Lithos最新文献

{"title":"Age and origin of the Amdo ophiolite, central Tibet: New constraints on the evolution of the Bangong-Nujiang archipelagic ocean","authors":"Yue Tang ,&nbsp;Qingguo Zhai ,&nbsp;Peiyuan Hu ,&nbsp;Yiming Liu ,&nbsp;Wei Wang","doi":"10.1016/j.lithos.2025.108006","DOIUrl":"10.1016/j.lithos.2025.108006","url":null,"abstract":"<div><div>The central segment of the Bangong-Nujiang suture zone features multiple branching sub-sutures, yet the tectonic characteristics and evolutionary history of the associated ocean basin remain poorly understood. This study presents a detailed analysis of the field geology, geochronology, and petrogeochemical features of the Amdo ophiolite, located in the northernmost part of the suture zone. The Amdo ophiolite preserves a relatively complete sequence of oceanic lithosphere, including mantle peridotites, cumulate gabbros, sheeted dikes, and pillow lavas, arranged from bottom to top. The oceanic crust sequence is unusually thin, measuring less than 3 km, suggesting formation in a restricted oceanic basin. Zircon U-Pb dating of mafic rocks and plagiogranites reveals that the Amdo ophiolite formed during 184181 Ma, consistent with the age of the Dongqiao ophiolite located to its west. Geochemically, the mantle peridotites display refractory compositions akin to forearc peridotites, while the mafic rocks exhibit high MgO, low TiO₂, and rare earth element (REE) patterns similar to N-MORB, with notable depletion in Nb, Ta, and Ti and enrichment in large-ion lithophile elements (LILE). These geochemical features are indicative of supra-subduction zone (SSZ) ophiolites. Combined with evidence from the regional forearc mélange, oceanic crust-type retrograde eclogite, and associated island arc magmatic rocks, the data suggest that the Amdo ophiolite originated from a trench-arc system. It represents the remnants of Early Jurassic forearc extension within the northern branch of the Bangong-Nujiang Ocean. Thus, our study further elucidates the early evolutionary processes of the northern branch within the Bangong-Nujiang archipelagic ocean. It provides crucial insights into the evolution of an archipelagic ocean and the complex orogenic processes involving the multiphase assembly of microcontinents and accretionary terranes.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108006"},"PeriodicalIF":2.9,"publicationDate":"2025-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143526716","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":"Petrogenesis and tectonic implications of Paleozoic S-type granitic gneisses of Nanga Parbat Syntaxis, North Pakistan","authors":"Amjad Hussain ,&nbsp;Kui-Dong Zhao ,&nbsp;Delores M. Robinson ,&nbsp;Sakine Moradi ,&nbsp;Muhammad Sajid ,&nbsp;Hafiz U. Rehman ,&nbsp;Qian Li ,&nbsp;Syed Mumtaz Hussain ,&nbsp;Rahat Ali ,&nbsp;Syed Asim Hussain","doi":"10.1016/j.lithos.2025.108008","DOIUrl":"10.1016/j.lithos.2025.108008","url":null,"abstract":"<div><div>This study integrates in-situ zircon U-Pb and Hf isotope data, and whole-rock geochemical analyses, along with field and petrographic features of granitic gneisses exposed in the Nanga Parbat Syntaxis. The aim is to constrain the petrogenesis and tectonic evolution of these rocks. Field and petrographic observations distinguish the studied rocks into two varieties: leucogranitic gneisses referred as type 1 and augen gneisses referred as type 2. Zircon U-Pb dating of type 1 yields a weighted mean age of ∼460 Ma while type 2 yields an age of ∼480 Ma, indicating that both types were emplaced during the early Paleozoic. Geochemically both types are strongly peraluminous, high-K calc-alkaline, and show high normative corundum, indicating an S-type granite magma source derived from the anataxis of heterogeneous supracrustal metasedimentary rocks. The highly negative εHf(t) values (−29.5 ∼ −8.8) further confirm types 1 and 2 rocks were derived from crustal material without a significant contribution from the mantle. Type 1 rocks are characterized by the presence of tourmaline, high Al₂O₃/TiO₂ (67.3–84.2)_, and low CaO/Na₂O (0.25–0.37) ratios, suggesting their formation through the partial melting of boron-rich metapelites under moderate temperatures (avg. 763 °C, based on Ti-in-zircon thermometry). In contrast, type 2 rocks lack tourmaline, show higher CaO/Na₂O ratios (0.60–0.70), lower Al₂O₃/ TiO₂ ratios (19.3–23.9), and are likely formed from hydration-driven partial melting of metagraywacke at an average temperature of ∼704 °C. The geochemical and isotopic data in this paper, and their comparison with coeval rocks from the Himalaya and other regions, suggest that magma of the studied Paleozoic granites originated from heterogenous metasedimentary sources, likely deposited in a back-arc basin followed by the subduction of the Proto-Tethyan Oceanic lithosphere, followed by slab roll-back and break-off. Such a tectonic setting possibly triggered mafic magmatic underplating and induced partial melting of the back-arc assemblages. Both rock types contain occasionally inherited zircon cores that yield ages of ∼2065 to ∼773 Ma, indicating remnants of earlier crustal growth events. Additionally, a few zircon grains with ages of ca. 53 and 25 Ma could be linked with the Cenozoic India-Asia collision-related magmatism, metamorphism, and post-collision anataxis.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108008"},"PeriodicalIF":2.9,"publicationDate":"2025-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143519643","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":"Structural and metamorphic evolution of Val d'Ala eclogites (Western Alps - Lower Piemonte Zone)","authors":"Manuel Roda,&nbsp;Marco Filippi,&nbsp;Matteo Assanelli,&nbsp;Federico Farina","doi":"10.1016/j.lithos.2025.108005","DOIUrl":"10.1016/j.lithos.2025.108005","url":null,"abstract":"<div><div>The ophiolites of the Piemonte Zone (PZ) are remnants of the Jurassic Alpine Tethys Ocean. Their transformation into eclogites attests to the deep subduction of the oceanic crust beneath the Adria plate during Alpine convergence. The Alpine evolution in the central part of the PZ is still poorly understood, and this work focuses on the structural and thermobarometric study of Val d'Ala eclogites, one of the Lanzo valleys south of the Gran Paradiso Massif. We investigated the petro-structural evolution of eclogites, analyzed their mineral chemistry and whole-rock composition, determined the protolith age using zircon geochronology, and estimated the Alpine P-T path. The protolith of the eclogites can be traced back to basalts with an N-MORB signature. Zircon geochronology indicates a protolith ²⁰⁶Pb/²³⁸U age of 158.5 <span><math><mo>±</mo></math></span> 1.3 Ma, about 7 Myr older than the nearby Fe<img>Ti gabbros. The first tectono-metamorphic stage (D1) developed under eclogite-facies conditions reaching up 2.5 GPa and 480–500 °C, indicating a thermal gradient of 6 °C/km during the Alpine evolution. The second stage (D2) involved the exhumation of the eclogites to 1–1.5 GPa at about 460 °C, under blueschist-facies conditions, while the final stages (D3/D4) occurred under greenschist-facies conditions at about 22 °C/km. Thus, the Val d'Ala eclogites evolved and were exhumed within a cold subduction zone during the burial of the Alpine Tethys Ocean, with final exhumation occurring during the continental collision between the European and Adria plates. The comparison with the other eclogites within the PZ suggests that all these ophiolites represent different oceanic lithospheric slices sampled at various depths and possibly times, recording different structural evolutions during their burial and exhumation in the mantle wedge of the same subduction zone.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108005"},"PeriodicalIF":2.9,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143508175","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":"Zircon and apatite constraints on the key factors controlling porphyry Mo mineralization in the Shijiawan deposit: Implication for Mo metallogeny in the Qinling Orogenic Belt","authors":"Long-Long Chen ,&nbsp;Li Tang ,&nbsp;Peng-Rui Lv ,&nbsp;Ya-Peng Chen ,&nbsp;Tao Zeng","doi":"10.1016/j.lithos.2025.108004","DOIUrl":"10.1016/j.lithos.2025.108004","url":null,"abstract":"<div><div>Porphyry Mo deposits are the most important source of global molybdenum reserves. The late Mesozoic granitic magmatism in intra-continental setting within the Qinling Orogenic Belt (QOB) in central China generated numerous Mo-fertile porphyries (total proven Mo resource of 8.43 Mt) together with barren granites. However, the factors controlling porphyry Mo mineralization potential remain equivocal. Here we present whole-rock