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The Great Dyke of the Kola Peninsula as a Marker of an Archean Cratonization in the Northern Fennoscandian Shield 科拉半岛大堤作为芬诺斯坎地盾北部太古宙克拉通化的标志
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S086959112206008X
A. V. Stepanova, A. V. Samsonov, E. B. Salnikova, S. V. Egorova, Yu. O. Larionova, A. A. Arzamastsev, A. N. Larionov, M. A. Sukhanova, R. V. Veselovskiy

The results of geochronological and petrological studies of the largest mafic dyke in the northern part of the Fennoscandian Shield, called the Great Dyke of the Kola Peninsula (GDK), are presented. According to U-Pb D-TIMS baddeleyite dating, the GDK crystallization age is 2680 ± 6 Ma. The age of host granites is 2.75–2.72 Ga (U-Pb, zircon, SHRIMP-II). The dyke has a simple internal structure with no signs of multistage melt injection. It comprises equigranular and plagioclase-porphyritic dolerites and gabbro that are amphibolitized to varying degrees. All rocks are low-Mg (Mg# less than 0.37) with low concentrations of Cr and Ni, and were derived through differentiation of more primitive melts. The analysis of geochemical and Sr-Nd isotopic data suggests that GDK melts could be formed by mixing of two types of mantle melts: depleted asthenospheric melt and enriched melt formed via melting of a lithospheric mantle. The weakly fractionated HREE patterns indicate that primary GDK melts originated at shallow (<60 km) depths outside the garnet stability field. The generation and injection of melts of the Neoarchean GDK occurred immediately after large-scale granitic magmatism and main crustal growth event in the Murmansk Craton and marked the cratonization of the continental lithosphere in the northeastern part of the Fennoscandian Shield.

本文介绍了芬诺斯坎地盾北部最大的基性堤坝——科拉半岛大堤(GDK)的年代学和岩石学研究结果。根据U-Pb D-TIMS bad - yite测年,GDK的结晶年龄为2680±6 Ma。寄主花岗岩年龄为2.75 ~ 2.72 Ga (U-Pb、锆石、SHRIMP-II)。岩脉内部结构简单,没有多级熔体注入的迹象。由不同程度角闪化的等粒状和斜长状斑岩白云岩和辉长岩组成。所有岩石均为低Mg (Mg# < 0.37),含低浓度的Cr和Ni,由更原始的熔体分异而成。地球化学和Sr-Nd同位素数据分析表明,GDK熔体可能是由两种类型的地幔熔体混合形成的:贫软流圈熔体和由岩石圈地幔熔融形成的富集熔体。弱分馏的ree模式表明初生GDK熔体起源于石榴石稳定场外的浅层(<60 km)深度。新太古代GDK熔体的生成和注入发生在摩尔曼斯克克拉通大规模花岗岩岩浆活动和主要地壳生长事件之后,标志着芬诺斯坎德盾东北部大陆岩石圈的克拉通化。
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引用次数: 0
А History of Coronitic Metagabbronorites in the Belomorian Province, Fennoscandian Shield: U-Pb (CA-ID-TIMS) Dating of Zircon–Baddeleyite Aggregates А Fennoscandian地盾Belomorian省冠状变辉长岩的历史:锆石- baddeleite聚落的U-Pb (CA-ID-TIMS)定年
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122060066
E. B. Salnikova, A. V. Stepanova, P. Ya. Azimov, M. A. Sukhanova, A. B. Kotov, S. V. Egorova, Yu. V. Plotkina, E. V. Tolmacheva, A. V. Kervinen, N. V. Rodionov, V. S. Stepanov

