Carbonate-silicate inclusions in garnet as evidence for a carbonate-bearing source for fluids in leucocratic granitoids associated with granulites of the Southern Marginal Zone,Limpopo Complex,South Africa     

《Gondwana Research》2020

We present a study of carbonate-bearing polyphase inclusions in garnets from leucocratic granitoids intruding metapelitic granulites of the Southern Marginal Zone (SMZ) of the Neoarchean Limpopo high-grade complex, South Africa, during the post-peak stage (2710–2650 Ma; U-Pb ages for zircons and monazites). Ternary feldspar thermometry suggests that the granitoid magma cooled from temperatures 800–900 °C at a pressure of ca. 6.5 kbar. Abundant CO₂ fluid inclusions in quartz and T-X_CO2 phase equilibria modeling via PERPLE_X imply action of an essentially carbonic fluid in the granitoids. Cores of almandine-rich garnet grains from the granitoids contain polyphase carbonate-bearing inclusions with a distinct negative crystal shape. The major carbonate in the inclusions is a strongly zoned magnesite-siderite variety, whereas pyrophyllite is the predominant silicate phase. Raman spectra of unexposed inclusions revealed a presence of CO₂, as well as CH₄ and H₂O. The carbonate-bearing inclusions coexist with larger polyphase inclusions composed of biotite, quartz, K-feldspar, plagioclase, sillimanite, which are interpreted as relics of granitic melts. Modeling the mineral assemblage preserved within the carbonate-bearing inclusions shows that their present mineral and chemical compositions are a product of interaction of the trapped aqueous‑carbonic fluid with host garnet during cooling below 400 °C. Despite strong modifications, the inclusions bear evidence for initial saturation of the fluid with Mg‑carbonate. This is taken as an evidence for an origin of the fluids by devolatilization of the Mg-rich carbonate-bearing ultrabasic greenstone rocks of the Kaapvaal Craton that were buried under the SMZ. Being generated at temperatures between 650 and 700 °C, the fluid subsequently participated in anatexis and coexisted with the granite magma during exhumation and interaction of the SMZ granulites with cratonic rocks.  相似文献   

Ecology of the bottom fauna and bioaccumulation of trace metals along the Lena River–Laptev Sea transect     

L. L. Demina  S. V. Galkin 《Environmental Earth Sciences》2018,77(2):43

The first data on ecology and trace metal (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb) bioaccumulation by macrozoobenthic organisms in area along the 130°E meridional transect from shallow water near the Lena River’s delta till the 78°N are presented. At the newly discovered methane seeps in the shallow Laptev Sea areas (72 m depth), a higher total abundance and biomass compared with background stations were recorded. In carbonate shells and soft tissues of Bivalvia Portlandia arctica and Astarte borealis, the high concentrations of Mn, Fe, Pb, Ni and Co were detected that varied in dependence from sampling site. In the dominating taxa of brittle stars (Ophiuroidea), there were found no significant differences between majority of trace metal content in organisms inhabiting the seeps area and background ones. An elevated content of some metals was detected in the Asteroidea bodies that may be attributed to its trophic behavior (deposit feeder).  相似文献   

Dynamics of natural conditions around modern glaciation location at the Eastern Sayan     

E. G. Suvorov  A. D. Kitov 《Environmental Earth Sciences》2018,77(2):48

Mountain massif Munku-Sardyk presents the highest mountain range and adjacent Stanovoy ridge highlands of the Eastern Sayan. There is situated modern glaciation site which was the most studied in the course of last 160 years. This periglacial area experienced different periods of cooling and warming in the Holocene and retained traces of the Sartan glaciation of Subboreal (3000–5000 years ago), the Little Ice Age, the evidences of Holocene optimum and general warming last time. The authors examined the variability of activity of modern glaciation and variation of natural conditions of the periglacial zone on climate and on dendrochronological data. Results of larch and Siberian stone pine growth data were revealed at the higher border of forest communities. Analysis of the growth of the “fossil” tree in the Holocene optimum showed that the absolute magnitude of its increment was two times higher than for up-to-date long-lived trees. Identified periods of the Peretolchin glacier retreat in 1900–1965 and 1983–2000 years took place with increased growth of trees and the rate of sedimentation in proglacial lake, and vice versa glacier advance on in 1965–1980 years was accompanied by slowing of tree increments and reduction in sedimentation rate. Since 2000, there has been growth of trees instability associated with a decrease in average monthly summer temperatures.  相似文献   

