Lithos最新文献

{"title":"Geochronology and geochemistry of igneous rocks in the Qinfang belt: Implications for spatio-temporal framework of Paleo-Tethys","authors":"Yue Qin ,&nbsp;Yun Zhou ,&nbsp;Xijun Liu ,&nbsp;Yongshan Zhao ,&nbsp;Zhenglin Li ,&nbsp;Liya Yang ,&nbsp;Chen Li ,&nbsp;Yongfeng Cai","doi":"10.1016/j.lithos.2024.107900","DOIUrl":"10.1016/j.lithos.2024.107900","url":null,"abstract":"<div><div>The formation and evolution of the Paleo-Tethys is well documented in Southeast Asia. The Qinfang tectonic belt in the South China Block contains numerous granitic and volcanic rocks; however, the timing of their formation remains unconstrained. In this study, a spatiotemporal framework for the Paleo-Tethys is proposed based on a comprehensive analysis of zircon U<img>Pb geochronological and geochemical data of the Indosinian igneous rocks in the Qinfang tectonic belt. Geochronological results showed that the granitic and volcanic rocks had zircon U<img>Pb ages of 252–245 Ma, indicating that contemporaneous granitic and volcanic activities occurred in the belt. The granite samples belonged to the peraluminous high-K calc-alkaline-shoshonitic series of rocks and showed geochemical signatures similar to those of the S-type granite. Their formation is related to the evolution of the Paleo-Tethys with the parental magma of the rocks likely derived by partial melting of crustal materials that differentiation by fractional crystallization. Combined with regional geological data, this suggests that the Indosinian magmatic assemblages, geochemical characteristics, and sedimentary sequences in the Qinfang tectonic belt are consistent with those in the Jinshajiang, Ailaoshan, and Hainan Island regions. This indicates that these regions belong to the Paleo-Tethyan tectonic domain during the Indosinian, and that the Qinfang tectonic belt likely represents a branched ocean basin of the Paleo-Tethys.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107900"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161064","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 geodynamic mechanism of Early Miocene post-collisional ultrapotassic rocks in the eastern Lhasa Terrane, southern Tibet","authors":"Chenyuan Hua ,&nbsp;Feng Huang ,&nbsp;Song Zhang ,&nbsp;Haiyan Fan ,&nbsp;Yunchuan Zeng ,&nbsp;Mingjian Li ,&nbsp;Shuo Wang ,&nbsp;Xi Chen ,&nbsp;Jing Hu ,&nbsp;Jifeng Xu","doi":"10.1016/j.lithos.2024.107931","DOIUrl":"10.1016/j.lithos.2024.107931","url":null,"abstract":"<div><div>Post-collisional ultrapotassic volcanic rocks (UPVRs) in the Tethyan domain archive crucial information about the composition and evolution of the lithospheric mantle, offering valuable insights into deep geodynamic processes. The Tibetan Plateau, particularly the Lhasa Terrane in its southern part, remains a subject of debate regarding the genesis and geodynamic mechanisms of the UPVRs. This study investigates geochronology, mineralogy, and whole-rock geochemistry of the UPVRs in the Majiang area of Lhasa Terrane, southern Tibet. Zircon U<img>Pb dating reveals that these rocks formed at ca. 21 Ma. Petrologically, the Majiang volcanic rocks are classified as trachyandesites, while geochemically they qualify as ultrapotassic rocks (characterized by K₂O &gt; 3 wt%, MgO &gt; 3 wt% and K₂O/Na₂O &gt; 2). They exhibit a broad range of SiO₂ contents (45.85–57.94 wt%) and high Mg# values (57.7–72.3). Elevated trace element concentrations, marked by enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs), suggest a mantle source influenced by fluid/melt interactions. The presence of phlogopite phenocrysts in the Majiang UPVRs suggests high magma temperatures (1116 ± 15 °C) and low crystallization pressures (1.3 ± 0.3 GPa). Trace element geochemical modeling indicates that the Majiang UPVRs likely originate from a garnet stable mantle domain and experience rapid magma ascent after their formation. The Majiang UPVRs exhibit high Th/U (8.97–19.08) and Th/La (2.27–2.45) ratios, low Hf/Sm (0.52–0.64) ratios, and enriched Sr<img>Nd isotopes (⁸⁷Sr/⁸⁶Sr_i = 0.717286–0.721658, ε_Nd(t) = −9.55 - -9.28). These geochemical signatures suggest derivation from an enriched lithospheric mantle metasomatized by oceanic sediments. Integration of published data reveals that the UPVRs in both the eastern and western Lhasa Terrane share close geochemical affinities, suggesting a common mantle source. However, limited UPVR exposures in the eastern Lhasa Terrane and slightly more depleted Sr<img>Nd isotopes in the Majiang UPVRs compared to those in the western Lhasa Terrane imply distinct Miocene geodynamic processes. Lithospheric convective thinning caused by post-collisional extension and mantle upwelling likely occurred more extensively in the eastern Lhasa Terrane. This process may have led to the gradual replacement of ancient lithospheric mantle by juvenile material in the east, contrasting with the more localized effects in the western Lhasa Terrane.