The significance of «S-C» structures found in the Berzosa-Honrubia region (Spanish Central System)

[Resumen] En el extremo oriental del Sistema Central Español, existen evidencias de un episodio tect6nico fini -hercínico, que se manifiesta en el desarrollo de una banda de 1 a 2 Km de anchura, de dirección submeridiana y buzamiento al este en la que son frecuentes estructuras de tipo «S-C» dúctiles. Esta banda probablemente extensional, se superpone a la estructura singular de segunda fase hercínica (D2), conocida como Zona de Cizalla de Berzosa (Z.C.B., CAPOTE, R. et alters, 1981; GONZALEZ CASADO,]. M., 1986), tradicionalmente interpretada como un cabalgamiento dúctil hacia el noroeste retrovergido por la fase de pliegues longitudinales D3. La zona descrita coincide además espacialmente con una banda donde existen procesos hidrotermales tardíos, los cuales podrían relacionarse genéticamente con la estructura citada. El probable episodio extensional descrito, puede relacionarse con la etapa de extensión regional generalizada que se desarrolla durante el final del ciclo hercínico en toda la cadena. Período este bien reflejado en muchos puntos del Sistema Central Español, en forma de importantes accidentes tectónicos extensionales, principalmente de dirección este-oeste y buzamiento norte o sur.[Abstract] In the east end of the Spanish Central System there are sorne evidence of a latehercynian tectonic event. Field evidences includes the presence of «S» and «C» planes (composite planar fabrics), in a band of 1 or 2 Km of wide, with an eastwest direction and dipping to the east. This area has probable an extensional origin and has been superimposed to a structure related to the herc.ynian second phase (D2) know as the Berzosa Shear Zone (B.S.Z., CAPOTE, R., et alters, 1981; GONZALEZ CASADO, J. M., 1986). The B.S.Z. has ben interpreted as a ductil thrust towards the nort-oest, backfolded by a phase of longitudinal folds 03. The investigated region shows a spatial correlation with a band where there are sorne late hidrotermal process, what could be genetic related with the studied structure. Microstructural evidence are internally consistent with field observations. It appears that data are compatible with N-S oriented extensional detachment, dipping to the east, with and east-under-west sense of movement. This event could be correlated with a period of regional extension found elsewhere in the Spanish Central System. Developped for aH the belt during the end of the hercynian cicle. This last even is weH developped in several points of the Spanish Central System and can be seen as severa! E-W oriented detachment systems, dipping to the N and S (extensional tectonics)

U-Pb SHRIMP zircon dating of Grenvillian metamorphism in Western Sierras Pampeanas (Argentina) : correlation with the Arequipa-Antofalla craton and constraints on the extent of the Precordillera Terrane

The Sierras Pampeanas of Argentina, the largest outcrop of pre-Andean crystalline basement in southern South America, resulted from plate interactions along the proto-Andean margin of Gondwana, from as early as Mesoproterozoic to Late Paleozoic times (e.g., Ramos, 2004, and references therein). Two discrete Paleozoic orogenic belts have been recognized: the Early Cambrian Pampean belt in the eastern sierras, and the Ordovician Famatinian belt, which partially overprints it to the west (e.g., Rapela et al., 1998). In the Western Sierras Pampeanas, Mesoproterozoic igneous rocks (ca. 1.0–1.2 Ga) have been recognized in the Sierra de Pie de Palo (Fig. 1) (McDonough et al., 1993 M.R. McDonough, V.A. Ramos, C.E. Isachsen, S.A. Bowring and G.I. Vujovich, Edades preliminares de circones del basamento de la Sierra de Pie de Palo, Sierras Pampeanas occidentales de San Juán: sus implicancias para el supercontinente proterozoico de Rodinia, 12° Cong. Geol. Argentino, Actas vol. 3 (1993), pp. 340–342.McDonough et al., 1993, Pankhurst and Rapela, 1998 and Vujovich et al., 2004) that are time-coincident with the Grenvillian orogeny of eastern and northeastern North America (e.g., Rivers, 1997 and Corrievau and van Breemen, 2000). These Grenvillian-age rocks have been considered to be the easternmost exposure of basement to the Precordillera Terrane, a supposed Laurentian continental block accreted to Gondwana during the Famatinian orogeny (Thomas and Astini, 2003, and references therein). However, the boundaries of this Grenvillian belt are still poorly defined, and its alleged allochthoneity has been challenged (Galindo et al., 2004). Moreover, most of the Grenvillian ages so far determined relate to igneous protoliths, and there is no conclusive evidence for a Grenvillian orogenic belt, other than inferred from petrographic evidence alone (Casquet et al., 2001). We provide here the first evidence, based on U–Pb SHRIMP zircon dating at Sierra de Maz, for a Grenville-age granulite facies metamorphism, leading to the conclusion that a continuous mobile belt existed throughout the proto-Andean margin of Gondwana in Grenvillian times

