Uranium in metamorphic rocks     

Jaroslav Dostal  Silvio Capedri 《Contributions to Mineralogy and Petrology》1978,66(4):409-414

The distribution of U has been studied in two metamorphic rock-series with a gradient of regional metamorphism. One series ranges from the lowest greenschist to amphibolite facies and the other one shows increasing metamorphic grade from amphibolite to granulite facies. Several medium and high pressure granulitic inclusions from alkali basalts were also analyzed. The abundances of U in the rocks do not appear to be affected by metamorphism below the granulite facies grade. Granulites are depleted in U in comparison with equivalent rocks of amphibolite facies grade. There are also differences in their U distribution, as the bulk of U in amphibolite facies rocks is located along the fractures and cleavage planes of ferro-magnesian minerals and in U-rich accessories, while in granulites, most of the U resides in accessory minerals. It seems that the depletion of U in granulites is due to a loss of U which is not located in accessory minerals or in the crystal structure of rock-forming minerals and may also be related to a migration of hydrous fluids, perhaps during dehydration.  相似文献   

Die ausseralpine Taphrogenese im kaledonisch-variszisch konsolidierten sardischen Vorlande     

Prof. Dr. Silvio Vardabasso 《International Journal of Earth Sciences》1964,53(2):613-630

Zusammenfassung Ein großer Graben teilt das sardische Vorland von Norden nach Süden, wobei nur der Osthorst (Gennargentu) vollständig, jedoch zersplittert, stehengeblieben ist. Vom Westhorst dagegen ragen nur einige Bruchstücke (Iglesiente, Nurra) vom Meer empor. Viele Seitengräben zweigen vom Hauptgraben ab, so daß die Verstellung der getroffenen Schollen ein asymmetrisches Bild der kratonischen Tektonik hervorgerufen hat.Die Grabenfüllung ist hauptsächlich durch Vulkanite erfolgt; die Sedimente spielen nur eine untergeordnete Rolle. Die Eruptionen beginnen mit dem Oligozän und enden mit dem Pleistozän. Eine Trennung in zwei Zyklen (vorhelvetisch bzw. nachtortonisch) gilt für Südsardinien nicht, weil hier submarine Explosionen (Diatremen) und Tuffiteinschaltungen auch während der mittelmiozänen Transgression vorgekommen sind.Geochemisch gehören die Vulkanite der Kalkalkalireihe, jedoch mit atlantischen und mediterranen Tendenzen. Wenn man eine lokale Aufschmelzung des unteren Sockels des sardischen Kratons annimmt, kann man eine palingenetische Abstammung der tertiären Liparite von variszischen Graniten verstehen.Die Bruchlinien bei der taphrogenetischen Deformation unseres alten Vorlandes lassen zwei dominierende Richtungen erkennen: Südost-Nordwest in Südsardinien (Campidano), Nordost-Südwest in Nordsardinien (Tirsograben und Logudoro). Im Rahmen der Strukturelemente des westlichen Mittelmeeres kann man auch eine horizontale Schollenverschiebung (eine Art Epirophorese im Kleinen!) für Sardinien annehmen, und zwar eine relative Bewegung des Iglesiente in Südost-Richtung, d.h. parallel der großen Abschwenkung des Balearenbogens.

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A great Graben cuts the Sardic Foreland. Its Eastern lip is preserved in a fractured state, the Western rim subsidized to a great extent. Side-grabens diverge from the rift asymmetrically. The Graben-fill consists mainly of igneous material of Oligocene to Recent age. Maindirections of taphrogenesis are NW (in the S-portion) and NE in Northern Sardinia. Locally lateral movements are suspected.

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Résumé Un grand graben divise l'avant-pays sarde du Nord au Sud; seul le horst oriental (Gennargentu) est resté tout à fait en place bien que fracturé. Du horst occidental seuls quelques blocs (Iglesiente, Nurra) émergent de la mer. De nombreux graben latéraux bifurquent à partir du graben principal, de sorte que le déplacement des blocs a entraîné une disposition asymétrique de la tectonique cratonique.Le remplissage du graben s'est fait essentiellement par des volcanites; les sédiments n'occupent qu'une place secondaire. Les éruptions débutent à l'Oligocène et se terminent au Pléistocène. Une division en 2 cycles (préhelvétique et posttortonique) ne s'applique pas à la Sardaigne du Sud, car ici des explosions sous-marines (Diatremes) et des intercalations de tuffites sont également intervenues durant la transgression du Miocène moyen.Du point de vue géochimique les volcanites appartiennent à la série calcoalcaline avec cependant une tendance atlantique et méditerranéenne. En admettant une fusion locale du socle inférieur du craton sarde, on comprend alors la dérivation palingénétique des liparites tertiaires à partir des granites varisques.Les lignes de fracture liées à la déformation taphrogénétique de notre ancien avant-pays montrent deux directions dominantes: SE-NW en Sardaigne méridionale (Campidano), NE-SW en Sardaigne septentrionale (graben du Tirso et de Logudoro). Dans le cadre des éléments structuraux de la Méditerranée occidentale on peut également admettre en Sardaigne un déplacement horizontal des compartiments (du genre épirophorèse en petit!), à savoir un déplacement relatif d'Iglesiente vers le sud-est, c'est-à-dire parallèlement au grand décalage de l'arc des Baléares.

