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Geoelectric evidence for centripetal resurge of impact melt and breccias over central uplift of Araguainha impact structure

TONG, C. H.; LANA, C.; MARANGONI, Y. R.; ELIS, V. R.
Fonte: GEOLOGICAL SOC AMER, INC Publicador: GEOLOGICAL SOC AMER, INC
Tipo: Artigo de Revista Científica
Português
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We present five profiles from electrical resistivity tomography (ERT), with surface constraints and gravity data, in the central uplift of the Araguainha impact structure in central Brazil. The central uplift, the overlying polymict breccias, and decameter-scale impact melt rocks are characterized by contrasting ranges of electrical resistivity. Our resistivity model provides empirical evidence that supports the existing model in which impact melt and breccias resurged toward the crater center in the final stages of the cratering process. On the basis of our results from the first use of ERT in impact cratering studies, we conclude that the deposition and flow of impact melt and breccias over the central uplift were influenced by the geometry of the lithologic boundaries in the central uplift.; Birkbeck, University of London; Claude Leon Foundation, South Africa; FAPESP[05/51530]

Utilização de geossintéticos para proteção de tubulações pressurizadas enterradas; The use of geosynthetics for the protection of pressurised buried pipes

Tupa, Néstor
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Tese
Português
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Tese (doutorado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, 2006.; Nas últimas décadas, o uso dos materiais geossintéticos como reforço das obras geotécnicas tem aumentado muito, ampliando os âmbitos de suas aplicações. Essa técnica apresenta grande potencial para uso em obras de segurança e minimizar os problemas de conservação do meio ambiente. Também, a procura de energia mais econômica e menos contaminante ao meio ambiente esta impulsionando a exploração de gás natural. O transporte desse combustível pode ser feito por gasodutos que são sistemas interessantes pelas suas vantagens de rapidez, quantidade massiva de transporte e economia. Porém, estas estruturas apresentam situações de acidentes (vazamentos e explosões), os mesmos são perigosos principalmente quando ocorrem em regiões povoadas ou que requeiram cuidados especiais, podendo apresentar conseqüências fatais, perdas materiais ou contaminar o meio ambiente. O presente trabalho estudou a aplicação de geossintéticos como elemento de reforço em aterros para proteção de tubulações pressurizadas enterradas de gasodutos visando minimizar os efeitos de uma explosão. Para o estudo foram implementados dois tipos de ensaios idealizando as seqüências do mecanismo de explosão de uma tubulação pressurizada enterrada. Assim...

Microwave Interferometric Sensors as a Tool for Space and Time Analysis of Active Volcano Deformations: the Stromboli Case

ANTONELLO Giuseppe; FORTUNY GUASCH Joaquim; TARCHI Dario; CASAGLI Nicola; DEL VENTISETTE Chiara; GUERRI Letizia; LUZI Guido; MUGNAI Francesco; LEVA Davide
Fonte: IEEE Publicador: IEEE
Tipo: Contributions to Conferences Formato: Printed
Português
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A Ground Based SAR Interferometer (GB-InSAR) was installed at Stromboli volcano (Italy) in February 2003 to continuously monitor the behaviour of the morphological depression known as Sciara del Fuoco, SdF with alerting purposes. This was decided as a consequence of the collapse of a large landslide from the NW slope of the SdF and the subsequent tsunami occurred on December 2002. The GB-InSAR system, working at Ku band, was set up on the stable right flank of the SdF; it has been continuously working and during this last five years has permitted to follow the temporal and spatial evolution of the mass movement in the SdF and the crater. Interferometric maps have permitted to assess the deformation field over a large portion of the target area and to characterize different processes. The system allowed to abserve in particular two main events occurred on 5 April 2003 (a major explosion) and on 27 February 2007 (beginning of the effusive phase) respectively. The potential of the use of DInSAR from satellite platforms working at C band to understand the dynamic of the whole volcano has been also investigated. Different images acquired from the ERS2, RADARSAR and ENVISAT satellites before and after the 2007 event, have been interferometrically processed as well. Notwithstanding the restricted number of available images...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): implications for deformation mechanisms and central uplift formation

