Numerical methods for estimating the degree of practical stability of inverse problems in geoelectrics     

M. I. Shimelevich  E. A. Obornev  I. E. Obornev  E. A. Rodionov 《Izvestiya Physics of the Solid Earth》2013,49(3):356-362

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The first data on the Early Proterozoic sialic basement in the eastern West Siberian Platform (studies of the Tyn'yar rhyolite–granite pluton)     

K.S. Ivanov  Yu.V. Erokhin  Yu.L. Ronkin  V.V. Khiller  N.V. Rodionov  O.P. Lepikhina 《Russian Geology and Geophysics》2012,53(10):997-1011

Despite the long history of research, the presence of Precambrian complexes in the West Siberian basement has not been proven. The Tyn'yarskaya 100 and Tyn'yarskaya 101 wells were drilled in the Vakh–Elogui interfluve, in the eastern West Siberian Plate (eastern Khanty-Mansi Autonomous District). At a depth of 1790 m, they stripped a rhyolite extrusion, which graded into A-type alkali granitoids with rare-metal and REE mineralization (thorite, thorogummite, pitchblende, REE-carbonates, chevkinite, and others) downsection. This volcanoplutonic complex is Early Permian (K–Ar age, ～ 270 Ma; Rb–Sr age, 275.7 Ma; Sm–Nd age, 276 Ma; U–Pb age, 277 Ma). Some zircon grains from granites are much older (2049 ± 23 Ma, SHRIMP II), suggesting a relationship between the Early Permian granitic magma and the ancient matter. This might have been a granite-metamorphic basement, the partial melting of which produced the Tyn'yar rhyolite–granite body. The Sm–Nd model ages also suggest the participation of a Precambrian substratum in the formation of the rocks under study. Thus, it is quite possible that the Tyn'yar area is underlain by a Proterozoic (～ 2 Ga) sialic basement, which is an edge of the Siberian Platform thinned by Late Proterozoic–Early Paleozoic rifting and extension.  相似文献   

The age of sedimentation and metamorphism of plagiogneisses of the Ganalskii and granulite complexes of the Ganalskii Range (East Kamchatka)     

V. K. Kuzmin  N. V. Rodionov 《Doklady Earth Sciences》2011,436(2):171-175

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Relationship between metamorphism and ore formation at the Sukhoi Log gold deposit hosted in black slates from the data of U-Th-Pb isotopic SHRIMP-dating of accessory minerals     

M. A. Yudovskaya  V. V. Distler  N. V. Rodionov  A. V. Mokhov  A. V. Antonov  S. A. Sergeev 《Geology of Ore Deposits》2011,53(1):27-57

The formation conditions and age of the Sukhoi Log gold deposit are considered on the basis of new isotopic-geochemical data. The U-Pb isotopic study of zircon and monazite from high-grade ore and host black slates at the Sukhoi Log deposit was carried out with SIMS technique using a SHRIMP II instrument. Two generations of monazite are distinguished on the basis of optical and scanning electron microscopy, cathodoluminescence, and micro X-ray spectroscopy. Monazite I is characterized by black opaque porphyroblasts with microinclusions of minerals pertaining to metamorphic slates and structural attributes of pre- and synkinematic formation. Monazite II occurs only within the ore zone as transparent crystals practically free of inclusions and as rims around monazite I. The REE contents are widely variable in both generations. Porphyroblastic monazite I differs in low U and Th (0.01–0.7 wt % ThO₂) contents, whereas transparent monazite II contains up to 4 wt % ThO2. The average weighted U-Pb isotopic age of monazite I is 650 ± 8.1 Ma (MSWD = 1.6; n = 9) and marks the time of metamorphism or catagenesis. The U-Pb age estimates of synore monazite II cover the interval of 486 ± 18 to 439 ± 17 Ma. Zircons of several populations from 0.5 to 2.6 Ga in age are contained in the ore. Most detrital zircon grains have porous outer rims composed of zircon and less frequent xenotime with numerous inclusions of minerals derived from slates. The peaks of ²⁰⁶Pb/²³⁸U ages in the most abundant zircon populations fall on 570 and 630 Ma and correspond to the age of newly formed metamorphic mineral phases. The discordant isotopic ages indicate that the U-ThPb isotopic system of ancient detrital zircons was disturbed 470–440 Ma ago in agreement with isotopic age of monazite II and the Rb-Sr whole -rock isochron age of black slates (447 ± 6 Ma). The new data confirm the superimposed character of the gold-quartz-sulfide mineralization at the deposit. Black shales of the Khomolkho Formation of the Bodaibo Synclinorium were affected by metamorphism over a long period; the peaks of metamorphism and catagenesis are dated at 570 and 650–630 Ma. The high-temperature ore formation was probably related to a hidden granitic pluton emplaced 450–440 Ma ago, that is, 200 Ma later than the events of greenschist metamorphism. Hercynian granitoid magmatism (320–270 Ma) did not exert a substantial effect on the U-Th-Pb isotopic system in accessory minerals from the ore and could not have been a major source of ore-forming fluids.  相似文献   