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Riassunto Una geoanticlinale emergente dal centro del Mediterraneo occidentale formava l'Avampaese Sardo durante il Mesozoico.Questa dorsale, già consolidata con le orogenesi caledonica ed ercinica, poi peneplanata e solo in parte invasa da mari epicontinentali, dopo aver subito ampie oscillazioni, è stata alla fine ridotta in frammenti da una tettonica disgiuntiva terziaria.I pilastri, residui dello sbloccamento, formano il caratteristico rilievo attuale di media montagna (tipo Gennargentu), isolato da depressioni a sviluppo ed orientamento ineguali, convergenti verso una zona a direzione meridiana. Questa è la fossa principale del Sistema («fossa tettonica sarda» per eccellenza, fra il Golfo dell'Asinara a N e quello di Cagliari a S).In questa grande fossa la pianura del Campidano, nella Sardegna meridionale, non è che la depressione attuale, risultante dallo spostamento dell'asse di maggior sprofondamento, tuttora in via di assetto.D'altra parte, parecchie «fosse laterali», minori, penetrando nell'antico massiccio, hanno staccato dallo stesso altrettante schegge. Lo sbandamento di questi frammenti dei pilastri tettonici conferisce alle fosse una asimmetria caratteristica, specialmente evidente dalla Valle del Tirso al Golfo dell'Asinara.Lo sprofondamento delle fosse tettoniche è stato accompagnato da un vulcanismo a intensità decrescente dall'Oligocene al Plistocene.La distinzione in due cicli (pre-elveziano, rispettivamente post-tortoniano) non è valida per la Sardegna meridionale, dove (Marmilla e Campidano) le manifestazioni vulcaniche (diatremi e intercalazioni di tufiti) sono continuate anche durante l'invasione marina del Miocene medio.Nella colmata delle fosse tettoniche prevalgono le vulcaniti sui sedimenti; tra le lave prevalgono quelle acide sulle basiche, talvolta in alternanza fra loro.Dalle discordanze tra le varie fasi eruttive e dalle intercalazioni lacustri fra le stesse risulta che entro le fosse tettoniche sono awenute dislocazioni secondarie per piegamento.Dal punto di vista geochimico le lave appartengono alla serie alcalicalcica con tendenze verso le serie alcaline (atlantica e mediterranea). Se si ammette peró una parziale fusione della base granitica del cratone formante l'Avampaese Sardo, il vulcanismo delle nostre fosse tettoniche potrebbe essere un riflesso di oscuri rapporti fra palingenesi e tafrogenesi.In fine, nel tentativo di inserire le dislocazioni disgiuntive, che hanno colpito durante il Terziario l'Avampaese Sardo, si potrà forse riconoscere anche una traslazione orizzontale di zolle (epiroforesi) ed in particolare uno spostamento in blocco dell'Iglesiente, al di qua della fossa tettonica del Campidano, in direzione concordante con la grande deviazione verso Sud-est dell'arco delle Isole Baleari.

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Uranium in spinel peridotite inclusions in basalts from Sardinia   总被引：2，自引：0，他引：2  

Jaroslav Dostal  Silvio Capedri 《Contributions to Mineralogy and Petrology》1976,54(4):245-254

The uranium distribution in spinel peridotite inclusions and their host basalt from Sardinia, Italy, was determined by fission-track mapping. Whole-rock U concentrations range from 14 to 55 ppb. Although the partitioning of U among major silicate phases of the inclusions — olivine, orthopyroxene and clinopyroxene — remains roughly constant, the U content in the minerals is highly variable, e.g. ranging from 27 ppb to 177 ppb in clinopyroxene. The U variation in the minerals shows no apparent correlation with their major element chemistry. Liquid which equilibrated with the assemblages of inclusions with high U content, had U concentrations higher than those found in basaltic rocks. It is suggested that the inclusions were contaminated with a phase strongly enriched in U and subsequently recrystallized. The available data show that spinel peridotite inclusions of basaltic rocks frequently have complex multistage evolution and thus cannot provide a representative picture of the upper mantle radioactivity.  相似文献   

Lithosphere mechanical behavior inferred from tidal gravity anomalies: a comparison of Africa and South America     

