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The Origin of Olivine Basalts from Medvezhya Mount (Avachinsky Group of Volcanoes, Kamchatka): The Evidence for Assimilation of Sulfide-Bearing Cumulates 堪察加阿瓦钦斯基火山群Medvezhya山橄榄玄武岩的成因:含硫化物堆积同化的证据
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-28 DOI: 10.1134/S0869591123030074
D. P. Savelyev, N. V. Gorbach, M. V. Portnyagin, V. D. Shcherbakov

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 Fo87.8 to Fo78.2. 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.

在俯冲相关岩浆演化过程中,液态不混溶或硫化物相结晶的作用和条件一直是一个有争议的话题,这与斑岩铜矿床的成因和大陆地壳的演化有关。我们对阿瓦钦斯基火山群梅德韦日亚山玄武岩中含有岩浆硫化物包裹体的稀有火山岩进行了研究。岩石属原始(mg# = 66 mol %)中钾岛弧橄榄玄武岩。正常分带的橄榄石在斑晶中占主导地位(约98%)。除了MnO含量从0.20 wt %增加到0.55 wt %, Fe/Mn从60 wt %下降到35 wt %,橄榄石组成从Fo87.8变化到Fo78.2外,堪察加玄武岩的橄榄石组成是典型的。该组橄榄石含有大量尖晶石组矿物的包裹体,其组成从铬尖晶石到镁磁铁矿不等。含硫化物包裹体橄榄石斑晶的特征是不存在或弱逆带,Ca、Ni、Mn、Cr和Al含量降低。主要类型橄榄石的结晶温度为1036 ~ 1241℃,含硫化物橄榄石的结晶温度为1010 ~ 1062℃。资料表明,主要橄榄石群的结晶发生在相对较浅的条件下,并伴有强烈的岩浆氧化。相反,含硫化物橄榄石的分带格局和组成特征表明其异种成因,可能是低温富水和(或)低钙岩浆在深地壳条件下结晶形成的。研究结果证实了下地壳条件下氧化岛弧岩浆含硫化物相饱和的可能性,但这一过程较为少见,在低压结晶阶段并不典型。
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引用次数: 0
Conditions and Magmas Sources of the Summit and Flank Eruptions of Klyuchevskoy Volcano in 2020–2021: Isotope (Sr–Nd–Pb–O)-geochemical data 2020-2021年克柳切夫斯科伊火山顶、侧翼喷发条件与岩浆来源:同位素(Sr-Nd-Pb-O)-地球化学数据
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-28 DOI: 10.1134/S0869591123030037
R. I. Cherkashin, O. V. Bergal-Kuvikas, A. V. Chugaev, Yu. O. Larionova, I. N. Bindeman, A. L. Khomchanovsky, E. Yu. Plutakhina

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 Ol, Cpx, and Pl 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 Ol, Cpx, and Pl 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.

