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 comple x in the volcaniclastic fill of the Miocene Tejeda caldera (20 x 35 km) on Gran Canaria (Canary Islands). The dikes intruded concentrically around a c entral axis of radial symmetry and dip uniformly an average of similar to 4 1 degrees toward the center. Single-crystal Ar-40/Ar-39 ages of dikes and s yenite stocks ranging from 12.3 +/- 0.1 to 7.32 +/- 0.05 Ma suggest more or less continuous intrusive activity during both volcanically active and ina ctive phases. Intrusions were emplaced at average intervals of similar to 5 -10 k.y., while explosive eruptions took place at >50 k.y. intervals. The e stimated aggregate volume of evolved cone sheet magma added at shallow leve l (<2000 m below sea level) amounts to similar to 250 km(3) compared to >>5 00 km(3) of evolved extrusive volcanics erupted during the same period. Formation of the Tejeda cone sheets most likely resulted from deformation p rocesses 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 up-doming of the overlying caldera fill resulted in the formation of cone-shaped fractures.