Sample records for orientation grain
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1

ESTUDIO DEL DESGASTE EROSIVO POR CAVITACIÓN DE UN ACERO AUSTENÍTICO DE ALTO NITRÓGENO APOYADO EN EL USO DE LA DIFRACCIÓN DE ELECTRONES RETROPROYECTADOS-EBSD/ ASSESSMENT OF CAVITATION-EROSION WEAR OF A HIGH NITROGEN AUSTENITIC STAINLESS STEEL FROM ELECTRON BACKSCATTERING DIFFRACTION-EBSD

Mesa Grajales, Dairo Hernán; Garzón Ospina, Carlos Mario; Tschiptschin, André Paulo
2010-08-01

Resumen en español Muestras de acero inoxidable con estructura austenítica y contenido aproximado de nitrógeno de 0,9% en peso en solución sólida fueron sometidas a ensayos de cavitación vibratoria en agua destilada, con el fin de estudiar la evolución del desgaste erosivo por cavitación (EC) a escala del tamaño de grano (mesoescala). Las muestras fueron obtenidas por medio de nitruración gaseosa a alta temperatura (HTGN) del acero inoxidable dúplex UNS S31803, las cuales fueron c (mas) aracterizadas por difracción de electrones retroproyectados (EBSD), a fin de obtener información de la orientación cristalina de los granos en la superficie a ser cavitada. La técnica de microscopía electrónica de barrido (SEM), fue usada para acompañar el proceso de desgaste para diferentes tiempos de ensayo. Como resultados de los ensayos de cavitación se determinó la pérdida de masa y se hizo un estudio secuencial de la apariencia superficial de las muestras para determinar los mecanismos de desgaste operantes en cada etapa. Los resultados fueron analizados a la luz de la caracterización cristalográfica previa. Para propósitos de comparación, fue usado el acero austenítico convencional UNS S30403. A partir de los resultados se observó que tanto la nucleación del daño como su evolución se dan de forma heterogénea a escala del tamaño de grano, resultado atribuido a la anisotropía en la deformación plástica. El carácter heterogéneo del daño por cavitación fue atribuido principalmente a las características de los límites de grano y a la microtextura dentro de los granos Resumen en inglés Stainless steel samples with 100% austenitic microstructure and alloyed with 0.9 wt-% of nitrogen in solid solution were tested under vibratory cavitation experiments in distilled water to study the cavitation-erosion wear (EC) at grain size level (mesoscale). Fully austenitic samples were obtained by high temperature gas nitriding (HTGN) a commercially available dúplex stainless steel, UNS S31803. The samples were characterized by electron backscattering diffraction, EB (mas) SD to obtain the crystalline orientation of individual grains. In addition, mass loss measurements were obtained and surface damage evolution was analyzed by scanning electron microscopy (SEM) at different times of the test. These results were analyzed as a function of the prior crystallographic characterization. For comparison, a conventional austenitic stainless steel, UNS S30403, was also investigated. It was observed that both the nucleation and the growth of damage are heterogeneous at the grain-size scale due to mesoscale plasticity anisotropy, induced during the CE tests. The heterogeneous character of the cavitation damage is related to both the grain boundary character and the microtexture inside the grains

Scientific Electronic Library Online (Spanish)

2

CARACTERIZACIÓN ESTRUCTURAL Y MORFOLÓGICA DE PELÍCULAS DE ZnO CRECIDAS SOBRE SUSTRATOS DE VIDRIO/ STRUCTURAL AND MORPHOLOGICAL CHARACTERIZATION OF ZnO FILMS DEPOSITED ON GLASS SUPPORTS

