Lithos最新文献

{"title":"Adakitic magmatism at the birth of the large Achala Intrusive Complex: Evidence of a thickened crust at the onset of Devonian foreland magmatism of SW Gondwana margin","authors":"Matías M. Morales Cámera , Juan A. Dahlquist , Edgardo G. Baldo , Pablo H. Alasino , Juan A. Moreno , José M. Fuenlabrada , Miguel A.S. Basei","doi":"10.1016/j.lithos.2025.108132","DOIUrl":"10.1016/j.lithos.2025.108132","url":null,"abstract":"<div><div>The San Clemente satellite pluton (SCP), located on the eastern flank of the Achala Intrusive Complex (AIC) or Achala Batholith in southwestern Gondwana, represents a crucial record of Devonian foreland magmatism. This study integrates petrological and geochemical data, including whole-rock Sr–Nd and zircon Hf isotopes, as well as geochronological data (U–Pb in zircon and titanite), to constrain the petrogenesis of the SCP. The pluton consists of two main units: the San Clemente granodioritic unit (SCU) and the La Herradura monzogranitic unit (LHU), along with quartz-dioritic and tonalitic enclaves. Petrographic and field evidence suggest an incremental, east-to-west magmatic construction history, involving sequential and nearly synchronous emplacement of quartz-dioritic and tonalitic magmas, followed by the SCU and subsequently the LHU.</div><div>U–Pb geochronological data indicate a protracted magmatic history for the satellite pluton and its enclaves, spanning from the Early to Middle Devonian. This activity is recorded in both antecrysts (∼404 Ma) and autocrysts (390–384 Ma), marking the onset of construction of the Achala Intrusive Complex. The presence of antecrysts points to early magmatic processes occurring in a deep crustal mush reservoir, whereas the autocryst ages reflect the development of a magma chamber at or near the final emplacement level.</div><div>Petrological, geochemical, and isotopic data classify the SCU as High-SiO₂ Adakites (HSA) (SiO₂ = 68.7–70.7 %, K₂O/Na₂O = 0.4–0.6, A/CNK (molar percent Al<sub>2</sub>O<sub>3</sub>/[CaO + Na<sub>2</sub>O + K<sub>2</sub>O]) = 1.04–1.05, with high Sr/Y and La<sub>N</sub>/Yb<sub>N</sub> ratios, suggesting a source derived from the partial melting of a thickened mafic lower crust with limited input from the mantle (εNd<sub>t</sub> = −2.3 to −1.8; <sup>87</sup>Sr/<sup>86</sup>Sr<sub>t</sub> = 0.7047–0.7043; εHf<sub>t</sub> = −9.0 to +2.2). The LHU exhibits hybrid compositions, combining peraluminous two-mica granites with adakitic affinities (SiO₂ = 71.9 %, K₂O/Na₂O = 1.12, ASI = 1.07, with high Sr/Y and La<sub>N</sub>/Yb<sub>N</sub> ratios), indicative of a dominant felsic crustal source with minor mafic contributions (εNd<sub>t</sub> = −4.6; <sup>87</sup>Sr/<sup>86</sup>Sr<sub>t</sub> = 0.7057; εHf<sub>t</sub> = −12.0 to +2.2). The enclaves show geochemical affinities to primitive andesites and sanukitoids (SiO₂ = 56.1–57.4 %, MgO = 5.2–7.0 %, Mg# (molar percent 100 × MgO/(MgO+FeOt)) = 59–65, Cr = 124–151 ppm, Ni = 121–124 ppm, Ba = 235–1323 ppm, Sr = 501–753 ppm, Ce = 47–275 ppm), reflecting a metasomatized lithospheric mantle source with crustal contamination (εNd<sub>t</sub> = −2.8 to −3.0; <sup>87</sup>Sr/<sup>86</sup>Sr<sub>t</sub> = 0.7066–0.7091; εHf<sub>t</sub> = −3.5 to +3.8).</div><div>These findings indicate that the San Clemente pluton preserves key evidence that the formation of the AIC began with partial melting near the base of a thickened crust, followed by more","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108132"},"PeriodicalIF":2.9,"publicationDate":"2025-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144147858","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":"Chemical discrimination of magmatic vs. metamorphic blue corundum: The problem of corundum formed in partial melt and its implications for sapphire exploration and deposit modeling","authors":"Philippe M. Belley ,&nbsp;Ofure Onodenalore ,&nbsp;Lindsey Abdale ,&nbsp;Lee