Lithos最新文献

{"title":"U–Pb–Hf and morphological evolution of zircon from granites associated with world-class tungsten skarn deposits in the northern Canadian Cordillera","authors":"Kirsten L. Rasmussen , Hendrik Falck , Yan Luo , D. Graham Pearson , Pilar Lecumberri–Sanchez","doi":"10.1016/j.lithos.2024.107752","DOIUrl":"10.1016/j.lithos.2024.107752","url":null,"abstract":"<div><p>The northern Canadian Cordillera is the most significant tungsten district in North America. Here, high-grade tungsten skarn deposits are associated with small, reduced, high-K calc-alkaline, S-type biotite granite plutons belonging to the 102–96 Ma Tungsten plutonic suite (TPS). A detailed U–Pb–Hf and morphological study of magmatic zircon from plutons in the southern half of the TPS belt was undertaken to better understand magmatic processes leading to the generation of the associated tungsten deposits. Antecrystic zircon from the TPS plutons began crystallizing during a transpressional regime ca. 117 Ma, suggesting the TPS magmas were active for up to 21 Myr prior to their upper crustal emplacement and final crystallization. This prolonged magmatic activity necessitates a magma origin in long-lived, deep crustal magma chambers. Hafnium isotopic compositions in zircon for the southern TPS as a whole form a non-radiogenic, univariate, and relatively wide ranging population (ε<sub>Hf<em>i</em></sub> = −17.6 ± 4.5), but U–Pb–Hf trends become apparent when the data are sub-divided into sample groups with similar age, zircon morphology, and geographic location. These evolutionary trends in magmatic zircon are most simply explained by interactions between the parent melt and dissolving inherited zircon grains. This, along with changing zircon morphology, is consistent with gradual cooling and crystallization pathways exhibited by S-type magmas. Differing evolutionary trends in the U–Pb–Hf isotopic data between sample groups, however, suggest there were multiple magma batches that evolved independently, possibly in separate pockets within large, deep magma chambers. Zircon morphologies also suggest some grains in all sample groups were equilibrated with hotter and more alkaline magmas, although there is no textural or compositional evidence in the zircon for mixing of magmas with widely different compositions. An unconstrained inversion of local aeromagnetic data indicates reduced batholiths could be present 4–6<sup>+</sup> km below the surface and that the plutons are apophysies to (or, higher level injections from) these deeper bodies. Although these batholiths can only be short-term holding chambers for magmas ascending from deep crustal levels, they may have been important for the segregation of mineralizing fluids. Since no single magmatic evolutionary pattern in the unaltered TPS plutons can be definitively linked to tungsten mineralization, pulses of mineralizing fluid may have been derived instead from the underlying batholiths. The 20<sup>+</sup> Myr duration of deep magmatic activity exhibited by the TPS is similar to timeframes suggested for magmas associated with tungsten deposits in southern China, and may have allowed extended fractionation of a large volume of crustally derived magma to concentrate tungsten into late-stage melts. The emplacement of upper crustal batholiths and plutons in both regions during or following a transi","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107752"},"PeriodicalIF":2.9,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002652/pdfft?md5=453529699ff85e05fa8ffd28714cd9d1&pid=1-s2.0-S0024493724002652-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142083708","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":"Corrigendum to “The Muskox intrusion: Overview of a major open-system layered intrusion and its role as a sub-volcanic magma reservoir in the Mackenzie large igneous province” [LITHOS 474–475 (2024) 107560]","authors":"James S. Scoates , R.F. Jon