MORENO MONTOYA, LUIS; ARANGO, PEDRO JOSÉ
2007-03-01

Resumen en español Utilizando la técnica PAPVD (Plasma Assisted Physical Vapor Deposition) por arco pulsado se crecieron películas delgadas de ZnO sobre sustratos de vidrio. Las películas fueron crecidas variando el voltaje de la descarga, la presión del gas y el número de descargas. Las propiedades estructurales tales como: cristalinidad, microestructura y rugosidad superficial fueron investigadas por Difracción de Rayos X, Microscopía Electrónica de Barrido en Ambiente y Microscop (mas) ía de Fuerza Atómica. Se encontró que el material depositado es efectivamente ZnO, con una estructura cristalina hexagonal, una orientación preferencial en la dirección (002), alta textura cristalográfica, parámetros de red promedio de a = 3,250495 Å y c =5,21608 Å, espesores con valores del orden de los cientos de nanómetros, tamaño de grano promedio del orden de 0,529 mm y rugosidad promedio de 98,6 Å, además, se detectó la presencia de irregularidades, grietas y microgotas en la superficie de las mismas. Resumen en inglés Using the PAPVD (Plasma Assisted Physical Vapor Deposition) technique by pulsed arc, were grown films of ZnO on glasses substrates. The films were grown by varying the voltage of the discharge, the pressure of the gas and the number of discharges. The structural properties, such as crystallinity, microstructure, and surface roughness of ZnO films, were investigated using X Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). It was (mas) found that the material deposited is effectivitly ZnO, with a hexagonal crystalline structure, with a preferential orientation in planes (002), high crystallographic texture, parameters of net average of a0=3,250495 Å and c0=5,21608 Å, thickness of the films finding values in the order of hundred of nanometers, size of grain average of 0,529 mm, and roughness average of 98,6 Å. Also it was detected the presence of irregularities, cracks and micro-droplets in the surface of the films.

Scientific Electronic Library Online (Spanish)

3

Wear of aligned silicon nitride under dry sliding conditions

Belmonte, Manuel; Miranzo, Pilar; Osendi, María Isabel; Gomes, J. R.
2009-01-05

Digital.CSIC (Spain)

5

The salt-responsive transcriptome of chickpea roots and nodules via deepSuperSAGE

Molina, Carlos; Zaman-Allah, Mainassara; Khan, Faheema; Fatnassi, Nadia; Horres, Ralf; Rotter, Björn; Steinhauer, Diana; Amenc, Laurie; Drevon, Jean-Jacques; Winter, Peter; Khal, Günter
2011-02-14

Digital.CSIC (Spain)

7

Submicron structure and acoustic properties of ZnO films deposited on (100) InP by pulsed laser deposition

Vasco, E.; Rubio Zuazo, J.; Vázquez, Luis; Prieto, C.; Zaldo, Carlos
2001-01-01

Digital.CSIC (Spain)

11

Oilcrop-sun: A Development, Growth, and Yield Model of the Sunflower Crop

Villalobos, F. J.; Hall, Anthony J.; Ritchie, Joe T.; Orgaz Rosua, Francisco
1996-05-01

Digital.CSIC (Spain)

12

Morfodinámica de playas del sudeste de la provincia de Buenos Aires (1983 a 2004)/ Morphodynamics of beaches of the southeast of Buenos Aires (1983 at 2004)

