Lithos最新文献

{"title":"First-principles calculations of equilibrium inter-mineral nickel isotope fractionation in the mantle","authors":"","doi":"10.1016/j.lithos.2024.107848","DOIUrl":"10.1016/j.lithos.2024.107848","url":null,"abstract":"<div><div>The nickel (Ni) isotopic systematics has been increasingly utilized to understand the processes governing planetary differentiation. However, there is a lack of fundamental knowledge regarding equilibrium Ni isotope fractionation among mantle minerals, which hampered further applications of Ni isotopes in this domain. In this study, we conducted first-principles calculations to determine the reduced partition function ratios of ⁶⁰Ni/⁵⁸Ni (10³lnβ₆₀_–₅₈) in major Ni-doped mantle minerals, including olivine, orthopyroxene, clinopyroxene, pyrope and spinel. Our calculations reveal that the 10³lnβ₆₀_–₅₈ is insensitive to the Ni concentration within the mineral Ni concentration ranges investigated here, and the 10³lnβ₆₀_–₅₈ increases in the order of pyrope &lt; clinopyroxene &lt; orthopyroxene &lt; olivine &lt; spinel. Moreover, the 10³lnβ₆₀_–₅₈ demonstrates a predominantly linear relationship with the average force constant (&lt; F &gt;) of Ni that is mainly influenced by the average Ni<img>O bond length. By comparing the measured inter-mineral Ni isotopic differences in mantle rocks with our predicted results, we find that olivine, spinel and orthopyroxene in most peridotitic samples have attained Ni isotopic equilibrium. Conversely, clinopyroxene appears to fall out of equilibrium with other mineral phases, likely attributed to its metasomatic origin. Furthermore, in conjunction with the melt-olivine Ni isotope fractionation factor obtained from theoretical calculation and laboratory experiment, we demonstrate that mantle silicate melting produces melts with a heavier Ni isotopic signature compared to the source. Consequently, the systematically lighter Ni isotopic compositions observed in global basalts cannot be purely attributed to silicate melting-induced Ni isotope fractionation. An additional process, perhaps sulfide dissolution, must be invoked.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142586047","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":"Sulfur and metal mobilization during the life cycle of an oceanic core complex: Implications for seafloor massive sulfide deposits formation at slow and ultra-slow spreading ridges","authors":"","doi":"10.1016/j.lithos.2024.107843","DOIUrl":"10.1016/j.lithos.2024.107843","url":null,"abstract":"<div><div>Seafloor massive sulfide (SMS) deposits at slow and ultra-slow spreading ridges are often spatially related to, or hosted in oceanic core complexes (OCCs). The specific oceanic crust architecture, magmatism, hydrothermal fluid circulation and lithologies at OCCs, however, imply different S and metal (e.g. Cu, Zn, Co, Ni) fluxes relative to well-structured oceanic crust at-fast spreading ridges and which are not yet fully constrained. The study of S and metal distribution in the ODP Hole 735B deep drill core from the Atlantis bank allows to understand these fluxes along detachment faults and to better constrain the source zone of S and metals for OCC-related SMS deposits. Significant depletion of S, Cu, Zn and Ni are observed within the upper 250 m of the drill core where intense deformation and hydrothermal fluid circulation occurred. During the complex tectono-magmatic-hydrothermal evolution of the Atlantis Bank, four important stages are recognized for S and metal mobilization: 1) magmatic stratification leading to a higher proportion of sulfide-rich and S, Cu, Zn and Co fertile oxide gabbros in the root zone of the Atlantis Bank detachment, 2) high temperature ductile deformation leading to magmatic sulfide reworking and onset of sulfide leaching with limited metal mobilization, 3) extensive sulfide leaching and metal mobilization during amphibolite to greenschist facies metasomatism and, 4) late stage secondary sulfide precipitation and S enrichment during low temperature fluid circulation. Mass balance calculations from the source zones of the Atlantis Bank detachment highlights that metal mobilization during hydrothermal alteration of gabbroic rocks along detachment faults can fully account for the formation of OCC-related SMS deposits at slow and ultraslow spreading ridges. The Atlantis Bank detachment system, however, is gabbroic-dominated and represent the magmatic end-member of OCCs and further work is necessary for understanding metal fluxes in ultramafic-dominated detachment systems.