Petrology最新文献

{"title":"Paleozoic Tensional Intraplate Magmatism and Mantle Evolution in Central Iran Zone: Geochemistry, Nd-Sr Isotope Data of Lamprophyres","authors":"Sara Veysi,&nbsp;Seyed Mohsen Tabatabaei Manesh,&nbsp;Nargess Shirdashtzadeh,&nbsp;José Francisco Santos","doi":"10.1134/S0869591123040082","DOIUrl":"10.1134/S0869591123040082","url":null,"abstract":"<p>A Permian-Triassic lamprophyric magmatism has developed as dyke and subvolcanic intrusions in the northeast of Isfahan Province, in Central Iran, where is so-called the Chahriseh-Bagherabad area. These rocks mainly consist of olivine, pyroxene, amphibole, and biotite as major minerals and apatite, biotite, muscovite, and opaque as minor minerals with porphyritic texture and with felsic xenoliths and xenocrysts. The Chahriseh-Bagherabad lamprophyres (CBL) magma has undergone significant crustal contamination and fractional crystallization. Based on whole rock geochemistry, these rocks belong to alkaline lamprophyres, derived from a low degree (less than 5%) partial melting of an amphibole-garnet lherzolite mantle and enriched by the lithospheric mantle in the source region. Their ⁸⁷Sr/⁸⁶Sr (0.70435–0.70696) and ¹⁴³Nd/¹⁴⁴Nd (0.51260–0.51276) values were supported by an enriched mantle source of the EMІI-type that has been contaminated by the continental upper crust. Thus, the CBL samples are alkaline rock formed by tensional intraplate magmatism in a Paleo-Tethyan subduction zone in the lower Paleozoic to late Permian in which metasomatism and mantle enrichment occurred. The lamprophyres magmas ascend due to tensional stress during rotation and displacement of the central-eastern Iranian microcontinent.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 4","pages":"459 - 474"},"PeriodicalIF":1.5,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4753345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrogeochemical Characteristics of Late Devonian Metagabbro-Dolerites of the Kara Astrobleme, Nenets Autonomous District, Russia","authors":"R. I. Shaibekov,&nbsp;N. S. Ulyasheva,&nbsp;E. M. Tropnikov,&nbsp;G. V. Ignatiev","doi":"10.1134/S0869591123040070","DOIUrl":"10.1134/S0869591123040070","url":null,"abstract":"<div><p>The paper presents the results of detailed petrographic and petrogeochemical studies of metagabbro-dolerites from the central part of the Kara astrobleme. The data obtained made it possible to narrow the petrographic diversity of the rocks to two varieties: quartz-free metagabbro-dolerites and quartz-bearing metagabbro-dolerites, which were formed through differentiation of a single magmatic melt. The geochemical features of the rocks indicate the heterogeneity of the magma-generating source. The rock-forming minerals of the quartz-free and quartz-bearing metagabbro-dolerites are characterized by the presence of planar elements of the low and middle stages of impact metamorphism.</p></div>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 4","pages":"424 - 439"},"PeriodicalIF":1.5,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4757483","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 of the Changlinggang A-type Syenites in the Western South China Block: Implications for Late Cretaceous Tectonic Evolution of the Neo-Tethys","authors":"Zheng Liu,&nbsp;Guo-Chang Wang,&nbsp;Shu-Cheng Tan,&nbsp;Hao Liu,&nbsp;Mei-Li Li","doi":"10.1134/S0869591123040069","DOIUrl":"10.1134/S0869591123040069","url":null,"abstract":"<p>It is debated whether Cretaceous magmatism and mineralization in southeastern Yunnan (China) resulted from the subduction of Neo-Tethys or Paleo-Pacific lithosphere. To address this problem, we report whole-rock geochemical and Sr–Nd isotopic compositions and zircon U–Pb ages and Lu–Hf isotopic compositions from the Changlinggang syenites in the southeastern Yunnan Sn mineralization belt, western South China Block. LA–ICP–MS zircon U–Pb dating suggests that syenites were emplaced during the Late Cretaceous (79.2 ± 0.5 Ma). They contain nepheline and aegirine, and have high (K₂O + Na₂O) contents (16.0–18.6 wt %), K₂O/Na₂O ratios (0.7–1.7), FeO^T/(FeO^T + MgO) ratios (0.83–0.97), 10⁴ × Ga/Al ratios (2.3–3.7), and (Zr + Nb + Ce + Y) contents (505–2138 ppm), which are typical of A-type granitoids. The samples have slightly more enriched initial Sr–Nd isotopic compositions than the coeval Jiasha gabbros, with (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7088–0.7101 and ε_Nd(Т) values of –7.5 to –6.6. The geochemical data suggest that the Changlinggang syenites were derived by partial melting of enriched lithospheric mantle that had been metasomatized by subducted-sediment-derived melts, followed by crustal assimilation and fractional crystallization of the partial melt during ascent. These results, along with those of previous studies, indicate that Cretaceous magmatism and mineralization in southeastern Yunnan were emplaced in an extensional setting related to subduction of Neo-Tethys lithosphere. Therefore, we propose that the Neo-Tethyan slab was subducted under the western South China Block during the Late Cretaceous.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 4","pages":"440 - 458"},"PeriodicalIF":1.5,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4753425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermodynamic Model of the Fluid System H2O–CO2–NaCl–CaCl2 at P-T Parameters of the Middle and Lower Crust","authors":"M. V. Ivanov","doi":"10.1134/S0869591123040045","DOIUrl":"10.1134/S0869591123040045","url":null,"abstract":"<p>Based on the earlier obtained equations of state for the ternary systems H₂O–CO₂–CaCl₂ and H₂O–CO₂–NaCl, an equation of state for the four-component fluid system H₂O–CO₂–NaCl–CaCl₂ is derived in terms of the Gibbs excess free energy. A corresponding numerical thermodynamic model is built. The main part of the numerical parameters of the model coincides with the corresponding parameters of the ternary systems. The NaCl–CaCl₂ interaction parameter was obtained from the experimental liquidus of the salt mixture. Similar to the thermodynamic models for H₂O–CO₂–CaCl₂ and H₂O–CO₂–NaCl, the range of applicability of the model is pressure 1–20 kbar and temperature from 500 to 1400°C. The model makes it possible to predict the physicochemical properties of the fluid involved in most processes of deep petrogenesis: the phase state of the system (homogeneous or multiphase fluid, presence or absence of solid salts), chemical activities of the components, densities of the fluid phases, and concentrations of the components in the coexisting phases. The model was used for a detailed study of the phase state and activity of water on the H₂O–CO₂–salt sections when changing the ratio <span>({{{{x}_{{{text{NaCl}}}}}} mathord{left/ {vphantom {{{{x}_{{{text{NaCl}}}}}} {({{x}_{{{text{NaCl}}}}} + {{x}_{{{text{CaC}}{{{text{l}}}_{{text{2}}}}}}})}}} right. kern-0em} {({{x}_{{{text{NaCl}}}}} + {{x}_{{{text{CaC}}{{{text{l}}}_{{text{2}}}}}}})}})</span> from 1 to 0. Changes in the composition and density of coexisting fluid phases at a constant activity of water and changes in the total composition of the system are studied. A set of phase diagrams on sections H₂O–NaCl–CaCl₂ for different mole fractions of CO₂ is obtained. Pressure dependencies of the maximal activity of water in the field of coexisting unmixable fluid phases are obtained for several salt compositions of the system. Due to removal of restrictions resulting from a smaller number of components in ternary systems, the thermodynamic behavior of systems with a mixed composition of the salt significantly differs from the behavior of those with a single salt component.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 4","pages":"413 - 423"},"PeriodicalIF":1.5,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1134/S0869591123040045.