Chemie Der Erde-Geochemistry最新文献

{"title":"Melting experiments of an L6 ordinary chondrite: Implications for the formation of alkali-rich achondrites","authors":"S. Iannini Lelarge ,&nbsp;M. Masotta ,&nbsp;L. Folco ,&nbsp;T. Ubide ,&nbsp;M.D. Suttle ,&nbsp;L. Pittarello","doi":"10.1016/j.chemer.2025.126293","DOIUrl":"10.1016/j.chemer.2025.126293","url":null,"abstract":"<div><div>We conducted high-pressure (1 GPa) melting experiments (1100–1400 °C) on the equilibrated ordinary chondrite DAV 01001 (L6) to investigate partial melting scenarios of planetary embryo in the early solar system. At 1100 °C, no melting of the silicate phase is observed, and the initial chondritic texture is preserved, but the metallic-sulphidic phases formed two immiscible Fe–Ni and S-rich liquids. Melting of silicate minerals began at 1200 °C, progressing from plagioclase to high-Ca and low-Ca pyroxene and olivine. As melting advanced, the formation of new olivine and low-Ca pyroxene resulted in the production of trachy-andesitic melt at 1200 °C, basaltic trachy-andesitic melt at 1300 °C, and andesitic melt at 1400 °C. These silicate melts have chemical similarities with some anomalous achondrites (e.g., GRA 60128/9). At the same time, minerals of new formation resemble those of primitive achondrites (e.g., brachinites, ureilites, IAB silicate inclusions, acapulcoites and lodranites). The rapid mineral-liquid re-equilibration suggests that basaltic liquids can form only above 1400 °C and that relatively high degrees of melting (&gt;20 %) and crystallisation are necessary to explain the observed diversity of achondritic lithologies. These findings suggest that partial melting and recrystallization processes within planetary embryos could have played a critical role in the early solar system, contributing to the early differentiation of planetary bodies and the diversity of achondritic lithologies, including (but not limited to) alkali-rich achondrites.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126293"},"PeriodicalIF":2.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143873763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deciphering the magmatic evolution of the Hyblean Cretaceous volcanism (SE Sicily, Italy): New geochemical, isotopic and noble gas analyses","authors":"M. Di Bella ,&nbsp;D. Romano ,&nbsp;V. Volpi ,&nbsp;F. Italiano ,&nbsp;A. Correale ,&nbsp;M. Petrelli ,&nbsp;G. De Rosa ,&nbsp;A. Tripodo ,&nbsp;G. Sabatino","doi":"10.1016/j.chemer.2025.126289","DOIUrl":"10.1016/j.chemer.2025.126289","url":null,"abstract":"<div><div>The coupling of helium isotopes in fluid inclusions with conventional geochemical data provided a new perspective on the volcanic processes that took place during the Cretaceous in southern Sicily. Our new investigations reveal that during two distinct volcanic phases in the Late Cretaceous, magmas formed from low degrees of partial melting of a heterogeneous mantle source characterized by spinel lherzolite and varying garnet content. The collected samples, including lava flows, dikes, and sills, exhibit a wide range of rock types, from picritic basalts to hawaiites. Two different magma types were identified: one displaying a bell-shaped pattern akin to ocean island basalts (OIB) and another with an irregular pattern marked by positive spikes in Nb, K, Pb, Sr, Zr, and Ti. Strontium and Neodymium isotope compositions are weakly radiogenic, while the Pb isotope systematics show strong radiogenic values (²⁰⁶Pb/²⁰⁴Pb = 19.64–20.42; ²⁰⁷Pb/²⁰⁴Pb = 15.61–15.70; ²⁰⁸Pb/²⁰⁴ Pb = 39.26–39.98), corresponding to the mantle focal zone (FOZO) component. The observed ³He/⁴He ratios of 3.48 to 6.48 R_c/R_a in pyroxene fluid inclusions reflect the occurrence of pre-eruptive processes such as diffusion-induced fractionation or diffusive exchange taking place during magma residence in the crust. The ³He/⁴He ratios from 7.75 to 9.31 R_c/R_a in olivine crystals are typical of MORB-type basalts, and they likely represent the original signature of the mantle source. The olivine R_c/R_a values may