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572700","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":"Magmatic stability of eudialyte-group minerals (EGM) and element distribution between EGM and peralkaline silica-undersaturated melts","authors":"","doi":"10.1016/j.lithos.2024.107839","DOIUrl":"10.1016/j.lithos.2024.107839","url":null,"abstract":"<div><div>Eudialyte-group minerals (EGM) are unique tracers of peralkaline silica-undersaturated melts. They receive global interest as potential resources for high-field-strength elements (HFSE, e.g., Zr, Nb, Ta) and rare-earth elements (REE), which are critical materials for modern technologies. The main condition for magmatic crystallization of EGM in general is that the concentration of Zr in the parental melt should reach saturation. The solubility of EGM in peralkaline melts from the system Na₂O–CaO–Al₂O₃–SiO₂ ± H₂O at temperatures between 750 and 1000 °C and pressures of 100 and 200 MPa was investigated. Newly formed crystalline phases in the run products are EGM grains, parakeldyshite and albite. EGM are stable between 750 and 900 °C, and melt incongruently to parakeldyshite between 900 and 1000 °C. EGM crystallization from peralkaline silica-undersaturated melts at nominally dry conditions and 750–850 °C requires a minimum of 0.2–0.22 wt% ZrO₂ in the melt. In experiments with the addition of H₂O, saturation is attained at much higher ZrO₂ concentrations (1.1–2.85 wt%) in the same temperature interval. REE and HFSE are strongly compatible with eudialyte-group minerals as the EGM-melt distribution coefficients (<em>D</em>) vary from 2 to 90 with falling temperature. The lowest <em>D</em> values are observed in experiments with the highest Zr solubility, i.e., at high temperature and in hydrated compositions. Light REE and especially La tend to have lower <em>D</em> values than the heavy REE.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593514","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":"Indosinian magmatism in NE Vietnam: Petrogenesis and geodynamic implications of Triassic mafic suites from the Song Hien region","authors":"","doi":"10.1016/j.lithos.2024.107842","DOIUrl":"10.1016/j.lithos.2024.107842","url":null,"abstract":"<div><div>The Song Hien region is located at the southern margin of the South China Block and includes Early–Middle Triassic mafic suites. The petrogenesis and tectonic context of these rocks are important to comprehending one of the most challenging periods in the tectonic evolution of northern Vietnam related to the South China–Indochina collision. In the present study, we provide the first systematic examination of whole-rock geochemical and Sr<img>Nd isotopic compositions of mafic suites from the NE Vietnam. The studied Early–Middle Triassic suites are dominated by basalts. The rocks are enriched in LILEs, U, and Th and depleted in Nb and Ta and show a wide range of geochemical and Sr<img>Nd isotopic compositions ((La/Yb)_CN = 0.4–4.6; Dy/Dy^⁎ = 0.7–1.3; (⁸⁷Sr/⁸⁶Sr)<em>i</em> = 0.7053–0.7125; <em>ε</em>Nd(t) = (+3.7)–(−8.0)). They all originated from shallow melting of a subduction-modified lithospheric mantle, and the compositional diversity of these basalts is attributed mainly to geochemical and Nd-isotopic heterogeneity in the mantle source. The geochemical and Sr<img>Nd isotopic features of the studied mafic suites indicate a negligible contribution of the asthenospheric mantle to magma generation and differ significantly from those of the Emeishan plume-related basalts. A model in which Early–Middle Triassic mafic magmatic activity in the NE Vietnam region is the result of decompression melting driven by convective thinning of the South China mantle lithosphere during the 250–240 Ma period is discussed in the study. This period corresponds to the South China–Indochina continental collision. In the NE Vietman region, the Early–Middle Triassic <em>syn</em>-collisional magmatism has an important metallogenic context, controlling Ni<img>Cu sulfide and Sn(<img>Cu) mineralizations.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142551923","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":"Nanoscale Os isotopic quantification of Wadi Tayin dunite platinum group minerals by atom probe tomography","authors":"","doi":"10.1016/j.lithos.2024.107841","DOIUrl":"10.1016/j.lithos.2024.107841","url":null,"abstract":"<div><div>Serpentinites record processes that redistribute major and trace elements between mantle and crust. Platinum Group Elements (PGEs) are trace elements in serpentinites hosted in sulphides and alloys. Alloys are challenging to find, and most analytical techniques lack the spatial resolution to analyse them. This research adopts automatic mineral mapping technique to detect PGM grains in a sample from the Wadi Tayin (Oman) peridotite and uses atom probe tomography, a nanoscale quantitative analytical technique, to analyse the grain. This work applies and assesses the applicability of atom probe tomography to measure the ¹⁸⁷Os/¹⁸⁸Os isotopic ratio of natural alloys and uses the ratio to constrain the source of Os. A novel algorithm is used to automatically determine the number of counts of the ¹⁸⁷Os and ¹⁸⁸Os peaks, to calculate the isotopic ¹⁸⁷Os/¹⁸⁸Os ratio and the analytical uncertainty. The ¹⁸⁷Os/¹⁸⁸Os ratio is 0.126 ± 0.003, consistent with the isotopic composition reported by literature in the dunite of the Main Mantle Section of the Wadi Tayin ophiolite.