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107931"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161623","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 mid-Cretaceous Hohonu Batholith (South Island, New Zealand): Identifying magmatic sources and processes during onset of crustal extension","authors":"Robert Bolhar ,&nbsp;Stephen D Weaver ,&nbsp;Rose Turnbull ,&nbsp;Tod E Waight ,&nbsp;Martin J Whitehouse ,&nbsp;Roland Maas ,&nbsp;Uwe Ring","doi":"10.1016/j.lithos.2024.107847","DOIUrl":"10.1016/j.lithos.2024.107847","url":null,"abstract":"<div><div>The Hohonu Batholith is an aggregation of mostly mid-Cretaceous granitoid plutons on the West Coast of the South Island of New Zealand emplaced during a transitional period between subduction-related compression and continental lithospheric extension. This study reports an integrated dataset, comprising in-situ U-Pb, O and Hf isotope compositions and REE, Ti and other trace and major elements (Zr-Hf, Th-U) for zircons extracted from four representative plutons within the batholith. Our results provide detailed insight into the protracted thermal, chronological and geochemical histories. LA-ICPMS U-Pb zircon ages indicate a primary episode of magma genesis and emplacement from 107 to 113 Ma, confirming published SIMS dating. However, a younger previously unrecognized age population of ∼91–96 Ma is identified, primarily (although not exclusively) in zircon rims. This younger age event coincides with the timing of protracted lithospheric extension and crustal thinning of the Zealandia continent. The cryptic younger zircon ages suggest that Hohonu granitoids experienced a partial thermal overprint (accompanied by Pb loss) mostly recorded in rims. Differences in bulk rock geochemistry between plutons are inferred to reflect variable conditions of partial melting controlled by source mineralogy and H₂O content. Isotope and trace element compositions, along with Ti-thermometry, measured on the same micro-volume of CL-imaged zircons, are used to test if source characteristics were imparted from melt to minerals in zircon-saturated silicic systems. Similarities are revealed in the zircon record of the selected plutonic rocks, confirming their broadly consanguineous relationship and the fundamental role of open-system behaviour, involving hybridization or assimilation between mantle-derived (or juvenile mafic) and crustal-derived components, as previously inferred from whole rock Nd-Sr isotope systematics. However, intra-sample decoupling of zircon O-Hf isotope systematics may also be linked to residual source unmixing. This possibility, in addition to mafic recharge, may have obscured melt source compositional characteristics, and hence zircon REE appear as unsuitable fingerprints of source(s) and conditions of partial melting in this granitoid system. Simple compositional and thermal magma evolution trends appear punctuated by episodes of mafic recharge, presumably during lithospheric thinning.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107847"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161624","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":"Garnet and clinopyroxene from 1.98 Ga Kimozero kimberlites, Karelia, Russia: Evidence of the multistage evolution of the ancient lithospheric mantle","authors":"A.A. Nosova ,&nbsp;A.V. Kargin ,&nbsp;K.G. Erofeeva ,&nbsp;A.Ya. Dokuchaev ,&nbsp;I.A. Kondrashov ,&nbsp;O.I. Okina","doi":"10.1016/j.lithos.2024.107911","DOIUrl":"10.1016/j.lithos.2024.107911","url":null,"abstract":"&lt;div&gt;&lt;div&gt;We present the major and trace element data for garnets and clinopyroxenes from the heavy mineral concentrate of the 1.98 Ga Kimozero kimberlites, Karelia, Russia, in the context of mantle petrology and evolution.&lt;/div&gt;&lt;div&gt;All studied garnets are characterized by high-Cr-Ca compositions with CaO and Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; contents up to 13 wt% and classified as garnets from the wehrlite paragenesis. The uvarovite content could reach up to 0.29 mol%. Kimozero garnets are characterized by low TiO&lt;sub&gt;2&lt;/sub&gt; concentrations and highly enriched in light rare earth elements, distinguishing them from the classical garnet from peridotite xenoliths and megacrysts from Phanerozoic kimberlites.