Papers by Pedro Oyhantçabal
International Journal of Earth Sciences, 2015
U–Pb and Hf zircon (SHRIMP and LA–ICP–MS), Ar/Ar hornblende and muscovite, and Rb–Sr whole rock–m... more U–Pb and Hf zircon (SHRIMP and LA–ICP–MS), Ar/Ar hornblende and muscovite, and Rb–Sr whole rock–muscovite isochron data from the mylonites of the Sarandí del Yí Shear Zone, Uruguay, were obtained in order to assess the tectonothermal evolution of this crustal–scale structure. Integration of these results with available kinematic, structural and microstructural data of the shear zone as well as with geochronological data from the adjacent blocks allowed to constrain the onset of deformation along the shear zone at 630–625 Ma during the collision of the Nico Pérez Terrane and the Río de la Plata Craton. The shear zone underwent dextral shearing up to 596 Ma under upper– to middle–amphibolite facies conditions, which was succeeded by sinistral shearing under lower–amphibolite to upper–greenschist facies conditions until at least 584 Ma. After emplacement of the Cerro Caperuza granite at 570 Ma, the shear zone underwent only cataclastic deformation between the late Ediacaran and the Cambrian. The Sarandí del Yí Shear Zone is thus related to the syn– to post–collisional evolution of the amalgamation of the Río de la Plata Craton and the Nico Pérez Terrane. Furthermore, the obtained data reveal that strain partitioning and localization with time, magmatism emplacement and fluid circulation are key processes affecting the isotopic systems in mylonitic belts, revealing the complexity in assessing the age of deformation of long–lived shear zones.
Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 2007
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 3... more 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 ... Dimensional stones in Uruguay: situation and perspectives ... Pedro Oyhantçabal, Siegfried Siegesmund, ...
Precambrian Research, 2010
Thus, it is truly tectonics which governs stratigraphy, and the two branches of the geological sc... more Thus, it is truly tectonics which governs stratigraphy, and the two branches of the geological sciences are inseparable. A structural geologists who is not a stratigrapher is only a geometer, not a geologist; for he reasons about abstract surfaces and volumes, emptied of their history; and a stratigrapher who never concerned himself with tectonics would produce only a dead stratigraphy," (Gignoux, 1950, p. 3).
International Geology Review, 2010
Actas XII Congreso Latinoamericano de Geología, 2005
El Cinturón Dom Feliciano (Fragoso Cesar 1980) está representado en Uruguay por lo que Preciozzi ... more El Cinturón Dom Feliciano (Fragoso Cesar 1980) está representado en Uruguay por lo que Preciozzi et al. (1991) definieron como Cinturón Cuchilla de Dionisio. Reúne al conjunto de unidades afectadas por metamorfismo y deformación durante el período Brasiliano (sensu Almeida et al. 1973) y al magmatismo de igual intervalo de edad, que se desarrolla constituyendo una faja en el sureste del Uruguay. Diversas sucesiones supracorticales han sido reconocidas en el Dominio occidental de este cinturón en el Uruguay, a saber, Fm. Zanja del Tigre (Sánchez-Bettucci 1998), Grupo Lavalleja (Bossi 1966), Grupo Arroyo del Soldado (Gaucher et al. 1996) y Formaciones Playa Hermosa (Masquelin y Sánchez Bettucci 1993) y Las Ventanas (Midot 1984), entre otras. El Grupo Lavalleja ha sido correlacionado con el Grupo Porongos y con el Complejo Metamórfico Brusque de Brasil (Hasui et al. 1975; Silva y Dias 1981). Este Grupo posee un basamento granítico-gnéissico probablemente asociado al Bloque Valentines (Preciozzi et al. 1979) y al Terreno Pavas, con edades Paleoproterozoicas y Arqueanas (Hartmann et al. 2001).
Actas V Congreso Uruguayo de Geología, 2010, May 1, 2010
La Zona de Cizalla Sarandí del Yí divide el Cratón del Río de la Plata en los terrenos Nico Pérez... more La Zona de Cizalla Sarandí del Yí divide el Cratón del Río de la Plata en los terrenos Nico Pérez y Piedra Alta. El extremo sur de esta Zona se extiende con dirección Norte - Sur desde los alrededores de la localidad de Minas hasta Punta Solís. La litología predominante del área de estudio consiste en una milonita granítica con abundante moscovita y biotita.
