Sr, C and O isotope composition of marbles from the Sierra 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 Río de la Plata craton, which at the time occupied a position farther to the north

Neoproterozoic A-type magmatism in the Western Sierras Pampeanas (Argentina): evidence for Rodinia break-up along a proto-Iapetus rift?

A-type orthogneisses of mid Neoproterozoic age (774 ± 6 Ma, U-Pb SHRIMP zircon age), are reported for the first time from the Grenvillian basement of the Western Sierras Pampeanas in Argentina. These anorogenic meta-igneous rocks represent the latest event of Rodinia break-up so far recognized in Grenvillian basement exposures across Andean South America. Moreover, they compare well with A-type granitoids and volcanic rocks along the Appalachian margin of Laurentia (Blue Ridge), thus adding to former evidence that the Western Sierras Pampeanas Grenvillian basement was left on the conjugate rifted margin of eastern Laurentia during Rodinia break-up and the consequent opening of the Iapetus ocean

Metamorfismo de baja presión y alta temperatura en las unidades metasedimentarias ordovícicas del sector norte de la Sierra de Los Llanos, Sierras Pampeanas Orientales (Argentina)

La Sierra de Los Llanos (Sierras Pampeanas Orientales) se compone principalmente de plutones granodioríticos, considerados como la extensión norte del batolito Los Llanos-Ulapes del Ordovícico inferior (483-497 Ma, y en menor proporción por monzogranitos intruyendo a la granodiorita (Unidad Asperezas, de ca. 477 Ma;), gabros, dioritas formando mingling con la granodiorita, y granitos anatécticos de ca. 479 Ma; (Pankhurst et al., 1998, Pankhurst et al., 2000 referencias allí citadas). Dentro de esta sierra, se localizan septos de dimensiones kilométricas de rocas metasedimentarias que afloran de manera discontinua e intercalada con las unidades plutónicas.Uno de estos septos se localiza en el sector noroeste de esta sierra, en cercanías a la localidad de El Alto (Figura 1), compuesto por una sucesión metasedimentaria de esquistos micáceos y cuarzo-micáceos con andalucita-cordierita, gneises y migmatitas, con desarrollo localizado de corneanas en respuesta a la intrusión tardía de cuerpos básicos (Pascua et al., 1998; Pankhurst et al., 1998). En esta contribución se presenta la descripción de paragénesis no citadas en trabajos previos del área y un estudio preliminar de la evolución tectono-térmica y estimación de las condiciones P-T para el evento térmico principal utilizando cálculos multireaccionales.Fil: Verdecchia, Sebastián O. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Murra, Juan A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Baldo, Edgardo G. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Colombo, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Geologí

An Ediacarian carbonate platform in the Eastern Sierras Pampeanas of Argentina: Sr isotopic relations in marbles of the Sierra de Ancasti

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Neoproterozoic A-type magmatism in the Western Sierras Pampeanas (Argentina): evidence for Rodinia break-up along a proto-Iapetus rift?

A-type orthogneisses of mid Neoproterozoic age (774 ± 6 Ma, U-Pb SHRIMP zircon age), are reported for the first time from the Grenvillian basement of the Western Sierras Pampeanas in Argentina. These anorogenic meta-igneous rocks represent the latest event of Rodinia break-up so far recognized in Grenvillian basement exposures across Andean South America. Moreover, they compare well with A-type granitoids and volcanic rocks along the Appalachian margin of Laurentia (Blue Ridge), thus adding to former evidence that the Western Sierras Pampeanas Grenvillian basement was left on the conjugate rifted margin of eastern Laurentia during Rodinia break-up and the consequent opening of the Iapetus ocean.Centro de Investigaciones Geológica

Isotope (Sr, C) and U–Pb SHRIMP zircon geochronology of marble-bearing sedimentary series in the Eastern Sierras Pampeanas, Argentina : Constraining the SW Gondwana margin in Ediacaran to early Cambrian times

