Lithos最新文献

{"title":"Diverse magmatism along the northern margin of Tarim during the Ediacaran: Transition from Rodinian dispersing to Gondwana assemblage","authors":"Guangyou Zhu , Zhiyong Chen , Weiyan Chen , Lei Yan , Kun Zhao , Huichuan Liu","doi":"10.1016/j.lithos.2024.107823","DOIUrl":"10.1016/j.lithos.2024.107823","url":null,"abstract":"<div><div>The Ediacaran igneous rocks and sedimentary sequences play a key role for our understanding the transition from dispersing of the Rodinian continents to the assemblage of the Gondwana. On the other hand, some continental massifs at the marginal area of the Rodinia and Gondwana could preserve solid evidences for deciphering the geodynamic background from the break-up of Rodinia to the assemblage of Gondwana. In this contribution, we report field observations, petrography, ages and systematic geochemistry of the diverse Ediacaran igneous activities in the northern margin of the Tarim Block, which was favored as a marginal continental massif in the Rodinia configuration by most geologists. The Ediacaran igneous rocks along the northern margin of Tarim include the Baicheng and Yangxia granites, Tiemenguan syenite, Kurle mafic dykes and the basalt layers in the Zamoketi Formation (northeastern Tarim) and the Sugetbrak Formation (northwestern Tarim). Precise zircon U<img>Pb dating revealed that these distinct rocks were broadly coeval with crystallization/eruption ages of 630–600 Ma. Bulk-rock elemental and Sr<img>Nd isotope compositions as well as zircon Lu<img>Hf isotope compositions demonstrate that the Baicheng and Yangxia granites were derived from Neoarchean mafic lower crust and underwent intensive fractionation before their emplacements. The Tiemenguan syenites have potassic andesitic compositions, in combination with their pronounced enriched Nd<img>Hf isotopes and extremely high Zr saturation temperatures (∼900 °C), we argue that their possible shoshonitic primary magmas were derived from previously metasomatized subcontinental lithospheric mantle source (amphibole-bearing) and then, coupling with assimilation and fractional crystallization (AFC) effects in magma chamber and/or en route to the emplacement space. This can account for their intriguing geochemical features. The ca. 615 Ma Zamoketi and Sugetbrak basalts and the slightly younger porphyrite dykes (ca. 580 Ma) cutting the Zamoketi basalt layer, show typical OIB-like geochemical signatures, they were most likely derived from a depleted asthenospheric mantle source with variable fractionation of olivine and pyroxene and negligible crustal contamination before eruption. On the whole, the geochemistry of the diverse Ediacaran igneous rocks unambiguously demonstrates that they were genetically related to an extensional environment. In combination with the significant passive continental features of the Ediacaran-Cambrian sedimentary sequences, we consider that these Ediacaran igneous rocks were the latest phase of igneous activity related to the dispersing of the Tarim at the margin of the Rodinia supercontinent.</div><div>The dispersing of the Rodinian supra-continent was diachronic with the assemblage of the Gondwana. Late Tonian to Ediacaran dispersing of the Tarim from northern margin of Australia induced the opening of the Proto-Tethys Ocean. Then the initiation of the sou","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107823"},"PeriodicalIF":2.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446564","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}

{"title":"Li enrichment in peridotites and chromitites tracks mantle-crust interaction","authors":"Igor González-Pérez ,&nbsp;José M. González-Jiménez ,&nbsp;Sarah A.S. Dare ,&nbsp;Erwin Schettino ,&nbsp;Rubén Piña ,&nbsp;Claudio Marchesi ,&nbsp;Lola Yesares ,&nbsp;Fernando Gervilla","doi":"10.1016/j.lithos.2024.107819","DOIUrl":"10.1016/j.lithos.2024.107819","url":null,"abstract":"<div><div>The ultramafic massifs of the Serranía de Ronda in southern Spain are the Earth's largest exposures of subcontinental lithospheric mantle (SCLM) peridotites (∼450 km²). These ultramafic massifs experienced asthenosphere melt percolation during their crustal emplacement. Mixing of these mafic melts with anatectic melts and fluids led to the formation of a world's unique Ni-arsenide-rich chromitite ores (hereafter Cr<img>Ni ores) associated with orthopyroxenite and/or cordieritite (i.e., &gt; 90 % volume of cordierite) hosted within the peridotites. This study uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to investigate the Li in rock-forming minerals of peridotite and Cr<img>Ni ores to evaluate the role of Li as crustal tracer. Clinopyroxene crystallized from asthenospheric melts exhibits high Li contents (up to 8.5 ppm), exceeding the average values of the upper mantle (∼ 0.7 ppm), whereas orthopyroxene, olivine, and Cr-spinel from peridotite are mostly Li-depleted. In contrast, all rock-forming minerals of Cr<img>Ni ores have abnormally high Li contents, displaying an overall Li enrichment trend toward the external parts of ultramafic massifs, on the way to the crustal rocks. This trend is evident in Cr-spinel from the Cr<img>Ni ores, which display 6.9–7.9 ppm Li in the deepest portions of the massif (Arroyo de la Cala Cr<img>Ni ore) up to 1.4–8.5 ppm in the shallowest part (La Gallega Cr<img>Ni ore), as well as in orthopyroxenes that have 31.3–44.7 ppm Li in Arroyo de la Cala, and 45.1–51.4 ppm Li in La Gallega. Cordierite is present only in the Cr<img>Ni ores situated in the external part of the ultramafic massifs, exhibiting 113.15–160.82 ppm Li in the Barranco de las Acedías Cr<img>Ni ore and 36.5–60.5 ppm Li in La Gallega Cr<img>Ni ore. Similarly to Li, LREE, fluid-mobile elements (K, Rb, Ba), and Sr in orthopyroxenes from the Cr<img>Ni ores display enrichment from the inner to the outer parts of the ultramafic massif. These geochemical variations suggest that Li enrichment in Cr<img>Ni ores and host peridotites was a twofold process: (1) asthenospheric melt percolation slightly increased Li abundances in the SCLM peridotites by modal and cryptic metasomatism involving clinopyroxene; (2) additional infiltration of Li-bearing crustally-derived fluids during the intracrustal emplacement of the mantle section boosted the Li contents of minerals in the Cr<img>Ni ores. Our results highlight that Li may effectively track the interaction of the SCLM with crustal components.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107819"},"PeriodicalIF":2.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428309","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}

{"title":"Late Paleozoic–Early Mesozoic subduction history of Mudanjiang Ocean: New insights from greenschist in the Heilongjiang Complex, NE China","authors":"Simiao Wang ,&nbsp;Yu Dong ,&nbsp;Junhui Bi ,&nbsp;Yan Jing ,&nbsp;Wenchun Ge ,&nbsp;Hao Yang ,&nbsp;Jielu Yu ,&nbsp;Zheng Ji","doi":"10.1016/j.lithos.2024.107808","DOIUrl":"10.1016/j.lithos.2024.107808","url":null,"abstract":"<div><div>This paper presents zircon U-Pb ages, whole-rock major and trace element data, and Sr-Nd-Hf isotopic compositions for the greenschists from the Heilongjiang Complex in NE China. Based on the geochronological and geochemical characteristics, the greenschists from the Heilongjiang Complex can be categorized into three series: Early Permian tholeiitic series (275 ± 1 Ma and 273 ± 1 Ma), Middle Permian alkaline series (261 ± 1 Ma), and Early Jurassic alkaline series (179 ± 1 Ma). The Early Permian tholeiitic greenschist samples are characterized by remarkable negative Nb and Ta anomalies, and they exhibit relatively low whole-rock (⁸⁷Sr/⁸⁶Sr)_i values (0.703896–0.704252), along with positive ε_Nd(t) values (+7.66 to +8.65) and positive ε_Hf(t) values (+0.92 to +11.51), implying that their protoliths originated from the partial melting of a depleted mantle wedge that has been metasomatized by subducted slab fluids. The Middle Permian alkaline greenschist samples have high Nb (17.3–19.0 ppm), TiO₂ (1.40–1.64 wt%), and P₂O₅ (0.60–0.68 wt%) concentrations, and they are enriched in large ion lithophile elements and light rare earth elements, and depleted in high field strength elements and heavy rare earth elements, with high whole-rock (⁸⁷Sr/⁸⁶Sr)_i values (0.709434–0.709949), negative ε_Nd(t) values (−4.73 to −4.72) and varied ε_Hf(t) values (−10.11 to +4.86), which compositionally align with those of Nb-enriched basalts. Based on the geochronological and geochemical characteristics, we propose that the protolith generation of Middle Permian alkaline greenschists was associated with the partial melting of a mantle wedge that had been metasomatized by subduction slab-derived melts. The Early Jurassic alkaline greenschist samples display OIB affinities, characterized by whole-rock (⁸⁷Sr/⁸⁶Sr)_i values ranging from 0.705161 to 0.705926, ε_Nd(t) values between +6.16 and +6.19, and ε_Hf(t) values from +3.44 to +9.32, indicating the formation of the protolith for the Early Jurassic alkaline greenschist was related to the upwelling of the asthenosphere resulting from slab break-off. By integrating regional geological data, we can trace the subduction evolution of the Mudanjiang Ocean back to the Early Permian, and the slab break-off during the Early Jurassic likely corresponded to the early stage of the closure of the Mudanjiang Ocean.