Lithos最新文献

{"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}

{"title":"Geochemical study of UHP serpentinites in southwestern Tianshan, China and its implications for trace elements deep recycling","authors":"Tingting Shen ,&nbsp;José Alberto Padrón-Navarta ,&nbsp;Thomas Bader ,&nbsp;Congcong Lin ,&nbsp;Tian Qiu ,&nbsp;Jingsui Yang","doi":"10.1016/j.lithos.2024.107867","DOIUrl":"10.1016/j.lithos.2024.107867","url":null,"abstract":"<div><div>Serpentinites play a crucial role in the recycling of elements and volatiles in subduction zones. We studied the geochemistry of Changawuzi serpentinites from Chinese southwestern Tianshan, which underwent ultrahigh-pressure (UHP) metamorphism. The bulk rock compositions of the serpentinites suggest that Changawuzi serpentinites originated from a variably depleted mantle and were subsequently enriched in fluid-mobile elements (FMEs) during initial serpentinization. Integrated analyses of trace element concentrations (Cs, U, As, and Sb), Sr–Nd–Pb isotopic compositions, and geological context collectively indicate that serpentinization likely occurred within the interior of the subducted slab. During the early stages of subduction, the concentrations of rare earth elements (REE), high-field-strength elements (HFSE), and other trace elements (such as Cs, Rb, Ba, Th, and U) decrease from low-grade lizardite to high-grade antigorite, as well as from primary clinopyroxene to metamorphic diopside. FMEs, particularly boron (B), are significantly enriched in lizardite, and the majority are liberated during prograde subduction, resulting in the metamorphic transformation from lizardite to antigorite. The uptake and variation of Sb and As in Changawuzi serpentinites are relatively minor. At peak metamorphic conditions, olivine, Ti-chondrodite and Ti-clinohumite become the main minerals hosting trace elements (such as REE, B, Sb, As and Li) that were released during partial antigorite dehydration and clinopyroxene re-equilibration. Ti-chondrodite/Ti-clinohumite as isolated grains or as lamellae within metamorphic olivine have the potential to carry HFSE, FMEs (particularly B and Li) and H₂O into the deeper mantle beyond the dehydration of serpentinites, potentially impacting arc magmatism and the global cycling of these elements.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107867"},"PeriodicalIF":2.9,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703894","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":"U-Pb ages and Hf isotopic composition of detrital zircon in western Algarve Triassic sandstone (SW Iberia): Implications for crustal evolution, provenance, and paleogeography","authors":"Manuel Francisco Pereira,&nbsp;Cristina Gama","doi":"10.1016/j.lithos.2024.107871","DOIUrl":"10.1016/j.lithos.2024.107871","url":null,"abstract":"<div><div>The Triassic paleogeographic configuration before the Central Atlantic Ocean's opening and the Pangea's breakup establishes that Iberia was close to North America and North Africa. We present U<img>Pb and Hf isotope data of Triassic siliciclastic rocks of the Western Algarve basin (Southwest Iberia, Portugal) to draw inferences on their provenance to define the crustal evolution of the potential sources. Detrital zircon age populations of five samples of Triassic sandstones (68–80 % Neoproterozoic; 5–23 % Paleoproterozoic; 5–14 % Mesoproterozoic; &lt;5 % Archaen and &lt; 4 % Paleozoic) differ significantly from those of the underlying Carboniferous turbidites of the South Portuguese Zone suggesting provenance from outside present-day SW Iberia. Hf isotope signatures of the zircon grains from the western Algarve Triassic sandstones unravel a complex crustal evolution characterized by successive cycles of input of juvenile magmas and magmas derived from the reworking of older crust. Archean detrital zircon grains with positive εHf(t) values and model ages of 3.1–3 Ga indicate juvenile crust formation (Leonian event), while a grain dated at ca. 2.6 Ga showing negative εHf(t) values and model ages of 3.1 Ga suggests