Pub Date : 2025-01-19DOI: 10.1016/j.lithos.2025.107948
Pengjie Cai , Dongyang Lian , Jonathan C. Aitchison , Dominique Cluzel , Renjie Zhou , Huichao Rui , Rongzong Bo , Haitao Ma , Jingsui Yang , Ahmed E. Masoud
The geochemical evolution of mantle peridotite during subduction initiation (SI) remains an issue in geosciences. This study presents geochemical and Ca isotopic data for Tiébaghi lherzolites from the New Caledonia ophiolite to constrain their petrogenesis and the nature of melt-rock interaction during the nascent stage of subduction. Petrographic and geochemical analyses reveal that the Tiébaghi lherzolites are characterized by olivine with Fo contents of 89.5–90.7, high-Al Spinel (Cr# = 45.1–50.9; Al2O3 = 24.99–29.29 wt%), orthopyroxene with high CaO (0.87–2.47 wt%) and Al2O3 (2.19–4.91 wt%) coupled with relatively low Mg# (89.4–91.3), and clinopyroxene with high Al2O3 (2.72–6.44 wt%) and relatively low Mg# (90.4–92.5). Lherzolites from northwestern New Caledonia are thought to have escaped the suprasubduction re-melting, resulting in the formation of the highly depleted harzburgites that form the bulk of the ophiolite. They display a restricted range of δ44/40Ca values (0.75–0.93 ‰), which are lower than the proposed δ44/40Ca value of Earth's upper mantle. This isotopic signature is interpreted to reflect interaction with a low δ44/40Ca metasomatic agent, possibly a carbonate-rich melt derived from the subducting slab. These findings suggest that the Tiébaghi lherzolites preserve a geochemical record of the early stages of melt-rock interaction during subduction initiation, emphasizing the role of carbonate melt metasomatism in altering the composition of the nascent mantle wedge.
{"title":"Geochemical constraints on subduction-related mantle metasomatism of the Tiébaghi ophiolitic lherzolite in New Caledonia","authors":"Pengjie Cai , Dongyang Lian , Jonathan C. Aitchison , Dominique Cluzel , Renjie Zhou , Huichao Rui , Rongzong Bo , Haitao Ma , Jingsui Yang , Ahmed E. Masoud","doi":"10.1016/j.lithos.2025.107948","DOIUrl":"10.1016/j.lithos.2025.107948","url":null,"abstract":"<div><div>The geochemical evolution of mantle peridotite during subduction initiation (SI) remains an issue in geosciences. This study presents geochemical and Ca isotopic data for Tiébaghi lherzolites from the New Caledonia ophiolite to constrain their petrogenesis and the nature of melt-rock interaction during the nascent stage of subduction. Petrographic and geochemical analyses reveal that the Tiébaghi lherzolites are characterized by olivine with Fo contents of 89.5–90.7, high-Al Spinel (Cr# = 45.1–50.9; Al<sub>2</sub>O<sub>3</sub> = 24.99–29.29 wt%), orthopyroxene with high CaO (0.87–2.47 wt%) and Al<sub>2</sub>O<sub>3</sub> (2.19–4.91 wt%) coupled with relatively low Mg# (89.4–91.3), and clinopyroxene with high Al<sub>2</sub>O<sub>3</sub> (2.72–6.44 wt%) and relatively low Mg# (90.4–92.5). Lherzolites from northwestern New Caledonia are thought to have escaped the suprasubduction re-melting, resulting in the formation of the highly depleted harzburgites that form the bulk of the ophiolite. They display a restricted range of δ<sup>44/40</sup>Ca values (0.75–0.93 ‰), which are lower than the proposed δ<sup>44/40</sup>Ca value of Earth's upper mantle. This isotopic signature is interpreted to reflect interaction with a low δ<sup>44/40</sup>Ca metasomatic agent, possibly a carbonate-rich melt derived from the subducting slab. These findings suggest that the Tiébaghi lherzolites preserve a geochemical record of the early stages of melt-rock interaction during subduction initiation, emphasizing the role of carbonate melt metasomatism in altering the composition of the nascent mantle wedge.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107948"},"PeriodicalIF":2.9,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143320301","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 : 2025-01-18DOI: 10.1016/j.lithos.2025.107945
Hélène Legros , S. Andrew DuFrane , Yan Luo , Chiranjeeb Sarkar , Gideon Lambiv , D. Graham Pearson
Rare Earth Elements are classified as critical resources in Canada and the Thor Lake (Nechalacho) REE deposit is one of the largest in North America. The Thor Lake area is composed of the Nechalacho Layered Suite (previously dated at ca. 2176 Ma) and multiple pegmatitic bodies with variable REE enrichment. This study focuses on the pegmatitic T-zone where bastnäsite, the main REE mineral, is abundant and displays both magmatic and hydrothermal features. The T-zone pegmatite is believed to be a late magmatic event and this study uses UPb geochronology on bastnäsite as well as Nd isotopic constraints to understand the late stages of emplacement and REE metal sources that led to mineralization. This study determines the first direct ages on the ore mineral of this deposit. Several populations of REE carbonate, corresponding to different formation ages, were distinguished according to their Ca enrichment. Unaltered bastnäsite yields a weighted mean age of 2050.9 ± 34.9 Ma (propagated; MSWD = 2.2) that we interpret as the exsolution of a hydrothermal fluid from the T-zone pegmatite melt. This shows that the T-zone was emplaced ca. 100 Ma after the Nechalacho Layered Suite, coeval with the rift initiation along the southern margin of the Slave craton. Nd isotope compositions further show that the T-Zone and the Nechalacho Layered Suite, although disconnected in time, share the same REE-enriched source, demonstrating that mineralization was reactivated but dominated by the same original REE source that was probably remelted, despite subsequent “up-grading”. The alteration of bastnäsite into parisite is traced by its enrichment in Ca. The altered bastnäsite (parasite) yields one UPb age of 1763.9 ± 47.6 Ma (propagated; MSWD = 7.5) that we interpret as correlated to crustal hydrothermal fluid events. The ca. 1764 Ma age is coeval to the Great Slave Lake shear zone reactivation and likely generated through large-scale crustal fluid flow related to that event. Another calculated age at ca. 820 Ma could not be correlated to any specific event and is likely the result of Pb loss and other fluid-related alteration process. This study highlights the complex multiphased history of the Thor Lake (Nechalacho) deposit and the importance of hydrothermal processes for bastnäsite mineralization.
