Publication: Nuevos datos geocronológicos (Rb-Sr, K-Ar) de granitoides hercínicos de la Sierra de Guadarrama
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Publication Date
1995
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Sociedad Geológica de España
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Abstract
Se han realizado análisis isotópicos de Rb-Sr en roca total para datar unidades intrusivas graníticas de la Sierra de Guadarrama. El plutón de Villacastín ha dado una edad de 323 ± 47 Ma con un valor de"Sr/86Sri = 0,70701 ± 0,00255. El plutón de La Granja define una recta de regresión de edad 299 ± 55 Ma y"Sr/8·Sri = 0,71212 ± 0,00370. El plutón de La Atalaya Real es de edad 284 ± 13 Ma con"Sr/8·Sri = 0,7129 ± 0,00118. El plutón de Alpedrete define una errorcrona de edad 261 ± 33 y"Sr/8·Sri = 0,71117 ± 0,00131. Con ello, la edad del plutonismo post-pico metamórfico del sector se
reduce a un período de unos 50 Ma frente a los 70 Ma previamente establecidos. También se definen dos pulsos principales de actividad ígnea alrededor de los 320 ± 5 Ma y 295 ± 5 Ma. Las edades Rb-Sr y K-Ar en biotitas apuntan a cambios significativos en la velocidad de enfriamiento del área plutónica, que pasaría de 10-20 °ClMa en los momentos de mayor actividad intrusiva a valores mucho más bajos
(próximos a 1 °ClMa), sobre todo en momentos claramente post-hercínicos (< 250 Ma)
Whole-rock Rb-Sr isotopic analyses on granites from the Sierra de Guadarrama have been performed. Samples from the Villacastín granite yield an age of 323 ± 47 Ma with an intercept at 0.70701 ± 0.00255. La Granja granite yields an age of 299 ± 55 Ma and intercept 0.71212 ± 0.00370. The six samples of La Atalaya granite define a regression line of age 284 ± 13 Ma and intercept at 0.7129 ± 0.00118. An errorchron from the Alpedrete pluton yields a value of 261 ± 33 Ma and intercept 0.71117 ± 0.00131. These data imply that the time-spanof the post-metamorphic-peak plutonism in Sierra de Guadarrama is around 50 Ma, which is 20 Ma narrower than that deduced from previous data. Also, two pulses of granite intrusions at 320 and 295 Ma can be defined on the basis of these new ages. Rb-Sr aíld K-Ar ages obtained from biotite separates suggest an important change in the coooling rate from initial values around 10-20 °ClMa during plutonism towards les ser values (around 1 °ClMa) during the post-hercynian evolution (<250 Ma)
Whole-rock Rb-Sr isotopic analyses on granites from the Sierra de Guadarrama have been performed. Samples from the Villacastín granite yield an age of 323 ± 47 Ma with an intercept at 0.70701 ± 0.00255. La Granja granite yields an age of 299 ± 55 Ma and intercept 0.71212 ± 0.00370. The six samples of La Atalaya granite define a regression line of age 284 ± 13 Ma and intercept at 0.7129 ± 0.00118. An errorchron from the Alpedrete pluton yields a value of 261 ± 33 Ma and intercept 0.71117 ± 0.00131. These data imply that the time-spanof the post-metamorphic-peak plutonism in Sierra de Guadarrama is around 50 Ma, which is 20 Ma narrower than that deduced from previous data. Also, two pulses of granite intrusions at 320 and 295 Ma can be defined on the basis of these new ages. Rb-Sr aíld K-Ar ages obtained from biotite separates suggest an important change in the coooling rate from initial values around 10-20 °ClMa during plutonism towards les ser values (around 1 °ClMa) during the post-hercynian evolution (<250 Ma)