The geological setting of Carboniferous magmatism in the proto-Andean margin of Gondwana, Sierra Pampeanas, Argentina

Fil: Dahlquist, J. A. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Dahlquist, J. A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Basei, M. Universida de de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Alasino, P. H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Alasino, P. H. Universidad Nacional de la Rioja. INGeReN-CENIIT; Argentina.Fil: Alasino, P. H. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina.Fil: Campos, M. Universidade de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Casquet, C. Universidad Complutense. Departamento de Petrología y Geoquímica; España.Our petrogenetic understanding of the Carboniferous granites of the Sierras Pampeanas has improved in recent years, but their geodynamic setting is still not well constrained. Domeier and Torsvik (2014) affirm that there is no documented and unambiguous evidence of an active margin in the proto-Andean margin of Gondwana before the late Carboniferous (~ 320 Ma).Fil: Dahlquist, J. A. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Dahlquist, J. A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Basei, M. Universida de de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Alasino, P. H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Alasino, P. H. Universidad Nacional de la Rioja. INGeReN-CENIIT; Argentina.Fil: Alasino, P. H. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina.Fil: Campos, M. Universidade de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Casquet, C. Universidad Complutense. Departamento de Petrología y Geoquímica; España.Geoquímica y Geofísic

Síntesis geocronológica de la evolución paleozoica inferior del borde sur occidental de Gondwana en las Sierras Pampeanas, Argentina

Las Sierras Pampeanas Argentinas constituyen un buen registro de la evolución Pre-Devónica del margen sur occidental del Gondwana.Los trabajos multidisciplinarios recientes y especialmente la información geocronológica, recolectada a lo largo de una transecta E-W de aproximadamente unos 500 km, permiten precisar la edad y los rasgos geológicos de los dos principales ciclos tectono-magmáticos involucrados en la evolución paleozoica inferior de esta parte del basamento argentino.El Ciclo Orogénico Pampeano comienza con una etapa de sedimentación en un margen pasivo (560-530 Ma), que evoluciona hacia una situación de margen activo con generación de un arco magmático tipo Andino, a los 533 - 528 Ma. El ciclo finaliza hacia los 523 Ma. en una colisión de tipo ortogonal, con un importante engrosamiento cortical, anatexis regional y generación de granitos "S". El "Ciclo Orogénico Famatiniano" se inicia a los 499-496 Ma y se caracteriza por la implantación de un arco magmático intemo de tipo trondhjemitico, seguido hacia el oeste por un importante arco magmático externo, contemporáneo con el anterior y formado por granodioritas de tipo "I" y grandes batolitos graníticos de tipo "S". Durante el Famatiniano tiene también lugar la formación de una cuenca de retroarco ensiálica con magmatismo básico. El final de este ciclo (450-420 Ma) está marcado por el desarrollo de importantes fajas de milonitización que marcan la colisión oblicua del Terreno Precordillera respecto al margen de Gondwana

Hydrothermal alteration in granites from La Cabrera (Spanish Central System). Study of secondary minerals (SEM) in halos of calcium bearing mineral druses

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasFALSEEspaña. Ministerio de Educación y Cienciapu

Sr, C and O isotope composition of marbles from the Sierra de de Ancasti, Eastern Sierras Pampeanas, Argentina: age and constraints for the Neoproterozoic–Lower Paleozoic evolution of the proto-Gondwana margin

The Sierra Brava Complex on the eastern flank of the Sierra de Ancasti consists of marbles, metabasites, calc-silicate rocks, psammo-pelitic schists and gneisses. In the central part of this sierra a thick succession of banded schists (Ancasti Formation) crops out. Regional metamorphism of these rocks is attributed to the Famatinian orogeny (Ordovician), metamorphic grade increasing westwards and southwards and culminating in a migmatite complex on the western side of the Sierra. The meta-carbonate rocks are subdivided into a northeastern group (low-grade calcite marbles), and a southeastern group (high-grade calcite and calcite-dolomite marbles). Twenty-three marble samples were analysed for Sr isotope composition and Rb, Mn, Mg and Ca contents, and six for C and O isotope composition. An Ediacaran depositional age of 570 –590Ma is inferred by reference to the trend of 87Sr/86Sr in Neoproterozoic seawater. Thus the metacarbonates are probably slightly older than the Ancasti Formation (equivalent to the Puncoviscana Formation of northern Argentina), which has a maximum sedimentation age of ca. 570Ma. Ediacaran depositional ages have also been reported for metacarbonates elsewhere in Argentina, Uruguay and Brazil. We propose that the Sierra de Ancasti carbonates on one hand, and those in the Western Sierras Pampeanas (Difunta Correa Sequence) and –tentativelythe Corumbá Group of Brazil on the other, represent platforms on opposite margins of the extinct Clymene Ocean, whereas Neoproterozoic carbonate successions such as the Loma Negra Formation (Tandilia, southern Argentina) and the Arroyo del Soldado Group (Uruguay) were deposited on the eastern side (present coordinates) of the Rio de la Plata craton, which at the time occupied a position farther to the north.Peer reviewe

