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1.
The results of observations on the Large Phased Array of the Lebedev Physical Institute made as part of a survey of the northern sky at 102.5 MHz are reported. Survey source lists for the declination ranges 27.5°–33.5° and 67.5°–70.5° are given, together with their coordinates, flux densities, and identifications with 4C objects. In total, there are 920 sources with flux densities S 102.5≥3.0 Jy in the two zones, which cover 0.73 star. The observing and data-reduction methods are described, and the reliability and completeness of the catalog are estimated. 相似文献
2.
Dolomitic marble on the island of Naxos was deformed at variable temperatures ranging from 390 °C to >700 °C. Microstructural investigations indicate two end-member of deformation mechanisms: (1) Diffusion creep processes associated with small grain sizes and weak or no CPO (crystallographic preferred orientation), whereas (2) dislocation creep processes are related with larger grain sizes and strong CPO. The change between these mechanisms depends on grain size and temperature. Therefore, sample with dislocation and diffusion creep microstructures and CPO occur at intermediate temperatures in relative pure dolomite samples. The measured dolomite grain size ranges from 3 to 940 μm. Grain sizes at Tmax >450 °C show an Arrhenius type evolution reflecting the stabilized grain size in deformed and relative pure dolomite. The stabilized grain size is five times smaller than that of calcite at the same temperature and shows the same Arrhenius-type evolution. In addition, the effect of second phase particle influences the grain size evolution, comparable with calcite. Calcite/dolomite mixtures are also characterized by the same difference in grain size, but recrystallization mechanism including chemical recrystallization induced by deformation may contribute to apparent non-temperature equilibrated Mg-content in calcite. 相似文献
3.
《Applied Geochemistry》1997,12(4):383-395
594 sediment samples from the Galapagos Rift System (GRS) and the crest of the East Pacific Rise (EPR) were chemically analyzed for 12 elements. Carbonate-free compositional datasets associated with each of 3 regions, the GRS, the EPR 2°N–4°S and the EPR 10°S–42°S, were separately subjected to endmember analysis. The compositions of endmember estimates were constructed for each dataset. These composition largely confirmed theidentities of endmembers that had previously been inferred from the varimax rotated loadings of a conventional factor analysis (of the correlation matrices) of the same 3 datasets.In view of the widely-reported unreliability of the correlation structure of compositional data, the confirmation by endmember analysis of the results of a factor analysis is itself quite remarkable. However, the particular advantage of endmember analysis is that the chemical compositions of extreme sources are estimated, and may readily be interpreted. The samples in the dataset can then be expressed as mixtures of these extreme sources. By contrast, the varimax rotated loadings of a factor analysis indicate only those elements that are associated together on a single factor which may or may not be an endmember, the composition of which nevertheless remains unknown. 相似文献
4.
Petrology and geochemistry of back-arc basin basalts from Lau Basin spreading ridges at 15°, 18° and 19°S 总被引：1，自引：0，他引：1
Dr. T. J. Falloon Dr. A. Malahoff Dr. L. P. Zonenshaina Dr. Y. Bogdanova 《Mineralogy and Petrology》1992,47(1):1-35
Summary Fresh back-arc basin lavas were recovered during five dives of the submersible Mir during the 1990 cruise of the research vessel Akademik Mstislav Keldysh to the Lau Basin. Three dives were conducted on the central spreading center of the King's Triple Junction (KTJ) in the northeastern part of the Lau Basin east of Niuafo'ou Island at approximately 15°S. The lavas from the KTJ can be divided into types I and II based on their similarities to N-MORB and the BABB magma type ofSinton andFryer (1987) respectively. One dive each was made on the Central Lau Spreading Center (CLSC) at 18°S and the Eastern Lau Spreading Center (ELSC) at 19°S. Lavas sampled on the CLSC were associated with active hydrothermal sulphide chimneys occurring at the base of a collapsed caldera structure on the central volcanic axial high. Sampled lavas from both the CLSC and ELSC are all of type I geochemistry.The results of the Keldysh 90 cruise are integrated with previous work to evaluate the geochemical characteristics of the Lau Basin crust as a whole and geochemical zonation models for back-arc basin development. An important part of this review of Lau Basin basalt geochemistry is the recognition of boninites and rocks of boninitic affinity which occur at off-ridge locations throughout the Lau Basin. These are suggested to erupt during the initial stages of development of new spreading ridges associated with episodes of ridge jump or the propagation of back-arc spreading ridges into arc crust.Hf-Th-Ta systematics of the Lau Basin lavas are used to identify unmodified mantle source compositions and possible subduction-related enriched components. Unmodified mantle source compositions range from D-, N-, and E-MORB to OIB. All Lau Basin lavas show some evidence of enrichment by a H2O ± LILE ± LREE-enriched component, a slab derived hydrous fluid. The slab-derived fluid is not homogeneous in composition perhaps reflecting the presence or absence of a subducted sediment component.The sampled lavas from the KTJ confirm the uniqueness of the BABB magma type ofSinton andFryer (1987).