Scoates","doi":"10.1016/j.lithos.2024.107754","DOIUrl":"10.1016/j.lithos.2024.107754","url":null,"abstract":"","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107754"},"PeriodicalIF":2.9,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002676/pdfft?md5=695b33ba8bbf47e407c6225a09c5eee4&pid=1-s2.0-S0024493724002676-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142050282","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":"Characterization and origin of high-Al chromitites: A case study of chromite deposit in the Kudi ophiolite in the NW Tibetan Plateau","authors":"Jian-Guo Liu ,&nbsp;Ben-Xun Su ,&nbsp;Xia Liu ,&nbsp;Wen-Jun Li ,&nbsp;Yang Bai ,&nbsp;Jian Wang ,&nbsp;Xiang-Jie Wen ,&nbsp;Shi-Chun Li","doi":"10.1016/j.lithos.2024.107753","DOIUrl":"10.1016/j.lithos.2024.107753","url":null,"abstract":"<div><p>Chromitite occurrences in ophiolites are commonly classified into high-Cr (Cr# &gt; 60) and high-Al (Cr# &lt; 60) varieties. High-Cr chromitites have been extensively studied, whereas the origin of high-Al chromitites remains enigmatic mainly due to strong alteration of the relevant rocks. This study undertook a comprehensive examination of alteration-free high-Al chromitites and their hosting peridotites from the Kudi ophiolite in the NW Tibetan Plateau, complemented by a synthesis of global data of high-Al and high-Cr chromite deposits. Our results reveal that harzburgites, hosting both types of chromite deposits, exhibit similar major oxide compositions in their constituent minerals. In contrast, the constituent minerals in the dunite envelopes and chromitites display distinct major and trace element compositions, which are probably controlled by the compositions of infiltrating melts. For both chromite deposits, the forsterite (Fo) contents of olivine increase from harzburgite (90.0–91.6) to dunite (89.9–94.6) and chromitite (90.0–97.2). Mineral compositions of olivine show significant variabilities at the contact boundaries between densely disseminated and sparsely disseminated chromitites. These features suggest that fluid immiscibility plays an important role in the formation of high-Al chromitite. A continuous spectrum of major oxide compositions of chromite from high-Al to high-Cr chromitites suggests a progressive shift in the parental magma compositions from mid-ocean ridge basalt-like to boninitic melts, implying a rapid tectonic transition during subduction initiation.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107753"},"PeriodicalIF":2.9,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141997567","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":"Kyanite microstructural and microchemical characteristics reveal differences in growth, deformation and chemical modification: A case study from the Paleoproterozoic suture zone of South Harris, NW Scotland","authors":"Eleanore Blereau ,&nbsp;Sandra Piazolo ,&nbsp;Patrick Trimby ,&nbsp;Etienne Skrzypek","doi":"10.1016/j.lithos.2024.107748","DOIUrl":"10.1016/j.lithos.2024.107748","url":null,"abstract":"<div><p>Based on petrological association, cathodoluminescence (CL), trace element signatures and orientation relationships, two generations of kyanite are distinguished in a high temperature, high pressure garnet-biotite-aluminosilicate bearing migmatite of South Harris, NW Scotland. The migmatite shows a garnet and biotite rich domain (<em>Grt-Bt domain)</em> which is cut at a low angle by a dominantly coarse-grained plagioclase-quartz leucosome. In addition, a fine-grained plagioclase-quartz-kyanite domain (<em>Plag-Qtz-Ky domain</em>) is present intercalated with the <em>Grt-Bt domain</em> and subparallel to the plagioclase-quartz domain. Type 1 kyanite is coarse grained and associated with Bt clusters and garnet within the <em>Grt-Bt domain</em>. It grew relatively early, <em>syn</em>- to post-garnet growth, in a suprasolidus environment resulting in crystallographically determined oscillatory CL and trace element zoning. Grains record evidence of progressive deformation in the crystal plastic regime, where deformation is accommodated by dislocation glide, climb and deformation twinning. The dominant activated slip system is (100)&lt;001&gt; with minor component of &lt;100&gt;, while deformation twins show a ∼ 180° rotation around ∼&lt;001&gt; axis and a twin plane near (001). Grains appear to be impervious to deformation induced diffusion with