GROWTH AND DESTRUCTION OF GRAN-CANARIA DEDUCED FROM SEISMIC-REFLECTION AND BATHYMETRIC DATA

The morphology and structure of the submarine flanks of Gran Canaria h ave been mapped using Hydrosweep swath bathymetry and high-resolution reflection seismic data. The growth and destruction of the island has been characterized previously by three major periods of volcanic activ ity (16-9 Ma, 4.5-3.5 Ma, younger than 3 Ma) separated by erosional in tervals; Two major sector collapses along the west coast, inferred fro m the coastal morphology, are believed to have formed at the end of th e shield-binding phase. One is characterized by a 19-km-wide reentrant along the northwestern; coast that may have formed synchronously with the formation of the 20-km-diameter Miocene Tejeda Caldera. High sedi mentation rates around Gran Canaria (> 50 m/Myr) tend to cover and bur y major landslide blocks. SSW off the island, several canyons continue seaward into a major sediment fan. A 9.5-km-wide volcaniclastic ridge in this fan is interpreted to represent deposits of the I Pliocene su baerial Rogue Nublo debris avalanche. We tentatively interpret the slo pe break at a depth of 600-800 m as the transition between subaerial a nd subaqueous chilled lavas at the end.of the shield-building phase. T he subsidence caused by the volcanic load (30,000 km(3)) on the lithos phere may thus amount to no more than 800 m. Several canyons on the is land can be traced down the submarine flanks to a depth of 3.5 km, ind icating that at least deeper portions below the level of subsidence we re eroded by mass flows continuing seaward from the subaerial canyons. Four submarine volcanoes were identified west and northeast of the is land.