Neoproterozoic ‘anomalous’ kimberlites of Guaniamo, Venezuela: Mica kimberlites of ‘isotopic transitional’ type     

Felix V. Kaminsky  Sergei M. Sablukov  Ludmila I. Sablukova  Dominic M.DeR. Channer 《Lithos》2004,76(1-4):565-590

In Venezuela, kimberlites have so far only been found in the Guaniamo region, where they occur as high diamond grade sheets in massive to steeply foliated Paleoproterozoic granitoid rocks. The emplacement age of the Guaniamo kimberlites is 712±6 Ma, i.e., Neoproterozoic. The Guaniamo kimberlites contain a high abundance of mantle minerals, with greater than 30% olivine macrocrysts. The principal kimberlite indicator minerals found are pyrope garnet and chromian spinel, with the overwhelming majority of the garnets being of the peridotite association. Chrome-diopside is rare, and picroilmenite is uncommon. Chemically, the Guaniamo kimberlites are characterized by high MgO contents, with low Al₂O₃ and TiO₂ contents and higher than average FeO and K₂O contents. These rocks have above average Ni, Cr, Co, Th, Nb, Ta, Sr and LREE concentrations and very low P, Y and, particularly, Zr and Hf contents. The Nb/Zr ratio is very distinctive and is similar to that of the Aries, Australia kimberlite. The Guaniamo kimberlites are similar in petrography, mineralogy and mantle mineral content to ilmenite-free Group 2 mica kimberlites of South Africa. The Nd-Sr isotopic characteristics of Guaniamo kimberlites are distinct from both kimberlite Group 1 and Group 2, being more similar to transitional type kimberlites, and in particular to diamondiferous kimberlites of the Arkhangelsk Diamond Province, Russia. The Guaniamo kimberlites form part of a compositional spectrum between other standard kimberlite reference groups. They formed from metasomatised subcontinental lithospheric mantle and it is likely that subduction of oceanic crust was the source of this metasomatised material, and also of the eclogitic component, which is dominant in Guaniamo diamonds.  相似文献   

The new state flags as the iconographic symbols of the post-Soviet space     

Sergei Matjunin 《GeoJournal》2001,52(4):311-313

State flags may be appreciated as iconographic symbols according to Jean Gottmann's definition. Especially interesting is to analyze the state flags in the moment of their creation – as for example on the territory of the former Soviet Union where almost all the new independent states have to create or restore their state symbols. On many of these flags we can see the historical elements, the political and geographical situation of a new state or even religious beliefs of most of the inhabitants. On the state flags we can also observe the state ideology, but its interpretation may be ambiguous, e.g., the green color on the state flag means either that the state is proud of its rich nature or that Islam is a state religion. Ambitions are expressed on the flags of the entities, which are fighting for their independence.  相似文献   

Modelling the compliance of crustal rock—I. Response of shear-wave splitting to differential stress     

Sergei V. Zatsepin  Stuart Crampin 《Geophysical Journal International》1997,129(3):477-494

We show that seismic shear waves may be used to monitor the in situ stress state of deep inaccessible rocks in the crust. The most widespread manifestation of the stress-related behaviour of seismic waves is the shear-wave splitting (shear-wave birefringence) observed in almost all rocks, where the polarizations of the leading split shear waves are usually subparallel to the direction of the local maximum horizontal stress. It has been recognized that such shear-wave splitting is typically the result of propagation through distributions of stress-aligned fluid-filled microcracks and pores, known as extensive-dilatancy anisotropy or EDA. This paper provides a quantitative basis for the EDA hypothesis. We model the evolution of anisotropic distributions of microcracks in triaxial differential stress, where the driving mechanism is fluid migration along pressure gradients between neighbouring microcracks and pores at different orientations to the stress field. This leads to a non-linear anisotropic poroelasticity (APE) model for the stress-sensitive behaviour of fluid-saturated microcracked rocks. A companion paper shows that APE modelling matches a range of observed phenomena and is a good approximation to the equation of state of a stressed fluid-saturated rock mass.  相似文献   

