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41.
Javier Rodríguez Zaurín Joanna Holt Clive N. Tadhunter Rosa M. González Delgado 《Astrophysics and Space Science》2009,324(2-4):225-229
We use long-slit spectra taken with the William Herschel Telescope on La Palma and high-resolution Hubble Space Telescope imaging to study the gas kinematic in the halo of the ultraluminous infrared/radio galaxy PKS1345+12 (z=0.122). Our long-slit spectra show line splitting at the locations of massive star clusters ( $10^{6}<M_{\mathrm{SSC}}^{\mathrm{YSP}}<10^{7}$ M⊙), indicating that they are moving at up to 450 km?s?1 with respect to the local ambient gas. Given their kinematics, it is plausible that these super star clusters have been formed either in fast-moving gas streams or tidal tails that are falling back into the nuclear regions as part of the merger process, or as a consequence of jet-induced star formation linked to the extended, diffuse radio emission detected in the halo of the galaxy. 相似文献
42.
Enrique Pérez Richard de Grijs Rosa M. González Delgado 《Astrophysics and Space Science》2009,324(2-4):79-81
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45.
Sandro Conticelli Sara Marchionni Davide Rosa Guido Giordano Elena Boari Riccardo Avanzinelli 《Contributions to Mineralogy and Petrology》2009,157(1):41-63
The Roccamonfina volcano is characterised by two stages of volcanic activity that are separated by volcano-tectonic caldera
collapses. Ultrapotassic leucite-bearing rocks are confined to the pre-caldera stage and display geochemical characteristics
similar to those of other volcanoes in the Roman Province. After the major sector collapse of the volcano, occurred at ca.
400 ka, shoshonitic rocks erupted from cinder cones and domes both within the caldera and on the external flanks of the pre-caldera
Roccamonfina volcano. On the basis of new trace element and Sr–Nd–Pb isotope data, we show that the Roccamonfina shoshonitic
rocks are distinct from shoshonites of the Northern Roman Province, but are very similar to those of the Neapolitan volcanoes.
The last phases of volcanic activity erupted sub-alkaline magmas as enclaves in trachytic domes, and as lavas within the Monte
Santa Croce dome. Ultrapotassic rocks of the pre-caldera composite volcano are plagioclase-bearing leucitites characterised
by high levels of incompatible trace elements with an orogenic signature having troughs at Ba, Ta, Nb, and Ti, and peaks at
Cs, K, Th, U, and Pb. Initial values of 87Sr/86Sr range from 0.70926 to 0.70999, 143Nd/144Nd ranges from 0.51213 to 0.51217, while the lead isotope rations vary between 18.788–18.851 for 206Pb/204Pb, 15.685–15.701 for 207Pb/204Pb, and 39.048–39.076 for 208Pb/204Pb. Shoshonites show a similar pattern of trace element depletions and enrichments to the earlier ultrapotassic leucite-bearing
rocks but have a larger degree of differentiation and lower concentrations of incompatible trace elements. On the other hand,
shoshonitic rocks have Sr, Nd, and Pb isotopes consistently different than pre-caldera ultrapotassic leucite-bearing rocks.
87Sr/86Sr ranges from 0.70665 to 0.70745, 143Nd/144Nd ranges from 0.51234 to 0.51238, 206Pb/204Pb ranges from 18.924 to 19.153, 207Pb/204Pb ranges from 15.661 to 15.694, and 208Pb/204Pb ranges from 39.084 to 39.212. High-K calc-alkaline samples have intermediate isotopic values between ultrapotassic plagioclase
leucitites and shoshonites, but the lowest levels of incompatible trace element contents. It is argued that ultrapotassic
magmas were generated in a modified lithospheric mantle after crustal-derived metasomatism. Interaction between the metasomatic
agent and lithospheric upper mantle produced a low-melting point metasomatised veined network. The partial melting of the
veins alone produced pre-caldera leucite-bearing ultrapotassic magmas. It was possibly triggered by either post-collisional
isotherms relaxation or increasing T°C due increasing heat flow through slab tears. Shoshonitic magmas were generated by further melting, at higher temperature,
of the same metasomatic assemblage with addition 10–20% of OIB-like astenospheric mantle material. We suggest that addition
of astenospheric upper mantle material from foreland mantle, flowing through slab tearing after collision was achieved.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
46.
