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1.
The Meseta de Somuncura forms the largest basaltic plateau (20 000 km2 ) of southern Argentina (extra-Andean domain). Most of these tholeiitic to alkaline rocks were extruded at ˜ 25 Ma (late Oligocene). The absence of rifting–thinning processes, plume activity, or slab-window phenomena leaves only one major possibility for the generation of Somuncura: asthenospheric ('OIB-like') corner flow leading to a transient thermal anomaly above the subducting plate. It is suggested herein that the intake of hot asthenosphere was forced into a favourable topography (concave-up) of the subducting plate, when a major plate reorganization event (Farallon to Nazca) was taking place in late Oligocene to early Miocene time. The fast and vigorous intake of asthenosphere would have been induced by slab roll-back, leading to decoupling of the subducting plate. The Somuncura volcanic episode can be regarded as a marker of the passage from the extremely oblique subduction of Farallon, to the birth of the Nazca plate and roughly perpendicular convergence between South America and Nazca. 相似文献
2.
3.
Victor Cárdenes Alvaro Rubio-Ordoñez Carmela Monterroso Lope Calleja 《Chemie der Erde / Geochemistry》2013
This article analyzes the geochemical and mineralogical composition of the roofing slate deposits of the Iberian Peninsula. Most roofing slate deposits are found on Middle and Upper Ordovician terrains, although there are also deposits in the Ediacaran, Cambrian and Devonian terrains. Samples of slate were taken in most of the active quarries of the Iberian Peninsula, and being analyzed by X-ray Diffraction and Fluorescence. Each lithotect or slate productive formation has its own specific proportions of major and trace elements, being able to differentiate between them by using these relationships. This fact is particularly interesting in geological exploration and prospecting, as it allows knowing exactly the slate lithotect, and also for restoration work in the architectural heritage, due to the ability of identifying the source of the original slate tiles. 相似文献
4.
Flavia Burger Alvaro Ayala David Farias Thomas E. Shaw Shelley MacDonell Ben Brock James McPhee Francesca Pellicciotti 《水文研究》2019,33(2):214-229
We present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response, and runoff generation from a high‐elevation catchment in central Chile over the period 2000–2015 to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000 and 2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years. 相似文献
5.
6.
Wolf Uwe Reimold Alvaro Penteado Crsta Maximilian Hasch Astrid Kowitz Natalia Hauser Joana Paula Sanchez Luiz Sergio Amarante Simes Grace Juliana de Oliveira Patrice T. Zaag 《Meteoritics & planetary science》2019,54(10):2384-2397
Cerro do Jarau is a conspicuous, circular morpho‐structural feature in Rio Grande do Sul State (Brazil), with a central elevated core in the otherwise flat “Pampas” terrain typical for the border regions between Brazil and Uruguay. The structure has a diameter of approximately 13.5 km. It is centered at 30o12′S and 56o32′W and was formed on basaltic flows of the Cretaceous Serra Geral Formation, which is part of the Paraná‐Etendeka Large Igneous Province (LIP), and in sandstones of the Botucatu and Guará formations. The structure was first spotted on aerial photographs in the 1960s. Ever since, its origin has been debated, sometimes in terms of an endogenous (igneous) origin, sometimes as the result of an exogenous (meteorite impact) event. In recent years, a number of studies have been conducted in order to investigate its nature and origin. Although the results have indicated a possible impact origin, no conclusive evidence could be produced. The interpretation of an impact origin was mostly based on the morphological characteristics of the structure; geophysical data; as well as the occurrence of different breccia types; extensive deformation/silicification of the rocks within the structure, in particular the sandstones; and also on the widespread occurrence of low‐pressure deformation features, including some planar fractures (PFs). A detailed optical microscopic analysis of samples collected during a number of field campaigns since 2007 resulted in the disclosure of a large number of quartz grains from sandstone and monomict arenite breccia from the central part of the structure with PFs and feather features (FFs), as well as a number of quartz grains exhibiting planar deformation features (PDFs). While most of these latter grains only carry a single set of PDFs, we have observed several with two sets, and one grain with three sets of PDFs. Consequently, we here propose Cerro do Jarau as the seventh confirmed impact structure in Brazil. Cerro do Jarau, together with Vargeão Dome (Santa Catalina state) and Vista Alegre (Paraná State), is one of very few impact structures on Earth formed in basaltic rocks. 相似文献
7.
Climate change might lead to large shifts in tourist flows, with large economic implications. This article simulates the effect
of future climate change by the 2080s on outdoor international tourism expenditure within Europe. The assessment is based
on the statistical relationship between bed nights and a climate-related index of human comfort, after accounting for other
determinants of bed nights such as income and prices. It is concluded that climate change could have significant impacts on
the regional distribution of the physical resources supporting tourism in Europe. For example, in summer, Southern Europe
could experience climate conditions that are less favourable to tourism than the current climate, while countries in the North
could enjoy better conditions. The economic effects of these changes are likely to be sizeable, albeit difficult to assess.