Bertola, Germán R.
2006-07-01

Resumen en español En las costas del sudeste de Buenos Aires hay dos relieves geomorfológicos de importancia, las playas arenosas bajas con grandes campos de médanos, y las playas de bolsillo ubicadas entre acantilados de loess u ortocuarcitas. Al Norte y Sur de la ciudad de Mar del Plata, hay extensos campos de médanos que conforman la Barrera Oriental y Austral. La conformación de estas costas es relativamente moderna ya que se han formado con posterioridad a la fluctuación holocena (mas) del nivel del mar. El objetivo del presente estudio se centró en analizar los cambios morfológicos naturales y artificiales de las playas de los partidos de Pinamar, Villa Gesell, Mar Chiquita, General Pueyrredón, General Alvarado, Lobería y Necochea, mediante la descripción y discusión de resultados obtenidos en relevamientos de playa realizados desde 1983 al 2004, con especial énfasis en la dinámica sedimentaria de sus playas y las características físicas naturales o introducidas por el hombre, como por ejemplo construcción de obras de defensa o movimiento de arenas. Los relevamientos se ejecutaron en playas con diferente orientación, dinámica, cantidad y calidad de sedimento, así como distinto grado de alteración producido por las actividades humanas. Los perfiles permitieron analizar la magnitud y velocidad de los cambios morfológicos, al tiempo que se estudiaron las variaciones texturales de las distintas zonas de la playa, reconociendo su variabilidad y la significación estadística de la misma. El trabajo se basó en la comparación de relevamientos planialtimétricos de las playas según métodos convencionales, en la evaluación de las características físicas de las olas que llegan a ellas para alcanzar una clasificación morfodinámica basada en las ecuaciones del número de Dean, parámetro W, el número de Battjes y el parámetro de Guza e Inman. Las texturas se analizaron de muestreos superficiales de sedimentos de la playa distal y de playa frontal mediante los parámetros de Folk y Ward. También fueron evaluadas las pendientes de las playas. En la discusión se evaluó la morfodinámica de playas, sus texturas, la respuesta de las playas mixtas de arena/grava, los ciclos estacionales, tormentas sudestadas y eventos El Niño, así como el efecto de las dorsales de arena (sand ridges) y la refracción. También se evalúa la actividad antrópica, con la construcción de espigones, el relleno artificial, las construcciones sobre la playa, los pluviales, la fijación de médanos y las actividades extractivas. Las conclusiones sostienen la idea de cuatro procesos que interactúan en las modificaciones morfodinámicas de las playas analizadas como son los ciclos estacionales invierno/verano, los ciclos episódicos ligados a períodos tormentosos y de inundaciones, los efectos antrópicos, y la presencia de bancos arenosos submareales que modifican el ángulo de incidencia de las olas produciendo efectos locales. Resumen en inglés Along the coast of the Southeastern Buenos Aires Province (Fig. 1), there are two important geomorphologic relieves: low sandy beaches with dune fields, and pocket beaches located between loessic or quarcitic cliffs. To the North and South of Mar del Plata City, extense dune fields conform the Eastern and Southern barriers. These dune fields are very modern, since they have been formed as consequence of a Holocene sea-level fluctuation (Schnack et al., 1982; Violante and (mas) Parker 1993; Isla, 1997). The objective of the study was to analyse the natural and artificial morphological changes of the beaches of Pinamar, Villa Gesell, Mar Chiquita, General Pueyrredón, General Alvarado, Lobería and Necochea counties, and the description and discussion of results obtained from 1983 to 2004. Special emphasis was made to the sedimentary dynamics of these beaches and the changes induced by man-made structures (groynes fields) and sand mining. The beaches have different orientation, dynamics, grain size, as well as different human alteration degree. The work was based on the comparison of beach profiles according to conventional methods (Fox and Davis, 1978; Isla, 1992; Isla et al., 1994; Bértola, 2001), the evaluation of the morphological classification based on Dean's number (Dean, 1973), Omega parameter (Masselink and Short, 1993), Battje´s number (Short, 1996), and the parameter of Guza and Inman (1975). Surface grain sizes were analysed using the parameters of Folk and Ward (1957) and evaluating beach slope changes. North Area Morphology: These are oceanic beaches, with average width of 72 m., The berm remains stabilised or it is in setback. Berm width increases at the touristic area in Mar de las Pampas. Villa Gesell beaches (Spa Los Históricos) suffered significant variations. In the pristine areas, there is presence of dunes after the backshore, although many of them are forested. Balance: In this area, there are no structures or estuaries that could affect the littoral drift. The Pinamar-Cariló sector has recorded an important accumulation (27,580 m³) diminishing toward the North of the urban area. The beach of Villa Gesell has also registered accumulation (18,200 m³), except in certain areas of the centre of the urban area, where erosion existed. Toward the South of Mar de las Pampas, the trend is depositional again. Grain sizes: The sediments of the backshore have increased their size up to 1994 and begin stable since 2000. In the foreshore, the mean (phi) has a reduction tendency. It diminished from 1994 to 1996 where it stops then increases very slowly. In some samples of Mar de las Pampas and Mar Azul, bioclastic composition dominates that would indicate a source of contribution from the South that coincides with old places of extraction of sands for construction. In addition, to the South of Villa Gesell, the erosion of dunes exhumes old beach crests or non-operative overwash composed by sand with shells and gravels (Isla, 1998). Slopes: Slope increases from South to North, with anomalous values in the centre of Pinamar. Temporarily, the general slopes increase their value in the time since 1998. Central Area Morphology: General Pueyrredón beaches change from North to South in: a) beaches among closed groynes, b) artificially refilled