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951.
The study of REE distribution in the clay fraction of sedimentary rocks from two coalfields made it possible to distinguish
several types of REE distribution, which correlate with their mineral composition. It is shown that the REE fractionation
was related to the mineral reconstruction of the primary clay fraction and some detrital minerals in the course of postsedimentary
transformations of rocks during diagenesis, early catagenesis, and beginning of late catagenesis. These transformations were
governed by several factors, such as the composition of sediments; hydrochemical features of accumulation environment; the
chemical composition, dynamics, and feeding sources of pore solutions; the porosity and permeability of sediments and rocks;
and the content of organic matter and its reaction ability. 相似文献
952.
G. T. Skublov Yu. B. Marin S. G. Skublov Yu. N. Tarasenko 《Geology of Ore Deposits》2008,50(7):535-550
Volkhovites—tektite-like glasses—have been detected in the Holocene glacial drift along the right bank of the Volkhov River. A cryptomagmatic model of their formation and pre-Holocene age of volkhovite melts, cinder, and frothed glasses has been suggested (Skublov et al., 2007). Four geochemical types of volkhovites are distinguished: (1) manganous (Mn, Fe, Cr, V, Si, Nb, Pb, H), (2) magnesian (Mg, Al, Ti, F, B), (3) potassic (K, Rb, Cs), and (4) calcic (Ca, REEs, Ba, U, Th, Ta, Hf, Y, Sc, Cl). In light of the geochemical data, volkhovites are regarded as natural silicate glasses of kimberlite-carbonatite composition. Their types are called kimberlitic (Mn type), kimberlitic-carbonatitic (Mg type), lamproitic-carbonatitic (K type), and carbonatitic (Ca type). Volkhovites are suggested to be indicators of undiscovered diamond mineralization of kimberlite or carbonatite (Chagatai) types. 相似文献
953.
Barotropic stability of a stationary Rossby wave of wavelength 30° longitude superposed on the uniform monsoon zonal flow has been examined. The wave is unstable to perturbations and the growth rate depends on the meridional scale. These perturbations grow by drawing on the kinetic energy of the stationary Rossby wave. 相似文献
954.
V. V. Yarmolyuk V. P. Kovach V. I. Kovalenko E. B. Salnikova A. M. Kozlovskii A. B. Kotov S. Z. Yakovleva A. M. Fedoseenko 《Petrology》2011,19(1):55-78
Data on the composition, inner structure, and age of volcanic and siliceous-terrigenous complexes and granitoids occurring
in association with them in the Caledonian Lake zone in Central Asia are discussed in the context of major relations and trends
in the growth of the Caledonian continental crust in the Central Asian Foldbelt (CAFB). The folded structures of the Lake
zone host basalt, basalt-andesite, and andesite complexes of volcanic rocks that were formed in distinct geodynamic environments.
The volcanic rocks of the basalt complex are noted for high concentrations of TiO2 and alkalis, occur in association with fine-grained siliceous siltstone and siliceous-carbonate rocks, are thus close to
oceanic-island complexes, and were likely formed in relation to a mantle hotspot activity far away from erosion regions supplying
terrigenous material. The rocks of the basalt-andesite and andesite complexes have lower TiO2 concentrations and moderate concentrations of alkalis and contain rock-forming amphibole. These rocks are accompanied by
rudaceous terrigenous sediments, which suggests their origin in island-arc environments, including arcs with a significantly
dissected topography. These complexes are accompanied by siliceous-terrigenous sedimentary sequences whose inner structure
is close to those of sediments in accretionary wedges. The folded Caledonides of the Lake zone passed through the following
evolutionary phases. The island arcs started to develop at 570 Ma, their evolution was associated with the emplacement of
layered gabbroids and tonalitetrondhjemite massifs, and continued until the onset of accretion at 515–480 Ma. The accretion
was accompanied by the emplacement of large massifs of the tonalite-granodiorite-plagiogranite series. The postaccretionary
evolutionary phase at 470–440 Ma of the Caledonides was marked by intrusive subalkaline and alkaline magmatism. The Caledonides
are characterized by within-plate magmatic activity throughout their whole evolutionary history, a fact explained by the accretion
of Vendian-Cambrian oceanic structures (island arcs, oceanic islands, and back-arc basins) above a mantle hotspot. Indicators
of within-plate magmatic activity are subalkaline high-Ti basalts, alkaline-ultrabasic complexes with carbonatites and massifs
of subalkaline and alkaline gabbroids, nepheline syenites, alkaline granites, subalkaline granites, and granosyenites. The
mantle hotspot likely continued to affect the character of the lithospheric magmatism even after the Caledonian folded terrane
was formed. 相似文献
955.