2021年,克柳切夫斯科伊火山(堪察加半岛)发生了一次独特的事件。经过30多年的峰顶喷发,形成了一个侧面喷口。它是以苏联科学院通讯委员G.S.戈尔什科夫的名字命名的。此次火山喷发是在2020-2021年山顶火山口活动结束后立即开始的,喷发地点位于火山西北部海拔2850米的地方,此前没有观测到侧火山作用的表现。本文介绍了2020-2021年克柳切夫斯科伊火山峰顶和侧翼喷发熔岩的地球化学和同位素Sr-Nd-Pb-O数据。进行了对比岩相分析,分析了这些熔岩中Ol、Cpx和Pl斑晶的化学组成。两次喷发的熔岩均为碱性正常的氧化铝安山岩玄武岩。峰顶喷发和G.S. Gorshkov火山口熔岩中主要氧化物的变化为SiO2 53.1 ~ 53.2%和51.6 ~ 53.2%,MgO 5.6%和5.5 ~ 6.0 wt %;分别。温度和压力估算表明,斜长石结晶发生在峰顶喷发熔岩1210 ~ 1118°С和12.3 ~ 3.6 kbar,侧翼喷口熔岩1203 ~ 1119°С和9.0 ~ 3.3 kbar。两次火山喷发熔岩中主要元素含量、斜长石生成条件的相似性以及Ol、Cpx和Pl斑晶的组成变化表明,两次火山喷发岩浆的成因关系与顶、侧喷发岩浆有关。2016年和2020-2021年克柳切夫斯科伊火山顶喷发熔岩,以及之前几次克柳切夫斯科伊火山顶喷发熔岩具有持续的Sr-Nd-Pb同位素特征:87Sr/86Sr = 0.703625-0.703626, 143Nd/144Nd = 0.513085-0.513102, 206Pb/204Pb = 18.3148-18.3179。最后一次峰顶和侧面喷发熔岩的207Pb/204Pb(15.5022 ~ 15.5107)和208Pb/204Pb(37.9597 ~ 38.0143)同位素比值明显高于以往喷发的所有克柳切夫斯科伊熔岩,表明地壳水平岩浆演化更为复杂。火山喷发熔岩的δ18O值为6.49 ~ 7.39‰(SMOW),与克柳切夫斯科伊火山资料一致。与上次高峰喷发熔岩相比,高什科夫火山喷发熔岩在MgO值不变的情况下富含Ba、Zr、Sr等不相容元素,表明其岩浆演化路径不同。G.S. Gorshkov火山口熔岩87Sr/86Sr比值(0.703673 ~ 0.703743)的急剧升高,是克柳切夫斯科伊火山熔岩中未曾观测到的,说明火山西北部初始熔体的地壳同化作用强烈。
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引用次数: 1
Sulfide Mineralization in Pyrometamorphosed Upper Crustal Xenoliths, Bezymianny Volcano, Kamchatka 堪察加Bezymianny火山上地壳热变质捕虏体中的硫化物成矿作用
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-28 DOI: 10.1134/S0869591123030049
V. O. Davydova, V. D. Shcherbakov, N. A. Nekrylov, P. Yu. Plechov, V. O. Yapaskurt

Bezymianny volcano eruptions transport numerous xenoliths to the surface. Crustal xenoliths contain unique information about the crust structure and composition of crustal rocks located around the active magmatic system. We describe the chemical and mineral composition of upper crustal xenoliths that pyrometamorphosed (recrystallized and partially melted) in the Bezymianny shallow chamber. We reconstructed protoliths and hydrothermal processes for several rocks, which were previously altered, based on pre-pyrometamorhic relics (primary igneous associations in some xenoliths and rare hydrothermal relics). Moderate-K andesites, basaltic andesites, and basalts of Kamen and Bezymianny volcanoes dominate among the xenoliths. During pyrometamorphism, a microgranoblastic assemblage composed of homogenous pyroxenes, plagioclase, Fe-Ti oxides, and interstitial glass is formed in these xenoliths. Less common xenoliths are presented by high-K basaltic trachyandesite (plateau basalt from the basement of the Klyuchevskaya group of volcanoes). Quartz–carbonate–sulfide mineralization is present in some of them, which formed prior to xenolith entrapment and pyrometamorphism. When xenoliths were entrapped by magma, recrystallization of hydrothermally altered rock produced Fe-wollastonite–hedenbergite association (in some cases with garnet), untypical for Bezymianny. Some of these xenoliths have extremely high copper content (up to 1500 ppm).