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Zusammenfassung Dieser Artikel berichtet über erste Ergebnisse einer Forschungsexpedition in das Lau Basin, ausgeführt mit dem Forschungsschiff Akademiker Mstislav Keldysh und dem Mini-U-Boot Mir. Drei Tauchfahrten führten zur zentralen Achse der King's triple junction (KTJ) im nordöstlichen Teil des Lau Basins östlich der Insel Niuafo'ou (15°S). Die dort beprobten Laven werden auf der Basis ihrer chemischen Zusammensetzung eingeteilt in die Typen I und II, entsprechend der Klassifikation vonSinton andFryer (1987) in N-MORB und BABB. Eine vierte Tauchfahrt zum zentralen Lau Spreading Center (CLSC, 18°N) erbrachte Fragmente von Sulphidschloten eines aktiven Black Smoker innerhalb einer kollabierten Calderastructur. Eine fünfte Tauchfahrt zum östlichen Lau Spreading Center (ELSC, 19°N) erbrachte Laven vom Typus I (entsprechend N-MORB).Unter Berücksichtigung früherer Arbeiten gestatten die Ergebnisse der Keldysh 90 Expedition eine geochemische Charakterisierung des Lau Basins, sowie eine Bewertung bestehender Zonierungsmodelle fur die Entstehung und Evolution von Backarc Basins. Entlang der gesamten Achse im Lau Basin, aber abseits des eigentlichen aktiven Spreading Centers, werden Boninite und Laven boninitischer Affinität beobachtet. Diese Boninite können als integraler Teil des Frühstadiums eines Backarc Spreading Centers gedeutet werden, und entstehen möglicherweise dort, wo Spreading Centers in die Kruste eines Inselbogens vordringen oder dann, wenn es zu einer abrupten Positionsänderung der Achse kommt.Die Hf-Th-Ta Konzentrationen und Verhältnisse in Lau Basin Laven gestatten die Identifikation mehrerer Mantel-Endglieder (entsprechend D-MORB, N-MORB, E-MORB, und OIB), sowie einer an H2O und LILE-LREE angereicherten Komponente, die mit Subduktionstätigkeit und anschließender Mantelmetasomatose in Zusammenhang gebracht wird. Die angereicherte Komponente war vermutlich inhomogen aufgrund variabler Anteile subduzierter Sedimente. Die Laven des Lau Basins bestätigen die vonSinton andFryer (1987) vorgeschlagene geochemische Sonderstellung von BABB Magmentypen.
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5.