A. Groat ,&nbsp;Mostafa Fayek","doi":"10.1016/j.lithos.2025.108125","DOIUrl":"10.1016/j.lithos.2025.108125","url":null,"abstract":"<div><div>Blue and brown corundum from the Blue Jay sapphire occurrence, British Columbia, Canada, which occurs in restite-rich pods suspended in voluminous leucosome formed from the partial melting of a metapelitic protolith, plots as “magmatic” in well-established chemical discrimination diagrams for blue sapphire based on trace element concentrations and ratios (Mg, Fe, Ti, Cr, Ga). The “magmatic” classification in these diagrams was previously known to apply only to blue corundum from syenites and some alkali basalts, where corundum is interpreted to have formed from magmatic (sensu stricto) crystallization and not as a restitic phase. Blue Jay corundum δ¹⁸O_VSMOW values are in the range of ca. 4–6 ‰, which is commonly interpreted to reflect a mantle-like signature, inconsistent with the petrogenesis of the Blue Jay corundum-bearing restite in leucosome. Blue Jay corundum represents an important exception to the common rules of geological origin estimation using trace elements and oxygen isotopes. These new data must be taken into consideration when developing genetic models for xenocrystic sapphire or identifying possible source rocks for detrital sapphire.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108125"},"PeriodicalIF":2.9,"publicationDate":"2025-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144115327","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":"Mixing of subduction zone and intracontinental magmas at Dexing porphyry Cu (AuMo) deposit, China: Evidence from Ti isotopic compositions","authors":"O. Nadeau ,&nbsp;S. De Souza ,&nbsp;Jin Li (回复)","doi":"10.1016/j.lithos.2025.108124","DOIUrl":"10.1016/j.lithos.2025.108124","url":null,"abstract":"<div><div>At Dexing porphyry Cu (Au<img>Mo) deposit, China, the tectonic setting in which granodioritic porphyry magma was generated has remained contentious: petrogenetic models involve either subduction zone magma in a continental arc setting, or magma genesis during Gan Hang intracontinental rifting. Interestingly, Ti stable isotopic variations (δ^49/47Ti_OL-Ti) show the potential to help distinguish subduction zone-, mid-ocean ridge-, and intraplate-related rocks, when compared against SiO₂ concentrations. Here, although the samples represent differentiated magmas that were significantly hydrothermally altered, the δ^49/47Ti_OL-Ti values and SiO₂ concentrations are shown to be insignificantly affected by hydrothermal alteration. A SiO₂-δ^49/47Ti_OL-Ti tectonomagmatic discrimination diagram shows Dexing granodioritic porphyry with a subduction zone signature, and related mafic microgranular enclaves (MME) representing intraplate magma, in agreement with some literature. The simplest way to explain such relations is that already proposed for Dexing and consists in subduction zone-related calc-alkaline (adakitic) magmatism, followed by slab delamination, extension, asthenospheric up flow, and intraplate alkaline magmatism.</div><div>Two holes drilled vertically and sampled semi-continuously, over 300 m through the center of the porphyry and 400 m through its margin, show compositional heterogeneity at the meter scale, and repeating cycles of high and low δ^49/47Ti_OL-Ti values, SiO₂, and immobile high field strength element concentrations. These cycles are best explained by a polyphase emplacement of the porphyry through multiple injections of magmas, which must have evolved through fractional crystallization, in a system consisting of interconnected pathways established over ranges of depths and pressures, also showing variations in temperature and composition. The data presented here support field relations, petrographic observations, and suggest the injection and mixing of intraplate mafic magma with subduction zone porphyry magma, and evolution through fractional crystallization and partial assimilation of surrounding metapelites.