Abstract

Felsic orthogneisses occur widely in the Ollo de Sapo Domain of the Central Iberian Zone, most of which were previously considered to represent a Precambrian basement to the Palaeozoic sequences of this domain. However, new U–Pb dating across the Berzosa‐Riaza shear zone (Sierra de Guadarrama, Central Spain) indicates an Early Ordovician age for the most representative types of orthogneisses in the eastern part of the Ollo de Sapo Domain. Dated rocks include the volcaniclastic Cardoso gneiss (480±2 Ma); from the low–medium‐grade hanging wall; the Riaza gneiss (468₋₈⁺¹⁶ Ma, mylonitic granite) in the Berzosa‐Riaza shear zone; three types of ‘leucogneiss’ (Buitrago gneiss; 488₋₈⁺¹⁰ Ma, megacrystic granite; 482₋₁₁⁺¹⁴ Ma, aplitic vein; and 482₋₈⁺⁹ Ma, gneissic leucogranite); and the La Morcuera granitic augen gneiss (477±4 Ma) in the high‐grade footwall. The new age of the Cardoso gneiss brackets to the Mid–Late Arenig, the so‐called Early Ordovician Sardic unconformity, characteristic of the Central Iberian Zone. These new ages suggest that the broadly coeval volcanism and plutonism were closely associated with the Sardic events, and that these orthogneisses were part of a felsic magmatic belt which extended along the Ollo de Sapo Domain of the Central Iberian Zone. This magmatic belt is interpreted to have been active during the Early Ordovician break‐up of the peri‐Gondwanan margin of the Iapetus Ocean.