Stratigraphie et géologie structurale de la parte orientale de la Sierra de Guadarrama (Espagne Centrale)

Abstract

In the first part a description of the stratigraphy of the hercynian basement rocks in the eastern part of the Sierra de Guadarrama is given. They consist of the gneisses of Hiendelaencina and La Bodera, which are equivalent to the "Olio de Sapo" Formation of Galicia (Upper Precambrian). These are followed by a series ranging from Upper Cambrian to Emsian, chiefly composed of quartzites, sandstones and slates. The basement rocks are overlaid by mesozoic formations (red conglomerates, sandstones and argilites), the age of which is discussed. In the second part a brief description is given of the volcanic rocks (andésites) which outcrop west of Atienza. The third part describes the structural geology of the region studied.During the hercynian tectogeny three phases of superposed folding have been distinguished. The first phase, which is syn-metamorphic, is the most important. It gave rise to the main structures : eastward overturned and recumbent folds, with an SI axial plane cleavage. The second phase has caused a tightening of the existing structures and has yielded essentially minor folds. An S2 cleavage has developed locally. During the third phase the central zone has been affected by an anticlinal upheaval with a NW - SE trend. The eastern termination of the Sierra de Guadarrama (the region near Riba de Santiuste-Cercadillo), which is distinguished by a different folding style, has been described separately. A series of eternal area projections illustrates the structural analysis of the hercynian tesisogeny. The post-hercynian tectonics are characterized by the development of vertical faults.