that the Archean crust became reworked later (Liberian event). Zircon grains dated between 2.4 and 2.5 Ga having positive to slightly negative εHf(t) values and model ages of 3.3–2.6 Ga model ages correspond to magmatism older than the Eburnean event known in the Reguibat shield, involving a juvenile component mixed with variable proportions of reworked Archean crust. Younger Paleoproterozoic grains (ca. 2.10 to 2.05 Ga; Eburnean-Birimian event) having positive εHf(t) values and model ages of 2.3–2.1 Ga and negative εHf(t) values and model ages of 3.6–2.6 Ga, also indicate interaction of juvenile sources with mixing of old crust. Mesoproterozoic grains show positive εHf(t) values and model ages of 2.3–2.1 Ga, suggesting juvenile crust formation and reworking of the Eburnean crust. Neoproterozoic (ca. 695–555 Ma) detrital zircon with positive εHf(t) values and model ages of 0.76–0.58 Ga point to juvenile crust formation (i.e. Cadomian/Pan-African and Avalonian arcs). They also have negative εHf(t) values in the range − 21.6 to −11.7 and model ages of 3.2–2.1 Ga, suggesting reworking of older crust. In summary, the εHf(t) values and U<img>Pb age pattern of the zircon grains from the Triassic siliciclastic rocks are similar to NW Africa and North America potential sources. Still, there is a notable gap in juvenile crust production during the Siderian in the peri-Eastern Laurentia, Avalonia, and Ganderia potential sources unknown in NW Africa. The lack of ca. 525–380 Ma and ca. 380–330 Ma detrital zircon in the western Algarve Triassic sandstones makes it challenging to admit an Atlantic margin of North America and SW Iberia provenance.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"490 ","pages":"Article 107871"},"PeriodicalIF":2.9,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658300","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":"Zinc and iron isotopic compositions of Cenozoic basalts in Inner Mongolia: New insights into deep carbon recycling related to Paleo-Asian slab subduction","authors":"Zhao-Xue Wang ,&nbsp;Tianhao Wu ,&nbsp;Sheng-Ao Liu","doi":"10.1016/j.lithos.2024.107866","DOIUrl":"10.1016/j.lithos.2024.107866","url":null,"abstract":"<div><div>The origin of Cenozoic basalts in Inner Mongolia has been debated in recent years. Although the heavier-than-mantle zinc isotopic compositions indicate recycled carbonate in their sources, the recycled carbonate has been attributed to two different subducting oceanic slabs (Paleo-Asian vs. Paleo-Pacific). To further address this issue, Cenozoic basalts located in the west of the North-South Gravity Lineament (NSGL) in Inner Mongolia are investigated, and the sampling profile is approximately parallel to the NSGL (i.e., from southwest to northeast; SW-NE). These basalts have notably heavier zinc (δ⁶⁶Zn = 0.47–0.52 ‰) and iron (δ⁵⁶Fe = 0.18–0.24 ‰) isotopic compositions than those of the mantle, which cannot be interpreted by magmatic processes (differentiation and partial melting). Instead, the involvement of recycled carbonates in sources is a viable explanation for the high δ⁶⁶Zn characteristics, supported by high P₂O₅ contents and low Hf/Hf*. In addition, samples with high δ⁵⁶Fe also display high Fe/Mn (69–81) related to Cenozoic basalts from the east of the NSGL, indicating the existence of a pyroxenite component in sources in addition to carbonated peridotites. Combining with literature data, we found that basalts distributed in the SW-NE direction in Inner Mongolia have similarly heavy Zn and Fe isotopic compositions. This provides further constraints that mantle carbonate metasomatism in the west of the NSGL was most likely to have been caused by southeastward subduction of the Paleo-Asian oceanic slab, instead of northward subduction of the Paleo-Asian oceanic slab or subduction of the Paleo-Pacific oceanic slab.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"492 ","pages":"Article 107866"},"PeriodicalIF":2.9,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703893","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}