Pub Date : 2025-11-19DOI: 10.1016/j.lithos.2025.108333
Maksim V. Kuznetsov , Alexander M. Kozlovsky , Valery M. Savatenkov , Vladimir V. Yarmolyuk , Lidia V. Shpakovich , Tserentsegmid Oyunchimeg
<div><div>The Trans-Altai Gobi (TAG) in southern Mongolia is considered one of the largest tectonic structures within the Central Asian Orogenic Belt, formed by island- and back-arc magmatism in the Middle–Late Paleozoic Paleo-Asian Ocean (PAO). Although the island-arc origin of certain TAG ophiolites is well established, the back-arc nature of others remains unproven owing to the lack of reliable geochemical and isotopic data. The Altan Uul (AU) ophiolite complex, located in the westernmost Nemegt Ridge of the eastern TAG, has previously been interpreted as a remnant of back-arc oceanic crust, rendering petrological studies of the AU essential for understanding the mantle sources and geodynamic processes of the PAO in the Middle–Late Paleozoic.</div><div>The AU ophiolite comprises the Late Silurian–Early Devonian tholeiitic and calc-alkaline gabbros and basalt–dacite–rhyolite volcanics metamorphosed in greenschist facies. AU rocks can be divided into two groups according to their trace element patterns: one exhibiting island-arc basalt (IAB)-like characteristics and the other showing mid-ocean ridge basalt (MORB)-like signatures. Rocks from both groups are depleted in light rare earth elements (La<sub>N</sub>/Yb<sub>N</sub> = 0.1–0.9) and demonstrate very high ε<sub>Nd(t)</sub> (+8.0 − +10.2), along with generally low <sup>87</sup>Sr/<sup>86</sup>Sr<sub>(t)</sub> (0.70262–0.70443), <sup>206</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> (17.158–17.665), and <sup>207</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> (15.371–15.447) ratios. These geochemical and isotopic features of ophiolitic rocks indicate that they originated from two sources: subduction-modified depleted mantle and depleted mantle. The progressive enrichment in trace elements from basalts to rhyolites, coupled with their similar Sr–Nd–Pb isotopic compositions, suggests that felsic rocks formed through the differentiation of mafic melts. The identified mantle sources of igneous rocks and subordinate role of cherts in the AU structure imply that the AU ophiolite formed in a back-arc basin. As a PAO domain, this basin separated the TAG island-arc system from the Altai active continental margin of Siberia during the Middle Paleozoic.</div><div>The AU ophiolite is intruded by unmetamorphosed plagiogranites with a zircon SHRIMP age of 344 ± 3 Ma. Plagiogranites have low K content and combine IAB- and MORB-like trace elements (La<sub>N</sub>/Yb<sub>N</sub> = ∼1.4) and isotopic (ε<sub>Nd(t)</sub> = +9.2, <sup>87</sup>Sr/<sup>86</sup>Sr<sub>(t)</sub> = 0.70443, <sup>206</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> = 17.671, and <sup>207</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> = 15.431) signatures. These findings suggest that plagiogranites formed via melting of AU ophiolitic rocks or similar mafic rocks of the TAG basement when the area was subjected to Early Carboniferous continental margin magmatism. Our data support the hypothesis that closure of the AU back-arc basin and accretion of the TAG island-arc to t
{"title":"First geochemical and isotope data for the Altan Uul ophiolite (southern Mongolia) reveal West Pacific-type tectonic evolution of the Trans-Altai Gobi in the Middle–Late paleozoic","authors":"Maksim V. Kuznetsov , Alexander M. Kozlovsky , Valery M. Savatenkov , Vladimir V. Yarmolyuk , Lidia V. Shpakovich , Tserentsegmid Oyunchimeg","doi":"10.1016/j.lithos.2025.108333","DOIUrl":"10.1016/j.lithos.2025.108333","url":null,"abstract":"<div><div>The Trans-Altai Gobi (TAG) in southern Mongolia is considered one of the largest tectonic structures within the Central Asian Orogenic Belt, formed by island- and back-arc magmatism in the Middle–Late Paleozoic Paleo-Asian Ocean (PAO). Although the island-arc origin of certain TAG ophiolites is well established, the back-arc nature of others remains unproven owing to the lack of reliable geochemical and isotopic data. The Altan Uul (AU) ophiolite complex, located in the westernmost Nemegt Ridge of the eastern TAG, has previously been interpreted as a remnant of back-arc oceanic crust, rendering petrological studies of the AU essential for understanding the mantle sources and geodynamic processes of the PAO in the Middle–Late Paleozoic.</div><div>The AU ophiolite comprises the Late Silurian–Early Devonian tholeiitic and calc-alkaline gabbros and basalt–dacite–rhyolite volcanics metamorphosed in greenschist facies. AU rocks can be divided into two groups according to their trace element patterns: one exhibiting island-arc basalt (IAB)-like characteristics and the other showing mid-ocean ridge basalt (MORB)-like signatures. Rocks from both groups are depleted in light rare earth elements (La<sub>N</sub>/Yb<sub>N</sub> = 0.1–0.9) and demonstrate very high ε<sub>Nd(t)</sub> (+8.0 − +10.2), along with generally low <sup>87</sup>Sr/<sup>86</sup>Sr<sub>(t)</sub> (0.70262–0.70443), <sup>206</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> (17.158–17.665), and <sup>207</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> (15.371–15.447) ratios. These geochemical and isotopic features of ophiolitic rocks indicate that they originated from two sources: subduction-modified depleted mantle and depleted mantle. The progressive enrichment in trace elements from basalts to rhyolites, coupled with their similar Sr–Nd–Pb isotopic compositions, suggests that felsic rocks formed through the differentiation of mafic melts. The identified mantle sources of igneous rocks and subordinate role of cherts in the AU structure imply that the AU ophiolite formed in a back-arc basin. As a PAO domain, this basin separated the TAG island-arc system from the Altai active continental margin of Siberia during the Middle Paleozoic.