Cone sheet formation and intrusive growth of an oceanic island; the Miocene Tejeda Complex on Gran Canaria (Canary Islands)

More than 500 trachytic to phonolitic cone sheet dikes, hypabyssal syenite stocks, and subordinate radial dikes form a 20-km-diameter intrusive complex in the volcaniclastic fill of the Miocene Tejeda caldera (20X35 km) on Gran Canaria (Canary Islands). The dikes intruded concentrically around a central axis of radial symmetry and dip uniformly an average of approximately 41 degrees toward the center. Single-crystal (super 40) Ar/ (super 39) Ar ages of dikes and syenite stocks ranging from 12.3+ or -0.1 to 7.32+ or -0.05 Ma suggest more or less continuous intrusive activity during both volcanically active and inactive phases. Intrusions were emplaced at average intervals of approximately 5-10 k.y., while explosive eruptions took place at >50 k.y. intervals. The estimated aggregate volume of evolved cone sheet magma added at shallow level (<2000 m below sea level) amounts to approximately 250 km (super 3) compared to nearly equal 500 km (super 3) of evolved extrusive volcanics erupted during the same period. Formation of the Tejeda cone sheets most likely resulted from deformation processes due to resurgent doming, initiated by the recurrent replenishment of a flat, laccolith-like shallow magma chamber. Magma supply exceeding the volume that could be compensated for by updoming of the overlying caldera fill resulted in the formation of cone-shaped fractures.