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108124"},"PeriodicalIF":2.9,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144108255","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":"Clinopyroxenite generation via high-pressure crystallization of a moderately evolved MORB-type basalt: Experiments from 1.0 to 2.5 GPa","authors":"G. Borghini,&nbsp;C.F. Crotti,&nbsp;P. Fumagalli","doi":"10.1016/j.lithos.2025.108123","DOIUrl":"10.1016/j.lithos.2025.108123","url":null,"abstract":"<div><div>Pyroxenites represent widespread lithological heterogeneities found in the upper mantle in various geodynamical settings. Their origin can be attributed to different magmatic or metamorphic processes or a combination of them. Several mantle pyroxenites are believed to result from melt segregation at high-pressure conditions (<em>P</em> ≥ 1 GPa) of mantle-derived evolved melts. In this study, we performed experiments at 1–2.5 GPa and 1100–1300 °C to investigate the mineralogy and mineral chemistry in pyroxenites formed through high-pressure crystallization of a MORB-like evolved (X_Mg = 0.6) basalt. High temperature (<em>T</em> &gt; 1200 °C) isothermal experiments revealed that clinopyroxene is the liquidus phase. In order to simulate closed-system crystallization after deep melt segregation in the mantle, some experiments experienced isobaric cooling down to 1100 and 1150 °C. Garnet precipitates after clinopyroxene from the basaltic melt at <em>P</em> ≥ 1.5 GPa. At 1 GPa, low-forsterite olivine was observed also in association with plagioclase at 1100 °C. Upon cooling, X_Mg in clinopyroxene decreases (down to 0.66) accompanied by a slight decrease in Ca and an increase in Ti content. At increasing pressure, clinopyroxenes exhibit progressively higher Na and Al contents with decreasing Ca and Cr concentrations. Grossular and Almandine contents in garnet are inversely correlated with temperature. Pyroxenites generated through infiltration and crystallization of MORB-type basalt are garnet clinopyroxenites at P from 1.5 to 2.5 GPa and plagioclase+olivine clinopyroxenites at 1 GPa. Mineral compositions and modal abundances derived from experiments have been employed to estimate the bulk compositions of pyroxenites formed through pure high-pressure crystallization. Computed bulk-rock resemble some garnet clinopyroxenites documented in orogenic and ophiolitic ultramafic massifs.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108123"},"PeriodicalIF":2.9,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144072219","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":"Subducted oceanic crust in the source of post-collisional magmatism: Geochemical constraints from the Early Devonian volcanic rocks in the East Kunlun Orogenic Belt, Northern Tibetan Plateau","authors":"Song-Yue Yu ,&nbsp;Lie-Meng Chen ,&nbsp;Zhong-Jie Bai ,&nbsp;Wen Chen ,&nbsp;Yuan-Yuan Zhou ,&nbsp;Shu-Kuan Wu ,&nbsp;Zhi-An Wang","doi":"10.1016/j.lithos.2025.108122","DOIUrl":"10.1016/j.lithos.2025.108122","url":null,"abstract":"<div><div>The post-collisional volcanic rocks are widely distributed in orogenic belts and may preserve the geochemical signatures of previous crust-mantle interaction between mantle-wedge peridotite and subducting oceanic slab. However, uncertainties persist regarding the mechanisms by which subducted oceanic crustal materials participate in the formation of post-collisional magmas. The nature and quantity of recycled crustal materials in the mantle source of the post-collisional magmas are not well constrained. Here, we present an integrated study of whole-rock major and trace elements and Sr-Nd-Hf isotopes together with zircon U<img>Pb dating for the Dagangou volcanic rocks from the East Kunlun Orogenic Belt (EKOB). Our results demonstrated that the Dagangou volcanic rocks from the EKOB were formed at 409.2 ± 3.5 