</div><div>The AU ophiolite is intruded by unmetamorphosed plagiogranites with a zircon SHRIMP age of 344 ± 3 Ma. Plagiogranites have low K content and combine IAB- and MORB-like trace elements (La<sub>N</sub>/Yb<sub>N</sub> = ∼1.4) and isotopic (ε<sub>Nd(t)</sub> = +9.2, <sup>87</sup>Sr/<sup>86</sup>Sr<sub>(t)</sub> = 0.70443, <sup>206</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> = 17.671, and <sup>207</sup>Pb/<sup>204</sup>Pb<sub>(t)</sub> = 15.431) signatures. These findings suggest that plagiogranites formed via melting of AU ophiolitic rocks or similar mafic rocks of the TAG basement when the area was subjected to Early Carboniferous continental margin magmatism. Our data support the hypothesis that closure of the AU back-arc basin and accretion of the TAG island-arc to t","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108333"},"PeriodicalIF":2.5,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576650","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 tectonothermal processes that shaped the Pamir Plateau are intricately revealed through the development of the giant Shakhdara gneiss domes in South Pamir, which expose a broad spectrum of structural levels. Here, we present whole-rock elements, zircon UPb geochronology and trace elements, titanite UPb ages, and in situ LuHf isotope of high-grade metamorphic rocks and pegmatites from the Shakhdara dome in the Southwest Pamir to unravel the temporal framework and crustal melting. Zircon UPb ages of gneisses (35–13 Ma) and pegmatites (28–11 Ma) are coeval with titanite UPb ages of eclogite and amphibolites (21–11 Ma). The pegmatites exhibit significant isotopic variability, with εHf(t) values ranging from −15.89 to +2.90 during ca. 28–21 Ma and − 44.53 to −7.59 during ca. 20–11 Ma. The magmas were primarily sourced from partial melting of the lower crust, with substantial contributions from the South Pamir basement and limited juvenile input from underplated depleted mantle-derived materials. The strongly enriched Hf isotopes reflect subduction-related processes involving the Indian lithosphere, which must have commenced prior to the Ma break–off of the Neo-Tethys oceanic slab. This was followed by thickening of the Pamir crust. Our new dating results, in conjunction with published data, show that the South Pamir underwent protracted crustal melting (35–11 Ma), which overlaps with prograde metamorphism (35–13 Ma) and early retrograde metamorphism (21–16 Ma). Prograde metamorphism was followed by crustal melting and pegmatite emplacement (28–11 Ma). Gravitational instability triggered delamination and a tectonic shift from contraction to extension, facilitating asthenospheric heat influx. This heat, combined with retrograde metamorphism, sustained magmatic activity and high-grade metamorphism, marking the final phase of Cenozoic tectonothermal evolution.
{"title":"Protracted crustal melting and formation of the giant Shakhdara gneiss dome, South Pamir","authors":"Murodov Azamdzhon , Wei Dan , Xin Ma , Amjad Hussain , Sharifjon Odinaev , Dzhovid Yogibekov , Ilhomjon Oimuhammadzoda , Davlatkhudzha Murodov , Sherzod Abdulov , Mustafo Gadoev , Gong-Jian Tang","doi":"10.1016/j.lithos.2025.108335","DOIUrl":"10.1016/j.lithos.2025.108335","url":null,"abstract":"<div><div>The tectonothermal processes that shaped the Pamir Plateau are intricately revealed through the development of the giant Shakhdara gneiss domes in South Pamir, which expose a broad spectrum of structural levels. Here, we present whole-rock elements, zircon U<img>Pb geochronology and trace elements, titanite U<img>Pb ages, and in situ Lu<img>Hf isotope of high-grade metamorphic rocks and pegmatites from the Shakhdara dome in the Southwest Pamir to unravel the temporal framework and crustal melting. Zircon U<img>Pb ages of gneisses (35–13 Ma) and pegmatites (28–11 Ma) are coeval with titanite U<img>Pb ages of eclogite and amphibolites (21–11 Ma). The pegmatites exhibit significant isotopic variability, with <sub>εHf</sub>(t) values ranging from −15.89 to +2.90 during ca. 28–21 Ma and − 44.53 to −7.59 during ca. 20–11 Ma. The magmas were primarily sourced from partial melting of the lower crust, with substantial contributions from the South Pamir basement and limited juvenile input from underplated depleted mantle-derived materials. The strongly enriched Hf isotopes reflect subduction-related processes involving the Indian lithosphere, which must have commenced prior to the Ma break–off of the Neo-Tethys oceanic slab. This was followed by thickening of the Pamir crust. Our new dating results, in conjunction with published data, show that the South Pamir underwent protracted crustal melting (35–11 Ma), which overlaps with prograde metamorphism (35–13 Ma) and early retrograde metamorphism (21–16 Ma). Prograde metamorphism was followed by crustal melting and pegmatite emplacement (28–11 Ma). Gravitational instability triggered delamination and a tectonic shift from contraction to extension, facilitating asthenospheric heat influx. This heat, combined with retrograde metamorphism, sustained magmatic activity and high-grade metamorphism, marking the final phase of Cenozoic tectonothermal evolution.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108335"},"PeriodicalIF":2.5,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576594","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 : 2025-11-19DOI: 10.1016/j.lithos.2025.108336
Ezgi Ulusoy , Yusuf Kağan Kadıoğlu , Yavuz Bedi