&lt;/div&gt;&lt;div&gt;Based on the variations in garnet composition, we suggest that at 1.98 Ga, the lithospheric mantle of the Karelian craton underwent several tectonothermal events. The high Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; compositions of the studied garnets we propose that the protolith of the Kimozero garnets was a highly depleted high-Mg# high-Cr mantle substrate that underwent extensive melting in the spinel-garnet stability region and that the Cr-rich garnet has a spinel precursor. The high CaO content and elevated LREE and HFSE concentrations indicate that the Kimozero garnets suggested multiple stages of mantle metasomatism. Garnets with high CaO and Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; composition and weakly sinusoidal REE patterns with low Zr/Hf and La/Yb ratios and high Ti/Eu ratios suggested water-rich carbonate fluid as the agent of mantle metasomatism. An increasing the Zr/Hf and La/Yb ratios with low Ti/Eu and significant LREE enrichment in some Kimozero garnets indicates an increasing role of carbonate fluid in the metasomatic processes. Enrichment in the HREE and Zr concentrations, along with decreasing CaO and Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; in garnet, may reflect an additional stage of mantle metasomatism associated with early stages of mantle plume ascent.&lt;/div&gt;&lt;div&gt;Clinopyroxene xenocrysts are predominantly Cr-diopsides with Mg# values ranging 0.85–0.92 with Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; (1.32–4.03 wt%) and Na&lt;sub&gt;2&lt;/sub&gt;O (1.67–2.81 wt%) concentrations, low TiO&lt;sub&gt;2&lt;/sub&gt; contents and enrichment in light rare earth elements (Ce&lt;img&gt;Nd) compared to heavy rare earth elements. Such clinopyroxenes could be formed by a metasomatic process, specifically the interaction of melts that have equilibrated to MARID-type mantle metasomatites with the depleted lithospheric mantle.&lt;/div&gt;&lt;div&gt;The mineralogy of xenocrysts from the Kimozero kimberlite differs from the widespread xenogenic mantle mineralogy of the Neoproterozoic and Phanerozoic kimberlites. The high-Cr and low-Ti contents of the garnets and clinopyroxenes and the presence of uvarovite garnets could be the characteristics of the ancient lithospheric mantle, which was not preserved until the Phanerozoic due to the cooling of the Earth, and numerous plume and metasomatic events that perturbed the subcontinental","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107911"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161512","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 and boron isotope composition of multiple generations of tourmaline from the Nassarawa lithium-rich pegmatites, Nigeria: Implications for the mechanism of lithium enrichment","authors":"Junteng Lv ,&nbsp;Xin Chen ,&nbsp;Junsheng Jiang ,&nbsp;Hans-Peter Schertl ,&nbsp;Liang Cao ,&nbsp;Xiaojia Jiang","doi":"10.1016/j.lithos.2024.107936","DOIUrl":"10.1016/j.lithos.2024.107936","url":null,"abstract":"<div><div>Pegmatites are the primary global source of rare metal lithium (Li). While previous studies highlight the importance of high granitic magma differentiation in the formation of lithium-rich pegmatites, the processes and timescales of magmatic fractionation remain unclear. Specifically, it is uncertain whether lithium-rich melts originate from multiple magmatic pulses or a single continuous fractional crystallization event. This study presents elemental mapping, in-situ trace element analysis, and boron isotope data for four generations of tourmaline sourced from the lithium mineralization of the Nassarawa-Keffi pegmatitic belt in Nigeria. Tourmaline grains intergrowth with plagioclase, quartz, and K-feldspar, display compositional zoning and resorption-precipitation textures, indicating incremental growth predominantly influenced by the injection of multistage magma batches. The notable periodic increases in Li and Mn contents, accompanied by decreases in Fe, as well as the distinct variation trends in the Li/Sc, Li/K, and Li/Ge ratios across the four tourmaline generations, suggest the involvement of at least four distinct melt pulses. The narrow δ¹¹B values observed across all tourmaline generations indicate a single magmatic source. The observed decrease in δ¹¹B values in the later tourmaline generations is likely due to fluid exsolution and mineral crystallization processes. Subsequent magma pulses exhibit higher lithium concentrations than earlier, suggesting that multistage melt pulses and high fractional crystallization within a deep magmatic reservoir are essential for lithium enrichment in the Nassarawa lithium-rich pegmatites. Based on these findings, we propose an alternative model in which multiple melt-release events from a single cooling magmatic reservoir contribute to the formation of lithium-rich pegmatites.