all zoning remaining sharp despite crystal plastic deformation. Grains in direct contact with the <em>Plag-Qtz-Ky domain</em> show late modification of the CL and trace element signature suggesting melt-mediated interface-coupled dissolution-precipitation reaction. This modification resulted in crosscutting lobate high trace element regions and irregular rims with low Cr and V content. These rims show similar CL and trace element characteristics as Type 2 kyanite which are exclusively seen within the <em>Plag-Qtz-Ky domain</em> suggesting that Type 2 grains are cogenetic with Type 1 rims. Type 2 grains are finer grained than Type 1 grains and show near uniform CL and trace element distributions with rare oscillatory zoned and relatively higher Cr &amp; V bright cores. Type 2 show either no or very localized internal deformation features. However, they exhibit a clear shape preferred orientation which coincides with a crystallographic preferred orientation where the longest shape axis is parallel to &lt;001&gt;. We propose that Type 2 kyanite grains underwent melt-present deformation by rigid body rotation in an externally derived melt with different trace element chemistry than the host rock. This melt thus interacted chemically by melt-mediated interface-coupled dissolution-precipitation reactions with the surrounding rocks forming the Type 1 rims.</p><p>Our study shows detailed analysis of kyanite is an important tool for giving constraints on the deformation, <em>P–T</em> and melting history of high-grade metamorphic rocks and migmatites.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107748"},"PeriodicalIF":2.9,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002615/pdfft?md5=c3b3e60aa4b46184dc5497128266104e&pid=1-s2.0-S0024493724002615-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141991287","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":"Non-typical fractionation behaviors in a lepidolite-subtype pegmatite: Implications for the internal evolution of a naturally fluxed system","authors":"Chun-Long Wang ,&nbsp;Shao-Yong Jiang ,&nbsp;Feng Yuan ,&nbsp;Noreen J. Evans ,&nbsp;Abdurehim Dawut ,&nbsp;Jie Zhang ,&nbsp;Zhi-Yong Li","doi":"10.1016/j.lithos.2024.107749","DOIUrl":"10.1016/j.lithos.2024.107749","url":null,"abstract":"<div><p>Despite their relatively rare occurrence, lepidolite-subtype pegmatites host abundant Li–Nb–Ta–Cs–Sn mineralization and represent a high-flux pegmatitic system with abnormally high F and Li activity. Characterization of highly fluxed melts and the impact of fluxes and exsolved fluids on fractionation of peraluminous melts have mainly been studied in experimental systems, with natural system correlations remaining poorly understood. Consequently, we conducted a systematic mineralogical study of a lepidolite-subtype pegmatite in the North Qinling orogenic belt, Central China. An abnormal “concave downward” fractionation trend for primary columbite-group minerals on the quadrilateral diagram is identified, and irregularly zoned columbite crystals coexist with F-rich minerals in one of the core zones have the highest Ta contents (normally 50.17–63.13 wt% Ta₂O₅) and Ta/(Nb + Ta) ratios (up to 0.65). Despite the consistently Ta-dominated B-site in the crystal lattice of microlite-group minerals, extreme compositional variations at the A- and Y-sites are observed. Compared with microlites in intermediate zones, the abrupt increase in U in microlite crystals in core zones and late units (up to 20.16 wt% UO₂), is ascribed to the melt-fluid interaction with exsolved U-rich aqueous fluids. In addition, the fractional crystallization of F-bearing minerals resulted in a gradual decrease in F contents in microlite-group minerals from extremely F-rich (2.68–4.84 wt% F) in intermediate zones to low F species (mainly 0.82–1.71 wt% F) in core and late zones. Moreover, autometasomatism by a late fluxed melt and hydrothermal metasomatism by late aqueous fluids are identified in columbite- and microlite-group minerals. This work highlights that these non-typical fractionation behaviors related to the activity of fluxes (especially F) and the exsolution of aqueous fluids during the internal evolution of pegmatitic melts, are critical for the generation of lepidolite-subtype pegmatites. Fluorine was gradually enriched in the pegmatitic melt, and reached its highest level during crystallization of the (inner) intermediate and core zones. Non-equilibrium crystallization occurred throughout pegmatite evolution, and late units were most probably formed from aqueous fluid-enriched residual melts, rather than by hydrothermal replacement.