Only few (six) focal mechanism, in CMT Catalog, have been so far known for intraplate shallow events in the Andean chain close to Chile–Argentina state border at latitudes ∼35° S. We add two more mechanisms, depths and moment magnitudes by carefully analyzing full waveforms of weak events recorded by broad-band stations of the Chile Argentina Geophysical Experiment (southern profile). The moment magnitudes of both events (Mw = 3.6 and 3.7) are lower than the duration magnitudes (Md = 4.0 and 4.29) reported by NEIC. The source depth, constrained by waveforms for one of the studied events (5.5–8.5 km) seems to be considerably shallower than the hypocenter depth located by means of arrival times (∼20 km). The waveform analysis was complemented by first-motion polarities which resulted in an uncertainty assessment of the focal mechanism. Event 1 (2001-11-03) has a strike-slip mechanism with a small normal component and almost vertical nodal planes in the north-south and east-west directions. The north-south nodal plane could be related to the Calabozos faults system. Event 2 (2002-02-16) has a strike-slip mechanism with a small thrust component. The latter event (its subhorizontal nodal plane) could be associated with the El Diablo-El Fierro fault system. Dextral strike-slip solutions are consistent with recent studies in the area. 相似文献
6.
S. A. Silantyev N. S. Bortnikov K. N. Shatagin V. E. Bel’tenev N. N. Kononkova Ya. V. Bychkova E. A. Krasnova 《Petrology》2016,24(4):336-366
The paper presents petrological and geochemical data on mantle peridotite, basalt, and metamorphic rocks sampled in Cruise 36 of the R/V Professor Logachev at the MAR axial zone between 17° and 20° N. These data are interesting not only as providing new information on the inner structure of the oceanic crust in the still-poorly known axial MAR segment but also in the context of the fundamental problem of interaction between magmatic and hydrothermal systems in slow-spreading mid-oceanic ridges. The MAR axial zone between 17° and 20° N was determined to host both weakly and strongly depleted residual peridodites, which suggests that the degree of mantle source melting significantly varied along the ridge axis in this segment. The MAR crest zone comprises slabs of serpentinized peridotite brought to the seafloor surface at various time. The most strongly depleted mantle peridotites likely uplifted later than the mildly and weakly depleted rocks in the same areas. A mantle reservoir beneath the MAR axial zone at 20° N is not isotopically related to the mantle source of the parental MORB melts, and high-Mg metabasites exposed at 17°56- N were derived from a crustal source that was modified near the root zone of a high-temperature hydrothermal system. The studied area seems to display traces of an extinct hydrothermal field and likely an ore occurrence related to it. 相似文献
7.
8.
Three major diastrophic cycles, defined by their structural style and their spatial distribution are recognized in the Andean Basement of this region. The oldest structures are related to the Panamerican Orogeny (500 to 700 m. a.) which produced in the Central Craton multiply deformed complexes of schists, gneisses and granites, that are covered discordantly by unmetamorphosed Cambrian and Ordovician beds. West of the Central Craton Ordovician sedimentary beds are folded with a simple structural style and intruded by granites. Both the sedimentry beds and the granites are covered discordantly by undeformed Devonian sequences. The folding of the Ordovician is attributed to the ocloyic phase of the Caledonian movements. West of the ocloyic belt is another foldbelt consisting of strongly folded Devonian beds attributed to the chanic phase (hercynian). The chanic belt is intruded by carboniferous and permian granites and covered discordantly by Carboniferous and Permian sequences.The features observed in the eastern slope of the Andes suggest that the Paleozoic foldbelts are intracratonic. Whether there are accreted terrains in the Pacific Coastal Cordillera is matter of controversy.
