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11.
Radio Astrophysical Observatory, Latvian Academy of Sciences; Leningrad State University. Translated from Astrofizika, Vol. 28, No. 3, pp. 586–594, May–June, 1988. 相似文献
12.
E. V. Yutkina A. A. Nosova L. V. Sazonova Yu. O. Larionova I. A. Kondrashov L. V. Shumlyanskyy A. Yu. Albekov K. A. Savko 《Petrology》2017,25(3):241-271
The rift system of the Dnieper–Donets trough (DDT) is the largest magmatic area in the East European Platform. Basalts of the Voronezh Crystalline Massif (VCM) are spatially constrained to the eastern shoulder of DDT and occur far away (at a distance of 150–200 km) from the rift axis. The rocks are hosted in the Paleoproterozoic Vorontsovskii terrane and are grouped in a few fields within an area of 200 × 100 km. Basalts at most of the fields were erupted at the boundary between mid- and late Frasnian time in the Late Devonian and can be studied exclusively in core material recovered by boreholes. Newly obtained mineralogical, geochemical, and isotopic-geochemical data show that the Devonian volcanic rocks in VCM are tholeiites (Bas) and basaltic andesites/andesites (ABas). The geological section was examined most exhaustively in the Novokhopersk area (Borehole 175). The bottom of the vertical section is made up of basaltic andesites and andesites (ABas) (thickness 34 m), which rest on an eroded surface of late Frasnian sandstones. The rocks are overlain by a thin (8 m thick) tholeiite sheet (Bas2), which gives way to ABas (13 m) upsection. The top portion of the vertical section is composed of tholeiites with petrography and geochemical evidence of crustal contamination (Bas1) (apparent thickness 5 m). Geochemical parameters of Bas (mg# 42–52 at SiO2 47–51 wt %) are typical of continental tholeiites. The rocks have (87Sr/86Sr)0 = 0.7043–0.7048 and εNd(372) = 2.1–3.5. ABas (mg# 28–31 at SiO2 52–60 wt %) are enriched in Y (48 ppm), and possess Nb/Nb* = 0.7–0.8 and high Zn/Cu = 1.9–2.3. The rocks have (87Sr/86Sr)0 = 0.7034–0.7048 and Nd–εNd(372) = 0.1. Some portions of Bas melts assimilated the upper crustal material, which was similar to Paleoproterozoic granites, and ABas are contaminated in the lower crust with derivatives of Early Cambrian alkaline mafic melts. Petrographic data and simulations of fractional crystallization show that olivine and high-Mg clinopyroxene were the first to crystallize from the melt. After this, clinopyroxene and plagioclase simultaneously crystallized at temperatures from 1070 to 1020°C in Bas and at 1040–900°C at f O2 below QFM + 1 in ABas. The source of ABas was likely a network of hornblendite or amphibole pyroxenite veins in peridotite in the lithospheric mantle or amphibolized peridotite cumulate in an underplating zone; and Bas were derived from spinel peridotites of an asthenospheric diapir. The setting of the basalts relative to the DDT axis and the asymmetric zoning of magmatism in DDT (with kimberlites and other deep rocks constrained to the western shoulder and tholeiites occurring in the axial part of the rift and its eastern shoulder) can be explained by the model of an asymmetric rift structure with a translithospheric detachment gently dipping beneath VCM. 相似文献
13.
14.