Crucially, they are shown to depend on tourists’ temporal flexibility with respect to holiday planning. The greater the prominence
of institutional rigidities such as school holidays, the larger the differences between winning and losing regions in terms
of economic impact. 相似文献
8.
Günther J. Redhammer Fernando Cámara Matteo Alvaro Fabrizio Nestola Gerold Tippelt Sebastian Prinz Jan Simons Georg Roth Georg Amthauer 《Physics and Chemistry of Minerals》2010,37(10):685-704
A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) Å, β = 108.844(6)°, V = 442.75(16) Å3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T tr the thermal volume expansion is due to dilatation of the structure in the $(\bar{1}\,0\,1) A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) ?, β = 108.844(6)°, V = 442.75(16) ?3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters
and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T
tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds
to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T
tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T
tr the thermal volume expansion is due to dilatation of the structure in the ([`1] 0 1)(\bar{1}\,0\,1) plane, mostly along [0 1 0], and pure shear in the (0 1 0) plane due to the decrease of β. From comparison with silicate analogues, the germanate clinopyroxenes are more expansible, while the P21/c expands more than the C2/c phase. The evolution of Q
2 (calculated as the normalized intensity of b-type reflections) with T in the framework of the Landau theory has been done using a standard expression for a first order phase transition. We observe
a jump of Q
02 = 0.538(2) at T
tr, with T
c of 481(7) K, b/a = −2,290 K, and c/a = 3,192 K, and thus far from being tri-critical point. A closely related composition (LiFe3+Si2O6) shows an equivalent phase transition at 228 K, which is very close to the tri-critical point and 561 K cooler. This result
indicates that a change in the composition of tetrahedral sites can have dramatic effects on the P21/c ↔ C2/c displacive phase transition in clinopyroxenes. The major changes observed in the evolution of the crystal structure with
T are observed in the M2 polyhedron, with a volume decrease by ca. 13.3%, compared to ca. 1.3% observed in the M1 polyhedron.
The tetrahedra behave as rigid units with neither a significant change of volume at T > T
tr (<1‰), nor a change of tilting of the basal plane. No change in coordination is observed at T > T
tr in the M2 polyhedron, which remains sixfold coordinated although a strong deformation of this polyhedron is observed. This
deformation is related to a strong change by 51.4° at T
tr of the kinking angle (O3–O3–O3 angle) of the B-chain of tetrahedra, which switches from O-rotated to S-rotated [from 143.3(5)°
to 194.7(6)°]. The A-chain is S-rotated at T < T
tr [206.8(5)° at 703 K] and extends by 12° at the transition. 相似文献
9.
The effects of low-temperature on the crystal structure of a natural epidote [Ca1.925Fe0.745Al2.265Ti0.004Si3.037O12(OH), a = 8.8924(7), b = 5.6214(3), c = 10.1547(6)? and β = 115.396(8)° at room conditions, Sp. Gr. P21
/m] have been investigated with a series of structure refinements down to 100 K on the basis of X-ray single-crystal diffraction
data. The reflection conditions confirm that the space group is maintained within the T-range investigated. Structural refinements at all temperatures show the presence of Fe3+ at the octahedral M(3) site only [%Fe(M3) = 70.6(4)% at 295 K]. Only one independent proton site was located and two possible
H-bonds occur, with O(10) as donor and O(4) and O(2) as acceptors. The H-bonding scheme is maintained down to 100 K and is
supported by single crystal room-T polarised FTIR data. FTIR Spectra over the region 4,000–2,500 cm−1 are dominated by the presence of a strongly pleochroic absorption feature which can be assigned to protonation of O(10)–O(4).
Previously unobserved splitting of this absorption features is consistent with a NNN influence due to the presence of Al and
Fe3+ on the nearby M(3) site. An additional relatively minor absorption feature in FTIR spectra can be tentatively assigned to
protonation of O(10)–O(2). Low-T does not affect significantly the tetrahedral and octahedral bond distances and angles, even when distances are corrected
for “rigid body motions”. A more significant effect is observed for the bond distances of the distorted Ca(1)- and Ca(2)-polyhedra,
especially when corrected for “non-correlated motion”. The main low-T effect is observed on the vibrational regime of the atomic sites, and in particular for the two Ca-sites. A significant reduction
of the magnitude of the thermal displacement ellipsoids, with a variation of U
eq
(defined as one-third of the trace of the orthogonalised U
ij
tensor) by ~40% is observed for the Ca-sites between 295 and 100 K. Within the same T-range, the U
eq
of the octahedral and oxygen sites decrease similarly by ~35%, whereas those of the tetrahedral cations by ~22%. 相似文献
10.
Alvaro Giménez 《Experimental Astronomy》1994,5(1-2):91-97
The observation of apsidal motions in eclipsing binaries is a very rewarding area of research which requires only moderate or small telescopes equipped with a photoelectric photometer. Important contributions can be made to the study of stellar internal structure through these observations, as well as the verification of the theory of general relativity using the equations of orbital motion. The main objectives of such an observational effort are described, together with a list of candidate binary systems. An appeal to photometrists with small telescopes around the world is made to observe these eccentric and well-detached eclipsing binaries. 相似文献