geochemistry, zircon U-Pb-Hf and trace elements, and apatite compositions from the Shijiawan monzogranite porphyry, biotite granodiorite porphyry, and mineralized K-feldspar granite porphyry. In conjunction with the data from coeval fertile and barren granitoids in the QOB, we evaluate the key factors including the magma source, water content, oxygen fugacity, and volatiles for the porphyry Mo mineralization. The porphyries of the Shijiawan deposit show emplacement ages of 139–136 Ma and I-type granite affinity, with Sr<img>Nd and Hf isotopes mixing models suggesting a crust-mantle mixed source and involving ∼24 % mantle-derived materials. The mineralized K-feldspar granite porphyries show a higher contribution of mantle-derived materials as indicated by more depleted Hf isotopes and higher REE contents in apatite than those of barren phases. Their higher whole rock La/Yb (39–56) and V/Sc (5.9–12.5), apatite ΣLREE contents, and lower zircon saturation temperatures (average T_Zr = 776 °C) also suggest higher water content (&gt;6 wt%) than barren porphyries. In the QOB, the Late Jurassic to Early Cretaceous Mo-fertile porphyries and barren granites have similar crust-mantle mixed sources, but the porphyries with larger Mo tonnage have higher mantle contribution and higher magma water content leading to efficient fluid exsolution, as recorded by the extremely low Cl content of apatite crystallized in residual melt. The relatively high fluorine (F) content and occurrence of fluorite indicate that F can effectively promote Mo mineralization. In addition, both fertile porphyries and barren granites show consistently high oxygen fugacity (ΔFMQ = 0–2, Ce⁴⁺/Ce³⁺ &gt; 100) and S content (&gt; 715 ppm). The higher mantle contribution, magma water content, and F are probably the key controlling factors for porphyry Mo mineralization in this region. The comparable oxygen fugacity and sulfur content of the fertile and barren intrusions suggest that although these factors are prerequisites for mineralization, but might not be the prime controlling factors of the porphyry Mo potential.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 108004"},"PeriodicalIF":2.9,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143454817","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 and fertile metavolcano-sedimentary sequence facilitated epigenetic Cu mineralization in the Jianglang Dome, southeastern Songpan-Ganze Orogen","authors":"Yanpei Dai ,&nbsp;Yudi Zhu ,&nbsp;Shengxian Liang ,&nbsp;Qing Zhou","doi":"10.1016/j.lithos.2025.107996","DOIUrl":"10.1016/j.lithos.2025.107996","url":null,"abstract":"<div><div>The Jianglang Dome in the southeastern Songpan-Ganze Orogen, contains a metavolcano-sedimentary sequence (Liwu Group) which hosts high-grade stratiform Cu deposits. Here we report geochemical, chronological and isotopic data of the Liwu Group, to explore the petrogenetic model, metal fertility and basement nature. This sequence is composed of metasedimentary and intercalated metabasic rocks, which contain detrital zircons and xenocrysts with U-Pb ages of 2812–540 Ma (<em>n</em> = 159). Among them, several zircons yield three discordia curves with lower intercepts of 547 Ma (<em>n</em> = 8), 543 Ma (<em>n</em> = 19) and 548 Ma (<em>n</em> = 16). Besides, the youngest concordant zircons show magmatic affinity, and have a weighted mean age of 544.5 Ma (<em>n</em> = 11). These age data are coeval with ca. 545 Ma arc magmatism in the Northern Gondwana, and we assign a Late Neoproterozoic age of ca. 544.5–538.8 Ma for the Liwu Group protoliths. This result, according to a chalcopyrite Re-Os isochron age of 549 ± 11 Ma (<em>n</em> = 5), indicates syngenetic mineralization. The metabasic rocks show depletion in HFSE, MORB-like REE patterns, whole-rock positive ε_Nd(t) values of +11.3 to +6.2, and varying zircon ε_Hf(t) values of +12.8 to −17.9. These rocks were thus derived from high-degree melting of spinel lherzolite, and suffered slightly crustal contamination. The metasedimentary rocks have moderate weathering (CIA = 82.8–54.4), moderate maturity (ICV = 1.05–0.72), whole-rock negative ε_Nd(t) values of −9.0 to −9.8, and wide zircon ε_Hf(t) values of +12.0 to −20.3; they were fed from adjacent continental blocks and volcanic arc. Our integrated data suggest that the Liwu Group protoliths were formed in an incipient back-arc basin along the Gondwana margin. Metabasic and metasedimentary rocks in this basin, were fertile in metal elements (e.g., Cu and Co) and thus facilitated epigenetic mineralization. Combined with regional comparison, our results indicate further mineralization potential in the analogous domes of the Songpan-Ganze Orogen.