Ma, coeval with the regional post-collisional magmatism. These volcanic rocks were divided into two magma series: calc-alkaline and tholeiitic, with the calc-alkaline lavas erupting slightly earlier than the tholeiitic lavas. The calc-alkaline volcanic rocks display relatively high SiO₂ (51.3–59.9 wt%), La/Sm (3.6–6.1), Th/La (0.2–0.5), ⁸⁷Sr/⁸⁶Sr_i (0.7070 to 0.7234), and low FeOT (5.6–9.0 wt%), Nb/U (2.9–7.8), ε_Nd (−8.85 to −1.17) and ε_Hf (−3.78 − +2.60). In contrast, the tholeiitic volcanic rocks exhibit relatively low SiO₂ (49.3–55.3 wt%), La/Sm (2.0–4.2), Th/La (0.1–0.4), ⁸⁷Sr/⁸⁶Sr_i (0.7043 to 0.7111), and high FeOT (8.0–10.2 wt%), Nb/U (3.3–14.8), ε_Nd (−3.19 − +2.86) and ε_Hf (−0.10 − +8.30). Our modeling calculations suggest that the enriched pyroxene-rich metasomatites in the mantle wedge have played a dominant role (~60–80 %) in the generation of the calc-alkaline volcanic rocks. In contrast, both the depleted peridotite in the asthenospheric mantle and the enriched metasomatites in the mantle wedge have made significant contributions to the formation of tholeiitic volcanic rocks. The Dagangou volcanic rocks from EKOB were generated by partial melting of the depleted peridotite in the asthenospheric mantle and the pyroxene-rich metasomatites in the lithospheric mantle, which was triggered by the detachment of the Proto-Tethyan slab and subsequent upwelling of the asthenospheric mantle.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108122"},"PeriodicalIF":2.9,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144072082","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":"Deformation microstructures and fabric development of clinopyroxene in antigorite serpentinite: Insights from Val Malenco, Italian Alps","authors":"Wenlong Liu ,&nbsp;Junfeng Zhang ,&nbsp;Yongfeng Wang ,&nbsp;Yi Cao ,&nbsp;Lili Xu ,&nbsp;Zhenmin Jin","doi":"10.1016/j.lithos.2025.108118","DOIUrl":"10.1016/j.lithos.2025.108118","url":null,"abstract":"<div><div>The (100)[001] clinopyroxene (cpx) fabric, characterized by clustering of the [001] axes along the lineation and the [100] axes normal to the foliation, is a common cpx fabric in lower crustal and mantle rocks. However, the physical processes remain unclear for the formation of this common cpx fabric. This study investigates the deformation microstructures of cpx in an antigorite serpentinite from the Val Malenco, located in the eastern central Italian Alps. The cpx grains can be classified into four types: porphyroclasts cpx, lenticular polyphase aggregate bands, fine-grained polyphase aggregates along olivine grain boundaries, and fine-grained cpx aggregate pockets. Microstructural observations, along with major and trace element analyses, suggest that the porphyroclasts cpx are remnants of primary peridotite, while other cpxs are metasomatic products by fluid activity. Notably, the cpx grains in the lenticular polyphase aggregate bands show a strong (100)[001] fabric, with a significant correlation between shape preferred orientation (SPO) and crystallographic preferred orientation (CPO) in fine-grained cpx aggregates. Intracrystalline deformation features are rare in cpx, indicating the operation of mechanisms other than dislocation creep. Based on the analyses of chemical composition and microstructure, we propose that dissolution-precipitation creep and oriented growth, governed by deviatoric local stress, are key mechanisms for the development of the strong (100)[001] cpx fabric in the Val Malenco serpentinized peridotite. This work also sheds light on the interpretation of strong (100)[001] cpx fabrics observed in lower crustal and upper mantle rocks in fluid rich environments.