indicate an interaction with recycled (U+Th)-poor lithologies or high ³He/⁴He materials in the upper mantle source. Furthermore, the ³He/⁴He isotope ratios of olivines differ from those determined in the same region for Plio-Pleistocene volcanic products, for which a common origin has been suggested in the majority of previous studies. In light of our findings, the hypothesis that the Hyblean Late Cretaceous and Plio-Pleistocene volcanics are part of a single magmatic suite should be reexamined. Overall, our results indicate that the evolution of those volcanic rocks was influenced by fractional crystallization and accumulation processes providing additional details on the mantle source that may have been overlooked in the past.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126289"},"PeriodicalIF":2.6,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143808325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The petrology and geochemistry of the Montagna Grande-Monte Gibele trachytic shield volcano (Pantelleria, Italy)","authors":"John C. White ,&nbsp;Ray Macdonald ,&nbsp;Pierangelo Romano ,&nbsp;Bogusław Bagiński ,&nbsp;Silvio G. Rotolo ,&nbsp;Beata Marciniak-Maliszewska ,&nbsp;Alessandra Cinquegrani","doi":"10.1016/j.chemer.2025.126288","DOIUrl":"10.1016/j.chemer.2025.126288","url":null,"abstract":"<div><div>The 45.7 ± 1.0 ka (2σ) eruption of the compositionally zoned (comenditic trachyte to pantellerite) Green Tuff ignimbrite on the volcanic island of Pantelleria, Italy, was followed by the extrusion of a series of post-caldera metaluminous to mildly peralkaline trachyte lavas between 26.2 ± 2.0 and 22.3 ± 2.9 ka (2σ). This study uses whole-rock major- and trace-element compositions, mineral compositions, geothermobarometry, and petrogenetic models to examine the role of trachytes in the evolution of the Pantelleria magma system. Although previous studies have suggested that all of these units are consanguineous and form a liquid line of descent (LLOD) from metaluminous trachyte to peralkaline trachyte and pantellerite, mineralogical and geochemical evidence, as well as the results of modelling, suggest a much more complex origin. The crystallization of alkali feldspar from metaluminous trachyte liquids (descended from alkali to transitional basaltic magma <em>via</em> fractional crystallization) drives the composition of the residual melt to increasingly peralkaline compositions: pantelleritc trachyte first and then, after &gt;65 % crystallization, to pantellerite. This also results in the formation of a syenitic cumulate. Later intrusion of new mafic melt into the cumulate initiates partial melting, which produces comenditic trachyte melts characterized by low concentrations of incompatible trace elements (Rb, Zr, Nb, Th), high concentrations of Ba and Sr, and strong positive Eu anomalies. Entrainment of trachytic alkali feldspars into these melts as antecrysts further enhances these characteristics in whole-rock compositions. The origin of compositional zoning in the Green Tuff can be attributed to fractional crystallization from metaluminous trachyte within the lower pantelleritic portion and to partial melting of the syenitic cumulate for the upper comenditic trachyte portion.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126288"},"PeriodicalIF":2.6,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143776468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Permo-Triassic magmatism in the Damaraland Igneous Province, NW Namibia: The Ondurakorume alkaline‑carbonatite complex","authors":"Andreja Ladisic ,&nbsp;Michael A.W. Marks ,&nbsp;Benjamin F. Walter ,&nbsp;R. Johannes Giebel ,&nbsp;Aratz Beranoaguirre ,&nbsp;Gregor Markl","doi":"10.1016/j.chemer.2025.126287","DOIUrl":"10.1016/j.chemer.2025.126287","url":null,"abstract":"<div><div>The four spatially associated igneous complexes of Kalkfeld, Ondurakorume, Osongombo and Etaneno are situated within the Damaraland Igneous Province (northwestern Namibia), which formed in response to the rifting of the South Atlantic during the