The Lower Paleogene Biostratigraphic Scale of the Northern Pacific Based on Deep-Water Benthic Foraminifera     

D. M. Ol’shanetsky 《Russian Journal of Pacific Geology》2018,12(2):93-118

Based on the stratigraphic distribution of benthic foraminifera in the lower bathyal–abyssal sediments uncovered by boreholes drilled under the framework of the Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) in the Northern and Southern Pacific, the Lower Paleogene biostratigraphic zonal scale based on deep-water benthic foraminifera is proposed. The proposed scale includes eight subdivisions: six zones and two subzones. The boundaries of the zonal subdivisions are determined by biotic events (appearance or disappearance (extinction)) of stratigraphically important taxa and are correlated to the zonal scales based on planktonic foraminifera and calcareous nanoplankton. Most of these events are considered to be subglobal.  相似文献   

Paleogene–Neogene Boundary of Primorye,Russian Far East     

B. I. Pavlyutkin  T. I. Petrenko  I. Yu. Chekryzhov 《Russian Journal of Pacific Geology》2018,12(2):119-134

Complex geological and paleobotanic analysis of sections of the boundary Oligocene–Miocene sediments of southern Primorye is conducted. The presence of a stratigraphic hiatus is identified in the transitional complexes of the Pushkino and Pavlovka depressions but not in the sections of the Rakovka depression; thus, it is suggested to use one of them (borehole no. 15) to choose the stratotype of the Paleogene–Neogene boundary. The previous conclusion on the presence of economic coal deposits of Primorye within the Paleogene part of the Tertiary complex is supported. It is suggested to use the section which is exposed by the Rakovka brown coal open pit (point 9209) as a stratotype of the upper subformation of the Pavlovka Formation.  相似文献   

New Data on the Ages of the Matituk and Pomyr Formations of Northern Sakhalin     

P. Yu. Kovtunovich  L. M. Chumakov  I. B. Tsoy 《Russian Journal of Pacific Geology》2018,12(4):303-319

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Hydrogeochemical Features of Thermal Waters of South Trungbo (Central Vietnam)     

D. A. Novikov  Doan Van Tuyen  Thi Kim Van Phan  N. A. Kharitonova 《Russian Journal of Pacific Geology》2018,12(1):63-79

The results of studying the features of the hydrogeological structure and chemical and isotope composition of thermal waters from the central part of Vietnam that are characterized by intense manifestations of intrusive magmatism are presented. It is established that low–and high–thermal waters with temperature varying within 30–85°C are developed in the area under study. The value of total mineralization of the hydrotherms ranges from 0.05 to 10.05 g/dm³. It is assumed that the circulation of thermal waters that are different in temperature and chemical composition occurs at two levels. The regular change of the hydrotherm composition in the direction from mineralized chloride sodium, including with increased Ca content, to fresh sodium bicarbonate is revealed. The ratio of δ¹⁸O–δ²H isotopes indicates that the water component is based on meteoric water. In the coastal areas, there is an isotope shift towards the ocean waters, which is also confirmed by the hydrogeochemical data. The key factors for forming the chemical composition of the thermal waters in South Trungbo are their genetic type, the interaction processes in the “water–rock–gas–organic substance” system, and their equilibrium–nonequilibrium state.  相似文献   

Basic formation mechanisms of Lake Doroninskoye soda water,East Siberia,Russia     

Svetlana V. Borzenko  Leonid V. Zamana  Larisa I. Usmanova 《中国地球化学学报》2018,37(4):546-558

