Fig 2 - uploaded by Nestor Vegas
Content may be subject to copyright.
-A-D: Fotografías de estructuras observadas en afloramientos del plutón de La Fronda A y B: Pliegues complejos que afectan a un bandeado composicional. C: Bandeado afectado por pliegues superpuestos del tipo 3 de Ramsay (1976). D: Bandeado (paralelo al eje mayor de la fotografía ) y foliación perpendicular al mismo. E y F: Microfotografías de láminas delgadas donde se observan kink bands en biotita, maclas curvadas y kink bands en plagioclasa (E), y subgranos de cuarzo en damero (F).
Contexts in source publication
Context 1
... la foliación y el bandeado composicional son concordantes, pero en varios sectores se aprecia una oblicuidad notoria, e incluso perpendicularidad, en- tre esas dos estructuras planares. Estos sectores anómalos están relacionados in- variablemente con la presencia de plie- gues de dimensiones, morfologías y orientaciones sumamente variables ( Fig. 2 A-D). La mayoría de los pliegues son isoclinales y carecen de engrosamiento en la zona de charnela. En ocasiones se aprecian figuras de pliegues superpuestos del tipo 3 de Ramsay (1976) (Fig. 2 C). Las zonas de charnela permiten distinguir dos grupos de cristales de mica: el prime- ro está integrado por cristales en los que se llegan a ...
Context 2
... sectores anómalos están relacionados in- variablemente con la presencia de plie- gues de dimensiones, morfologías y orientaciones sumamente variables ( Fig. 2 A-D). La mayoría de los pliegues son isoclinales y carecen de engrosamiento en la zona de charnela. En ocasiones se aprecian figuras de pliegues superpuestos del tipo 3 de Ramsay (1976) (Fig. 2 C). Las zonas de charnela permiten distinguir dos grupos de cristales de mica: el prime- ro está integrado por cristales en los que se llegan a reconocer kink bands a simple vista y que dibujan el bandeado composicional, mientras que el segundo corresponde a cristales euhédricos que definen una foliación de plano axial de los pliegues ...
Context 3
... (Fig. 2 C). Las zonas de charnela permiten distinguir dos grupos de cristales de mica: el prime- ro está integrado por cristales en los que se llegan a reconocer kink bands a simple vista y que dibujan el bandeado composicional, mientras que el segundo corresponde a cristales euhédricos que definen una foliación de plano axial de los pliegues (Fig. 2 ...
Context 4
... coexisten con agregados policristalinos de cuarzo que conservan formas equiaxiales, lo que sugiere que se trata de una deformación en condiciones sub- solidus, previa a la cristalización comple- ta del magma. La presencia de mirmequitas, maclas curvadas y maclas mecánicas en plagioclasa o de agregados de cuarzo con subestructura en damero (Fig. 2 E-F), avalan que la deformación se produjo en condiciones de alta tempe- ...
Context 5
... al bandeado composicional y a una primera foliación paralela al bandeado, definida por cristales de mica y de plagioclasa. Estas estructuras planares han sido deformadas posterior- mente por los pliegues y por la foliación de plano axial descritos. Tanto las característi- cas geométricas de los pliegues, como las microestructuras observadas (Fig. 2) o los bajos valores de la anisotropía de la suscep- tibilidad magnética avalan el origen magmático de los ...
Similar publications
A pesar que la Argentina todavía puede ser considerado un país de propietarios, la vivienda en alquiler es una práctica en crecimiento y trasversal a todos los hogares, independientemente de su nivel de ingresos. Sin embargo, la disponibilidad de viviendas asequibles es inadecuada y gran parte de los hogares inquilinos se encuentran gravemente afec...
The República Argentina has a total surface of approximately 2.8 million km2.
El Índice que acá presentamos consiste en un análisis de componentes principales de características socioeconómicas. Con una interfaz interactiva y grandes volúmenes de datos públicos del INDEC podemos recorrer y analizar diversos patrones a través de la geografía Argentina que sirven como insumo tanto para la elaboración de políticas públicas como...
Citations
... The complex structural and metamorphic evolution of this basement reflects the overprinting of successive orogenic cycles (González Bonorino, 1950;Gordillo and Lencinas, 1979;Ortiz Suárez et al., 1992;Rapela et al., 1998Rapela et al., , 2018Ramos et al., 2014;Casquet et al., 2018;Weinberg et al., 2018). Between Late Cambrian to Middle Ordovician times (510-460 Ma), the metamorphic basement was intruded by plutons and dykes of tonalite, trondhjemite, granodiorite and to, a lesser degree, granite that make part of a trondhjemite-tonalite-granite (TTG) Famatinian magmatic arc (Rapela et al., 1998;Pankhurst et al., 2000;D'Eramo, 2003;D'Eramo et al., 2006a;2006b;Rapela et al., 2018). The geochemical features of the TTG magmatism in Córdoba, i.e., Na 2 O, CaO and Sr enrichment, K 2 O, FeO, Cs, Y and U depletion, low Rb/Sr ratios, positive or absent Eu anomalies, high [La/Yb] N ratios, relatively low 87 Sr/ 86 Sr initial ratios and variable ε Nd values, suggest that a deep magmatic source of probably astenospheric origin was incorporated to the magma leading to the formation of the trondhjemite plutons of the Sierra Chica de Córdoba (D'Eramo et al., 2006a). ...