Zusammenfassung Im Andenbasement dieser Region lassen sich drei diastrophische Hauptzyklen, die durch ihren strukturellen Baustil und ihre geographische Verbreitung definiert sind, unterscheiden. Die ältesten Strukturen sind verknüpft mit den Bewegungen der Panamerikanischen Orogenese (500–700 m. a.), welche im Zentralkraton einen polydeformierten Komplex von Schiefern, Gneissen und Graniten erzeugte. Diesem lagern diskordant kambrische und ordovizische Sequenzen ohne Metamorphose und präandiner Deformation auf. Nach Westen zu gibt es einen Gürtel stark deformierter ordovizischer Sedimente, die einen einfacheren Baustil als das präkambrische Basement aufweisen, und diskordant von undeformierten devonischen Abfolgen bedeckt sind. Die Faltung des Ordoviziums wird der Ocloyischen Phase der Kaledonischen Bewegung zugerechnet.Weiter westwärts tritt ein jüngerer Faltengürtel aus devonischen Sedimenten auf, die während der Chanischen Phase der Herzynischen Bewegung intensiv deformiert wurden, und von karbonischen und permischen Sequenzen diskordant überlagert sind.Der Ocloyische Gürtel ist von postordovizischen Graniten die von devonischen Schichten überlagert sind, und der Chanische Gürtel von karbonischen und permischen Graniten intrudiert. Im präkambrischen Basement des Zentralkratons treten einerseits präkambrische Granite auf, denen diskordant kambrische Schichten auflagern. Andererseits findet man Granite mit paläozoischen Isotopenaltern, letztere aber in Gebieten, wo wegen des Fehlens von Deckschichten eine stratigraphische Kontrolle unmöglich ist.Die gemachten Beobachtungen scheinen darauf hinzudeuten, daß die paläozoischen Faltengürtel intrakratonisch sind. Ob es allochtone »terrains« in der pazifischen Küstenkordillere gibt, ist Gegenstand der Kontroverse.
Resumen En el basamento de los Andes de esta región se distinguen tres ciclos diastróficos mayores definidos por sus estilos estructurales y su distributión espacial. Las estructuras mas antiguas responden a movimientos que culminaron con la Orogénesis Panamericana (500–700 m. a.) que produjo en el Cratógeno Central un complejo de esquistos, gneises y granitos polideformados, al que se le superponen discordantemente secuencias cámbricas y ordovicicas sin metamorfismo ni déformatión preandina. Hacia el oeste hay un cinturón de sedimentos ordovícicos intensamente deformados con un estilo de plegamiento mas simple que el del basamento precámbrico y cubierto discordantemente por secuencias marinas devónicas sin deformatión. Los movimientos responsables de este plegamiento se atribuyen a la fase oclóyica de los movimientos caledónicos. Más hacia el oeste se manifiesta una franja de deformatión mas jóven atribuída a la Fase chánica de los movimientos hercínicos, en ella se encuentran sedimentitas devónicas intensamente plegadas cubiertas discordantemente por secuencias carbónicas y pérmicas.El cinturón oclóyico esta acompanãdo por granitos postordovícicos cubiertos por Devónico. Asimismo, el cinturón chánico (hercínico) esta intruido por granitos probablemente carbónicos. Con respecta a los granitos intruidos en el zócalo antiguo, hay algunos indudablemente precámbricos por estar cubiertos discordantemente por secuencias cámbricas sin metamorfismo, además hay granitos de edad dudosa que han dado valores isotópicos paleozoicos pero en lugares donde el control estratigráfico no es posible por ausencia de la cobertura paleozoica. De acuerdo a los hechos observados en la ladera oriental de los Andes surge la idea de que los cinturones de plegamiento paleozoicos son intracratónicos, aun es materia de controversia si en la Cordillera de la Costa junto al Pacifico hay terrenos alóctonos acrecionados.
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9.
David Völker Jacob Geersen Eduardo Contreras-Reyes Javier Sellanes Silvio Pantoja Wolfgang Rabbel Martin Thorwart Christian Reichert Martin Block Wilhelm Reimer Weinrebe 《International Journal of Earth Sciences》2014,103(7):1765-1787
The continental shelf and slope of southern Central Chile have been subject to a number of international as well as Chilean research campaigns over the last 30 years. This work summarizes the geologic setting of the southern Central Chilean Continental shelf (33°S–43°S) using recently published geophysical, seismological, sedimentological and bio-geochemical data. Additionally, unpublished data such as reflection seismic profiles, swath bathymetry and observations on biota that allow further insights into the evolution of this continental platform are integrated. The outcome is an overview of the current knowledge about the geology of the southern Central Chilean shelf and upper slope. We observe both patches of reduced as well as high recent sedimentation on the shelf and upper slope, due to local redistribution of fluvial input, mainly governed by bottom currents and submarine canyons and highly productive upwelling zones. Shelf basins show highly variable thickness of Oligocene-Quaternary sedimentary units that are dissected by the marine continuations of upper plate faults known from land. Seismic velocity studies indicate that a paleo-accretionary complex that is sandwiched between the present, relatively small active accretionary prism and the continental crust forms the bulk of the continental margin of southern Central Chile. 相似文献
10.
