em><sub><em>2</em></sub>, trending N-S, parallel to the mylonites (where only <em>Set</em><sub><em>2</em></sub> is present). A decrease in spacing between reaction bands of <em>Set</em><sub><em>2</em></sub> highlights a strain gradient from the undeformed meta-peridotite cores to the mylonites. This gradient, associated with oriented growth of Ol<sub>2</sub> in the mylonites, suggests that the reaction bands developed during mylonitization. Brc relics mostly localized within the reaction bands indicate that formation of Ol<sub>2</sub> was originally controlled by the Brc distribution. Such channel networks have been described in previous works as the result of channel-forming reactive porosity related to initial breakdown of thermodynamically favoured domains. The formation of the reaction bands may be therefore related to formation of low-Si fluids in Brc-rich areas, which triggered Atg breakdown and formation of porosity by flowing along planes consistent with the stress field.</div><div>Later stage, Al-free serpentine (Atg + chrysotile/lizardite) locally replaces Ol<sub>2</sub> along a pervasive network of microcracks exploiting the reactive sites of <em>Set</em><sub><em>1</em></sub>-<em>Set</em><sub><em>2</em></sub> structures. An enrichment in fluid-mobile elements (As, Sb, Ba, W, Li, B) in prograde Ol<sub>2</sub> and later-stage Al-free serpentine provides evidence of two stages of infiltration of slab-derived fluids, indicating open-system conditions during eclogite-facies deformation and during retrogression. We speculate that the Erro-Tobbio Unit was subducted at an early stage of Adria-Europe convergence and settled atop the interface within the deep slow-earthquakes depth range, above the continuously under-riding and dehydrating Alpine slab. In this environment, the Erro-Tobbio Unit was affected by intense chemical exchange du
{"title":"Fluid infiltration along reactive porosity networks at the subduction interface: Evidence from the eclogite-facies Erro-Tobbio Unit (Ligurian Alps)","authors":"S. Cacciari , E. Cannaò , G. Toffol , M. Scambelluri , L.F.G. Morales , G. Pennacchioni","doi":"10.1016/j.lithos.2025.107950","DOIUrl":"10.1016/j.lithos.2025.107950","url":null,"abstract":"<div><div>In subduction zones, seismicity and rock rheology are strongly influenced by the presence of fluids. However, the mechanisms governing fluid extraction and transport along the subduction interface are still debated. The meta-peridotite of the Erro-Tobbio Unit (Ligurian Alps) records fluid-rock interaction and associated deformation that occurred at intermediate subduction depths. Fluid pathways are represented by reaction bands of metamorphic olivine (Ol<sub>2</sub>) and Ti-clinohumite, formed by the breakdown of brucite (Brc) and antigorite (Atg) at 1.8–2.5 GPa and 500–650 °C. Field and microstructural analyses allowed the role of deformation in the development of ORBs to be assessed. In-situ determination of trace elements by LA-ICP-MS allowed the scale of fluid circulation along reaction-induced channels to be constrained.</div><div>The reaction bands occur within both meta-peridotite cores and wrapping horizons of prograde antigorite mylonites. The meta-peridotite shows two main sets of reaction bands: <em>Set</em><sub><em>1</em></sub>, oriented at high angle to the bounding mylonites, and <em>Set</em><sub><em>2</em></sub>, trending N-S, parallel to the mylonites (where only <em>Set</em><sub><em>2</em></sub> is present). A decrease in spacing between reaction bands of <em>Set</em><sub><em>2</em></sub> highlights a strain gradient from the undeformed meta-peridotite cores to the mylonites. This gradient, associated with oriented growth of Ol<sub>2</sub> in the mylonites, suggests that the reaction bands developed during mylonitization. Brc relics mostly localized within the reaction bands indicate that formation of Ol<sub>2</sub> was originally controlled by the Brc distribution. Such channel networks have been described in previous works as the result of channel-forming reactive porosity related to initial breakdown of thermodynamically favoured domains. The formation of the reaction bands may be therefore related to formation of low-Si fluids in Brc-rich areas, which triggered Atg breakdown and formation of porosity by flowing along planes consistent with the stress field.</div><div>Later stage, Al-free serpentine (Atg + chrysotile/lizardite) locally replaces Ol<sub>2</sub> along a pervasive network of microcracks exploiting the reactive sites of <em>Set</em><sub><em>1</em></sub>-<em>Set</em><sub><em>2</em></sub> structures. An enrichment in fluid-mobile elements (As, Sb, Ba, W, Li, B) in prograde Ol<sub>2</sub> and later-stage Al-free serpentine provides evidence of two stages of infiltration of slab-derived fluids, indicating open-system conditions during eclogite-facies deformation and during retrogression. We speculate that the Erro-Tobbio Unit was subducted at an early stage of Adria-Europe convergence and settled atop the interface within the deep slow-earthquakes depth range, above the continuously under-riding and dehydrating Alpine slab. In this environment, the Erro-Tobbio Unit was affected by intense chemical exchange du","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"498 ","pages":"Article 107950"},"PeriodicalIF":2.9,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143207829","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 : 2025-01-21DOI: 10.1016/j.lithos.2025.107954
