• pt-pt
  • en
  • fr
CAPE VERDE GEOLOGICAL SITUATION
The CAPE VERDE archipelago is situated in the eastern part of tje Atlantic Ocean 500 km off the African coast.

The archipelago emerges from the abssal plain at a depth of about 4000 m. The Island are aligned along two nearly perpendicular directions. The north-south direction is connected with a deep structure marking this part of the ocean since the Mesozoic, whereas the east-west direction may be related to a transverse fracture zone.

The volcanic activity started at the inception of the archipelago at least during the Jurassic. The oldest known volcanic eruptions are deep submarine formations and range in age from the Jurassic to the Cretaceous. The islands were formed in more recent times by uplift of the ocean floor followed by piling up of volcanic products erupted in shallow water and later under subarial conditions. The volcanic activity still persists, as indicated by the presence of na active volcano, Fogo Island. Most inlands are covered by young lava flows. Some of the islands are deeply eroded so that the internal structure of the volcanic complexes appears at the surface.

The main characteristics of the chemical composition of the volcanic products of the archipelago is their alkalic composition, strongly undersaturated in silica. The predominant volcanic rocks are basanites, nephelinites and phonolites, whereas the plutonic rocks are essexistes and syenites. The compositions of the same magmatic association. Field arguments show, however, that they within the same plutonic series, narrow relations exist between the basic and ultrabasic types on one hand, and the leucocratic and plutonic alike, belong to the same differentation series.

The geographical situation of the islands, aside the continental slope, suggests that no connection exists between these islands and the Africa continent.Hence, there is no reason to belive in the existence of a crust of continental type beneath the islands.

The basic magma is considered to be a primary mantle-redived magma, which has undergone no contamination by the continental crust. Nevertheless the strong alkali basalts and their differentiation production produts on the oceanic islands. Considering the geographical position and the geophysycal characteristiscs of the underlying crust, the is no doubt that the magmatism of the Cape Verde archipelago is rather unusual when compared to that of other oceanic islands.
Top