In northwestern Türkiye, near the Türkiye-Bulgaria border, the Late Cretaceous Demirköy Intrusive Suite forms a key component of the northern Tethyan magmatic arc developed during the subduction of the Neotethyan oceanic lithosphere beneath the Eurasian margin. The Demirköy Intrusive Suite intrudes the metamorphic basement of the Strandja Crystalline Complex and consists of gabbro, diorite, quartz diorite, granodiorite, and granite. Except for the mafic units (gabbro-diorite), which are characterised by intrusive contacts with all surrounding rocks, the suite lithologies exhibit transitional field relationships, indicating a genetic linkage among the felsic units. Geochemically, the felsic rocks are subalkaline-calc-alkaline, metaluminous to peraluminous, whereas the mafic rocks occupy the tholeiitic–alkaline transition field. Trace-element and REE systematics point to a mantle-crust interaction origin with upper-crustal contributions, and isotopic compositions (εNd(t) = +0.7 to +3.1 for felsic; +1.3 to +2.4 for mafic rocks) indicate derivation from a mafic parental magma sourced from subduction-modified mantle, variably affected by fractional crystallisation and AFC–CC processes. Zircon UPb ages of 82.4–80.3 Ma for both mafic and felsic rocks, together with amphibole 40Ar/39Ar cooling ages of 84.0–79.5 Ma, confirm emplacement during the Santonian–Campanian interval. Textural observations and field relationships indicate that the system consists of coeval mantle-derived mafic magmas and felsic magmas produced through the mixing and hybridisation of crustal melts. These lines of evidence collectively support a model of bimodal magmatism generated from two distinct sources rather than through a single differentiation process. The DIS provides new insights into the petrogenesis of arc-related bimodal magmatism and improves our understanding of crust–mantle interaction and magma evolution along convergent continental margins worldwide.
{"title":"Geochronology and petrogenesis of the Late Cretaceous Demirköy Intrusive Suite (Strandja Mountains, NW Türkiye): bimodal characteristics","authors":"Ezgi Ulusoy , Yusuf Kağan Kadıoğlu , Yavuz Bedi","doi":"10.1016/j.lithos.2025.108336","DOIUrl":"10.1016/j.lithos.2025.108336","url":null,"abstract":"<div><div>In northwestern Türkiye, near the Türkiye-Bulgaria border, the Late Cretaceous Demirköy Intrusive Suite forms a key component of the northern Tethyan magmatic arc developed during the subduction of the Neotethyan oceanic lithosphere beneath the Eurasian margin. The Demirköy Intrusive Suite intrudes the metamorphic basement of the Strandja Crystalline Complex and consists of gabbro, diorite, quartz diorite, granodiorite, and granite. Except for the mafic units (gabbro-diorite), which are characterised by intrusive contacts with all surrounding rocks, the suite lithologies exhibit transitional field relationships, indicating a genetic linkage among the felsic units. Geochemically, the felsic rocks are subalkaline-calc-alkaline, metaluminous to peraluminous, whereas the mafic rocks occupy the tholeiitic–alkaline transition field. Trace-element and REE systematics point to a mantle-crust interaction origin with upper-crustal contributions, and isotopic compositions (εNd(t) = +0.7 to +3.1 for felsic; +1.3 to +2.4 for mafic rocks) indicate derivation from a mafic parental magma sourced from subduction-modified mantle, variably affected by fractional crystallisation and AFC–CC processes. Zircon U<img>Pb ages of 82.4–80.3 Ma for both mafic and felsic rocks, together with amphibole <sup>40</sup>Ar/<sup>39</sup>Ar cooling ages of 84.0–79.5 Ma, confirm emplacement during the Santonian–Campanian interval. Textural observations and field relationships indicate that the system consists of coeval mantle-derived mafic magmas and felsic magmas produced through the mixing and hybridisation of crustal melts. These lines of evidence collectively support a model of bimodal magmatism generated from two distinct sources rather than through a single differentiation process. The DIS provides new insights into the petrogenesis of arc-related bimodal magmatism and improves our understanding of crust–mantle interaction and magma evolution along convergent continental margins worldwide.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108336"},"PeriodicalIF":2.5,"publicationDate":"2025-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576651","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 : 2025-11-15DOI: 10.1016/j.lithos.2025.108325
Ekaterina S. Kiseeva , Rondi M. Davies , Nester M. Korolev , Shuai Ma , Michael C. Jollands , Linghan Liu , Hongluo L. Zhang , Ilya Kupenko , Alexandr I. Chumakov
The Wyoming Craton is one of the best-preserved Archaean fragments of Laurentia. For billions of years it's consisted of a thick Archaean root surrounded by Proterozoic suture zones. In this study we characterise the geochemistry of 20 eclogitic xenoliths and, for five samples determine the ferric-ferrous ratios and oxygen fugacities, from the Aultman, Maxwell, and Schaffer kimberlite pipes from the Colorado–Wyoming State Line kimberlite district with EPMA, LA-ICP-MS, and Synchrotron Mössbauer spectroscopy. We measured major and trace element concentrations in garnet and clinopyroxene, which were used to reconstruct bulk-rock compositions and determine the pressure-temperature conditions along the craton's 38 mW/m2 geotherm. We subdivide xenoliths into gabbroic eclogites (with an ancient oceanic gabbro protolith), pyroxenitic (of various origins), high-Mg eclogites (derived from oceanic basalts), and one high-Ca eclogite (likely with an oceanic crust protolith). Major element compositions show a range between predominantly pyrope- and almandine-rich garnet. Clinopyroxenes range from Al–Na-rich diopside (in the more Mg-rich xenoliths) to omphacite in gabbroic eclogites, with a wide range of jadeite (18–54 mol%). All xenoliths formed at depths between ∼90 and 170 km. No strong metasomatic overprint is observed in any samples except for one, which exhibits strong LREE enrichment and high