Lithos最新文献

{"title":"Identification of fractionation processes in the Himalayan leucogranites-Case study from the Nyalam region","authors":"Lei Yang ,&nbsp;Calvin F. Miller ,&nbsp;Jia-Min Wang ,&nbsp;Xiao-Chi Liu ,&nbsp;Fu-Yuan Wu","doi":"10.1016/j.lithos.2024.107876","DOIUrl":"10.1016/j.lithos.2024.107876","url":null,"abstract":"<div><div>As the product of a collisional belt, Himalayan leucogranites provide insights into the geodynamic and thermal evolution of tectonically thickened crust. Nevertheless, the petrogenesis of these leucogranites is still a much-debated topic. They are typically interpreted as the primary melt formed by partial melting of the Greater Himalayan Crystalline Complex (GHC). There is, however, another view that they are the products of fractional crystallization of less evolved parent magmas. This study aims to explore these competing petrogenetic models. We collected biotite granite, two-mica granite, tourmaline granite, and garnet granite in the Nyalam region for mineralogical and geochemical studies. The granites occur as small laccoliths, sills, and dikes in the upper GHC and the South Tibet Detachment System (STDS). The plagioclase in biotite granite is oligoclase and andesine (An &gt;20) but is more sodic (An &lt;20) in other rocks. From biotite granite to two-mica granite to tourmaline granite, Mg and Ti in biotite and Zr/Hf in zircon gradually decrease, and Al^VI and <em>X</em>_<em>Fe</em> in biotite and Hf in zircon increase correspondingly. Garnet is typically euhedral and spessartine-rich (spessartine &gt;30 wt%), and it only appears in garnet granite, suggesting an increase of Mn/(Fe + Mg) in the melt. These variations suggest that biotite granite is the least evolved rock, and that two-mica granite, tourmaline granite, and garnet granite are increasingly fractionated. This fractionation trend is supported by trace element compositions. Rb-Sr-Ba trace element modeling suggests that the feldspars (plagioclase and k-feldspar) are the main fractionated minerals. Zr<img>Hf modeling indicates that the decrease of Zr/Hf ratio in the melt is related to the fraction of zircon fractionated, which is controlled by the change of temperature and melt composition. Additionally, very high Rb/Sr (&gt;20), low Zr/Hf (&lt;20), and strongly negative Eu anomaly (0.2) in garnet granite strongly suggest that the melt experienced extensive fractionation. Compiled Himalayan leucogranite geochemistry presents a similar pattern to our data and modeling result, suggesting that the variety of Himalayan leucogranites might relate to fractional crystallization. In addition, the composition of leucogranites in the Nyalam is a function of spatial position and age. The leucogranites that were produced during the activity of STDS and developed close to STDS have more evolved compositions, indicating that the development of STDS might have played an essential role in the differentiation of leucogranite in the Himalaya.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107876"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Accessory minerals fingerprint post-collisional anatectic metamorphism in continental collision zones","authors":"Yong-Jie Yu ,&nbsp;Ren-Xu Chen ,&nbsp;Qiong-Xia Xia ,&nbsp;Zhi-Hui Mu ,&nbsp;Zhuang-Zhuang Yin ,&nbsp;Guo-Chao Sun","doi":"10.1016/j.lithos.2024.107875","DOIUrl":"10.1016/j.lithos.2024.107875","url":null,"abstract":"<div><div>Mineral behavior during anatectic metamorphism is a direct factor controlling the chemical and isotopic compositions of melts and residues. However, the mechanism that causes disequilibrium melting remains poorly understood. A combined study of petrological, geochronological and geochemical analyses was carried out on a stromatic migmatite outcrop, the Luoerling migmatite in the North Dabie zone. The in-source leucosomes and leucocratic veins are products of in situ partial melting and later magmatic intrusion, respectively. The finding of Neoproterozoic, Late Triassic and Early Cretaceous zircons suggests that the migmatites have Neoproterozoic protoliths, and experienced eclogite-facies metamorphism during collisional orogeny and anatectic metamorphism in the post-collisional stage. The occurrence of peritectic amphibole suggests that anatectic metamorphism mainly occurs through biotite hydration melting. The occurrence of orthopyroxene and clinopyroxene indicates local dehydration melting under granulite-facies conditions. Leucosomes show considerably higher ⁸⁷Sr/⁸⁶Sr_i, but lower ε_Nd(t) and ε_Hf(t) values than the corresponding melanosomes. Such isotopic differences between leucosomes and melanosomes result mainly from