... The Calmayo pluton (Fig. 1), similar to the nearby El Hongo and San Agustin trondhjemite plutons, belongs to the G-2 magmatic group defined by Rapela et al. (1998). The three plutons were emplaced at crustal levels close to the brittle-ductile transition (D'Eramo, 2003;D'Eramo et al., 2006aD'Eramo et al., , 2006b. High-to medium-temperature metasomatic skarns are commonly observed when marbles are in contact with the trondhjemites. ...
... Other similar examples have been reported by Mamtani et al. (2013), Majumder and Mamtani (2009) and Bhatt et al. (2017). The geometry obtained from gravity modeling in the Calmayo pluton is similar to that obtained on other plutons around the world, such as those of the French Massif Central (Vigneresse, 1990), and some other examples of the Sierras Pampeanas (D'Eramo et al., 2006b). The gravimetric study reveals the presence of a single root or feeding channel, which would have a submeridional major axis (NNW). ...
This study provides new insights about mechanisms of synkinematic interplay between dyking emplacement and ductile narrow shear zones formation in the Sierra Chica de Córdoba. A detailed analysis of structural, microstructural, geometric-scaling and geochronologic data is performed in order to demonstrate the important role that minor and meso-scale felsic dykes played in the formation of paired shear zones symmetrically from dyke contacts. This magmatism and associated deformation conspicuously overprint medium-to high grade metamorphic and igneous rocks of Pampean age. Internally, the shear zones are formed by mylonites with mineral paragenesis in the amphibolite facies and foliation planes totally concordant to dyke contacts. Low rheological contrast between igneous intrusions and host rocks, together with fast rates of magma channeling and emplacement, were responsible for a brittle mechanical regime at moderate to high temperatures (500–700 °C). Melt-filled shear fractures rapidly propagated while the host rock was being mylonitized at ductile conditions. Shear structures controlling dyke construction and mylonite formation adjust to a strike-slip dominated dextral transtensional regime. The predicted axes of finite maximum shortening (Z) and maximum extension (X) have NNE and NNW directions, respectively. Ar/Ar muscovite cooling ages determined for pegmatite dykes, yielded minimum crystallization ages between 451 ± 1 and 435 ± 3 My. These geochronological data are further supported by field structural relationships and the regional knowledge, pointing to a Famatinian age for magmatism and related narrow shear zones. This paper constitutes a new contribution reporting the occurrence of magmatism and strike-slip-dominated dextral transtension deformation in the inner foreland of the Famatinian accretionary orogen, developed in the Early Paleozoic along the southwestern Gondwana margin.
... The complex structural and metamorphic evolution of this basement reflects the overprinting of successive orogenic cycles (González Bonorino, 1950;Gordillo and Lencinas, 1979;Ortiz Suárez et al., 1992;Rapela et al., 1998Rapela et al., , 2018Ramos et al., 2014;Casquet et al., 2018;Weinberg et al., 2018). Between Late Cambrian to Middle Ordovician times (510-460 Ma), the metamorphic basement was intruded by plutons and dykes of tonalite, trondhjemite, granodiorite and to, a lesser degree, granite that make part of a trondhjemite-tonalite-granite (TTG) Famatinian magmatic arc (Rapela et al., 1998;Pankhurst et al., 2000;D'Eramo, 2003;D'Eramo et al., 2006a;2006b;Rapela et al., 2018). The geochemical features of the TTG magmatism in Córdoba, i.e., Na 2 O, CaO and Sr enrichment, K 2 O, FeO, Cs, Y and U depletion, low Rb/Sr ratios, positive or absent Eu anomalies, high [La/Yb] N ratios, relatively low 87 Sr/ 86 Sr initial ratios and variable ε Nd values, suggest that a deep magmatic source of probably astenospheric origin was incorporated to the magma leading to the formation of the trondhjemite plutons of the Sierra Chica de Córdoba (D'Eramo et al., 2006a). ...
... The Calmayo pluton (Fig. 1), similar to the nearby El Hongo and San Agustin trondhjemite plutons, belongs to the G-2 magmatic group defined by Rapela et al. (1998). The three plutons were emplaced at crustal levels close to the brittle-ductile transition (D'Eramo, 2003;D'Eramo et al., 2006aD'Eramo et al., , 2006b. High-to medium-temperature metasomatic skarns are commonly observed when marbles are in contact with the trondhjemites. ...