贝兹米亚尼火山喷发将大量捕虏体带到地表。地壳捕虏体包含有关地壳结构和地壳岩石组成的独特信息,这些地壳岩石位于活动岩浆系统周围。我们描述了在贝兹曼尼浅室中热变质(再结晶和部分熔化)的上地壳捕虏体的化学和矿物组成。基于前热变质遗迹(部分捕虏体中的原生火成岩组合和罕见的热液遗迹),我们重建了一些先前蚀变的岩石的原岩和热液过程。中钾安山岩、玄武岩安山岩以及卡门火山和贝兹曼尼火山的玄武岩在捕虏体中占主导地位。在热变质过程中,这些捕虏体中形成了由均质辉石、斜长石、铁钛氧化物和间隙玻璃组成的微粒母岩组合。不太常见的包体是高钾玄武质粗面山岩(来自克柳切夫斯卡亚火山群基底的高原玄武岩)。石英-碳酸盐-硫化物成矿作用早于捕虏体包裹和热变质作用。当捕虏体被岩浆包裹时,热液蚀变岩石的再结晶产生了铁硅灰石-镁钙石组合(在某些情况下与石榴石结合),这在贝兹曼尼是不典型的。其中一些捕虏体含有极高的铜含量(高达1500ppm)。
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引用次数: 0
Subduction and Oceanic Magmatism Records in Plutonic Rocks of the Kamchatsky Mys Ophiolite, Eastern Kamchatka 堪察加东部堪察加梅斯蛇绿岩深成岩中的俯冲和大洋岩浆作用记录
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-28 DOI: 10.1134/S0869591123030025
B. A. Bazylev, M. V. Portnyagin, D. P. Savelyev, G. V. Ledneva, N. N. Kononkova

The paper presents petrographic, mineralogical, and geochemical data on dunites, pyroxenites, peridotites, and gabbroids of the Kamchatsky Mys ophiolite. These data were acquired to distinguish cogenetic assemblages of igneous rocks, gain an insight into their geodynamic settings, and test various criteria of genetic links between the different magmatic rocks of ophiolites. The ultramafic and mafic rocks are shown to belong to two series, which differ in the compositions of the primary minerals, bulk rocks, and estimated trapped melts. The rocks of these series are found out to have been produced by geochemically different melts in different geodynamic settings, and during different episodes of mantle magmatism. The rocks of the high-Ti series (gabbro of the Olenegorsk massif, dunite and melanogabbro xenoliths in them, and vein gabbro in these xenoliths) crystallized from N-MORB melts in an oceanic spreading center. The rocks of the low-Ti series (dunite, pyroxenite, and gabbro veins in the residual spinel peridotites of the Mount Soldatskaya massif, as well as pyroxenite, peridotite, and gabbro alluvium and diluvium in the central and western parts of the peninsula) crystallized from water-rich boninite melts in relation to initial subduction magmatism. Taken into account the absence of boninite lavas from the Kamchatsky Mys ophiolite, the plutonic ultramafic rocks (including the rocks of the veins) might be the only evidence of subduction boninitic magmatism in the ophiolites. It was demonstrated that conclusions about the geodynamic settings of plutonic ultramafic and mafic rocks and recognition of cogenetic relations of these rocks with spatially associated basalts are more reliable when derived from the compositions of the trapped melts, which are estimated from their bulk geochemistry and primary mineral compositions, than when they are based on the mineral compositions only.