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"486 ","pages":"Article 107749"},"PeriodicalIF":2.9,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142050337","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 origin of alkali granites and Th-U ± REE enrichments in Kestanbol Magmatic complex (NW Anatolia) revisited: Evidences from bulk-rock geochemistry and isotopic data, zircon UPb, biotite Ar/Ar and apatite (UTh)/He geochronology","authors":"Zeynep Doner ,&nbsp;Ali Tugcan Unluer ,&nbsp;Şenel Özdamar ,&nbsp;Oral Sarıkaya ,&nbsp;Michael F. Roden ,&nbsp;Mustafa Kaya ,&nbsp;Huseyin Kocaturk ,&nbsp;Mustafa Kumral ,&nbsp;Fahri Esenli","doi":"10.1016/j.lithos.2024.107751","DOIUrl":"10.1016/j.lithos.2024.107751","url":null,"abstract":"<div><p>This paper presents new field, petrographic, geochemical, Sr<img>Nd isotopic and geochronological data from Kestanbol Magmatic Complex (KMC) in the western Anatolia. Zircon U<img>Pb ages from the KMC were in the range 21.91 Ma and 21.52 Ma, indicating Miocene emplacement. ⁴⁰Ar/³⁹Ar dating results of biotites from the same samples show a narrow range of ages between 20.0 and 22.7 and a weighted mean of 21.41 ± 0.40 Ma, and those of hornblende analysis yield ages between 21.52 and 31.19 Ma with a weighted mean of 22.70 ± 0.99 Ma, are interpreted as the cooling age of the KMC. The average (U-Th/He) ages from the KMC yielded an average of 21.5 Ma and 19.8 Ma. These new age data indicate rapid cooling following the emplacement of the KMC at ∼21 Ma. We suggest that the cooling was due to rapid uplift in the western Anatolia. The studied monzonitic, syenitic and alkaline subvolcanic rocks of the northern KMC are characterized by high K₂O (4.34–10.7 wt%), low to moderate SiO₂ (50.0–69.9 wt%), and P₂O₅ (0.03–1.07 wt%). They have moderate initial ⁸⁷Sr/⁸⁶Sr (0.707245–0.707875) and high initial ¹⁴³Nd/¹⁴⁴Nd (0.512441–0.512508) ratios, consistent with some crustal contamination. The studied rocks are enriched in Th (up to 204 ppm), U (up to 54.9 ppm), REE (up to 565.9 ppm) and, some LILE's including K (up to 8.85%), Rb (up to 447.1 ppm), Sr (up to 2053 ppm) and Ba (up to 2578 ppm). The geochemical and isotopic data suggest that the magmatic evolution of KMC is dominated by events including post-collisional tectonics, flux induced partial melting, fractional crystallization. The enrichments of incompatible elements are mostly caused by the fractional crystallization and K-metasomatism that affected the earlier magmatic phases during the cooling of the complex.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107751"},"PeriodicalIF":2.9,"publicationDate":"2024-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141985598","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":"Estimating values of Fe3+/ΣFe in pyroxenes with the electron microprobe","authors":"William Lamb ,&nbsp;Andrew Mott ,&nbsp;Robert Popp ,&nbsp;Greg Chmiel","doi":"10.1016/j.lithos.2024.107746","DOIUrl":"10.1016/j.lithos.2024.107746","url":null,"abstract":"<div><p>Values of Fe³⁺/ ΣFe (ΣFe = Fe³⁺ + Fe²⁺) were determined for six (6) pyroxenes, (five (5) diopsides and one (1) enstatite), using the single dissolution technique of <span><span>Fritz and Popp, 1985</span></span> (FP85). These same pyroxenes were analyzed with the electron microprobe (EMP), and values of Fe³⁺/ΣFe were determined using charge balance from average EMP compositions. Typically, these averages were based on thirty (30) analyses on multiple grains of the same sample, although some pyroxenes were characterized with as few as 9 and as many as 120 analyses.