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991.
R. A. Oktyabr’skii N. V. Vladykin A. M. Lennikov A. A. Vrzhosek T. A. Yasnygina S. V. Rasskazov E. Yu. Moskalenko T. A. Velivetskaya 《Geochemistry International》2010,48(8):778-791
New geochemical data are discussed on the magmatic complexes of the Koksharovka alkaline ultrabasic massif of Late Jurassic
age obtained by the ICP-MS method. Based on the first results on rare earth geochemistry of carbonatites and associating pyroxenites
and geological observations, the magmatic origin of the Koksharovka carbonatites was substantiated, and the problems of formation
of accompanying igneous rocks were considered. 相似文献
992.
N. A. Krivolutskaya V. F. Smol’kin N. M. Svirskaya V. P. Mamontov A. S. Fanygin B. V. Belyatskii I. A. Roshchina 《Geochemistry International》2010,48(5):465-491
The comparative-geochemical study was first conducted for the ultrabasic-basic massifs of the central part of the Belomorian
mobile belt, which were previously ascribed to the drusite complex on the basis of the presence of coronal textures. The studied
magmatic bodies are geochemically heterogeneous and can be subdivided into three groups: (1) high-Mg rocks (MgO > 20 wt %)
with elevated Cr content, enriched trace element patterns, and deep negative Ta-Nb anomaly (Sorkajoki Massif). Intrusions
of this group are geochemically close to the layered plutons of Northern and Eastern Karelia (Kivakka, Burakovsky) and to
the intrusions of the Kola Peninsula (Monchepluton and others); (2) low-Mg intrusions (MgO < 10 wt %) with elevated contents
of Fe, Ti, and P (403-m Height Massif). The rocks composing these intrusions are characterized by subhorizontal trace element
patterns and weak Ta-Nb anomaly; (3) intrusions with intermediate MgO contents (10–20 wt %), flat, occasionally depleted REE
patterns, and lack of Ta-Nb anomaly (Mt. Grob Tundra). The identified geochemical differences do not depend on the degree
of metamorphic transformations, but were presumably caused by differences in phase and chemical composition of parental magmas,
as well as by conditions of their crystallization. It was substantiated that ultrabasic-basic massifs presently united into
the drusite complex are genetically diverse and acquired similar textural appearance due to regional metamorphism. Thus, the
presence of coronal textures is insufficient to ascribe the intrusions to the drusite complex, their mineralogical and geochemical
composition should be taken into account. 相似文献
993.
V. A. Drits T. A. Ivanovskaya B. A. Sakharov B. B. Zvyagina A. Derkowski N. V. Gor’kova E. V. Pokrovskaya A. T. Savichev T. S. Zaitseva 《Lithology and Mineral Resources》2010,45(6):555-576
The detailed mineralogical and structural-crystal-chemical characteristics are reported for the first time for glauconite grains extracted from the fine-platy silty-sandy dolomites at the roof of the lower subformation of the Yusmastakh Formation (Riphean, Anabar Uplift, North Siberia). Based on the complex study (X-ray diffraction, classical chemical analysis, microprobe analysis, IR-spectroscopy, thermogravimetric analysis, scanning electron microscopy with microprobe analysis, and Mössbauer spectroscopy), it was demonstrated that the studied glauconite sample is characterized by unique chemical and structural heterogeneity.The mineral structure consists of micaceous (90%), smectite (6%), and di-trioctahedral chlorite (4%) layers. Mica is classed with Al-glauconite (Al > Fe3+) with elevated Mg content. The elevated Mg mole fraction of the mineral is caused by the presence of Mg-bearing brucite-type interlayers of di-trioctahedral chlorite and the high Mg content in the octahedral sheets of 2: 1 layers. It was first discovered that glauconites are characterized by the heterogeneous distribution of cations over the available trans- and cis-octahedra due to the coexistence of trans- and cis-vacant octahedra and small trioctahedral clusters in octahedral sheets. The distribution of isomorphic cations over the accessible octahedral sites is also heterogeneous due to the tendency of Fe, Mg and Al, Mg cations to segregation and formation of corresponding domains.It was found that structure of the studied glauconite has a specific stacking defect: in addition to the predominant subsequent layers of similar azimuthal orientation according to 1M type (~77%), some layer fragments are rotated at 180° (~15%) and ±120° (8%). The structural-crystal-chemical heterogeneity of the mineral is explained by the fact that its microcrystals grew in the dolomitic sediment under nonequilibrium conditions of the reduction zone of a shallow-water basin with a sufficiently high content of Mg cations, which significantly contributed to the glauconite formation. 相似文献
994.