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"508 ","pages":"Article 108118"},"PeriodicalIF":2.9,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143935765","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":"Hydrous and oxidised deep lithospheric mantle revealed by amphibole megacrysts from the northwest North China Craton","authors":"Lin-Lin Hu ,&nbsp;Hong-Kun Dai ,&nbsp;Qing Xiong ,&nbsp;Shao-Kui Pan ,&nbsp;Jiang-Gu Lu ,&nbsp;Jian-Ping Zheng","doi":"10.1016/j.lithos.2025.108121","DOIUrl":"10.1016/j.lithos.2025.108121","url":null,"abstract":"<div><div>The destruction of the North China Craton (NCC) is generally attributed to the complex thermal-mechanical-chemical effects of the (Paleo-) Pacific plate subduction on the lithospheric mantle. However, the effects of other tectonic regimes, especially the subduction of the Paleo-Asian oceanic (PAO) plate, remain poorly constrained. Here, this is explored using major- and trace-element, and Sr-isotope data on newly discovered amphibole megacrysts in the ∼89 Ma basalts from Langshan area, northwest NCC. The megacrysts are chemically homogeneous with a few Fe–Ti oxide inclusions and classified as Pargasite &amp; Magnesio-Hastingsite with high Mg# (71.6–78.3) and contents of Al₂O₃ (14.55–15.39 wt%), TiO₂ (2.65–3.02 wt%) and K₂O (1.88–2.12 wt%). They are characterized by low rare earth element (REEs) concentrations (21.4 to 40.6 ppm), notable enrichments in fluid-loving elements (e.g., Ra, Ba, Sr) and variable Sr-isotopic ratios (0.7018–0.7049). The megacrysts are inferred to crystallize from oxidised (mean ΔFMQ = +0.8) and hydrous (3.6–4.7 wt%) parental magmas in the crust-mantle transition zone (1.1–1.2 GPa). Such parental melts are likely derived from amphibole-bearing lithospheric mantle due to the impregnation of hydrous fluids released from the shallowly subducted PAO slab. Together with studies on the host basalt-xenolith association and the general knowledge on the eastern NCC lithosphere, our study reveals hydration and oxidization effects related to the fossil subduction from the north and emphasizes the modification of the craton lithospheric mantle by accumulated effects from circum-craton subduction episodes.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108121"},"PeriodicalIF":2.9,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144069071","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":"Infracrustal reworking and cryptic crustal growth during the Variscan Orogeny: Stable isotopic evidence from (ultra-) potassic magmatic rocks of the Moldanubian Zone, Bohemian Massif","authors":"Vojtěch Janoušek ,&nbsp;Tomáš Magna ,&nbsp;Anne-Sophie Tabaud ,&nbsp;Torsten Vennemann ,&nbsp;John M. Hora ,&nbsp;František V. Holub","doi":"10.1016/j.lithos.2025.108115","DOIUrl":"10.1016/j.lithos.2025.108115","url":null,"abstract":"<div><div>Isotopic ratios of some elements in rocks derived from a mixture of mantle and crust-derived components can mask the true extent of mantle involvement in melt generation. The mantle trace-element budget (including, for example, Sr and Nd) can be swamped by metasomatism via fluids/melts from deeply subducted mature continental crust, whereas the major-element budget can remain largely intact. Such a scenario may occur in hot collisional orogens and result in underestimation of ‘juvenile’ (mantle-derived) material added to the crust in these settings (‘cryptic crustal growth’).</div><div>Variscan (ultra-)potassic magmatic rocks from the Moldanubian Zone of the Bohemian Massif have crust-like δ⁷Li (−2.0 ‰ to +2.3 ‰) and δ¹⁸O (+7.8 ‰ to +9.9 ‰), consistent with the above-described situation. Together with previously published Sr–Nd–Mg isotopic data, geological, geophysical, and petrographic information, those metasomatic components were identified as Ordovician–Silurian felsic metaigneous rocks and metabasites of the Saxothuringian bimodal magmatic association. During deep subduction, these lithologies sampled adjacent mantle lithosphere and were transformed into typical Moldanubian (U)HP–(U)HT granulites, releasing fluids/melts that reacted with surrounding depleted mantle, forming glimmerite veins.