beaches, c) oceanic open beaches, and d) beaches at the foot of cliffs; in Miramar there are also beaches among groynes, but these with more spacing to each other (e). Beaches between groynes characterise La Perla area, with average widths of 64 m. Beach fills were conducted from Playa Popular to Playa Grande, their widths are of 107 m. The oceanic beaches extending from Mar del Plata Harbour to the Punta Mogotes Lighthouse and have 102 m. Beaches at the foot of cliffs (Costa Hermosa to Los Acantilados) are narrow, about 60 m. Those beaches between groynes from Chapadmalal to Miramar are 75 m. The beaches oriented to the Southeast have higher dynamics (Alfar, Chapadmalal and Miramar) with volumetric variations of the order of several thousands of cubic meters. Some have antrophic action that modifies totally and in a few days their morphology, for what we should absorb of the seasonal effects of erosion in winter and accumulation in the analysis of the results in spring. To the end of winter, beaches recover. Balance: The beaches of General Pueyrredón and Miramar are mixed and complex. There are pocket beaches, and beaches with abrasion plains; there is an important component of constructions of coastal defences. Mar del Plata beaches recorded an erosive trend (-2.266 m³) excluding the refilled volumes of 1998. This demonstrates the natural eroded tendency in the beaches without artificial feeding. Toward the North of the urban area of Mar del Plata there is accumulation, in their Central section there is erosion and toward the South of the urbanisation (Punta Mogotes Lighthouse) there is accumulation again. To the South -cliff areas-, erosion dominates. As expected, the highest variability was recorded at the refilled beaches, but there are significant dynamics at other of them (Acevedo, Spa Camping El Faro and Los Acantilados). General Alvarado beaches registered an important accumulation of 28.000 m³ of sand, of which 20% belongs to the urban coastline of Miramar (Spa HR). Grain sizes: In these beaches, the sediments have gone increasing the mean from 1998. The beaches increased the size of their sands toward the North, with fine grains in the refilled beaches and for the effect of tombolo in Los Pinos Beach (Alfar). In some samples of Chapadmalal, coarse grains of basaltic and andesitic composition have been detected in the bottom of the backshore, and pebbles of loess in the top of the backshore. This would indicate a particular dynamics that accumulates rolling stones transported by coastal drift from the South, the first one presumably of patagonic pebbles and of eroded material of the cliff bordering, in the second. Slopes: Beach slopes decrease from North to South, with abrupt peaks in the centre of the urban areas of Mar del Plata. The extreme values in the slopes were observed in the resort places from the downtown. Temporarily, the variations in the slopes were very important; in general a tendency was appreciated to increase the slope of the general beach along the time (except in beaches like Alfonsina, Las Dunas and Los Acantilados). South Area Morphology: The beaches of this area are open and with Loess cliffs. From Miramar to Mar del Sur beach widths extend to 79 m, and from Mar del Sur to Necochea they are narrower (68 m). Touristic activities diminish southwards. The beaches with more dynamics are those that possess groynes, cliffs and abrasion plains, as long as the beach open of Cruz del Moro has had smaller volumetric variations. Some beaches have suffered antrophic action (Costa Bonita or Cruz del Moro) that modified their morphology. Balance: They are heterogeneous beaches, with cliffs and engineering works in Mar del Sur and Costa Bonita, and open beaches in Cruz del Moro and Arenas Verdes. It begins to be important the action of the streams that in certain cases obstruct the longshore drift or they are plugged by effect of the same one. In General Alvarado accumulation is appreciated toward the North and South of the urban area of Miramar, with an important accumulation in Mar del Sur. Lobería presents erosion in its entire coast (-14.746 m³) with more loss in its Eastern sector. Costa Bonita beaches have more dynamics and Cruz del Moro suffer less variability. In both municipalities, erosion cycles and accumulation were observed along the year in correspondence to seasonal variations. Grain sizes: In the beaches of this area, an increase of the value of the mean is appreciated from 1995. In the backshore, grain size diminishes toward the South and in the foreshore, increase toward the South. Slopes: Slopes increase from North to South. With relationship to the foreshore, the slopes are had increasing through the time and all the beaches have had important variations equally. In the discussion, morphodynamics and grain sizes were evaluated, considering specially the dynamics of beaches composed of sand and gravel. The human impact was evaluated in relation to groin construction, nourishment works, buildings at the beach, dune afforestation and sand mining. The conclusions sustain the idea of four interaction processes: 1) seasonal cycles, 2) storms and flood effects, 3) human impact, 4) presence of sand ridges that modify the angle of incidence of the waves producing local effects. The refilled beaches have passed of being reflective to dissipative; as it has only modified slopes and grain size (but not climate of waves), there is still erosive. Erosive beaches have higher slopes (more than 4%). The increase of the slope toward the North indicates more narrow beaches with smaller areas of dry sand. Southeastern beaches are therefore more vulnerable to storm effects. The differential refraction of the waves in the Southeast, generates the continuous energy concentration in certain places of the coast (for example the cliffs in Mar del Plata). Induced for sand ridges there is convergence -erosion- and divergence -sedimentation- of orthogonal separated by few kilometres of distance. The protection of the coast cannot be considered as an individual responsibility, and for it, although local solutions exist, they don't work to regional scale; therefore, the coastal defence should be a cooperative effort among all the coastal municipalities.