SrN/YN and CeN/YbN ratios (elements normalised to MORB). Approximately half of the xenoliths show evidence for partial melting manifested as LREE depletion. Garnets are depleted in ferric iron (0.02–0.04 Fe3+/Fe(tot)) except for one sample (0.08 Fe3+/Fe(tot)). Clinopyroxenes contain 0.17–0.41 Fe3+/Fe(tot). Calculated oxygen fugacities show a range between −2.3 and − 5.6 relative to the fayalite–magnetite–quartz redox buffer, indicating a wide spread of redox conditions in the protolith, and possibly a small degree of metasomatic re-enrichment instrumental in increasing fO2 during residence in the cratonic mantle. In agreement with previous work on xenoliths from nearby kimberlites, our study suggests that the Colorado–Wyoming State Line xenoliths sample ancient, depleted, and partially melted oceanic crust. This interpretation accords with a model in which proto-continental lithosphere was underthrust and wedged during Proterozoic collisional tectonics related to Yavapai terrane accretion along the Cheyenne Belt, thereby stacking Proterozoic (eclogitic) slabs against Archaean (peridotitic) lithospheric fragments.
{"title":"Geochemistry of the Wyoming Craton from eclogite and pyroxenite xenoliths from the Aultman, Maxwell, and Schaffer kimberlites at the Colorado-Wyoming State Line","authors":"Ekaterina S. Kiseeva , Rondi M. Davies , Nester M. Korolev , Shuai Ma , Michael C. Jollands , Linghan Liu , Hongluo L. Zhang , Ilya Kupenko , Alexandr I. Chumakov","doi":"10.1016/j.lithos.2025.108325","DOIUrl":"10.1016/j.lithos.2025.108325","url":null,"abstract":"<div><div>The Wyoming Craton is one of the best-preserved Archaean fragments of Laurentia. For billions of years it's consisted of a thick Archaean root surrounded by Proterozoic suture zones. In this study we characterise the geochemistry of 20 eclogitic xenoliths and, for five samples determine the ferric-ferrous ratios and oxygen fugacities, from the Aultman, Maxwell, and Schaffer kimberlite pipes from the Colorado–Wyoming State Line kimberlite district with EPMA, LA-ICP-MS, and Synchrotron Mössbauer spectroscopy. We measured major and trace element concentrations in garnet and clinopyroxene, which were used to reconstruct bulk-rock compositions and determine the pressure-temperature conditions along the craton's 38 mW/m<sup>2</sup> geotherm. We subdivide xenoliths into gabbroic eclogites (with an ancient oceanic gabbro protolith), pyroxenitic (of various origins), high-Mg eclogites (derived from oceanic basalts), and one high-Ca eclogite (likely with an oceanic crust protolith). Major element compositions show a range between predominantly pyrope- and almandine-rich garnet. Clinopyroxenes range from Al–Na-rich diopside (in the more Mg-rich xenoliths) to omphacite in gabbroic eclogites, with a wide range of jadeite (18–54 mol%). All xenoliths formed at depths between ∼90 and 170 km. No strong metasomatic overprint is observed in any samples except for one, which exhibits strong LREE enrichment and high Sr<sub>N</sub>/Y<sub>N</sub> and Ce<sub>N</sub>/Yb<sub>N</sub> ratios (elements normalised to MORB). Approximately half of the xenoliths show evidence for partial melting manifested as LREE depletion. Garnets are depleted in ferric iron (0.02–0.04 Fe<sup>3+</sup>/Fe<sub>(tot)</sub>) except for one sample (0.08 Fe<sup>3+</sup>/Fe<sub>(tot)</sub>). Clinopyroxenes contain 0.17–0.41 Fe<sup>3+</sup>/Fe<sub>(tot)</sub>. Calculated oxygen fugacities show a range between −2.3 and − 5.6 relative to the fayalite–magnetite–quartz redox buffer, indicating a wide spread of redox conditions in the protolith, and possibly a small degree of metasomatic re-enrichment instrumental in increasing <em>f</em>O<sub>2</sub> during residence in the cratonic mantle. In agreement with previous work on xenoliths from nearby kimberlites, our study suggests that the Colorado–Wyoming State Line xenoliths sample ancient, depleted, and partially melted oceanic crust. This interpretation accords with a model in which proto-continental lithosphere was underthrust and wedged during Proterozoic collisional tectonics related to Yavapai terrane accretion along the Cheyenne Belt, thereby stacking Proterozoic (eclogitic) slabs against Archaean (peridotitic) lithospheric fragments.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"522 ","pages":"Article 108325"},"PeriodicalIF":2.5,"publicationDate":"2025-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692682","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 : 2025-11-15DOI: 10.1016/j.lithos.2025.108327
Yidi Hong , Tao Wu , Marie Edmonds , Liyan Tian , Jianggu Lu , Hengrui Zhu , Taoran Song
The southernmost Mariana Trench, characterized by extreme water depths (>10,000 m), remains a poorly understood region within the Izu-Bonin-Mariana (IBM) convergent margin. Whether this region experienced a similar magmatic evolution to the northern IBM arc remains uncertain. In this study, we present mineralogical and geochemical data pertaining to igneous rocks acquired at 9792–9586 m depths in the north slope of the southernmost Mariana Trench. Based on the whole rock geochemistry, Sr-Nd-Hf-Pb isotopic compositions, and mineral compositions, four rock types are identified: forearc basalt (FAB), boninite, high-Mg andesite (HMA), and cumulate gabbro. The FAB is characterized by lower ratios of incompatible elements (e.g., Ti/V ratios) than typical mid-ocean ridge basalt (MORB), consistent with decompression melting of a depleted mantle source during subduction initiation. The boninites show high-Si signatures and we infer they experienced subsequent mantle metasomatism by slab-derived components. The HMA, with SiO2 > 65 wt% and complex plagioclase zoning, is the evolved product of fractional crystallization of boninitic magmas. The cumulate gabbros are dominated by plagioclase and clinopyroxene, and