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Carlo Doglioni Eugenio Carminati Mattia Crespi Marco Cuffaro Mattia Penati Federica Riguzzi 《地学前缘(英文版)》2015,6(3):401-418
The possibility of a net rotation of the lithosphere with respect to the mantle is generally overlooked since it depends on the adopted mantle reference frames,which are arbitrary.We review the geological and geophysical signatures of plate boundaries,and show that they are markedly asymmetric worldwide.Then we compare available reference frames of plate motions relative to the mantle and discuss which is at best able to fit global tectonic data.Different assumptions about the depths of hotspot sources(below or within the asthenosphere,which decouples the lithosphere from the deep mantle) predict different rates of net rotation of the lithosphere relative to the mantle.The widely used no-net-rotation(NNR) reference frame,and low(0.2°-0.4° /Ma) net rotation rates(deep hotspots source) predict an average net rotation in which some plates move eastward relative to the mantle(e.g.,Nazca).With fast(1° /Ma) net rotation(shallow hotspots source),all plates,albeit at different velocity,move westerly along a curved trajectory,with a tectonic equator tilted about 30° relative to the geographic equator.This is consistent with the observed global tectonic asymmetries. 相似文献
83.
Steven J. Schwartz Timothy Horbury Christopher Owen Wolfgang Baumjohann Rumi Nakamura Patrick Canu Alain Roux Fouad Sahraoui Philippe Louarn Jean-André Sauvaud Jean-Louis Pinçon Andris Vaivads Maria Federica Marcucci Anastasios Anastasiadis Masaki Fujimoto Philippe Escoubet Matt Taylor Steven Eckersley Elie Allouis Marie-Claire Perkinson 《Experimental Astronomy》2009,23(3):1001-1015
Most of the visible universe is in the highly ionised plasma state, and most of that plasma is collision-free. Three physical
phenomena are responsible for nearly all of the processes that accelerate particles, transport material and energy, and mediate
flows in systems as diverse as radio galaxy jets and supernovae explosions through to solar flares and planetary magnetospheres.
These processes in turn result from the coupling amongst phenomena at macroscopic fluid scales, smaller ion scales, and down
to electron scales. Cross-Scale, in concert with its sister mission SCOPE (to be provided by the Japan Aerospace Exploration
Agency—JAXA), is dedicated to quantifying that nonlinear, time-varying coupling via the simultaneous in-situ observations
of space plasmas performed by a fleet of 12 spacecraft in near-Earth orbit. Cross-Scale has been selected for the Assessment
Phase of Cosmic Vision by the European Space Agency.
相似文献
84.
Tudisco Erika Vitone Claudia Mondello Cristina Viggiani Gioacchino Athanasopoulos Stefanos Hall Stephen A. Cotecchia Federica 《Acta Geotechnica》2022,17(5):1585-1603
Acta Geotechnica - This paper reports the main results of an experimental study on the mechanics of intensely fissured natural clays, extending our previous studies on scaly clay from Santa Croce... 相似文献
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Variation of polycyclic aromatic hydrocarbons (PAHs) levels was assessed in Tapes philippinarum from the Lagoon of Venice. Clams were transplanted from a polluted area next to Porto Marghera to two rearing areas of the Southern Lagoon. Analyses of PAHs were made in sediments and clams by GC/MS at first sampling and after 30, 60 and 180 days. Principal component analysis was performed to elucidate bioaccumulation and depuration pattern and input sources. Biota-Sediment-Accumulation-Factor (BSAF) was applied to evaluate the PAHs input sources from sediment. Condition index was calculated to compare the seasonal variation of clam tissue to PAHs levels. To propose results not affected by seasonal changes in flesh weight of clams, the approach based on the calculation of PAHs/SW index was applied. From the results, it was concluded that PAHs/SW index is more recommendable to asses temporal variation of PAHs levels in Manila clams. 相似文献
88.
Federica Schiavi Katsura Kobayashi Takuya Moriguti Eizo Nakamura Massimo Pompilio Massimo Tiepolo Riccardo Vannucci 《Contributions to Mineralogy and Petrology》2010,159(4):541-561
During its 1800-year-long persistent activity the Stromboli volcano has erupted a highly porphyritic (HP) volatile-poor scoriaceous
magma and a low porphyritic (LP) volatile-rich pumiceous magma. The HP magma is erupted during normal Strombolian explosions
and lava effusions, while the LP one is related to more energetic paroxysms. During the March–April 2003 explosive activity,
Stromboli ejected two typologies of juvenile glassy ashes, namely highly vesicular LP shards and volatile-poor HP shards.
Their textural and in situ chemical characteristics are used to unravel mutual relationships between HP and LP magmas, as
well as magma dynamics within the shallow plumbing system. The mantle-normalized trace element patterns of both ash types
show the typical arc-lava pattern; however, HP glasses possess incompatible element concentrations higher than LP glasses,
along with Sr and Eu negative anomalies. HP shards are generally characterized by higher Li contents (to ~20 ppm) and lower
δ7Li values (+1.2 to −3.8‰) with respect to LP shards (Li contents of 7–14 ppm and δ7Li ranging between +4.6 and +0.9‰). Fractional crystallization models based on major and trace element compositions, combined
with a degassing model based on open-system Rayleigh distillation and on the assumption that melt/fluidDLi > 1, show that abundant (~30%) plagioclase precipitation and variable degrees of degassing can lead the more primitive LP
magma to evolve toward a differentiated (isotopically lighter) HP magma ponding in the upper conduit and undergoing slow continuous
degassing-induced crystallization. This study also evidences that in March 2003 Stromboli volcano poured out a small early
volume of LP magma that traveled slower within the conduit with respect to later and larger volumes of fast ascending LP magma
erupted during the April 5 paroxysm. The different ascent rates and cooling rates of the two LP magma batches (i.e., pre-
and post-paroxysm) resulted in small, but detectable, differences in their chemical signatures. Finally, this study highlights
the high potential of in situ investigations of juvenile glassy ashes in petrologic and geochemical monitoring the volcanic
activity and of Li isotopes as tracers of degassing processes within the shallow plumbing system. 相似文献
89.
The evolution of mammalian communities is a significant tool for reconstructing past environments and climate. In this paper, a palaeoecological and palaeoenvironmental reconstruction based on the study of the Italian mammal faunas ranging from Middle Pliocene to the Holocene is presented using the cenogram method and quantification of temperatures based on arvicolid species richness. These analyses reveal open and arid conditions during glacial periods and less open and more humid conditions during interglacials, with some differences between north and central–south Italy. Northern and Southern communities reflect similar trends in the evolution of palaeoenvironments and in the variation of the temperatures, but differences in estimated temperatures, which indicate a more temperate climate for southern Italy throughout the period, are considered here. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
90.