David E. Ellis 《Geochimica et cosmochimica acta》1978,42(8):1271-1281
At 750°C and 4000 bar scapolite is stable relative to plagioclase + calcite over the range of plagioclase compositions An53–An83. The assemblage plagioclase + scapolite + calcite is stable relative to plagioclase + calcite over the ranges of plagioclase composition An48-An53 and An83–An91.5. When NaCl is present in the coexisting fluid the range of scapolite compositions stable relative to plagioclase increases. High mole fractions of NaCl in the fluid stabilize scapolite relative to plagioclases from An25 to An87 in the presence of excess calcite. Determination of the ratios of the synthetic scapolites shows that the range of stable scapolite compositions is significantly larger than heretofore proposed, and that even the chloride and carbonate bearing scapolites must be considered a four component solid solution. The KD for the exchange of NaCl and CaCo3 between coexisting scapolite, fluid and carbonate is given by the equation In . This equation implies that Cl-poor natural scapolites coexisted with fluids low in NaCl, and that regional occurrences of Cl-rich scapolites are likely to represent metamorphosed evaporite sequences. 相似文献
11.
A. K. Sharma M. V. Rokade R. Kondala Rao S. Gurubaran P. T. Patil 《Journal of Earth System Science》2010,119(4):461-470
The main aim of the paper is to describe mesosphere and lower thermosphere (MLT) wind field observed between June 2000 and
May 2002 by medium frequency (MF) radars at two locations near the equatorial region and at tropical latitude. We have presented
and compared observations of mean horizontal winds in the mesosphere and lower thermosphere (MLT) region over Kolhapur (16.8°N,
74.2°E) and Tirunelveli (8.7°N, 77.8°E). Our analysis reveals annual oscillation in the zonal wind and semi-annual oscillation
in the meridional wind over Kolhapur. On the other hand, results over Tirunelveli reveal semi-annual oscillation (SAO) in
the zonal wind and annual oscillation in the meridional wind. Also we have observed enhanced magnitude of wind speed in spring
equinox period of 2002 exhibiting the signatures of the quasi-biennial oscillation (QBO) over Tirunelveli. 相似文献
12.
《Geochimica et cosmochimica acta》1999,63(19-20):3247-3259
The rate of Si release from dissolving bytownite feldspar in abiotic batch reactors increased as temperatures increased from 5° to 35°C. Metabolically inert subsurface bacteria (bacteria in solution with no organic substrate) had no apparent effect on dissolution rates over this temperature range. When glucose was added to the microbial cultures, the bacteria responded by producing gluconic acid, which catalyzed the dissolution reaction by both proton- and ligand-promoted mechanisms. The metabolic production, excretion, and consumption of gluconic acid in the course of glucose oxidation, and therefore, the degree of microbial enhancement of mineral dissolution, depend on temperature. There was little accumulation of gluconic acid and therefore, no significant enhancement of mineral dissolution rates at 35°C compared to the abiotic controls. At 20°C, gluconate accumulated in the experimental solutions only at the beginning of the experiment and led to a twofold increase in dissolved Si release compared to the controls, primarily by the ligand-promoted dissolution mechanism. There was significant accumulation of gluconic acid in the 5°C experiment, which is reflected in a significant reduction in pH, leading to 20-fold increase in Si release, primarily attributable to the proton-promoted dissolution mechanism. These results indicate that bacteria and microbial metabolism can affect mineral dissolution rates in organic-rich, nutrient-poor environments; the impact of microbial metabolism on aluminum silicate dissolution rates may be greater at lower rather than at higher temperatures due to the metabolic accumulation of dissolution-enhancing protons and ligands in solution. 相似文献
13.