The estimation of crystallization and metamorphic reworking ages of mafic rocks in the polycyclic Precambrian areas is a difficult problem. Magmatic baddeleyite can be partially or completely replaced by polycrystalline zircon within a wide range of temperature and pressures, from greenschist to granulite facies. Evaluation of the age of each phase of the zircon–baddeleyite aggregates can provide information on both the age of the magmatic crystallization and metamorphism. U-Th-Pb (SHRIMP-II) and U-Pb (ID-TIMS) geochronological studies were carried out for single baddeleyite grains and zircon–baddeleyite aggregates from gabbronorites (“drusites”) of the Ambarnsky massif (Belomorian Province, Fennoscandian Shield). The petrological studies indicate the simultaneous growth of coronas at the olivine–plagioclase boundary and zircon rims around baddeleyite. U-Pb (ID-TIMS) dating of single baddeleyite grains yielded 2411 ± 6 Ma crystallization age of gabbronorites of the Ambarnsky massif. U-Pb (ID-TIMS) dating coupled with the discrete chemical abrasion give an age of 1911 ± 35 Ma for metamorphic zircon rims. The obtained results indicate that coronitic textures in the gabbronorites were formed 500 million years later than the magmatic crystallization of rocks as a result of the granulite-facies metamorphism that was probably related to the Lapland-Kola orogeny.

多旋回前寒武纪地区基性岩结晶和变质改造时代的确定是一个难题。从绿片岩到麻粒岩相,多晶锆石在温度和压力范围内均可部分或完全取代岩浆坏辉岩。对锆石-坏辉石集合体各相年龄的评价可以提供岩浆结晶和变质作用年龄的信息。对Fennoscandian地盾省Belomorian省Ambarnsky地块辉长岩(“drusites”)中的单个坏辉长岩颗粒和锆石-坏辉长岩聚集体进行了U-Th-Pb (SHRIMP-II)和U-Pb (ID-TIMS)年代学研究。岩石学研究表明,在橄榄石-斜长石边界和坏长岩周围的锆石边缘同时生长。U-Pb (ID-TIMS)定年法测定了Ambarnsky地块辉长岩的结晶年龄(2411±6 Ma)。U-Pb (ID-TIMS)测年与离散化学磨损相结合,确定变质锆石的年龄为1911±35 Ma。结果表明,辉长岩中的冕状结构形成时间比岩石岩浆结晶晚5亿年,其成因可能与拉普兰—科拉造山运动有关。
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引用次数: 2
Eocene Calc-Alkaline Volcanic Rocks from Central Iran (Southeast of Khur, Isfahan Province); an Evidence of Neotethys Syn-Subduction Magmatism 伊朗中部(伊斯法罕省Khur东南部)始新世钙碱性火山岩新特提斯同步俯冲岩浆活动的证据
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122060042
Paniz Shadman, Ghodrat Torabi, Tomoaki Morishita

Eocene volcanic rocks with basaltic-trachyandesite and trachybasalt composition which cross-cut the Cretaceous sedimentary rocks, are exposed in the northwestern part of the Central-East Iranian Microcontient (CEIM) (SE of Khur, Isfahan Province, Iran). The rock-forming minerals of these volcanic rocks are olivine (chrysolite and hyalosiderite, Mg# = 0.69–0.71), clinopyroxene (augite with Mg# = 0.74–0.84), orthopyroxene (enstatite with Mg# = 0.61–0.62) and plagioclase (andesine and labradorite with An48.3-65.1). Phenocrysts set in a fine-grained matrix of the same minerals plus sanidine (Or59.1Ab36.6An4.3) with minor amounts of opaque minerals (magnetite and ilmenite). Secondary minerals are chlorite and calcite. The main textures of these volcanic rocks are porphyritic, microlitic porphyritic, poikilitic, and glomeroporphyritic. The Eocene volcanic rocks of the Khur area are characterized by SiO2 content of 51.8 to 54.9 wt %, Al2O3 amounts of 14.35 to 16.47 wt %, and TiO2 values of 0.88 to 0.92 wt %. They exhibit strong enrichment in light rare earth elements (LREE) relative to heavy REE (HREE) (La/Lu ratio up to 102.35), enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSE), and present negative anomaly in Eu (Eu/Eu* = 0.72–0.87). Chemical characteristics and homogeneity of these volcanic rocks reveal their calc-alkaline nature and suggest that they were derived from a same parental magma and underwent a similar melt extraction. Major and trace elements geochemical features of the analyzed samples indicate that the parental magma was possibly derived from relatively low degrees of partial melting of a mantle wedge spinel lherzolite which was previously enriched by fluids/melts released from the Neo-Tethyan subducted slab.