early Cretaceous. Spatially-resolved LA-ICP MS U-Pb age dating on zircon and titanite confirms the Cretaceous age for Etaneno (mean of 139.2 ± 6.7 Ma), while Triassic and Permian emplacement ages are indicated for nepheline syenites from Kalkfeld (249.6 ± 3.2 and 249.4 ± 2.9 Ma) and Ondurakorume (272.1 ± 1.5 Ma). Furthermore, apatite ages for nepheline syenites from Etaneno (mean of 122.8 ± 3.8 Ma) and Kalkfeld (217.4 ± 24.5 Ma), and for carbonatites of Ondurakorume (248.1 ± 4.8 Ma) broadly agree with the zircon and titanite ages, while apatite from basement marbles yields a presumably metamorphic age of 479.6 ± 2.6 Ma and 465.1 ± 7.0 Ma.</div><div>Detailed petrographic analysis of syenites, nepheline syenites, carbonatites, silicocarbonatites and fenites from Ondurakorume reveals variable interaction processes between alkaline-silicate rocks and carbonatites. Syenites and nepheline syenites contain interstitial calcite with burbankite or carbocernaite inclusions (as commonly found in calcite carbonatites) and baddeleyite-zircon replacement textures. In some carbonatites and in silicocarbonatites, local contamination with (nepheline) syenites and granitic basement caused elevated Si activity, triggering enhanced formation of clinopyroxene, amphibole and mica.</div><div>Compositional variations in the released fenitizing fluids are indicated by clinopyroxene compositions that vary from nearly end-member aegirine (Aeg_69-91Di_0-10Hed_0-7) in proximal fenites to less sodic aegirine-augite (Aeg_54-96Di_0-17Hed_0-16) in more distal fenite samples, with the latter containing additional sodic amphibole. Compared to clinopyroxene in nepheline syenites and carbonatites, clinopyroxene in fenites shows elevated Ti contents (mostly &gt;0.05 apfu Ti) that are highest in distal fenites (up to 0.22 apfu Ti), suggesting Ti mobility. These changes suggest either a compositional evolution during fluid-rock interaction or two different fluid sources (carbonatites and (nepheline) syenites, respectively).</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126287"},"PeriodicalIF":2.6,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143776469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From error ellipse to Bayesian estimation: Strategies for optimizing T-W diagrams in UPb dating","authors":"Yao Mu ,&nbsp;Can Ge ,&nbsp;Fangyue Wang ,&nbsp;Xiuyu Li ,&nbsp;He Sun ,&nbsp;Haiou Gu ,&nbsp;Feng Yuan","doi":"10.1016/j.chemer.2025.126286","DOIUrl":"10.1016/j.chemer.2025.126286","url":null,"abstract":"<div><div>This study examines the application of the T-W diagram (Tera-Wasserburg Concordia Diagram) in uranium‑lead (U<img>Pb) isotope dating technology, especially for samples containing common lead. The core of the research lies in evaluating and optimizing the accuracy, precision, and determination of confidence intervals of T-W diagram dating. We propose a new formula based on the geometric mean method for correcting the calculation of error ellipses to reduce bias from high data noise levels. The study further elaborates on the application of the error-correlated independent weighted least squares method in determining the confidence intervals of linear models and intersection ages. Through simulation analysis, we evaluate the performance of least square methods in terms of dating accuracy and precision with both well-distributed and poorly distributed data. In view of the limitations of least square methods, a Bayesian method based on intercept constraints or the evolution model of terrestrial common lead is proposed, significantly improving the accuracy, precision, and success rate of dating analysis. The new methodology of this study not only provides a more reliable analytical tool for the field of radiometric dating, but is also applicable to single-point age analysis.