本文介绍了堪察加梅斯蛇绿岩的泥质岩、辉石岩、橄榄岩和辉长岩的岩石学、矿物学和地球化学资料。获取这些数据是为了区分火成岩的共成组合,了解它们的地球动力学背景,并测试蛇绿岩不同岩浆岩之间的成因联系的各种标准。超镁铁质岩和基性岩分属于两个系列,它们在原生矿物、大块岩石和估计的圈闭熔体组成上存在差异。这些系列的岩石在不同的地球动力学背景下,在不同的地幔岩浆活动时期,由地球化学上不同的熔体形成。高钛系列岩石(奥列涅戈尔斯克地块的辉长岩、其中的暗长辉长岩和黑长辉长捕虏体以及这些捕虏体中的脉状辉长岩)在一个海洋扩张中心的N-MORB熔体中结晶。低钛系列岩石(Soldatskaya山地块残余尖晶石橄榄岩中的泥质、辉石岩和辉长岩脉,以及半岛中部和西部的辉石岩、橄榄岩和辉长岩冲积层和洪积层)是在初始俯冲岩浆作用下由富水的博长岩熔体结晶而成的。考虑到堪察加梅斯蛇绿岩中不存在博英质熔岩,深成超基性岩石(包括脉状岩石)可能是蛇绿岩中俯冲博英质岩浆作用的唯一证据。研究结果表明,通过圈闭熔体的整体地球化学特征和原生矿物组成估算其地球动力学背景,以及与空间伴生玄武岩的同成关系,要比仅根据矿物组成推断更为可靠。
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引用次数: 0
Magmatism in Kamchatka and the Kurile Islands 堪察加和千岛群岛的岩浆活动
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-28 DOI: 10.1134/S0869591123030086
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引用次数: 0
Compositions of Kimberlite Melts: A Review of Melt Inclusions in Kimberlite Minerals 金伯利岩熔体成分:金伯利岩矿物熔体包裹体研究综述
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-15 DOI: 10.1134/S0869591123020030
A. V. Golovin, V. S. Kamenetsky
<p>The paper presents a comprehensive review of currently available data on melt inclusions entrapped in minerals of kimberlites of different age and different provenance in ancient cratons. The crystallized melt inclusions represent snapshots of kimberlite melts at different stages of their evolution. All of the inclusions are completely crystallized and consist of daughter minerals and shrinkage bubbles, which sometimes contain low-density CO<sub>2</sub>, but no aqueous fluids and quenched silicate glasses have been found so far. Although more than 60 mineral species have been identified among the daughter phases in the inclusions, all inclusions hosted in various minerals from different kimberlites have closely similar or even identical composition. The daughter minerals are various Na–K–Ca, Na–Ca, Na–Mg, K–Ca, Ca–Mg, Ca, Mg, and Na carbonates; Na–Mg and Na carbonates with additional anions Cl<sup>–</sup>, <span>({text{SO}}_{4}^{{2 - }})</span>, and <span>(text{PO}_{4}^{3 - })</span>; and alkali sulfates, chlorides, phosphates, sulfides, oxides, and silicates. Alkali carbonates, sulfates, and chlorides are usually absent from among the groundmass phases of most kimberlites sampled worldwide, except the Udachnaya-East kimberlite in Siberia. However, this mineral assemblage, in association with such widespread kimberlite minerals as olivine, micas, monticellite, spinel-group minerals, perovskite, rutile, ilmenite, calcite, and dolomite, is common in the crystallized melt inclusions in all studied kimberlites. Carbonates (~30 to 85 vol %) always dominate over silicates (no more than 18 vol %) in all inclusions. All inclusions also contain variable (2 to 55 vol %.) amounts of chlorides (halite and sylvite). In cases where the abundance of carbonates is relatively low (30–50 vol %), the other major phases within inclusions are chlorides (18–55 vol %) rather than daughter silicates, as could be expected based on the traditional paradigm of the silicate composition of kimberlite melts. Published data on melt inclusions in the kimberlite minerals strongly imply that parental kimberlite melts were generated and further evolved within the Na<sub>2</sub>O–K<sub>2</sub>O–CaO–MgO–CO<sub>2</sub>–Cl system, that is, they were alkali-rich carbonate/carbonate–chloride liquids. According to various estimates, SiO<sub>2</sub> content in kimberlite melts could have varied during different stages of their evolution from a few to 19 wt %. Clearly, kimberlite bodies are altered in the crust via interaction with meteoric and/or connate waters, resulting in serpentinization of kimberlite olivine and dissolution of many bona fide magmatic minerals, such as alkali carbonates, sulfates, and chlorides. In the traditional approach to studying kimberlites, the role of such components as Na<sub>2</sub>O, CO<sub>2</sub>, Cl, and to a lesser extent K<sub>2</sub>O, S, and F in the petrogenesis of kimberlite magmas and rocks have been largely underestimated, while the roles of o
本文综合评述了古克拉通不同年代、不同物源金伯利岩矿物中包裹体的现有资料。结晶的熔体包裹体代表了金伯利岩熔体在不同演化阶段的快照。所有的包裹体都是完全结晶的,由子矿物和收缩气泡组成,其中有时含有低密度的二氧化碳,但到目前为止还没有发现含水流体和淬火的硅酸盐玻璃。虽然在包裹体的子相中已鉴定出60多种矿物,但来自不同金伯利岩的各种矿物所含的包裹体都具有非常相似甚至相同的成分。子矿物为各种Na - K-Ca、Na - Ca、Na - Mg、K-Ca、Ca - Mg、Ca、Mg、Na碳酸盐;Na - mg和Na碳酸盐与附加阴离子Cl -, ({text{SO}}_{4}^{{2 - }})和(text{PO}_{4}^{3 - });以及碱硫酸盐、氯化物、磷酸盐、硫化物、氧化物和硅酸盐。除了西伯利亚的Udachnaya-East金伯利岩外,在世界上大多数金伯利岩的取样中,通常不存在碱碳酸盐、硫酸盐和氯化物。然而,这种矿物组合与广泛分布的金伯利岩矿物如橄榄石、云母、蒙脱石、尖晶石群矿物、钙钛矿、金红石、钛铁矿、方解石和白云石一起,在所有研究的金伯利岩的结晶熔融包裹体中是常见的。碳酸盐(30至85卷 %) always dominate over silicates (no more than 18 vol %) in all inclusions. All inclusions also contain variable (2 to 55 vol %.) amounts of chlorides (halite and sylvite). In cases where the abundance of carbonates is relatively low (30–50 vol %), the other major phases within inclusions are chlorides (18–55 vol %) rather than daughter silicates, as could be expected based on the traditional paradigm of the silicate composition of kimberlite melts. Published data on melt inclusions in the kimberlite minerals strongly imply that parental kimberlite melts were generated and further evolved within the Na2O–K2O–CaO–MgO–CO2–Cl system, that is, they were alkali-rich carbonate/carbonate–chloride liquids. According to various estimates, SiO2 content in kimberlite melts could have varied during different stages of their evolution from a few to 19 wt %. Clearly, kimberlite bodies are altered in the crust via interaction with meteoric and/or connate waters, resulting in serpentinization of kimberlite olivine and dissolution of many bona fide magmatic minerals, such as alkali carbonates, sulfates, and chlorides. In the traditional approach to studying kimberlites, the role of such components as Na2O, CO2, Cl, and to a lesser extent K2O, S, and F in the petrogenesis of kimberlite magmas and rocks have been largely underestimated, while the roles of olivine- and serpentine-forming components, such as of SiO2, MgO, and H2O are still exaggerated.
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引用次数: 4
Variations in Trace Element and Isotope Composition of Neoarchean Mafic Granulites of the Southwest Siberian Craton: a Consequence of Various Mantle Sources or Crustal Contamination 西南西伯利亚克拉通新太古代基性麻粒岩微量元素和同位素组成的变化:不同地幔源或地壳污染的结果
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-15 DOI: 10.1134/S0869591123020066
O. M. Turkina