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107996"},"PeriodicalIF":2.9,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143429902","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":"New U-Pb baddeleyite ages and geochemistry of mafic rocks of Matthews Ridge, NW Guyana: Extension of the Paleoproterozoic Avanavero Large Igneous Province","authors":"B. Borba de Carvalho ,&nbsp;B. Cousens ,&nbsp;K. Chamberlain ,&nbsp;R. Ernst ,&nbsp;C. Hunter","doi":"10.1016/j.lithos.2025.107982","DOIUrl":"10.1016/j.lithos.2025.107982","url":null,"abstract":"<div><div>Avanavero mafic dykes and sills are widespread in the Amazonian craton, South America. Although the complete extent of Avanavero magmatism is currently unclear, similar intrusions have been found in places where it had not been previously mapped such as Matthews Ridge, NW Guyana, the focus of this study. We present new geochemical, U-Pb geochronology, and Sm-Nd isotopic data for Matthews Ridge dykes and sills, and a comparison with Avanavero samples from the literature. Our new in-situ U-Pb analysis on baddeleyite grains by SHRIMP yielded an age of 1787 ± 12 Ma, which overlaps within error both the SHRIMP and the ID-TIMS ages reported in the literature and confirms that the unmetamorphosed dolerites from NW Guyana are part of the Avanavero large igneous province (LIP) event. Geography and geochemistry indicate the presence of two groups of Avanavero mafic intrusions. Group 1 includes occurrences in the north of the Guiana Shield (including the units in Matthews Ridge) and are characterized by mostly low Ti concentrations; Group 2 is limited to occurrences in southern Guiana Shield and have high Ti concentrations. Fractional crystallization pathways differ between the groups, with olivine playing a significant role for Group 1, and olivine + clinopyroxene + plagioclase for Group 2. Distinct Ca/Al ratios may suggest different parental magma and varying degrees of crustal contribution within Group 1. The isotopic data suggest that Group 1 and Group 2 are cogenetic and represent different magma batches that came from the same source by potentially different fractionation paths. The low negative to low positive ɛNd values, together with low Nb/Yb, indicate that the samples from both groups are consistent with a continental intraplate setting where primary magmas were contaminated by the lithospheric mantle previously metasomatized during an earlier subduction event.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107982"},"PeriodicalIF":2.9,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143438079","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":"Continental crustal growth and thickness changes caused by the Paleo- to Neo-Tethys Ocean transition: Evidence from the Early Jurassic magmatism in the Lhasa terrane","authors":"Jia-Jun Zhang ,&nbsp;Chao-Ming Xie ,&nbsp;Meng-Long Duan ,&nbsp;Hong-Can Chen ,&nbsp;Xi-Tai Bai ,&nbsp;Ming-Wei Xu ,&nbsp;Zhe Shi","doi":"10.1016/j.lithos.2025.107994","DOIUrl":"10.1016/j.lithos.2025.107994","url":null,"abstract":"<div><div>The Late Triassic–Early Jurassic is a significant period for the evolution of the Paleo-Tethys to Neo-Tethys Ocean on the Tibetan Plateau, which includes complex geological processes of Tethys Ocean plate subductions and continent-arc-continent collisions. It is also an important period for the formation and evolution of the crust of many terranes (such as the Lhasa and South Qiangtang terranes) in the Tibetan Plateau. As a probe to understand the composition and structure of the crust, igneous rocks play an important role in improving our understanding of continental crustal formation and evolution. In this study, zircon U-Pb dating, zircon Hf isotopes, and the whole-rock geochemistry of Early Jurassic magmatic rocks in the Tangjia-Sumdo area of the Lhasa terrane of the Tibetan Plateau were studied. The results indicate that the compositions are granite (187.4 ± 1 and 196.5 ± 1 Ma), granite porphyry (196.0 ± 1 Ma), granodiorite (196.4 ± 1 Ma), quartz monzonite (188.1 ± 1 Ma), and