S. A. Silantyev E. A. Krasnova M. Cannat N. S. Bortnikov N. N. Kononkova V. E. Beltenev 《Geochemistry International》2011,49(4):323-354
This study aimed at reconstructing the sequence of events in the magmatic and metamorphic evolution of peridotites, gabbroids,
and trondhjemites of the oceanic core complexes of the Ashadze and Logachev hydrothermal vent fields. The study object was
the collections of plutonic rocks made during cruises 22 and 26 of the R/V Professor Logachev, Cruise 41 of the R/V Akademik Mstislav Keldysh, and the Russian-French expedition Serpentine aboard the R/V Pourquoi pas? The data reported here suggest that the oceanic core complexes of the Ashadze and Logachev fields were formed via the same
scenario in the two MAR regions. On the other hand, the analysis of petrological and geochemical characteristics of the rocks
indicated that the oceanic core complexes of the MAR axial zone between 12°58′ and 14°45′N show a pronounced petrological
and geochemical heterogeneity manifested in variations in the degree of depletion of mantle residues and the Nd isotopic compositions
of the rocks of the gabbro-peridotite association. The trondhjemites of the Ashadze hydrothermal field can be considered as
partial melting products of gabbroids under the influence of hydrothermal fluid. It was supposed that the presence of trondhjemites
in the MAR oceanic core complexes can be used as a marker for the highest temperature deep-rooted hydrothermal systems. Perhaps,
the region of the MAR axial zone in which petrologically and geochemically contrasting oceanic core complexes are spatially
superimposed served as sites for the development of large hydrothermal clusters with a considerable ore-forming potential. 相似文献
14.
Suzanne Mahlburg Kay Helen A. Jones Robert W. Kay 《Contributions to Mineralogy and Petrology》2013,166(1):165-192
The alkaline volcanic rocks of the 1.8–0.9 Ma Auca Mahuida and post-mid-Pliocene Rio Colorado backarc volcanic fields east of the Andean Southern Volcanic Zone at ~37°–38°S have pronounced intraplate-like chemical signatures with some striking similarities to oceanic DM-EM1-like lavas of the south Atlantic Tristan da Cunha type. These backarc lavas are considered to have formed as a series of mantle batches typified by 4–7 % melting, with decompression melting initiating in a garnet-bearing mantle above a steepening subduction zone, and final equilibration occurring near the base of a ~65- to 70-km-thick lithosphere at temperatures of ~1,350–1,380 °C. Evolved Auca Mahuida mugearite to trachytic samples are best explained by crystal fractionation with limited mixing of partial melts of recently underplated basalts, in line with isotopic signatures that preclude significant radiogenic contamination in a preexisting refractory crust. Higher Ba/La and subtly higher La/Ta ratios than in nearby ~24–20 Ma primitive basalts or oceanic (OIB) lavas are attributed to the residual effects of slab fluids introduced during a shallow subduction episode recorded in the arc-like chemistry of the adjacent 7–4 Ma Chachahuén volcanic complex. Positive Sr, K and Ba spikes on mantle-normalized patterns of both primitive Auca Mahuida and ~24–20 Ma basalts, like those in EM-like OIB basalts, are attributed to mixing of continental lithosphere into the asthenosphere. In Patagonia, this mixing is suggested to have peaked as the South America continent accommodated to major late Oligocene plate convergence changes, as similar Sr, K and Ba spikes and DM-EM1 signatures are absent in ~50–30 Ma backarc lavas north of 51°S, and all of those south of 51°S. Introduction of an EM1-like component associated with lateral mantle flow of a Tristan da Cunha source is largely precluded by its Cretaceous age and distance to Patagonia. 相似文献
15.