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107808"},"PeriodicalIF":2.9,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428470","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}

{"title":"Serpentinization of the Ronda Massif (Spain): Structural controls and fluid origin","authors":"Bastien Audran ,&nbsp;Philippe Boulvais ,&nbsp;Yannick Branquet ,&nbsp;Pierre Gautier ,&nbsp;Marc Ulrich ,&nbsp;Guillaume Raymond ,&nbsp;Georges Beaudoin ,&nbsp;Daniel Layton-Matthews ,&nbsp;Evelyne Leduc ,&nbsp;Maëlys Bévan ,&nbsp;Rémi Coltat","doi":"10.1016/j.lithos.2024.107817","DOIUrl":"10.1016/j.lithos.2024.107817","url":null,"abstract":"<div><div>Serpentinization is a ubiquitous hydrothermal alteration of ultramafic rocks. In the Ronda Massif (Andalusia, Spain), which represents the largest body of subcontinental peridotite exposed at the Earth surface, most studies focused on high-temperature deformation and petrology of mantle rocks. Serpentinization remains poorly constrained. Petro-structural and O and H isotope investigations allow us to identify three successive stages of serpentinization. The first stage of serpentinization is characterized by a widespread lizardite mesh-texture. The extent of serpentinization indicates a regional gradient, with a low proportion of serpentine (around 15 %) in the core of the Sierra Bermeja Massif. The second stage corresponds to highly localized serpentinization, characterized by the presence of lizardite, bastite and high content of magnetite. The third stage was intimately associated with brittle deformation, consisting of fibrous veins and a coating network within cataclastic shear zones. Structural analysis of shear veins of the third serpentinization stage enables identification of a regional <em>syn</em>-serpentinization extensional deformation that corresponded to a multi-directional horizontal stretching and a vertical shortening direction (i.e., flattening). All stages of serpentinization display comparable isotopic compositions, with the mean of δ¹⁸O values at ∼ +5.0 ‰ and δD at ∼ −80.5 ‰, suggesting that the two last stages occurred under conditions of fluid-rock interactions that preserved the compositions acquired during stage 1. The fluid source for this stage 1 was likely deeply seated, with a possible contribution of meteoric-derived fluids. Stage 3 serpentinization occurred at 170 ± 50 °C based on magnetite-serpentine isotopic equilibrium. We propose a model of continuous serpentinization that occurred during the rapid exhumation of the Ronda Massif during the Early Miocene period. The <em>syn</em>-serpentinization extensional brittle deformation we document may be compatible either with orogenic thickening (i.e., syn-thrusting) or with early post-thickening collapse.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107817"},"PeriodicalIF":2.9,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142427795","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}

{"title":"Magma through-flow and embedding of magmatic crystals in metasedimentary country rocks adjacent to the Peninsula Granite, Cape Granite Suite (South Africa)","authors":"Russell Bailie ,&nbsp;Musa Mhlanga ,&nbsp;Jürgen Reinhardt ,&nbsp;Deon van Niekerk","doi":"10.1016/j.lithos.2024.107812","DOIUrl":"10.1016/j.lithos.2024.107812","url":null,"abstract":"<div><div>The Sea Point contact in Cape Town, South Africa showcases the interaction between the Malmesbury Group metasedimentary rocks and the intrusive S-type Peninsula Granite of the Cape Granite Suite. The Malmesbury Group, comprising weakly metamorphosed mudstones and siltstones, has been intruded by various granitic injections of varying composition and mineralogical make-up. These granitic injections, displaying diffuse contacts with the country rock and termed “hybrid” granites, indicate varying