they have isotopic compositions that differ significantly from Mariana arc gabbros, but share similar mineralogical and geochemical features with previously reported FAB-like gabbros. The cumulate gabbros are interpreted as crystallization products of primitive magmas during early subduction rather than arc-stage cumulates. Although the general magmatic sequence resembles that of the northern IBM arc, the southernmost Mariana samples display some distinctive geochemical features. The boninites in particular exhibit higher ratios of incompatible elements (e.g., Th/Yb), reflecting stronger slab contributions. These findings suggest that the southernmost Mariana Trench preserves a multi-stage record of subduction initiation and represents a distinct tectono-magmatic domain within the IBM system. Our study provides new constraints on the spatial variations in subduction initiation along the IBM convergent margin.
{"title":"Magmatic evolution of the southernmost Mariana Trench revealed by igneous rocks sampled at > 9.5 km depth","authors":"Yidi Hong , Tao Wu , Marie Edmonds , Liyan Tian , Jianggu Lu , Hengrui Zhu , Taoran Song","doi":"10.1016/j.lithos.2025.108327","DOIUrl":"10.1016/j.lithos.2025.108327","url":null,"abstract":"<div><div>The southernmost Mariana Trench, characterized by extreme water depths (>10,000 m), remains a poorly understood region within the Izu-Bonin-Mariana (IBM) convergent margin. Whether this region experienced a similar magmatic evolution to the northern IBM arc remains uncertain. In this study, we present mineralogical and geochemical data pertaining to igneous rocks acquired at 9792–9586 m depths in the north slope of the southernmost Mariana Trench. Based on the whole rock geochemistry, Sr-Nd-Hf-Pb isotopic compositions, and mineral compositions, four rock types are identified: forearc basalt (FAB), boninite, high-Mg andesite (HMA), and cumulate gabbro. The FAB is characterized by lower ratios of incompatible elements (e.g., Ti/V ratios) than typical mid-ocean ridge basalt (MORB), consistent with decompression melting of a depleted mantle source during subduction initiation. The boninites show high-Si signatures and we infer they experienced subsequent mantle metasomatism by slab-derived components. The HMA, with SiO<sub>2</sub> > 65 wt% and complex plagioclase zoning, is the evolved product of fractional crystallization of boninitic magmas. The cumulate gabbros are dominated by plagioclase and clinopyroxene, and they have isotopic compositions that differ significantly from Mariana arc gabbros, but share similar mineralogical and geochemical features with previously reported FAB-like gabbros. The cumulate gabbros are interpreted as crystallization products of primitive magmas during early subduction rather than arc-stage cumulates. Although the general magmatic sequence resembles that of the northern IBM arc, the southernmost Mariana samples display some distinctive geochemical features. The boninites in particular exhibit higher ratios of incompatible elements (e.g., Th/Yb), reflecting stronger slab contributions. These findings suggest that the southernmost Mariana Trench preserves a multi-stage record of subduction initiation and represents a distinct tectono-magmatic domain within the IBM system. Our study provides new constraints on the spatial variations in subduction initiation along the IBM convergent margin.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108327"},"PeriodicalIF":2.5,"publicationDate":"2025-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576545","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 : 2025-11-14DOI: 10.1016/j.lithos.2025.108330
Junfu Zhang , Jie Tang , Yang Yu , Shuai Xiong , Wenliang Xu
Northeast Asia experienced a transformation from the Eastern Asian to Northeastern Asian big mantle wedge (BMW) due to subduction of the Paleo-Pacific Plate and then the Pacific Plate since the late Early Cretaceous. However, few studies have examined the evolution of the upper mantle during this transformation. Here we report compositional data for olivine phenocrysts from late Early Cretaceous–Miocene (103, 33, 21, and 11 Ma) basalts in the eastern Northeast China (ENC). These new data, along with the bulk rock compositions, provide new insights into the evolution of the upper mantle. The 103 Ma basalts have arc-like trace element patterns, and their olivine phenocrysts are relatively Ni-poor (379–849 ppm), Mn- (1807–3103 ppm) and Ca-rich (1504–2086 ppm), and have low Fe/Mn ratios (67–70) as compared with olivines from mantle peridotites. This reflects a peridotite-dominated (∼84 %) mantle source. Compared with the 103 Ma basalts, the 33 and 21 Ma basalts have ocean island basalt-like trace element patterns, and their olivine phenocrysts have relatively high Ni contents (775–2015 ppm) and Fe/Mn ratios (73–95). These features indicate pyroxenitic (100 % on average for the 33 Ma basalts) and mixed pyroxenitic–peridotitic (∼48 % pyroxenite on average for the 21 Ma basalts) mantle sources. The 11 Ma basalts have weakly arc-like trace element patterns, and their olivine phenocrysts have high Ni (1050–1267 ppm) and low Mn (1710–1913 ppm) contents, relatively high Fe/Mn ratios (71–79), and similar Ca contents (1368–2017 ppm) to the olivines in the 103 Ma basalts. These basalts also had a mixed pyroxenitic–peridotitic mantle source (∼46 % pyroxenite on average). The mass proportion of pyroxenite in the sources of the ENC basalts increased during 103–33 Ma and decreased during 33–11 Ma. The former reflects a significant addition of recycled materials during 103–33 Ma, and the latter records back-arc extension and a decrease in recycled materials during 33–11 Ma. This indicates that recycled materials associated with a subducted slab affect the composition and evolution of the upper mantle in a BMW.