E. L. Shkol’nik E. A. Zhegallo G. N. Baturin N. I. Khamkhadze E. A. Eganov T. G. Kuz’mina 《Lithology and Mineral Resources》2010,45(3):275-284
The paper presents results of the detailed study of phosphorites from manganiferous beds of the Chiatura deposit. The relatively
high-grade (P2O5 20–28%) phosphorites are represented by various rocks ranging from the variety dominated by massive phosphates with a rare
aleuritic admixture of quartz and feldspar grains to rocks mainly composed of terrigenous material with phosphates in the
matrix. Phosphates make up the matrix of various organic remains: differently preserved diatom algae and microbial species.
Some relatively large organic remains (in particular, sponge spicules) are typically composed of iron minerals (with manganese
admixture) rather than phosphates. Manganese ores comprise phosphorite fragments composed of phosphatized cyanobacterial mat.
Phosphorites of the Chiatura deposit were likely formed in a shallow-water zone away from the continental land. 相似文献
995.
I. M. Gorokhov M. A. Semikhatov T. L. Turchenko P. Yu. Petrov N. N. Mel’nikov G. V. Konstantinova E. P. Kutyavin 《Stratigraphy and Geological Correlation》2010,18(5):480-491
Fine-grained clayey subfractions (SF) with particle sizes of 1–2, 0.6–1.0, 0.3–0.6, 0.2–0.3, 0.1–0.2, and <0.1 μm were extracted
from shales of the Vendian Staraya Rechka Formation in the Anabar Massif and studied by XRD and Rb-Sr methods. All the clayey
subfractions are represented by illite with high crystallinity indices, which are characteristic of the low-temperature diagenesis/catagenesis
zone and grow with the decrease of the particle size. The Rb-Sr systematics in clayey subfractions combined with mineralogical
data provide grounds for the conclusion that illite from clayey rocks of the Staraya Rechka Formation was forming during two
periods: approximately 560 and 391–413 Ma ago. The first illite generation was likely formed in the course of lithostatic
subsidence of the Staraya Rechka sediments and the second one, during the Devonian lithogenesis stage. It is assumed that
age of the first generation (∼560 Ma) is close to that of the Staraya Rechka Formation. This inference is consistent with
biostratigraphic, chemostratigraphic, and geochronological data obtained for both rocks of the Anabar Massif and Vendian sediments
from other regions of Siberia. 相似文献
996.
Mesoproterozoic olivine gabbronorites of the Bashkirian anticlinorium,the South Urals: Parental melts and specifics of magma evolution 总被引:1,自引:0,他引:1
A. A. Nosova L. V. Sazonova V. M. Gorozhanin O. F. Kuz’menkova E. O. Dubinina 《Petrology》2010,18(1):50-83
This paper is devoted to detailed study of picritic rocks (olivine melanogabbronorites) and comagmatic gabbrodolerites from
sills and dikes in the central part of the Bashkirian meganticlinorium. These rocks are ascribed to the Kama-Belsk magmatic
province (KBP) that was formed in the eastern East European Platform (EEP) in the Mesoproterozoic time. The study of minerals
(EMPA, SIMS), rocks, and their oxygen isotope compositions showed the contribution of crustal contamination, fractional crystallization
and cumulus processes in their formation. The geochemical indicators of crustal contamination (Nb/Nb*, (Nb/La)
n
, δ18O, and others) show strong variations, which indicates uneven crustal contribution in the parental melts during rock formation
(10–25%). The study of weakly contaminated (δ18O = 5.3‰) olivine melanogabbronorites (MgO = 22.55 wt %) from the small Ishlya-1 subvolcanic body, which contain subordinate
amount of cumulus (24%), high-magnesian olivine (Fo91.3), and high-Cr spinel (cr# 0.67), as well as HREE depleted clinopyroxenes, allowed us to retrieve the composition of parental
melt. The latter contained about 20 wt % MgO and was formed by 19–26% melting of mantle source (potential mantle temperature
T
m of 1530–1545°C).
Geochemical characteristics of KBP reflect the formation of primary melts by melting of mantle column at different depths,
mixing of the melts, and significant contamination by crustal material. The dominant role in the formation of the rocks of
the Ishlya area and Mashak Complex was played by derivatives of spinel peridotites, while the rocks of the Bakal-Satka area
were derived from garnet peridotites. 相似文献
997.