The Sierras de Cordoba Metasedimentary Series consists of marbles and metasiliciclastic rocks of Ediacaran to early Cambrian age (ca. 630 and 540 Ma) that underwent high-grade metamorphism during the collisional Pampean orogeny in the early Cambrian. The ages of the marbles were determined from the Sr-isotope composition (blind dating) of screened samples of almost pure calcite marble and were further constrained with C- and O-isotope data and U–Pb SHRIMP detrital zircon ages of an interbedded paragneiss. Two groups of samples are recognised with Sr-isotope composition ca. 0.7075 and 0.7085 that are considered stratigraphically significant. The first is inferred early Ediacaran, the second late Ediacaran to early Cambrian. The Sierras de Cordoba Metasedimentary Series is correlated for the first time with marble-bearing metasedimentary series in several sierras to the west and north of Sierras de Cordoba (e.g., the Difunta Correa Sedimentary Sequence and the Ancajan Series), implying that all were probably parts of an originally extensive sedimentary cover. These series bear evidence of sedimentary sources in the Mesoproterozoic (and Paleoproterozoic) basement of the Western Sierras Pampeanas (part of the large MARA continental block) and farther west (Laurentia?). In terms of the age of limestones/marbles and detrital zircon patterns, the Sierras de Cordoba Metasedimentary Series differs strongly from the older section of late Ediacaran to early Cambrian Puncoviscana Formation of northwestern Argentina, which mostly outcrops in northern Sierra Chica and Sierra Norte, with sedimentary input from western Gondwana sources. The Sierras de Cordoba Metasedimentary Series and the Puncoviscana Formation were probably juxtaposed during the Pampean orogeny along a complex suture zone that was further folded and/or imbricated at mid-crustal depths. The peak of metamorphism was attained at 527 ± 2 Ma. According to the evidence found here most of the Sierras Pampeanas to the west of the Sierras de Cordoba were part of the lower colliding plate during the final amalgamation of SW Gondwana.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones Geológica

Isotope (Sr, C) and U–Pb SHRIMP zircon geochronology of marble-bearing sedimentary series in the Eastern Sierras Pampeanas, Argentina. Constraining the SW Gondwana margin in Ediacaran to early Cambrian times

The Sierras de Córdoba Metasedimentary Series consists of marbles and metasiliciclastic rocks of Ediacaran to early Cambrian age (ca. 630 and 540 Ma) that underwent high-grade metamorphism during the collisional Pampean orogeny in the early Cambrian. The ages of the marbles were determined from the Sr-isotope composition (blind dating) of screened samples of almost pure calcite marble and were further constrained with C- and O-isotope data and U–Pb SHRIMP detrital zircon ages of an interbedded paragneiss. Two groups of samples are recognised with Sr-isotope composition ca. 0.7075 and 0.7085 that are considered stratigraphically significant. The first is inferred early Ediacaran, the second late Ediacaran to early Cambrian. The Sierras de Córdoba Metasedimentary Series is correlated for the first time with marble-bearing metasedimentary series in several sierras to the west and north of Sierras de Córdoba (e.g., the Difunta Correa Sedimentary Sequence and the Ancaján Series), implying that all were probably parts of an originally extensive sedimentary cover. These series bear evidence of sedimentary sources in the Mesoproterozoic (and Paleoproterozoic) basement of the Western Sierras Pampeanas (part of the large MARA continental block) and farther west (Laurentia?). In terms of the age of limestones/marbles and detrital zircon patterns, the Sierras de Córdoba Metasedimentary Series differs strongly from the older section of late Ediacaran to early Cambrian Puncoviscana Formation of northwestern Argentina, which mostly outcrops in northern Sierra Chica and Sierra Norte, with sedimentary input from western Gondwana sources

Geocronología de las Sierras de Córdoba : revisión y comentarios

Fil: Baldo, Edgardo G.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Investigaciones en Ciencia de La Tierra; CórdobaFil: Rapela, Carlos Washington. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Pankhurst, Robert J.. British Geological Survey; Reino UnidoFil: Galindo, Carmen. Universidad Complutense. Instituto de Geociencias. Departamento de Petrología y Geoquímica; EspañaFil: Casquet, César. Universidad Complutense. Instituto de Geociencias. Departamento de Petrología y Geoquímica; EspañaFil: Verdecchia, Sebastián O.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Investigaciones en Ciencia de La Tierra; CórdobaFil: Murra, Juan A.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Investigaciones en Ciencia de La Tierra; Córdob

Neoproterozoic A-type magmatism in the Western Sierras Pampeanas (Argentina): evidence for Rodinia break-up along a proto-lapetus rift

A-type orthogneisses of mid Neoproterozoic age (774 ± 6Ma, U-Pb SHRIMP zircon age), are reported for the first time from the Grenvillian basement of the Western Sierras Pampeanas in Argentina. These anorogenic meta-igneous rocks represent the latest eve