A SIMS zircon age for a biostratigraphically dated Upper Viséan (Asbian) bentonite in the Central-European Variscides (Bardo Unit,Polish Sudetes)   总被引：1，自引：1，他引：0  

Ryszard Kryza  Jolanta Muszer  Joanna Haydukiewicz  Czesław August  Marta Jurasik  Nickolay Rodionov 《International Journal of Earth Sciences》2011,100(6):1227-1235

A Lower Carboniferous platform sedimentary sequence (the Paprotnia Beds) in the Bardo Unit of the central Sudetes (NE part of the Bohemian Massif, SW Poland) is biostratigraphically well dated, based on rich macro- and micro-fossil evidence, as Late Viséan (late Asbian, crenistria, Go III α zone). The beds contain several bentonite layers, one of which was dated using the U–Pb SHRIMP method on volcanic zircons and yielded an age of 334 ± 3 Ma. This date fits well to the recently established chronostratigraphic limits of the Viséan, and is consistent with the newest isotopic age constraints of 336.5–332 Ma for the Asbian boundaries.  相似文献   

Trace-element study and age dating of zircon from chromitites of the Bushveld Complex (South Africa)     

Marina Yudovskaya  Judith Kinnaird  Anthony J. Naldrett  Nickolay Rodionov  Anton Antonov  Sergey Simakin  Dmitry Kuzmin 《Mineralogy and Petrology》2013,107(6):915-942

The layered Bushveld Complex hosts a number of chromitite layers, which were found to contain significant amounts of zircon grains compared with adjacent silicate rocks. Cathodoluminescent-dark, partially metamict cores and transparent rims of composite zircon grains were analyzed for trace elements with SIMS and LA-ICPMS techniques. The cores are enriched in REE, Y, Th and U and are characterized by distinctly flatter REE patterns in contrast to those of the rims and transparent homogenous crystals. Zircon from the different stratigraphic units has specific Th/U ratios, the highest of which (1.5–4) occurs in a Merensky Reef zircon core. The Ti content of Bushveld zircon ranges from 12 to 52 ppm correlating to a crystallization temperature range of 760–930 °C. The geochemical characteristics of the first zircon generation are consistent with its high-temperature crystallization as the first major U, Th and REE acceptor from a highly-evolved residue of the high-Mg basalt magma, whereas the rims and coreless crystals have crystallized from percolating intercumulus liquid of new influx of the same magma. U-Pb SHRIMP dating of zircon cores and rims does not reveal a distinguishable difference between their ages indicating the absence of inherited zircon. Concordia ages of 2,051?±?9 Ma (2σ, MSWD?=?0.1) and 2,056?±?5 Ma (2σ, MSWD?=?0.05) for zircons from the Merensky Reef and the Upper Platreef located equally near the top of the Critical Zone are in agreement with published ages for the Merensky Reef. Zircon from the deeper-seated Lower Group, Middle Group and Lower Platreef chromitites yields younger concordia ages that may reflect prolonged late-stage volatile activity.  相似文献   

Age, Sm-Nd systematics, and geochemistry of tonalite-trondhjemite-granodiorite gneisses of the northern part of the Baltic Shield     

V. R. Vetrin  N. V. Rodionov  P. A. Serov 《Doklady Earth Sciences》2013,452(1):930-935

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voboz: an almost-parameter-free halo-finding algorithm     

Mark C. Neyrinck  Nickolay Y. Gnedin  Andrew J. S. Hamilton 《Monthly notices of the Royal Astronomical Society》2005,356(4):1222-1232

We have developed an algorithm, called voboz (VOronoi BOund Zones), to find haloes in an N -body dark matter simulation; it has as little dependence on free parameters as we can manage. By using the Voronoi diagram, we achieve non-parametric, 'natural' measurements of each particle's density and set of neighbours. We then eliminate much of the ambiguity in merging sets of particles together by identifying every possible density peak, and measuring the probability that each does not arise from Poisson noise. The main halo in a cluster tends to have a high probability, while its subhaloes tend to have lower probabilities. The first parameter in voboz controls the subtlety of particle unbinding, and may be eliminated if one is cavalier with processor time; even if one is not, the results saturate to the parameter-free answer when the parameter is sufficiently small. The only parameter that remains, an outer density cut-off, does not influence whether or not haloes are identified, nor does it have any effect on subhaloes; it only affects the masses returned for supercluster haloes.  相似文献   