Scientific Electronic Library Online (Spanish)

14

Micromorphological characterization and lithification of microbial mats from the Ebro Delta (Spain)

Wierzchos, Jacek; Berlanga, Mercedes; Ascaso, Carmen; Guerrero, Ricardo
2006-01-01

Digital.CSIC (Spain)

15
16

Materiales cerámicos texturados PbxBi4Ti3+xO12+3x, (x=0,1,2,3). Parte I: Sinterización y estructura

Lascano, L.; Caballero Cuesta, Amador; Villegas, Marina; Moure Jiménez, Carlos; Durán Botia, Pedro; Fernández Lozano, José Francisco
1999-12-01

Digital.CSIC (Spain)

20

Formación de surcos sedimentarios por cataratas submarinas en el interior del cañón de Cap de Creus

Puig, Pere; Palanques, Albert; Orange, D. L.; Lastras, G.; Canals, Miquel
2008-01-01

Digital.CSIC (Spain)

22

Estructuras de deformación (¿sismitas?) en la Formación Río Negro, provincia de Río Negro, Argentina

Schillizzi, Roberto; Luna, Liliana; Falco, Juan Ignacio
2010-07-01

Resumen en español A Las estructuras de deformación (ED) en sedimentos blandos comprenden las alteraciones que se producen casi simultáneamente con la sedimentación. Estos procesos se hallan en relación directa con las características internas de los materiales sedimentarios y de los factores externos que actúan sobre ellos. Sus resultados incluyen deformaciones como inyecciones, fracturas, volcanes y laminaciones convolutas que afectan total o parcialmente la estratificación. Los se (mas) dimentos blandos deformados por sismos se incluyen bajo la denominación general de sismitas (seismites). Como objetivo de esta investigación se plantea reconocer, por primera vez, estructuras de deformación ubicadas en la Formación Río Negro presentes en el sector norte del Golfo San Matías, en inmediaciones del Faro Río Negro. La metodología empleada consistió en el reconocimiento y descripción de las estructuras, para lo cual se extrajeron muestras para determinar granulometría, mineralogía y contenido de materia orgánica. Se fotografiaron los distintos sectores con deformaciones con el fin de establecer modelos comparativos. El sector estudiado, de 4 km de extensión, se ubica entre el faro de Río Negro y el inicio del Banco Verde y morfológicamente corresponde a un frente acantilado con orientación ENE-OSO. En él se determinaron las siguientes ED: a- de carga simple, pseudonódulos contiguos y aislados, y estructuras complejas; b- de escape de fluidos y c- estructuras de deslizamiento basal y por presión dirigida. El origen de las deformaciones se debe a las características de las sedimentitas y a los procesos que las afectan tales como los efectos por carga, escapes de fluidos y las presiones dirigidas. Como origen de estos procesos se señalan: la presión de la columna litológica, las olas de tormentas y los terremotos. Por los rasgos hallados las deformaciones del litoral rionegrino tendrían un origen sísmico, proceso ocurrido en un único evento durante el ciclo Andino cuyos inicios se fijan hace aproximadamente 45 Ma. Por otra parte sus techos y bases no se hallan asociados a otros procesos de deformación y sus espesores no exceden el metro de potencia. Además se hallan acotadas a la zona de transición entre los miembros medio y superior de la Formación Río Negro descansando en algunos casos sobre arcilitas y en otros sobre limolitas, originadas en un paleorelieve de interdunas. Resumen en inglés Soft-sediment deformation structures (SSD) are alterations produced almost simultaneously with sedimentation. They are directly related to internal characteristics of sedimentary materials as well as to external factors acting on them. Results derived from such alterations are evidenced as injections, fractures, volcanoes and convolute laminations, among other forms, affecting stratification either totally or partially. Soft-sediment deformation structures resulting from (mas) seisms are known as seismites. The present study aims at determining for the first time the presence of SSD structures in the Río Negro Formation, located in the northern area of San Matías Gulf, near Río Negro Lighthouse, Argentina (Fig. 1). To this end, structures were firstly identified and further described. Samples were subsequently collected for the determination of grain-size, mineralogy and organic matter content. Photographs of the different sectors evidencing deformations were taken in order to determine further comparative