Details

Autor(en) / Beteiligte

• Ancochea, Eumenio
• Huertas, María José
• Hernán, Francisco
• Brändle, José Luis

Titel

A new felsic cone-sheet swarm in the Central Atlantic Islands: The cone-sheet swarm of Boa Vista (Cape Verde)

Ist Teil von

• Journal of volcanology and geothermal research, 2014-03, Vol.274, p.1-15

Ort / Verlag

Oxford: Elsevier B.V

Erscheinungsjahr

2014

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The island of Boa Vista is one of the oceanic islands with the largest amount of felsic rocks reported in the world (50% of the total outcropping igneous rocks of Boa Vista). The felsic rocks are trachytes and phonolites generated within the second main stage of the volcanic activity that lasted about four million years. Three consecutive felsic episodes are distinguished: the first occurred between 14.5Ma and 13.5Ma, the second between 13.6Ma and 12.0Ma, and the third and last between 12.0Ma and 10.4Ma. Their geochemical composition reveals the presence of crystal fractionation processes with participation of feldspars and amphibole as well as different accessory phases involved in each episode. The Boa Vista felsic cone-sheet swarm, the youngest third episode, is formed by several hundreds of peralkaline ne-phonolitic sheets distributed within a circular surface about 11km in radius. The cone-sheets conform a single general pattern characterized by a decreasing dip outward the structure, together with a constant dip of each individual sheet. The average inclination of sheets is around 40° in the sectors next to the centre of the structure whereas it is only about 30° next to its periphery. The magmatic focus of the sheets is located over 3km deep almost coinciding with the convergence centre of a contemporary basic radial dike swarm. •A cone sheet swarm is for the first time described in the island of Boa Vista.•Hundreds of phonolitic cone-sheets give place to a structure 20km in diameter.•This is the third cone sheet swarm identified in the Central Atlantic Ocean islands.•Three successive felsic episodes are characterized and dated between 14.5 and 10.4Ma.•Third felsic episode is constituted by a cone-sheet swarm dated between 12 and 10.4Ma.