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101.
Renato L. Prado Isabel C. Espin Fenoll Irfan Ullah Gianna C. Maciel Miura Alvaro P. Crsta Roberto P. Zanon dos Santos Wolf Uwe Reimold Vagner R. Elis Erico Imbernon Claudio Riccomini Liliana Alcazar Diogo 《Meteoritics & planetary science》2019,54(10):2357-2372
The origin of the nearly circular Colônia structure, located at the southwestern edge of the city of São Paulo, Brazil, has been the subject of a long‐standing debate, ever since the 1960s when the structure was first investigated by geophysical methods. The structure still raises interest for geological research, as its sedimentary infill holds important paleoclimatic information about the evolution of the tropical rainforest, as well as the interplay between the South American summer monsoon, the Intertropical Convergence Zone, and the southern Westerly wind belt—for possibly as long as several million years. In addition, the search for evidence to conclusively establish the origin of this structure continues, and the answer most likely lies in the lower portions of the basin's sedimentary infill, which also holds a significant potential for underground water resources. Here, we present the results from recent seismic (reflection and HVSR), gravimetric, and geoelectrical surveys. They have provided a reliable image of the sedimentary infill, and the maximum depth to basement within the structure has been constrained consistently by the different methods to approximately ?400 m. The geophysical data have also allowed to map the lateral contact between the crystalline basement rocks and the sedimentary infill, which indicates a diameter of approximately 2.8 km for the sedimentary basin, with 3.6 km being the diameter of the outermost limit of the structure. A total of six seismic stratigraphic boundaries were identified within the sedimentary infill, providing a framework for the planning of a deep drilling campaign and subsequent sampling program aimed at geological and paleoclimatology studies. 相似文献
102.
Water balance,nutrient and carbon export from a heath forest catchment in central Amazonia,Brazil
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Fabrício B. Zanchi Maarten J. Waterloo Andrés Peralta Tapia Maria S. Alvarado Barrientos Marcos A. Bolson Flávio J. Luizão Antônio O. Manzi Albertus J. Dolman 《水文研究》2015,29(17):3633-3648
Carbon storage values in the Amazon basin have been studied through different approaches in the last decades in order to clarify whether the rainforest ecosystem is likely to act as a sink or source for carbon in the near future. This water balance, dissolved organic carbon (DOC) and nutrient export study were carried out in a micro‐scale heath forest (Campina) catchment in central Amazonia, Brazil. For a 1‐year study period (18 March 2007 until 19 March 2008), rainfall amounted to 3054 mm; of which, 1532 mm was evaporated by the forest (4.1 mm day?1). Rainfall interception loss amounted to 15.6% of gross rainfall. Surface runoff amounted to 485 mm, whereas another 1071 mm was discharged as regional groundwater outflow. Accumulated DOC exports in surface runoff amounted to 15.3 g m?2 year?1, whereas the total carbon exported was 55.9 g m?2. This is much higher than that observed for a nearby tall rainforest catchment in central Amazonia (DOC export < 20 g m?2). As Campina heath forest areas cover a significant proportion of the Amazon Basin, these differences in ecosystem hydrological carbon exports should be taken into account in future studies assessing the carbon budget for the Amazon Basin. Macro‐nutrient exports were low, but those of calcium and potassium were higher than those observed for tall rainforest in the Amazon, which may be caused by a lower retention capacity of the heath forest ecosystem. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
103.
104.
Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure,Brazil
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Lidia Pittarello Fabrizio Nestola Cecilia Viti Alvaro Penteado Crósta Christian Koeberl 《Meteoritics & planetary science》2015,50(7):1228-1243
Shatter cones are one of the most widely recognized pieces of evidence for meteorite impact events on Earth, but the process responsible for their formation is still debated. Evidence of melting on shatter cone surfaces has been rarely reported in the literature from terrestrial impact craters but has been recently observed in impact experiments. Although several models for shatter cones formation have been proposed, so far, no one can explain all the observed features. Shatter cones' from the Vista Alegre impact structure, Brazil, formed in fine‐grained basalt of the Jurassic‐Cretaceous Serra Geral Formation (Paraná large igneous province). A continuous quenched melt film, consisting of a crystalline phase, mica, and amorphous material, decorates the striated surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine‐grained matrix, occur subparallel to the striated surface. Several techniques were applied to characterize the crystalline phase in the melt, including Raman spectroscopy and transmission electron microscopy. Results are not consistent with any known mineral, but they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of tensile fracturing at the tip of a fast propagating shock‐induced rupture, which led to the formation of shatter cones at the tail of the shock front, likely during the early stage of the impact events. 相似文献
105.