degrees of assimilation of the country rocks. The injections occurred parallel to the country rock's fabric and anisotropies, particularly along the well-developed S₁ foliation. The granites exhibit compositional variations and contain K-feldspar megacrysts in a variable grain-sized groundmass. Some of these megacrysts are found within the Malmesbury Group, with or without quartzofeldspathic material envelopes. Most researchers agree that large K-feldspar megacrysts in granites develop through near-solidus growth, resulting from prolonged exposure to renewed magma input. However, the origin of K-feldspar and other phenocrysts in the adjacent country rocks is debated, with proposed mechanisms including entrapment due to magma through-flow and in situ growth due to K-metasomatism from granitic magma-derived fluids. This study compares the textures and chemistry of K-feldspar megacrysts in various granite types at the Sea Point contact with those in the Malmesbury Group country rock to determine the origin of the latter. The megacrysts in all lithologies show notable textural and compositional similarities, exhibiting poorly defined compositional zoning and consistent variations in K₂O, Na₂O, and BaO, along with rare earth element concentrations. These attributes suggest that the megacrysts formed through renewed magma injection and prolonged growth involving multiple magma pulses. The study proposes that filter pressing, where melt fractions separate from a crystal mush during crystallisation, occurred during active deformation so that filter pressing was strain-induced. During magma intrusion in a <em>syn</em>- to post-tectonic compressive regime, the melt and associated crystals moved into openings, with the melt fraction more easily mobilised and driven out compared to the crystal fraction during transpression. This left K-feldspar megacrysts embedded or mantled by the country rock. These isolated crystals, with or without associated crystallised magmatic material, mark former magma flow pathways through the country rock, contributing to understanding magma emplacement mechanisms and the formation of the continental crust.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107812"},"PeriodicalIF":2.9,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428471","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}

{"title":"Corrigendum to “Revisiting the formation of lunar anorthosites via the Rb-Sr isotope systematics” [Lithos, volume 486–487, (2024) 107780]","authors":"Qing Zhou ,&nbsp;Heng-Ci Tian ,&nbsp;Liyu Shan ,&nbsp;Sen Hu ,&nbsp;Wei Yang ,&nbsp;Maoyong He ,&nbsp;Lei Zhang ,&nbsp;Yangting Lin ,&nbsp;Xianhua Li","doi":"10.1016/j.lithos.2024.107810","DOIUrl":"10.1016/j.lithos.2024.107810","url":null,"abstract":"","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107810"},"PeriodicalIF":2.9,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656726","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}

{"title":"Spatial and temporal characteristics of volatiles in the Cenozoic mantle beneath eastern China","authors":"Qianling Zhou ,&nbsp;Chenglong Yu ,&nbsp;Yang-Yang Wang ,&nbsp;Dongbo Tan ,&nbsp;Erhao Shan ,&nbsp;Dongyong Li ,&nbsp;Xiaoxia Wang ,&nbsp;Yigan Lu ,&nbsp;Fengtai Tong ,&nbsp;Yilin Xiao","doi":"10.1016/j.lithos.2024.107815","DOIUrl":"10.1016/j.lithos.2024.107815","url":null,"abstract":"<div><div>Subduction of the paleo-Pacific Plate has transported volatiles from the surface to the interior of the Earth and significantly altered the chemical and physical properties of the Cenozoic mantle beneath eastern China. However, the characteristics of volatiles other than H₂O in the Cenozoic mantle remain poorly constrained. To describe the spatiotemporal distribution of volatiles, including S, Cl, and H₂O, in the Cenozoic mantle beneath eastern China, we performed reheating experiments and determined the composition of olivine-hosted melt inclusions from a large area (5.9 × 10⁵ km²) of basalts. Calculations of the mantle-source compositions indicate that the Cenozoic mantle in North China is enriched in S but deficient in H₂O and Cl, relative to that in South China. The distinctive features of volatiles likely arise from the different types of recycled materials in the mantle sources (such as Cl-containing sediments, carbonates, or sulfides in the altered oceanic crust) and their different proportions (from &lt;1.7 % to 7 % of subducted sediments). Both the North China and South China mantles reached high volatile contents at 17.5–11.9 Ma, indicating that the activation of the South China mantle and the destruction of the North China Craton may have occurred simultaneously. These novel findings improve our understanding of mantle evolution beneath eastern China and will help in evaluating the contributions of slab subduction to the spatiotemporal heterogeneity of the lithospheric mantle during the Cenozoic.