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4756463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Age and Isotope-Geochemical Characteristics of Ta, Nb, W, Sn Mineralization Associated with Rare-Metal Granites (Khangilay Ore District, Eastern Transbaikalia)","authors":"E. V. Badanina,&nbsp;L. F. Syritso,&nbsp;A. A. Ivanova,&nbsp;N. G. Rizvanova","doi":"10.1134/S0869591123040033","DOIUrl":"10.1134/S0869591123040033","url":null,"abstract":"<div><p>The age relations between the formation of the parent massif and the crystallization time of the associated ore mineralization were established based on isotope-geochronological study of the massif-deposits of the Khangilay ore cluster with various metallogenic specialization in Eastern Transbaikalia. In the Orlovka Li–F granite massif, the crystallization time of columbite–tantalite (145 ± 1 Ma) and cassiterite (144.2 ± 0.3 Ma) (U-Pb, ID-TIMS) is almost identical to the crystallization time of zircon (140.6 ± 2.9 Ма (U-Pb, SHRIMP) and 145 ± 1 Ma (U-Pb, CA-ID-TIMS)), which is an age marker of the formation of massifs. This fact testifies to the magmatogenic nature of rare-metal mineralization. In the Spokojnoye massif – the “standard type” of rare-metal peraluminous granites—a 0.6–3.8 Ma time gap was revealed between the time of massif formation (141.3 ± 1.8 Ма, U-Pb, SHRIMP, 146.9 ± 0.7 Ма, Rb-Sr isotopic system) and crystallization of wolframite (141.8 ± 0.6, Rb-Sr isotopic system and 140.1 ± 1.4 Ма, Sm-Nd isotopic system). This interval likely corresponds to the life time of the hydrothermal system, which produced tungsten mineralization.</p></div>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 4","pages":"383 - 393"},"PeriodicalIF":1.5,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1134/S0869591123040033.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4756452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Experimental Investigation into Interaction between Amphibole and Highly Saline H2O–NaCl–KCl Fluid at 750°C, 700 MPa: Implications to Alkaline Metasomatism of Amphibole Rocks","authors":"L. I. Khodorevskaya,&nbsp;D. A. Varlamov,&nbsp;O. G. Safonov","doi":"10.1134/S0869591123040057","DOIUrl":"10.1134/S0869591123040057","url":null,"abstract":"&lt;p&gt;The paper presents experimental data on the interaction of amphibole with NaCl–H&lt;sub&gt;2&lt;/sub&gt;O and (K, Na)Cl–H&lt;sub&gt;2&lt;/sub&gt;O solutions at varying salt content. When interacting with H&lt;sub&gt;2&lt;/sub&gt;O–NaCl fluid, amphibole remains the predominant mineral in all experiments, and the newly formed minerals are Na-phlogopite, plagioclase, and nepheline/sodalite. At &lt;span&gt;({{a}_{{{{{text{H}}}_{{text{2}}}}{text{O}}}}})&lt;/span&gt; &gt; 0.6, the amphibole melts. When amphibole interacts with H&lt;sub&gt;2&lt;/sub&gt;O–NaCl–KCl fluid at &lt;span&gt;({{X}_{{{{{text{H}}}_{2}}{text{O}}}}})&lt;/span&gt; &lt; 0.40 and &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt;/(&lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt; + &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;NaCl&lt;/sub&gt;) in the fluid, defined as &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;NaCl&lt;/sub&gt; = 0.506 – 0.84&lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt;, the amphibole is replaced by the association of nepheline with sodic plagioclase, sodalite, and biotite. At &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt;/(&lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt; + &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;NaCl&lt;/sub&gt;) &gt; 0.3, nepheline, sodalite, and plagioclase become unstable, K-feldspar is formed, and biotite, clinopyroxene, and amphibole remain stable. At &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt;/(&lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt; + &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;NaCl&lt;/sub&gt;) &gt; 0.5, the association &lt;i&gt;Cpx + Bt + Kfs + Grt&lt;/i&gt; (grossular–andradite) is stable. Thus, grossular–andradite garnet is an indicator of a high potassium activity in the fluid, whereas nepheline testifies that the sodium activity was high. Na → K exchange is typical of the amphibole and biotite, and Ca → Na exchange occurs in the clinopyroxene, and all of these minerals (but neither nepheline nor garnet) remain generally stable within a wide range of the K/Na ratio in the fluid. Clinopyroxene in the experiments