Yokoyama, Elder; Trindade, Ricardo Ivan Ferreira da; Lana, Cristiano de Carvalho; Souza Filho, Carlos Roberto de; Baratoux, D.; Marangoni, Y?ra Regina; Tohver, Eric
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
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The weakening mechanisms involved in the collapse of compleximpact craters are controversial. The Araguainhaimpact crater, in Brazil, exposes a complexstructure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (< 10 ?m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magneticfabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of compleximpactstructures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
38.477207%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: Elsevier; Amsterdam Publicador: Elsevier; Amsterdam
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.042556%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Martian Subsurface Properties and Crater Formation Processes Inferred From Fresh Impact Crater Geometries

Valiant, Gregory J.; Stewart, Sarah
Fonte: Meteoritical Society Publicador: Meteoritical Society
Tipo: Artigo de Revista Científica
Português
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The geometry of simple impact craters reflects the properties of the target materials, and the diverse range of fluidized morphologies observed in Martian ejecta blankets are controlled by the near-surface composition and the climate at the time of impact. Using the Mars Orbiter Laser Altimeter (MOLA) data set, quantitative information about the strength of the upper crust and the dynamics of Martian ejecta blankets may be derived from crater geometry measurements. Here, we present the results from geometrical measurements of fresh craters 3-50 km in rim diameter in selected highland (Lunae and Solis Plana) and lowland (Acidalia, Isidis, and Utopia Planitiae) terrains. We find large, resolved differences between the geometrical properties of the freshest highland and lowland craters. Simple lowland craters are 1.5-2.0 times deeper (>= 5 sigma(o) difference) with >50% larger cavities (>= 2 sigma(o)) compared to highland craters of the same diameter. Rim heights and the volume of material above the preimpact surface are slightly greater in the lowlands over most of the size range studied. The different shapes of simple highland and lowland craters indicate that the upper similar to 6.5 km of the lowland study regions are significantly stronger than the upper crust of the highland plateaus. Lowland craters collapse to final volumes of 45-70% of their transient cavity volumes...

Bacia de Campo Alegre-SC: aspectos petrológicos, estratigráficos e caracterização geotectônica; not available

Citroni, Sérgio Brandolise
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 20/07/1998 Português
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A Bacia de Campo Alegre situa-se no nordeste do Estado de Santa Catarina, cobrindo uma área de cerca de 500 \'km POT.2\'. É preenchida por sedimentos epiclásticos, piroclásticos e por grande volume de lavas básicas e ácidas, principalmente de composição traquítica. As litologias presentes foram agrupados em dez formações: * Formação Papanduvinha, correspondendo a conglomerados de leques aluviais.* Formação São Bento do Sul, formada por conglomerados e arenitos subordinados de ambiente fluvial entrelaçado. * Formação Rio do Bugre, com arenitos e pelitos fluviais e de ambiente subaquático ainda não determinado. * Formação Corupá, turbiditos e arenitos, restrita à Sub-bacia de Corupá; estas quatro primeiras formações são agrupadas dentro do Grupo Bateias. * Formaçào Rio Negrinho, constituída por lavas basálticas, andesíticas e traquíticas, intercaladas com pelitos laminados, as lavas básicas apresentam-se localmente como derrames subaquosos. 8 Formação Avenca Grande, formada por fluxos ignimbríticos ácidos, parcialmente intercalados aos basaltos e parcialmente aos pelitos da Formação Rio Negrinho. * Formação São Miguel, principal unidade vulcânica, com lavas traquíticas, quartzo-traquíticas e riolíticas...

