Magma emplacement in transpression: The Santa Olalla Igneous Complex (Ossa-Morena Zone, SW Iberia)

Abstract

The Santa Olalla Igneous Complex, a late-Variscan group of intrusions located in the Ossa-Morena Zone (SW Iberia), has been the focus of a gravity and structural study. The structure outlined by the foliation map is complex, showing two different structural domains: one characterized by vertical, and the other by horizontal, magmatic foliations. The vertical fabrics are restricted to the NE half of the complex, which is in direct contact with a Variscan sinistral strike-slip fault (Cherneca fault) whereas the horizontal fabrics are developed in the SW half of the complex, which is characterized by a horizontal tabular geometry. Gravity modeling indicates that the deeper floor of the plutons is closely related to the NE margin and the Cherneca fault. An emplacement and structural evolution model for this igneous complex is proposed following these structural and gravity results: (1) magma ascent was favored by releasing bends in the trace of the Cherneca fault; (2) when magma reached the present level it intruded to the SW with a horizontal sheet geometry generating the subhorizontal foliation domain; (3) after emplacement, the NE half of the complex suffered the external tectonic stress field provoked by sinistral motion along the Cherneca fault, subsequently generating the subvertical magmatic foliation domain.