Lithos最新文献

{"title":"Petrogenesis of Early Cretaceous sodic lamprophyres from Central Tibet: Slab break-off triggers metasomatized lithosphere and asthenosphere interaction","authors":"Lirui Yu ,&nbsp;Nan Wang ,&nbsp;Xudong Ma ,&nbsp;Wei Chen ,&nbsp;Kejun Hou ,&nbsp;Zhibo Liu ,&nbsp;Qingfei Sun","doi":"10.1016/j.lithos.2025.108030","DOIUrl":"10.1016/j.lithos.2025.108030","url":null,"abstract":"<div><div>Lamprophyres are rare but important rocks that can provide crucial information about deep mantle source regions and geodynamic settings. The Bangong–Nujiang collision zone was formed by the collision of the Qiangtang and Lhasa terranes and experienced intense post-collisional magmatism. However, the deep mantle processes and mechanisms involved in this magmatism remain controversial. Here, we present the first complete petrological, geochemical, and geochronological characterization of sodic lamprophyres in the northern Lhasa terrane, central Tibet, with the aim of deciphering their relationship with late Early Cretaceous magmatic flare-up events. These lamprophyres were emplaced at ∼114 Ma. They exhibit sodic alkaline series affinities with high Na₂O contents (2.17–3.52 wt%) and Na₂O/K₂O ratios (1.8–3.8) and are also characterized by variable MgO contents (5.0–7.9 wt%) and Mg# values (52–68); slight enrichment in LREEs ([La/Yb]_<em>N</em> = 4.9–5.9); relatively flat HREE patterns ([Gd/Yb]_<em>N</em> = 1.46–1.53); no Eu anomalies (Eu/Eu* = 0.94–1.04); and Rb, Ba, Th, U, and Pb enrichments as well as Nb and Ta depletions. The samples have relatively low initial ⁸⁷Sr/⁸⁶Sr ratios (0.70848–0.70886) and <em>ε</em>_Nd(<em>t</em>) values (−3.2 − −2.4) and variable zircon <em>ε</em>_Hf(<em>t</em>) values (−4.4 − +10.4). These geochemical characteristics indicate that these rocks were derived from an enriched lithospheric mantle source. However, relatively depleted Hf isotopic compositions and Ti/V (20.2–32.5) ratios are comparable to those of MORB. The calculated melting temperature ranges from 1159 to 1244 °C, with an average of 1183 °C, further supporting the involvement of a high-temperature asthenospheric component. The rapid emplacement and relatively low melting pressure (8.0–10.4 kbar) imply that they formed in an extensional setting. Therefore, we propose that the parental magma of the lamprophyres was generated by the interaction of asthenospheric and metasomatized lithospheric mantle due to slab break-off beneath the Bangong–Nujiang collision zone.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108030"},"PeriodicalIF":2.9,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143561851","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":"Metamorphic evolution and tectonic significance of garnet-bearing amphibolites from the upper valley of the Hatu River, East Kunlun Orogenic Belt","authors":"Xiaohui Liu ,&nbsp;Zeng Lü ,&nbsp;Zhenyu Chen ,&nbsp;Shuguang Song ,&nbsp;Yanjun Guo","doi":"10.1016/j.lithos.2025.108027","DOIUrl":"10.1016/j.lithos.2025.108027","url":null,"abstract":"<div><div>The East Kunlun Orogenic Belt (EKOB), traditionally divided into northern (or Qimantagh Belt), central, and southern segments, has undergone a long and complex evolution. Eclogites exhumed from subduction zones are significant for reconstructing the tectonometamorphic histories of these continental blocks. However, they have not yet been reported from the southern EKOB. In this study, we first identified a suite of garnet-bearing metabasic riverbed cobbles in the upper Hatu valley, southern EKOB, some of which contain calcic clinopyroxene–plagioclase (Cpx–Pl) and/or amphibole–quartz (Amp–Qz) intergrowths typical of omphacite pseudomorphs. The absence of Cpx–Pl symplectite in strongly foliated amphibolites likely indicates complete amphibolitization of clinopyroxene, which may have been greatly enhanced by ductile deformation. The Cpx–Pl symplectite-bearing amphibolites experienced four metamorphic stages: (1) a prograde epidote amphibolite facies stage indicated by primary garnet inclusions, (2) a peak eclogite facies stage with the assemblage of garnet + omphacite + rutile + quartz + amphibole + biotite, (3) a symplectitization stage forming the Cpx–Pl intergrowth, and (4) an amphibolite facies stage forming a kelyphitic rim around garnet. Phase equilibrium modeling supports the eclogite facies