在伊朗中东部微大陆(伊朗伊斯法罕省Khur东南)西北部,暴露出与白垩系沉积岩相交叉的玄武岩-粗面玄武岩和粗面玄武岩组成的始新世火山岩。这些火山岩的造岩矿物为橄榄石(黄璧石和透明黄铁矿,Mg# = 0.69 ~ 0.71)、斜辉石(辉石,Mg# = 0.74 ~ 0.84)、正辉石(顽辉石,Mg# = 0.61 ~ 0.62)和斜长石(安长石和拉长石,Mg# = 48.3 ~ 65.1)。斑晶镶嵌在由相同矿物加水晶石(Or59.1Ab36.6An4.3)和少量不透明矿物(磁铁矿和钛铁矿)组成的细粒基质中。次生矿物为绿泥石和方解石。这些火山岩的主要结构为斑岩、微岩屑斑岩、斑岩和肾小球斑岩。呼尔地区始新世火山岩的SiO2含量为51.8 ~ 54.9 wt %, Al2O3含量为14.35 ~ 16.47 wt %, TiO2含量为0.88 ~ 0.92 wt %。它们表现出轻稀土元素(LREE)相对重稀土元素(HREE)的强富集(La/Lu比值高达102.35),大离子亲石元素(LILEs)富集,高场强元素(HFSE)亏缺,Eu呈负异常(Eu/Eu* = 0.72 ~ 0.87)。这些火山岩的化学特征和均匀性揭示了它们的钙碱性特征,表明它们起源于相同的母岩浆,并经历了相似的熔融提取过程。分析样品的主要元素和微量元素地球化学特征表明,母岩浆可能来源于地幔楔尖晶石橄榄岩相对较低程度的部分熔融,该岩浆先前被新特提斯俯冲板块释放的流体/熔体富集。
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引用次数: 0
Comparative Characteristics of the Layering of Mafic–Ultramafic Intrusions of the Oulanka Group, Northern Karelia 北卡累利阿奥兰卡群镁铁质-超镁铁质岩体层状对比特征
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122060091
A. R. Tskhovrebova, E. V. Koptev-Dvornikov, D. A. Bychkov

The Oulanka group is a compact group of three peridotite–gabbronorite intrusions that is convenient for testing various petrogenetic concepts. The three intrusions are similar in age and occur not far from one another but differ in the composition of their original magmas, are characterized by different sets of cumulus mineral assemblages, and are different in inner structure and rhythmic layering. We applied cluster analysis of the contents of major elements to reproduce the cumulus mineral assemblages of the isochemically altered rocks of the Tsipringa and Lukkulaisvaara massifs. Although the parental magmas of the Kivakka and Tsipringa massifs were of different composition and their crystallization sequences were also different, the vertical sections of these massifs can be clearly subdivided into zones according to their cumulus mineral assemblages, with the limited development of rhythmic interbedding (with individual rhythms ranging from a few to a few dozen meters in thickness). Conversely, the Lukkulaisvaara intrusion does not possess any clearly distinguishable cumulus zones, and large-scale rhythmic layering is traceable throughout the entire thickness of the massif (with rhythms ranging from a few dozen to a few hundred meters in thickness). The different character of the rhythmic layering of the three intrusions may provide an insight into the different scenarios of magma convection in the chambers.

奥兰卡群是由3个橄榄岩-辉长岩侵入体组成的致密群,便于检验各种岩石成因概念。三次侵入岩年龄相近,发生地点相距不远,但原始岩浆组成不同,具有不同套积云矿物组合特征,内部构造和韵律分层也不同。利用主元素含量的聚类分析,重现了齐普林加和卢卡库莱斯瓦拉地块等化学蚀变岩的积云矿物组合。Kivakka和Tsipringa地块的母岩浆虽然成分不同,结晶序列也不同,但根据它们的积云矿物组合,在垂向剖面上可以清晰地划分成带,韵律互层发育有限(单个韵律厚度从几米到几十米不等)。相反,Lukkulaisvaara岩体没有任何明显可区分的积云带,在整个地块厚度上都可以追踪到大规模的有节奏分层(厚度从几十米到几百米不等)。三次侵入岩的韵律层理特征不同,可为岩浆在岩浆室中对流的不同情况提供线索。
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引用次数: 0
The Effect of CO2 Reduction in Low-Water Melts at Low Hydrogen Fugacity: Experiment at 500 MPa and Thermodynamic Model 低氢逸度低水熔体中CO2还原的影响:500 MPa实验和热力学模型
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122060078
A. G. Simakin, V. N. Devyatova, G. V. Bondarenko