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126286"},"PeriodicalIF":2.6,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143739074","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Polymetallic interactions of Zn-Pb-Cu in blue/green-colored speleothems from Malaval Cave (France)","authors":"Martin Vlieghe ,&nbsp;Gaëtan Rochez ,&nbsp;Stéphane Pire-Stevenne ,&nbsp;Alexandre Felten ,&nbsp;Marie Dechamps ,&nbsp;Sébastien R. Mouchet ,&nbsp;Francesca Cecchet ,&nbsp;Olivier Bruguier ,&nbsp;Jean-Louis Galéra ,&nbsp;Gipsi Lima-Mendez ,&nbsp;Marc Llirós Dupré ,&nbsp;Johan Yans","doi":"10.1016/j.chemer.2025.126285","DOIUrl":"10.1016/j.chemer.2025.126285","url":null,"abstract":"<div><div>Speleothems rarely exhibit stunning colors such as red, yellow, green, or blue. The colorations are often linked to elevated heavy metal ion concentration in the drip water and thus to a metal source/pollution in the catchment area. Here the blue-green speleothems coloration in Malaval Cave (Lozère, France) is characterized by a wide panel of optical, mineralogical and geochemical techniques. These techniques were applied on several small blue or white stalactites and a larger greenish stalactite. The speleothems are mostly composed of aragonite and contain variable amounts of Zn, Cu and Pb, which cause the colorations. Zn and Cu are mostly present in substitution in the aragonite and Cu²⁺ is the main cause of the blue coloration. Zn is also found in small amorphous gel particles, containing minor amounts of Mg, Cu and Si. These phases are responsible for microscopical scale variations in the blue coloration. Pb is present as Pb²⁺ ions in substitution within the aragonite, creating a saturated blue-to-greenish coloration. This coloration may depend on the Pb/Zn ratio due to metallic interaction. Pb, Zn and Cu ratios indicate that Pb likely deposited from distinct fluids and at a different timing than Cu and Zn. All three metals likely originate from the leaching of Pb<img>Zn ores in the Jurassic formations surrounding the cave.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126285"},"PeriodicalIF":2.6,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143706136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Genesis of the Langwashan Fe deposit, NW China: Constraints from pyrite and magnetite geochemistry, and in-situ Rb-Sr dating","authors":"Yuanlin Chen ,&nbsp;Huan Li ,&nbsp;Wenting Jiang ,&nbsp;Majid Ghaderi ,&nbsp;Adi Maulana ,&nbsp;Liming Ouyang ,&nbsp;Kun Liu","doi":"10.1016/j.chemer.2025.126284","DOIUrl":"10.1016/j.chemer.2025.126284","url":null,"abstract":"<div><div>The Langwashan Fe deposit, with 80 million tons of proven iron ore reserves, is located in the eastern portion of the Tianshan orogenic belt, NW China. Previous research carried out detailed geological, geochemical, and geophysical studies on the deposit, while there are still different views on the ore genesis. In this study, electron probe micro-analysis and laser ablation (multi-collector) inductively coupled plasma mass spectrometry analysis of variable minerals in ore samples were conducted. Based on ore texture, in-situ biotite Rb<img>Sr dating, magnetite and pyrite composition, and mineral assemblage, the Langwashan Fe mineralization has been divided into two metallogenic periods: volcanic hydrothermal metallogenic period (∼344 Ma) and skarn metallogenic period (∼239 Ma). The Early Carboniferous mineralization is characterized by layered ore bodies, a narrow range of δ³⁴S values (+1.37 to +2.77 ‰), and low Co/Ni ratio in early pyrite (Py I), and high Ti, V, Cr, Ni, and Co contents in early magnetite (Mag I), showing single and deep origin for the fluid. In contrast, the Early Triassic mineralization has irregular-shaped ore bodies, higher contents of Si, Al, Mn, Mg, and Ca in late magnetite (Mag II), higher Co, Ni, As, and Cu contents, and a wider range of δ³⁴S values (−0.18 to +3.35 ‰) in late pyrite (Py II), indicating mixed origin for the fluid. Thus, we propose that the Langwashan Fe deposit is formed by the superposition of two types of mineralization. The Early Carboniferous Hongshishan inter-arc oceanic basin subducted beneath the southern Tarim plate, and the iron-bearing magma migrated along the volcanic channel and annular faults, forming the first period of layered Fe ore bodies together with the volcanic rock deposition. During the Early Triassic, a hidden intrusion was generated in an extensional environment in the region, interacting with surrounding rocks through metasomatism, forming superimposed skarn-type Fe ore bodies. The two periods of mineralization determined in Langwashan have great significance for further exploration and prospecting of Fe ore deposits in the Tianshan orogenic belt.