{"title":"Variations in pyroxenitic and peridotitic mantle contributions to Early Cretaceous–Miocene basalts in Northeast Asia: Constraints from the geochemistry of olivine phenocrysts","authors":"Junfu Zhang , Jie Tang , Yang Yu , Shuai Xiong , Wenliang Xu","doi":"10.1016/j.lithos.2025.108330","DOIUrl":"10.1016/j.lithos.2025.108330","url":null,"abstract":"<div><div>Northeast Asia experienced a transformation from the Eastern Asian to Northeastern Asian big mantle wedge (BMW) due to subduction of the Paleo-Pacific Plate and then the Pacific Plate since the late Early Cretaceous. However, few studies have examined the evolution of the upper mantle during this transformation. Here we report compositional data for olivine phenocrysts from late Early Cretaceous–Miocene (103, 33, 21, and 11 Ma) basalts in the eastern Northeast China (ENC). These new data, along with the bulk rock compositions, provide new insights into the evolution of the upper mantle. The 103 Ma basalts have arc-like trace element patterns, and their olivine phenocrysts are relatively Ni-poor (379–849 ppm), Mn- (1807–3103 ppm) and Ca-rich (1504–2086 ppm), and have low Fe/Mn ratios (67–70) as compared with olivines from mantle peridotites. This reflects a peridotite-dominated (∼84 %) mantle source. Compared with the 103 Ma basalts, the 33 and 21 Ma basalts have ocean island basalt-like trace element patterns, and their olivine phenocrysts have relatively high Ni contents (775–2015 ppm) and Fe/Mn ratios (73–95). These features indicate pyroxenitic (100 % on average for the 33 Ma basalts) and mixed pyroxenitic–peridotitic (∼48 % pyroxenite on average for the 21 Ma basalts) mantle sources. The 11 Ma basalts have weakly arc-like trace element patterns, and their olivine phenocrysts have high Ni (1050–1267 ppm) and low Mn (1710–1913 ppm) contents, relatively high Fe/Mn ratios (71–79), and similar Ca contents (1368–2017 ppm) to the olivines in the 103 Ma basalts. These basalts also had a mixed pyroxenitic–peridotitic mantle source (∼46 % pyroxenite on average). The mass proportion of pyroxenite in the sources of the ENC basalts increased during 103–33 Ma and decreased during 33–11 Ma. The former reflects a significant addition of recycled materials during 103–33 Ma, and the latter records back-arc extension and a decrease in recycled materials during 33–11 Ma. This indicates that recycled materials associated with a subducted slab affect the composition and evolution of the upper mantle in a BMW.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108330"},"PeriodicalIF":2.5,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576540","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 : 2025-11-14DOI: 10.1016/j.lithos.2025.108322
Bei-Er Guo , Kui-Dong Zhao , Guo-Qi Liu , Hao-Lan Liu , Wei Chen , Shao-Yong Jiang , Gregory M. Yaxley
Rare-metal granites are highly evolved, peraluminous intrusions characterized by extreme enrichments in incompatible elements. However, the mechanisms responsible for such enrichment remain contentious. The Yashan granitic complex in South China, renowned for its well-developed Li-Ta-Nb mineralization, consists of three granite groups and a stockscheider, arranged from the base to the top of the pluton, as well as several albitite dikes that intruded the pluton later. Geochemically, the Yashan granites are strongly peraluminous and enriched in P₂O₅ and rare metals (including Li, Rb, Be, Cs, Sn, Nb, Ta, and W) while being depleted in Ca, Fe, Ti, and Mg. This compositional signature suggests an S-type granitic magma derived from partial melting of metasedimentary rocks. This study identified abundant Li-bearing minerals, such as lepidolite, petalite, amblygonite-montebrasite, and elbaite, as well as beryl in certain granites within the complex. Detailed mineralogical analyses indicate that these minerals are predominantly of magmatic origin. Rapid crystallization of K-feldspar in the stockscheider appears to have generated a flux-rich boundary layer, which, combined with the accumulation of a magmatic volatile phase, promoted the precipitation of rare-metal minerals in the upper part of the pluton. Moreover, sustained thermal energy within the magma chamber likely facilitated the upward migration of residual melt, ultimately leading to the formation of the mineralized albitite dikes. These integrated findings advance our understanding of rare-metal granite genesis by highlighting the combined roles of magmatic fractionation, volatile-driven differentiation, and magma chamber dynamics in the concentration of incompatible elements.