We investigate the seismic properties of modern crustal seismicity in the northwestern Sierras Pampeanas of the Andean retroarc region of Argentina. We modelled the complete regional seismic broadband waveforms of two crustal earthquakes that occurred in the Sierra de Velasco on 28 May 2002 and in the Sierra de Ambato on 7 September 2004. For each earthquake we obtained the seismic moment tensor inversion (SMTI) and tested for its focal depth. Our results indicate mainly thrust focal mechanism solutions of magnitudes Mw 5.8 and 6.2 and focal depths of 10 and 8 km, respectively. These results represent the larger seismicity and shallower focal depths in the last 100 years in this region. The SMTI 2002 and 2004 solutions are consistent with previous determinations for crustal seismicity in this region that also used seismic waveform modelling. Taken together, the results for crustal seismicity of magnitudes ≥5.0 in the last 30 years are consistent with an average P-axis horizontally oriented by an azimuth of 125° and T-axis orientation of azimuth 241° and plunge 58°. This modern crustal seismicity and the historical earthquakes are associated with two active reverse faulting systems of opposite vergences bounding the eastern margin of the Sierra de Velasco in the south and the southwestern margin of the Sierra de Ambato in the north. Strain recorded by focal mechanisms of the larger seismicity is very consistent over this region and is in good agreement with neotectonic activity during the last 11,000 years by Costa (2008) and Casa et al. (in press); this shows that the dominant deformation in this part of the Sierras Pampeanas is mainly controlled by contraction. Seismic deformation related to propagation of thrusts and long-lived shear zones of this area permit to disregard previous proposals, which suggested an extensional or sinistral regime for the geomorphic evolution since Pleistocene. 相似文献
106.
Matteo Alvaro Fabrizio Nestola Fernando Cámara M. Chiara Domeneghetti Vittorio Tazzoli 《Physics and Chemistry of Minerals》2011,38(5):379-385
A high-pressure single-crystal X-ray diffraction study has been carried out on a P21/c natural Mg-rich pigeonite sample with composition ca. Wo6En76Fs18 using a diamond anvil-cell. The unit-cell parameters were determined at 14 different pressures to 7.14 GPa. The sudden disappearance of the b-type reflections (h + k = odd) and a strong discontinuity (about 2.8%) in the unit-cell volume indicated a first-order P21/c–C2/c phase transition between 4.66 and 4.88 GPa. The P(V) data of the P21/c phase were fitted to 4.66 GPa by a third-order Birch–Murnaghan equation of state (BM3 EoS), whereas the limited number of experimental data collected within the C2/c phase between 4.88 and 7.14 GPa were fitted using the same equation of state but with K′ constrained to the value obtained for the P21/c fitting. The equation of state coefficients are V 0 = 424.66(6) Å3, K T0 = 104(2) GPa and K′ = 8(1) for the P21/c phase, and V 0 = 423.6(1) Å3, K T0 = 112.4(8) GPa, and K′ fixed to 8(1) for the C2/c phase. The axial moduli for a, b, and c for the P21/c phase were obtained using also a BM3-EoS, while for the C2/c phase only a linear calculation could be performed, and therefore the same approach was applied for comparison also to the P21/c phase. In general the C2/c phase exhibits axial compressibilities (β c > β a >> β b) lower than those of the P21/c phase (β b > β c ≈ β a; similar to those found in previous studies in clinopyroxenes and orthopyroxenes). The lower compressibility of the C2/c phase compared with that of the P21/c could be ascribed to the greater stiffness along the b direction. A previously published relationship between P c and M2 average cation radius (i.r.) has been updated using all the literature data on P21/c clinopyroxene containing large cations at M2 site and our new data. The following weighted regression was obtained: P c (GPa) = 26(4) ? 28(5) × i.r (Å), R 2 = 0.97. This improved equation can be used to predict the critical pressure of natural P21/c clinopyroxene samples just knowing the composition at M2 site. 相似文献
107.
Gustavo González Bonorino Víctor Rinaldi Liliana del Valle Abascal Patricia Alvarado Gustavo G. Bujalesky Arturo Güell 《Natural Hazards》2012,61(2):337-349
Patagonia, including the island of Tierra del Fuego, lies in southernmost South America at the junction of the South American,
Antarctic, and Scotia tectonic plates. Historical and instrumental records have documented several local earthquakes of damaging
magnitude, posing a threat to the rapidly growing population of 300,000 and the expanding industrial and service infrastructure.
Short and inaccurate instrumental records of local seismic events and a diffuse epicenter distribution not clearly related
to the recognized seismogenic structures have hindered an adequate evaluation of the seismic hazard for this region. To improve
this situation, a paleoseismological study was carried out on two gravelly strandplains on the Atlantic coast of Patagonia.
