共查询到20条相似文献,搜索用时 15 毫秒
1.
V. N. Smirnov K. S. Ivanov Yu. L. Ronkin V. A. Koroteev P. A. Serov A. Gerdes 《Doklady Earth Sciences》2017,474(1):516-519
According to isotopic analysis of rocks of the Reft gabbro–diorite–tonalite complex (Middle Urals), gabbro and related diorite and dikes and vein-shaped bodies of plagiogranitoids, crosscutting gabbro, are similar to the depleted mantle substance in εNd(T) = 8.6–9.7 and εHf(T) = 15.9–17.9. Their model Hf ages are correlated with the time of crystallization. Here, the tonalites and quartz diorites constituting most of the Reft massif are characterized by lower values: εNd(T) = 3.7–6.0, εHf(T) = 11.1–12.7, and T DM values significantly exceeding the age datings. This is evidence that Neoproterozoic crustal rocks were a source of parental magma for these rocks. The primary 87Sr/86Sr ratio in rocks of both groups is highly variable (0.70348–0.70495). The data obtained allow us to reach the conclusion that the Reft gabbro–diorite–tonalite complex was formed as a result of nearly synchronous processes occurring in the crust and the mantle within a limited area. 相似文献
2.
Nicolas Carry Fredéric Gueydan Didier Marquer Jean Pierre Brun 《International Journal of Earth Sciences》2011,100(5):1087-1094
HP/UHP and LT metamorphic units that commonly occur in the inner parts of mountain belts result from the subduction of continental and oceanic material, most often exhumed prior to continental collision. The prograde pressure–temperature history of HP–UHP rocks strongly depends on the convergence rate and on the subduction zone geometry. The maximum pressure recorded provides a proxy for the depth of shearing off and stacking of HP metamorphic nappes. A 2-D thermal model of continental subduction at lithospheric scale is used to compute the length and pressure peak of detached HP metamorphic units as a function of the slab dip angle and the convergence rate. Model results are applied to the metamorphic nappe pile of the inner Alps. A mean convergence rate of 1 cm/year during the subduction of the Briançonnais terrane is indicated by the paleogeographic reconstructions between 46 and 38 Ma. On this basis, the available petrological data and lengths of metamorphic units are used to compute the variations of the slab dip angle. The slab dip angle is shown to increase, from the northeast to the southwest, along the Alpine arc with estimated values of 20° for Suretta, 30–45° for Monte Rosa and Gran Paradiso, and 60° for Dora Maira. From Eocene to Oligocene times, the increase in slab dip angle is controlled by changes of buoyancy, due to the spatial configuration of the Valaisan trough and the incoming of crustal material within the subduction zone. 相似文献
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Nodules consisting of fluorapatite are concentrated as a discrete band in the polymetallic sulfide ore of the Gamsberg deposit in central Bushmanland, South Africa. Their shape, zonal features, and geochemistry, in particular rare earth element (REE) abundances, are similar to authigenic francolite concretions that precipitate during diagenesis in organic-rich muds. As a result, the apatite nodules are regarded as primary. The nodules have a strong lithostratigraphic control, occurring at the transition of siliciclastic-hosted pyrite–sphalerite–graphite mineralization to calc-silicate-hosted pyrrhotite–sphalerite mineralization. Mineralogical and chemical evidence indicates that this transition also corresponds to a paleo-redox boundary that separates sediments deposited under oxygen-deficient conditions from those that developed in a more oxygenated environment. The apatite nodules can morphologically and chemically clearly be distinguished from coarse apatite grains that occur in oxide-facies iron formations stratigraphically above the ore horizon. However, similar REE profiles and in particular positive Eu anomalies in both types of apatite are indicative of a close genetic relationship between the two units and favor a common hydrothermal origin of the P. The contrasting morphologies and chemical signatures of the two occurrences can rather be attributed to differences in behavior of the phosphates during precipitation within the contrasting host sediments (chemical versus fine-grained clastic). Taking modern phosphorites as an analogue, these results are used to postulate a genetic model for the deposition of the sulfide ore and associated iron formations. The model envisages differentiation of the depositional basin into oxygen-deficient basin facies hosting the sulfide ore and oxygenated shelf facies, which are composed of manganiferous iron formations. The intimate association of sedimentary apatite with base metal sulfides indicates that basin conditions were conducive to the precipitation of both phases. This relationship might act as a potential exploration guide in similar basins elsewhere.Editorial handling: E. Frimmel 相似文献
