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Frankfurt am Main, Germany

Gallastegui G.,Instituto Geologico Y Minero Of Espana Igme | Gonzalez-Menendez L.,Instituto Geologico Y Minero Of Espana Igme | Rubio-Ordonez A.,University of Oviedo | Cuesta A.,University of Oviedo | Gerdes A.,Institute For Geowissenschaften Mineralogie
Journal of Iberian Geology | Year: 2014

Late Palaeozoic conglomerate formations (Del Ratón and El Planchón) from the Andean Precordillera (Argentina) were studied to unravel their age, composition and provenance. The conglomerates from the Del Ratón Formation are formed by igneous clasts of acid, intermediate and basic compositions (volcanic and plutonic). Laser Ablation (ICP-MS) zircon U-Pb study has yielded an age of 348±2 Ma (late Tournaisian) for the crystallization of a granitic clast, interpreted as a maximum deposition age for the Del Ratón Formation. Geochemistry of these clasts (high LILE/HFSE and La/Yb ratios, negative Nb-Ta anomalies) suggests a calc-alkaline batholithic source, probably located along the Andean Frontal Cordillera currently to the west, where similar calc-alkaline igneous rocks have been described. The El Planchón Formation overlies the Del Ratón Formation and, in the studied conglomerates, there are only igneous clasts of mafic composition (volcanic/subvolcanic). These mafic clasts have a very similar petrography and geochemistry to the Late Ordovician mafic igneous rocks of the Western Precordillera (low LILE/HFSE and La/Yb ratios, no negative Nb-Ta anomalies). Therefore we suggest that the El Planchón conglomerate clasts were probably delivered mainly from northern sources within the Precordillera terrane. This change in clast provenance is tentatively related to a shift in mountain uplift from the Frontal Cordillera (in the west) to the Precordillera (in the east) after the early Visean.

Pereira M.F.,University of Evora | Sola A.R.,National Laboratory of Energy and Geology | Chichorro M.,New University of Lisbon | Lopes L.,University of Evora | And 2 more authors.
Gondwana Research | Year: 2012

The Estremoz Anticline in the Ossa-Morena Zone (SW Iberia) includes upper Ediacaran detrital rocks unconformably overlain by lower Cambrian detrital and carbonate rocks. The spectra of detrital zircon U-Pb ages dominated by Cryogenian and Ediacaran ages (with a typical gap in Mesoproterozoic ages) of the upper Ediacaran greywackes and lower Cambrian arkosic sandstones indicate provenance from sources placed near or at the North-Gondwana margin. These late Ediacaran and early Cambrian basins developed in a paleoposition close to the West African Craton and related to a long-lived Neoproterozoic magmatism (c. 850-700. Ma - Pan-African suture; c. 700-635. Ma - early Cadomian arc; and c. 635-545. Ma - late Cadomian arc).The rhyolites of the Volcanic-Sedimentary Complex of Estremoz whose stratigraphic position so far has been a controversy, yielded an upper Cambrian age (Furongian) at about 499. Ma indicating that carbonate production was episodic in SW Iberia during the Cambrian. This new evidence should be taken into account in the reshaping of paleogeographic reconstruction models that have erroneously insisted on placing Iberia at southerly cold water higher latitudes (>60°S) during the Furongian. © 2012 International Association for Gondwana Research.

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