In the study of the evolution of orogenic belts, granites are indispensable sources of information. Age relations, elemental and isotopic compositions, fabrics and three-dimensional forms provide further insights as to the growth and recycling of the continental crust and give pivotal clues to the identity of unexposed basement terranes.
The emplacement of granite batholiths is often considered to occur during long and continuous magmatic processes. This view has important consequences on major issues such as thermal evolution of orogenic belts and tectonic control of granitoid emplacement. It has been demonstrated that a large apparent age range is generally an artefact, caused by the use of inadequately precise dating methods (e.g. Schaltegger, 1997). The Rb–Sr whole-rock isochron method is plagued by variable initial 87Sr/86Sr ratios, limited spread of Rb/Sr ratios and relatively easy post-magmatic disturbance of the isotopic system. In contrast, the U–Pb ages obtained by Isotope Dilution and Thermo-Ionisation Mass Spectrometry (ID-TIMS) have the potential to unravel the precise timing of granitoid magma generation and emplacement.
In this paper, we present a synthesis of available structural, petrologic, geochemical and (ID-TIMS) U–Pb geochronological data for the Beiras granite batholith. The significance of this work is discussed in the general context of the Iberian Variscan Belt, and in terms of the thermal conditions required to generate large volume of granite magmas in collisional orogens.