Se relevaron datos estructurales de foliación, lineación de estiramiento e indicadores cinemáticos. La foliación milonítica se encuentra plegada, siendo el eje de los pliegues paralelo a la lineación de estiramiento. La orientación promedio de la foliación es N 010º/60º NW formando un pequeño ángulo con la zona de cizalla, que sugiere un sentido de cizalla sinestral. La lineación de estiramiento es sub-horizontal, con una inmersión que varía entre 20º al 012º y 15º al 200º indicando tectónica transcurrente. En los afloramientos es frecuente observar porfiroclastos de feldespato indicando sentido sinestral.
El análisis petrográfico muestra que el cuarzo se presenta formando “ribbons” policristalinos, producto de recristalización por rotación de subgranos y migración de borde de grano. El feldespato se encuentra en porfiroclastos parcialmente recristalizados desarrollando estructuras de tipo “core and mantle”.
Los indicadores cinemáticos como porfiroclastos tipo sigma, “mica fish” y foliación oblicua definen sistemáticamente sentido sinestral.
La presencia de biotita estable y mirmequitas en el plano de la foliación, junto a las microestructuras descritas en cuarzo y feldespato, permiten inferir condiciones de temperatura entre 450ºC y 550ºC durante la deformación.
Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 2008
The mechanical properties of sandstones are a critical parameter and of vital importance for seve... more The mechanical properties of sandstones are a critical parameter and of vital importance for several topics
in the applied geosciences. For a systematic study eight sandstone varieties (Bad Bentheim, Bebertal, Obernkirchen, Sander, Schleerither, Tambach, Weser grau, Weser rot) were selected. All lithotypes were studied with respect to the mineralogical composition and its fabrics. They differ in composition, porosity (from 6 to 26 %) and
in the pore radii distribution. The impact of partial water saturation on the uniaxial compressive strength (UCS) is highly variable and is a function of the micro to macro pore ratio. Sandstones belonging to the intermediate and low porosity group show higher values of the UCS and a pronounced sensitivity to the water saturation. The reduction in the UCS with increasing water content is significant, with values of up to 50 % strength loss. In general, if weakening occurs, it occurs when the water saturation is below 30 percent. Bad Bentheim and Obernkirchen sandstones are less sensitive to the water saturation/UCS relation. The proportion of pores below 0.1μm could have a significant control on the strength loss and hygric expansion. The correlation observed between the reduction of the UCS and the hygric expansion could be explained by swelling clay minerals or be caused by the disjoining pressures within the small pores.
In the basement at both sides of the Shear Zone, a first deformation stage is recognized as a hig... more In the basement at both sides of the Shear Zone, a first deformation stage is recognized as a high temperature mylonitic foliation associated with migmatization. The microstructures indicate that diffusion creep was an important deformation mechanism, probably enhanced by ...
V South American …, Jan 1, 2006
The Solís de Mataojo Complex (SMC) is a syn-transcurrent intrusive, emplaced in the Sarandí del Y... more The Solís de Mataojo Complex (SMC) is a syn-transcurrent intrusive, emplaced in the Sarandí del Yí Shear Zone. In its southern extreme this shear zone is the boundary between the Río de la Plata Craton and the Dom Feliciano Belt. The SMC consists of tonalites, granodiorites, and granites. The high K 2 O+Na 2 O, Ba and Sr and the REE pattern are typical of medium to high-K 2 O calc-alkaline post-collisional granites ("I Caledonian-type"). A new age of 584±13 Ma (Pb/Pb on sphene) was obtained for the tonalite facies (34º35.4'S -055º26.5'W).
Precambrian …, Jan 1, 2010
Thus, it is truly tectonics which governs stratigraphy, and the two branches of the geological sc... more Thus, it is truly tectonics which governs stratigraphy, and the two branches of the geological sciences are inseparable. A structural geologists who is not a stratigrapher is only a geometer, not a geologist; for he reasons about abstract surfaces and volumes, emptied of their history; and a stratigrapher who never concerned himself with tectonics would produce only a dead stratigraphy," (Gignoux, 1950, p. 3).