conditions of 660 °C–750 °C and 13–16 kbar. Fine-grained garnet and amphibole in thin sodic plagioclase films between quartz grains may have formed as a result of peritectic reactions during partial melting at the eclogite facies stage rather than during decompression. Porphyroblastic epidote embayed by plagioclase and amphibole in the epidote-rich amphibolites likely indicates an interaction between epidote and the intergranular melt. U<img>Pb ages of the metamorphic zircons at ∼460 Ma probably correspond to the Early Paleozoic subduction of the Proto-Tethys Ocean, which may have contributed to the formation of the back-arc basaltic rocks of the Nachitai Group in the southern EKOB. This study supports the Mid-Ordovician as an important growth episode for the multiple subduction–accretionary system of the entire EKOB.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108027"},"PeriodicalIF":2.9,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601612","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":"Transitional chromitites within the Maqsad crust-mantle transition zone of the Semail ophiolite formed above the nascent forearc setting","authors":"Rong-Zhong Bo ,&nbsp;Peng-Jie Cai ,&nbsp;Dong-Yang Lian ,&nbsp;Jing-Sui Yang ,&nbsp;Sobhi Nasir ,&nbsp;Hui-Chao Rui ,&nbsp;Yu-Xiao Lu ,&nbsp;Chu-Qi Cao ,&nbsp;Ahmed E. Masoud","doi":"10.1016/j.lithos.2025.108021","DOIUrl":"10.1016/j.lithos.2025.108021","url":null,"abstract":"<div><div>The Semail ophiolite is a classic example of a well-preserved ophiolite, hosting over 450 documented podiform chromite deposits. This study investigates a transitional chromitite occurrence in the crust-mantle transition zone (CMTZ) of the Maqsad area within the Sumail massif of the Semail ophiolite. The chromitites, enveloped by dunites, exhibit massive and disseminated textures. Host harzburgites, representing upper mantle residues, underwent ∼20–35 % partial melting followed by metasomatism from subducting slab-derived melts/fluids. These peridotites show geochemical affinities with Izu-Bonin-Mariana (IBM) forearc peridotites, indicating a forearc tectonic setting. The Maqsad chromitites, with Cr# values of 54.3–66.2, are classified as transitional chromitites. Their geochemical features resemble chromites crystallized from mid-ocean ridge basalt (MORB) melts. Elevated oxygen fugacity (<em>f</em>_O2) values compared to abyssal peridotites further support their formation in a supra-subduction zone (SSZ)environment. Based on the petrogeological and geochemical characteristics of the host rocks, we propose that the parental magma of the Maqsad transitional chromitites derived from a nascent forearc mantle above an SSZ setting, with MORB-like affinity.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108021"},"PeriodicalIF":2.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143553026","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":"Early miocene adakitic porphyries in the Chagai arc, Pakistan: Petrogenesis, tectonic setting and implications for porphyry Cu-Au mineralization","authors":"Xiu-Quan Miao ,&nbsp;Chuan-Dong Xue ,&nbsp;Xue-Ping Yang ,&nbsp;Yun-Ying Zhang ,&nbsp;Jian-Lin Chen","doi":"10.1016/j.lithos.2025.108023","DOIUrl":"10.1016/j.lithos.2025.108023","url":null,"abstract":"<div><div>Numerous porphyry Cu-Au deposits were formed in the Chagai arc, western Pakistan, but their origin remains debated. To address this issue, we conducted zircon U-Pb dating, zircon Hf-O and plagioclase Sr isotopic analyses, and geochemical characterization of ore-bearing biotite granitic porphyries (BGP) from the Saindak area in the Chagai arc. These BGP, formed during the early Miocene (21.9–21.7 Ma), exhibit adakite-like geochemical characteristics, including high SiO₂ (60.5–67.9 wt%) and low Y (6.41–9.13 ppm) contents, coupled with high Sr/Y (26.2–116) ratios. The depleted Hf (ε_Hf(t) = 2.42–9.73) and mantle-like O (δ¹⁸O = 4.99–6.06 ‰) isotopic compositions of zircon grains, along with depleted Sr ((⁸⁷Sr/⁸⁶Sr)_<em>i</em> = 0.70297–0.70482) isotopic compositions and high anorthite (An = 56.5–69.4 %) contents of plagioclase crystals, suggest that these BGP rocks were derived from an oceanic slab. Slab melting may cause the exceptionally high Cu (667–3060 ppm, average of 1416 ppm) contents of the studied BGP samples, which facilitates the formation of porphyry Cu-Au deposits.