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107815"},"PeriodicalIF":2.9,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142312922","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}

{"title":"Permian flood basalt protoliths for Jurassic amphibolites and eclogites in SW Iran: Implications for subduction of a magma-rich passive margin","authors":"Rezvaneh Jamali Ashtiani ,&nbsp;Axel K. Schmitt ,&nbsp;Jamshid Hassanzadeh ,&nbsp;Arash Sharifi ,&nbsp;Christina Günter","doi":"10.1016/j.lithos.2024.107811","DOIUrl":"10.1016/j.lithos.2024.107811","url":null,"abstract":"<div><div>Magma-rich passive margins are characterized by mafic intrusions and lavas, making their density comparable to that of the adjoining oceanic crust. As a result, these margins may sink along with the oceanic crust when subduction begins. This possibility warrants further investigation in the geologic record. A fitting example can be found in the Sanandaj-Sirjan Zone (SaSZ), north of the Neotethyan Zagros suture in Iran, where amphibolite to eclogite-facies metabasites are exposed in the Zayanderud high-pressure metamorphic complex. We present U<img>Pb zircon ages, whole rock elemental analyses, and Sr-Nd-Hf isotope data to constrain the ages, chemical and isotopic composition, as well as the tectonic setting of the metabasite protoliths. Ion microprobe U<img>Pb zircon geochronology on petrographic thin sections reveals Early–Middle Permian protolith ages for small (≤10 μm in diameter) zircon crystals that have been metamorphically overgrown in the eclogite. The elemental and Sr-Nd-Hf isotopic compositions of eclogites and amphibolites indicate a continental flood basalt affinity. Trace element and isotopic signatures closely resemble those of widespread Permian flood basalts erupted during breakup of Pangea and the opening of the Neotethys Ocean, with well-studied examples from Oman, the Himalayas, and the Asian Large Igneous Provinces in Tarim, Tianshan, and Emeishan. Earlier investigations suggested that the eclogitization occurred in the Early–Middle Jurassic. Our findings support a scenario where a magma-rich passive margin was established during the Permian and subsequently sank into the mantle at the onset of Jurassic subduction along this segment of the Neotethys. This studied example advocates a poorly explored possibility of the deep sinking of magma-rich passive margins at the beginning of subduction.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107811"},"PeriodicalIF":2.9,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142551924","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}

{"title":"Magnesium isotope constraints on the role of recycled carbonate-rich sediments in the formation of ultrapotassic magmatic rocks at a continental arc setting","authors":"Yu Chen ,&nbsp;Yi-Xiang Chen ,&nbsp;Fatma Gülmez ,&nbsp;Ş. Can Genç ,&nbsp;Guo-Chao Sun ,&nbsp;Zi-Fu Zhao","doi":"10.1016/j.lithos.2024.107816","DOIUrl":"10.1016/j.lithos.2024.107816","url":null,"abstract":"<div><div>The formation of orogenic ultrapotassic magmatism in a subduction setting is still unclear as it requires various co-processing mechanisms. To address this problem, especially to investigate the role of carbonate metasomatism in the mantle source, whole-rock Mg-Sr-Nd isotopic compositions have been measured for ultrapotassic magmatic rocks from the Central Pontides arc, northern Turkey, one of the rare examples of subduction-related ultrapotassic magmatism. These ultrapotassic rocks have relatively low (⁸⁷Sr/⁸⁶Sr)_i (0.70461–0.70687) and ε_Nd(t) (0.3 to 2.6) values and display much lower δ²⁶Mg values (−0.73 ‰ to −0.19 ‰) than the normal mantle. The petrological and geochemical characteristics of the Pontide Ultrapotassic rocks (PUR) indicate that the low δ²⁶Mg values do not result from surficial weathering, diffusion, or magmatic differentiation, but rather reflect the presence