{"title":"Direct UPb dating and Nd isotopes of REE carbonate mineral unravel protracted history of ore precipitation at the Thor Lake (Nechalacho) deposit, NWT Canada","authors":"Hélène Legros , S. Andrew DuFrane , Yan Luo , Chiranjeeb Sarkar , Gideon Lambiv , D. Graham Pearson","doi":"10.1016/j.lithos.2025.107945","DOIUrl":"10.1016/j.lithos.2025.107945","url":null,"abstract":"<div><div>Rare Earth Elements are classified as critical resources in Canada and the Thor Lake (Nechalacho) REE deposit is one of the largest in North America. The Thor Lake area is composed of the Nechalacho Layered Suite (previously dated at ca. 2176 Ma) and multiple pegmatitic bodies with variable REE enrichment. This study focuses on the pegmatitic T-zone where bastnäsite, the main REE mineral, is abundant and displays both magmatic and hydrothermal features. The T-zone pegmatite is believed to be a late magmatic event and this study uses U<img>Pb geochronology on bastnäsite as well as Nd isotopic constraints to understand the late stages of emplacement and REE metal sources that led to mineralization. This study determines the first direct ages on the ore mineral of this deposit. Several populations of REE carbonate, corresponding to different formation ages, were distinguished according to their Ca enrichment. Unaltered bastnäsite yields a weighted mean age of 2050.9 ± 34.9 Ma (propagated; MSWD = 2.2) that we interpret as the exsolution of a hydrothermal fluid from the T-zone pegmatite melt. This shows that the T-zone was emplaced ca. 100 Ma after the Nechalacho Layered Suite, coeval with the rift initiation along the southern margin of the Slave craton. Nd isotope compositions further show that the T-Zone and the Nechalacho Layered Suite, although disconnected in time, share the same REE-enriched source, demonstrating that mineralization was reactivated but dominated by the same original REE source that was probably remelted, despite subsequent “up-grading”. The alteration of bastnäsite into parisite is traced by its enrichment in Ca. The altered bastnäsite (parasite) yields one U<img>Pb age of 1763.9 ± 47.6 Ma (propagated; MSWD = 7.5) that we interpret as correlated to crustal hydrothermal fluid events. The ca. 1764 Ma age is coeval to the Great Slave Lake shear zone reactivation and likely generated through large-scale crustal fluid flow related to that event. Another calculated age at ca. 820 Ma could not be correlated to any specific event and is likely the result of Pb loss and other fluid-related alteration process. This study highlights the complex multiphased history of the Thor Lake (Nechalacho) deposit and the importance of hydrothermal processes for bastnäsite mineralization.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107945"},"PeriodicalIF":2.9,"publicationDate":"2025-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143356880","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 : 2025-01-10DOI: 10.1016/j.lithos.2024.107938
Aley El-Shazly , Ethan Backus , J. Paul Summers , Breana Felix , Sierra Rose Willard
The Little Pine Garnet Mine area in the Western part of the Blue Ridge, southern Appalachian Mountains has outcrops of gedrite - anthophyllite – chlorite ± garnet ± biotite ± staurolite schists with minor quartz, ilmenite, rutile ± plagioclase ± sillimanite, interbedded with hornblende gneisses and muscovite – bearing quartzofeldspathic gneisses. Major and trace element analysis suggests that the gedrite - chlorite schists represent metamorphosed E-MORBs, whereas the hornblende gneisses represent metamorphosed greywackes. Isocon diagrams and cluster of slopes analysis shows that the E-MORB protoliths were enriched in Mg, Fe, Zn and HREE, and depleted in Ca, Na, and Si ± Sr ± Ba by hydrothermal alteration on the seafloor at T = 200–300 °C and high water: rock ratios >10 before metamorphism. Application of conventional thermobarometry and multiequilibrium calculations leads to the conclusion that the peak mineral assemblages Grt – Ged – St – Bt – Rt and Grt – Hbl – Pl – Bt – Rt formed at 8–9 kbar, 700 °C, before equilibrating isothermally at P = 7–8 kbar. Mineral assemblage diagrams calculated for a Ged – Chl schist and a Grt – Hbl gneiss confirm these conditions and show that the Ged schists retrogressed into the field of Ged – Ath – St – Chl – Ilm ± Pl at ∼4–5 kbar, 600–630 °C. Regional metamorphism most likely occurred during the Taconic orogeny.