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108023"},"PeriodicalIF":2.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143528864","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":"The significance of water in the genesis of ophiolitic chromitites","authors":"Hugh Rollinson","doi":"10.1016/j.lithos.2025.108022","DOIUrl":"10.1016/j.lithos.2025.108022","url":null,"abstract":"<div><div>Many ophiolitic chromitites contain hydrous silicate phases, implying that hydrothermal processes were involved in their genesis. This observation challenges the standard magmatic/ melt-rock reaction model for mantle chromitite genesis. This review explores three possible relationships between hydrous fluids and the genesis of chromitites formed in the mantle section of ophiolites. The models are described and critiqued in the light of our current experimental, geochemical and field-based understanding of ophiolitic chromitites, using in particular evidence from chromitites from the well-studied mantle section of the Oman ophiolite.</div><div><span><span>Matveev and Ballhaus (EPSL, 2002)</span></span> and more recently <span><span>Su et al. (Science China Earth Sci., 2021)</span></span> have proposed an immiscibility model in which chromite is preferentially partitioned into a hydrous fluid and thus separates from the parental silicate melt. Here it is argued that there are problems with the scalability of this model. In addition there are petrographic and geochemical inconsistencies which do not conform to the proposed hydrothermal fluid-silicate melt partitioning.</div><div>Johan et al. (Eur. J. Mineral., 2017) and Arai and Akizawa, (Amer. Mineral., 2014) have championed the view that chromite can be precipitated directly from a hydrothermal fluid. This is evidenced by chromite-diopsidites in the Oman ophiolite. Recent experimental studies also support this view through the complexing of Cr²⁺ in a chlorine-rich fluid. However, this model is also an inadequate explanation for the majority of mantle chromitites because chromite-diopsidite occurrences are extremely rare in the mantle section of ophiolites, of small volume, and the chromitites formed have a different composition from typical ophiolitic mantle chromitites.</div><div>For these reasons, the preferred model and the one advocated in this paper derives from the work of Edwards et al. (GSA Spec Pap. 2000) in which water is present as a dissolved species in the parental melt from which the chromitites form. It is argued that mantle chromitites are associated with hydrous MORB and boninitic melts in which the presence of water modifies the structure of the melt to permit an increased solubility of Cr during partial melting. The model is supported with Cr solubility data from wet mantle melting experiments and from the modelling of Cr partitioning during mantle melting, using data from harzburgites from the mantle section of the Oman ophiolite. As the hydrous melts percolate through mantle harzburgites they become more siliceous through orthopyroxene dissolution triggering chromite crystallisation. The same melts also crystallise the hydrous phases sodic amphibole and micas.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108022"},"PeriodicalIF":2.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143526713","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":"The magma source of the rare earth element-mineralized carbonatite–syenite complexes in the Oligocene Mianning–Dechang belt, western Sichuan, Southwest China","authors":"Yan Liu ,&nbsp;Zengqian Hou ,&nbsp;Huichuan Liu ,&nbsp;Zhiyao Zeng ,&nbsp;Haoyu Luo","doi":"10.1016/j.lithos.2025.108020","DOIUrl":"10.1016/j.lithos.2025.108020","url":null,"abstract":"<div><div>Carbonatite–syenite complexes contain over half of the rare earth element (REE) resources worldwide, particularly the light REEs. These deposits are thought to be mainly sourced from REE-enriched subcontinental lithospheric mantle (SCLM). However, the precise nature of the mantle source is debated due to ambiguous interpretations of Sr–Nd–Pb isotope and trace element data. Four Oligocene REE deposits in the Mianning–Dechang (MD) REE belt in Sichuan Province, China (Maoniuping, Lizhuang, Muluozhai, and Dalucao) are ideal for investigating the magma sources in such deposits. These deposits