The broad-spectrum herbicide glyphosate has become the largest-selling crop-protection product worldwide. The increased use of glyphosate is associated with the appearance of a growing number of tolerant or resistant weeds, with socio-environmental consequences apart from the loss of productivity. In 2002, a glyphosate-resistant biotype of johnsongrass (Sorghum halepense (L.)) appeared in Argentina and now covers at least 10,000 ha. This paper analyzes the driving forces behind the emergence and spread of this weed and also examines management responses and their implications.Preventive strategies against glyphosate-resistant johnsongrass fail because of the institutional setting. Reactive measures, however, transfer the risks to the society and the environment through the introduction of novel genetically modified crops that allow the use of yet more herbicide. This in turn reinforces the emergence of herbicide-resistant weeds, constituting a new phenomenon of intensification, the “transgenic treadmill”. 相似文献
47.
Alejandro Lara Andrea Borgazzi Odim Jr. Mendes Reinaldo R. Rosa Margarete Oliveira Domingues 《Solar physics》2008,248(1):155-166
We have constructed a time series of the number of coronal mass ejections (CMEs) observed by SOHO/LASCO during solar cycle
23. Using spectral analysis techniques (the maximum entropy method and wavelet analysis) we found short-period (< one year)
semiperiodic activity. Among others, we found interesting periodicities at 193, 36, 28, and 25 days. We discuss the implications
of such short-period activity in terms of the emergence and escape of magnetic flux from the convection zone, through the
low solar atmosphere (where these periodicities have been found for numerous activity parameters), toward interplanetary space.
This analysis shows that CMEs remove the magnetic flux in a quasiperiodic process in a way similar to that of magnetic flux
emergence and other solar eruptive activity. 相似文献
48.
Maria Di Rosa Chiara Frassi Michele Marroni Francesca Meneghini Luca Pandolfi 《地学学报》2020,32(1):34-43
Despite the important role played by the Sardinia‐Corsica block in the reconstruction of the Western Mediterranean geodynamics, the extent of involvement of the “Autochthonous” European margin exposed in Corsica (France) (i.e., Hercynian Corsica) in the Alpine orogeny remains uncertain. Stratigraphic and sedimentological studies in the post‐Variscan deposits on the Hercynian Corsica are scarce and even scarcer are the structural and metamorphic constraints. To face these uncertainties, we present new stratigraphic, structural and metamorphic data from the area of Razzo Bianco, Central Corsica, where a complete sequence belonging to the European continental margin is exposed. Field and structural investigations demonstrate that the sequence represents the easternmost edge of the downgoing European plate. Metamorphic studies on the Eocene deposits indicate that the margin was buried at depth up to blueschist facies conditions and, subsequently, it was progressively exhumed mainly through the activation of oblique top‐to‐the NW shear zones. 相似文献
49.