spans Ca–Fe–Mg compositions with a varying, sometimes high, Al content, and the amphiboles belong to the pargasite–hastingsite series. With an increase in &lt;span&gt;({{a}_{{{{{text{H}}}_{{text{2}}}}{text{O}}}}})&lt;/span&gt; (&lt;span&gt;({{X}_{{{{{text{H}}}_{{text{2}}}}{text{O}}}}})&lt;/span&gt; &gt; 0.57), i.e., a decrease in the gross salinity of the fluid, melts are generated, and their composition varies from trachyte to phonolite. An increase in the &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt;/(&lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;KCl&lt;/sub&gt; + &lt;i&gt;Х&lt;/i&gt;&lt;sub&gt;NaCl&lt;/sub&gt;) ratio in the fluids leads to a decrease in alumina content of the melts. An increase in the total salinity of the fluid leads to an increase in the content of potassium in the melt and a decrease in the content of chlorine in it. The experiments have shown that interaction between amphibole and fluids containing high NaCl and KCl concentrations results in mineral associations typically produced by alkaline metasomatism of amphibole-bearing rocks and concomitant HCl enrichment in the fluid phase. The substitution of highly saline fluids for highly acidic ones leads to the leaching of Ca, Mg, Fe from the metamorphic rocks, and the transport and redeposition of these components. It follows that significant removal of FeO, MgO, CaO from rocks is sometimes a consequence of the interaction of the host rocks with saline ","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 4","pages":"394 - 412"},"PeriodicalIF":1.5,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4757482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 Data on the Rock and Mineral Composition of Kharchinsky and Zarechny Volcanoes, Central Kamchatka Depression: Heterogeneity of the Mantle Source and Peculiarities of Magma Evolution in the Crust","authors":"N. V. Gorbach,&nbsp;N. A. Nekrylov,&nbsp;M. V. Portnyagin,&nbsp;K. Hoernle","doi":"10.1134/S0869591123030050","DOIUrl":"10.1134/S0869591123030050","url":null,"abstract":"<p>Kharchinsky and Zarechny volcanoes and the Kharchinsky Lake zone of monogenic cones are unique eruptive centers of magnesian lavas located above the northern margin of the Pacific plate subducting beneath Kamchatka. This paper presents new geochemical data on the composition of rocks (55 samples) and minerals (over 900 analyses of olivine, pyroxenes, amphibole, and plagioclase) of these centers analyzed by XRF and LA-ICP-MS (rocks) and electron microprobe (minerals). Most of the studied rocks are magnesian (Mg# = 60–75 mol %) medium-K basalts and basaltic andesites. Moderate-magnesian (Mg# = 52–59 mol %) basaltic andesites are present among the monogenic cones of Kharchinsky Lake. The rare rock varieties include the high-K basalts–basaltic andesites of dikes in the center of Kharchinsky volcano and the magnesian andesites (Mg# = 58–61 mol %) of the extrusions of Zarechnу volcano. The distribution of trace-element contents in these samples demonstrates enrichment in large-ion lithophile elements and light REEs at depletion in high field strength elements and heavy REEs, as is typical of arc rocks. The high-K basalts and basaltic andesites show anomalous enrichment in Ba (&gt;1000 ppm), Th (&gt;3.8 ppm), U (&gt;1.8 ppm), Sr (&gt; 800 ppm, Sr/Y &gt; 50), and light REE (La &gt; 20 ppm), and their compositions are close to those of low-Si adakites. The basalts and basaltic andesites contain phenocrysts of high-Mg olivine (up to <i>Fo</i>_92.6) and clinopyroxene (Mg # up to 91 mol %). The rocks show petrographic and geochemical evidence of fractional crystallization, along with the processes of mineral accumulation and magma mixing. Some of the olivine phenocrysts show high NiO contents (up to 5000 ppm) and an elevated Fe/Mn ratio (up to 80), which were interpreted as evidence of the participation of a pyroxenite source in the magma generation processes. The use of the Ca/Fe and Ni/Mg ratios allowed us to distinguish the composition fields and evolution trends of olivine associated with different sources: peridotite and pyroxenite, which were formed by a reaction between mantle-wedge peridotites and high-Si melts of the subducted oceanic crust. The new data are consistent with other lines of evidence of melting of the subducted Pacific plate edge beneath the northern part of the Central Kamchatka Depression at the Kurile–Kamchatka and Aleutian subduction zone junction and testify to a significant heterogeneity of the mantle in this area.