models. Morphology in the study area is associated to cliffs with vertical, fractured fronts and with an average height of 70 m in whose base torn-down blocks are accumulated. The geological structure of the study area is related to the Cuenca del Colorado and the Comarca Nordpatagónica, whose basement is mainly composed of Paleozoic and Mesozoic crystalline rocks. The sedimentary tertiary cover from the Miocene-Pliocene is represented by light-blue sandstones of the Río Negro Formation (Andreis, 1965). This unit was formed in an aeolian environment with intercalations of clay-silt shallow lagoons and a marine episode located in the mid area of the Río Negro Formation. At the top of the Río Negro Formation there are Pleistocene-Holocene sedimentites having a thickness of up to 5 m. Within the local structural framework of our study area there are fractures with a NE-SW and a NW-SE direction, which are related with fractures N55º, N90º and N350º azimuth located in the abrasion platform. According to Dzulinsky and Walton (1965), Lowe (1975), Brencley and Newall (1977), Clauss (1993), van Loon (2002), Owen (2003), Neuwerth et al. (2006), Alfaro et al. (2006), Montenat et al. (2007), among others (Table 1), and, taking into account the geometry of deformations, laboratory reconstructions and field observations from our study area, it can be concluded that the classifications of SSD structures tend to establish morphologic and genetic systematizations. The following characteristics were identified in our study area: limited deformations among stratigraphic horizons; a lateral continuity of SSD structures at considerable distances; and a confinement between non-deformed strata and its lithological association with psamitic-pelitic sediments. The study area, which is 4 km long and is located between Río Negro Lighthouse and the beginning of Banco Verde, is from the morphological point of view, a cliffed front with an ENE-WSW orientation. Different types of SSD structures were identified in this area. For example, from the morphological point of view and according to the loading mechanisms observed, simple-load structures (Fig. 2), attached and detached pseudonodules (Figs. 3, 4 and 5) and complex structures (Fig. 6) were identified. Furthermore, from the genetic point of view and according to the intrusion processes observed in soft sediments, water-scape structures (Fig. 7) and plate- or fountain-like deformations (Fig. 8) were found. From the genetic point of view, and based on the collapse and pressure mechanisms observed, basal slumping (Fig. 9) and directed-pressure structures (Fig. 11) were also found. The above-mentioned SSD structures were analyzed and interpreted following Strachan´s model (2002) (Fig. 10) and Laird´s model (1968) (Fig. 12). The origin of SSD structures depends on the characteristics of sedimentites and on the mechanisms that produce them. In the study area, the materials susceptible to deformation come from an interdune environment that is characterized by granulometric variations derived from the fluctuating and restrictive climatic conditions (Cojan and Thiry, 1992) that typify the Río Negro Formation. Fine-grained materials having low cohesion and poor sorting such as the sediments of deformed strata (Fig. 13) produced SSD structures as a result of high pore pressure and liquefaction effects (Tsuchida and Hayashi, 1971; Obermeier, 1996). Grain packing with a porous value as that allows intercommunication among grains and saturated material, is also crucial to the formation of SSD structures. The mineralogic content of deformed levels is composed of i) quartz, chalcedony, orthose, plagioclase, pyroxenes and biotite, opaques (magnetite and ilmenite, autigenic pyrite) in crystalline aggregates; ii) undetermined Fe oxides; and iii) colorless and light-brown unaltered volcanic glass shards, clays identified as smectite-illite interstratified and scarce kaolinite. Grains are mainly subangular and, to a lesser extent, sub-round and round. The surface of the majority of grains in the study area was found clean and with some marks. The percentage of CaCO3 was found to vary from 0.5 to 3% and that of total organic carbon (TOC) was found to reach 1.5%. Deformations may be produced as a result of load deformation mechanisms, fluid escape, basal slumping or pressure-directed