Magmatic structures and kinematics emplacement of the Variscan granites from Central Portugal (Serra da Estrela and Castro Daire areas)

Abstract

The late-D3 Variscan granites, which represent the most important volume of granites of Central Portugal, are studied here for their magmatic and solid-state fabrics by means of the Anisotropy of Magnetic Susceptibility (AMS) technique in a 5000 km 2 area located between Guarda and Castro Daire, including the Serra da Estrela region. Two main directions, N150E and N20E, of stretching lineations are found indicating that the emplacement of these “late kinematic” granitoids was tectonically controlled. A three-stage model is proposed in which a) openings along N150-striking dextral strike-slip faults allow the first granitic magmas to be emplaced in the upper crust of Palaeozoic metasediments and syn-D3 granitoids; b) openings along N20-striking possibly sinistral strike-slip faults conjugates to the prior strike-slip faults and allow the enlargement of the granitic plutons; and c) the final emplacement of this huge volume of granitic rocks was mainly controlled by the magma pressure, which explains the rarity of structures related to this stage of granites emplacement in the country rocks. This structural study of granitic rocks yields new constraints on the tectonic evolution of this part of the Variscan orogenic belt at c. 300 Ma.