{"title":"Orthoamphibole – Chlorite schists from the Little Pine Garnet Mine, Southern Appalachians: Chemical controls, P-T evolution and tectonic implications","authors":"Aley El-Shazly , Ethan Backus , J. Paul Summers , Breana Felix , Sierra Rose Willard","doi":"10.1016/j.lithos.2024.107938","DOIUrl":"10.1016/j.lithos.2024.107938","url":null,"abstract":"<div><div>The Little Pine Garnet Mine area in the Western part of the Blue Ridge, southern Appalachian Mountains has outcrops of gedrite - anthophyllite – chlorite ± garnet ± biotite ± staurolite schists with minor quartz, ilmenite, rutile ± plagioclase ± sillimanite, interbedded with hornblende gneisses and muscovite – bearing quartzofeldspathic gneisses. Major and trace element analysis suggests that the gedrite - chlorite schists represent metamorphosed <em>E</em>-MORBs, whereas the hornblende gneisses represent metamorphosed greywackes. Isocon diagrams and cluster of slopes analysis shows that the E-MORB protoliths were enriched in Mg, Fe, Zn and HREE, and depleted in Ca, Na, and Si ± Sr ± Ba by hydrothermal alteration on the seafloor at <em>T</em> = 200–300 °C and high water: rock ratios >10 before metamorphism. Application of conventional thermobarometry and multiequilibrium calculations leads to the conclusion that the peak mineral assemblages Grt – Ged – St – Bt – Rt and Grt – Hbl – Pl – Bt – Rt formed at 8–9 kbar, 700 °C, before equilibrating isothermally at <em>P</em> = 7–8 kbar. Mineral assemblage diagrams calculated for a Ged – Chl schist and a Grt – Hbl gneiss confirm these conditions and show that the Ged schists retrogressed into the field of Ged – Ath – St – Chl – Ilm ± Pl at ∼4–5 kbar, 600–630 °C. Regional metamorphism most likely occurred during the Taconic orogeny.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107938"},"PeriodicalIF":2.9,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143395796","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}
Formation, evolution, and preservation of early continental crust have been a subject of intense debate. This is testified by the fragmentary nature of our understanding on the composition of early earth mantle, temporal evolution of the composition and thickness of continental crust, and the linkage between granitoid diversification, spatial crustal heterogeneity and geodynamic processes. In pursuant to these problems, we investigated the poorly-studied Paleoarchean granitoids exposed in the south-eastern part of the Singhbhum Craton. At ∼3.50 Ga, shallow (low-pressure) crustal melting produced sodic granitoids (trondhjemite) in this area. This was followed by emplacement of both low- and high-pressure sodic granitoids (tonalite and trondhjemite) over ∼3.33–3.29 Ga and K-rich granites at ∼3.28 Ga; we link this magmatism with crustal thickening allowing intracrustal melting at variable depths. All the granitoids display suprachondritic to near-chondritic zircon epsilon values. This fact reflects continued addition of juvenile crust from depleted mantle (with minor input from older crust) and its rapid differentiation into felsic composition. The process implies a unique crust formation mechanism in Paleoarchean. Our synthesis suggests that the Paleoarchean granitoid crust within Singhbhum Craton can be divided into several blocks surrounded by slivers of greenstone belts. Crust generation histories of these blocks are often diachronous and follow distinct evolution paths (in terms of spatial and temporal pattern of granitoid diversification) which can be linked to the thickness variation and compositional heterogeneity of the cratonic crust.