</p><p>Differences between average values of Fe³⁺/ΣFe determined using the two methods were ≤ 0.02 for pyroxenes with Fe-contents &gt;9 wt% FeO_T (all Fe as FeO_T). Pyroxenes with lower Fe contents of approximately 4 to 6 wt% FeO_T exhibit differences that fall between 0.02 and 0.06. One pyroxene, with the lowest Fe-content (1.79 wt% FeO_T; 0.055 atoms per formula unit or apfu), exhibits the largest difference Fe³⁺/ ΣFe difference between EMP and FP85 of 0.14. Values of the standard deviation (1σ), based on average values of Fe³⁺/ ΣFe (EMP), range from 0.03 to 0.22, which are also inversely correlated to the Fe content. For pyroxenes with FeO_T &gt; 4.0 wt%, and with compositions similar to those examined in this study, it is possible to use charge balance to determine values of Fe³⁺/ΣFe(EMP) to better than ±0.07.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107746"},"PeriodicalIF":2.9,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142011568","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":"An embryonic intra-oceanic subduction in the Bangong−Nujiang Meso-Tethys: insights from Late Jurassic NdHf isotopic decoupling adakitic granodiorites in the Dongco ophiolite of central Tibet","authors":"Xin-Miao Wang,&nbsp;Chen Ji,&nbsp;Kai-Jun Zhang,&nbsp;Ru-Ye Tian,&nbsp;Kang-Yu Li","doi":"10.1016/j.lithos.2024.107750","DOIUrl":"10.1016/j.lithos.2024.107750","url":null,"abstract":"<div><p>Subduction of the Bangong−Nujiang Meso-Tethys not only bred world-class Cu − Au polymetallic deposits in central Tibet but also created the initial elevation of the Tibetan Plateau during the Late Cretaceous following its final closure. Consequently, the Meso-Tethys carry critical codes for the evolution of Tethyan realm and the development of the Tibetan Plateau but some fundamental aspects still remain poorly explored. Here we proposed an embryonic intra-oceanic subduction event in the Bangong−Nujiang Meso-Tethys during the Late Jurassic based on investigations of adakitic granodiorites intruded within the Dongco ophiolite suite, central Tibet. These granodiorites were dated at 150–156 Ma by zircon U<img>Pb isotopes and geochemically display an affinity with high-silica adakite (Sr/Y = 24–47; La/Yb = 6–16), specifically marked by high SiO₂, Al₂O₃ and Na₂O contents but low MgO, CaO + Na₂O contents as well as extremely low Yb and Y contents. They have (⁸⁷Sr/⁸⁶Sr)_i ratios varying from 0.7061 to 0.7069, ε_Nd(t) values of −0.83 to 0.50, and ε_Hf(t) values of 3.3 to 8.9 (with one exception at −5.0), showing a distinct Nd<img>Hf isotopic decoupling (Δε_Hf(t) = 2.1–7.6; Δε_Hf(t) = ε_Hf(t)–1.55 × ε_Nd(t)–1.21). Geochemical modeling indicates that they were derived from partial melting of subducted Meso-Tethyan oceanic crust and moderate amounts of sediments. Residual plagioclases in the source region likely resulted in relatively lower Sr and La contents than typical high-silica adakite. Combined with previous studies, we suggest that the Dongco granodiorites formed in the early stage of an intra-oceanic subduction zone in the Bangong−Nujiang Meso-Tethys where subsidence of colder lithosphere inductively commenced along an active transform fault bounded by younger lithosphere during the Late Jurassic. This embryonic intra-oceanic subduction possibly occurred locally and was very short-lived.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107750"},"PeriodicalIF":2.9,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141953913","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":"Mineralogy and geochronology of pegmatites in the Kontum Massif, Central Vietnam: Implications for evolution of rare-metal mineralization","authors":"Tuan Anh Nguyen ,&nbsp;Xiaoyong Yang ,&nbsp;Tuan Anh Tran ,&nbsp;My Dung Tran ,&nbsp;Thi Hien Vu ,&nbsp;Zhuang Zhao","doi":"10.1016/j.lithos.2024.107747","DOIUrl":"10.1016/j.lithos.2024.107747","url":null,"abstract":"<div><p>The Lavi pegmatite located within the Kontum Massif of central Vietnam, represents a newly discovered rare-element pegmatites with significant economic potential. However, the emplacement age of the Lavi pegmatite and processes governing rare-element mineralization remain unclear. This study endeavors to elucidate these aspects through an examination of mineral chemical compositions and U-Pb isotopes of