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107936"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161860","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":"Petrography and geochemistry of heterogeneous mantle peridotites from the Banovina Ophiolite Complex, Croatia","authors":"Šime Bilić ,&nbsp;Vesnica Garašić ,&nbsp;Alan B. Woodland ,&nbsp;Hans-Michael Seitz","doi":"10.1016/j.lithos.2025.107942","DOIUrl":"10.1016/j.lithos.2025.107942","url":null,"abstract":"<div><div>This study investigated the petrographic and geochemical characteristics of highly serpentinised and heterogenic mantle peridotites exposed in Banovina, central Croatia, which represent the basal ophiolitic unit of the Central Dinaridic Ophiolite Belt (CDOB). Results indicate the existence of two structurally and chemically different sets of peridotites that outcrop along two geographically distinct belts. The northern belt contains mostly serpentinite breccias and serpentinised, depleted and predominantly porphyroclastic lherzolites (N spinel lherzolites and N plagioclase lherzolites) that form part of an ophiolitic mélange. In contrast, the southern belt contains larger masses of peridotites that comprise predominantly fertile lherzolites (S spinel lherzolites) with equigranular to porphyroclastic textures. Bulk rock chemistry reveals that the S spinel lherzolites have lower Cr# and Mg# and higher Al₂O₃, CaO, Na₂O, TiO₂ and REE contents than the N lherzolites. The same relations are also observed when comparing pyroxenes compositions from S and N lherzolites. Trace element signatures of clinopyroxene and orthopyroxene from the two belts are completely different and indicate a different petrogenetic history. Spinels from all N lherzolites have higher Cr# than those from the S lherzolites. Differences between N plagioclase and N spinel lherzolites are most evident from the significantly higher Cr# and TiO₂ in the spinel from plagioclase lherzolites, reflecting subsolidus plagioclase formation. Geochemical and petrographic analysis indicates a subcontinental origin of the S spinel lherzolites and a suboceanic (MOR) origin of the N lherzolites. Both types come with their own petrographic and geochemical heterogeneities that suggest complex and multi-phase petrogenesis. Overall, the results correlate well with studies from other neighboring CDOB localities.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107942"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161958","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":"New integrations of UPb zircon data from Caledonian intrusions in the Southern Uplands of Scotland","authors":"Chloe A.R. Gemmell ,&nbsp;Iain Neill ,&nbsp;Mark Wildman ,&nbsp;Careen MacRae ,&nbsp;David Currie ,&nbsp;Joshua F. Einsle","doi":"10.1016/j.lithos.2024.107941","DOIUrl":"10.1016/j.lithos.2024.107941","url":null,"abstract":"<div><div>The Laurentian margin in Britain and Ireland experienced the Caledonian-Acadian orogenies resulting from Palaeozoic closure of the Iapetus Ocean and accretion of Baltica and peri-Gondwanan terranes. However, the age and significance of magmatism remain contested, without a geologically consistent geodynamic reconstruction. We have interrogated the U<img>Pb zircon record of intrusive complexes within the Southern Uplands-Down-Longford accretionary complex, focused on the Southern Uplands in Scotland. New texturally constrained laser ablation data are presented from the Carsphairn, Black Stockarton Moor, Bengairn, and Cheviot complexes. In these locations, most zircons contain poorly zoned cores with ²⁰⁶Pb/²³⁸U ages no older than ∼ 424 Ma, chemically comparable with younger magmatic overgrowths. Magmatic overgrowth ages confirm emplacement of Carsphairn at ∼ 414–411 Ma, Black Stockarton Moor and Bengairn at ∼ 410–408 Ma, and Cheviot at ∼ 400 Ma. Across the accretionary complex, the onset of zircon growth from ∼ 424 Ma appears to mark slab roll-back processes. Zircon cores may represent stalling and crystallisation of magmas in the deep crust, whilst emplacement into the shallow crust after ∼ 415 Ma accompanies the onset of regional transtension. We do not feel there is sufficient evidence to directly attribute magmatism to slab breakoff, despite this process being popularly championed in Scottish and Irish geology. We discuss the latest geodynamic interpretations of magmatism during the Caledonian-Acadian events, including events to the south of the Iapetus suture, and argue that complete zircon histories have a role to play in reconstruction of ancient orogens.