The Isla Cristalina de Rivera crystalline complex in northeastern Uruguay underwent a multistage ... more The Isla Cristalina de Rivera crystalline complex in northeastern Uruguay underwent a multistage magmatic and metamorphic evolution. Based on SHRIMP U–Pb zircon, Th–U–Pb monazite (CHIME-EPMA method) and K–Ar age data from key units several events can be recognized: (1) multistage magmatism at 2,171–2,114 Ma, recorded on zircon of the granulitic orthogneisses and their 2,093–2,077 Ma overgrowths; (2) a distinct amphibolite facies metamorphism at 1,980 Ma, recorded by monazite; (3) greenschist facies reworking and shearing at ca. 606 Ma (monazite and K–Ar on muscovite) along the Rivera Shear Zone, and finally (4) intrusion of the post-tectonic Sobresaliente and Las Flores granites at around 585 Ma. Lithological similarities, geographic proximity and coeval magmatic and metamorphic events indicate a similar tectonometamorphic evolution for the Isla Cristalina de Rivera, the Valentines Block in Uruguay and the Santa Marıa Chico Granulitic Complex in southern Brazil, since at least 2.1 Ga.
The Isla Cristalina de Rivera crystalline complex in northeastern Uruguay underwent a multistage ... more The Isla Cristalina de Rivera crystalline complex in northeastern Uruguay underwent a multistage magmatic and metamorphic evolution. Based on SHRIMP U–Pb zircon, Th–U–Pb monazite (CHIME-EPMA method) and K–Ar age data from key units several events can be recognized: (1) multistage magmatism at 2,171–2,114 Ma, recorded on zircon of the granulitic orthogneisses and their 2,093–2,077 Ma overgrowths; (2) a distinct amphibolite facies metamorphism at 1,980 Ma, recorded by monazite; (3) greenschist facies reworking and shearing at ca. 606 Ma (monazite and K–Ar on muscovite) along the Rivera Shear Zone, and finally (4) intrusion of the post-tectonic Sobresaliente and Las Flores granites at around 585 Ma. Lithological similarities, geographic proximity and coeval magmatic and metamorphic events indicate a similar tectonometamorphic evolution for the Isla Cristalina de Rivera, the Valentines Block in Uruguay and the Santa Marıa Chico Granulitic Complex in southern Brazil, since at least 2.1 Ga.
Congreso Uruguayo de …, Jan 1, 1990
SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.
orton.catie.ac.cr
SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.
Congreso Uruguayo de …, Jan 1, 1990
SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.
… ^ j1er. Montevideo, UY. 25-27 abr. …, Jan 1, 1990
SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.
… ^ j1er. Montevideo, UY. 25-27 abr. …, Jan 1, 1990
SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.
… de Geología^ j1er. …, Jan 1, 1990
... Signatura: 55(899) CON. Aut. Analit.: Oyhantçabal, Pedro; Medina Estefan, Eduardo; Spoturno P... more ... Signatura: 55(899) CON. Aut. Analit.: Oyhantçabal, Pedro; Medina Estefan, Eduardo; Spoturno Pioppo, Julio Jorge. Conferencia: Congreso Uruguayo de Geología^j1er. Montevideo, UY. 25-27 abr. 1990. Título: Geología y petrología del stock de gabro del arroyo Mahoma. ...
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Papers by Pedro Oyhantçabal
Se relevaron datos estructurales de foliación, lineación de estiramiento e indicadores cinemáticos. La foliación milonítica se encuentra plegada, siendo el eje de los pliegues paralelo a la lineación de estiramiento. La orientación promedio de la foliación es N 010º/60º NW formando un pequeño ángulo con la zona de cizalla, que sugiere un sentido de cizalla sinestral. La lineación de estiramiento es sub-horizontal, con una inmersión que varía entre 20º al 012º y 15º al 200º indicando tectónica transcurrente. En los afloramientos es frecuente observar porfiroclastos de feldespato indicando sentido sinestral.