Origin of peraluminous granites and granodiorites, Iberian massif, Spain: an experimental test of granite petrogenesis 总被引:27,自引:0,他引:27
Antonio Castro Alberto E. Patiño Douce L. Guillermo Corretgé Jesús D. de la Rosa Mohammed El-Biad Hassan El-Hmidi 《Contributions to Mineralogy and Petrology》1999,135(2-3):255-276
The discrimination between potential source materials involved in the genesis of Iberian granites and granodiorites, as well
as the role of mantle-crust interactions, are examined using constraints imposed by melting experiments, melting-assimilation
experiments and Sr-Nd isotope systematics. The Sr-Nd isotope relationships indicate the existence of different genetic trends
in which juvenile mantle materials are involved by different mechanisms: (1) a source trend, traced by a particular evolution
of the pre-Hercynian basement and indicating mantle participation at the time of sedimentation; (2) a set of magmatic trends
traced by gabbro-tonalite-enclave-granodiorite associations, implying the incorporation of new mantle material at the time
of granite generation. These relationships strongly support a pure crustal origin for the peraluminous leucogranites, derived
from partial melting of crustal protoliths, and a hybrid origin for the peraluminous granodiorites. These granodiorites are
the most abundant granitic rocks of the Central Iberian zone (CIZ) of the Iberian massif, implying that processes of hybridisation
by assimilation and/or magma mixing played an important role in granitoid production during the Hercynian orogeny. These hypotheses
have been tested by means of melting and assimilation experiments. Melting experiments in the range 800–900 °C and at pressures
of 3, 6, 10 and 15 kbar indicate that: (1) several potential source materials such as Bt-Ms gneisses and metagreywackes are
suitable for the production of peraluminous leucogranite melts; (2) the melt compositions are always leucogranitic, regardless
of pressure; (3) pressure exerts a strong influence on the fertility of the source: experiments at 3 kbar produce more than
20 vol% of melt, compared with less than 5 vol% of melt produced at 10 and 15 kbar and at the same temperature. The melting-assimilation
experiments carried out at 1000 °C and 4, 7 and 10 kbar and using a proportion of 50% gabbro and 50% gneiss give high melt
proportions (more than 50 vol.%) and noritic residues. These melts have the composition of leucogranodiorites, and overlap
with part of the compositional range of peraluminous granodiorites of the Iberian massif. The generation of more mafic granodiorites
may be explained by the incorporation of some residual orthopyroxene to the granodiorite magmas. The low solubility of Fe + Mg
prevents the generation of granodiorite melts with more than 3 wt% of MgO + FeO at all crustal pressures. The large volumes
of peraluminous, hybrid granodiorites, produced by assimilation of crustal rocks by mantle magmas, imply that an important
episode of crustal growth took place during the Late-Palaeozoic Hercynian orogeny in the Iberian massif.
Received: 30 June 1998 / Accepted: 27 November 1998 相似文献
50.
Eugenio Nicotra Marco Viccaro Rosanna De Rosa Marco Sapienza 《Bulletin of Volcanology》2014,76(8):1-24
Critical to understanding explosive eruptions is establishing how accurately representative pyroclasts are of processes during magma vesiculation and fragmentation. Here, we present data on densities, and vesicle size and number characteristics, for representative pyroclasts from six silicic eruptions of contrasting size and style from Raoul volcano (Kermadec arc). We use these data to evaluate histories of bubble nucleation, coalescence, and growth in explosive eruptions and to provide comparisons with pumiceous dome carapace material. Density/vesicularity distributions show a scarcity of pyroclasts with ~65–75 % vesicularity; however, pyroclasts closest to this vesicularity range have the highest bubble number density (BND) values regardless of eruptive intensity or style. Clasts with vesicularities greater than this 65–75 % “pivotal” vesicularity range have decreasing BNDs with increasing vesicularities, interpreted to reflect continuing bubble growth and coalescence. Clasts with vesicularities less than the pivotal range have BNDs that decrease with decreasing vesicularity and preserve textures indicative of processes such as stalling and open system degassing prior to vesiculation in a microlite-rich magma, or vesiculation during slow ascent of degassing magma. Bubble size distributions (BSDs) and BNDs show variations consistent with 65–75 % representing the vesicularity at which vesiculating magma is most likely to undergo fragmentation, consistent with the closest packing of spheres. We consider that the observed vesicularity range may reflect the development of permeability in the magma through shearing as it flows through the conduit. These processes can act in concert with multiple nucleation events, generating a situation of heterogeneous bubble populations that permit some regions of the magma to expand and bubbles to coalesce with other regions in which permeable networks are formed. Fragmentation preserves the range in vesicularity seen as well as any post-fragmentation/pre-quenching expansion which may have occurred. We demonstrate that differing density pyroclasts from a single eruption interval can have widely varying BND values corresponding to the degree of bubble maturation that has occurred. The modal density clasts (the usual targets for vesicularity studies) have likely undergone some degree of bubble maturation and are therefore may not be representative of the magma at the onset of fragmentation. 相似文献