Impact

Lohse, Detlef; Bergmann, Raymond; Mikkelsen, Rene'; Zeilstra, Christiaan; van der Meer, Devaraj; Versluis, Michel; van der Weele, Ko; van der Hoef, Martin; Kuipers, Hans
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/06/2004 Português
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According to Shoemaker, the "impact of solid bodies is the most fundamental process that has taken place on the terrestrial planets", as they shape the surfaces of all solar system bodies. A lot of information on this process has been extracted from remote observations of impact craters on planetary surfaces. However, the nature of the geophysical impact events is that they are non-reproducible. Moreover, their scale is enormous and direct observations are not possible. Therefore, we choose an alternate and of course downscaled experimental approach in order to guarantee reproducible results: We prepare very fine sand in a well defined and fully decompactified state by letting gas bubble through it. After turning off the gas stream, we let a steel ball fall on the sand. The series of events in the experiments and corresponding discrete particle simulations is as follows: On impact of the ball, sand is blown away in all directions ("splash") and an impact crater forms. When this cavity collapses, a granular jet emerges and is driven straight into the air. A second jet goes downwards into the air bubble entrained during the process, thus pushing surface material deep into the ground. The air bubble rises slowly towards the surface, causing a granular eruption. In addition to the experiments and the discrete particle simulations we present a simple continuum theory to account for the void collapse leading to the formation of the upward and downward jets. We show that the phenomenon is robust and even works for oblique impacts: the upward jet is then shooting backwards...

Liquid jet eruption from hollow relaxation

Ghabache, Élisabeth; Séon, Thomas; Antkowiak, Arnaud
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/12/2013 Português
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A cavity hollowed out on a free liquid surface is relaxing, forming an intense liquid jet. Using a model experiment where a short air pulse sculpts an initial large crater, we depict the different stages in the gravitational cavity collapse and in the jet formation. Prior eversion, all cavity profiles are found to exhibit a shape similarity. Following hollow relaxation, a universal scaling law establishing an unexpected relation between the jet eruption velocity, the initial cavity geometry and the liquid viscosity is evidenced experimentally. On further analysing the jet forms we demonstrate that the stretched liquid jet also presents shape similarity. Considering that the jet shape is a signature of the initial flow focusing, we elaborate a simple model capturing the key features of the erupting jet velocity scaling.

Compressible air flow through a collapsing liquid cavity

Gordillo, Stephan Gekle \and José Manuel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/01/2010 Português
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We present a multiscale approach to simulate the impact of a solid object on a liquid surface: upon impact a thin liquid sheet is thrown upwards all around the rim of the impactor while in its wake a large surface cavity forms. Under the influence of hydrostatic pressure the cavity immediately starts to collapse and eventually closes in a single point from which a thin, needle-like jet is ejected. Existing numerical treatments of liquid impact either consider the surrounding air as an incompressible fluid or neglect air effects altogether. In contrast, our approach couples a boundary-integral method for the liquid with a Roe scheme for the gas domain and is thus able to handle the fully \emph{compressible} gas stream that is pushed out of the collapsing impact cavity. Taking into account air compressibility is crucial, since, as we show in this work, the impact crater collapses so violently that the air flow through the cavity neck attains supersonic velocities already at cavity diameters larger than 1 mm. Our computational results are validated through corresponding experimental data.; Comment: Submitted to Comput Mech

Comparison of "warm and wet" and "cold and icy" scenarios for early Mars in a 3D climate model