{"title":"Paleoarchean continental crust formation by reworking of juvenile crust: Evidence from SE part of Singhbhum Craton, eastern India","authors":"Manoj Kumar Sahoo , Sukanta Dey , Keqing Zong , Yongsheng Liu , Aniruddha Mitra , Anirban Mitra","doi":"10.1016/j.lithos.2025.107944","DOIUrl":"10.1016/j.lithos.2025.107944","url":null,"abstract":"<div><div>Formation, evolution, and preservation of early continental crust have been a subject of intense debate. This is testified by the fragmentary nature of our understanding on the composition of early earth mantle, temporal evolution of the composition and thickness of continental crust, and the linkage between granitoid diversification, spatial crustal heterogeneity and geodynamic processes. In pursuant to these problems, we investigated the poorly-studied Paleoarchean granitoids exposed in the south-eastern part of the Singhbhum Craton. At ∼3.50 Ga, shallow (low-pressure) crustal melting produced sodic granitoids (trondhjemite) in this area. This was followed by emplacement of both low- and high-pressure sodic granitoids (tonalite and trondhjemite) over ∼3.33–3.29 Ga and K-rich granites at ∼3.28 Ga; we link this magmatism with crustal thickening allowing intracrustal melting at variable depths. All the granitoids display suprachondritic to near-chondritic zircon epsilon values. This fact reflects continued addition of juvenile crust from depleted mantle (with minor input from older crust) and its rapid differentiation into felsic composition. The process implies a unique crust formation mechanism in Paleoarchean. Our synthesis suggests that the Paleoarchean granitoid crust within Singhbhum Craton can be divided into several blocks surrounded by slivers of greenstone belts. Crust generation histories of these blocks are often diachronous and follow distinct evolution paths (in terms of spatial and temporal pattern of granitoid diversification) which can be linked to the thickness variation and compositional heterogeneity of the cratonic crust.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107944"},"PeriodicalIF":2.9,"publicationDate":"2025-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143356521","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 : 2025-01-01DOI: 10.1016/j.lithos.2024.107881
Maria Rosaria Renna , Federico Farina , Maria Ovtcharova
The Porto complex (western Corsica, France) is a post-Variscan, shallow-level intrusive system where mafic and felsic rocks are closely associated. To assess the timeframe and impact of successive injections of mantle-derived melts on a granite magma reservoir and gain a better understanding on the evolution of the complex, we performed high precision UPb dating combined with trace element and Hf isotope compositions of zircon separated from both mafic intrusives and associated granites.
Zircons from the granites have similar 206Pb/238U ages and initial Hf isotopic compositions. The saturation of zircon in the felsic magma occurred before emplacement and mingling with the mafic magma, between 282.55 ± 0.28 Ma and 281.65 ± 0.42 Ma, and at ∼800 °C. The initial ɛHf values of zircons (3.7 ± 2.0 to 5.3 ± 1.0) indicates that the felsic magma source experienced addition of crustal material to a mantle component. Interaction with late-hydrothermal fluids, most likely related to an event affecting the Porto complex after its emplacement, was responsible for the modification of LREE, Ti, Fe and Mn compositions in zircons affected by intense metamictization.
Zircons from the mafic rocks have slightly enriched initial ɛHf values (5.7 ± 1.6 to 6.9 ± 1.6) relative to depleted mantle composition. UPb zircon dating identified two chronologically distinct mafic melts injections, at 280.93 ± 0.21 Ma and 279.63 ± 0.15 Ma, which are representative of the time of mafic magma emplacement and mingling with the felsic magma.
To explain the long-time interval occurring between the saturation of zircon in the felsic magma and the time the granite emplaced, mingled and crossed its solidus, we propose that during cooling, the zircon-bearing granite magma reservoir was intruded, most likely at the base of the felsic mush, by injections of hotter, mafic magmas that caused at least two successive events of rejuvenation and remobilization, which promoted the shallow intrusion of variably differentiated felsic magmas.
{"title":"Rejuvenation of a granitic magma reservoir by mafic injections: Evidence from zircon UPb geochronology, Hf isotopes and trace element compositions (Porto complex, Western Corsica)","authors":"Maria Rosaria Renna , Federico Farina , Maria Ovtcharova","doi":"10.1016/j.lithos.2024.107881","DOIUrl":"10.1016/j.lithos.2024.107881","url":null,"abstract":"<div><div>The Porto complex (western Corsica, France) is a post-Variscan, shallow-level intrusive system where mafic and felsic rocks are closely associated. To assess the timeframe and impact of successive injections of mantle-derived melts on a granite magma reservoir and gain a better understanding on the evolution of the complex, we performed high precision U<img>Pb dating combined with trace element and Hf isotope compositions of zircon separated from both mafic intrusives and associated granites.</div><div>Zircons from the granites have similar <sup>206</sup>Pb/<sup>238</sup>U ages and initial Hf isotopic compositions. The saturation of zircon in the felsic magma occurred before emplacement and mingling with the mafic magma, between 282.55 ± 0.28 Ma and 281.65 ± 0.42 Ma, and at ∼800 °C. The initial ɛ<sub>Hf</sub> values of zircons (3.7 ± 2.0 to 5.3 ± 1.0) indicates that the felsic magma source experienced addition of crustal material to a mantle component. Interaction with late-hydrothermal fluids, most likely related to an event affecting the Porto complex after its emplacement, was responsible for the modification of LREE, Ti, Fe and Mn compositions in zircons affected by intense metamictization.