Alizadeh Noudeh Shiva , Rolland Yann , Rossi Magali , Bosch Delphine , Münch Philippe , Iemmolo Arthur , Bruguier Olivier , Mohammad Rahgoshay
Early Cenozoic magmatism is widespread in the Central Tethyan orogenic belt linking the tectonic zones of Iran, South Armenian Block (Lesser Caucasus) and Turkey, but its relationship to the Southern Neotethys Ocean is questioned. This study focusses on the southern part of Talysh massif, NW Iran, where thick geological successions of high potassic magmatic rocks erupted in the Eocene. This paper reports geochronological and geochemical data for this succession, which is mostly comprised of shoshonitic basalt and rare rhyolitic pyroclastic rocks emplaced during an Eocene magmatic flare-up. 40Ar/39Ar dating of magmatic hornblende and biotite from basalts and trachy-andesites and U/Pb zircon dating of a dacitic tuff show that the magmatic event is spread on a 10 Myr range, from 50 to 40 Ma. Four main stages are documented at ∼49.8, 45–43, 43.2–41.6 and 39.8 Ma. One zircon yielded a significantly older U/Pb age of 616 ± 16 Ma, which involves recycling of a Neoproterozoic crystalline basement. Mafic lavas are enriched in LILE and depleted in HFSE, with high Th/Yb, Ba/Th and Nb/Zr ratios. In addition, Sr, Nd, Pb and Hf isotopic ratios suggest an enriched mantle source, with assimilation of continental crust during differentiation processes. These data are in agreement with partial melting of a garnet-bearing subduction-modified subcontinental mantle and interactions with a spinel-bearing mantle during magmatic ascent. This magmatic flare-up could have been triggered by an Asthenosphere upwelling. This upwelling could be caused to combined onset of south-dipping subduction of the Transcaucasus basin and verticalization of the north-dipping subduction taking place to the south of Iran. Asthenosphere flow and magmatic ascent were likely facilitated by trans-lithospheric strike-slip faults and block rotations highlighted by paleomagnetic data. A transition from calc-alkaline towards a more alkaline magmatic component with time, from south to north of the Talysh Massif, suggests a slab steepening in response to roll-back in the Late Eocene. Subsequent to this period, volcanism ceased in the South Talysh and markedly declined in the North Talysh massif, where it underwent a transformation into an adakitic-type magmatism during the Late Miocene and Quaternary.
{"title":"Geochronological, isotopic and petrogenetic investigations of Cenozoic Volcanic rocks in the Talysh Massif, NW Iran: Insights for the Eocene magmatic flare-up","authors":"Alizadeh Noudeh Shiva , Rolland Yann , Rossi Magali , Bosch Delphine , Münch Philippe , Iemmolo Arthur , Bruguier Olivier , Mohammad Rahgoshay","doi":"10.1016/j.lithos.2025.107954","DOIUrl":"10.1016/j.lithos.2025.107954","url":null,"abstract":"<div><div>Early Cenozoic magmatism is widespread in the Central Tethyan orogenic belt linking the tectonic zones of Iran, South Armenian Block (Lesser Caucasus) and Turkey, but its relationship to the Southern Neotethys Ocean is questioned. This study focusses on the southern part of Talysh massif, NW Iran, where thick geological successions of high potassic magmatic rocks erupted in the Eocene. This paper reports geochronological and geochemical data for this succession, which is mostly comprised of shoshonitic basalt and rare rhyolitic pyroclastic rocks emplaced during an Eocene magmatic flare-up. <sup>40</sup>Ar/<sup>39</sup>Ar dating of magmatic hornblende and biotite from basalts and trachy-andesites and U/Pb zircon dating of a dacitic tuff show that the magmatic event is spread on a 10 Myr range, from 50 to 40 Ma. Four main stages are documented at ∼49.8, 45–43, 43.2–41.6 and 39.8 Ma. One zircon yielded a significantly older U/Pb age of 616 ± 16 Ma, which involves recycling of a Neoproterozoic crystalline basement. Mafic lavas are enriched in LILE and depleted in HFSE, with high Th/Yb, Ba/Th and Nb/Zr ratios. In addition, Sr, Nd, Pb and Hf isotopic ratios suggest an enriched mantle source, with assimilation of continental crust during differentiation processes. These data are in agreement with partial melting of a garnet-bearing subduction-modified subcontinental mantle and interactions with a spinel-bearing mantle during magmatic ascent. This magmatic flare-up could have been triggered by an Asthenosphere upwelling. This upwelling could be caused to combined onset of south-dipping subduction of the Transcaucasus basin and verticalization of the north-dipping subduction taking place to the south of Iran. Asthenosphere flow and magmatic ascent were likely facilitated by trans-lithospheric strike-slip faults and block rotations highlighted by paleomagnetic data. A transition from calc-alkaline towards a more alkaline magmatic component with time, from south to north of the Talysh Massif, suggests a slab steepening in response to roll-back in the Late Eocene. Subsequent to this period, volcanism ceased in the South Talysh and markedly declined in the North Talysh massif, where it underwent a transformation into an adakitic-type magmatism during the Late Miocene and Quaternary.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107954"},"PeriodicalIF":2.9,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143320297","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}
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