displacements. Due to load deformation mechanisms, structures are linked to gravity-related movements occurring during the initial stages of deposition. For these deformations to occur, grain-size at the overlaying levels should be thicker than at the underlying levels, for example, sandstones rather than silstones or claystones. These deformations are related to water saturation at the deformed level (fluidization-liquefaction). Therefore, deformation mechanisms, which involve both expulsion and rotation of fragments as well as fluid escape, are characterized by the action of lithostatic pressure which produces movement (deformation) and by the action of the underlying sedimentary levels. Deformations may also result from a fluid escape mechanism, i.e., from a mechanism associated to i) the spatial arrangement of grains (packing), ii) their shape, iii) their tendency to inequigranularity, and iv) the communication among macro- and micro- pores as well as the high or low sinuosity connection among themselves (Net and Limarino, 2000). Further requirements for deformations to occur include particular thixotrophic conditions, especially the presence of colloids among grains. The rupture of unions of particles either by hitting or by shearing is, among others, a cause which produces an unbalance between hydrostatic pressure and lithostatic pressure. If the latter is altered, the energetic unbalance makes fine sediments flow among the weakly lithified sandstones whose extrusion will occur via both vertical and horizontal pore ducts (Lopez Gamundi, 1986; Clauss, 1993). Basal slumping produces deformations that are associated not only to soft sediments deposited in natural slopes but also to interbedded sand- and mud-levels. Layers tend to have a prismatic-shaped geometry whose materials are under ductile-to-fragile conditions, in which antique layers support younger ones. Once horizontality is affected, movement, which is marked by a rupture of the original slope, begins. The lower levels are expected to transport the upper ones without affecting the original succession of layers. At the delay of movement derived from the compressive effect of the displacement front, fluids extrude forming cones or cut dikes (Fig. 10). Several deformations of this type initiate movement as result of differences in the hydrostatic gradient (Strachan, 2002). Deformations may be also produced as a result of pressure-directed displacements which are conditioned by the compaction level, thickness and ability of materials to deform. Thus, deformations occur because the original level is saturated in water as a result of the ductile behavior of materials (Bracco et al., 2005). Laird (1968) claims that SSD structures should meet some of the following requirements to be considered of seismic origin: slightly curved strata walls and floors to follow the original stratification and interruption of continuity of the stratum that is marked by a scar in which the sedimentary fillings keep their characteristics both above and below stratification. There could be rotated sediment clasts below the discontinuity as a result of a thrust-induced drag of the upper sedimentary packing. These processes could be, in turn, triggered either by the charge or pressure of the lithologic column, storm waves and seismicity. Storm-wave impact may also produce deformation in soft sediments. Nonetheless, no high energy structures such as cross-beddings or tsunami-type chaotic sedimentation were observed in our study area. Noteworthingly, for stormwave-derived liquefaction to occur, waves should reach magnitudes higher than 6 m (Alfaro et al., 2002), this being a phenomenon that was not recorded in our study area. Taken together, findings from the present study indicate that SSD structures in our study area are seismic alterations that occurred in an event during the Andean cycle whose beginnings are traced approximately 45 My ago. The fact that i) both the roofs and bottoms of these structures are not associated to other processes of deformation, ii) their thickness does not exceed one meter, and iii) they are confined to a transitional area between the middle and top members of the Río Negro Formation, lying in some cases on claystones and in some other cases, on siltstones, originated in an interdune paleorelief, confirms their seismic origin.