</div><div>Zircons from the mafic rocks have slightly enriched initial ɛ<sub>Hf</sub> values (5.7 ± 1.6 to 6.9 ± 1.6) relative to depleted mantle composition. U<img>Pb zircon dating identified two chronologically distinct mafic melts injections, at 280.93 ± 0.21 Ma and 279.63 ± 0.15 Ma, which are representative of the time of mafic magma emplacement and mingling with the felsic magma.</div><div>To explain the long-time interval occurring between the saturation of zircon in the felsic magma and the time the granite emplaced, mingled and crossed its solidus, we propose that during cooling, the zircon-bearing granite magma reservoir was intruded, most likely at the base of the felsic mush, by injections of hotter, mafic magmas that caused at least two successive events of rejuvenation and remobilization, which promoted the shallow intrusion of variably differentiated felsic magmas.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107881"},"PeriodicalIF":2.9,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138836","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 : 2025-01-01DOI: 10.1016/j.lithos.2024.107846
Baoliang Li , Huan Wang , Liqiang Wang , AaoRiGeLe Zhou , Teng Gao , Chenghao Ren
{"title":"Corrigendum to “Genesis and metallogenic potential of the ca.90 Ma Jiangcisha magmatic rocks in the western Shiquanhe suture zone, Xizang, China” [Lithos 472-473 (2024) 107556]","authors":"Baoliang Li , Huan Wang , Liqiang Wang , AaoRiGeLe Zhou , Teng Gao , Chenghao Ren","doi":"10.1016/j.lithos.2024.107846","DOIUrl":"10.1016/j.lithos.2024.107846","url":null,"abstract":"","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107846"},"PeriodicalIF":2.9,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143128074","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 : 2024-12-22DOI: 10.1016/j.lithos.2024.107929
Jörg Ostendorf , Robert Anczkiewicz , Milan Kohút
This contribution presents bulk-rock geochemical data with Sr-Nd-Hf isotopes and LA-ICP-MS U-Pb zircon geochronology for volcanic rocks from the Slanské Vrchy Mountains (E-Slovakia), a c. 50 km long volcanic chain located at the western flank of the Miocene Transcarpathian Basin System. The studied volcanics are represented by calc-alkaline andesites and dacites. More mafic composition was only found in a basaltic andesite enclave. Robust concordant U-Pb zircon ages for andesites (n = 6) and dacites (n = 3) range from 12.3 Ma to 11.8 Ma, indicating quasi-contemporaneous post-collisional volcanism. The basaltic andesite, andesites, and dacites have overlapping and correlated isotopic compositions (87Sr/86Sr(12Ma) = 0.7071 to 0.7104, εNd(12Ma) = −7.0 to −1.0, and εHf(12 Ma) = −6.2 to +2.8), which reflect mantle-crust interaction. A general lack of clear correlations between fractionation indicator SiO2 and isotope ratios as well as overlapping isotopic compositions of the andesites and dacites preclude simple coupled assimilation fractional crystallization (AFC) processes. Furthermore, the overall paucity of inherited zircons indicates limited assimilation at upper crustal levels. Pyroxene geothermobarometry points to a complex transcrustal volcanic system, which most likely involved processes of mixing, assimilation, storage, and homogenization (MASH) in the lower crust. Initial melt generation in the mantle was probably triggered by mantle upwelling in a generally extensional tectonic regime, but details on the nature of the mantle source remain enigmatic.
{"title":"Timing and petrogenesis of late orogenic calc-alkaline volcanism in the Slovak Transcarpathians: Implications for the evolution of the Carpathian collisional process","authors":"Jörg Ostendorf , Robert Anczkiewicz , Milan Kohút","doi":"10.1016/j.lithos.2024.107929","DOIUrl":"10.1016/j.lithos.2024.107929","url":null,"abstract":"<div><div>This contribution presents bulk-rock geochemical data with Sr-Nd-Hf isotopes and LA-ICP-MS U-Pb zircon geochronology for volcanic rocks from the Slanské Vrchy Mountains (E-Slovakia), a c. 50 km long volcanic chain located at the western flank of the Miocene Transcarpathian Basin System. The studied volcanics are represented by calc-alkaline andesites and dacites. More mafic composition was only found in a basaltic andesite enclave. Robust concordant U-Pb zircon ages for andesites (<em>n</em> = 6) and dacites (<em>n</em> = 3) range from 12.3 Ma to 11.8 Ma, indicating quasi-contemporaneous post-collisional volcanism. The basaltic andesite, andesites, and dacites have overlapping and correlated isotopic compositions (<sup>87</sup>Sr/<sup>86</sup>Sr<sub>(12Ma)</sub> = 0.7071 to 0.7104, εNd<sub>(12Ma)</sub> = −7.0 to −1.0, and εHf<sub>(12 Ma)</sub> = −6.2 to +2.8), which reflect mantle-crust interaction. A general lack of clear correlations between fractionation indicator SiO<sub>2</sub> and isotope ratios as well as overlapping isotopic compositions of the andesites and dacites preclude simple coupled assimilation fractional crystallization (AFC) processes. Furthermore, the overall paucity of inherited zircons indicates limited assimilation at upper crustal levels. Pyroxene geothermobarometry points to a complex transcrustal volcanic system, which most likely involved processes of mixing, assimilation, storage, and homogenization (MASH) in the lower crust. Initial melt generation in the mantle was probably triggered by mantle upwelling in a generally extensional tectonic regime, but details on the nature of the mantle source remain enigmatic.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"496 ","pages":"Article 107929"},"PeriodicalIF":2.9,"publicationDate":"2024-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143321016","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 : 2024-11-26DOI: 10.1016/j.lithos.2024.107876