the influx of external fluids derived from the surrounding eclogites and gneisses, indicating a coupled dehydration-hydration mechanism in the continental subduction zone. Peritectic and anatectic zircon, monazite, titanite and apatite that formed during anatectic metamorphism exhibit different petrological and geochemical characteristics. Peritectic and anatectic accessory minerals in the leucosomes and leucocratic veins exhibit smaller variations in Nd-Hf isotopes than those in the melanosomes, suggesting that the anatectic melts were homogenized during transport. Differential dissolution and growth of monazite, titanite and apatite affect the Sm-Nd isotopes of residues and melts during anatectic metamorphism. The dissolution of apatite plays a significant role in the hydration melting of metagranite. The continuous dissolution of relict zircon during cooling/transportation of melt results in decreased ε_Hf(t) values in anatectic zircon, whereas the incomplete dissolution of relict zircon results in whole-rock Hf-Nd decoupling. The difference in Nd-Hf isotopes among whole-rock and different genetic minerals can distinguish between dehydration and hydration melting. Therefore, this study highlights that a combination of multiple isotope analyses on whole-rock and accessory minerals may be conducive to understanding not only the mechanism and process of disequilibrium melting but also the nature of anatectic metamorphism in collisional orogens.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107875"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The behaviour of scandium during crustal anatexis: Implications for the petrogenesis of Sc-enriched granitic magma","authors":"Tom Andersen ,&nbsp;Marlina A. Elburg","doi":"10.1016/j.lithos.2024.107874","DOIUrl":"10.1016/j.lithos.2024.107874","url":null,"abstract":"<div><div>Scandium (Sc) is a compatible element in mafic silicate minerals, in particular amphibole, garnet and clinopyroxene, and is enriched in ultramafic rocks. Nevertheless, its concentration is also sufficiently high in some evolved granites and granite pegmatites to form minerals with essential Sc. In some granitic occurrences, Sc-bearing minerals occur in miarolitic cavities, indicating the importance of late- to post-magmatic fluids. In contrast, some granite pegmatites have thortveitite (Sc₂Si₂O₇) and other Sc-rich minerals, including Sc-enriched garnet as part of evolved <em>magmatic</em> mineral assemblages. The maximum Sc concentration in garnet in thortveitite-bearing, Mesoproterozoic granite pegmatites of probable anatectic origin in South Norway is ca. 2000 ppm, corresponding to ca. 100 ppm in a coexisting silicate melt. As for any trace element, the behaviour of Sc during crustal anatexis is controlled by the amount of melt formed and the mineralogy of the solid residue. The melting process can be modelled from thermodynamical data on solids and melts for given protolith compositions, temperature and pressure. Simulations in a range of mafic/ultramafic to felsic systems show that mafic protoliths will form Sc-depleted anatectic melts, and correspondingly Sc-enriched solid residues under relevant pressure and temperature conditions (2-10 kbar, 700-800 °C). Limited enrichment in melt relative to protolith is only seen in granodioritic-tonalitic bulk compositions, reaching maximum concentrations of 30–60 ppm. The effect of fluorine during melting and subsequent fractionation is to lower the solidus temperature, depolymerise the silicate melt, and lower partition coefficients for Sc between mafic silicate minerals and felsic melt. Contamination with mafic material has only limited effect, as it will eventually sequester Sc into hybrid mafic silicate mineral assemblages and lead to reduction of the Sc concentration of the remaining melt fraction. Further increase of the Sc concentration requires fractional crystallisation of minerals with low <em>K</em>_D, i.e. mainly feldspar minerals and quartz, which may be facilitated by selective, local contamination by quartz and feldspar from granitic country rocks.