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J.K. Tomson Y.J. Bhaskar Rao T. Vijaya Kumar J. Mallikharjuna Rao 《Gondwana Research》2006,10(1-2):115
Major, trace element compositions and Sr–Nd isotopic characteristics of charnockitic gneisses from the Southern Granulite Terrain (SGT), South India are presented. The study region encompasses the central segment of the Cauvery Shear Zone system (CSZ) and regions within the Madurai Block (MB) immediately south of it (designated here as the CSZ/MB and MB domains). Differences in the compositions and source characteristics between charnockitic rocks of the CSZ vis-à-vis those of the CSZ/MB and MB regions are highlighted. Foremost, the charnockites and enderbites of the CSZ show highly fractionated REE patterns with positive Eu-anomalies, depleted HREE, Y and near chondritic εNd0 and initial-87Sr/86Sr at ca. 2.5 Ga, consistent with hydrous partial melting of amphibolitic crust with residual garnet and hornblende for the parental melts. By contrast, modeled at ca. 1.8 Ga and 0.8 Ga, the CSZ/MB and MB charnockitic rocks, which show a wider range of Ti and P, relatively lower degree of HREE depletion, commonly negative Eu-anomalies and undepleted Y, present clear evidence for involvement of Archaean crustal components in sources of their magmatic protoliths. There is also evidence for significant intracrustal melting processes within a thickened crust at elevated temperatures between 800 and 1000 °C. Implications to the controversial Archaean–Neoproterozoic terrane boundary problem of the SGT are discussed. 相似文献
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I. N. Tomson O. P. Polyakova V. Yu. Alekseev V. A. Baskina 《Geology of Ore Deposits》2006,48(1):74-76
Two types of metalliferous carbonaceous rocks that differ in associated metals are considered. One of them is characterized by gold occurring in finely dispersed arsenopyrite and arsenic-bearing pyrite, and the other, by finely impregnated native metals in carbonaceous matter. Rocks of the first type also contain elements of the platinum group, while those of the second type bear rhenium, silver, iron, molybdenum, and other metals. Graphitic mineralization is usually localized in the shear zone associated with alkaline basalts. 相似文献
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The coccolith assemblages from seafloor sediments over the inner shelf in the northern region of the KwaZulu- Natal Bight on the east coast of South Africa were identified and their distribution determined. In all, 29 Recent species and taxonomic groups, as well as 29 reworked species were recorded. The distribution of the Recent species appears to be governed by environmental features that have been documented in other studies: temperature, salinity, nutrient concentration and water circulation pattern, which reveals the long-term existence of a circulation cell in the sector between Durban Bay and the Thukela River. The outer edge of the cell consists of nutrient-enriched mixed layers and is characterised by an enhanced abundance of Gephyrocapsa oceanica, whereas the central region consists of a stratified nutrient-depleted water mass with elevated abundance of Umbilicosphaera sibogae, Florisphaera profunda, and a group of umbelliform species. The elevated levels of G. oceanica, coupled with the rarity of U. sibogae, F. profunda and the umbelliform species, confirm the presence of a permanent upwelling cell off Richards Bay. The maximum abundance of F. profunda found between Richards Bay and Lake Nhlabane indicates a region of nutrient-depleted (except for nitrite) conditions. 相似文献
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At Bear Lake, in the Flin Flon-Snow Lake greenstone belt of Manitoba, 400+ m of thick-to very thick-bedded, generally ungraded, basaltic andesite tuff-breccia, breccia, and lapilli-tuff are intercalated with pillowed lava flows in the upper part of an early Proterozoic submarine basaltic andesite shield volcano. The fragmental rocks comprise angular, amygdaloidal blocks and lapilli, many with partial chilled selvages, in a matrix of blocky, non-amygdaloidal to highly amygdaloidal vitric basaltic andesite ash and small lapilli. Minor thin-to medium-bedded, commonly normally graded tuff occurs in the upper part of the sequence. Clasts in fragmental beds consistently have higher amygdule contents than intercalated lava flows. Although similar to pillow-fragment breccias, the Bear Lake fragmental rocks were produced by extended surtseyan-type, phreatomagmatic eruptions, with associated fire fountain activity, at a progressively subsiding, shallow water vent. Periodic tephra slumping generated debris flows that transported particles down the uppe, gentle slope of the volcano to a depositional site at a water depth of less than 1 km. Turbidity currents probably carried much fine tephra to deeper water; tuff was deposited in the preserved section only after explosive volcanism ceased. 相似文献
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The desorption of contaminants from soils/sediments is one of the most important processes controlling contaminant transport and environmental risks. None of the currently adopted desorption models can accurately quantify desorption at relatively low concentrations; these models often overestimate the desorption and thus the risks of hydrophobic organic chemicals, such as benzene and chlorinated solvents. In reality, desorption is generally found to be biphasic, with two soil-phase compartments. A new dual-equilibrium desorption (DED) model has been developed to account for the biphasic desorption. This model has been tested using a wide range of laboratory and field data and has been used to explain key observations related to underground storage tank plumes. The DED model relates the amount of a chemical sorbed to the aqueous concentration, with simple parameters including octanol-water partition coefficient, solubility, and fractional organic carbon; thus, it is the only biphasic model, to date, that is based on readily available parameters. The DED model can be easily incorporated into standard risk and transport models. According to this model, many regulatory standards of soils and sediments could be increased without increasing the risks. 相似文献
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Relation between porphyry deposits and their vein satellites 总被引：1，自引：0，他引：1
A. A. Sidorov I. N. Tomson N. E. Savva A. V. Volkov V. Yu. Prokof’ev E. E. Kolova 《Doklady Earth Sciences》2006,409(2):859-863