Lei Yang , Calvin F. Miller , Jia-Min Wang , Xiao-Chi Liu , Fu-Yuan Wu
As the product of a collisional belt, Himalayan leucogranites provide insights into the geodynamic and thermal evolution of tectonically thickened crust. Nevertheless, the petrogenesis of these leucogranites is still a much-debated topic. They are typically interpreted as the primary melt formed by partial melting of the Greater Himalayan Crystalline Complex (GHC). There is, however, another view that they are the products of fractional crystallization of less evolved parent magmas. This study aims to explore these competing petrogenetic models. We collected biotite granite, two-mica granite, tourmaline granite, and garnet granite in the Nyalam region for mineralogical and geochemical studies. The granites occur as small laccoliths, sills, and dikes in the upper GHC and the South Tibet Detachment System (STDS). The plagioclase in biotite granite is oligoclase and andesine (An >20) but is more sodic (An <20) in other rocks. From biotite granite to two-mica granite to tourmaline granite, Mg and Ti in biotite and Zr/Hf in zircon gradually decrease, and AlVI and XFe in biotite and Hf in zircon increase correspondingly. Garnet is typically euhedral and spessartine-rich (spessartine >30 wt%), and it only appears in garnet granite, suggesting an increase of Mn/(Fe + Mg) in the melt. These variations suggest that biotite granite is the least evolved rock, and that two-mica granite, tourmaline granite, and garnet granite are increasingly fractionated. This fractionation trend is supported by trace element compositions. Rb-Sr-Ba trace element modeling suggests that the feldspars (plagioclase and k-feldspar) are the main fractionated minerals. ZrHf modeling indicates that the decrease of Zr/Hf ratio in the melt is related to the fraction of zircon fractionated, which is controlled by the change of temperature and melt composition. Additionally, very high Rb/Sr (>20), low Zr/Hf (<20), and strongly negative Eu anomaly (0.2) in garnet granite strongly suggest that the melt experienced extensive fractionation. Compiled Himalayan leucogranite geochemistry presents a similar pattern to our data and modeling result, suggesting that the variety of Himalayan leucogranites might relate to fractional crystallization. In addition, the composition of leucogranites in the Nyalam is a function of spatial position and age. The leucogranites that were produced during the activity of STDS and developed close to STDS have more evolved compositions, indicating that the development of STDS might have played an essential role in the differentiation of leucogranite in the Himalaya.
{"title":"Identification of fractionation processes in the Himalayan leucogranites-Case study from the Nyalam region","authors":"Lei Yang , Calvin F. Miller , Jia-Min Wang , Xiao-Chi Liu , Fu-Yuan Wu","doi":"10.1016/j.lithos.2024.107876","DOIUrl":"10.1016/j.lithos.2024.107876","url":null,"abstract":"<div><div>As the product of a collisional belt, Himalayan leucogranites provide insights into the geodynamic and thermal evolution of tectonically thickened crust. Nevertheless, the petrogenesis of these leucogranites is still a much-debated topic. They are typically interpreted as the primary melt formed by partial melting of the Greater Himalayan Crystalline Complex (GHC). There is, however, another view that they are the products of fractional crystallization of less evolved parent magmas. This study aims to explore these competing petrogenetic models. We collected biotite granite, two-mica granite, tourmaline granite, and garnet granite in the Nyalam region for mineralogical and geochemical studies. The granites occur as small laccoliths, sills, and dikes in the upper GHC and the South Tibet Detachment System (STDS). The plagioclase in biotite granite is oligoclase and andesine (An >20) but is more sodic (An <20) in other rocks. From biotite granite to two-mica granite to tourmaline granite, Mg and Ti in biotite and Zr/Hf in zircon gradually decrease, and Al<sup>VI</sup> and <em>X</em><sub><em>Fe</em></sub> in biotite and Hf in zircon increase correspondingly. Garnet is typically euhedral and spessartine-rich (spessartine >30 wt%), and it only appears in garnet granite, suggesting an increase of Mn/(Fe + Mg) in the melt. These variations suggest that biotite granite is the least evolved rock, and that two-mica granite, tourmaline granite, and garnet granite are increasingly fractionated. This fractionation trend is supported by trace element compositions. Rb-Sr-Ba trace element modeling suggests that the feldspars (plagioclase and k-feldspar) are the main fractionated minerals. Zr<img>Hf modeling indicates that the decrease of Zr/Hf ratio in the melt is related to the fraction of zircon fractionated, which is controlled by the change of temperature and melt composition. Additionally, very high Rb/Sr (>20), low Zr/Hf (<20), and strongly negative Eu anomaly (0.2) in garnet granite strongly suggest that the melt experienced extensive fractionation. Compiled Himalayan leucogranite geochemistry presents a similar pattern to our data and modeling result, suggesting that the variety of Himalayan leucogranites might relate to fractional crystallization. In addition, the composition of leucogranites in the Nyalam is a function of spatial position and age. The leucogranites that were produced during the activity of STDS and developed close to STDS have more evolved compositions, indicating that the development of STDS might have played an essential role in the differentiation of leucogranite in the Himalaya.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107876"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746515","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 : 2024-11-26DOI: 10.1016/j.lithos.2024.107875