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107874"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early Cretaceous to Eocene magmatic evolution of Livingston Island, South Shetland Archipelago: Geochronological and isotope geochemical constraints from intrusive suites","authors":"Şafak Altunkaynak ,&nbsp;Ercan Aldanmaz ,&nbsp;Stefan Velev ,&nbsp;Margaret Forster ,&nbsp;Jin-Hui Yang","doi":"10.1016/j.lithos.2024.107877","DOIUrl":"10.1016/j.lithos.2024.107877","url":null,"abstract":"<div><div>The magmatic products exposed across Livingston Island comprise a part of the South Shetland magmatic arc built on an active continental margin. The main magmatic phases of Livingston Island include the Early to Late Cretaceous plutonic and volcanic rock associations, the Eocene plutons, and some sporadically distributed intrusions of Paleocene to Eocene dykes. The intrusions were emplaced into the strongly deformed turbiditic sedimentary rocks of the Miers Bluff Formation. ⁴⁰Ar<img>³⁹Ar and zircon U<img>Pb geochronologic data presented here define four distinct episodes of intrusive activity represented by the emplacement of the Hesperides (125 Ma), the Cerro Mirador (104–97 Ma), the Siddons Point (80 Ma) and the Barnard Point suites (42 Ma), in addition to some dyke intrusions with emplacement ages of 105 to 40 Ma. The intrusions are represented by mafic to intermediate compositions characterized by middle potassic, calc-alkaline affinities, with only a few samples from the Eocene activity exhibiting tholeiitic character. Trace element, Sr-Nd-Pb isotope and zircon Hf isotope variations indicate magma generation in a subduction setting with extensive involvement of continental crust-derived melts for the Early to Late Cretaceous activity. The effects of crustal input on melt chemistry appear to have diminished in time, especially from the Paleocene onwards, leading to magma generation with typical oceanic island arc geochemical signatures. This change in melt chemistry is likely partly related to the roll-back induced overriding plate extension which resulted in a time-integrated increase in the rate of melt movement and a decrease in the residence time in crustal levels. Slab steepening caused by the systematic decrease in plate convergence rate led to an enhanced involvement of isotopically depleted mantle component, producing a heterogeneous source with variable subduction signature.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107877"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746511","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":"East–west-trending tearing of the Indian slab beneath the eastern Tibetan Plateau: Insights from Eocene–Oligocene potassic adakite-like granites in western Yunnan","authors":"Yang Wang ,&nbsp;Hongrui Zhang ,&nbsp;Zengqian Hou","doi":"10.1016/j.lithos.2024.107878","DOIUrl":"10.1016/j.lithos.2024.107878","url":null,"abstract":"<div><div>Large-scale Eocene–Oligocene potassic adakite-like granites predominantly occur between 25° N and 27° N, north of the Ailaoshan suture in western Yunnan, eastern Tibetan Plateau. However, limited interpretations of their spatial characteristics hinder our understanding of the tectonic evolution in this region. Herein, we present new petrographic analyses, zircon U<img>Pb ages, whole-rock major and trace element compositions, Sr<img>Nd isotopic data and zircon Hf isotopic mapping for these granites. Zircon U<img>Pb ages indicate that the adakite-like granites were emplaced at approximately 37.1–33.6 Ma. These granites exhibit high-K calc-alkaline compositions, enriched light rare earth elements and significant depletion in heavy rare earth elements, characterised by high Sr contents (667–1795 ppm), Sr/Y ratios (35–158) and La/Yb ratios (13–62), alongside low Y (8.2–23.3 ppm) and Yb (0.71–1.13 ppm) contents. The adakite-like granites possess high initial ⁸⁷Sr/⁸⁶Sr ratios (0.70596–0.70687) and low ε_Nd(t) values (−5.73 to −0.65), with two-stage depleted mantle model ages (T_DM²) ranging from 1.3 to 0.9 Ga. Their zircon ε_Hf(t) values range from −5.1 to +0.7, with Neoproterozoic T_DM² ages of 1.4–1.1 Ga. Notably, these adakite-like rocks in western Yunnan exhibit an eastward decrease in zircon ε_Hf(t) and whole-rock ε_Nd(t) values. By integrating these findings with the Hf isotopic mapping results, we suggest spatial heterogeneity in lower crustal composition in western Yunnan. The lower crust in the western Yangtze block comprises Neoproterozoic arc roots, while the lower crust of the Simao block represents a superposition of Neoproterozoic and Permian–Triassic arc roots. Based on the abrupt changes in angle and depth of the eastward-subducting Indian slab, along with the spatial characteristics of the Eocene–Oligocene magmatism, we propose that east–west-trending tearing of the subducted Indian slab occurs along approximately 26° N beneath the eastern Tibetan Plateau.