gabbro (182.8 ± 1 Ma). The intermediate-acidic rocks (197–187 Ma) are all I-type granites and the products of the mixture of crust- and mantle-derived magma. The gabbro (∼183 Ma) is derived from the depleted mantle, which is the product of the partial melting of spinel and garnet lherzolites. Based on the geochemical data of intermediate-acidic magmatic rocks from the Triassic to Jurassic in the Lhasa terrane, the changes in the Sr/Y, (La/Yb) _N, Dy/Yb, and Sm/Yb values indicate that the crust of the Lhasa terrane thickened in the Late Triassic (240–200 Ma) and thinned in the Jurassic (200–160 Ma). We suggest that in the Late Triassic (240–200 Ma), the Sumdo Paleo-Tethys Ocean closed and the collisional orogeny between the southern and northern Lhasa terrane led to crustal thickening. The intermediate-acidic rocks (197–187 Ma) are the products of the break-off of the Sumdo Paleo-Tethys Ocean Plate. The gabbro (∼183 Ma) is formed by the intrusion and condensation of magma formed by the partial melting of the mantle wedge metasomatized by subducted sediments in an active continental margin, which is the product of the northward subduction of the Neo-Tethys Ocean. The transition between the Paleo- to Neo-Tethys ocean is an important mechanism for the growth and thickness changes of the crust in the Late Triassic–Early Jurassic of the Lhasa terrane, potentially contributing significantly to the vertical growth and change of the continental crust in the subduction zone.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107994"},"PeriodicalIF":2.9,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143430012","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":"Reconstruction of Cretaceous-Eocene arcs along the southern Asian margin under Neo-Tethyan subduction","authors":"Yongmin Liu ,&nbsp;Weiming Fan ,&nbsp;Touping Peng ,&nbsp;Rendeng Shi ,&nbsp;Shengsheng Chen ,&nbsp;Pengpeng Huangfu","doi":"10.1016/j.lithos.2025.107995","DOIUrl":"10.1016/j.lithos.2025.107995","url":null,"abstract":"<div><div>The distribution and episodic magmatism of the southern Asian continental arc since the Cretaceous remains unclear. Here, we systematically compiled zircon U<img>Pb ages and Hf isotopic data sets, including magmatic rocks exposed on surface, detrital zircons from erosion of magmatic rocks, and xenocrystal zircons entrapped by Cenozoic volcanics from deep magmatic rocks, to elucidate these questions. Magmatic flare-up at 140–110 Ma occurred from central and northern Lhasa through eastern Tengchong to Shan Scraps, which resulted from the combination of diachronous closure of Bangong-Nujiang Tethys Ocean and subduction of a consolidated Neo-Tethys Ocean from Lhasa to Shan Scraps. During late Cretaceous-Eocene times, an extended Neo-Tethyan continental arc was built on the southern Asian margin from southern Lhasa, through Tengchong-Shan Scarps to Sumatra, excluding West Burma. The continental arc shows spatiotemporal variations in magmatism across different sections. Magmatism in eastern southern Lhasa and Sumatra is dominated by juvenile crust growth with flare-ups at 105–85 Ma and 65–45 Ma. In contrast, magmatic flare-ups at 75–45 Ma and ancient crust reworking are recorded in western southern Lhasa, Tengchong, and Shan Scraps. The spatial and temporal variations in magmatic flare-ups of Neo-Tethyan continental arc are probably related to asynchronous rollback of the Neo-Tethyan slab under different sections. During late Cretaceous-early Paleocene times, the multi-stage changes of Neo-Tethyan slab dip caused asynchronous extension-compression cycles on southern Asian continental margin.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107995"},"PeriodicalIF":2.9,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143422096","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":"Origin, petrogenesis and tectonic implications of the Jiasha potassic intrusive complex in the giant Gejiu SnCu polymetallic field, SW China","authors":"Zhi Shang ,&nbsp;Yongqing Chen","doi":"10.1016/j.lithos.2025.107993","DOIUrl":"10.1016/j.lithos.2025.107993","url":null,"abstract":"<div><div>The potassic intrusive complex is a series of mafic to felsic rock assemblages with high potassium content and is characterized by large amounts of K-feldspar, plagioclase, biotite and, hornblende. The Jiasha potassic intrusive complex (JPIC) comprises