El análisis petrográfico muestra que el cuarzo se presenta formando “ribbons” policristalinos, producto de recristalización por rotación de subgranos y migración de borde de grano. El feldespato se encuentra en porfiroclastos parcialmente recristalizados desarrollando estructuras de tipo “core and mantle”.
Los indicadores cinemáticos como porfiroclastos tipo sigma, “mica fish” y foliación oblicua definen sistemáticamente sentido sinestral.
La presencia de biotita estable y mirmequitas en el plano de la foliación, junto a las microestructuras descritas en cuarzo y feldespato, permiten inferir condiciones de temperatura entre 450ºC y 550ºC durante la deformación.
in the applied geosciences. For a systematic study eight sandstone varieties (Bad Bentheim, Bebertal, Obernkirchen, Sander, Schleerither, Tambach, Weser grau, Weser rot) were selected. All lithotypes were studied with respect to the mineralogical composition and its fabrics. They differ in composition, porosity (from 6 to 26 %) and
in the pore radii distribution. The impact of partial water saturation on the uniaxial compressive strength (UCS) is highly variable and is a function of the micro to macro pore ratio. Sandstones belonging to the intermediate and low porosity group show higher values of the UCS and a pronounced sensitivity to the water saturation. The reduction in the UCS with increasing water content is significant, with values of up to 50 % strength loss. In general, if weakening occurs, it occurs when the water saturation is below 30 percent. Bad Bentheim and Obernkirchen sandstones are less sensitive to the water saturation/UCS relation. The proportion of pores below 0.1μm could have a significant control on the strength loss and hygric expansion. The correlation observed between the reduction of the UCS and the hygric expansion could be explained by swelling clay minerals or be caused by the disjoining pressures within the small pores.
Se relevaron datos estructurales de foliación, lineación de estiramiento e indicadores cinemáticos. La foliación milonítica se encuentra plegada, siendo el eje de los pliegues paralelo a la lineación de estiramiento. La orientación promedio de la foliación es N 010º/60º NW formando un pequeño ángulo con la zona de cizalla, que sugiere un sentido de cizalla sinestral. La lineación de estiramiento es sub-horizontal, con una inmersión que varía entre 20º al 012º y 15º al 200º indicando tectónica transcurrente. En los afloramientos es frecuente observar porfiroclastos de feldespato indicando sentido sinestral.
El análisis petrográfico muestra que el cuarzo se presenta formando “ribbons” policristalinos, producto de recristalización por rotación de subgranos y migración de borde de grano. El feldespato se encuentra en porfiroclastos parcialmente recristalizados desarrollando estructuras de tipo “core and mantle”.
Los indicadores cinemáticos como porfiroclastos tipo sigma, “mica fish” y foliación oblicua definen sistemáticamente sentido sinestral.
La presencia de biotita estable y mirmequitas en el plano de la foliación, junto a las microestructuras descritas en cuarzo y feldespato, permiten inferir condiciones de temperatura entre 450ºC y 550ºC durante la deformación.
in the applied geosciences. For a systematic study eight sandstone varieties (Bad Bentheim, Bebertal, Obernkirchen, Sander, Schleerither, Tambach, Weser grau, Weser rot) were selected. All lithotypes were studied with respect to the mineralogical composition and its fabrics. They differ in composition, porosity (from 6 to 26 %) and
in the pore radii distribution. The impact of partial water saturation on the uniaxial compressive strength (UCS) is highly variable and is a function of the micro to macro pore ratio. Sandstones belonging to the intermediate and low porosity group show higher values of the UCS and a pronounced sensitivity to the water saturation. The reduction in the UCS with increasing water content is significant, with values of up to 50 % strength loss. In general, if weakening occurs, it occurs when the water saturation is below 30 percent. Bad Bentheim and Obernkirchen sandstones are less sensitive to the water saturation/UCS relation. The proportion of pores below 0.1μm could have a significant control on the strength loss and hygric expansion. The correlation observed between the reduction of the UCS and the hygric expansion could be explained by swelling clay minerals or be caused by the disjoining pressures within the small pores.