Gustavo González Bonorino Víctor Rinaldi Liliana del Valle Abascal Patricia Alvarado Gustavo G. Bujalesky Arturo Güell 《Natural Hazards》2012,61(2):337-349
Patagonia, including the island of Tierra del Fuego, lies in southernmost South America at the junction of the South American,
Antarctic, and Scotia tectonic plates. Historical and instrumental records have documented several local earthquakes of damaging
magnitude, posing a threat to the rapidly growing population of 300,000 and the expanding industrial and service infrastructure.
Short and inaccurate instrumental records of local seismic events and a diffuse epicenter distribution not clearly related
to the recognized seismogenic structures have hindered an adequate evaluation of the seismic hazard for this region. To improve
this situation, a paleoseismological study was carried out on two gravelly strandplains on the Atlantic coast of Patagonia.
Surveying combined ground-probing radar, vertical electric sounding, and seismic refraction. Coseismic normal faults buried
beneath the strandplain bodies were revealed and related to the morphology of the strandplains. The faults have probable ages
between 0.9 and 6.4 kyr BP and a recurrence rate of about 1 kyr. The more likely source for these structures is the Magallanes-Fagnano
fault, a continental transform fault that crosses Tierra del Fuego. The distance of more than 300 km from the buried coseismic
structures to the trace of the Magallanes-Fagnano fault argues for high-magnitude earthquake activity on this fault throughout
the Holocene. Urban development on soft glacial and alluvial substrates increases the hazard. 相似文献
16.
Zabuye Salt Lake in Tibet, China is a carbonate-type salt lake, which has some unique characteristics that make it different from other types of salt lakes. The lake is at the latter period in its evolution and contains liquid and solid resources. Its brine is rich in Li, B, K and other useful minor elements that are of great economic value. We studied the concentration behavior of these elements and the crystallization paths of salts during isothermal evaporation of brine at 15°C and 25°C. The crystallization sequence of the primary salts from the brine at 25°C is halite (NaCl) → aphthitalite (3K2SO4·Na2SO4) → zabuyelite (Li2CO3)→ trona (Na2CO3·NaHCO3·2H2O) → thermonatrite (Na2CO3·H2O) → sylvite (KCl), while the sequence is halite (NaCl) → sylvite (KCl) → trona (Na2CO3·NaHCO3·2H2O) → zabuyelite (Li2CO3) → thermonatrite (Na2CO3·H2O) → aphthitalite (3K2SO4·Na2SO4) at 15°C. They are in accordance with the metastable phase diagram of the Na+, K+-Cl?, CO32?, SO42?-H2O quinary system at 25°C, except for Na2CO3·7H2O which is replaced by trona and thermonatrite. In the 25°C experiment, zabuyelite (Li2CO3) was precipitated in the early stage because Li2CO3 is supersaturated in the brine at 25°C, in contrast with that at 15°C, it precipitated in the later stage. Potash was precipitated in the middle and late stages in both experiments, while boron was concentrated in the early and middle stages and precipitated in the late stage. 相似文献
17.
S. A. Silantyev L. V. Danyushevsky A. A. Plechova L. Dosso B. A. Bazylev V. E. Bel’tenev 《Petrology》2008,16(1):36-62
Data presented in the paper suggest significant differences between the thermodynamic conditions under which magmatic complexes were formed in MAR at 29°–34° N and 12°–18° N. The melts occurring at 29°–34° N were derived by the melting of a mantle source with a homogeneous distribution of volatile components and arrived at the surface without significant fractionation, likely, due to their rapid ascent. The MAR segments between 12° and 18° N combine contrasting geodynamic environments of magmatism, which predetermined the development of a large plume region with the widespread mixing of the melting products of geochemically distinct mantle sources. At the same time, this region is characterized by conditions favorable for the origin of localized zones of anomalous plume magmatism. These sporadic magmatic sources were spatially restricted to MAR fragments with the Hess crust, whose compositional and mechanical properties were, perhaps, favorable for the focusing and localization of plume magmatism. The plume source between 12° and 18°N beneath MAR may be geochemically heterogeneous. 相似文献
18.