Formation of graphite was observed in experiments on synthesis of dry carbon-bearing albite glasses in platinum capsules in an Internally Heated Pressure Vessel at 500 MPa and Т = 1200–1250°С. A thermodynamic model is proposed that explains the achievement of low oxygen fugacity near QFM-2 in the melt at low fugacity of hydrogen formed due to the decomposition of trace amounts of water in a compression medium (Ar gas). The unexpectedly low fugacity of oxygen is explained by the shift of equilibrium between the gases dissolved in the melt CO2 + H2 = H2O + CO to the right due to the low activity of molecular water at a low total content of H2O ~ 0.1–0.5 wt %. The high local СО concentrations in the melt lead to the platinum dissolution in form of carbonyl, corrosion of capsule walls, and redeposition of the metal at the contact with melt. With increase of water concentration in the melt (>1 wt %), the effect of reduction disappears.

在内热压力容器中,在500 MPa和Т = 1200 ~ 1250°С条件下,用铂胶囊合成干含碳钠长石玻璃,观察了石墨的形成。提出了一个热力学模型,解释了熔体在QFM-2附近低氧逸度的实现,这是由于在压缩介质(Ar气体)中分解微量水而形成的氢的低逸度。氧的逸度之所以如此之低,是由于在H2O总含量(0.1-0.5 wt %)低的情况下,水分子的活度较低,导致熔体中溶解的气体CO2 + H2 = H2O + CO的平衡向右移动。熔体中较高的СО局部浓度导致铂以羰基形式溶解,胶囊壁腐蚀,金属在与熔体接触处再沉积。随着熔体中水浓度的增加(1 wt %),还原效果消失。
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引用次数: 0
Eastern Margin of the Neoarchean Tunguska Superterrane: Data from Boreholes in the Central Part of the Siberian Platform 新太古代通古斯超级地体的东缘:西伯利亚地台中部钻孔资料
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122050058
A. V. Samsonov, K. G. Erofeeva, Yu. O. Larionova, A. N. Larionov, N. B. Kuznetsov, T. V. Romanyuk, N. V. Solovyova, O. M. Zhilicheva, A. S. Dubenskiy, V. S. Sheshukov

The paper presents data on granites and gneisses recovered by Kulindinskaya-1 hole drilled in the central part of the Siberian Craton. The biotite granites retain a porphyritic texture, correspond to I-type according to their compositional features, are enriched in LREE and moderately depleted in HREE, and have negative Eu, Sr, and Nb and positive Zr anomalies. The U−Pb zircon age of the granites is Neoarchean (2525 ± 10 Ma), with single cores of zircon grains dated at about 2.6 Ga, which likely suggests a crustal source of the granitic magmas. The model age TNd(DM) = 2.77 Ga of the granite shows that the crust from which the initial melts were derived had been formed shortly before the melting episode. In terms of age and all characteristics, the granites are close to those of the Yurubchen massif, which was drilled through in the western part of the Tunguska superterrane. The biotite gneiss was apparently derived from sedimentary rocks and was heavily reworked when the granites were emplaced. The enrichment of the gneiss in Cr and Ni is probably inherited from the sedimentary protolith, whereas the REE, HFSE, and LILE concentrations and distribution in the gneiss are similar to those of the granite. The concordant (D < 1%) U−Pb zircon ages (according to LA-ICP-MS data) broadly vary from 3284 to 2620 Ma, with two major peaks at 2717 and 2678 Ma. The model age of the gneiss TNd(DM) = 2.91 Ga confirms a contribution of the ancient crustal component to the sedimentary protolith of the rock. The minimum age of the detrital zircon, 2.62 Ga, determines the maximum age limit for sedimentation, and the minimum age limit is set by the age of the granite intrusions at 2.53 Ga. According to our data, the Archean gneisses and granites recovered by the Kulindinskaya-1 drillhole probably compose the eastern part of the Neoarchean Tunguska superterrane. Ereminskaya-101 drillhole, which was drilled 20 km northeast of Kulindinskaya-1, recovered gneisses with model ages TNd(DM) from 2.30 to 2.37 Ga, which belong to the adjacent Taimyr−Baikal suture zone with widespread Paleoproterozoic rocks. The contrasting crustal history of the adjacent complexes provides grounds to suggest that they were tectonically combined, which is an additional reason to consider the Taimyr−Baikal suture zone as a Paleoproterozoic collisional orogen.