have well-documented geological features and previously published Li–B–Sr–Nd–Pb isotope data, and contain fresh zircons in syenite (nordmarkites) formed by immiscibility from the carbonatites. Despite the abundant Sr<img>Nd isotope data, distinguishing between metasomatic contributions from the upper continental crust and marine sediments is challenging. To address this, we present zircon Hf<img>O isotope data for the MD REE belt, obtained by laser ablation–multi-collector–inductively coupled plasma–mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry, respectively. We use these data to trace the origins of the REE-enriched magmas. Given the complex geological history of this region, including ca. 260 Myr of subduction, we tested a multi-end-member magma source model that includes depleted mid-ocean ridge basalt mantle (DMM), high- and low-temperature altered oceanic crust (AOC), and marine sediments. Using a Monte Carlo simulation for this multi-end-member mixing, coupled with the longest increasing subsequence algorithm, we modeled the time-dependent contributions of these components during Proto-Tethyan oceanic subduction beneath the Yangtze Craton. Our results suggest that, by the end of subduction, marine sediments contributed approximately 13 %, 24 %, 25 %, and 22 % among these three endmembers to the magma sources of the Maoniuping, Dalucao, Lizhuang, and Muluozhai deposits, respectively. The DMM and AOC were the main components in the source. Although marine sediments that are enriched in REEs relative to DMM and AOC contributed significantly to the REE contents of the lithospheric mantle, our findings indicate that the scale of the REE deposits was not solely controlled by the incorporation of marine sediments. The results indicate the need for a reassessment of the role of marine sediments in the petrogenesis of carbonatite magma and formation of REE deposits.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108020"},"PeriodicalIF":2.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143528863","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":"Quantifying the contribution of sediment recycling in mantle: A case study of Early Cretaceous gabbroic intrusions in the northeastern North China Craton","authors":"Xiang-Yu Yan ,&nbsp;De-Bin Yang ,&nbsp;Wen-Liang Xu ,&nbsp;Feng Wang ,&nbsp;Shuo Wang ,&nbsp;Ke Wu","doi":"10.1016/j.lithos.2025.108016","DOIUrl":"10.1016/j.lithos.2025.108016","url":null,"abstract":"<div><div>Subduction-driven recycling of crustal components plays a crucial role in shaping the compositional heterogeneities of the mantle. However, determining the metasomatic proportion and age of sediment recycling remains challenging owing to the overprinting influence of other slab contributions. This study focuses on two Early Cretaceous (126–123 Ma) gabbroic intrusions from the northeastern North China Craton (NCC), China, which provide insights into how subducted sediments modulate mantle compositions. The olivine gabbro has higher MgO contents and lower FC3MS (FeO^T/CaO - 3MgO/SiO₂) values, suggesting peridotite-derived melts, relative to the gabbro that originates from pyroxenite mantle sources. The two gabbroic intrusions exhibit arc-like trace element distribution patterns, along with enriched whole-rock Sr–Nd and zircon Hf–O isotopic compositions. These characteristics indicate their derivation from fluxed melting of sub-continental lithospheric mantle sources hybridized by melts derived from ∼5 % terrigenous sediments. Based on the three-stage Pb isotopic growth model, the metasomatized time of the mantle sources occurred in the Late Jurassic (160–150 Ma), which provides new geochemical evidence supporting the Late Mesozoic subduction of the Paleo-Pacific Plate beneath the Eurasian continent. Using the program ABS5, we conducted quantitative calculations to estimate the pressure and temperature of sediment melting, with 3.1–3.2 GPa and 838–842 °C. Thus, our findings not only illustrate the specific contributions (i.e., proportion and age) of sediments input into the mantle, while also highlight the significant role of mantle metasomatism driven by recycled sediments in creating mantle compositional heterogeneities.