Episienitas de la Sierra de Guadarrama: un proceso hidrotermal regional de edad Pérmico Inferior ligado al inicio de la extensión alpina.

Abstract

The episyenites from the Sierra de Guadarrama (Spanish Central System) were formed by the hydrothermal alteration (dequartzification and alkalinization) of granitoids. The alteration took place on a regional seale, ín the Lower Permian (277 Ma), in a brief period of time. Structurally, these rocks define a regional extensional geodynamic frame, with a NNESSW main regional extension direction. TI-fis extensional regime --accompanied by high geothermal gradients-- is interpreted as the onset of the Alpine rifting. This interpretation is based on the fact that a former wrench episode, equivalent to the <Late-Hercynian> event of Arthaud & Matte (1977), has been recognized taking that took place in the time span 300 to 290 Ma. In turn, this wrench-faulting event was preceded by tbe Late-l-Iercynian extensional event related to tlie gravitative collapse of the collisional belt.