The paper presents geochemical and isotopic characteristics of Neoarchean (2.7–2.66 Ga) mafic granulites of the Sharyzhalgay uplift in the southwestern Siberian craton. Mafic and predominant felsic granulites compose fragments of the metamorphic complex among the Neoarchean and Paleoproterozoic granitoids. The mafic granulites are characterized by the mineral association Cpx + Pl ± Hbl ± Opx ± Qz and include two types with different major and immobile trace element contents. The dominant rocks of the first type have a wide range of Mg# and concentrations of TiO2 and immobile trace elements (REE, Zr, Nb), and mainly positive εNd(Т) values. The first type of mafic granulites show elevated (La/Sm)n and enrichment in Th and LREE relative to Nb, which is typical of subduction-related or crustally contaminated basalts. The absence of negative correlation between (La/Sm)n and εNd(Т) and a clear positive correlation of TiO2 with Nb testify against the effect of crustal contamination on the composition of the mafic granulites. The magmatic protoliths of the first type of mafic granulites are suggested to form by the melting of depleted peridotites of the subcontinental lithospheric mantle modified by melts derived from basalts or terrigenous sediments of the subducting plate. Mafic granulites of the second type have a narrower range of Mg#, TiO2 content, positive εNd(Т), flat rare earth patterns and no subduction signatures, which indicates an asthenospheric depleted mantle source. Mafic granulites contaminated by the Paleoarchean crust are characterized by increased (La/Sm)n, depletion in Nb relative to Th and LREE, and negative εNd(Т) values. Post-magmatic influence of granitoids leads to the enrichment of mafic granulites in biotite and apatite, an increase in concentrations of K2O, P2O5, a significant enrichment in Zr, Nb, Th, LREE, and negative εNd(Т) values. The difference between mafic granulites of the first and second types is not related to crustal contamination, but is caused by melting of two types of sources: asthenospheric and subcontinental lithospheric mantle. The subcontinental lithospheric mantle of the Irkut block was isotopically depleted at the Neoarchean time (∼2.7 Ga), and its enrichment in incompatible trace elements was likely caused by felsic melts generated from the rocks of subducting plate immediately prior to mafic magmatism.