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126284"},"PeriodicalIF":2.6,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry and origin of the banded Iron formations (BIFs) from the Western Dharwar craton, southern India: Implications for evolving redox conditions of Archean oceans","authors":"Aindrila Mukherjee ,&nbsp;Jayananda Mudlappa ,&nbsp;Pritam Nasipuri ,&nbsp;Aadhiseshan K.R. ,&nbsp;Satyanarayanan M.","doi":"10.1016/j.chemer.2025.126268","DOIUrl":"10.1016/j.chemer.2025.126268","url":null,"abstract":"<div><div>We present mineralogic and elemental data on the Banded Iron Formations (BIFs) from the volcano-sedimentary greenstone belts of the Western Dharwar Craton to address redox conditions of Archean Oceans and origin of BIFs. The studied BIFs are restricted to the uppermost stratigraphic levels in the Sargur Group and Dharwar Supergroup greenstone belts. The BIFs of the older Sargur greenstone sequence are characterized by thick chert layers, which are interspersed with thin Fe-oxide and silicate layers. Iron-rich amphibole grunerite indicates that BIFs from the Sargur Group underwent lower-amphibolite facies metamorphism. In contrast, oxide-silicate‑carbonate-sulphide facies BIFs characterize younger Dharwar Supergroup greenstone belts. Rare silicate assemblages (e.g., stilpnomelane orreibeckite) in BIFs of Dharwar Supergroup reveal greenschist facies metamorphism. Field, mineralogic and elemental characteristics of studied samples show affinity to Algoma-type BIFs. The studied BIFs show significant variation in SiO₂ (49.00–53.00 wt%) and Fe₂O₃ (27.00–51.5 wt%) content. The concentration of all other elements is typically &lt;1 wt% except two samples of BIFs from the Chitradurga basin exhibit higher Al₂O₃ (5.42 wt%) and CaO (9.56 wt%) reflecting traces of terrigenous input. The low ΣREE content (&lt;20 ppm) of studied BIFs from the Sargur Group Holenasirpur, Dharwar Supergroup Bababudan, and Chitradurga – Dharwar-Shimoga greenstone belts preclude continent derived terrigenous input whilst higher total REE (30–53 ppm) of two BIFs samples from the Chitradurga basin is in agreement with traces of terrigenous input. BIFs from the older Sargur Group and the younger Dharwar Supergroup exhibit positive Eu anomalies pointing to BIFs sourced from hydrothermal plumbing system. The trace element ratios (Y/Ho, Sm/Yb, and Eu/Sm) consistent with a dominant hydrothermal input in their origin. The mineralogical facies changes, combined with the redox-sensitive elemental signatures coupled with published redox sensitive isotope biomarkers suggest fluctuation in the redox conditions of ocean basins through Archean and oxygenation of ocean initiated at least two hundred million years before the Great Oxidation Event (GOE).</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126268"},"PeriodicalIF":2.6,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143609226","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrogenesis and tectonic significance of ∼1.6 Ga and ∼ 0.5 Ga A-type granite magmatism in the Assam-Meghalaya Gneissic Complex (NE India): Insights from geochronology, geochemistry and Sr-Nd isotopes","authors":"Rahul Nag ,&nbsp;H. Hrushikesh ,&nbsp;Nathan Cogné ,&nbsp;Bivin G. George ,&nbsp;Darius J.M. Thabah ,&nbsp;N. Prabhakar","doi":"10.1016/j.chemer.2025.126265","DOIUrl":"10.1016/j.chemer.2025.126265","url":null,"abstract":"<div><div>The widespread granite magmatism in the Assam-Meghalaya Gneissic Complex (AMGC) is crucial for understanding its tectono-magmatic evolution of NE India. This study presents geochemical and Sr-Nd isotopic