G. A. F. d’Almeida 《Geotectonics》2010,44(3):271-282
The Red Sea Rift has been an object of comprehensive studies by several generations of geologists and geophysicists. Many
publications and open-file reports provide insights into the geological history of this rift. Paleogene and Cretaceous rocks,
which are considered to be prerift, are locally exposed at the margins of the Red Sea Rift. At the same time, some evidence
indicates that at least some of these rocks are related to the early stage of the evolution of the Red Sea Rift. The available
geological data suggest that the Red Sea region started its active evolution in the Cretaceous. As follows from lithostratigraphic
data, the Cretaceous-Paleogene trough that predated the Oligocene-Quaternary rift covered this region completely or partially.
The pre-Oligocene magmatism and geological evidence show that the Cretaceous-Paleogene trough was of the rift type. The Cretaceous-Eocene
and Oligocene-Quaternary phases of rifting were separated by an epoch of uplifting and denudation documented by the erosion
surface and unconformity. 相似文献
998.
Younger and older zircons from rocks of the oceanic lithosphere in the Central Atlantic and their geotectonic implications 总被引:1,自引:0,他引:1
Local U-Pb dating of zircons separated from various rocks in the crest zone of the Mid-Atlantic Ridge (MAR) and Carter Seamount
(Sierra Leone Rise) is performed. Younger zircons formed in situ in combination with older xenogenic zircons are revealed
in enriched basalts, alkaline volcanic rocks, gabbroic rocks, and plagiogranites. Only older zircons are found in depleted
basalts and peridotites. Older zircons are ubiquitous in the young oceanic lithosphere of the Central Atlantic. The age of
the younger zircons from the crest zone of the MAR ranges from 0.38 to 11.26 Ma and progressively increases receding from
the axial zone of the ridge. This fact provides additional evidence for spreading of the oceanic floor. The rate of half-spreading
calculated from the age of the studied zircons is close to the rate of half-spreading estimated from magnetic anomalies. The
age of the younger zircons from Carter Seamount (58 Ma) corresponds to the age of the volcanic edifice. Older zircons make
up an age series from 53 to 3200 Ma. Clusters of zircons differing in age reveal quasiperiodicity of about 200 Ma, which approximately
corresponds to the global tectonic epochs in the geological evolution of the Earth. Several age groups of older zircons combine
grains close in morphology and geochemistry: (1) Neoproterozoic and Phanerozoic (53–700 Ma) prismatic grains with slightly
resorbed faces, well-preserved or translucent oscillatory zoning, and geochemical features inherent to magmatic zircons; (2)
prismatic grains dated at 1811 Ma with resorbed faces and edges, fragmentary or translucent zoning, and geochemical features
inherent to magmatic zircons; (3) ovoid and highly resorbed prismatic grains with chaotic internal structure and metamorphic
geochemical parameters; the peak of their ages is 1880 Ma. The performed study indicates that older xenogenic zircons from
young rocks in the crest zone of the MAR were captured by melt or incorporated into refractory restite probably in the sublithospheric
mantle at the level of magma generation in the asthenosphere. It is suggested that zircons could have crystallized from the
melts repeatedly migrating through the asthenosphere during geological history or were entrapped by the asthenosphere together
with blocks of disintegrated and delaminated continental lithosphere in the process of breakup of the continents older than
Gondwana. The variability in the age of older zircons even within individual samples may be regarded as evidence for active
stirring of matter as a result of periodically arising and destroyed within-asthenospheric convective flows varying in orientation
and scale. 相似文献
999.
V. V. Emel’yanenko 《Solar System Research》2010,44(4):281-289
One of the main particular features of the structure of the Kuiper Belt is that it contains clusters of objects of small orbital
eccentricity and inclination (“cold population”). In order to solve the problem of the origin of the objects, we considered
the process of the gravitational interaction of a comparatively small-mass planet with a planetesimal disk. We found that
one particular property of the process is that the planet changes its direction of migration. The interaction with the planet
results in the transportation of a considerable portion of planetesimals from the inner zone out to the Kuiper Belt. After
such a transition of the objects, the planet returns to the inner regions of the planetesimal disk. Numerical simulations
show that the reversible migration of a planet of a mass similar to that of the Earth can explain the main properties of the
Kuiper Belt’s cold population orbit distribution. 相似文献
1000.
G. Ya. Smol’kov V. P. Maksimov D. V. Prosovetskii A. M. Uralov I. A. Bakunina 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):31-33
An experience of radioheliographic prediction of powerful solar flares using active region microwave emission intensity and
circular polarization distribution is briefly described. 相似文献