本文介绍了西伯利亚克拉通西南部沙里扎盖隆起新太古代(2.7 ~ 2.66 Ga)基性麻粒岩的地球化学和同位素特征。镁铁质麻粒岩和长英质麻粒岩组成了新太古代和古元古代花岗岩类变质杂岩的碎片。基性麻粒岩以矿物组合Cpx + Pl±Hbl±Opx±Qz为特征,包括两种主要和不可移动微量元素含量不同的类型。第一类优势岩的mg#、TiO2和不动微量元素(REE、Zr、Nb)含量范围广,εNd(Т)值主要为正;第一类基性麻粒岩(La/Sm)n较高,Th和LREE相对于Nb富集,为典型的俯冲相关或地壳污染玄武岩。(La/Sm)n与εNd(Т)之间不存在负相关关系,TiO2与Nb之间存在明显的正相关关系,说明地壳污染对基性麻粒岩的组成没有影响。第一类基性麻粒岩的岩浆原岩被认为是由次大陆岩石圈地幔的贫橄榄岩熔融形成的,这些橄榄岩被俯冲板块的玄武岩或陆源沉积物的熔体修饰。第二类镁铁质麻粒岩的Mg#、TiO2含量范围较窄,εNd(Т)正,稀土模式平坦,无俯冲特征,表明其为软流圈贫地幔源。受古太古代地壳污染的镁铁质麻粒岩表现为(La/Sm)n增加,Nb相对于Th和LREE减少,εNd(Т)值为负。花岗岩类的后岩浆作用导致黑云母和磷灰石中的基性麻粒岩富集,K2O、P2O5浓度增加,Zr、Nb、Th、LREE显著富集,εNd(Т)值为负。第一类和第二类基性麻粒岩的差异与地壳污染无关,而是软流圈和次大陆岩石圈地幔两种来源的熔融作用所致。伊尔库特地块的次大陆岩石圈地幔在新太古代(~ 2.7 Ga)发生了同位素衰竭,其不相容微量元素的富集可能是由俯冲板块岩石在基性岩浆活动之前产生的长硅熔体造成的。
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引用次数: 1
Native Iron in Siberian Traps 西伯利亚圈闭中的天然铁
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-15 DOI: 10.1134/S0869591123020054
M. D. Tomshin, A. G. Kopylova, A. E. Vasilyeva

The study of trap intrusions with a large-scale occurrence of native iron allowed us to identify general features in their composition and origin. Intrusive bodies are weakly differentiated and have similar structure and mineralogical, petrochemical and geochemical composition. Two associations of rock-forming minerals were found in all studied bodies: early deep-seated (pre-chamber) and intra-chamber. Native iron forms nodular segregations, with a subordinate amount of cohenite, troilite and magnetite–wüstite. Metallic iron can accumulate Ni, Co, Au, and PGE. Their content in metal increases by hundreds or even thousands of times compared to host silicate rock. The formation of native iron is based on the fluid-magmatic interaction between magma and reducing components of the fluid, mainly of methane–hydrogen composition. As a result, an initially homogeneous basalt liquid is dispersed into silicate and metallic components. In the course of transportation, finely dispersed iron phases form droplet-liquid segregations with a monomolecular gas layer on their surface, thus preventing enlargement of metallic droplets. In the hypabyssal chamber, magma, including metallic spherules, is degassed, and droplets are merged to form nodular segregations of native iron.