Yong-Jie Yu , Ren-Xu Chen , Qiong-Xia Xia , Zhi-Hui Mu , Zhuang-Zhuang Yin , Guo-Chao Sun
Mineral behavior during anatectic metamorphism is a direct factor controlling the chemical and isotopic compositions of melts and residues. However, the mechanism that causes disequilibrium melting remains poorly understood. A combined study of petrological, geochronological and geochemical analyses was carried out on a stromatic migmatite outcrop, the Luoerling migmatite in the North Dabie zone. The in-source leucosomes and leucocratic veins are products of in situ partial melting and later magmatic intrusion, respectively. The finding of Neoproterozoic, Late Triassic and Early Cretaceous zircons suggests that the migmatites have Neoproterozoic protoliths, and experienced eclogite-facies metamorphism during collisional orogeny and anatectic metamorphism in the post-collisional stage. The occurrence of peritectic amphibole suggests that anatectic metamorphism mainly occurs through biotite hydration melting. The occurrence of orthopyroxene and clinopyroxene indicates local dehydration melting under granulite-facies conditions. Leucosomes show considerably higher 87Sr/86Sri, but lower εNd(t) and εHf(t) values than the corresponding melanosomes. Such isotopic differences between leucosomes and melanosomes result mainly from the influx of external fluids derived from the surrounding eclogites and gneisses, indicating a coupled dehydration-hydration mechanism in the continental subduction zone. Peritectic and anatectic zircon, monazite, titanite and apatite that formed during anatectic metamorphism exhibit different petrological and geochemical characteristics. Peritectic and anatectic accessory minerals in the leucosomes and leucocratic veins exhibit smaller variations in Nd-Hf isotopes than those in the melanosomes, suggesting that the anatectic melts were homogenized during transport. Differential dissolution and growth of monazite, titanite and apatite affect the Sm-Nd isotopes of residues and melts during anatectic metamorphism. The dissolution of apatite plays a significant role in the hydration melting of metagranite. The continuous dissolution of relict zircon during cooling/transportation of melt results in decreased εHf(t) values in anatectic zircon, whereas the incomplete dissolution of relict zircon results in whole-rock Hf-Nd decoupling. The difference in Nd-Hf isotopes among whole-rock and different genetic minerals can distinguish between dehydration and hydration melting. Therefore, this study highlights that a combination of multiple isotope analyses on whole-rock and accessory minerals may be conducive to understanding not only the mechanism and process of disequilibrium melting but also the nature of anatectic metamorphism in collisional orogens.
{"title":"Accessory minerals fingerprint post-collisional anatectic metamorphism in continental collision zones","authors":"Yong-Jie Yu , Ren-Xu Chen , Qiong-Xia Xia , Zhi-Hui Mu , Zhuang-Zhuang Yin , Guo-Chao Sun","doi":"10.1016/j.lithos.2024.107875","DOIUrl":"10.1016/j.lithos.2024.107875","url":null,"abstract":"<div><div>Mineral behavior during anatectic metamorphism is a direct factor controlling the chemical and isotopic compositions of melts and residues. However, the mechanism that causes disequilibrium melting remains poorly understood. A combined study of petrological, geochronological and geochemical analyses was carried out on a stromatic migmatite outcrop, the Luoerling migmatite in the North Dabie zone. The in-source leucosomes and leucocratic veins are products of in situ partial melting and later magmatic intrusion, respectively. The finding of Neoproterozoic, Late Triassic and Early Cretaceous zircons suggests that the migmatites have Neoproterozoic protoliths, and experienced eclogite-facies metamorphism during collisional orogeny and anatectic metamorphism in the post-collisional stage. The occurrence of peritectic amphibole suggests that anatectic metamorphism mainly occurs through biotite hydration melting. The occurrence of orthopyroxene and clinopyroxene indicates local dehydration melting under granulite-facies conditions. Leucosomes show considerably higher <sup>87</sup>Sr/<sup>86</sup>Sr<sub>i</sub>, but lower ε<sub>Nd</sub>(t) and ε<sub>Hf</sub>(t) values than the corresponding melanosomes. Such isotopic differences between leucosomes and melanosomes result mainly from the influx of external fluids derived from the surrounding eclogites and gneisses, indicating a coupled dehydration-hydration mechanism in the continental subduction zone. Peritectic and anatectic zircon, monazite, titanite and apatite that formed during anatectic metamorphism exhibit different petrological and geochemical characteristics. Peritectic and anatectic accessory minerals in the leucosomes and leucocratic veins exhibit smaller variations in Nd-Hf isotopes than those in the melanosomes, suggesting that the anatectic melts were homogenized during transport. Differential dissolution and growth of monazite, titanite and apatite affect the Sm-Nd isotopes of residues and melts during anatectic metamorphism. The dissolution of apatite plays a significant role in the hydration melting of metagranite. The continuous dissolution of relict zircon during cooling/transportation of melt results in decreased ε<sub>Hf</sub>(t) values in anatectic zircon, whereas the incomplete dissolution of relict zircon results in whole-rock Hf-Nd decoupling. The difference in Nd-Hf isotopes among whole-rock and different genetic minerals can distinguish between dehydration and hydration melting. Therefore, this study highlights that a combination of multiple isotope analyses on whole-rock and accessory minerals may be conducive to understanding not only the mechanism and process of disequilibrium melting but also the nature of anatectic metamorphism in collisional orogens.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107875"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746513","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 : 2024-11-26DOI: 10.1016/j.lithos.2024.107874