Scientific Electronic Library Online (Spanish)

24

Deformación, vetas, inclusiones fluidas y la evolución tectónica de las rocas cretácicas de Valle de Bravo, Estado de México, México/ Deformation, veins, fluid inclusions and the tectonic evolution of the Valle de Bravo Cretaceous rocks, Estado de Mexico, Mexico

Fitz-Díaz, Elisa; Tolsón, Gustavo; Camprubí, Antoni; Rubio-Ramos, Marco A.; Prol-Ledesma, Rosa María
2008-01-01

Resumen en español En el área de Valle de Bravo, Estado de México, afloran dos ensambles de rocas cretácicas con metamorfismo de muy bajo grado: (1) rocas metasedimentarias (EMS), y (2) rocas metavolcánicas (EMV). Estas unidades forman parte de la secuencia mesozoica volcanosedimentaria metamorfizada de Ixtapan de la Sal - Teloloapan. La historia de deformación en la zona está definida por tres eventos de acortamiento subhorizontales (D1, D2 y D3), que coinciden en rumbo NE-SW, pero c (mas) on direcciones alternadas de transporte tectónico. D1 tiene una vergencia general hacia 043°, D2 hacia 218° y D3 hacia 045°. Estos tres eventos han sido identificados en diversas localidades de los estados de Guerrero y Michoacán, representando importantes fenómenos de deformación a escala regional. D1 muestra deformación dúctil a escala de grano, mientras que D2 es dúctil-quebradizo y D3es netamente quebradizo. Mediante el análisis de microestructuras en lámina delgada, a escala de afloramiento y con la determinación cuantitativo-comparativa de vetas mediante análisis de imágenes, se propone que D1 representa el pico metamórfico y deformacional y que D2 y D3 ocurrieron durante la exhumación de las rocas. Asociadas a los eventos D1 y D2, se desarrollaron dos generaciones de vetas, V1 y V2, cuya abundancia depende del grado de penetratividad de la deformación; es decir, de los fenómenos de deformación a escala microscópica (principalmente disolución por presión/reprecipitación) que movilizan material soluble que se deposita en forma de vetas en etapas tardías de la deformación. Adicionalmente a las vetas V1 y V2, se identificó también un sistema de vetas tardías (V3) asociadas a fallas normales que cortan estructuras D3. Análisis petrográfico y microtermométrico de inclusiones fluidas en cristales de cuarzo y calcita se realizaron en las tres generaciones de vetas en un área de 15 km² en el EMS. Las temperaturas de homogeneización obtenidas fueron, en promedio, de 250 °C para V], entre 167 y 202 °C para V2, y 220 °C para V3. Las correspondientes salinidades aparentes obtenidas fueron, en promedio, de entre 6.1 y 7.4 (V1), 5.2 (V2),y 2.6y 4.6 (V3) % en peso de NaCl equivalente. Los datos obtenidos en las vetas están de acuerdo con una exhumación progresiva de las rocas del área de estudio, ya que tanto las temperaturas de homogeneización como las salinidades asociadas a deformación son menores en V2 que en V1 . Mientras que las temperaturas de V3 indican que fluidos relativamente más calientes circularon a lo largo de fallas normales posteriormente a D1, D2yD3. Resumen en inglés In the Valle de Bravo area, central Mexico, two assemblages of cretaceous rocks are exposed. Both units present very low grade metamorphism: (1) a meta-sedimentary rock assemblage (EMS), and (2) a meta-volcanic rock assemblage (EMV). These rocks are part of the Ixtapan de la Sal - Teloloapan volcano-sedimentary metamorphosed Mesozoic sequence. The history of deformation of the two assemblages is represented by three sub-horizontal shortening events (D1, D2yD3), that displ (mas) ay similar NE-SW orientation, but alternating tectonic transport direction. D1 has a general vergence toward 043 °, whereas D2 toward 218°, and D3 toward 045°. The three events have been recognized in different localities in Guerrero andMichoacan states, and they represent important shortening episodes at regional scale. Event D1 exhibits ductile deformation at grain scale, while D2 is brittle-ductile, and D3 presents strictly brittle characteristics. We propose that D1 is the peak metamorphic/deformational event and that D2 and D3 occurred during exhumation of the rocks. During D1and D2, two generations of veins (V1 and V2, respectively) were developed. Abundance of the veins has been related directly to the penetrativity of deformation; which suggests that the mobilization of soluble material (mainly by pressure-solution/re-precipitation) was the effective mechanism of deformation at the microscopic scale. This soluble material was deposited in veins in later stages of the deformation event and was more intense during D1. This is demonstrated by the analysis ofmicrostructures in thin section, by outcrop observations and by the comparative-quantitative determination of density of veins through image analysis. In addition to the earlier V1 and V2 veins, late veins (V3) were also identified, and are associated dominantly to normal faults that cut D3 structures. Petrography and microthermometric analyses on fluid inclusions were done on quartz and calcite crystals of the three generations of veins in a 15 km² area in the EMS. The average homogenization temperatures were: 250 °Cfor V1, between 167 and 202 °Cfor V2 and 220 °Cfor V3. Corresponding salinities obtained were: between 6.1 y 7.4 (V1), 5.2 (V1), and between 2.6 and 4.6 (V3) (weight % ofNaCl equivalent). The data obtained in V1 and V2 are in agreement with a progressive exhumation of the rocks in the studied area, while the temperatures measured in V3 indicate that hotter fluids circulated along normal faults and associated vertical fractures after D3.

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