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107941"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143162020","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":"The timing of the Middle Triassic magmatism in the Dolomites area (Southern Alps, Italy): UPb geochronology of zircon and titanite hosted in plutonic rocks and phonolite dykes","authors":"Nicolò Nardini ,&nbsp;Federico Casetta ,&nbsp;Ryan B. Ickert ,&nbsp;Lorenzo Tavazzani ,&nbsp;Disha C. Okhai ,&nbsp;Stefano Peres ,&nbsp;Elio Dellantonio ,&nbsp;Theodoros Ntaflos ,&nbsp;Massimo Coltorti","doi":"10.1016/j.lithos.2024.107894","DOIUrl":"10.1016/j.lithos.2024.107894","url":null,"abstract":"<div><div>The Middle Triassic magmatic event in the Southern Alps (Italy) is characterised by the emplacement and eruption of multiple magma batches with different geochemical affinities in a short time span. In this work, we present the first geochemical and geochronological data on highly differentiated alkaline dykes (phonolites) exposed in and near the Middle Triassic Predazzo magmatic complex (Southern Alps, Italy) and a first complete geochronological survey of the Predazzo pluton. The phonolites, cutting the Middle Triassic volcanic sequences, are sodalite- and aegirine-bearing and have titanite, apatite and magnetite as accessory phases. Their trace element concentration reflects a geochemical signature similar to the orogenic-like signature typical of the Middle Triassic magmatic rocks of the Predazzo complex. New in situ U<img>Pb dating on titanite from the phonolite dykes and U<img>Pb dating on zircon separates from all the magmatic units of the Predazzo pluton show that the phonolite dykes were emplaced between 233.8 ± 3.1 Ma and 238.1 ± 4.5 Ma, i.e., overlapping to and postdating the emplacement and crystallisation of plutonic rocks, which yield ages ranging from 237.97 ± 0.15 Ma to 238.31 ± 0.13 Ma. The ages obtained for the diverse suites of the pluton are in good agreement with previous dating and show that silica-saturated to -undersaturated rocks were placed within the same context in a short time span. Thermometry and hygrometry on titanite, clinopyroxene and K-feldspar revealed that phonolites represent volatile- and REE-rich (H₂O = 8 ± 0.6 wt%) highly differentiated alkaline melts intruding at relatively low T (752–868 °C), which easily caused the spatially related Cu<img>W mineralisation. Comparisons with sub-volcanic rocks exposed in the Central (Edolo) and Western Alps (Finero mafic complex) indicate that the phonolites still preserve the orogenic signature of the Middle Triassic event in the Southalpine, that characterise all magmas emplaced before the opening of the Alpine Tethys in the Late Triassic. These new geochronological constraints on the Predazzo pluton and phonolite dykes enable us to outline the complete sequence of magmatic events associated with the emplacement of the Predazzo volcano-plutonic complex during Mid-Triassic and to speculate about the genesis of Cu<img>W mineralisation.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107894"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161003","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":"The fate of solid-phase transfer in subduction zones: Evidence from Ti-oxides in Luobusa ophiolitic chromitite","authors":"Fahui Xiong ,&nbsp;Basem Zoheir ,&nbsp;Tian Qiu ,&nbsp;Xiangzhen Xu ,&nbsp;Weibin Gui ,&nbsp;Jingsui Yang","doi":"10.1016/j.lithos.2024.107892","DOIUrl":"10.1016/j.lithos.2024.107892","url":null,"abstract":"<div><div>The transport of hydrous components from a subducting oceanic plate to the supra-subduction lithospheric mantle and their influence on arc magmas is well-documented. Yet the transfer of solid-phase materials remains enigmatic, despite an increasing body of literature regarding inherited rutile in well-characterized arc magmas and ophiolitic chromitites. The mechanism governing the introduction of solid phases into the overlying mantle wedge as well as the duration of their residence are poorly understood. This study investigates mineralogical and geochemical characteristics of rutile inclusions in the Luobusa chromitite of southern Tibet.