对具有大规模天然铁赋存的圈闭侵入体的研究,使我们能够确定其组成和成因的一般特征。侵入体分异弱,构造相似,矿物学、石油化学和地球化学组成相似。在所有被研究的岩体中发现了两种形成岩石的矿物组合:早期深埋(前腔)和腔内。原生铁形成球状偏析,其次为纯白铁矿、三黄铁矿和磁铁矿。金属铁可以积累Ni、Co、Au和PGE。它们在金属中的含量比宿主硅酸盐岩石增加数百甚至数千倍。天然铁的形成是基于岩浆与流体还原性组分(主要是甲烷-氢成分)的流体-岩浆相互作用。结果,最初均匀的玄武岩液体分散成硅酸盐和金属成分。在运输过程中,分散较细的铁相形成液滴-液分离,表面形成单分子气体层,阻止了金属液滴的扩大。在浅成岩浆室,岩浆,包括金属球粒,被脱气,液滴合并形成原生铁的球状分离。
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引用次数: 1
Moissanite in Rocks of the Bobruisk Basement Inlier, Belarusian Crystalline Massif, East European Craton 东欧克拉通白俄罗斯结晶地块Bobruisk基底岩石中的莫桑石
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-15 DOI: 10.1134/S0869591123020042
V. I. Levitskiy, I. V. Levitskiy, L. A. Pavlova, M. V. Lukashova

A large range of minerals, native, intermetallic, and amorphous compounds containing K, Na, Fe, Mn, Ca, Ba, Sr, Cu, Pb, Co, Ni, Sn, Zn, Al, Ce, Nd, La, Pr, Sm, Y, Yb, Nb, Hf, W, Mo, Zr, Cr, V, Ag, Ti, Si, As, P, Bi, O, H, F, Cl, S, Se, C, B, N, and F has been identified in rocks from the Bobruisk basement inlier of the Belarusian crystalline massif in the western part of the East European craton. One of the identified phases was moissanite, which occurs as anhedral and subhedral grains up to 1.5 mm and is the 6H hexagonal polytype. One of the moissanite grains contained mineral inclusions inherent in meteorites: sinoite (Si2N2O), xifengite (Si5Fe3), and awaruite (Ni3Fe). The moissanite and native, intermetallic, and amorphous phases associated with it occur as rare disseminated grains of various size in rocks of three rock complexes in the basement of the Bobruisk inlier. This indicates that the mineralization is overprinted. The whole set of crystalline and amorphous phases found in association with moissanite is proposed to be named bobruiskites. The minerals were most probably formed by an meteorite impact on rocks of the East European craton.

一个大范围的矿物质,原生金属间化合物,和非晶态化合物含有钾、钠、铁、锰、钙、Ba、Sr、铜、铅、有限公司镍、锡、锌、铝、Ce、Nd,洛杉矶,公关,Sm, Y, Yb, Nb,高频,W,密苏里州,锆、Cr、V, Ag)、钛、硅、,P, Bi, O, H, F, Cl,年代,Se、C、B、N, F已被确定在岩石的地下室Bobruisk窗白俄罗斯水晶在东欧的西部克拉通地块。其中一种相为莫桑石,晶粒大小为半面体和半面体,尺寸为1.5 mm,为6H六方多型。其中一种莫桑石颗粒含有陨石中固有的矿物包裹体:硅辉石(Si2N2O)、锡云石(Si5Fe3)和硅辉石(Ni3Fe)。莫桑石和与之相关的原生、金属间和非晶相以不同大小的罕见浸染颗粒的形式出现在Bobruisk盆地基底的三个岩石复岩中。这表明成矿作用是套印的。与莫桑石有关的整套结晶相和非晶相被提议命名为波布里斯基。这些矿物很可能是由陨石撞击东欧克拉通的岩石形成的。
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引用次数: 0
Highly Fractionated Granites of the Raumid Massif (S. Pamir): Oxygen Isotope and Geochemical Study Raumid地块(S. Pamir)高分选花岗岩:氧同位素与地球化学研究
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2023-06-15 DOI: 10.1134/S0869591123020029
E. O. Dubinina, A. S. Avdeenko, V. N. Volkov, S. A. Kossova, E. V. Kovalchuk