Granate con alto contenido de tierras raras pesadas (HREE) y elevada relación Sm/Nd, en pegmatitas de la Sierra de Valle Fértil (Sierras Pampeanas, Argentina).

2 p.El trabajo se realizó en el marco de lso proyectos PB97-1246 (MEC) y BTE2001-1486 (MCYT) y PICT98-4189 (Argentina

A history of Proterozoic terranes in southern South America: From Rodinia to Gondwana

The role played by Paleoproterozoic cratons in southern South America from the Mesoproterozoic to the Early Cambrian is reconsidered here. This period involved protracted continental amalgamation that led to formation of the supercontinent Rodinia, followed by Neoproterozoic continental break-up, with the consequent opening of Clymene and Iapetus oceans, and finally continental re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early Cambrian. The evidence for this is based mainly on a combination of precise U-Pb SHRMP dating and radiogenic isotope data for igneous and metamorphic rocks from a large area extending from the Rio de la Plata craton in the east to the Argentine Precordillera in the west and as far north as Arequipa in Peru. Our interpretation of the paleogeographical and geodynamic evolution invokes a hypothetical Paleoproterozoic block (MARA) embracing basement ultimately older than 1.7 Ga in the Western Sierras Pampeanas (Argentina), the Arequipa block (Peru), the Rio Apa block (Brazil), and probably also the Paraguaia block (Bolivia).Centro de Investigaciones Geológica

The continental assembly of SW Gondwana (Ediacaran to Cambrian): a synthesis

SW Gondwana resulted from complex interplay between continental amalgamation and dispersal between ~ 650 and 490 Ma. The main cratons involved were Laurentia, Amazonia– MARA (Proterozoic Maz–Arequipa–Rio Apa, Casquet et al., 2012), Kalahari, Rio de la Plata (RPC), Congo and East Antarctica (Mawson block). Several collisional orogenic belts resulted, notably the East Africa–Antarctica, Brasiliano–Panafrican, Pampean–Saldania, and Ross– Delamerian orogens. East-Antarctica broke away from the western margin of Laurentia in Rodinia. After a long drift and counter-clockwise rotation (Dalziel, 2013) it collided with Congo and Kalahari to produce the southern part of the left-lateral transpressional East Africa–Antarctica orogen between 580 and 550 Ma, completing the amalgamation of East Gondwana. The Trans-Antarctic margin became an active one in the Ediacaran and subduction of the Pacific Ocean lithosphere occurred throughout the Paleozoic, forming a tract of the Terra Australis orogen. NW–SE directed compression in Late Cryogenian and Early Ediacaran times promoted closure of the Adamastor Ocean, resulting in the left-lateral transpressional Brasiliano–Pan African orogeny between 650 and 570 Ma. The Pampean orogenic belt to the west of the RPC resulted from right-lateral collision between Laurentia and its eastern extension MARA on the one hand and Kalahari–RPC on the other. Ocean opening started at ~ 630 Ma and subduction and further collision took place between 540 and 520 Ma, coeval with the northward drift of Laurentia (~ 540 Ma) away from MARA and the consequent formation of the proto-Andean margin of Gondwana. The margins of the intervening Puncoviscana ocean were covered by Laurentia-derived siliciclastic sediments and carbonates on the MARA side between 630 and ~ 540 Ma (Rapela et al, 2014; this symposium), and by the marine siliciclastic Puncoviscana Formation on the other. The latter formation, deposited between a 570 and ~530 Ma, received input from large alluvial fans descending from juvenile Mesoproterozoic and Neproterozoic sources (new Hf isotope evidence) largely located in the southern East Africa–Antarctica orogen. The Pampean orogen extended into the Saldania–Gariep orogen of southern South Africa (545–520 Ma) and was apparently discordant to the earlier Brasiliano–Pan African orogen. In late-Early to late Cambrian times the Pampean–Saldania realm evolved into a passive margin with siliciclastic platform sedimentation. The Pampean-Saldania realm was separated from the active Trans-Antarctic margin of East Antarctica by an inferred transform fault in Ediacaran to Cambrian times. Regional NW–SW shortening in the Ediacaran became N–S directed in the Cambrian, suggesting a major plate reorganization at this time.Peer reviewe