Growth of a magma-filled antiform from granite emplacement to post-intrusive cooling: The Campiglia Marittima study case (Northern Apennines, Italy)

Regional deformation often accompanies the migration and emplacement of igneous bodies at shallow crustal levels in all tectonic regimes. Understanding the tectonic regime of magma emplacement is, however, often challenging, as plutons – especially small plutons emplaced in shallow crustal settings – may cool rapidly and not register the strain induced by coeval regional deformation. As a consequence, a wide range of models of pluton emplacement in shallow crustal settings have been proposed over the years. Here, we describe the Botro ai Marmi Pluton from Campiglia Marittima (Tuscany, Italy), a shallow (< 3–4 km) intrusive body. The pluton occurs as an elongated body in the core of an antiformal structure, at the base of Mesozoic carbonates. Structural-geological mapping coupled with a new interpretation of the available gravimetric and borehole log data show that the igneous rocks strictly follow the hinge of the antiform and the periclinal termination of the structure, and that later igneous dikes occur on the outer arc of this structure. The Botro ai Marmi antiform is oriented parallel to similar antiforms and synforms in the area, related to the regional tectonic evolution. The analysis of the distribution of deformation and contact metamorphism in the aureole shows (1) that contact metamorphism is restricted to the antiform culmination and (2) that metamorphic foliations and high-strain domains, formed during peak and retrograde metamorphism, were folded during the development of the antiform. Therefore, we propose that the intrusion and deformation of the Botro ai Marmi Pluton was controlled by the growth of a thrust anticline that continued to propagate after the emplacement and cooling of the intrusive system.