本文介绍了在西伯利亚克拉通中部钻取的Kulindinskaya-1孔所恢复的花岗岩和片麻岩资料。黑云母花岗岩呈斑岩状,组成特征为i型,重稀土富集,重稀土中度亏缺,Eu、Sr、Nb呈负异常,Zr呈正异常。花岗岩的U - Pb锆石年龄为新太古代(2525±10 Ma),单核锆石颗粒年龄约为2.6 Ga,可能为地壳岩浆来源。花岗岩的模型年龄TNd(DM) = 2.77 Ga,表明产生初始熔体的地壳是在熔化期前不久形成的。花岗岩的年龄和各项特征与通古斯超地体西部钻穿的于鲁沁地块接近。黑云母片麻岩明显来源于沉积岩,并在花岗岩就位时被大量改造。片麻岩中Cr和Ni的富集可能继承自沉积原岩,而片麻岩中的REE、HFSE和LILE的浓度和分布与花岗岩相似。协和(D <U−Pb锆石年龄(根据LA-ICP-MS数据)在3284 ~ 2620 Ma之间变化较大,其中两个主要峰位于2717和2678 Ma。片麻岩的模式年龄TNd(DM) = 2.91 Ga,证实了古地壳成分对岩石沉积原岩的贡献。碎屑锆石的最小年龄为2.62 Ga,决定了沉积的最大年龄限制;花岗岩侵入物的最小年龄为2.53 Ga。根据我们的资料,Kulindinskaya-1钻孔恢复的太古代片麻岩和花岗岩可能构成了新太古代通古斯超级地体的东部。在Kulindinskaya-1东北方向20km处的Ereminskaya-101钻孔,发现片麻岩模式年龄TNd(DM)为2.30 ~ 2.37 Ga,属于邻近的Taimyr - Baikal缝合带,古元古代岩石分布广泛。相邻杂岩体的对比地壳历史提供了它们是构造组合的依据,这是将泰米尔-贝加尔湖缝合带视为古元古代碰撞造山带的另一个理由。
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引用次数: 1
Tantalite Solubility in Granitoid Melts and Evaluation of the Ta and Nb Diffusion Coefficients 花岗岩熔体中钽的溶解度及Ta、Nb扩散系数的评定
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122060030
V. Yu. Chevychelov

The paper presents experimental data on tantalite solubility in water-saturated granitoid melts with various alumina and alkaline elements concentrations at T = 650–850°C and P = 100 MPa. The maximum Ta concentration (effective solubility) in melt is shown to be always higher than the Nb concentration. As the melt composition is changed from alkaline to Al2O3-enriched, the Ta and Nb concentrations decrease by one to two orders of magnitude, and the Nb/Ta ratio simultaneously decreases (from ~0.8–0.7 to ~0.4–0.1) because the Nb concentration decreases notably more rapidly than that of Ta. This effect is enhanced at decreasing temperature. The effective Ta solubility in melt is demonstrated to be practically independent of the composition of the dissolving mineral of the columbite-tantalite series. The Ta, Nb, Mn, and Fe diffusion coefficients in granitoid melts are estimated. The Ta and Nb diffusion coefficients at T = 750°C and P = 100 MPa are ~10–10 cm2/s, and those of Fe and Mn are ~10–8.5 cm2/s. With an increase in temperature from 740 to 980°C, all of the diffusion coefficients increase by approximately 1.5 orders of magnitude. The configurations of the diffusion profiles of Ta concentration in melts change differently depending on change in the composition of the melt, temperature, or pressure.