Tululite,Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36: a new Ca zincate-aluminate from combustion metamorphic marbles,central Jordan     

Hani N. Khoury  Ella V. Sokol  Svetlana N. Kokh  Yurii V. Seryotkin  Elena N. Nigmatulina  Sergei V. Goryainov  Elena V. Belogub  Ian D. Clark 《Mineralogy and Petrology》2016,110(1):125-140

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On the Diagnostic Properties of Low Degree Acoustic Modes     

Ian W Roxburgh  Sergei V Vorontsov 《Astrophysics and Space Science》1998,261(1-4):21-22

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Numerical Computation of Hansen-like Expansions     

Sergei A. Klioner  Akmal A. Vakhidov  Nickolay N. Vasiliev 《Celestial Mechanics and Dynamical Astronomy》1998,68(3):257-272

Fourier expansions of elliptic motion functions in multiples of the true, eccentric, elliptic and mean anomalies are computed numerically by means of the fast Fourier transform. Both Hansen-like coefficients and their derivatives with respect to eccentricity of the orbit are considered. General behavior of the coefficients and the efficiency (compactness) of the expansions are investigated for various values of eccentricity of the orbit. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Palaeomagnetism of the Lower Ordovician Orthoceras Limestone, St. Petersburg, and a revised drift history for Baltica in the early Palaeozoic   总被引：2，自引：0，他引：2  

MarkA.Smethurst  AlexeyN.Khramov  Sergei Pisarevsky 《Geophysical Journal International》1998,133(1):44-56

Palaeomagnetic investigation of Lower Ordovician limestone in the vicinity of St. Petersburg yields a pole position at latitude 34.7°N, longitude 59.1°E ( dp / dm =5.7°/6.4°). A probable primary remanence origin is supported by the presence of a field reversal. The limestone carries one other remanent magnetization component associated with a Mesozoic remagnetization event.
An apparent polar wander path is compiled for Baltica including the new result, ranging in age from Vendian to Cretaceous. Ages of the published Lower to mid-Palaeozoic palaeomagnetic pole positions are adjusted in accordance with the timescale of Tucker & McKerrow (1995). The new Arenig result is the oldest of a series of Ordovician and Silurian palaeomagnetic pole positions from limestones in the Baltic region. There are no data to constrain apparent polar wander for the Tremadoc, Cambrian and latest Vendian. If the Fen Complex results, previously taken to be Vendian in age ( c . 565 Ma), are reinterpreted as Permian remagnetizations, an Early Ordovician–Cambrian–Vendian cusp in the polar wander path for Baltica is eliminated. The apparent polar wander curve might then traverse directly from poles for Vendian dykes on the Kola peninsula ( c . 580 Ma) towards our new Arenig pole ( c . 480 Ma). The consequence of this change in terms of the motion of Baltica in Cambrian times is to reduce significantly a rotational component of movement.
The new Arenig pole extends knowledge of Ordovician apparent polar wander an increment back in time and confirms the palaeolatitude and orientation of Baltica in some published palaeogeographies. Exclusion of the Fen Complex result places Baltica in mid- to high southerly latitudes at the dawn of the Palaeozoic, consistent with faunal and sedimentological evidence but at variance with some earlier palaeomagnetic reconstructions.  相似文献   

Biostratigraphy of the Mussau Trench (Caroline Basin)     

Albert G. Ablaev  Vladimir D. Khudik  Marya G. Biryulina  Sergei P. Pletnev  Akbar A. Ashurov 《Geo-Marine Letters》1992,12(4):236-239