monzogabbro, porphyritic monzonite, quartz monzonite, and monzogranite. The zircon U<img>Pb dating shows that the ages of monzogranite are 86.5–87.0 Ma. The ages of monzogabbro, porphyritic monzonite, and quartz monzonite are 85.7–86.9 Ma, 79.1–83.3 Ma, and 77.2–78.0 Ma. The JPIC belongs to metaluminous to weak peraluminous and show affinities of shoshonite. The JPIC have high (⁸⁷Sr/⁸⁶Sr)i values (0.7097–0.7118) and a wide range of εNd(t) values (−5.03 to −8.24). The zircon ¹⁷⁶Hf/¹⁷⁷Hf isotopic ratios are homogeneous (0.2825–0.2827), εHf(t) values vary from −2.1 to −7.1. The ratios of Pb isotope are: (²⁰⁶Pb/²⁰⁴Pb)<em>i</em> = 18.1180–18.5021, (²⁰⁷Pb/²⁰⁴Pb)<em>i</em> = 15.6180–15.7681, (²⁰⁸Pb/²⁰⁴Pb)<em>i</em> = 38.7160–39.3672. The whole-rock geochemical, zircon Hf and whole-rock Sr-Nd-Pb isotopic characteristics, together with mineral composition collectively suggest that the JPIC resulted from fractional crystallization and varying degrees of crustal contamination of enriched lithospheric mantle. The depletion of Nb, Ta and Ti in JPIC is inherited from the source region, which may be caused by the infiltration of slab-derived fluid or melt into the mantle when the Paleo-Pacific subducted to the South China. The late Cretaceous magmatism and mineralization activities in Gejiu is the product of the subduction of the Palaeo-Pacific Plate beneath the Eurasian continent, which probably formed under an Andean-type active continental margin setting.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"502 ","pages":"Article 107993"},"PeriodicalIF":2.9,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143488956","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":"Melting of amphibole-apatite-rich metasomes in the continental mantle and comparison of melt compositions with natural igneous rocks","authors":"Stephen F. Foley ,&nbsp;Isra S. Ezad ,&nbsp;Chutian Shu ,&nbsp;Michael W. Förster","doi":"10.1016/j.lithos.2025.107976","DOIUrl":"10.1016/j.lithos.2025.107976","url":null,"abstract":"<div><div>The source regions of alkaline igneous melts are thought to be mixtures of peridotite, pyroxenite and hydrous ultramafic rocks, but relatively few melting experiments are available for the last of these rock groups. Here, we expand the scope of experimental results on hydrous ultramafic rocks to assemblages rich in Ca-amphibole and apatite, which are found as xenoliths in eastern Australia. Experiments were conducted at 15 kbar on five hydrous ultramafic mineral assemblages; four consisted of equal amounts of Ca-amphibole and apatite, some with minor clinopyroxene and/or phlogopite. A fifth mix consisted of 50 % each of mica and clinopyroxene, but with lower Mg# (Mg/(Mg + Fe)) than in previous experiments. Results show that Ca-amphibole melts rapidly and completely within 50–100 °C of the solidus, producing melts with melilitite-nephelinite compositions similar to the amphibole. Apatite contribution to the melt is minor (P₂O₅ = 2.1–4.7 wt%) and clinopyroxene crystallises as a peritectic phase. These melts are distinct from those produced from mixtures containing alkali amphibole+phlogopite in having much lower SiO₂ (35–40 wt%) and low K₂O/Na₂O, but higher CaO and Al₂O₃. Melts of mica clinopyroxenites have intermediate SiO₂ (41–47 wt%) and much higher K/Al.</div><div>Trace element patterns for incompatible elements show that abundances for most elements are much lower than in natural nephelinites and melilitites as long as residual apatite retains elements with high D^ap/melt, but incompatible trace element abundances approach those of natural rocks if apatite melts out. Hydrous minerals exert strong control on many first-row transition elements (especially Ni and Cr) and may sequester these in the proximal parts of vein systems, removing them efficiently from migrating melts. The melting points of all hydrous ulltramafic rocks, whether rich in phlogopite, Ca-amphibole or K-richterite, are below that of water-undersaturated peridotite. High degrees of melting occur quickly if amphibole is abundant, and so significant amounts of melt may be mobile at temperatures below or close to the solidus of peridotite.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"500 ","pages":"Article 107976"},"PeriodicalIF":2.9,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143395797","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}