Wordsworth, Robin D.; Kerber, Laura; Pierrehumbert, Raymond T.; Forget, Francois; Head, James W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/06/2015 Português
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We use a 3D general circulation model to compare the primitive Martian hydrological cycle in "warm and wet" and "cold and icy" scenarios. In the warm and wet scenario, an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice-free northern ocean. Precipitation shows strong surface variations, with high rates around Hellas basin and west of Tharsis but low rates around Margaritifer Sinus (where the observed valley network drainage density is nonetheless high). In the cold and icy scenario, snow migration is a function of both obliquity and surface pressure, and limited episodic melting is possible through combinations of seasonal, volcanic and impact forcing. At surface pressures above those required to avoid atmospheric collapse (~0.5 bar) and moderate to high obliquity, snow is transported to the equatorial highland regions where the concentration of valley networks is highest. Snow accumulation in the Aeolis quadrangle is high, indicating an ice-free northern ocean is not required to supply water to Gale crater. At lower surface pressures and obliquities, both H2O and CO2 are trapped as ice at the poles and the equatorial regions become extremely dry. The valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41.8 degrees obliquity but uncorrelated with precipitation produced by the warm and wet simulation. Because our simulations make specific predictions for precipitation patterns under different climate scenarios...

Origin of basalts by hybridisation in andesite-dominated arcs

Cassidy, Michael; Edmonds, Marie; Watt, Sebastian F. L.; Palmer, Martin R.; Gernon, Thomas M.
Fonte: Oxford Journals Publicador: Oxford Journals
Tipo: Article; accepted version
Português
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This is the accepted manuscript. The final version is available from OUP at http://dx.doi.org/10.1093/petrology/egv002; Mafic magmas are common in subduction zone settings, yet their high density restricts their ascent to the surface. Once stalled in the crust, these magmas may differentiate, assimilate crust and other melts and mushes to produce hybridised intermediate magmas. The Soufriere Hills Volcano on Montserrat is a ?type locality? for these hybridisation processes and yet, just 3 km south of the crater, voluminous basalts have erupted from the South Soufriere Hills volcano within the same time period as the Soufriere Hills Volcano was erupting hybrid andesites (131 - 128 ka). Basaltic South Soufriere Hills magmas have 48 - 53 32 wt% SiO2 and 4 - 6 wt% MgO. They were hot (970 - 1160 ?C), volatile-rich (melt inclusions contain up to 6.2 wt% H2O) and were stored at 8 ? 13 km prior to eruption (based on olivine and pyroxene-hosted melt inclusion volatile geochemistry). Melt inclusions do not preserve basaltic liquids: they are andesitic to rhyolitic in composition, related to one another by a line of descent controlled by simple closed-system fractionation. Whole rock compositions, however, are best described by a hybridisation model involving ?back?-mixing of andesitic to rhyolitic melts with mafic crystal phases such as magnetite...

Complex craters: Relationship of stratigraphy and rings to impact conditions

O'Keefe, John D.; Ahrens, Thomas J.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 25/11/1999 Português
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One of the key issues associated with the understanding of large scale impacts is how the observable complex crater structural features (e.g., central peaks and pits, flat floors, ring shaped ridges and depressions, stratigraphic modifications, and faults) relate to the impactor's parameters (e.g., radius, velocity, and density) and the nonobservable transient crater measures (e.g., depth of penetration and diameter at maximum penetration). We have numerically modeled large-scale impacts on planets for a range of impactor parameters, gravity and planetary material strengths. From these we found that the collapse of the transient cavity results in the development of a tall, transient central peak that oscillates and drives surface waves that are arrested by the balance between gravitational forces and planetary strength to produce a wide range of the observed surface features. In addition, we found that the underlying stratigraphy is inverted outside of the transient cavity diameter (overturned flap region), but not inside. This change in stratigraphy is observable by remote sensing, drilling, seismic imaging and gravity mapping techniques. We used the above results to develop scaling laws and to make estimates of the impact parameters for the Chicxulub impact and also compared the calculated stratigraphic profile with the internal structure model developed by Hildebrand et. al. [1998]...