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"504 ","pages":"Article 108016"},"PeriodicalIF":2.9,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143552362","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":"Geochemistry, geochronology, and tectonic aspects of the Angicos plutonism: Insights into equigranular high-K calc-alkaline magmatism in the northern Borborema Province","authors":"Antomat Avelino de Macêdo Filho ,&nbsp;Alisson L. Oliveira ,&nbsp;Eduardo T. Mansur ,&nbsp;Valdecir A. Janasi ,&nbsp;Alanny C.C. Melo ,&nbsp;Francisco G.F. Lima ,&nbsp;Carlos F. Ávila ,&nbsp;Lorenzo Tavazzani ,&nbsp;Alana R. Dantas","doi":"10.1016/j.lithos.2025.108007","DOIUrl":"10.1016/j.lithos.2025.108007","url":null,"abstract":"<div><div>The Borborema Province is renowned for its prominent Ediacaran to Cambrian plutonism, constituting more than 15 % of its total area. Within this context, the Angicos Batholith is a NNE-trending elongated pluton with ca. 250 km², representing one of the largest bodies with equigranular texture in the northern part of the province. On the northwestern margin of the batholith, the Poço da Oiticica Stock forms a N-S elongated intrusion, while the NW-SE semicircular Flores Stock is situated on the northeastern side. Both exhibit compositions and textures like those of the batholith. Despite its volume, the understanding of the granitogenesis in this area remains limited due to a lack of comprehensive data concerning geochemistry, geochronology, and geological-geophysical mapping approaches. In this study, we present a new analytical dataset of Angicos Plutonism combined with remote sensing and aerogeophysical data to assist in geological-structural mapping. The equigranular granites are composed of orthoclase (Or_96-90Ab₄_–₁₀), oligoclase (An_21-17Ab_77-81Or₂_–₁), and Fe-biotite with smaller amounts of magnetite, ilmenite, apatite, allanite, monazite, fluorite, and zircon. These rocks exhibit SiO₂ contents ranging from 70 to 75 wt%, total alkalis from 8.8 to 9.0 wt%, and weakly peraluminous compositions. The batholith has enrichment in large ion lithophile elements and depletion in high-field strength elements. The light rare earth elements content is high [4 ≤ (La/Sm)_<em>N</em> ≤ 11], combined with negative Eu anomalies (Eu/Eu* = 0.4–0.9) and a fractionated spectra of heavy rare earth elements [4.2 ≤ (Gd/Yb)_<em>N</em> ≤ 7.7]. The newly obtained U-Pb age of 584.8 ± 0.9 Ma on the southern side of the body is compatible with the peak of plutonic activity in the northern Borborema Province. The compositional and textural similarity between the Angicos granites and younger neighboring stocks (∼550–530 Ma) highlight a long-lived period of high-K calc-alkaline magmatism in the region, with the Angicos Batholith representing one of the oldest members of this suite. The geochemical signature combined with the presence of xenoliths of banded gneisses along with inherited zircons of the Rhyacian Period, suggests crustal recycling in the region, where metaplutonic rocks of the Caicó Complex would be the main source of granites. The equigranular texture of such a large pluton would be justified by high undercooling rates. In this context, the extensional bridging accommodation mechanism in laterally alternating shear zones emerges as a plausible model for the emplacement of the Angicos Batholith.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108007"},"PeriodicalIF":2.9,"publicationDate":"2025-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143526781","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":"Late Neoproterozoic granitic magmatism in the Doba Basin of Southern Chad: Implications for the crustal evolution of North-Central Africa","authors":"J.G. Shellnutt ,&nbsp;H.T. Tran ,&nbsp;T.-Y. Lee ,&nbsp;M.-W. Yeh ,&nbsp;R.B.-J. Hsieh ,&nbsp;H.