Publication: Cronología Rb-Sr y K-Ar de diques de la Sierra de Guadarrama
(Sistema Central Español)
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Publication Date
1994
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Sociedad Geológica de España
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Abstract
Two calcalkaline granite porphyries, an E-W and a N-S trending one, and three monzonitic dykes
striking NE-SW, have been dated. For the first dyke a whole rock Rb-Sr isochrone age of 296±3 Ma, i.e.
Upper Carboniferous, is obtained. However, the second dyke pro vides only a regression age of
314±31 Ma. Whole rock K-Ar ages of the monzonitic dykes are 245±7,i.e. Lower-Middle Triassic, for
two of them, and 220±5 for the third. The first age rises doubts about the up-to-the-present alleged
posteriority of the E-W dykes relative to the large granitic plutonism in the area. The second is
geologically reasonable within the limits of error only, as N-S dykes must be younger than the Cabeza
Mediana pluton, which is 291 ±6 Ma old, and older than the hydrothermal episyenitic event dated at
274±6 Ma. For the monzonitic dykes the age of 245±7 Ma is taken as representative of the injection
episode, whilst the second age probably results from superimposed alteration. This alkaline episode
can be correlated with the opening of the Iberian trough.