columbite-tantalite (coltan) group minerals and monazite sourced from distinct types of Lavi pegmatite. Four distinct pegmatite types were identified based on mineral compositions: muscovite-albite (type I), muscovite-albite-beryl-montebrasite (type II), muscovite-cassiterite (type III), and lepidolite- topaz-albite (type IV). The detailed EPMA analysis of minerals found in different types indicates that the Lavi pegmatite can be generally classified as the rare-element pegmatite, with a notable lepidolite subtype. Rare elements are primarily hosted within minerals such as montebrasite, lepidolite, beryl, coltan, and cassiterite. Geochronological data reveal a weighted mean ²⁰⁶Pb/²³⁸U age of 254.7 ± 2.8 Ma for monazite (type I) and 255 ± 5.7 Ma for coltan (type IV), suggesting the close temporal association of barren pegmatite and Li- mineralized pegmatites. Additionally, the linear correlation of K/Rb vs. Rb and K/Cs vs. Cs in mica compositions indicates continuous fractional crystallization from a common magma source. These findings provide insights into the pegmatitic evolution and underscore the economic potential of the Lavi pegmatite for rare metal extraction.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107747"},"PeriodicalIF":2.9,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141985599","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":"Magnetization related to late-Variscan extensional collapse in the Lugo Dome (NW Iberian Massif): a metamorphic petrology approach","authors":"Manuela Durán Oreja ,&nbsp;Pavel Pitra ,&nbsp;Alicia López-Carmona ,&nbsp;José R. Martínez Catalán ,&nbsp;Puy Ayarza","doi":"10.1016/j.lithos.2024.107745","DOIUrl":"10.1016/j.lithos.2024.107745","url":null,"abstract":"<div><p>The Eastern Galicia Magnetic Anomaly (EGMA) is one of the most distinctive and best studied magnetic anomalies in Iberia. It is located in NW Spain and overlaps the Variscan gneissic domes of Lugo and Sanabria. The Lugo Dome, in the north of the EGMA, deforms a large thrust sheet, the Mondoñedo Nappe, allowing the outcropping of its relative autochthon in the Xistral Tectonic Window, where extensional detachments resulting from late-Variscan tectonics crop out. A younger major detachment, the Viveiro Fault, developed on the western limb of the dome. Detailed ground-based magnetic mapping and geological charts show a clear spatial relationship between magnetic maxima and the extensional structures. Magnetic and paleomagnetic studies carried out on samples from this region indicate that rocks in the detachments commonly bear magnetite and hematite carrying induced but also remanent magnetizations and a very well-defined anisotropy of the magnetic susceptibility with directions matching those of the late-Variscan extensional fabrics.</p><p>Three pairs of metasedimentary samples in equivalent structural positions display variously developed medium-pressure Barrovian parageneses attributed to the early compressional phases of the Variscan orogeny, and low-pressure Buchan-type parageneses associated with the late Variscan extension. Our phase diagram-based petrological study suggests that the non-magnetic samples preserve the Barrovian conditions of 560–640 °C, 5–8.7 kbar. The lithologically and structurally equivalent samples, originally non-magnetic, developed magnetite/hematite-bearing mineral assemblages during decompression and cooling to 500–620 °C, 1.5–6 kbar. This recrystallization was probably assisted by metasomatic oxidizing fluids. The induced component of magnetization is essentially carried by magnetite, while hematite seems the main carrier of remanence. These results support the existing cartographic, geophysical and paleomagnetic findings indicating that the magnetization in the Lugo Dome is related to late-Variscan extension.</p></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"484 ","pages":"Article 107745"},"PeriodicalIF":2.9,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024493724002585/pdfft?md5=ba55dae3676888a52d093392aad48869&pid=1-s2.0-S0024493724002585-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141978412","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}