Episienitas de la Sierra de Guadarrama:
un proceso hidrotermal regional de edad
Pérmico Inferior ligado al inicio
de la extensión alpina
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1996
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Universidad Complutense de Madrid. Departamento de Estratigrafía
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Abstract
Las episienitas de la Sierra de Guadarrama (Sistema Central español), las cuales son resultado de la alteración hidrotermal (decuarcificación y alcalinización) de granitoides, constituyen un conjunto litológico desarrollado en el Pérmico Inferior, con un carácter básicamente isócrono (277 Ma), a escala regional. Estructuralmente definen un marco geodinámico extensional, con dirección de extensión preferente NNE-SSO para este sector del basamento hercínico. Este régimen extensional, asociado a gradientes geotérmicos anormalmente altos, se enmarca en el comienzo de la distensión Alpina (rifting). Ello se debe a la detección en este sector de la Cadena Hercínica de una tectónica de desgarres previa, con una edad comprendida entre 300 y 290 Ma, y que es, a su vez, posterior a los episodios extensionales tardihercínicos asociados al colapso gravitacional de la cadena colisional. Esta etapa de desgarres corresponde a la etapa <Tardi-Hercínica» de Arthaud & Matte (1977).
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 NNE-SSWma in regional extension direction. This 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-Hercynian extensional event related to tlie gravitative collapse of the collisional belt.
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 NNE-SSWma in regional extension direction. This 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-Hercynian extensional event related to tlie gravitative collapse of the collisional belt.