If cordierite is treated as an anhydrous mineral, the composition of garnet and cordierite, coexisting with quartz and silliminate, depends on total pressure and temperature. Phase relations may be deduced by combining some available experimental work with several approximations. Assuming ideal ionic solution in garnet and cordierite, analyses of coexisting garnet and cordierite permit the determination of total pressure and temperature. Five rocks from the Daly Bay Complex, N. W. T., collected from locations up to 35 miles apart, indicate a range of 610–760 and 5.3–6.6 kb. 相似文献
956.
Segregation of incompatible elements at grain interfaces may have considerable influence on the physical and chemical properties of mantle rocks. Using a recently developed predictive model to estimate the interface enrichment of elements based on their mineral/melt partitioning (Hiraga and Kohlstedt, companion paper), we consider interface enrichment for a simplified model peridotite consisting of olivine, orthopyroxene, and clinopyroxene. Our calculated results reveal the following: (1) Significant amounts of heavy alkali elements and rare gases likely reside at grain-grain interfaces, whereas interface concentrations of less incompatible are less pronounced. (2) The contribution of the chemical components stored at interfaces to whole-rock chemistry strongly depends on mineral mode and, most importantly, on grain size. (3) Grain size reduction resulting from dynamic recrystallization can increase the total storage of highly incompatible elements on grain interfaces and thereby will diminish their concentration in mineral grains. (4) Analysis of Cs concentrations in mantle clinopyroxenes potentially provides estimates of the grain size of mantle rocks. (5) Transport through peridotite will be dominated by diffusion along interfaces rather than through grain interiors for elements less compatible than Lu. 相似文献
957.
Citizens as sensors: the world of volunteered geography 总被引:62,自引:0,他引:62
Michael F. Goodchild 《GeoJournal》2007,69(4):211-221
In recent months there has been an explosion of interest in using the Web to create, assemble, and disseminate geographic information provided voluntarily by individuals. Sites such as Wikimapia and OpenStreetMap are empowering citizens to create a global patchwork of geographic information, while Google Earth and other virtual globes are encouraging volunteers to develop interesting applications using their own data. I review this phenomenon, and examine associated issues: what drives people to do this, how accurate are the results, will they threaten individual privacy, and how can they augment more conventional sources? I compare this new phenomenon to more traditional citizen science and the role of the amateur in geographic observation. 相似文献
958.
Technical Note 总被引:10,自引:0,他引:10
959.
BANDANA SAMANT D M MOHABEY P SRIVASTAVA DEEPALI THAKRE 《Journal of Earth System Science》2014,123(1):219-232
The intertrappean sediments associated with Deccan Continental Flood Basalt (DCFB) sequence at Ninama in Saurashtra, Gujarat yielded palynoassemblage comprising at least 12 genera and 14 species including Paleocene taxa such as Intrareticulites brevis, Neocouperipollis spp., Striacolporites striatus, Retitricolpites crassimarginatus and Rhombipollis sp. The lava flows of Saurashtra represent the northwestern most DCFB sequence in India. It is considered that the Saurashtra lava flows represent the earliest volcanic activity in the Late Cretaceous of the Reunion Mantle Plume on the northward migrating Indian Plate. The present finding of the Paleocene palynoflora from Ninama sediments indicate Paleocene age for the associated lava flows occurring above the intertrappean bed which suggests that the Saurashtra plateau witnessed eruption of Deccan lava flows even during Paleocene. The clay mineral investigation of the Ninama sediments which are carbonate dominated shows dominance of low charge smectite (LCS) along with the presence of mica and vermiculite. Based on the clay mineral assemblage it is interpreted that arid climatic conditions prevailed during the sedimentation. The smectite dominance recorded within these sediments is in agreement with global record of smectite peak close to the Maastrichtian–Paleocene transition and climatic aridity. 相似文献
960.
Evolution of Ore-Forming Fluids and Ag-Cu Polymetal Mineralization in the Lanping Basin, Yunnan 总被引:1,自引:0,他引:1
EVOLUTION OF ORE-FORMING FLUIDS AND Ag-Cu POLYMETAL MINERALIZATION IN THE LANPING BASIN, YUNNAN“KeyProjectforResourcesandEconomics” (95 0 2 0 0 1 0 1)oftheMinistryofLandResources 相似文献