Scaling craters in carbonates: Electron paramagnetic resonance analysis of shock damage

Polanskey, Carol A.; Ahrens, Thomas J.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 25/03/1994 Português
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Carbonate samples from the 8.9-Mt nuclear (near-surface explosion) crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance (EPR). Samples from below the OAK apparent crater floor were obtained from six boreholes, as well as ejecta recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen and Kaibab limestone, which had been shocked to known pressures. Analysis of the OAK Crater borehole samples has identified a thin zone of allocthonous highly shocked (10–13 GPa) carbonate material underneath the apparent crater floor. This ∼5- to 15-m-thick zone occurs at a maximum depth of ∼125 m below current seafloor at the borehole, sited at the initial position of the OAK explosive, and decreases in depth towards the apparent crater edge. Because this zone of allocthonous shocked rock delineates deformed rock below, and a breccia of mobilized sand and collapse debris above, it appears to outline the transient crater. The transient crater volume inferred in this way is found to be 3.2±0.2×10^6 m^3, which is in good agreement with a volume of 5.3×10^6 m^3 inferred from gravity scaling of laboratory experiments [Schmidt et al....

STRUCTURAL MODELING OF THE VICHADA IMPACT STRUCTURE FROM INTERPRETED GROUND GRAVITY AND MAGNETIC ANOMALIES

Hernández,Orlando; Khurama,Sait; Alexander,Gretta C.
Fonte: Boletin de Geología Publicador: Boletin de Geología
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2011 Português
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A prominent positive free-air gravity anomaly mapped over a roughly 50-km diameter basin is consistent with a mascon centered on (4°30'N, -69°15'W) in the Vichada Department, Colombia, South America. Ground follow up gravity and magnetic anomalies were modeled confirming the regional free air gravity anomalies. These potential field anomalies infer a hidden complex impact basin structure filled with tertiary sedimentary rocks and recent quaternary deposits. Negative Bougueranomalies of 8 mGals to 15 mGals amplitude are associated with a concentric sedimentary basin with a varying thickness from 100m to 500 m in the outer rings to 700m to 1000m at the center of the impact crater basin. Strong positive magnetic anomalies of 100 nT to 300 nT amplitude infer the presence of a local Precambrian crystalline basement that was affected by intensive faulting producing tectonic blocks dipping to the center of the structure, showing a typical "domino structure" of impact craters such as that of Sudbury, Ontario, Canada. Basic to intermediate mineralized veins and dikes with contrasting density and magnetic susceptibility properties could be emplaced along these faulting zones, as inferred from local gravity and magnetic highs. The geologic mapping of the area is limited by the flat topography and absence of outcrops/ geomorphologic units. Nevertheless...

New 40Ar/39Ar ages from the Central Part of the Chiapanecan Volcanic Arc, Chiapas, Mexico

Mora,Juan Carlos; Layer,Paul W.; Jaimes-Viera,María del Carmen
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2012 Português
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The Chiapanecan Volcanic Arc (CVA), located in the central portion of the State of Chiapas, is a 150 km long chain of volcanic structures aligned in a NW-SE direction. The central part of the CVA is composed of an irregular northeast-trending alignment of more than 10 volcanic structures, generally centered along NNW-SSE trending faults splayed from the Motagua-Polochic Fault System. Among these structures are seven volcanic domes (Huitepec, Amahuitz, La Iglesia, Mispía, La Lanza, Venustiano Carranza, and Santotón), one explosion crater (Navenchauc), one collapse structure (Apas), and one dome complex (Tzontehuitz). In this work, we report thirteen new 40Ar/39Ar ages of rocks from seven domes that increase the available geochronometric data on Quaternary volcanic activity in the central part of Chiapanecan Volcanic Arc. From the new and previous data, we identified the Tzontehuitz Dome Complex as the oldest volcanic center in the CVA, yielding an age of 2.1 Ma, and the Venustiano Carranza Volcanic Dome as exhibiting the most recent activity in the zone, with an age of 0.225 Ma.