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New data are discussed on the distribution of mercury in the host volcanosedimentary and igneous rocks, hydrothermal—metasomatic rocks, and all types of modern newly formed materials (hydrothermal clays, argillized soil—pyroclastic beds, siliceous and limonite—hematite covers, bottom sediments, salt ‘sweat-outs’ of various compositions, etc.) typical of the supergene zone of geothermal deposits. By the example of the Nizhne-Koshelevskii (vapor-dominated) and Pauzhetka (water-type) geothermal deposits and thermal fields of the Koshelevskii volcanic massif and Kambal’nyi volcanic range (southern Kamchatka), the role of mercury was illustrated as an indicator element of the temperature, phase state, and dynamics of hydrothermal systems; intensity of rock argillization; and relative age (maturity) of geothermal deposits and thermal anomalies. 相似文献
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V. N. Smirnov Yu. L. Ronkin V. N. Puchkov N. G. Soloshenko M. V. Streletskaya 《Doklady Earth Sciences》2016,467(2):331-336
The analysis of the Sr and Nd isotopic composition in different granitoids of the Verkhisetsk, Shartash, Krasnopolsk, Petrokamensk, and Shabry massifs, which were successively formed in the island arc, continental marginal, and collisional geodynamic settings during the period from the Middle Devonian to the early Permian, revealed that 87Sr/86Sr0 values in them vary from 0.70331 to 0.70431 and εNd(t), from +1.9 to +6.2. The two-stage model Nd age of granitoids (938–629 Ma) indicates that their magma originates from material at least Neoproterozoic in age, not younger. The observed variations in the Nd model ages of granitoids and 87Sr/86Sr0 values provide grounds for assuming the primary heterogeneity of the source of granitoid melts. 相似文献
8.
Thierry Desjardins Bruno Turcq Jean-Pierre Nguetnkam Gaston Achoundong Magloire Mandeng-Yogo Fethyé Cetin Anne-Marie Lézine 《Comptes Rendus Geoscience》2013,345(7-8):266-271
In order to better understand the dynamics of the forest–savanna mosaic from central Cameroon, we analyzed 13C and 14C profiles of six oxisols: two under forests and four under savannas. The δ13C soil profiles collected in the forests indicate that these environments are stable at least since the mid-Holocene, whereas the areas currently covered by savannas were formerly occupied by more forested vegetations. The 14C dating of organic matter indicate that the late extension of the savannas in central Cameroon date from the Late Holocene, starting from 4000–3500 14C yr BP. 相似文献
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Doklady Earth Sciences - 相似文献
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The aim of this study is to investigate the nature of the solutions and the temperature during the bentonite formation by using δ18O and δ2H values and the relationship between chemical and isotopic composition of smectites from Cabo de Gata region. Therefore, 36 bentonite samples had been selected. For analyses the <2 μm fraction were separated. Most of the samples contain smectite above 90 wt%. The stable oxygen and hydrogen isotopic composition of the analysed smectites is close to the “montmorillonite line”. However, from isotopic composition two types of bentonite can be distinguished. The Sierra de Gata (SG) and Serrata de Nijar (SN) types show δ18O and δ2H values above and below this line, respectively. Temperatures obtained from geothermometer equation are similar to the temperatures values obtained from the equation of Savin and Lee (1988). Estimated formation temperatures of SG type are 25 and 49 °C higher compared to those of the SN type (6 and 25 °C).Correlations between structural cations versus isotopic composition show no statistical significance concerning all samples. However, separating the samples of SG (Sierra de Gata) from SN (Serrata of Nijar) a statistical significance for the individual areas is obtained. In both cases the effect is similar for 18O and for 2H. This could be due to the different composition of the solutions forming these bentonites. 相似文献