The Sm-Nd systematics of sanukitoids with an age of 2715–2740 Ma in the Western, Eastern, and Central domains of the Karelian craton with various crustal evolutionary histories indicates that the mafic and acid rocks of the sanukitoid series were derived from two contrasting sources: enriched lithospheric mantle and lower crust. The basic sanukitoids of the Western domain were derived from the mantle enriched long before its melting [?Nd(2715) = ?0.48 ± 0.22]. The source of the acid magmas was the young juvenile crust of TTG composition [?Nd(2715) increases to +1.2]. The mantle source of mafic sanukitoids in the Eastern domain was enriched shortly before melting [?Nd(2740) = +1.58 ± 0.01], whereas the acid melts came from an ancient crustal source [?Nd(2740) decreases to ?3.0]. For sanukitoids in the Central domain, the time span between the enrichment of the mantle source and its melting was the shortest [?Nd(2725) = +2.05 ± 0.15], and the contribution of the juvenile TTG crust was insignificant [?Nd(2725) deceases to +1.7]. The variations in the isotope characteristics of the acid members of the sanukitoid series are consistent with the known age heterogeneity of the crust of the domains. The lateral isotopic-geochemical heterogeneity of the lithospheric mantle source of the sanukitoids is thought to have been related to its two-stage reworking (at 3.2 and 2.8–2.9 Ga) under the effect of TTG granitoids, which are regarded as the melting products of the subducted oceanic crust. The sanukitoids provide information on the geochemical structure of the Archean lithosphere, which is reflected in Archean crust-building processes. The Rb-Sr isotope system of the Neoarchean sanukitoids underwent transformations on the mineralogical scale and within small massifs in the course of at least two Paleoproterozoic tectono-thermal events. A trace of the event at ～2.1 Ga is left in the Rb-Sr system of monomineralic fractions from a weakly deformed syenite of the sanukitoid series in the Central Domain. Later event (～1.7 Ga) was recorded in the minerals of the Teloveis sanukitoid massif, which hosts a gold mesothermal deposit in the Western domain. Monomineralic fractions of muscovite and biotite from the wall-rock metasomatites and of plagioclase, microcline, and biotite from metasomatites away from the orebodies yield isochron ages of 1719 ± 60 and 1717 ± 27 Ma. This age of the metasomatic alterations of the Neoarchean sanukitoids is able to explain the broad and unsystematic variations in the Rb-Sr isotope-geochemical characteristics of these rocks. Our data on the Paleoproterozoic age of the mesothermal gold ore mineralization at the Teloveis deposit provide additional lines of evidence for the complex tectonic and metallogenic evolution of the Karelian GGT in the Early Precambrian. 相似文献
15.
I. V. Chernyshev V. Yu. Prokof’ev N. S. Bortnikov A. V. Chugaev Yu. V. Goltsman V. A. Lebedev Yu. O. Larionova L. D. Zorina 《Geology of Ore Deposits》2014,56(1):1-14
The Darasun ore field situated in the southern West Stanovoi Terrane near the Mongolia-Okhotsk Suture comprises the Darasun (>100 t Au), Talatui (～38.2 t Au), and Teremki (3 t Au) lode gold deposits. In the opinion of many researchers, the Darasun deposit is spatially and paragenetically linked to granodiorite porphyry of the Amudzhikan Complex and related metasomatic rocks (beresites). Whole-rock samples of granodiorite porphyry, monomineralic fractions of plagioclase, K-feldspar, and biotite, as well as sericite from beresite (26 samples in total), were analyzed by the Rb-Sr method. Eight biotite and sericite samples were analyzed by the K-Ar method. The Rb-Sr mineral isochrons obtained for individual granodiorite porphyry samples yielded initial 87Sr/86Sr ratios varying from 0.70560 to 0.70591. The consistent results of both methods allowed us to accept the ages of granodiorite porphyry and beresite as 160.5 ± 0.4 and 159.6 ± 1.5 Ma, respectively. The age of granodiorite porphyry of the Amudzhikan Complex of 160.5 ± 0.4 Ma corresponds to the boundary between the Early and Middle Jurassic and marks the completion of collision between the East Siberian and Mongolia-China continents and related orogeny. Since that time, the eastern Transbaikal region has been involved in the postorogenic (within-plate) stage of evolution, characterized by the formation of large gold, uranium, and other ore deposits. 相似文献
16.