本文介绍了在T = 650 ~ 850℃,P = 100 MPa条件下,不同氧化铝和碱性元素浓度的水饱和花岗岩熔体中钽铁矿溶解度的实验数据。熔体中Ta的最大浓度(有效溶解度)总是高于Nb的浓度。随着熔体成分由碱性向al2o3富集转变,Ta和Nb浓度下降了1 ~ 2个数量级,Nb/Ta比值同时下降(从~0.8 ~ 0.7降至~0.4 ~ 0.1),因为Nb浓度的下降速度明显快于Ta。这种效应在温度降低时增强。熔体中Ta的有效溶解度实际上与钶钽铁矿系列溶解矿物的组成无关。估算了花岗岩熔体中Ta、Nb、Mn和Fe的扩散系数。T = 750℃,P = 100 MPa时,Ta和Nb的扩散系数为~10 ~10 cm2/s, Fe和Mn的扩散系数为~10 ~ 8.5 cm2/s。当温度从740℃升高到980℃时,所有的扩散系数都增加了大约1.5个数量级。熔体中Ta浓度扩散曲线的形态随熔体成分、温度或压力的变化而发生不同的变化。
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引用次数: 0
Re-Os Isotope and HSE Abundance Systematics of the 2.9 Ga Komatiites and Basalts from the Sumozero-Kenozero Greenstone Belt, SE Fennoscandian Shield: Implications for the Mixing Rates of the Mantle Fennoscandian Shield东南sumo0 - kenozero绿岩带2.9 Ga科马提岩和玄武岩Re-Os同位素和HSE丰度系统:地幔混合速率的意义
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122060054
Igor S. Puchtel

Rhenium-Os isotope and highly siderophile element (HSE, including Re, Os, Ir, Ru, Pt, and Pd) abundance systematics of Archean komatiites can be used to estimate the stirring rates of the mantle for the HSE and the timing of homogenization of late accreted materials within the mantle. In this study, we report Re-Os isotope and HSE abundance data for ~2.9 Ga komatiites and basalts from the Sumozero-Kenozero greenstone belt in the SE Fennoscandian Shield. The lavas are characterized by excellent preservation of the primary textural, chemical, and Re-Os isotope characteristics. The Re-Os isotopic data for spinifex-textured and cumulate komatiite and massive basalt samples from the lowermost sequences define a precise 10-point isochron (MSWD = 2.6) with an age of 2904 ± 18 Ma and an initial 187Os/188Os = 0.10758 ± 18 (γ187Os(2904) = +0.45 ± 0.17). This is the first direct age determination for the Sumozero-Kenozero lower komatiite-basalt sequences. Our modeling indicates that the mantle source of the komatiites and basalts evolved with a time-integrated 187Re/188Os = 0.418 ± 6. This ratio is well within the uncertainty of the bulk chondritic average 187Re/188Os = 0.410 ± 51 (2SD), also consistent with the chondritic evolution of the majority of komatiite mantle sources observed globally. The mantle source of the Sumozero-Kenozero komatiites has been calculated to contain the total HSE abundances of 58 ± 7% of those in the estimates for modern Bulk Silicate Earth (BSE). This estimate is in the middle of the range for other late Archean and Proterozoic komatiite systems. Using the estimated HSE abundances in the sources of komatiite systems as a function of their ages and ISOPLOT regression analysis, we calculated the average time in the past by which late accreted materials have been completely homogenized within the mantle to be 2.48 ± 0.23 Ga. These data require that the residence times of the late accreted planetesimals within the mantle, before complete homogenization, were on average 1.92 ± 0.23 Ga. This estimate represents a constraint on the average mixing rates of the mantle in terms of the HSE abundances in the Hadean and the Archean.