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 3","pages":"320 - 337"},"PeriodicalIF":1.5,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5088961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magnesian Basalts of the Medvezhia Caldera: Dominant Magmas and Their Sources, as Exemplified by Menshiy Brat Volcano, Iturup Island, Kuriles","authors":"D. V. Kuzmin,&nbsp;I. R. Nizametdinov,&nbsp;S. Z. Smirnov,&nbsp;T. Yu. Timina,&nbsp;A. Ya. Shevko,&nbsp;M. P. Gora,&nbsp;A. V. Rybin","doi":"10.1134/S0869591123030062","DOIUrl":"10.1134/S0869591123030062","url":null,"abstract":"<p>The paper presents new data on the formation conditions of basalts from Menshiy Brat postcaldera volcano in the Medvezhia caldera, Iturup Island. The liquidus mineral assemblage consists of olivine (<i>Fo</i> 85.3–90.1 mol %) and chromium spinel (Cr# = 0.46–0.6), which crystallized at 1090–1170°C and oxygen fugacity at NNO + 0.6 (σ = 0.2) to NNO + 0.2 (σ = 0.14) in the course of the eruption. Data on melt inclusions in the liquidus olivine demonstrate that its parental melts were low-Al₂O₃ and low-K₂O, with up to 15.5 wt % MgO, and with an average H₂O content of 5.5 wt %. The newly obtained data on volatile contents in the olivine-hosted melt inclusions suggest that the mafic melts were derived by the partial melting of a peridotitic-rich source with a small admixture of an olivine-free component at 1225°C, under active influence of the slab-derived fluids. These fluids were separated from the subducting slab at 670–705°C and depths of 95–105 km beneath Iturup Island. Our results enhance our understanding of the evolution of basic magmas that serve as a heat and volatile sources during the formation of large calderas.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 3","pages":"279 - 303"},"PeriodicalIF":1.5,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5088127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 Olivine Basalts from Medvezhya Mount (Avachinsky Group of Volcanoes, Kamchatka): The Evidence for Assimilation of Sulfide-Bearing Cumulates","authors":"D. P. Savelyev,&nbsp;N. V. Gorbach,&nbsp;M. V. Portnyagin,&nbsp;V. D. Shcherbakov","doi":"10.1134/S0869591123030074","DOIUrl":"10.1134/S0869591123030074","url":null,"abstract":"<div><p>The role and conditions of liquid immiscibility or crystallization of sulfide phase during evolution of subduction-related magmas remains a debated topic, which bears relevance to the genesis of porphyry copper deposits and evolution of the continental crust. We studied rare volcanic rocks with inclusions of magmatic sulfides in olivine—the basalts of Medvezhya Mount in the Avachinsky group of volcanoes. The rocks belong to primitive (Mg# = 66 mol %) middle-K island-arc olivine basalts. Olivine with normal zoning predominates (~98%) among phenocrysts. The olivine compositions are typical for Kamchatka basalts, except for an unusual trend of increase of MnO content from 0.20 to 0.55 wt % and decrease of Fe/Mn from 60 to 35 with a change of olivine composition from <i>Fo</i>_87.8 to <i>Fo</i>_78.2. Olivine of this group contains numerous inclusions of spinel-group minerals varying in composition from chromium spinel to magnesian magnetite. Olivine phenocrysts with sulfide inclusions are characterized by the absence of or weak reverse zoning and reduced contents of Ca, Ni, Mn, Cr, and Al. The estimated crystallization temperatures are 1036–1241°C for olivine of the prevailing type and 1010–1062°C for sulfide-bearing olivine. The data suggest that crystallization of the main olivine population occurred under relatively shallow conditions and was accompanied by strong magma oxidation. On the contrary, the zoning pattern and compositional features of sulfide-bearing olivine suggest its xenogenic origin and the probable crystallization under deep-crustal conditions from low-temperature water-rich and/or low-Ca magmas. The results obtained confirm the possibility of saturation of oxidized island-arc magmas with sulfide phase at lower crustal conditions, but show that this process is rare and not typical for low-pressure crystallization stage.