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107878"},"PeriodicalIF":2.9,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142720897","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":"Boron-metasomatism and fluid evolution revealed by the chemical and boron isotopic compositions of tourmalines from the Lhozhag area, Eastern Himalaya","authors":"Lining Cheng ,&nbsp;Chao Zhang","doi":"10.1016/j.lithos.2024.107879","DOIUrl":"10.1016/j.lithos.2024.107879","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The interaction between boron-rich (B-rich) fluid and metamorphic rocks, along with the induced tourmalinization, has been widely observed in metamorphic and magmatic-hydrothermal processes. This interaction may significantly influence the formation of ore deposits and petrophysical properties of crustal rocks. However, chemical exchange and element transformation during the boron-metasomatism process are still not clear. In this study, we present a detailed textural and geochemical study of tourmalines and other minerals from tourmaline-rich veins and their host rocks in the Lhozhag area, Eastern Himalaya. Two zones with different mineral assemblages were recognized in the tourmaline-rich veins: the Pl-Qtz zone in the core and the Tur-Ms zone in the rim. Petrographic evidence shows that the tourmaline-rich veins were produced by reactions between the host rocks (i.e. biotite schist) and B-rich fluids. Tourmaline grains show compositional zonation, and the core, mantle, and rim have distinctive major and trace elemental, and boron isotopic compositions. The core of tourmaline (Tur-C) is characterized by the highest Mg/(Mg + Fe) ratio and Sc, V, and Cr concentrations, as well as the lowest Ca, Ti, Mn, Li, Be, and Zn concentrations. The mantle of tourmaline (Tur-M) shows a continuous transition from Tur-C in both colour and composition, which might result from the metasomatic system evolving from wall-rock-controlled to fluid-controlled. The high Li, Zn, and Mn concentrations in Tur-M indicate that the involved fluids (first-stage fluid) were likely magmatic in origin. The rim of tourmaline (Tur-R) is texturally and compositionally homogeneous, generally with intermediate Mg/(Mg + Fe) ratios and Ca, Ti, Li, Sc, V, and Zn concentrations, as well as the lowest Sc, Cr, Sn, and Ba concentrations relative to both Tur-C and Tur-M. The sharp compositional contrast between Tur-M and Tur-R at their boundary suggests an injection of external metamorphic fluid (second-stage fluid). Ti-in-quartz thermometry results show that the temperature of fluid-rock interaction decreases from 700 °C for the formation of Tur-C to 500 °C for the formation of Tur-R. Based on fluid-tourmaline trace element partitioning coefficients at the above temperatures and measured tourmaline compositions, we reconstructed the compositions of both the first-stage magmatic and the second-stage metamorphic fluids. The extremely high Li concentrations (up to 1700 ppm) in the first-stage magmatic fluids reflect the enrichment of Li in the Lhozhag leucogranite magma, which is consistent with the occurrence of spodumene-bearing pegmatite in the Lhozhag area. The relatively high Li concentrations in both the second-stage metamorphic fluid (up to 1000 ppm) and biotite (ca. 2000 ppm) from wall rocks suggest that the biotite-rich metapelite could supply abundant Li to fluid during fluid-rock interaction. The boron isotopic composition of tourmaline also shows a systematic change, with th","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107879"},"PeriodicalIF":2.9,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746512","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":"Apatite geochemical indicators for magma mixing and fractional crystallization in the origin of A-type granite","authors":"Bao-Quan Zhou ,&nbsp;Jin-Hui Yang ,&nbsp;Jin-Feng Sun ,&nbsp;Hao Wang ,&nbsp;Yu-Sheng Zhu ,&nbsp;Ya-Dong Wu ,&nbsp;Qing-Feng Mei ,&nbsp;Lei Xu ,&nbsp;Jing Ran","doi":"10.1016/j.lithos.2024.107873","DOIUrl":"10.1016/j.lithos.2024.107873","url":null,"abstract":"<div><div>Geological and geochemical observations show that magma mixing and fractional crystallization are fundamental processes in the origin of A-type granites, with the dominant process determining their specific genesis. However, it is difficult to evidently distinguish such two processes using whole-rock geochemistry. Apatite has a long crystallization history and can precipitate from the melt during the whole magmatic evolution process, and its geochemical and Sr isotopic data would constrain the magma mixing and crystal fractionation processes. Here we present the integrated geochemical data and Sr isotopic compositions of apatite from mafic microgranular enclaves (MMEs) and their host A-type granites in the early Cretaceous Qianshan pluton to fingerprint apatite geochemical indicators for tracing magma mixing and fractional crystallization. The