</div><div>The analytical uncertainty is one order of magnitude higher than conventional bulk rock techniques, such as negative-thermal ionisation mass spectrometry (N-TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). However, the precision is sufficient to conclude that the non-radiogenic ¹⁸⁷Os/¹⁸⁸Os ratio is compatible with a mantle origin for the alloy. Decreasing whole-rock Re with increasing LOI and the overprinting of magmatic pentlandite by magnetite demonstrate that progressive serpentinisation may have modified the Re budget. The results indicate that atom probe tomography can analyse ¹⁸⁷Os/¹⁸⁸Os ratio quantitatively in micron-sized natural alloys and provide insights into natural processes.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142552113","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":"Petrogenesis of early Paleozoic syn-collisional granitoids and enclaves in Western Kunlun, Northwest China: Implications for the growth of continental crust","authors":"","doi":"10.1016/j.lithos.2024.107844","DOIUrl":"10.1016/j.lithos.2024.107844","url":null,"abstract":"<div><div>The Western Kunlun Orogenic Belt (WKOB), along the northwestern margin of the Qinghai–Xizang Plateau, was formed by the collision of Gondwana-derived terranes to the south and the Tarim Block to the north and was closely associated with closure of the Proto-Tethys Ocean during the late Neoproterozoic to early Paleozoic. We present a combined zircon U<img>Pb geochronology, whole-rock composition, and Sr–Nd–Hf isotopic study of syn-collisional granitoid plutons and mafic microgranular enclaves (MMEs) in the region. Zircon U<img>Pb dating yields ages of 443.8 ± 4.4, 451.9 ± 4.2, 462.9 ± 3.5, and 456 ± 4.2 Ma for the Tongayoupuagezi, Shanjie, and Pishigai plutons and MMEs from the Pishigai pluton, respectively. The granitoids are metaluminous to weakly peraluminous (A/CNK = 1.00–1.17) and belong to the high-K calc-alkaline series. They have (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7058–0.7154, ε_Nd(t) values of −8.78 to −0.93, and ε_Hf(t) values of −19.72 to +6.87. The MMEs have variable SiO₂ contents (45.7–60.2 wt%) and are more mafic than the host granitoids, but have similar Sr–Nd–Hf isotopic compositions to the host granitoids [(⁸⁷Sr/⁸⁶Sr)_<em>i</em> = 0.7102–0.7110; ε_Nd(t) = −6.57 to −3.56; ε_Hf(t) = −7.17 to −1.81]. The MMEs are fragments of cumulates formed during the early stages of magma evolution. The granitoids were produced by the partial melting of a mélange source. The new data support the view that the Middle–Late Ordovician syn-collisional granitoids with MMEs distributed along the WKOB represent a magmatic response to terrane collision. This suggests that juvenile crustal growth in older orogenic systems, which occurs by arc addition, also involves some vertical addition during the final stage of orogenic collision. Our study suggests that mélange diaper melting is a key mechanism of crustal growth during the syn-collision stage in continental collision zones, associated with slab breakoff.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142551922","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 high-precision U-Pb zircon geochronology of the Howley Islands intrusions, Central Newfoundland Appalachians: Hydrous magmatism of Emsian age (ca. 400 Ma) along a multi-million-ounce orogenic gold belt","authors":"","doi":"10.1016/j.lithos.2024.107837","DOIUrl":"10.1016/j.lithos.2024.107837","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The Howley Islands intrusions consist of three coarse-grained amphibole-phlogopite/biotite quartz gabbro dykes and one medium-grained amphibole-biotite quartz diorite body that cut rocks of the Exploits Subzone in central Newfoundland along strike from the multi-million-ounce Valentine gold deposits. The petrogeneses and ages of these rocks were investigated to better constrain the process evolution of the orogenic gold belt that extends for more than 200 km across central Newfoundland.&lt;/div&gt;&lt;div&gt;The quartz gabbro dykes are composed of magnesio-ferri-hornblende-cummingtonite-phlogopite/biotite macrocrysts mantled by plagioclase (labradorite to oligoclase)-quartz coronas. The gabbros are LILE- and LREE-enriched, transitional arc-like rocks that formed from a different melt source and parental magma than the quartz diorite body. The quartz diorite is plagioclase-rich (50 modal % andesine), contains only trace cummingtonite, lacks phlogopite, and preserves rare diopside overgrown by magnesio-ferri-hornblende. This intrusion is more alkaline and OIB-like than the quartz gabbros and exhibits the influence of a deeper, more enriched mantle component, although both melts variably interacted with deep lithosphere. The quartz gabbro dykes and quartz diorite body may represent melts of the lower lithosphere and upper asthenosphere, respectively.