</div><div>Moldanubian (ultra-)potassic magmatic rocks derived from the glimmerite-veined mantle domains therefore have a dual geochemical character: incompatible elements (and Sr, Nd, Pb, Li isotopic systems) have the isotopic fingerprint of subducted continental crust, whereas high MgO, mg#, transition metal contents and Mg isotopic ratios reflect their origin from mantle peridotite. In detail, the fate of each elements/isotopic systems depends on the crustal slab and mantle wedge compositions, partitioning into slab-derived fluid/melt, mode of metasomatism and melting of the resulting incompatible-element-enriched metasomes. The picture is further blurred by crystal fractionation and interactions with the overriding orogenic crust at a stage of advanced anatexis.</div><div>Based on our study, we propose two new terms: (1) ‘infracrustal reworking’ for contamination of lithospheric mantle by deeply subducted material (partial melts/fluids derived therefrom) followed by its swift re-emergence in the (ultra-)K magmas, and (2) ‘intracrustal reworking’ for remobilization of pre-existing crust by partial melting and/or erosion and sedimentation, i.e. solely within continental crustal reservoir. Use of the term ‘juvenile’, canonical depleted mantle end-member composition and Nd isotopes mapping in hot collisional orogens (e.g. Variscan and Himalayan–Tibetan belts) is discouraged.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108115"},"PeriodicalIF":2.9,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137873","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":"Conditions of diamond and graphite crystallization in the reduced metal-bearing mantle","authors":"Yuri N. Palyanov,&nbsp;Igor N. Kupriyanov,&nbsp;Yuri M. Borzdov,&nbsp;Denis V. Nechaev,&nbsp;Ivan D. Novoselov","doi":"10.1016/j.lithos.2025.108120","DOIUrl":"10.1016/j.lithos.2025.108120","url":null,"abstract":"<div><div>According to modern concepts, some natural diamonds, including CLIPPIR diamonds, were formed via crystallization from metal‑carbon melts under reducing conditions of the mantle, but many questions regarding their genesis remain debatable. In the present work, the influence of methane‑hydrogen fluid on diamond crystallization was studied in the Ni₇Fe₃-C system with anthracene (C₁₄H₁₀) additives at pressure 5.5 GPa and temperature 1400 °C using multi-anvil split-sphere high-pressure apparatus BARS. It has been found that an increase in the anthracene content from 0 to 2 wt% leads to a decrease in the degree of graphite-to-diamond conversion from 100 % to zero indicating the inhibitory role of the additive. With increasing anthracene content, the growth of diamond single crystals ([C₁₄H₁₀] ≤ 0.72 wt%) is replaced by spontaneous crystallization ([C₁₄H₁₀] = 0.9 wt%), then antiskeletal diamond crystals and metastable graphite are formed ([C₁₄H₁₀] = 1.17–1.61 wt%), at higher anthracene contents ([C₁₄H₁₀] = 2–2.69 wt%) only metastable graphite crystallizes. Inclusions of metal, graphite, methane and hydrogen are found in crystallized diamonds. With increasing anthracene addition in the system, the nitrogen impurity in the diamonds decreases from 190 to 225 ppm to ≤20 ppm. To elucidate the influence of pressure and temperature on diamond crystallization, the second series of experiments was carried out at an anthracene content of 2 wt%, pressure of 7.5 GPa, in the temperature range of 1400–1700 °C. It has been established that at temperatures of 1400 and 1500 °C diamond and metastable graphite crystallize, and at 1600 and 1700 °C only diamond crystallization is realized. The degree of graphite-to-diamond transformation increases from 0 to 5 to 100 % with increasing temperature in the range of 1400–1700 °C. Thus, three main factors controlling the processes of diamond and metastable graphite crystallization in metal‑carbon systems have been experimentally established: the concentration of CH₄-H₂ fluid, which has an inhibitory effect on the processes of diamond formation, as well as pressure and temperature, the increase of which significantly expands the region of diamond crystallization. It is substantiated that the inclusions of metal, graphite, methane and hydrogen, antiskeletal structure of crystal faces and reduced nitrogen concentrations in diamonds can be indicative features of diamonds formed in the reduced metal-bearing mantle with an increased content of methane‑hydrogen fluid.