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A. B. Vrevskii 《Petrology》2018,26(2):121-144
The paper reports newly obtained geological and isotopic-geochemical data on the volcano-sedimentary complex of the Uraguba Neoarchean greenstone structure in the Kola–Norwegian province of the Fennoscandian Shield. New U–Th–Pb geochronologic data (SIMS) on the metadacite (2790 ± 9 Ma) from a rock unit of interbedding metadacite, komatiite tuff, and lava breccia and on veins of plagioclase–microcline granite (2697 ± 10 and 2696 ± 9 Ma) that cuts the komatiite constrain the time span when supracrustal complex of the Uraguba structure was produced and underwent tectono-metamorphic transformations to approximately 100 Ma. The metavolcanic rocks of the komatiite–tholeiite association of the Uraguba structure belong to two distinct isotopic-geochemical types, which are spatially separated from one another and were produced by melting different mantle sources. Geological and isotopic-geochemical data indicate that the Uraguba structure is analogous to such unique tectonic structures on cratons as the Neoarchean Belingwe and Bulawayo belts in the Zimbabwe Shield, Kalgoorlie Belt in the Eastern Goldfilds province at the Yilgarn Craton, Kuhmo–Tipasjarvi Belt in the Karelian epi-Archean craton, and the Warawoona Paleoarchean Belt in the Pilbara Craton. 相似文献
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A. B. Vrevskii 《Petrology》2018,26(3):246-254
Numerical modeling of the generation and evolution of parental melts of the komatiite–tholeiite association of the Uraguba structure was carried out using previously obtained geochemical and isotope data. It was established that komatiite, komatiite and tholeiite basalts depleted in LREE and having εNd(Т = 2.79) = +2.9…+3.2 were generated by equilibrium partial melting (F > 15%) of a depleted source (garnet-bearing Ol0.63 + Opx0.22 + Cpx0.06 + Grt0.09 mantle peridotite) at 4–8 GPa, while the genesis of primary melts of LREE-enriched komatiites (LaN/SmN ~ 1.2–1.6) with εNd(Т = 2.79) = +2.5…+2.2 was related to the equilibrium partial melting (F > 20%) of an “enriched mantle peridotite” (EM–Ol0.60 + Opx0.20 + Cpx0.08 + Grt0.12) at pressure of 2.5–4 GPa. Coexistence in space and time of two types of melting products of mantle peridotites formed at different depths is explained by melting of different parts of adiabatically ascending mantle plume. 相似文献
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Doklady Earth Sciences - Numerical modeling of the dynamics of the block structure and the resulting seismicity of the Altai–Sayan–Baikal region has been carried out. The earthquake... 相似文献
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I. A. Starodubtseva 《Stratigraphy and Geological Correlation》2013,21(1):36-47
The paper presents a biography of S.N. Nikitin, one of the outstanding Russian geologists of the late 19th and early 20th centuries, and provides a review of his contribution to study of the Mesozoic of Central Russia. 相似文献
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This paper studies the basis and nature of the long-term factors that may have influenced the electoral behavior of St. Petersburgers between 1989 and 1995 from the perspective of geography. Our analysis shows two distinct periods in St. Petersburgs recent electoral history marked by differing behavioral motivations of voters in the city. The first period was marked by only one ideological cleavage between marketers and hard-liners. In 1993 protest motivation managed to erode the predominance of ideology as the determining variable in voting behavior, and began to act as a new independent variable. This marked the beginning of the second period. Four major groupings of St. Petersburg electorate are described in terms of the basic ideological cleavages, party affiliations and geographical gravity centers. 相似文献
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Geographies of identity theft in the U.S.: understanding spatial and demographic patterns, 2002–2006
Identity theft is among the fastest growing white-collar crimes in the United States, although official recognition of it
as a criminal act is a relatively recent development. Utilizing theoretical framework established in crime geography, GIS
mapping and spatial statistics are employed to conduct a spatial analysis of identity theft in the U.S. from 2002 to 2006.
Distinct regional variations, such as high rates in the western and southwestern states, and low rates in New England and
the central plains states, are identified for identity theft. Significant spatial patterns of identity theft victims alongside
social demographic variables are also revealed in order to better understand the regional patterns that may suggest underlying
social causes contributing to identity theft. Potential social variables, such as race/ethnicity and urban–rural populations,
are shown to have similar patterns that may be directly associated with U.S. identity theft victims. 相似文献
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N. J. Pawar 《Journal of the Geological Society of India》2016,87(4):499-499
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The northeastern Gangdese Pb–Zn–Ag–Fe–Mo–W polymetallic belt (NGPB), characterized by skarn and porphyry deposits, is one of the most important metallogenic belts in the Himalaya–Tibetan continental orogenic system. This belt extends for nearly four hundred kilometers along the Luobadui–Milashan Fault in the central Lhasa subterrane, and contains more than 10 large ore deposits with high potential for development. Three major types of mineralization system have been identified: skarn Fe systems, skarn/breccia Pb–Zn–Ag systems, and porphyry/skarn Mo–Cu–W systems. In this study, we conducted a whole-rock geochemical, U–Pb zircon geochronological, and in situ zircon Hf isotopic study of ore-forming rocks in the NGPB, specifically the Jiangga, Jiaduopule, and Rema skarn Fe deposits, and the Yaguila Pb–Zn–Ag deposit. Although some of these deposits (porphyry Mo systems) formed during the post-collisional stage (21–14 Ma), the majority (these three systems) developed during the main (‘soft collision’) stage of the India–Asia continental collision (65–50 Ma). The skarn Fe deposits are commonly associated with granodiorites, monzogranites, and granites, and formed between 65 and 50 Ma. The ore-forming intrusions of the Pb–Zn–Ag deposits are characterized by granite, quartz porphyry, and granite porphyry, which developed in the interval of 65–55 Ma. The ore-forming porphyries in the Sharang Mo deposit, formed at 53 Ma. The rocks from Fe deposits are metaluminous, and have relatively lower SiO2, and higher CaO, MgO, FeO contents than the intrusions associated with Mo and Pb–Zn–Ag mineralization, while the Pb–Zn–Ag deposits are peraluminous, and have high SiO2 and high total alkali concentrations. They all exhibit moderately fractionated REE patterns characterized by lower contents of heavy REE relative to light REE, and they are enriched in large-ion lithophile elements and relatively depleted in high-field-strength elements. Ore-forming granites from Fe deposits display 87Sr/86Sr(i) = 0.7054–0.7074 and εNd(t) = − 4.7 to + 1.3, whereas rocks from the Yaguila Pb–Zn–Ag deposit have 87Sr/86Sr(i) = 0.7266–0.7281 and εNd(t) = − 13.5 to − 13.3. In situ Lu–Hf isotopic analyses of zircons from Fe deposits show that εHf(t) values range from − 7.3 to + 6.6, with TDM(Hf)C model ages of 712 to 1589 Ma, and Yaguila Pb–Zn–Ag deposit has εHf(t) values from − 13.9 to − 1.3 with TDM(Hf)C model ages of 1216 to 2016 Ma. Combined with existing data from the Sharang Mo deposit, we conclude that the ore-forming intrusions associated with the skarn Fe and porphyry Mo deposits were derived from partial melting of metasomatized lithospheric mantle and rejuvenated lower crust beneath the central Lhasa subterrane, respectively. Melting of the ancient continental material was critical for the development of the Pb–Zn–Ag system. Therefore, it is likely that the source rocks play an important role in determining the metal endowment of intrusions formed during the initial stage of the India–Asia continental collision. 相似文献