The processes of crystallization differentiation, retrograde isotopic exchange, and autometamorphism are considered with reference to the Eocene granites of the Raumid massif, which consists of eight intrusive phases and serves as an example of a “natural laboratory”. The work is based on oxygen isotope, petrographic, and geochemical study of representative samples from each intrusive phase of the massif. The isotopic and geochemical studies were carried out for all rock-forming minerals (Qz, Pl, Kfs, Bt) and their altered varieties. Based on geochemical features, the Raumid granites correspond both to A-type granites and to highly fractionated I-type granites. Our results show that the rocks of the Raumid massif are not the geochemical analog of the Eocene granitoids from the Qiangtang terrane of the Central Tibet or the Vanj complex, as it previously assumed (Chapman et al., 2018). We estimated that differentiation of felsic melts of the Raumid pluton occurred at T = 750–800°C, and P = 4.5–7.8 kbar and was mainly controlled by Pl crystallization. The melts were intruded into the hypabyssal zone in at least two stages: early (γ1–γ3) and late (γ4–γ8), although it is possible that the rocks of the γ7 and γ8 phases formed an additional separate stage. The closure temperature of the oxygen isotopic system of quartz (TQz) ranges from 420 to 610°C. The effect of the multiple intrusions of the melts on the TQz and apparent cooling rates is considered. The study of altered and unaltered minerals showed that autometamorphism partially overlapped with the retrograde oxygen isotope exchange in the cooling rock. The modelled δ18О values during Pl and Kfs alteration describes well the observed isotope data when the crystallization takes place at limited content of water fluid (W/M = 0.3–0.05) which could release during the Raumid’s magmas crystallization.

以Raumid地块始新世花岗岩为例,研究了其结晶分异、逆向同位素交换和自变质作用的过程。Raumid地块由8个侵入期组成,是一个“天然实验室”。这项工作是基于对该地块每个侵入期的代表性样品的氧同位素、岩石学和地球化学研究。对所有造岩矿物(Qz、Pl、Kfs、Bt)及其蚀变品种进行了同位素和地球化学研究。根据地球化学特征,Raumid花岗岩既属于a型花岗岩,也属于高分异的i型花岗岩。我们的研究结果表明,Raumid地块的岩石并不像之前假设的那样,是西藏中部羌塘地块或Vanj杂岩的始新世花岗岩类的地球化学模拟物(Chapman et al., 2018)。我们估计Raumid岩体的长硅熔体分异发生在T = 750 ~ 800℃,P = 4.5 ~ 7.8 kbar,主要受Pl结晶控制。熔体侵入浅成带至少分为两个阶段:早期(γ - 1 - γ - 3)和晚期(γ - 4 - γ - 8),尽管γ - 7和γ - 8相的岩石可能形成另外一个单独的阶段。石英氧同位素体系的封闭温度(TQz)为420 ~ 610℃。考虑了熔体多次侵入对TQz和表观冷却速率的影响。对蚀变和未蚀变矿物的研究表明,自变质作用与冷却岩石中的逆行氧同位素交换有部分重叠。模拟的Pl和Kfs蚀变δ18О值很好地描述了在Raumid岩浆结晶过程中释放的有限含量的水流体(W/M = 0.3 ~ 0.05)发生结晶时观测到的同位素数据。
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引用次数: 1
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Petrology
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