</div><div>In the investigated chromitite, rutile, associated with ilmenite, corundum, ulvöspinel, zircon, and melt silicate inclusions, exhibits geochemical characteristics indicative of derivation from crustal mafic rocks. Estimated formation or recrystallization temperatures of rutile range from 570 to 675 °C at approximately 1.2 GPa. These temperature estimates illustrate the challenges of obtaining accurate dating, as the rutile U<img>Pb system resets near 600 °C. The Fe/Zr ratios in Luobusa rutile serve as indicators of H₂O/Zr ratios, suggesting a significant role for hydrous components in the behavior of high field strength elements (HFSE) during subduction processes.</div><div>A fluid-assisted transport mechanism likely facilitated the movement of HFSE, such as Ti, V, Zr, Nb, and Ta, within accessory mineral phases into the supra-subduction mantle wedge. The presence of rutile and polymorphs of TiO₂, including Ti_0.82Si_0.18O₂ and TiO₂-II, within chromite crystals underscores the extensive recycling and recrystallization processes occurring under diverse mantle conditions during the genesis and evolution of the Luobusa ophiolites.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107892"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161069","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":"Troilite nano-inclusions in apatite: Implications for melt immiscibility from a lamprophyric magma","authors":"Marina Martínez ,&nbsp;Mercè Corbella","doi":"10.1016/j.lithos.2024.107896","DOIUrl":"10.1016/j.lithos.2024.107896","url":null,"abstract":"<div><div>Calcium phosphate apatite is a volatile-rich mineral ubiquitous in terrestrial and planetary igneous rocks and can form by a variety of processes. However, the utilization of this powerful mineral for unraveling complex magmatic systems is challenged due to its crystallographic complexity. Recent work has demonstrated that examination by transmission electron microscopy (TEM) can reveal nanostructures that are of paramount importance for a correct interpretation of its chemistry. Here, we have examined different apatite grains from two thin sections of Les Guilleries lamprophyre dykes (NE Spain), representing the last pulses of deep magma ascension at the end of the Variscan orogeny. We have identified two different generations of F-rich apatites (magmatic and hydrothermal), which have been examined by SEM, EPMA, TEM, and Raman spectroscopy. Primary, magmatic apatites are close to rounded and even-sized, whereas secondary, hydrothermal apatites are highly acicular, cut most of the mineral phases, and contain slightly higher amounts of Cl and detectable rare-earth elements compared to magmatic apatites. Transmission electron microscopy work shows that magmatic apatites contain abundant nano-inclusions (∼5–60 nm in size) in their cores, consisting of euhedral, negative crystals of troilite, an amorphous phase, and/or a possible gas phase. We argue that fluctuations of temperature during ascent of the lamprophyric magma triggered S saturation and subsequent unmixing of a Fe<img>S melt from the silicate magma. The immiscible Fe<img>S melt was trapped in negative crystals of rapidly growing apatite grains. During ascent of the magma, an additional fluctuation of temperature slowed its growth rate and prevented the generation of new, negative crystals, thus the rims of these apatite grains grew free of inclusions. Upon cooling, troilite crystallized at a temperature of ∼950 °C and relatively high oxygen and sulfur fugacities (log <em>f</em>S₂ ≈ −7; log <em>f</em>O₂ &lt; −8.5). The crystallizing troilite was likely followed by exsolution of a Si,Cl-bearing aqueous fluid and a gas phase. Finally, some Cl (∼0.43 wt%) and Si (∼2.87 wt%) from the aqueous fluid phase within the inclusions migrated outwards and interacted with the host apatite at very localized scales (a few nanometers). This study suggests that the unmixing of Fe<img>S melts during calc-alkaline magmatism may be more common than previously recognized, which has important implications for potentially concentrate economically valuable elements that may lead to the formation of ore deposits.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"494 ","pages":"Article 107896"},"PeriodicalIF":2.9,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143161072","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}