稀有金属花岗岩是高度演化的过铝质岩体，其特征是不相容元素极度富集。然而，这种浓缩的机制仍然存在争议。华南丫山花岗岩杂岩以Li-Ta-Nb矿化发育而闻名，由岩体底部至顶部排列的3个花岗岩群和1个岩垛组成，并有几条侵入岩体的钠长岩岩脉。地球化学上，丫山花岗岩是强过铝质的，富含P₂O₅和稀有金属（包括Li， Rb, Be, Cs, Sn, Nb， Ta和W），同时耗尽Ca， Fe， Ti和Mg。这一成分特征表明，s型花岗质岩浆来源于变质沉积岩的部分熔融。本研究在该杂岩中发现了丰富的含锂矿物，如锂云母、花瓣云母、辉长石-蒙太白石和铁白石，以及某些花岗岩中的绿柱石。详细的矿物学分析表明，这些矿物主要为岩浆成因。在stockscheider中，钾长石的快速结晶似乎形成了富通量的边界层，并结合岩浆挥发相的积累，促进了稀有金属矿物在岩体上部的沉淀。此外，岩浆房内持续的热能可能促进了残余熔体的向上迁移，最终导致矿化钠长岩岩脉的形成。这些综合发现突出了岩浆分馏、挥发物驱动分异和岩浆室动力学在不相容元素浓度中的综合作用，促进了我们对稀有金属花岗岩成因的认识。
{"title":"Intense magmatic differentiation of the Yashan rare-metal granites in South China: Insights from geochemistry of Li-bearing minerals","authors":"Bei-Er Guo , Kui-Dong Zhao , Guo-Qi Liu , Hao-Lan Liu , Wei Chen , Shao-Yong Jiang , Gregory M. Yaxley","doi":"10.1016/j.lithos.2025.108322","DOIUrl":"10.1016/j.lithos.2025.108322","url":null,"abstract":"<div><div>Rare-metal granites are highly evolved, peraluminous intrusions characterized by extreme enrichments in incompatible elements. However, the mechanisms responsible for such enrichment remain contentious. The Yashan granitic complex in South China, renowned for its well-developed Li-Ta-Nb mineralization, consists of three granite groups and a stockscheider, arranged from the base to the top of the pluton, as well as several albitite dikes that intruded the pluton later. Geochemically, the Yashan granites are strongly peraluminous and enriched in P₂O₅ and rare metals (including Li, Rb, Be, Cs, Sn, Nb, Ta, and W) while being depleted in Ca, Fe, Ti, and Mg. This compositional signature suggests an S-type granitic magma derived from partial melting of metasedimentary rocks. This study identified abundant Li-bearing minerals, such as lepidolite, petalite, amblygonite-montebrasite, and elbaite, as well as beryl in certain granites within the complex. Detailed mineralogical analyses indicate that these minerals are predominantly of magmatic origin. Rapid crystallization of K-feldspar in the stockscheider appears to have generated a flux-rich boundary layer, which, combined with the accumulation of a magmatic volatile phase, promoted the precipitation of rare-metal minerals in the upper part of the pluton. Moreover, sustained thermal energy within the magma chamber likely facilitated the upward migration of residual melt, ultimately leading to the formation of the mineralized albitite dikes. These integrated findings advance our understanding of rare-metal granite genesis by highlighting the combined roles of magmatic fractionation, volatile-driven differentiation, and magma chamber dynamics in the concentration of incompatible elements.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108322"},"PeriodicalIF":2.5,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576560","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 : 2025-11-14DOI: 10.1016/j.lithos.2025.108321
Camilo Conde , Richard Spikings , Carlos Zuluaga , Jorge Gómez , Alexey Ulyanov , Massimo Chiaradia
Tectonic models of the Cretaceous Andean margin in Colombia are restricted by few accurate crystallisation ages because a majority of exposure is dominated by altered, mafic igneous rocks. Cretaceous basalts to andesites of the Quebradagrande Complex form the western flank of the Central Cordillera in Colombia, although they have experienced advanced propylitic alteration at the seafloor. We present zircon 206Pb/238U dates and 40Ar/39Ar analyses of groundmass and plagioclase extracted from volcanic rocks of the Quebradagrande Complex, which have been used to estimate their time of crystallisation. These have been combined with new whole rock geochemistry and isotopic tracing (Sr, Nd and Pb), and 206Pb/238U dates of detrital zircons extracted from turbidites that are mapped as part of the Quebradagrande Complex to constrain their tectonic origin, which will improve our knowledge of the evolution of the northern Andes prior to the accretion of the Caribbean Large Igneous Province. These data show that the Quebradagrande Complex comprises typical arc-like basalts to andesites and E-MORB-like basalts, which have been interpreted to define a continental arc that formed above thinned continental crust in an extensional setting. Combining the new data with previous work suggests the entire Andean margin north of the Huancabamba Deflection (north of 5°S) experienced significant extension that started at ∼145 Ma, eventually forming the mafic volcanic rocks of the Quebradagrande Complex starting at ∼114 Ma, which are equivalent to the Alao and probably Celica arcs in Ecuador. Extension continued until ∼110 Ma, after which a transpressive phase drove mild compression in South America, exhuming the margin and forming unconformities in the retro-foreland. Active margin magmatism continued until the collision of the Caribbean Large Igneous Province at ∼75 Ma.