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Strong vibrations of the Earth’s crust in the frequency range of 7–9 Hz, referred to as the “voice of the sea,” have been recorded in the course of processing synchronous experimental data obtained during recording of variations in the deformation of the Earth’s crust using a shore laser strainmeter, atmosphere pressure variations using a laser nanobarograph, and hydrosphere pressure variations using a laser meter for hydrospheric pressure and wind velocity variations. The nature of these vibrations and their transformation to adjacent geospheres have been discussed. 相似文献
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Yu. M. Gavrilyuk A. V. Gusev V. A. Krysanov V. V. Kulagin A. M. Motylev S. I. Oreshkin V. N. Rudenko V. A. Silin A. N. Tsepkov 《Astronomy Reports》2012,56(8):638-652
An analysis of experimental data from the ??Ulitka?? high-frequency gravitational-gradient meter installed in the underground Baksan Neutrino Observatory of the Russian Academy of Sciences is presented, focusing on the planned use of this instrument as an ??anti-coincidence filter?? for the OGRAN gravitational-wave antenna. The statistics of the Ulitka noise background over a year??s observing are analyzed, and compared with the background measured earlier when Ulitka was located on the territory of the Sternberg Astronomical Institute in Moscow. A reduction in the rate of occurrence of large nonthermal spikes is noted. We have found associations between earthquakes and excitations of the seismically isolated high-frequency mode of the longitudinal oscillations of Ulitka. 相似文献
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The composition and evolution of an Oligocene regolith on top of the Sesia–Lanzo Zone (Western Alps)
Notburga Kapferer Ivan Mercolli Alfons Berger 《International Journal of Earth Sciences》2011,100(5):1115-1127
An Oligocene paleosurface (regolith) lies on top of the high-pressure metamorphic rocks of the Sesia–Lanzo Zone near Biella,
NW Italy. Only the saprock, the lowermost part in a regolith profile, is preserved. No evidence for any paleosoil can be observed.
Field observations indicate that the regolith developed through in situ mechanical fracturing of the rocks of the Sesia–Lanzo
Zone in a continental environment. Density estimations of the regolith and the underlying rocks of the Sesia–Lanzo Zone confirm
the field observations and imply that a relatively small amount of alteration minerals was formed. The main detected alteration
phases are chlorite, various carbonates, quartz, clay minerals, Fe-oxides, and Fe-hydroxides. Chlorite differing in chemistry
and crystallographic ordering demonstrates different stages of alteration. Oxygen and carbon isotopic composition of carbonates
suggests temperatures higher than surface conditions. Illite and chlorite thermometry indicates temperatures related to the
anchizone (~250–300°C). These data are considered as a robust indication of the re-burial of the regolith together with its
substrate and its volcanic cover. The burial is closely related to the tilting of the preserved stratigraphic sequence formed
by the rocks of the Sesia–Lanzo Zone, the regolith, and the rocks of the Biella Volcanic Suite (Lanza, in Schweiz Miner Petrogr
MItt 57: 281–290, 1977; Lanza, in Geologishe Rundschau 68: 83–92, 1979). Furthermore, the burial is consistent with this sequence of subaerial rocks being very close to the intrusion depth of
the Valle del Cervo Pluton at the time of its emplacement (4–7 km; Zanoni et al., in Rend Online SGI Note Brevi 1: 199–202,
2008; Zanoni et al., in Int Geol Rev 52: 1244–1267, 2010 and references therein). 相似文献
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K. S. Alekseeva L. P. Popova A. V. Postnikov O. V. Postnikova 《Doklady Earth Sciences》2016,470(2):1014-1018
The Lower Cambrian Usol’e Formation in the Kamov arch of the Baikit anteclise includes stratiform intrusions confined to several levels. According to isotopic?geochronological investigations, the age of stratiform intrusions composed of olivine dolerites is estimated to be 256.0 ± 3.2 Ma. 相似文献
17.
New factual materials on methane eruptions into the water of Lake Baikal in August 1912 are considered. The regional press
is used as the information source. The spatio-temporal relationship between the gas eruptions and earthquakes, observed in
South Baikal in 1912, is revealed, which permits us to consider this effect as a consequence of seismic activity intensification.
Intensive methane discharge into water is a potential danger for the lake’s ecosystem as was proved by massive death of water
organisms in South Baikal in 1912 during the described phenomena. 相似文献
18.
