Sources of dissolved REE in mountainous streams draining granitic rocks, Sierras Pampeanas (Córdoba, Argentina)   总被引：1，自引：0，他引：1  

M. Gabriela García  Karina L. Lecomte  Andrea I. Pasquini  Stella M. Formica  Pedro J. Depetris 《Geochimica et cosmochimica acta》2007,71(22):5355-5368

Stream waters draining granitic terrains from the highest part (850 to 2200 m a.s.l.) of Sierras Pampeanas (Córdoba, Argentina, ∼32°S, ∼65°W) were sampled in order to define sources and distribution of dissolved rare earth elements (REE), and to describe the geochemical processes that govern their mobility. The contribution of the regional granite to the dissolved REE pool in stream water is limited due to the physical conditions predominating in the area (i.e., steep slopes and semiarid climate). Therefore, precipitation is considered a seasonally significant source controlling REE concentration in stream water. Dissolved REE concentrations are inversely correlated with monthly precipitation and rainfall frequency. During the rainy season (i.e., the austral summer) REE concentrations in stream water are lower than during the dry season (i.e., austral winter). Such low concentrations reflect the balance between the REE input from precipitation and their removal by adsorption. In contrast, during the dry season, the longer residence time of water within fractures and colluvium determines an increased REE concentration in the base flow. Lower pH values also contribute to raise REE concentration through desorption from mineral surfaces.  相似文献   

Late Pleistocene–Holocene environments in Valle Carbajal, Tierra del Fuego, Argentina   总被引：1，自引：0，他引：1  

Ana María Borromei  Andrea Coronato  Mirta Quattrocchio  Jorge Rabassa  Silvia Grill  Claudio Roig   《Journal of South American Earth Sciences》2007,23(4):321-335

The authors discuss Late Pleistocene–Holocene depositional environments in one of the Fuegian Andes valleys on the basis of palynological, geomorphological, and sedimentological analyses from two sites located near the Beagle Channel. The results obtained at these localities reinforce and refine the Late Pleistocene–Holocene climatic pattern previously recorded there. A colder period, associated with the Younger Dryas stadial event, is suggested by low Nothofagus pollen frequency, and communities of grass, low scrub, and shrub heath expanded into the low/middle slopes (10,310 ¹⁴C yr BP). By ca. 9500 ¹⁴C yr BP, warmer and drier conditions occurred, as evidenced by the development of open-grown vegetation in the valley floors (pollen zone O-3), followed by the expansion of open Nothofagus woodland (pollen zone O-2) in the middle Holocene. The milder climate subsequently changed, as indicated by the spreading of the closed forest and mire (pollen zone O-1), to more humid and cooler conditions during the last ca. 5000 yr BP.  相似文献   

Determining the Sula block kinematics in the triple junction area in Indonesia by GPS   总被引：1，自引：0，他引：1  

Andrea Walpersdorf  Christophe Vigny  P. Manurung  C. Subarya  & S. Sutisna 《Geophysical Journal International》1998,135(2):351-361

  相似文献   

New Definition of Discovery for Solar System Objects     

Andrea Milani  Giovanni F. Gronchi  Zoran Knežević 《Earth, Moon, and Planets》2007,100(1-2):83-116

We propose a new formal definition of discovery for a Solar System object. It is based on an objective and mathematically rigorous algorithm to assess when a set of observations is enough to constitute a discovery. When this definition is satisfied, in almost all cases the orbit is defined well enough to establish the nature of the object discovered (Main Belt vs. Near Earth Asteroid, Trans-Neptunian vs. long period comet). The frequency of occurrence of exceptions is estimated by a set of numerical experiments. The availability of a non-subjective definition of discovery allows some rules to be adopted for the assignment of discovery credit with a minimum risk of dispute. Such rules should be fair, encourage good practice by the observers and acknowledge the contribution of the orbit computers providing the identifications and the orbits, as well as the one of all the contributing observers.  相似文献   

International viewpoint and news     

Andrea Martin  Philip E. LaMoreaux 《Environmental Geology》2007,52(6):1223-1224

  相似文献   

Using XMM-Newton to measure the spectrum of the Vela pulsar and its phase variation     

Armando Manzali  Andrea De Luca  Patrizia A. Caraveo 《Astrophysics and Space Science》2007,308(1-4):601-605

We report on our analysis of two XMM-Newton observations of the Vela pulsar performed in December 2000 (total exposure time: 96.5 ks). We succeeded in resolving the pulsar spectrum from the surrounding bright nebular emission taking advantage both of the accurate calibration of the EPIC point spread function and of the Chandra/HRC surface brightness map of the nebula. This made it possible to assess to pulsar spectral shape disentangling its thermal and non-thermal components. Exploiting the photon harvest, we have also been able to perform a phase-resolved study of the pulsar emission.   相似文献   

Jet Deflection by a Quasi-Steady-State Side Wind in the Laboratory     

David J. Ampleford  Andrea Ciardi  Sergey V. Lebedev  Simon N. Bland  Simon C. Bott  Jeremy P. Chittenden  Gareth N. Hall  Adam Frank  Eric Blackman 《Astrophysics and Space Science》2007,307(1-3):29-34

We present experimental data on the steady state deflection of a highly supersonic jet by a side-wind in the laboratory. The use of a long interaction region enables internal shocks to fully cross the jet, leading to the development of significantly more structure in the jet than in previous work with a similar setup (Lebedev et al., 2004). The ability to control the length of the interaction region in the laboratory allows the switch between a regime representing a clumpy jet or wind and a regime similar to a slowly varying mass loss rate. The results indicate that multiple internal oblique shocks develop in the jet and the possible formation of a second working surface as the jet attempts to tunnel through the ambient medium.  相似文献   

XMM–Newton observations of soft gamma-ray repeaters     

Sandro Mereghetti  Paolo Esposito  Andrea Tiengo 《Astrophysics and Space Science》2007,308(1-4):13-23

All the confirmed Soft Gamma-ray Repeaters have been observed with the EPIC instrument on the XMM–Newton satellite. We review the results obtained in these observations, providing the most accurate spectra on the persistent X-ray emission in the 1–10 keV range for these objects, and discuss them in the context of the magnetar interpretation.   相似文献   

The continental record of Ediacaran volcano‐sedimentary successions in southern Brazil and their global implications     

Liliane Janikian  Renato Paes De Almeida  Ricardo Ivan Ferreira Da Trindade  Antonio Romalino Santos Fragoso‐Cesar  Manoel Souza D′Agrella‐Filho  Elton Luis Dantas  Eric Tohver 《地学学报》2008,20(4):259-266

The Ediacaran is one of the most important periods on Earth evolution, including the first appearance of soft‐bodied macrofossils, major climatic changes and a supposed rise in free oxygen. In southernmost Brazil, this period is represented by Camaquã Supergroup, including the Bom Jardim Group and the Acampamento Velho Formation, both of which record continental palaeoenvironmental changes in a more than 5000 m thick stratigraphic succession. Age constraints are given by seven Ar‐Ar and U‐Pb determinations on volcanic rocks, which bracket these units between c. 605 and 574 Ma, revealing the best dated and most continuous documented Ediacaran continental succession to date. Depositional systems evolution supports a Phanerozoic‐type glacial context during the last Neoproterozoic glacial event and presents the Picada das Graças Formation (580 ± 3.6 Ma) as the first dated non‐glacial unit coeval to the Gaskiers Formation.  相似文献   

Cosmic stellar relics in the Galactic halo     

Stefania Salvadori  Raffaella Schneider  Andrea Ferrara 《Monthly notices of the Royal Astronomical Society》2007,381(2):647-662

  相似文献