{"title":"Geochronological, geochemical and isotopic characterization of the early to late Cretaceous margin within Colombia","authors":"Camilo Conde , Richard Spikings , Carlos Zuluaga , Jorge Gómez , Alexey Ulyanov , Massimo Chiaradia","doi":"10.1016/j.lithos.2025.108321","DOIUrl":"10.1016/j.lithos.2025.108321","url":null,"abstract":"<div><div>Tectonic models of the Cretaceous Andean margin in Colombia are restricted by few accurate crystallisation ages because a majority of exposure is dominated by altered, mafic igneous rocks. Cretaceous basalts to andesites of the Quebradagrande Complex form the western flank of the Central Cordillera in Colombia, although they have experienced advanced propylitic alteration at the seafloor. We present zircon <sup>206</sup>Pb/<sup>238</sup>U dates and <sup>40</sup>Ar/<sup>39</sup>Ar analyses of groundmass and plagioclase extracted from volcanic rocks of the Quebradagrande Complex, which have been used to estimate their time of crystallisation. These have been combined with new whole rock geochemistry and isotopic tracing (Sr, Nd and Pb), and <sup>206</sup>Pb/<sup>238</sup>U dates of detrital zircons extracted from turbidites that are mapped as part of the Quebradagrande Complex to constrain their tectonic origin, which will improve our knowledge of the evolution of the northern Andes prior to the accretion of the Caribbean Large Igneous Province. These data show that the Quebradagrande Complex comprises typical arc-like basalts to andesites and <em>E</em>-MORB-like basalts, which have been interpreted to define a continental arc that formed above thinned continental crust in an extensional setting. Combining the new data with previous work suggests the entire Andean margin north of the Huancabamba Deflection (north of 5°S) experienced significant extension that started at ∼145 Ma, eventually forming the mafic volcanic rocks of the Quebradagrande Complex starting at ∼114 Ma, which are equivalent to the Alao and probably Celica arcs in Ecuador. Extension continued until ∼110 Ma, after which a transpressive phase drove mild compression in South America, exhuming the margin and forming unconformities in the retro-foreland. Active margin magmatism continued until the collision of the Caribbean Large Igneous Province at ∼75 Ma.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108321"},"PeriodicalIF":2.5,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576546","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}
Garnet and zircon are the most common and robust geochronometer minerals for crustal rocks. The physical and chemical stability of this mineral, the high temperature of isotopic system closure, and the ability to carry information about multiple geological events make it possible to use it as indicators of the conditions of rocks formation, and as geochronometer for dating rocks of high-grade polymetamorphic complexes. A comprehensive geochemical investigation of garnet from granulites and eclogites of the Bergen Arcs complex reveals regular variations in garnet composition in terms of major and trace elements. The composition of trace elements in minerals was investigated by SIMS method. Garnet cores from the Bergen Arcs eclogites represent relicts of granulite garnet preserved throughout the eclogite-facies overprint. Garnet rims, which show contrastingly different chemistry in both major and trace elements, result from granulite garnet recrystallization during the eclogite metamorphism. It is suggested that during the eclogitization of granulites, which occurred with increasing pressure and decreasing temperature, heavy rare earth elements were redistributed from zircon to garnet, whereas light rare earth elements, on the contrary, migrated from garnet to clinopyroxene and clinopyroxene-plagioclase symplectites. Despite the fact that the transformation of granulites into eclogites occurred under the influence of fluid, REE were not removed from the system, i.e. the process of eclogitization of the Bergen Arcs granulites complex is assumed to be isochemical. This work demonstrates behavioral features of trace and rare earth elements during eclogite metamorphism, which must be taken into account in geochronological and thermobarometric studies.
{"title":"Granulite-to-eclogite conversion at the Bergen Arcs (South Norway) as recorded in garnet and zircon zoning","authors":"L.I. Salimgaraeva, S.G. Skublov, A.V. Berezin, O.L. Galankina","doi":"10.1016/j.lithos.2025.108329","DOIUrl":"10.1016/j.lithos.2025.108329","url":null,"abstract":"<div><div>Garnet and zircon are the most common and robust geochronometer minerals for crustal rocks. The physical and chemical stability of this mineral, the high temperature of isotopic system closure, and the ability to carry information about multiple geological events make it possible to use it as indicators of the conditions of rocks formation, and as geochronometer for dating rocks of high-grade polymetamorphic complexes. A comprehensive geochemical investigation of garnet from granulites and eclogites of the Bergen Arcs complex reveals regular variations in garnet composition in terms of major and trace elements. The composition of trace elements in minerals was investigated by SIMS method. Garnet cores from the Bergen Arcs eclogites represent relicts of granulite garnet preserved throughout the eclogite-facies overprint. Garnet rims, which show contrastingly different chemistry in both major and trace elements, result from granulite garnet recrystallization during the eclogite metamorphism. It is suggested that during the eclogitization of granulites, which occurred with increasing pressure and decreasing temperature, heavy rare earth elements were redistributed from zircon to garnet, whereas light rare earth elements, on the contrary, migrated from garnet to clinopyroxene and clinopyroxene-plagioclase symplectites. Despite the fact that the transformation of granulites into eclogites occurred under the influence of fluid, REE were not removed from the system, i.e. the process of eclogitization of the Bergen Arcs granulites complex is assumed to be isochemical. This work demonstrates behavioral features of trace and rare earth elements during eclogite metamorphism, which must be taken into account in geochronological and thermobarometric studies.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"518 ","pages":"Article 108329"},"PeriodicalIF":2.5,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145576541","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 : 2025-11-13DOI: 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":"2025-11-13","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}
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