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"508 ","pages":"Article 108120"},"PeriodicalIF":2.9,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143935768","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":"Discovery of a petalite-type pegmatite in the eastern Himalaya and implications for rare-metal mineralization","authors":"Lei Xie ,&nbsp;Rucheng Wang ,&nbsp;Le Rao ,&nbsp;Fuyuan Wu","doi":"10.1016/j.lithos.2025.108112","DOIUrl":"10.1016/j.lithos.2025.108112","url":null,"abstract":"<div><div>The Himalayan Orogen contains many leucogranitic plutons associated with Li mineralization, including those at Pusila, Gyirong, Lhozhag, and Kuqu. Pegmatites associated with these plutonic bodies typically host Li-bearing minerals, including spodumene, petalite, lepidolite, and elbaite. Lithium enrichment has also been identified in the Gaowu pegmatite, eastern Himalaya. Two distinct types of pegmatite (the dominant tourmaline pegmatite [Tur Peg] and minor garnet pegmatite [Grt Peg]) are observed intruding both the Gaowu pluton and the surrounding country rocks (Rouqiecun Group in Tethyan Himalayan sedimentary sequence). Unlike the Li minerals reported in Himalayan leucogranitic systems, petalite was discovered in the Gaowu Tur Peg and is the only primary Li-bearing mineral, with zinnwaldite and Li-bearing muscovite being secondary Li-bearing minerals. In this study, we investigated the petrogenesis of the pegmatites and related Li mineralization using the chemical compositions of petalite, micas, tourmaline, garnet, beryl, oxide minerals, and zircon, B isotope data for tourmaline, and U–(Th)–Pb ages of monazite and columbite-group minerals in the Gaowu pegmatites. The pegmatites and mineralization yield ages of ca. 23 Ma, coeval with the earliest Gaowu leucogranite and tectonic activity of the South Tibetan Detachment System (STDS). The narrow range of B isotopic compositions of leucogranite and the pegmatite (mean values of −12.32 ‰ ± 0.08 ‰ and − 12.58 ‰ ± 0.069 ‰, respectively) show they had the same source and underwent similar processes. The decreasing tourmaline and increasing garnet and beryl abundances from the leucogranite, through Tur Peg, to Grt Peg reflect an increasing degree of fractionation, and are associated with increasing zircon Hf content (up to 18 wt% HfO₂), garnet spessartite component (i.e. close to endmember composition), and Mn^# values (Mn/[Mn + Fe]) of columbite-group minerals; i.e. close to manganocolumbite endmember composition. The various occurrences of petalite correspond to crystallization during the magmatic-hydrothermal processes. Based on the P-T-controlled crystallization of Li-alumosilicate minerals (spodumene, petalite, and eucryptite etc.), the Gaowu petalite-bearing Tur Peg is inferred to have crystallized in a low pressure and may have been intruded at a shallow level in association with tectonic activity of STDS. The presence of zinnwaldite and Li-bearing muscovite indicates a Li-F-rich fluid during the late stage of the magmatism. In addition, beryl Li contents (up to ~3800 ppm) could be a useful indicator of potential Li mineralization in the Himalaya, given that the beryl is the most common accessory mineral in the Himalayan pegmatite.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"510 ","pages":"Article 108112"},"PeriodicalIF":2.9,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144069069","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}