A. V. Kargin A. A. Nosova Yu. O. Larionova V. A. Kononova S. E. Borisovsky E. V. Koval’chuk I. G. Griboedova 《Petrology》2014,22(2):151-183
Mineralogical and petrological-geochemical features of the Mesoproterozoic (1.23–1.20 Ga) alkaline ultrabasic rocks from the Kostomuksha-Taloveis (Russia) and Lentiira-Kuhmo (Finland) areas, West Karelia, have been studied. In terms of mineralogy and geochemistry, these rocks more resemble group II kimberlites of South Africa (orangeites) than olivine lamproites or ultramafic lamprophyres. On the basis of phenocryst composition, the studied orangeites are divided into three types: Cpx-Phl-Ol, Phl-Ol, and Phl-Carb orangeites. The Cpx-Phl-Ol orangeites from the Kostomuksha cluster clearly differ from analogous rocks from the Lentiira cluster. The composition of Phl-Ol orangeites is indicative of derivation by intense fractional crystallization; Cpx-Phl-Ol orangeites from the Kostomuksha area display evidence of intense lithosphere assimilation. The Phl-Carb orangeites from the Taloveis cluster and Cpx-Ol orangeites from the Lentiira cluster most closely approximate primary melts. The Kostomuksha orangeites are characterized by lowto moderate-radiogenic (87Sr/86Sr)1220 ratio varying from 0.7038 to 0.7067. The Phl-Carb orangeites of Taloveis have less radiogenic Nd isotope composition (?Nd from ?11 to ?12) as compared to the Cpx-Phl-Ol and Phl-Ol orangeites of Kostomuksha (?Nd from ?6.9 to ?9.4). The Cpx-Phl-Ol orangeites from Lentiira contain fresh olivine. By morphology and composition, there are three olivine generations: (1) large rounded, usually zoned crystals with Fo 92 core, 0.33–0.37 wt % NiO, and 0.03–0.04 wt% CaO, which are interpreted as xenocrysts from depleted peridotites; (2) anhedral rounded zoned olivines of intermediate size with Fo 82–83 cores, 0.03–0.05 wt % CaO, 0.12–0.17 wt % NiO, and up to 0.40 wt % MnO. These olivines were entrapped by orangeite melt and presumably represent a cumulate of basaltic melts or were derived from metasomatized peridotites; (3) fine euhedral olivines and xenocryst rims corresponding to Fo 88–89 with 0.10–0.42 wt % CaO, 0.14–0.35 wt % NiO, and up to 0.07–0.21 wt % MnO; their origin was presumably related to the crystallization from kimberlite melt. The calculation of $f_{O_2 }$ of kimberlite melt during crystallization of perovskites using Nb-Fe perovskite oxyba-rometer showed that Cpx-Phl-Ol orangeites of Kostomuksha and orangeites of Lentiira crystallized at similar oxygen fugacities corresponding to ΔNNO from ?3.3 to ?1.1 and from ?3.3 to ?0.9, respectively. The Sm-Nd and Rb-Sr isotope study provided evidence for the contribution from ancient enriched source in the genesis of the orangeites. It was proposed that their mantle source was formed in two stages: (1) metasomatic reworking of previously depleted lithospheric source at the Karelian Craton base during Paleoproterozoic orogenic events 2.1–2.0 Ga ago; (2) extension-related generation of orangeite melts 1.27–1.20 Ga ago. 相似文献
17.
K. A. Savko A. V. Samsonov A. N. Larionov Yu. O. Larionova N. S. Bazikov 《Petrology》2014,22(3):205-233
The eastern part of the Voronezh Crystalline Massif hosts coeval S- and A-granitoids. The biotite-muscovite S-granites contain elevated concentrations of Si, Al, and alkalis (with K predominance) and relatively low concentrations of Ca, Mg, Ti, Sr, and Ba, show pronounced negative Eu anomalies, and have low concentrations of Y and HREE. The biotite A-granitoids are enriched in Fe, Ti, P, HFSE, REE and have strongly fractionated REE patterns with deep Eu minima. According to their Rb/Nb and Y/Nb ratios, these rocks are classified with group A2 of postcollisional granites. The SIMS zircon crystallization age of the granitoids lies within the range of 2050–2070 Ma. Both the A- and the S-granitoids have positive ?Nd(T) values, which suggests that they should have had brief crustal prehistories and were derived from juvenile Paleoproterozoic sources. The simultaneous derivation of the A- and S-granites was caused by the melting of the lower crust in response to the emplacement of large volumes of mafic magma in an environment of postcollisional collapse and lithospheric delamination with the simultaneous metamorphism of the host rocks at high temperatures and low pressures. The S-granites are thought to be derived via the melting of acid crustal material in the middle and lower crust. The A2 granites can possibly be differentiation products of mafic magmas that were emplaced into the lower crust and were intensely contaminated with crustal material. 相似文献
18.