Surveying combined ground-probing radar, vertical electric sounding, and seismic refraction. Coseismic normal faults buried
beneath the strandplain bodies were revealed and related to the morphology of the strandplains. The faults have probable ages
between 0.9 and 6.4 kyr BP and a recurrence rate of about 1 kyr. The more likely source for these structures is the Magallanes-Fagnano
fault, a continental transform fault that crosses Tierra del Fuego. The distance of more than 300 km from the buried coseismic
structures to the trace of the Magallanes-Fagnano fault argues for high-magnitude earthquake activity on this fault throughout
the Holocene. Urban development on soft glacial and alluvial substrates increases the hazard. 相似文献
108.
Chad?D.?DeeringEmail author Thomas?A.?Vogel Lina?C.?Patino David?W.?Szymanski Guillermo?E.?Alvarado 《Contributions to Mineralogy and Petrology》2012,163(2):259-275
Northwestern Costa Rica is built upon an oceanic plateau that has developed chemical and geophysical characteristics of the
upper continental crust. A major factor in converting the oceanic plateau to continental crust is the production, evolution,
and emplacement of silicic magmas. In Costa Rica, the Caribbean Large Igneous Province (CLIP) forms the overriding plate in
the subduction of the Cocos Plate—a process that has occurred for at least the last 25 my. Igneous rocks in Costa Rica older
than about 8 Ma have chemical compositions typical of ocean island basalts and intra-oceanic arcs. In contrast, younger igneous
deposits contain abundant silicic rocks, which are significantly enriched in SiO2, alkalis, and light rare-earth elements and are geochemically similar to the average upper continental crust. Geophysical
evidence (high Vp seismic velocities) also indicates a relatively thick (~40 km), addition of evolved igneous rocks to the
CLIP. The silicic deposits of NW Costa Rica occur in two major compositional groups: a high-Ti and a low-Ti group with no
overlap between the two. The major and trace element characteristics of these groups are consistent with these magmas being
derived from liquids that were extracted from crystal mushes—either produced by crystallization or by partial melting of plutons
near their solidi. In relative terms, the high-Ti silicic liquids were extracted from a hot, dry crystal mush with low oxygen
fugacity, where plagioclase and pyroxene were the dominant phases crystallizing, along with lesser amounts of hornblende.
In contrast, the low-Ti silicic liquids were extracted from a cool, wet crystal mush with high oxygen fugacity, where plagioclase
and amphibole were the dominant phases crystallizing. The hot-dry-reducing magmas dominate the older sequence, but the youngest
sequence contains only magmas from the cold-wet-oxidized group. Silicic volcanic deposits from other oceanic arcs (e.g., Izu-Bonin,
Marianas) have chemical characteristics distinctly different from continental crust, whereas the NW Costa Rican silicic deposits
have chemical characteristics nearly identical to the upper continental crust. The transition in NW Costa Rica from mafic
oceanic arc and intra-oceanic magma to felsic, upper continental crust-type magma is governed by a combination of several
important factors that may be absent in other arc settings: (1) thermal maturation of the thick Caribbean plateau, (2) regional
or local crustal extension, and (3) establishment of an upper crustal reservoir. 相似文献
109.
Carmen Morales Joaquín Trapero José F. Gómez Verónica Orozco Alvaro Gimenez Stuart Bowyer Jerry Edelstein Eric Korpela Michael Lampton Jeff Cobb 《Astrophysics and Space Science》2001,276(1):141-150
We present here stellar spectra of B stars obtained with the EURD spectrograph, one of the three instruments on board MINISAT-01. EURD is a spectrograph specially designed to detect diffuse radiation in thewavelength range between 350 and 1100 Å with 5 Å spectral resolution. EURD main scientific targets are: the spectrum of interstellar medium,atmospheric airglow, decaying neutrinos, Moon and early type stars. 相似文献
110.
Alvaro Domínguez 《Monthly notices of the Royal Astronomical Society》2002,334(2):435-443
This work reports on the application of the Eulerian perturbation theory to a recently proposed model of cosmological structure formation by gravitational instability. Its physical meaning is discussed in detail and put in perspective of previous works. The model incorporates in a systematic fashion corrections to the popular dust model owing to multistreaming and, more generally, the small-scale, virialized degrees of freedom. It features a time-dependent length-scale L ( t ) estimated to be L / r 0 10-1 [ r 0 ( t ) is the non-linear scale, at which 2 =1] . The model provides a new angle on the dust model and allows us to overcome some of its limitations. Thus, the scale L ( t ) works as a physically meaningful short-distance cut-off for the divergences appearing in the perturbation expansion of the dust model when there is too much initial power on small scales. The model also incorporates the generation of vorticity by tidal forces; according to the perturbational result, the filtered vorticity for standard cold dark matter initial conditions should be significant today only at scales below 1 h 1 Mpc. 相似文献