Marta S.M. Mantovani  Wladimir Shukowsky  Silvio R.C. de Freitas  Benjamim B. Brito Neves 《Earth and Planetary Science Letters》2005,230(3-4):397-412

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The effect of Congo River freshwater discharge on Eastern Equatorial Atlantic climate variability     

Stefano Materia  Silvio Gualdi  Antonio Navarra  Laurent Terray 《Climate Dynamics》2012,39(9-10):2109-2125

The surface ocean explains a considerable part of the inter-annual Tropical Atlantic variability. The present work makes use of observational datasets to investigate the effect of freshwater flow on sea surface salinity (SSS) and temperature (SST) in the Gulf of Guinea. In particular, the Congo River discharges a huge amount of freshwater into the ocean, affecting SSS in the Eastern Equatorial Atlantic (EEA) and stratifying the surface layers. The hypothesis is that an excess of river runoff emphasize stratification, influencing the ocean temperature. In fact, our findings show that SSTs in the Gulf of Guinea are warmer in summers following an anomalously high Congo spring discharge. Vice versa, when the river discharges low freshwater, a cold anomaly appears in the Gulf. The response of SST is not linear: temperature anomalies are considerable and long-lasting in the event of large freshwater flow, while in dry years they are less remarkable, although still significant. An excess of freshwater seems able to form a barrier layer, which inhibits vertical mixing and the entrainment of the cold thermocline water into the surface. Other processes may contribute to SST variability, among which the net input of atmospheric freshwater falling over EEA. Likewise the case of continental runoff from Congo River, warm anomalies occur after anomalously rainy seasons and low temperatures follow dry seasons, confirming the effect of freshwater on SST. However, the two sources of freshwater anomaly are not in phase, so that it is possible to split between atypical SST following continental freshwater anomalies and rainfall anomalies. Also, variations in air-sea fluxes can produce heating and cooling of the Gulf of Guinea. Nevertheless, atypical SSTs cannot be ascribed to fluxes, since the temperature variation induced by them is not sufficient to explain the SST anomalies appearing in the Gulf after anomalous peak discharges. The interaction processes between river runoff, sea surface salinity and temperature play an effective role in the interannual variability in the EEA region. Our results add a new source of variability in the area, which was often neglected by previous studies.  相似文献   

The Jiddat al Harasis 073 strewn field,Sultanate of Oman     

Edwin GNOS  Silvio LORENZETTI  Otto EUGSTER  A. J. Timothy JULL  Beda A. HOFMANN  Ali Al‐KATHIRI  Manuel EGGIMANN 《Meteoritics & planetary science》2009,44(3):375-387

Abstract— The recently discovered Jiddat al Harasis (JaH) 073 strewn field is the largest found so far in the Sultanate of Oman, covering an area of 19 × 6 km. The 3463 single stones collected range in weight from 52.2 kg down to <1 g (total weight 600.8 kg) and show a pronounced mass sorting. The strewn field shape can be approximated by a NW‐SE‐oriented ellipsoid, indicating an atmospheric entry from SE at a low angle relative to the surface. The meteorite belongs to the L6 ordinary chondrite group and shows S4 average shock grade. Smaller stones generally show a higher weathering grade resulting in a spread from W2 and W4. Enhanced weathering of the stones causing fragmentation after the fall is observed in sandy depressions. Five ¹⁴C measurements on stones of variable size and weathering grade yielded ¹⁴C from 3.8 to 49.9 dpm/kg. Three samples give a ¹⁴C/ ¹⁰Be age consistent with about 14.4 ka. For two samples the cosmogenic, trapped, and radiogenic noble gases were measured. The ratio of the ⁴He and ⁴⁰Ar gas retention ages of 0.29 ± 0.10 and that of the ³He and ²¹Ne cosmic ray exposure ages of 0.36 ± 0.08 Ma indicate that JaH 073 experienced a complex exposure history and lost ⁴He and ⁴⁰Ar due to a major collision. Fragmentation statistics indicate a single major atmospheric disruption and an originally relatively spherical shape of the object. Assuming the material collected represents the majority of fallen mass, and 90–99% of the original weight was lost by ablation, the pre‐atmospheric minimum radius of the meteoroid with density 3.4 g cm^?3would have been at least 75 cm.  相似文献   

Considerazioni intorno ad alcuni metodi per il calcolo delle riduzioni topografiche nei rilievi eötvössiani     

Prof. Dr. Silvio Ballarin 《Pure and Applied Geophysics》1943,5(1-2):93-106

Riassunto L'Autore in questa Nota confronta un procedimento grafico, proposto ed illustrato in precedenti ricerche, con le formole delloSchweydar che sono senza dubbio le più adoperate attualmente nella valutazione delle correzioni topografiche da apportare agli elementi rilevati con la bilancia di torsione, e richiama, fra l'altro, l'attenzione sulle condizioni di applicabilità degli sviluppi e sull'espressione generale dei coefficienti che entrano nella formazione di questi. Completano il lavoro alcune relazioni per il controllo del calcolo dei coefficienti.