... Other similar examples have been reported by Mamtani et al. (2013), Majumder and Mamtani (2009) and Bhatt et al. (2017). The geometry obtained from gravity modeling in the Calmayo pluton is similar to that obtained on other plutons around the world, such as those of the French Massif Central (Vigneresse, 1990), and some other examples of the Sierras Pampeanas (D'Eramo et al., 2006b). The gravimetric study reveals the presence of a single root or feeding channel, which would have a submeridional major axis (NNW). ...
In this paper, the evolution of the fabric and 3D geometry of the Calmayo trondhjemitic pluton (512.1 ± 3.4 Ma; Sierra Chica, Córdoba, Argentina) is analyzed using Anisotropy of Magnetic Susceptibility (AMS) measurements combined with structural and microstructural data. Gravity data reveal that the pluton is a funnel-shaped body resting on one main root zone detected below the central portion of the pluton. The microstructural observations in the trondhjemite rocks show a progressive textural overprint from magmatic, through high-T to low-T solid-state deformation textures. This overprint is interpreted to be a consequence of the dynamic emplacement and local deformation, particularly close to the adjacent Soconcho shear zone. Late oxidation of the magnetic mineral assemblage (martitization of magnetite) is more intense in the central and southern sectors close to the root zone, explaining the flat magnetic response of this area, and contrasting with a noisy domain to the northeast where magnetite is preserved. We propose that the Calmayo pluton was constructed by several pulses that ascended through a root zone or main conduit. This root zone represents feeder dykes that exploited tension fractures linked to the Soconcho shear zone. Fluids responsible for the late oxidation would have followed similar paths through this protracted shear zone.
... Hongo and La Fronda plutons combining information from country rocks with structural and magnetic fabric data from the trondhjemites (D'Eramo et al., 2006a(D'Eramo et al., , 2006b(D'Eramo et al., and 2013. The La Fronda pluton is a small massif elongated N-S (25 km 2 ), whereas the Calmayo (10 km 2 ) and El Hongo (4 km 2 ) plutons are elongated ENEeWSW (Fig. 1). ...
... The coupling between magma injection and the regional stress field may have controlled the shape of the pluton, the magma flow history and its folding (Stevenson, 2009). An AMS study reveals that the magnetic planar fabric is parallel to either the layering or the axial plane foliation (Fig. 6b, D'Eramo et al., 2006b). Deformation related to space generation for magma emplacement could explain the formation of folds in magmas having low melt fractions, as proposed by Pignotta and Benn (1999). ...
Processes like injection, magma flow and differentiation and influence of the regional strain field are here described and contrasted to shed light on their role in the formation of small plutons and large batholiths their magmatic structures. The final geometric and compositional arrangement of magma bodies are a complex record of their construction and internal flow history. Magma injection, flow and differentiation, as well as regional stresses, all control the internal nature of magma bodies. Large magma bodies emplaced at shallow crustal levels result from the intrusion of multiple magma batches that interact in a variety of ways, depending on internal and external dynamics, and where the early magmatic, growth-related structures are commonly overprinted by subsequent history. In contrast, small plutons emplaced in the brittle-ductile transition more likely preserve growth-related structures, having a relatively simple cooling history and limited internal magma flow. Outcrop-scale magmatic structures in both cases record a rich set of complementary information that can help elucidate their evolution. Large and small granitic bodies of the Sierra Pampeanas preserve excellent exposures of magmatic structures that formed as magmas stepped through different rheological states during pluton growth and solidification. These structures reveal not only the flow pattern inside magma chambers, but also the rheological evolution of magmas in response to temperature evolution.
Structural aspects of granites related to mechanisms for structures development and their timing of formation are still a subject of lively debate. Many authors suggest that structures generated during magmatic stages (i.e. from early magmatic flow with mineral grains suspended in melt to late magmatic grain-supported flow) are only hardly preserved in granitic bodies. In this contribution, several magmatic structures in granitoid plutons from Sierras Pampeanas are showed, where small plutons and batholithic-sized bodies are both analysed. We discuss: a) map-scale lithological variations, such as principal magmatic units, where magma dynamics are evidenced by mixing processes within magmatic chamber; b) metre to decametre-scale magmatic layering that may be isomodal or modally-graded; c) overprinting submagmatic structures indicating interplay between plutons or pluton internal units according to regional deformation; d) composite magmatic layering and schlieren commonly associated to mafic microgranular enclaves, locally within synmagmatic shear zones. These structural features can be ascribed to three main processes: a) assembly of differentiated magmatic pulses; b) local hydrodynamic sorting related to density currents in a mush; c) mechanical disruption and chemical hybridization of mafic magmas during ascent and emplacement; among others. The identification of preserved structures in granitoids, their timing and mechanisms of formation, as well as the structural dynamic of the surrounding crust, play a prominent role in proposing emplacement models for granitic plutons.