</p></div>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 3","pages":"263 - 278"},"PeriodicalIF":1.5,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5086054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 and Magmas Sources of the Summit and Flank Eruptions of Klyuchevskoy Volcano in 2020–2021: Isotope (Sr–Nd–Pb–O)-geochemical data","authors":"R. I. Cherkashin,&nbsp;O. V. Bergal-Kuvikas,&nbsp;A. V. Chugaev,&nbsp;Yu. O. Larionova,&nbsp;I. N. Bindeman,&nbsp;A. L. Khomchanovsky,&nbsp;E. Yu. Plutakhina","doi":"10.1134/S0869591123030037","DOIUrl":"10.1134/S0869591123030037","url":null,"abstract":"<div><p>In 2021, a unique event occurred on Klyuchevskoy volcano (Kamchatka). After over 30-year prevalence of summit eruptions, a flank vent was formed. It was named after the Corresponding Member of the USSR Academy of Sciences G.S. Gorshkov. The eruption began immediately after the end of the summit crater activation in 2020–2021 at an altitude of 2850 m in the northwestern part of the volcano, where manifestations of flank volcanism were not observed earlier. This paper presents geochemical and isotopic Sr–Nd–Pb–O data on lavas of the summit and flank eruptions of Klyuchevskoy volcano in 2020–2021. A comparative petrographic analysis was carried out and the chemical composition of the <i>Ol</i>, <i>Cpx</i>, and <i>Pl</i> phenocrysts in these lavas was analyzed. The lavas of both eruptions are alumina andesitic basalts of normal alkalinity. Variations of major oxides in the lavas of the summit eruption and G.S. Gorshkov vent are SiO₂ 53.1–53.2 wt % and 51.6–53.2 wt %, MgO 5.6 wt % and 5.5–6.0 wt %; respectively. Temperature and pressure estimates showed that plagioclase crystallization occurred at 1210–1118°С and 12.3–3.6 kbar in lavas of the summit eruption and at 1203–1119°С and 9.0–3.3 kbar in lavas of the flank vent. The contents of major elements, similar conditions of plagioclase generations and compositional variations of <i>Ol</i>, <i>Cpx</i>, and <i>Pl</i> phenocrysts in the lavas of both eruptions indicate a genetic relationship of the magmas that fed the summit and flank eruptions. The lavas of the 2016 and 2020–2021 summit eruptions, as well as the lavas of the previous summit eruptions of Klyuchevskoy volcano are characterized by the persistent Sr–Nd–Pb isotopic characteristics: ⁸⁷Sr/⁸⁶Sr = 0.703625–0.703626, ¹⁴³Nd/¹⁴⁴Nd = 0.513085–0.513102, ²⁰⁶Pb/²⁰⁴Pb = 18.3148–18.3179. Isotopic ratios ²⁰⁷Pb/²⁰⁴Pb (15.5022–15.5107) and ²⁰⁸Pb/²⁰⁴Pb (37.9597–38.0143) are significantly higher for the lavas of the last summit and flank eruptions than for all Klyuchevskoy lavas of the past eruptions, which indicates more complex magma evolution at crustal levels. The values of δ¹⁸O = 6.49–7.39‰ (SMOW)-in the lavas of the considered eruptions are consistent with previously published data on Klyuchevskoy volcano. The lavas of the Gorshkov vent are enriched with Ba, Zr, Sr and other incompatible elements at constant MgO values in comparison with the lavas of the last summit eruptions, which points to the different evolutionary paths of their magmas. Sharply increased values of the ⁸⁷Sr/⁸⁶Sr ratio (0.703673–0.703743) in the lavas of the G.S. Gorshkov vent, which were not previously observed in the lavas of Klyuchevskoy volcano, testify to the intense crustal assimilation of initial melts in the northwestern part of the volcano.</p></div>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"31 3","pages":"304 - 319"},"PeriodicalIF":1.5,"publicationDate":"2023-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5088123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}