The geodynamic significance of shoshonitic plutonism at the Ossa-Morena Zone, Portugal

In this meeting we will start by addressing the “K problem” as stated by Germaine A. Joplin (1968). Since then the meaning and classification of high-K rocks and in particularly of shoshonites, have been a matter of debate. Recently, there has been a growing interest in the occurrence of post-collisional high-k granitoids with mafic enclaves in the European Variscan orogeny (i.e. Mg-K granitoids or durbachites–vaugnerites). Here we will focus on two small basic to intermediate plutons (Veiros and Vale de Maceira) that, during the Devonian (c. 362 Ma), intruded Cambrian to Silurian meta-sediments close to the contact between the Elvas-Alter do Chão and Estremoz-Barrancos Sectors. We will show that Veiros and Vale de Maceira igneous bodies correspond to intrusive equivalents of a typical shoshonite association, highlighting the differences between these massifs and the plutonic calc-alkaline association of Campo Maior. Furthermore, we will try to disclosure the source type and the tectonic setting of the studied shoshonitic rocks, which intruded in a time span of less than 10 Ma after the formation and exhumation of eclogites. In the end, we will consider all the available data on Devonian magmatism to unfold a simplistic geodynamic model taking into account the strong relationship between the genesis of shoshonitic magmatism and subduction-related mantle metasomatism.