-Y. Lee","doi":"10.1016/j.lithos.2025.108015","DOIUrl":"10.1016/j.lithos.2025.108015","url":null,"abstract":"<div><div>The Doba Basin is one of four oil producing basins of southern Chad that developed within the West and Central Africa Rift System during the Late Cretaceous opening of the Central Atlantic Ocean. The Cretaceous basins were built upon older Ediacaran basins that formed after the collision between the Congo-São Francisco Craton and the continental crust of North-Central Africa. Oil exploration drill wells in the Doba Basin (Mouroumar-1, Benoy-W2, Kiagor-1, Djabi-1, Bebalem-1) encountered granitic rocks at depths from 2250 m to 3230 m. The granitic rocks were dated by zircon U<img>Pb methods and yielded ages of 594 ± 4.4 Ma (Benoy), 594 ± 4.2 Ma (Kiagor), 595 ± 4.3 Ma (Bebalem), and 579 ± 4.1 Ma (Mouroumar). The older granitoids are magnesian and metaluminous to weakly peraluminous, and compositionally similar to volcanic-arc granites. The younger granites are magnesian to ferroan and classify as within-plate or post-collisional granite. The magmatic zircon Hf isotopes (ε_Hf(<em>t</em>) = −12.5 to 0.0) and whole rock Nd isotopes (ε_Nd(<em>t</em>) = −3.3 to −8.2) show that all granitoids were derived from an isotopically enriched source. Crystallization pressure estimates from biotite and titanite indicate that they were emplaced in the upper crust (1–4 kbar). The volcanic-arc granitoids likely had lower parental magma temperatures (∼800 °C) than the post-collisional granitoid (∼900 °C). The results from this study along with previously published results demonstrate that contemporaneous (620–590 Ma) volcanic-arc magmatism stretched 1000–1500 km from the Doba Basin through the Guéra Massif to the Ouaddaï Massif and was followed by post-collisional magmatism at ≤580 Ma. The implication is that the southeastern and eastern portions of the Saharan Metacraton were not structurally contiguous with the western and northwestern portions until after ∼590 Ma. Consequently, the continental crust of North-Central Africa is not a coherent craton, but rather it is a composite shield terrane similar to the Arabian Nubian Shield or Central Asian Orogenic Belt.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108015"},"PeriodicalIF":2.9,"publicationDate":"2025-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143526715","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":"Lead isotopes track intracrustal fractionation with implications for crustal thickness","authors":"Priyanjan Datta ,&nbsp;Janne Liebmann ,&nbsp;Christopher L. Kirkland ,&nbsp;Bryant Ware ,&nbsp;David R. Mole","doi":"10.1016/j.lithos.2025.108017","DOIUrl":"10.1016/j.lithos.2025.108017","url":null,"abstract":"<div><div>Lead isotopes provide valuable insight into the geological processes involved in the formation of continental crust, revealing information that may be difficult to access through other isotopic systems. While Lu-Hf (or Sm-Nd) and oxygen isotopes conceptually track mantle extraction or interaction with the hydrosphere, respectively, Pb isotopes are more sensitive to intracrustal processes. Here, we present new in situ LA-MC-ICP-MS K-feldspar and TIMS whole-rock Pb isotope data from I-, S-, and A-type granites covering an east-west transect across major lithotectonic boundaries in the Delamerian and the Lachlan Fold Belts, southeastern Australia. Initial Pb isotopic ratios determined from U- and Th-poor minerals (e.g., K-feldspar) and granite whole-rock samples (corrected for radiogenic Pb ingrowth) show no correlation with granite type nor have a statistically significant relationship with most whole-rock geochemistry and show little correlation with Nd isotopes. However, Pb isotope ratios reveal similar spatial patterns to various proxies of crustal thickness, such as regional gravity free-air anomalies, topographic elevation, and Moho depth, as well as changes in Sr/Y and Eu anomalies, which may be linked to melt extraction depths. These results support an interpretation in which Pb isotope signatures are set in the magma source region within the crustal column, essentially unaffected by later-stage fractionation. Lead isotopes thus effectively distinguish lower crustal, U- and Th-depleted sources from upper crustal, enriched sources. An enigmatic lower crustal Selwyn Block has previously been inferred in central Lachlan Fold Belt. Lead isotope data may provide insight into this block, resolving a U and Th depleted zone aligning with its areal extent, suggesting a previous high-grade melt depletion event. We conclude that granite Pb isotope signatures ultimately track the degree of intracrustal fractionation prior to the final melt extraction, which contributes to building a thickened crust.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"506 ","pages":"Article 108017"},"PeriodicalIF":2.9,"publicationDate":"2025-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143715209","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}