Sm-Nd systematics and petrology of postorogenic granitoids in the northern Baltic Shield     

V. R. Vetrin  N. V. Rodionov 《Geochemistry International》2008,46(11):1090-1106

In the northern part of the Baltic Shield, quartz diorites, diorites, and monzodiorites compose massifs of postorogenic granites, in which younger granite phases are restricted to their central parts, and dike rocks (aplites, pegmatites, and granite porphyries) occur in the apical parts. The rocks of the Litsa-Araguba Complex (which is located in the northwestern part of the Kola Peninsula and was examined most thoroughly) compose seven intrusions 850 km² in total area, which were formed in mesoabyssal and hypabyssal depth facies. The massifs consist of quartz diorites and monzodiorites dated at 1774 ± 9 Ma, diorites, diorite porphyries, and lamprophyres, which are distinguished as phase 1. The porphyritic and equigranular granites, granodiorites, quartz monzonites, granites, alaskites and related vein leucogranites, pegmatites, and granite porphyries of phases 2 (main), 3, and 4 have an age of 1772–1762 Ma. Data obtained on the Sm-Nd systematics of the rocks indicate that their ?_Nd(1765) values are close to those for rocks of phases 1, 2, and 3 (from ?6.8 to ?8.8) and vary from ?5.0 to ?11.9 for the leucocratic granites of phase 4. The model age values are, respectively, 2.37–2.62 and 2.58–3.23 Ga. These data suggest that the parental melts were of anatectic genesis and were produced by the melting of mostly metasomatically altered garnet granulites from the lower crust. The leucogranites and alaskites of phase 4, which occur as relatively thin bodies in the rocks of the Archean Complex penetrated by the Kola Superdeep Borehole, were derived from a Neoarchean sialic source or produced by the contamination of the parental melts with the material of the Late Archean upper crust. The SHRIMP-II zircon age of the lower crustal migmatized garnet granulites lies within the range of 1831 ± 23 to 1392 ± 21 Ma in the concordia plot. All dates of the rocks are characterized by a unimodal distribution with most values lying within the range of 1650–1800 Ma and approximated by a discordia with T₁ = 1750 ± 30 Ma, MSWD = 3.1. This age value can be interpreted as an averaged age of the lower crustal granitization and corresponds, within the errors, to the age of postorogenic granite intrusions in the upper crust.  相似文献   

Monte-Carlo and multifluid modelling of the circumnuclear dust coma II. Aspherical-homogeneous, and spherical-inhomogeneous nuclei     

V.V. Zakharov  A.V. Rodionov  J.F. Crifo 《Icarus》2009,201(1):358-380

We use our newly developed Dust Monte-Carlo (DMC) simulation technique [Crifo, J.F., Lukianov, G.A., Rodionov, A.V., Zakharov, V.V., 2005. Icarus 176, 192-219] to study the dynamics of dust grains in the vicinity of some of the benchmark aspherical, homogeneous cometary nuclei and of the benchmark spherical, inhomogeneous nuclei studied by us precedingly. We use the interim unrealistic simplifying assumptions of grain sphericity, negligible nucleus rotation rate, and negligible tidal force, but take accurately into account the nucleus gravitational force, gas coma aerodynamic force, and solar radiation pressure force, and consider the full mass range of ejectable spherical grains. The resulting complicated grain motions are described in detail, as well as the resulting complicated and often counter-intuitive dust coma structure. The results are used to answer several important questions: (1) When computing coma dust distributions, (a) is it acceptable to take into consideration only one or two of the above mentioned forces (as currently done)? (b) to which accuracy must these forces be known, in particular is it acceptable to represent the gravity of an aspherical nucleus by a spherically symmetric gravity? (c) how do the more efficient but less general Dust Multi-Fluid (DMF) computations compare with the DMC results? (2) Are there simple structural relationships between the dust coma of a nucleus at small heliocentric distance rh, and that of the same nucleus at large rh? (3) Are there similarities between the gas coma structures and the associated dust coma structures? (4) Are there dust coma signatures revealing non-ambiguously a spherical nucleus inhomogeneity or an homogeneous nucleus asphericity? (5) What are the implications of the apparently quite general process of grain fall-backs for the evolution of the nucleus surface, and for the survival of a landed probe?  相似文献