&lt;/div&gt;&lt;div&gt;The abundance of coarse- to medium-grained amphibole and phlogopite/biotite in the samples is consistent with crystallization of hydrous magmas and rapid, water-enhanced crystal growth, with cooling paths recorded by chemically zoned grains of magnesio-ferri-hornblende and plagioclase. One quartz gabbro displays reverse core to rim chemical zoning of plagioclase from andesine to labradorite, which may reflect decreasing pressure during magma ascent and crystallization, magma mixing of evolved and more primitive magmas, and/or fluctuations in H&lt;sub&gt;2&lt;/sub&gt;O content. The presence of cummingtonite suggests crystallization at relatively low temperatures in shallow, low-pressure, upper crustal magma chambers. The quartz gabbros may represent melts equivalent to the nearby Howley Islands gabbro body, whereas the quartz diorite may represent a plagioclase cumulate along the margin of another melt chamber.&lt;/div&gt;&lt;div&gt;U-Pb CA-ID-TIMS zircon geochronology yielded ages of ca. 400.3 Ma for the gabbro dykes and 399.9 Ma for the quartz diorite intrusion, within the ca. 410–377 Ma age range for mineralization of the nearby Valentine gold deposits. The ca. 400 Ma intrusions, when considered in conjunction with regional models, reflect melting and hydrous magmatism in the mantle wedge above a retreating Avalonian slab that was dehydrating during the Acadian orogenic cycle. The coincidence of Pridoli (ca. 422 Ma) to Emsian (ca. 400 Ma) bimodal magmatism and orogenic gold mineralization in central Newfoundland reflects more than twenty million years of high geothermal gradients and fluid flow, which when combined w","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142551880","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":"Multistage magmatic and post-magmatic evolution of the Neoarchaean Closepet Batholith of Dharwar Craton in southern India - insights from the texture and chemical composition of titanite","authors":"","doi":"10.1016/j.lithos.2024.107840","DOIUrl":"10.1016/j.lithos.2024.107840","url":null,"abstract":"<div><div>Titanite is often used to describe the path of igneous, metamorphic, and hydrothermal processes. Therefore, titanite can unravel the multistage magmatic and post-magmatic evolution of granitoids. In this study, we present a comprehensive study of the ca. 2.57–2.51 Ga Closepet Batholith in the Dharwar Craton of southern India using titanite. This granitoid body provides a unique opportunity as various structural levels of the batholith are continuously outcropping. The textural and geochemical studies of titanite, supported by U<img>Pb isotopic dating, allowed us to distinguish five generations of magmatic and hydrothermal titanite. Three types of magmatic titanite demonstrate stage-growth crystallization (type I) and a change from reduced, high-temperature (type II) to oxidised, low-temperature conditions (type III). Hydrothermal titanite is recorded as altered titanite with zoned to patchy textures and secondary fractures and veinlets (type IV) and titanite inclusions within biotite (type V). Hydrothermal titanite (type IV) shows depletion in rare earth elements and high-field strength elements, indicating mobilization of those elements by a fluid. U<img>Pb dating by LA-ICP-MS of magmatic titanite type I yielded ages of ca. 2.5 Ga, consistent with the timing of formation of the Closepet Batholith. The relationship between titanite textures and chemistry indicates that titanite serves as a recorder of the multistage magmatic and post-magmatic evolution of the Closepet Batholith. In addition, our study shows that hydrothermal activity affected a large area, with fluids circulating over long distances within the upper structural levels of the Closepet Batholith.