of distinct metasomatizing agent in their mantle source. The low Hf/Hf*, Ti/Ti*, Fe/Mn and Ti/Eu ratios, high Ca/Al and (Na₂O + K₂O)/TiO₂ ratios, and lack of significant correlations between δ²⁶Mg and Fe/Mn or (Gd/Yb)_N suggest that the low δ²⁶Mg values cannot be reconciled with the contribution of recycled carbonated eclogites, but are induced by the addition of carbonate-rich sediments to their mantle source. This interpretation is also supported by the significant (La/Yb)_N vs. Ti/Eu and Hf/Sm vs. CaO/Al₂O₃ correlations for the ultrapotassic rocks. Using two end-member mixing calculations of Mg<img>Sr isotopic compositions, the mantle source of PUR is constrained to contain varying proportions of carbonates, mostly of dolomite composition. The addition of carbonate-rich sediments to the mantle may have occurred at depths of 100–150 km as indicated by the trace element compositions of PUR. In this regard, the enrichment of K and other large ion lithophile elements in the ultrapotassic rocks can be induced by the contribution of silicic sediments. Meanwhile, carbonatitic melts can be formed through the partial melting of carbonate-rich sediments in the subducting oceanic slab, which then reacts with the overlying mantle to form carbonated peridotite that serves as the source of ultrapotassic rocks with low-δ²⁶Mg, low-silica, and high LREEs. This study reports for the first time the Mg isotope data of ultrapotassic rocks formed in a continental arc setting and documents that carbonate-rich sediments play an important role in creating such rocks. Future work is needed to test whether this process is common in both oceanic arc and continental arc settings.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107816"},"PeriodicalIF":2.9,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142312809","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}

{"title":"Paleoproterozoic ultrahigh-temperature metamorphism in the Helanshan Complex, North China Craton: New constraints from chloritized sapphirine-bearing pelitic granulites","authors":"Shangjing Wu ,&nbsp;Changqing Yin ,&nbsp;Jiahui Qian ,&nbsp;Hengzhong Qiao ,&nbsp;Xiaoman Wang ,&nbsp;Yanfei Xia ,&nbsp;Yanling Zhang","doi":"10.1016/j.lithos.2024.107814","DOIUrl":"10.1016/j.lithos.2024.107814","url":null,"abstract":"<div><p>Identifying ultrahigh-temperature (UHT) metamorphism in granulite-facies metamorphic terrains and determining its pressure-temperature-time (P-T-t) paths are crucial steps toward elucidating the anomalously hot geodynamic evolution process. This study presents the inaugural identification of chloritized sapphirine-bearing granulites in the Helanshan Complex, located in the western segment of the Khondalite Belt, North China Craton. Three stages of metamorphic evolution were identified based on petrographic analyses, mineral chemistry, and phase equilibrium modelling: the pre-T_max stage involves the presence of rutile-stable phase assemblage, wherein rutile is partially substituted by ilmenite; the T_max stage involves the assemblage of garnet + plagioclase + K-feldspar + sillimanite + spinel ± sapphirine + quartz + ilmenite + melt, as evidenced by microscale (&lt;5 μm) blebs of variably chloritized sapphirine within spinel; and the retrograde cooling stage features the solidus assemblage of garnet + plagioclase + biotite + K-feldspar + sillimanite + cordierite + quartz + ilmenite + melt. Phase equilibrium modelling indicates T_max conditions of 958–1055 °C and 6.4–7.8 kbar, suggesting UHT conditions accompanied by a high geothermal gradient of approximately 150 °C/kbar. Furthermore, a clockwise P-T trajectory was established, involving pre-T_max decompression and post-T_max near-isobaric cooling. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon and monazite U-Pb dating of UHT pelitic granulites produced ages clustering around 1.91 Ga, marking the era of UHT metamorphism within the Helanshan Complex. This discovery broadens the scope of UHT metamorphism and indicates that the entire Khondalite Belt experienced a regional UHT metamorphic event during 1.93–1.91 Ga, which was likely induced by an initial radiogenic heating synergy followed by an augmented mantle heat flux.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107814"},"PeriodicalIF":2.9,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142274268","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}