太古宙科马长岩的铼-Os同位素和高亲铁元素(HSE,包括Re、Os、Ir、Ru、Pt和Pd)丰度系统可用于估算地幔对HSE的搅拌速率和地幔内晚期吸积物质的均匀化时间。本文报道了芬诺斯坎德地盾东南部sumo0 - kenozero绿岩带~2.9 Ga花岗岩和玄武岩的Re-Os同位素和HSE丰度数据。火山岩的主要特征是原始结构、化学和Re-Os同位素特征保存完好。从最下层的层序中得到的尖晶石纹理和堆积的科马铁矿和块状玄武岩样品的Re-Os同位素数据定义了一个精确的10点等时线(MSWD = 2.6),年龄为2904±18 Ma,初始187Os/188Os = 0.10758±18 (γ187Os(2904) = +0.45±0.17)。这是首次对sumo0 - kenozero下科马铁矿-玄武岩层序进行直接年龄测定。模拟结果表明,科马长岩和玄武岩的地幔源演化时间积分为187Re/188Os = 0.418±6。该比值完全符合总体球粒陨石平均值187Re/188Os = 0.410±51 (2SD)的不确定度,也与全球观测到的大多数科马地岩地幔源球粒陨石演化一致。经计算,sumo0 - kenozero科马岩源幔源中HSE总丰度为现代块状硅酸盐土(BSE)估算值的58±7%。对其他晚太古宙和元古宙的科马岩系的估算值处于中等范围。利用估算的科马地岩源中HSE丰度与年龄的函数关系和ISOPLOT回归分析,我们计算出过去晚期吸积物质在地幔内完全均匀化的平均时间为2.48±0.23 Ga。这些数据表明,在完全均匀化之前,晚期吸积星子在地幔内的停留时间平均为1.92±0.23 Ga。根据冥古宙和太古宙的HSE丰度,这一估计代表了对地幔平均混合率的限制。
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引用次数: 2
The Kulikovs: A Family of Geologists. Vyacheslav Stepanovich Kulikov, Viktoria Vladimirovna Kulikova, and Yana Vyacheslavovna Bychkova (Kulikova) 库利科夫家族:地质学家家族。Vyacheslav Stepanovich Kulikov、Viktoria Vladimirovna Kulikova和Yana Vyachesravovna Bychkova
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-11-15 DOI: 10.1134/S0869591122060108
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引用次数: 0
Mineralogical, Geochemical, and Nd-Sr Isotope Characteristics of Amphibolites from the Alag-Khadny High-Pressure Complex (SW Mongolia): Intracontinental Rifting as a Precursor of Continental-Margin Subduction 来自 Alag-Khadny 高压复合体(蒙古西南部)的闪长岩的矿物学、地球化学和钕-锶同位素特征:大陆内部断裂是大陆边缘俯冲的前兆
IF 1.5 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Pub Date : 2022-09-06 DOI: 10.1134/S0869591122040051
S. Yu. Skuzovatov, M. A. Gornova, A. A. Karimov
<div><p>Within subduction-accretion complexes, high-pressure rocks (blueschists, eclogites) are commonly juxtaposed with lower-grade rocks, which represent their retrograded counterparts or were involved into accretionary event at later stages, and thus characterize distinct stages of evolution of accretionary belts. In SW Mongolia, the Central Asian Orogenic Belt includes Neoproterozoic–Early Paleozoic paleosubduction complexes represented by eclogites and associated rocks of the Alag-Khadny accretionary complex. This paper reports the results of mineralogical, geochemical and isotopic studies of amphibolites from this complex, the geochemical nature and relationships of which with eclogites have been yet uncertain. The texture of the studied rocks varies from fine- and medium-grained granoblastic and nematoblastic amphibole–plagioclase–epidote rocks to medium-grained nematoblastic amphibole–epidote–albite–titanite amphibolites, which experienced intense recrystallization as a response to late deformations. Primary assemblages include pargasite and Mg-hornblende (<sup>[B]</sup>Na = 0.07–0.16, <sup>IV</sup>Al = 0.79–1.69, <sup>[A]</sup>(Na + K + 2Ca) = 0.14–0.64, <sup>[C]</sup>(Al+ Ti + Fe<sup>3+</sup>) = 0.58–1.29, Fe<sup>2+</sup>/(Fe<sup>2+</sup> + Mg) = 