data along with U-Pb zircon and U-Th-total Pb monazite ages of granites from western, central and eastern parts of the AMGC. Zircon U-Pb dating reveals two distinct episodes of granite magmatism during 1617–1603 Ma and 540–497 Ma. Geochemically, the ∼1.6 Ga and ∼ 0.5 Ga granites exhibit high SiO₂, Na₂O + K₂O, and moderate to low CaO and MgO contents. These granites show high Ga/Al ratios and display enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSE). The ∼1.6 Ga and ∼ 0.5 Ga granites are classified as A-type granites that were emplaced in post-collisional extensional tectonic setting. The ∼1.6 Ga granites show variable Nd composition [εNd(t) = 0.4 to −3.9] with Nd model ages (T_DM) of 2.6–2.2 Ga, indicating that these granites were derived from the partial melting of juvenile underplated mafic lower crust. In contrast, the ∼0.5 Ga granites show uniform negative εNd(t) values of −10.8 to −12.1 and younger Nd model ages (T_DM) of 2.2–1.7 Ga, suggesting that these granites were derived from the partial melting of the Paleoproterozoic to Mesoproterozoic continental crust beneath the AMGC. The two episodes of A-type granite magmatism in AMGC at ∼1.6 Ga and ∼ 0.5 Ga mark the collisional imprints of Columbia and East Gondwana assemblies, respectively.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126265"},"PeriodicalIF":2.6,"publicationDate":"2025-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143632046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical insights into the origins of compositionally distinct Early Permian Panjal Traps basalts: Implications for the transition from continental lithospheric to sub-lithospheric mantle melting regimes","authors":"Ashutosh Pandey ,&nbsp;T. Pon Gayathri ,&nbsp;K.-N. Pang ,&nbsp;Irfan M. Bhat ,&nbsp;H.K. Sachan","doi":"10.1016/j.chemer.2025.126264","DOIUrl":"10.1016/j.chemer.2025.126264","url":null,"abstract":"<div><div>The Early Permian Panjal Traps in northwestern Himalaya are the by far largest continuous expression of the Panjal-Qiangtang large igneous province (LIP). The eruption of the Panjal Traps is connected with the rifting at the northern continental margin of Gondwana, leading to the formation of the ribbon-shaped continent ‘Cimmeria’ and the opening of the Neo-Tethys Ocean. This study presents geochemical investigations on the lava flows from the Sonmarg area in the Kashmir Valley, representing the northeastern extremity of the Panjal Traps, to understand the spatio-temporal variations in the compositions of the traps and to constrain their petrogenesis and tectonic implications. The upper and lower flows show distinct geochemical characteristics, with the lower flows (classified as Group I basalts) showing negative high-field strength elements (Nb, Ta, Ti) anomalies similar to arc-related basalts and melts derived from the sub-continental lithospheric mantle (SCLM), and the upper flows (classified as Group II basalts) having geochemical traits similar to enriched mid-ocean ridge basalts (E-MORB). The geochemical affinity of the Group I basalts with arc-related basalts is interpreted as a result of significant assimilation of continental crust during ascent of these melts while undergoing fractionation of a gabbroic assemblage. It is inferred that the Group I basalts erupted during continental extension when continental crust was thinned and available for the uprising magma for assimilation. In contrast, the petrogenesis of the upper Group II basalts is inferred to occur in an extended rift where hot convecting sub-lithospheric mantle underwent adiabatic decompression melting. The transition from the eruption of Group I basalts to Group II basalts reflects the progressive evolution of mantle sources from sub-continental lithospheric mantle to sub-lithospheric mantle melting regimes during the passive continental extension at the northern margin of Gondwana in the Early Permian.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 1","pages":"Article 126264"},"PeriodicalIF":2.6,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}