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Zusammenfassung Der Verf. vergleicht ein graphisches Verfahren, welches von ihm in früheren Untersuchungen angegeben und erläutert worden ist, mit den Formeln vonSchweydar, welche zweifellos in der Berechnung der topographischen Korrektionen der Grössen die mit der Drehwaage gemessen werden die mehr gebrauchten sind. Ausserdem, gibt er die Anwendungsbedingungen für die Entwicklungen und über den allgemeinen Ausdruck der Koeffizienten welche in der Bildung jener Entwicklungen auftreten. Zuletzt, ist die Arbeit mit einigen Verbindungen zur Kontrolle der Berechnung der Koeffizienten ergänzt.

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Moto ondoso e vento nel Golfo di Trieste     

Prof. Silvio Polli 《Pure and Applied Geophysics》1952,21(1):102-109

Riassunto Dalle osservazioni dello stato del mare, eseguite a Trieste alle ore 8, 14 e 19, nel ventennio 1931–1950, si deducono le medie mensili, stagionali ed annue. Il moto ondoso risulta massimo alle ore 14 dei mesi estivi, minimo alle ore 8 degli stessi mesi. Il valore medio annuo è 1.7, lo stato medio del mare risulta poco meno che leggermente mosso. Nel ventennio l'andamento medio annuo non è nè crescente nè decrescente, presenta una concavità negli anni centrali. Tra la velocità del vento e lo stato ondoso sono stati determinati coefficienti di correlazione che variano, secondo i casi, da 0.49 a 0.94.

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Summary From the observations of the seawave-motion effectuated in Trieste at 8^h, 14^h and 19^h, during the years 1931–1950, the monthly and annual mean values are calculated. The maximum wave-motion results at 14^h of the summer months, the minimum one at 8^h of the same months. The mean annual value is 1.7, that is: a little inferior than «lightly moved». Between the wind-velocity and the wave-motion have been determined correlation-coefficients varying from 0.49 to 0.94.

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Peptide decomposition by extracellular hydrolysis in coastal seawater and salt marsh sediment     

Silvio Pantoja  Cindy Lee 《Marine Chemistry》1999,63(3-4)

Extracellular peptide hydrolysis rates were measured in seawater and sediment from Flax Pond salt marsh using peptide analogs (LYA-peptides) as substrates. This technique allows the direct measurement of specific hydrolysis products and thus provides insights into enzymatic hydrolysis pathways. In sediments, hydrolysis rate constants of LYA-peptides varied seasonally and with depth. Highest activity was found in spring and summer, and most cores exhibited a subsurface maximum. Calculations using the concentrations of chemically-measured peptides suggested that extracellular hydrolysis of peptides is faster than the rate of free amino acids uptake. However, not all peptides may be available for enzymatic hydrolysis. In both seawater and sediment, extracellular hydrolysis of peptides of up to 8 amino acids yielded smaller peptides and free amino acids. Hydrolysis rates depended on size of the peptide substrate, although a clear relationship with number of amino acid constituents was not evident. Peptides containing >2 amino acids were hydrolyzed 10–400 times faster than dipeptides or the fluorogenic substrate Leucine-MCA. Thus, dipeptidases are either uncommon in nature, or hydrolysis is carried out by nonspecific hydrolases that with a low affinity for dipeptides. This is also suggested by the presence of a lag time before dipeptide hydrolysis begins, and the absence of dipeptide hydrolysis in 0.2-μm-filtered. One implication of this finding is that measurements of hydrolysis rates using substrates like Leu-MCA may not accurately predict the magnitude of hydrolysis rates of macromolecules in the marine environment. Even though dipeptide hydrolysis is slow compared to that of larger peptides, LYA-dipeptides are preferentially produced from the hydrolysis of larger substrates. LYA-dipeptides do not penetrate cell membranes of microorganisms because of their size, but natural dipeptides are smaller and can be transported across the cell membrane. Since dipeptides do not appear to accumulate in natural waters, they must be rapidly removed by microorganisms.  相似文献   

地震三兄弟与宫城县附近的地震     

濑野徹三 《国际地震动态》2005,(6):45-46

2003年5月26日和7月26日在宫城县附近相继发生了宫城县近海地震(M7．0)和宫城县北部地震(M6．2)。地震学家们预测不久的将来在宫城县近海将会发生更大的地震(M7．5)。应该注意的是,从地震学的角度来看它们分属3种不同类型的地震。为了使非专业人员也容易理解,我将这3种不同类型的地震称之为“地震三兄弟”。这3兄弟,老大、老二在宫城县附近及其洋面上已和谐地出现,不久,老三也欲粉墨登场。  相似文献