0.18–0.46 at Fe<sup>3+</sup>/(Fe<sup>3+</sup>+Al) = 0.18–0.77), low-to-medium-Ca plagioclase (<i>An</i><sub>24–36</sub>), and epidote–clinozoisite (0.08 < <span>({{X}_{{{text{F}}{{{text{e}}}^{{{text{3 + }}}}}}}})</span> < 0.16), whereas the retrograde assemblage is represented by albite and Mg-hornblende. Calculations using amphibole composition and amphibole/amphibole–plagioclase thermobarometry revealed peak <i>P-T</i> conditions up to 570–630°С and 7–9 kbar ascribed to the high-<i>T</i> epidote-amphibolite facies with subsequent greenschist-facies retrogression. The major-element composition of the amphibolites corresponds to low-alkali moderate-Ti tholeiites, although their trace-element composition varies significantly from N-MORB to E-MORB-type basalts, which are variably enriched in LREE, Nb, Ta, Th, U, and show negative Eu and Ti anomalies due to fractionation of parental melts for precursor rocks. Isotopic composition of Nd (ε<sub>Nd</sub>(550) from +5.1 to –9.1) and Sr ((<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>550</sub> = 0.7057–0.7097) indicates distinct mainly moderately-depleted nature of mantle sources for the mafic rocks, but also highlights the involvement of “anomalous” mantle domains with unradiogenic Nd composition. The data supports that the precursor rocks of the amphibolites were formed during intracontinental extension of a continental margin, which was likely linked to opening of a limited Neoproterozoic oceanic basin with a subsequent Late Vendian–Early Cambrian convergence. The medium- to high-pressure metamorphism of amphibolites had similar <i>P-T</i> conditions to that of retrograde metamorphism of eclogites and associated metasediments and was directly related t
在俯冲-增生复合体中,高压岩(蓝闪长岩、斜长岩)通常与低品位岩并置,后者代表其逆退的对应岩,或在后期卷入增生事件,因此是增生带演化的不同阶段的特征。在蒙古西南部,中亚造山带包括新元古代-早古生代的古俯冲复合体,其代表是闪长岩和阿拉格-哈德尼增生复合体的伴生岩。本文报告了对这一复合体中的闪长岩进行矿物学、地球化学和同位素研究的结果。所研究岩石的质地各不相同,有细粒和中粒粒状和线粒状闪石-斜长石-橄榄石岩石,也有中粒状线粒状闪石-橄榄石-赤铁矿-钛铁矿闪长岩,这些岩石在晚期变形过程中经历了强烈的再结晶。原生组合包括辉石和镁角闪石([B]Na = 0.07-0.16, IVAl = 0.79-1.69, [A](Na + K + 2Ca) = 0.14-0.64, [C](Al+ Ti + Fe3+) = 0.58-1.29, Fe2+/(Fe2+ + Mg) = 0.18-0.46 at Fe3+/(Fe3++Al) = 0.18-0.77.77)、低到中等Ca的斜长石(An24-36)和闪石-闪长岩(0.08 < ({{X}_{text{F}}{{text{e}}}^{{text{3 + }}}}}}}}) < 0.16),而逆行集合体则以白云石和镁角闪石为代表。利用闪石成分和闪石/闪石-斜长石热压仪进行的计算显示,峰值P-T条件可达570-630°С和7-9千巴,归因于高T的闪石-斜长石面,随后出现绿辉石派逆变。闪长岩的主要元素组成与低碱中钛透辉岩一致,但其痕量元素组成从N-MORB到E-MORB型玄武岩差异很大,LREE、Nb、Ta、Th、U元素不同程度富集,Eu和Ti元素呈现负异常,这是由于前驱岩的母熔体分馏造成的。钕(εNd(550)从+5.1到-9.1)和锶((87Sr/86Sr)550 = 0.7057-0.7097)的同位素组成表明,岩浆岩的地幔源主要具有明显的中度贫化性质,但也突出了具有非辐射钕组成的 "异常 "地幔域的参与。这些数据支持了闪长岩的前身岩石是在大陆边缘的大陆内延伸过程中形成的,这很可能与一个有限的新元古代大洋盆地的开辟以及随后的晚文武世-早寒武世的汇聚有关。闪长岩的中高压变质作用与斜长岩及相关基岩的逆行变质作用具有相似的P-T条件,与早古生代的俯冲-充填变质作用(约550-540Ma)直接相关,或者是湖泊带与Dzabkhan地层之间的构造混杂带(约515-490Ma或更年轻)形成过程中最终增生的结果。
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Petrology
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