The region studied is situated in the Patia valley, in the southwestern Colombian Andes. It is made up two areas, the Los Azules massif and the El Tambo - El Penol region, both of which contain large amounts of basic and ultrabasic rocks.

The Los Azules massif consists of an ophiolitic sequence (ultrabasic cumulates, serpentinites and rodingites, basic cumulates, diabase dykes, pillow lavas and hyaloclastites) cut by dioritic and dacitic intrusions and overlain by Tertiary sediments. The complex tectonic evolution of the massif has been reconstructed. In addition, detailed mineralogical and petrological studies have been made.

The rocks occurring in the El Tambo - El Penol region include the sediments of the Grupo Dagua, the diabases of the Grupo Diabasico, and the Tertiary sediments and volcanics, with some serpentinite and diorite intrusions. Detailed mineralogical and petrological studies have been carried out on the Grupo Diabasico diabases and on the serpentinites with their quartz albite and rodingite inclusions.

The grupo Diabasico diabases and the Los Azules diabases are distinctly tholeiitic in character. However, it is impossible to assign their formation to a particular tectonic environment (ocean ridge or island arc). The chemistry of each group in discussed.

The magnetic properties of the Grupo Diabasico diabases have been studied.

This work answered several questions about the metamorphism and age of the sequences studied, as well as their role in the tectonic evolution in the western Colombian Andes. It appears that the two sequences have undergone ocean floor metamorphism and that they have acted as independent tectonic units. The emplacement of the ophiolites on the continental edge could be a result of plate tectonics; a mechanism linked to variations in the speed of movement of the South American plate is proposed.