Fracturing and deformation in the Chicxulub crater - Complex trace analysis of instantaneous seismic attributes

Salguero-Hernández,Eduardo; Urrutia-Fucugauchi,Jaime; Ramírez-Cruz,Luis
Fonte: Instituto de Geología, UNAM Publicador: Instituto de Geología, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2010 Português
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Large complex impact craters form by collapse from initial excavation stage of a deep narrow bowl-shaped transient cavity. Fracturing and shattering of solids with finite tensile shear limits occur related to shock-induced damage of target material, with fracturing and fragmentation occurring during transient cavity crater collapse processes. Geophysical studies of subsurface crater structure may assist in studying shock-induced effects of deformation and fracturing of target rocks. Here we present initial results of a study of subsurface fracturing/deformation in the Chicxulub crater from seismic reflection data. The analysis is based on the instantaneous seismic attributes envelope amplitude, instantaneous frequency and Q factor, at selected sectors of the crater by looking at petrophysical properties and seismic attenuation. Shock effects with shattering and fracturing of Mesozoic target rocks show a trend to decrease away from the rim zone. Cretaceous carbonates show less attenuation inside the crater than in exterior sectors. The relative attenuation quality factor Q is lower in sections outside the crater rim as compared with higher Q values inside the rim, and particularly at depth within the Cretaceous sequence. Carbonates in the western sector are characterized by slightly larger attenuation than in the eastern sector...

Dynamics of internal waves generated by mountain breeze in Alchichica Crater Lake, Mexico

Filonov,Anatoliy; Tereshchenko,Iryna; Alcocer,Javier; Monzón,Cesar
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2015 Português
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37.9807%
Hydrophysical measurements carried out in the deep tropical crater lake Alchichica, Mexico, showed the presence of intense internal waves with a one-day period, generated by the regular influence of a mountain breeze. The diurnal waves effectively generate semidiurnal internal waves that are close to the resonance oscillations of the lake. The internal waves brake close to the shoreline and into the lake's bottom, which generates baroclinic circulation and water masses mixing. According to the data obtained with a ADCP, two diurnal and two semidiurnal inclined waves propagate in the lake towards each other in depth and can form fluctuations of a vertical mode, if the depth of the lake is a multiple of one-half the vertical wavelength. This multiplicity applies to both the diurnal and semidiurnal waves. The simultaneous existence of horizontal and vertical modes corresponds to a volumetric mode, or resonant lake oscillation. The waves collapse near the shore slopes and the lake's bottom, inducing baroclinic circulation and local mixing

Rock magnetic and AMS fabrics characterization of suevitic breccias from the Cretaceous-Paleogene Chicxulub impact crater

Delgadillo-Peralta,Margarita; Urrutia-Fucugauchi,Jaime; Pérez-Cruz,Ligia; Velasco-Villarreal,Miriam
Fonte: Instituto de Geología, UNAM Publicador: Instituto de Geología, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 Português
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Results of a paleomagnetic and magnetic fabrics study of the basal suevitic breccias in the Chicxulub impact crater, Yucatán platform, Gulf of Mexico are presented. The breccias were cored in the Yaxcopoil-1 borehole, which is located at about 62 km radial distance from the crater center. The impactite sequence in the Yaxcopoil-1 borehole is ~100 m thick and formed by six subunits with distinct petrographic and geochemical characteristics. Here we investigate the basal subunit interpreted as: a ground surge in the transient cavity, a melt breccia with clastic material, or an excavation flow from the ejecta curtain interacting with the ejecta plume collapse. Characterization of the magnetic fabrics using rock magnetics and anisotropy of magnetic susceptibility (AMS) are used to investigate on the emplacement mechanism of the suevites. Magnetic hysteresis and k-T curves show that the magnetic mineralogy is dominated by low-Ti titanomagnetites and magnetite. The AMS fabrics record mixtures of oblate and prolate ellipsoids and principal susceptibility axial distributions with relatively high angular scatter, related to turbulent high temperature conditions during ejecta emplacement. Magnetic fabric parameters and principal susceptibility axial distributions correlate with modal composition...