Tom Andersen , Marlina A. Elburg
Scandium (Sc) is a compatible element in mafic silicate minerals, in particular amphibole, garnet and clinopyroxene, and is enriched in ultramafic rocks. Nevertheless, its concentration is also sufficiently high in some evolved granites and granite pegmatites to form minerals with essential Sc. In some granitic occurrences, Sc-bearing minerals occur in miarolitic cavities, indicating the importance of late- to post-magmatic fluids. In contrast, some granite pegmatites have thortveitite (Sc2Si2O7) and other Sc-rich minerals, including Sc-enriched garnet as part of evolved magmatic mineral assemblages. The maximum Sc concentration in garnet in thortveitite-bearing, Mesoproterozoic granite pegmatites of probable anatectic origin in South Norway is ca. 2000 ppm, corresponding to ca. 100 ppm in a coexisting silicate melt. As for any trace element, the behaviour of Sc during crustal anatexis is controlled by the amount of melt formed and the mineralogy of the solid residue. The melting process can be modelled from thermodynamical data on solids and melts for given protolith compositions, temperature and pressure. Simulations in a range of mafic/ultramafic to felsic systems show that mafic protoliths will form Sc-depleted anatectic melts, and correspondingly Sc-enriched solid residues under relevant pressure and temperature conditions (2-10 kbar, 700-800 °C). Limited enrichment in melt relative to protolith is only seen in granodioritic-tonalitic bulk compositions, reaching maximum concentrations of 30–60 ppm. The effect of fluorine during melting and subsequent fractionation is to lower the solidus temperature, depolymerise the silicate melt, and lower partition coefficients for Sc between mafic silicate minerals and felsic melt. Contamination with mafic material has only limited effect, as it will eventually sequester Sc into hybrid mafic silicate mineral assemblages and lead to reduction of the Sc concentration of the remaining melt fraction. Further increase of the Sc concentration requires fractional crystallisation of minerals with low KD, i.e. mainly feldspar minerals and quartz, which may be facilitated by selective, local contamination by quartz and feldspar from granitic country rocks.
{"title":"The behaviour of scandium during crustal anatexis: Implications for the petrogenesis of Sc-enriched granitic magma","authors":"Tom Andersen , Marlina A. Elburg","doi":"10.1016/j.lithos.2024.107874","DOIUrl":"10.1016/j.lithos.2024.107874","url":null,"abstract":"<div><div>Scandium (Sc) is a compatible element in mafic silicate minerals, in particular amphibole, garnet and clinopyroxene, and is enriched in ultramafic rocks. Nevertheless, its concentration is also sufficiently high in some evolved granites and granite pegmatites to form minerals with essential Sc. In some granitic occurrences, Sc-bearing minerals occur in miarolitic cavities, indicating the importance of late- to post-magmatic fluids. In contrast, some granite pegmatites have thortveitite (Sc<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>) and other Sc-rich minerals, including Sc-enriched garnet as part of evolved <em>magmatic</em> mineral assemblages. The maximum Sc concentration in garnet in thortveitite-bearing, Mesoproterozoic granite pegmatites of probable anatectic origin in South Norway is ca. 2000 ppm, corresponding to ca. 100 ppm in a coexisting silicate melt. As for any trace element, the behaviour of Sc during crustal anatexis is controlled by the amount of melt formed and the mineralogy of the solid residue. The melting process can be modelled from thermodynamical data on solids and melts for given protolith compositions, temperature and pressure. Simulations in a range of mafic/ultramafic to felsic systems show that mafic protoliths will form Sc-depleted anatectic melts, and correspondingly Sc-enriched solid residues under relevant pressure and temperature conditions (2-10 kbar, 700-800 °C). Limited enrichment in melt relative to protolith is only seen in granodioritic-tonalitic bulk compositions, reaching maximum concentrations of 30–60 ppm. The effect of fluorine during melting and subsequent fractionation is to lower the solidus temperature, depolymerise the silicate melt, and lower partition coefficients for Sc between mafic silicate minerals and felsic melt. Contamination with mafic material has only limited effect, as it will eventually sequester Sc into hybrid mafic silicate mineral assemblages and lead to reduction of the Sc concentration of the remaining melt fraction. Further increase of the Sc concentration requires fractional crystallisation of minerals with low <em>K</em><sub>D</sub>, i.e. mainly feldspar minerals and quartz, which may be facilitated by selective, local contamination by quartz and feldspar from granitic country rocks.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107874"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746514","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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