variable Sr isotopic compositions of apatites in the mafic microgranular enclaves (0.7097 to 0.7211) and the host biotite granite (0.7131 to 0.7171) suggest a magma mixing process, which cannot be revealed by consistent whole-rock Sr isotopic compositions. The trend between Eu/Eu* and rare earth elements + yttrium (REE + Y) contents and Sr contents in apatite among different samples mimics the magma mixing trend observed in whole-rock, suggesting that the broad range of Sr contents and abrupt increases in REE + Y contents can record the mixing process. However, the effect of fractional crystallization on the apatite composition depends on the partition behavior of elements in different minerals. Specifically, the continuous decreases in Eu/Eu* and Sr contents of apatites effectively indicate progressive feldspar crystallization, and the decreases in the (La/Sm)_N and (La/Yb)_N ratios of apatites suggest the crystallization of feldspar, biotite and apatite, while the increases of these ratios may trace the crystallization of minerals rich in MREE and/or HREE such as hornblende, zircon, and titanite. These observations confirm the sensitivity of apatite Sr isotopes and trace elements content, as well as REE patterns to magma mixing and fractional crystallization, thus providing valuable insights into the complicated magma evolution processes and petrogenesis of A-type granites. Furthermore, the universality of apatite in granitic rocks and the commonality of magmatic mixing and fractional crystallization in granite origin highlight the broader applicability of our study, offering a valuable perspective for understanding the origin of other granitoids.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107873"},"PeriodicalIF":2.9,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142720898","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":"Multistage crustal reworking in the Dabie orogen: Evidence from zircons in migmatites and retrograded eclogites","authors":"Ling Wang ,&nbsp;Min Ji ,&nbsp;Xiao-Ying Gao ,&nbsp;Xuan-Jin Chen","doi":"10.1016/j.lithos.2024.107872","DOIUrl":"10.1016/j.lithos.2024.107872","url":null,"abstract":"<div><div>Crustal rocks are likely to experience multistage reworking processes involving subsolidus metamorphic dehydration and suprasolidus partial melting in collisional orogens. Different types of metamorphic rocks usually exhibit unique geochronological signatures. However, the underlying reasons for these distinctions remain ambiguous. To address this issue, we conducted a combined study of petrology, whole-rock major–trace elements and Sr–Nd isotopes, as well as zircon U–Pb–Hf isotopes and trace elements, on migmatitic granitic gneisses (including melanosomes and leucosomes) and retrograded eclogites exposed in the same outcrop at the Huangwei area in the North Dabie zone, central-east China. Our results reveal contrasting protoliths and metamorphic features between migmatites and retrograded eclogites: (1) The protoliths of the retrograded eclogites are Paleoproterozoic mafic rocks, whereas those of the migmatites are Neoproterozoic granitic rocks. (2) The retrograded eclogites show petrographic features indicative of subsolidus fluid activity rather than partial melting, whereas the migmatites exhibit anatectic textures at macroscopic and microscopic scales. (3) Newly grown zircons in the retrograded eclogite solely record Triassic (221 ± 4 Ma) eclogite-facies metamorphism, whereas those in the migmatites preserve two episodes of high-temperature anatexis in the early Cretaceous (ca. 125 and 100 Ma). (4) Newly grown zircons in the melanosomes and leucosomes differ in their occurrences, U–Pb ages, trace element compositions, and Hf isotope ratios. The Triassic records are related to the continental collision/subduction of the South China Block beneath the North China Block, and the early Cretaceous records are associated with the thinning of the thickened lithospheric mantle and subsequent asthenospheric upwelling in the postcollisional stage. The distinct zircon records in the retrograded eclogites and migmatites stem from the contrasting zircon behavior during dehydration and anatectic metamorphism in different types of rocks. Notably, younger anatectic ages of ca. 100 Ma are newly identified in the Dabie orogen, and the contemporaneous magmatic activity is absent. This indicates that only local areas maintained suprasolidus metamorphic conditions for anatexis at ca. 100 Ma, which is related to the secular cooling of the orogenic lithosphere since the achievement of peak temperature, signifying the late stage of orogenic collapse. Therefore, a comprehensive understanding of the multistage crustal reworking processes needs a thorough examination of the metamorphic and anatectic history of various types of rocks in collisional orogens.