A sedimentary rock complex overlays the deep layers of oceanic crust in the Mussau Trench (and the conjugated underwater ridge) of the Caroline Basin. Paleontological analyses supported the previous idea of Oligocene-Quaternary deposits. In addition, Upper Cretaceous (Acila ex gr. demessa, Anisomyon sp., and others) and Eocene (Heterostegina sp., Discocyclina sp., and others) deposits have been found, suggesting shallow water environments in Late Cretaceous-Early Cenozoic time. Later on, regional submergence started. The complex of the deep-seated formations of the Mussau Trench is not younger than the Early Cretaceous oceanic crust of the Ontong-Java Plateau.  相似文献   

Chemical speciation of copper and zinc in surface waters of the western Black Sea     

Franois L. L. Muller  Sergei B. Gulin  shild Kalvy 《Marine Chemistry》2001,76(4):62

The chemical speciation of Cu and Zn was investigated by voltammetric titration methods in the surface waters (10 m) of the western Black Sea during an Istanbul–Sevastopol cruise conducted in November 1998. Supporting parameters (temperature (T), salinity (S), pH, alkalinity (Alk), suspended particulate matter (SPM) and dissolved and particulate ²³⁴Th) were obtained in order to distinguish hydrographic features against involvement of the metals in biogeochemical processes. In the Turkish continental slope region, the cruise track intersected a narrow vein of colder water originating on the western shelf. The core of this cold water vein was characterised by a relatively low salinity, higher specific alkalinity and higher metal (especially Cu) and metal-binding ligand concentrations.A very large portion of Cu (93–99.8%) and Zn (82–97%) was organically complexed. The degree of complexation was highest in shelf waters and lowest in the central gyre. Titration data for Cu were modelled by two classes of organic binding ligands characterised by (C_L1=3–12 nM, log K₁′=13.1–13.9) and (C_L2=20–70 nM, log K₂′=9.4–11.2). These ligands occurred mainly in the ‘dissolved’ phase, as defined by 0.4-μm filtration. The stronger Cu-binding ligand seemed to be produced in situ in response to Cu concentration, whereas the weaker Cu-binding ligand appeared to be derived from terrestrial sources and/or reducing shelf sediments. Titration results for Zn were generally represented by one class of ligands (C_L1=8–23 nM, log K₁′=9.4–10.2), which were almost uniformly distributed between the ‘dissolved’ (78±8%) and the particulate phase (22±8%). The concentration of these strong Zn-binding ligands showed a very good correlation with SPM (r²=0.64), which improved when the dissolved ligands alone were considered (r²=0.78). It is hypothesised that these ligands were produced in situ by the bacterial breakdown of particulate organic matter.  相似文献   

Holocene pollen record from a peatland in the West Caucasus,Abkhasia, Black Sea region     

Sergei B. Yazvenko 《Journal of Paleolimnology》1994,12(2):65-74

A pollen sequence spanning over 4000 years was recovered from a small (0.1 ha)Sphagnum-dominated peatland in the mountains near Sukhumi, Abkhasia, West Georgia. The peatland lies atc. 1650 m a.s.l. in denseFagus-Abies forest. The pollen record reveals totally forested surroundings throughout since at least 4000 years BP (90–95% AP). It begins with a complex forest dominated byFagus with large proportions ofCastanea, Acer andUlmus. ThenCastanea became dominant whileFagus was still prominent. This might indicate a warmer climate. Later development shows a dramatic decline ofCastanea. Its pollen drops down to 3–5%. RecentlyAbies has been experiencing an exponential growth. Now it comprises over 50% of the forest composition around the peatland. These changes have possibly been caused by human influence together with climatic change. The basin started as aPotamogeton-dominated shallow lake with ferns andAlisma along the margins. Later it developed into a sedge fen and finally aSphagnum andMenyanthes poor fen with scatteredCarex limosa. The record indicates a progression towards oligotrophy.This publication is the fifth paper in a series of papers presented at the session on Past Climatic Change and the Development of Peatlands at the ASLO and SWS Meetings in Edmonton, Canada, May 30–June 3, 1993. Dr. P. Kuhry and Dr S. C. Zoltai are serving as Guest Editors.  相似文献