A crustal transect through the northern and northeastern part of the volcanic edifice of Gran Canaria, Canary Islands

Abstract

Wide-angle reflection and refraction seismic data were obtained during METEOR cruise 24 in the N and NE of Gran Canaria (GC), Canary Islands. Seismic energy was generated with two 32 L air guns fired at 1 or 2 min intervals. Seven ocean bottom hydrophones (OBH) and 8 mobile land stations recorded seismic arrivals over a network of profiles covering the northern and northeastern sector up to 60 km away from coastline of GC. The detailed structure of the volcanic edifice and the adjacent ocean basin is revealed in the data set along three radial profiles. A 4 km thick sediment sequence overlies the 7 km thick igneous oceanic crust. The basement is characterized by a first order discontinuity with a velocity jump from 3.4 km/s in the sediment to 4.5 km/s. A pronounced lateral velocity variation was found beneath the island. A 5–6 km thick low velocity zone within the central volcanic edifice, at roughly 4–12 km depth south of the island center is interpreted as the Miocene syenitic feldspar-rich core with lower velocity than the recent volcanic core of more mafic composition beneath northern GC. The massive volcanic island flank thins rapidly away from the island with velocities decreasing gradually from 5.0 near the coast to 3.5 km/s in the outermost part 50–60 km away from the coastline. The clear doming of the lower crust (>6.6 km/s) to 8–10 km depth beneath the northern part of GC is attributed to relatively young mafic plutonic rocks. The Moho north and northeast of GC lies almost horizontal; its depth increases slightly from 14 km along the N–S oriented Profile 1 in the west to 16 km along the N–E oriented Profile 3 in the east. A minor flexure of 1–2 km is indicated by a very gentle dip of the Moho beginning around 10–15 km offshore. A zone of magmatic underplating at depths as low as 26 km is found beneath GC. The anomalous velocity–depth function of the igneous oceanic crust north and northeast of GC and the crustal structure beneath the island are clear evidence for fundamental modification and disruption of the original crustal structure by the Canarian magmatic and volcanic activity.