Nenita Bukalo Georges-Ivo Ekosse John Odiyo Jason Ogola 《Comptes Rendus Geoscience》2019,351(1):17-26
Increased interest in paleoenvironmental studies is a result of climatic changes occurring at present and predicted for the future. Such studies could be done using the stable isotope compositions (δ2H and δ18O) of kaolins, which provide knowledge on the paleoenvironmental conditions prevailing during the time of kaolinisation. In this study, the stable isotopic compositions of clay-size fraction of kaolins occurring in Cretaceous and Tertiary Formations of the Douala Sub-Basin in Cameroon are presented, with the aim of reconstructing the paleoenvironmental conditions of the Sub-Basin. To achieve this, the clay-size fraction (< 2 μm fraction) of 8 kaolinite-rich samples were analysed for their δ2H and δ18O compositions, and results were reported as part per mil (‰) relative to the SMOW standard. The δ18O values of kaolins found in the Cretaceous–Tertiary Formations of the Douala Sub-Basin varied between +18.2 and +21.0‰, whereas the δ2H values varied between –69 and –53‰. Nine of the eleven samples plotted on the right of the supergene–hypogene line. Five of these nine samples plotted very close to the kaolinite line, which represents the composition of kaolinite in equilibrium with meteoric water at 20 °C; suggesting a supergene weathering origin of these kaolins. The determination of the temperature of kaolinisation yielded mean formation temperatures of 22 ± 2 °C and 27 ± 6 °C for Cretaceous and Tertiary kaolins, respectively. Excluding the two samples falling in the hypogene field, averages of kaolinisation temperatures were 20 and 25 °C during the Cretaceous and Tertiary periods, respectively. These temperatures are slightly below the present mean annual temperature in Douala (27 °C), thereby suggesting that the climate was becoming warmer from the Cretaceous to the Present. Therefore, Douala had a cooler and rainy climate during the Cretaceous, and the climate is gradually becoming hotter and more humid, favouring the refinement of existing kaolins and the kaolinisation of kaolin-forming minerals in the Sub-Basin. 相似文献
19.
Redox problems in the “metallogenic specialization” of magmatic rocks and the genesis of hydrothermal ore mineralization 总被引:1,自引:0,他引:1
I. N. Kigai 《Petrology》2011,19(3):303-321
Considering the history and current state of the problem of the so-called metallogenic specialization of magmatic rocks, the
paper places emphasis onto various aspects of the genesis of ore mineralization depending on the redox state of magmas (as
a logical continuation of S. Ishihara’s works), fluids, and host rocks. These problems were inadequately poorly explored and
discussed by researchers dealing with ore deposits. Various possible variants of ore-forming redox processes for different
types of mineral deposits, with ore mineralization affiliated to granites (Ta, Sn, W, Mo, and Be) and mafic magmas (Au, Ag,
U, Cu, Zn, Pb, As, Sb, and Hg) and, accordingly, to crustal and mantle origin, are discussed. On the basis of analyzed geological
data, including those published over the past three decades, it is shown that the redox state of ore-producing magmas commonly
significantly impacted not only the ore potential of magmatic complexes but also the genetic type of the ore mineralization.
The redox state of the fluids predetermined the transport and precipitation speciation of metals. Influence mechanisms of
hydrocarbons from sedimentary country rocks and gaseous products of their pyrolysis on ore deposition of various metals are
considered. Understanding these mechanisms can be helpful for predicting the possible precipitation sites of ore mineralization
of noble, radioactive, and chalcophile metals. 相似文献
20.
《Journal of African Earth Sciences》1999,28(3):693-702
Results of RbSr, PbPb and SmNd whole rock, Rbr biotite and PbPb zircon evaporation analyses are presented for certain granitoid rocks from the Johannesburg Dome. These data indicate that the granodiorite, granite and leucosome from migmatite were emplaced ∼ 3090 Ma ago, were genetically related and were derived primarily from a source between ∼ 3300 and ∼ 3500 Ma old. A portion of the granodiorite and granite might have been derived from a source between ∼ 4000 and ∼ 4300 Ma old. The tonalite was emplaced ∼ 3170 Ma ago and was derived from a source between 3.3 and 3.5 Ga old. RbSr biotite-whole rock ages, ranging between about ∼ 2614 and ∼ 2080 Ma, probably reflect complete resetting during differential uplift, erosion and cooling of the granitoid rocks in the Neoarchæan and Palæoproterozoic. If so, they apparently were not influenced by the emplacement of the ∼ 2060 Ma Bushveld Igneous Complex or the ∼ 2000 Ma Vredefort event. The granodiorite, granite and leucosome were emplaced coeval with and may be genetically related to compositionally similar plutonic and volcanic rocks in the Barberton area, Vredefort structure and Dominion Group. 相似文献