The primary scientific goal of studying salt lakes is to better understand the formation of small continental-type hydrogeochemical systems. Many scientists have attributed the metamorphism of the chemical composition of salt lakes to the evaporative concentration of water. However, the formation of soda water is inconsistent with this hypothesis. Thus, analyzing intrabasinal biochemical processes and water—rocks interactions during the evaporative concentration of water allows us to understand the major mechanisms of the formation and evolution of water compositions. Therefore, the aim of this paper is to identify the key processes involved in the formation of the chemical composition of the water in Lake Doroninskoye. An analysis of the distribution of major components shows that Na⁺, HCO₃ ^?, CO₃ ^2?, and Cl^? are dominant in this water. High concentrations of these elements are the result of evaporative water concentration. Calcium, magnesium, and potassium are not accumulated because the water is saturated in minerals containing these elements. The main barrier to the growth of the sulfate content of water is sulfate reduction. This process also contributes to the additional reproduction of carbon dioxide, which reacts with the products of the hydrolysis of aluminosilicates OH^? to form HCO₃ ^? and CO₃ ^2?, thus further contributing to the natural processes of soda formation.  相似文献   

Biogeochemical Differentiation of Living Matter and Biodiversity in the Ardon Polymetallic Subregion of the Biosphere     

V. V. Ermakov  S. F. Tyutikov  A. P. Degtyarev  V. A. Safonov  V. N. Danilova  S. D. Khushvakhtova  U. A. Gulyaeva  E. V. Krechetova 《Geochemistry International》2018,56(4):318-331

Specific responses of plants and animals to changes in the contents of microelements (Pb, Cd, Cu, Zn, As, Se, etc.) in abiotic environmental components of the Ardon River Basin (North Ossetia) were studied by new biogeochemical indication methods. In comparison to background areas, a local increase in the Pb, Cd, Cu, Zn, and As contents in soils and organisms occurs under the impact of natural and technogenic factors. The heavy metal contents in Ardon River water are generally within hygienic norms. Activation of sulfurcontaining synthesis in the leaves of willow, sea buckthorn, and coltsfoot was revealed for the maximum heavy metal content in soils. On plots adjacent to the Unal tailing dump, the contents of pigments and their proportions in leaves of coltsfoot, dandelion, and willow do not differ from those in less contaminated areas. On technogenic plots, the species richness of plants decreases, as well as the mowed biomass and projective cover of herbaceous plants (to 40%); inhibition of plant growth, chlorosis, necrosis, and lamina deformation are observed. A new metallophyte species (Cladochaeta candidissima M. Bieb.) was revealed. The increase in lead and arsenic contents in soils and plants of the Ardon floodplain is accompanied by an increase in their concentrations in the blood and hair of animals.  相似文献   

Mercury in Hydrobionts and Their Habitat in Grønfjorden,West Spitsbergen,in Early Springtime     

N. V. Lebedeva  O. L. Zimina  N. N. Fateev  A. L. Nikulina  I. V. Berchenko  N. I. Meshcheryakov 《Geochemistry International》2018,56(4):332-343

The first data were obtained on the total mercury content in hydrobionts and their habitat in Grønfjorden, Spitsbergen, at the waste discharge sites of the settlement of Barentsburg in early spring 2017. The Hg concentration was below the detection limit in the water and varied from 7.1 to 42.3 ng/g of dry weight in the bottom sediments. Mercury concentration in the hydrobionts increased toward the inner fjord and was higher near the mouth of the Grøndalen River, which flows into the fjord. Elevated Hg concentrations at the mouth of the Grøndalen River indicate that much of the toxic metal is brought to the inner part of the fjord with riverine runoff, and this Hg source is likely more important than the surface supply of Hg transferred from local surface pollution centers at Barentsburg. The Hg concentration depended on the position of the marine organisms in the trophic chain and was the highest in the detritophage mollusks Thyasira gouldi, Cardium sp., and Macoma calcarea, the specialized predatory sea snail Cryptonatica affinis, and the cod Gadus morhua, which is a benthosophage–secondary predator. The total Hg concentrations in the hydrobionts and their habitat in Grønfjorden were generally relatively low and close to the background one.  相似文献