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536320","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":"Water content drives distinct evolution trajectory of Early Cretaceous granitoids in inland and coastal southeast China","authors":"","doi":"10.1016/j.lithos.2024.107836","DOIUrl":"10.1016/j.lithos.2024.107836","url":null,"abstract":"<div><div>Water plays a crucial role in determining the crystallization sequence of magma, which subsequently influences the chemical compositions of magmatic rocks across different tectonic settings. In this study, we compared the evolutionary features of granitic rocks along the coast and inland areas of southeast China, aiming to identify the key factors influencing their evolution. Our work indicates that multiple granitic intrusions formed between 126 and 142 Ma in the coastal region of southeastern China, which is consistent with the formation ages of large-scale granitoids in the inland Gan-Hang Belt. Isotopic characteristics suggest that the granitic rocks in southern Fujian originated from the melting of juvenile crust, while those in northern Fujian and eastern Zhejiang were formed from the partial melting of ancient crustal rocks, incorporating mafic magma evolved from the mantle. Most of the granitoids from the coastal region of southeastern China exhibit low zircon saturation temperatures (680–800 °C) and Zr/Sr ratios (&lt;1), suggesting their origin from a cold, wet magma reservoir. The porphyritic quartz diorite and porphyritic monzogranite represent the residual cumulate rocks of this hydrous magma reservoir, whereas the granitic porphyry and high-silica equigranular alkali feldspar granite evolved from the felsic melts extracted from the same reservoir. In contrast, most of the Early Cretaceous granitoids in the Gan-Hang Belt, located in the inland areas of southeast China, display high zircon saturation temperatures (800–900 °C) and Zr/Sr ratios (&gt;1), indicating their origin from hot, water-poor magma reservoirs. The porphyritic granites in this region represent residual cumulate rocks formed in water-poor magma reservoirs, whereas the high-silica equigranular granites evolved from hot felsic melts extracted from similar magma reservoirs. In the Early Cretaceous, the coastal region of southeastern China was closer to the Late Mesozoic paleo-Pacific subduction zone, where crystal-melt segregation within cold, wet magma reservoirs predominantly influenced magma evolution. Conversely, the granitoids in the Gan-Hang Belt in the inland region, located farther from the Late Mesozoic paleo-Pacific subduction zone, were associated with a rift tectonic setting and formed through crystal-melt segregation within hot, water-poor magma reservoirs. Our study underscores the critical role of water content in magma reservoirs in shaping the chemical composition of granitic rocks through crystal-melt segregation, thereby deepening our understanding of crustal formation processes across diverse tectonic environments.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536319","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":"Partial melting of HP–UHP felsic gneiss in the South Altyn Tagh reveals the rapid exhumation of a deeply subducted slab","authors":"","doi":"10.1016/j.lithos.2024.107835","DOIUrl":"10.1016/j.lithos.2024.107835","url":null,"abstract":"<div><div>The partial melting of HP–UHP rocks plays a crucial role in facilitating the exhumation of deeply subducted rocks. However, accurately determining the <em>P–T–t</em> conditions of the initial melting and subsequent crystallization is often challenging, which can hamper our understanding of the relationship between partial melting and exhumation. We present a detailed investigation of granitic veins in the (U)HP felsic gneiss in the eastern South Altyn Tagh (SAT), northwest China. These granitic veins have similar whole rock geochemical characteristics to those of the felsic gneiss: high K₂O (5.01–9.95 wt%) and Rb contents, and low Sr contents, with negative correlations between Rb/Sr ratios and Ba or Sr contents. This suggests that the veins were generated by muscovite-dehydration melting of the felsic gneiss. Garnet crystals in the felsic gneiss contain many titanite and multiphase solid inclusions in their mantles. Using the compositions of the garnet mantles and granitic veins, alongside pseudosection modelling of the felsic gneiss, we estimate that the initial melting conditions of the felsic gneiss occurred at 2.57–2.61 GPa and 1000 °C, just above the solidus. In situ U<img>Pb dating of titanite inclusions in the garnet mantles yields an initial melting age of ∼485 Ma. Furthermore, anatectic zircon grains in the granitic veins yield U<img>Pb ages of 488–484 Ma. Using Ti-in-zircon thermometry and ¹⁷⁶Lu/¹⁷⁷Hf-in-zircon geobarometry, we estimate that the anatectic zircon grains crystallized at 647–872 °C and 0.16–0.82 GPa. The estimated <em>P–T–t</em> path from the initial melting of the felsic gneiss to the crystallization of the granitic veins indicates rapid exhumation from ∼2.6 to 0.16–0.82 GPa. This exhumation can be attributed to partial melting, which weakened the rocks and enabled their ascent to shallower depths. Moreover, the potassic melts derived from partial melting of the felsic gneiss provide new insights into the genesis of potassic granitoids in subduction zones.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536318","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}