In the present work we studied Mg-ilmenite megacrysts from the Arkhangelsk kimberlites (the Kepino kimberlite field and mantle xenoliths from the Grib pipe). On the basis of isotopic (Rb/Sr, Sm/Nd, δ18O) and trace-element data we argue that studied Mg-ilmenite megacrysts have a genetic relation to the “protokimberlitic” magma, which was parental to the host kimberlites. Rb-Sr ages measured on phlogopite from ilmenite-clinopyroxenite xenoliths and the host Grib kimberlite overlap within the error (384 Ma and 372 ± 8 Ma, respectively; Shevchenko et al., 2004) with our estimation of the Kotuga kimberlite emplacement (378 ± 25 Ma). Sr and Nd isotopic compositions of megacrysts are close to the isotopic composition of host kimberlites (Mg-ilmenites from kimberlites have 87Sr/86Sr(t = 384) = 0.7050–0.7063, ?Nd(t = 384) = + 1.7, +1.8, ilmenite from ilmenite-garnet clinopyroxenite xenolith has 87Sr/86St(t = 384) = 0.7049, ?Nd(t = 384) = +3.5). Oxygen isotopic composition of ilmenites (δ18O = +3.8–+4.5‰) is relatively “light” in comparison with the values for mantle minerals (δ18O = +5–+6‰). Taking into account ilmenite-melt isotope fractionation, these values of δ18O indicate that ilmenites could crystallize from the “protokimberlitic” melt. Temperatures and redox conditions during the formation of ilmenite reaction rims were estimated using ilmenite-rutile and titanomagnetite-ilmenite thermo-oxybarometers. New minerals within the rims crystallized at increasing oxygen fugacity and decreasing temperature. Spinels precipitated during the interaction of ilmenite with kimberlitic melt at T = 1000–1100°C and oxygen fugacity $\Delta \log f_{O_2 }$ [QFM] ≈ 1. Rims comprised with rutile and titanomagnetite crystallized at T ≈ 1100°C, $\Delta \log f_{O_2 }$ [NNO] ≈ 4 and T = 600–613°C, $\Delta \log f_{O_2 }$ [QFM] ≈ 3.7, respectively. Rutile lamellae within ilmenite grains from clinopyroxenitic xenolith were formed T ≥ 1000–1100°C and oxygen fugacity $\Delta \log f_{O_2 }$ [NNO] = ?3.7. Since the pressure of clinopyroxene formation from this xenolith was estimated to be 45–53 kbar, redox conditions at 135–212 km depths could be close to $\Delta \log f_{O_2 }$ [NNO] = ?3.7. 相似文献
19.
A. A. Nosova L. V. Sazonova A. V. Kargin Yu. O. Larionova V. M. Gorozhanin S. G. Kovalev 《Petrology》2012,20(4):356-390
The Mesoproterozoic (1.38?C1.30 Ga) Kama-Belsk igneous province (KBP) was formed at the eastern margin of the East European Platform (EEP), in the Volga-Ural area and Bashkirian anticlinorium. It is made up of plutonic, volcanic, and subvolcanic (numerous dike and sill swarms) rocks of bimodal composition. KBP, as most of large igneous provinces, contains two geochemical types of basites: high-titanium (HTi) rocks with TiO2 > 1.5 wt % and low-titanium (LTi) rocks with TiO2 < 1.5?C2.0 wt %. They demonstrate zoned distribution, were derived from different mantle sources at different regimes of their partial melting. The high and low-titanium basites significantly differ in geochemical and isotopic (Sr, Nd, O) parameters. The HTi rocks are characterized by Ti/Y > 400, (Gd/Yb) n = 1.62?C4.08, (Dy/Yb) n = 1.31?C2.43; Nb/Nb* from 0.5 to 1.3, while the LTi rocks have Ti/Y < 400, (Gd/Yb) n = 1.23?C1.51, (Dy/Yb)n = 1.01?C1.26, and Nb/Nb* from 0.3 to 0.9. The HTi rocks have ?Nd(T) from + 1.3 to ?2.4, while the LTi rocks are characterized by ?Nd(T) from + 0.5 to ?6.1. The oxygen isotopic composition ??18O is 5.0?C5.9?? in the LTi rocks and 7.0?? in the HTi picrobasalts. According to obtained estimates, the parental melts for the LTi type (Mg# = 0.76) are comparable with high-Mg primary melts inferred for within-plate picrites. The parental melts for the HTi type (Mg# = 0.69) had higher Fe contents, which in combination with lowered Al2O3 and elevated TiO2, Na2O, and P2O5 make these rocks similar to ferropicrites. The HTi melts were presumably derived by partial melting of a pyroxenite in equilibrium with garnet-bearing residue, whereas the LTi melts were generated from peridotite protolith and left spinel-bearing residuum. Both the varieties of the basites were contaminated mainly by Paleoproterozoic crustal material. 相似文献
20.
V. A. Hagen-Thorn V. M. Larionov E. G. Larionova N. A. Kudryavtseva A. V. Tikhonov A. V. Hagen-Thorn A. A. Arkharov A. Di Paola F. D'Alessio 《Astronomy Letters》2004,30(4):209-217
We present the results of our multicolor observations of BL Lac in the period 1999–2001. We show that the spectral energy distribution of the variable component in the range from K to B had remained unchanged for three years. The power-law spectrum is indicative of its synchrotron nature. 相似文献