《International Geology Review》2012,54(14):1691-1719
This study investigates the formation of lower oceanic crust and geochemical variations of basalts along the Central Indian Ridge (CIR, lat. 7°45′–17°10′ S). Harzburgites, various gabbroic cumulates, medium- to fine-grained oxide gabbros, diabases, and pillow basalts were recovered by dredging from segment ends such as ridge-transform intersections (RTIs), non-transform discontinuities (NTDs), and transform offset areas. The occurrence of both harzburgites and gabbroic rocks with minor basalts at all segments ends, and leucogabbro intrusive into harzburgite at the 12°45′ S NTD indicates that oceanic crust at segment ends exposes mantle-derived harzburgites and gabbroic intrusions with a thin basaltic cover due to sparse magmatic activity. Basalts collected along the entire ridge show wide compositional variations between N (normal)- and E (enriched)-mid-ocean ridge basalt (MORB). T (transitional)-MORBs with enriched affinities are more prominent than N-MORBs. There is no tendency of enrichment towards specific directions. (La/Sm)N variations in MORB along the CIR (8°–21°S) fluctuates at a regional scale with local high positive anomalies reflecting compositional heterogeneity of the sub-CIR mantle domain. 相似文献
19.
G. N. Savelieva N. S. Bortnikov T. B. Bayanova S. V. Ikorskii I. L. Kamenskii 《Geochemistry International》2008,46(8):745-758
The paper presents characteristics of the Nd and Sr isotopic systems of ultrabasic rocks, gabbroids, plagiogranites, and their minerals and data on He and hydrocarbons in fluid inclusions in the same samples. The materials presented in this publication were obtained by studying samples dredged from the MAR crest zone at 5°–6° N (U/Pb zircon dating, geochemical and petrological-mineralogical studies). It was demonstrated that the variations in the isotopic composition of He entrapped in the rocks and minerals were controlled by variable degrees of mixing of juvenile He, which is typical of basaltic glass of MAR (DM source) and atmospheric He. An increase in the fraction of atmospheric He in the plutonic rocks and, to a lesser degree, in their minerals reflects the involvement of seawater or the hydrated material of the oceanic crust in the magmatic and postmagmatic processes. This conclusion finds further support in a positive correlation between the fraction of mantle He (R) and the 87Sr/86Sr ratio. The high-temperature hydration of ultrabasic rocks (amphibolization) was associated with an increase in the fraction of mantle He, while their low-temperature hydration (serpentinization) was accompanied by a drastic decrease in this fraction and a significant increase in the 87Sr/86Sr ratio. The insignificant variations in the 143Nd/144Nd (close to 0.5130) and 87Sr/86Sr (0.7035) in most of the gabbroids and plagiogranites, as well as the fraction of mantle He in these rocks, amphibolites, and their ore minerals, indicate that the melts were derived from the depleted mantle. Similar?Nd values of the gabbroids, plagiogranites, and fresh harzburgites (6.77–8.39) suggest that these rocks were genetically related to a single mantle source. The value of ?Nd = 2.62 of the serpentinized lherzolites likely reflects relations of these relatively weakly depleted mantle residues to another source. The aforementioned characteristics of the rocks generally reflect the various degrees of mixing of components of the depleted mantle with crustal components (seawater) during the metamorphic and hydrothermal processes that accompanied the formation of the oceanic crust. 相似文献
20.
Zhimulev E. I. Sonin V. M. Chepurov A. A. Chepurov A. I. Pokhilenko N. P. 《Doklady Earth Sciences》2022,506(1):630-634
Doklady Earth Sciences - The issue of the stability of carbonate matter (CaCO3) in subduction zones under reduced conditions remains topical. In addition, carbonates may be one of the key sources... 相似文献