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107872"},"PeriodicalIF":2.9,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703909","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 of volcanic rocks from the Andaman Sea: Insights into the nature of back-arc crust.","authors":"Sachin Kumar Tripathi ,&nbsp;Andrew Carter ,&nbsp;Archisman Dhar ,&nbsp;Resmi S. ,&nbsp;Biswajit Ghosh","doi":"10.1016/j.lithos.2024.107870","DOIUrl":"10.1016/j.lithos.2024.107870","url":null,"abstract":"<div><div>The forearc and back-arc region of the Andaman-Nicobar-Sumatra Subduction Zone are mainly submarine and poorly understood. To gain new insights sixty representative volcanic rocks were collected from the Andaman Sea region. Rock types range from basalt, basaltic andesite, andesite, dacite to rhyolite reflecting calc-alkaline, intermediate to acidic magma compositions. The rocks exhibit pronounced LREE enrichment with significant negative Nb, Ta and Ti anomalies and relative HREE depletion indicative of subduction zone related volcanism. The calc-alkaline rocks were generated by fractional crystallization along with crustal assimilation of older crustal rocks. A lower level of contamination is recorded in Barren Island samples, and mafic rocks from the Central Andaman Trough and Southern arc. Miocene zircon ²³⁸U/²⁰⁶Pb ages (10.8 ± 0.3 Ma, 19.8 ± 0.3 Ma and 19.5 ± 0.2 Ma) are recorded by West Sewell Ridge samples. Previous suggestions that hyperextended Malayan crust (Sundaland) existed below much of the Northern arc, Southern arc, Alcock and Sewell Rises and were later covered by volcanic crustal material is supported by the presence of inherited zircon cores and xenocrysts with ages spanning the Phanerozoic to Neoproterozoic (250, 320, 460–690, 800–1100, and 1400 Ma). These fit with the Malay-Sundaland as the main source of crustal contamination.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107870"},"PeriodicalIF":2.9,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703892","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":"Recycling of subducted continent slab in an accretionary orogen: Insight from the Liangwan potassic granitoids in the Tongbai orogen, Central China","authors":"Wen-Xiang Zhang ,&nbsp;Xing Zhang ,&nbsp;Guang-Yan Zhou ,&nbsp;Long Li ,&nbsp;Huan Chang ,&nbsp;Yuan-Bao Wu","doi":"10.1016/j.lithos.2024.107868","DOIUrl":"10.1016/j.lithos.2024.107868","url":null,"abstract":"<div><div>Granitoids provide a vital window to probe the lithological configuration and chemical evolution of orogenic belts. In this contribution, we present an integrated study of mineral compositions, zircon U<img>Pb ages and Hf<img>O isotopes, titanite U<img>Pb ages and Sm<img>Nd isotopes, as well as whole-rock element and Sr–Nd–Hf isotope compositions of the Liangwan granitic pluton in the northern Paleozoic accretionary orogenic unit of the Tongbai orogen, central China. The Liangwan pluton is composed mainly of monzogranites and contains abundant mafic microgranular enclaves (MMEs). The monzogranites have relatively high silica contents (SiO₂ = 67.40–69.91 wt%) and mainly exhibit shoshonite to high-K calc-alkaline and metaluminous features. The MMEs have similar mineral and geochemical compositions and zircon and titanite U<img>Pb ages of ca. 129 Ma to the monzogranites, suggesting that they are likely early-crystalized cumulates of the host monzogranites. The MMEs and monzogranites are both characterized by enrichment of large ion lithophile elements but depletion of high field-strength elements. The monzogranites have whole-rock initial Sr (<em>I</em>_sr) of 0.7069–0.7074, ε_Nd(t) of −14.2 to −13.7, and ε_Hf(t) of −17.5 to −17.2, zircon ε_Hf(t) of −17.8 to −17.0 and δ¹⁸O values of 5.27–5.98 ‰, and titanite ε_Nd(t) of −14.50 to −13.78. These features are distinct from the rocks in the northern Tongbai accretionary orogenic unit but similar to those of the post-collisional granitoids in the southern Tongbai collisional orogenic unit. The Liangwan pluton was likely stemmed from the subducted South China Block (SCB) underneath the northern segment of the Tongbai orogen. Our results show that the subducted continental mass can act as an alternative source for the magmatic rocks occurred in the accretionary unit.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107868"},"PeriodicalIF":2.9,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703891","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}