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Site 953 recovered a 14.8-Ma record of volcaniclastic sedimentation adjacent to Gran Canaria Island of the Canary Island archipelago. Changes in the lithology, age, and volume of clastic material reflect the evolution of Gran Canaria from a submarine stage to a mature subaerial edifice. Before the initiation of major felsic explosive volcanism on Gran Canaria at 14.0 Ma, there was a period during which numerous mafic volcaniclastic turbidites were generated from the emergent island (Unit V, Site 953). The deposits consist of sandto silt-sized mixtures of altered sideromelane, tachylite, small clasts of microcrystalline basalt, and crystals of clinopyroxene, feldspar, and Fe-Ti oxides. Biogenic components, such as foraminifer fragments, make up as much as 30%. Computer-assisted fractal analysis of sideromelane grain morphologies shows a decrease in morphological complexity with increasing age through Unit V. This change, along with a decrease in the modal abundance of tachylite with increasing age, is interpreted to represent an increasing role of deeper, submarine volcanism as the source of clastic particles early in the island’s development. The strongly mixed lithologies of the turbidites and the occurrence of common, rounded microcrystalline basalt fragments suggest that many of the layers were formed by the slumping of volcaniclastic material that had accumulated in shallow water from erosion of subaerial products, the entrance of lava flows into the sea, and shallow submarine eruptions. A median frequency of one flow event every 2000 yr has been determined from the thickness and accumulation rate of interbedded pelagic sediment in Unit V. h h l . n p st ite n c T o u 1 ria co pt ar s u n ite t v t u this ction osits the n its rty, the and R-6 any, avity tion. eximenccurentiose and 75R ons. petnting was icles ith a ajor partnalINTRODUCTION The growth of oceanic islands is an important component in the exchange of material from the Earth’s mantle to the surface. T history and evolution are critical to understanding the rates at w magma is supplied to the crust and at which marine and subaeria cesses convert primary volcanic products into clastic sediments ciphering the growth processes of oceanic volcanoes based o subaerial sequences is often difficult because of the incomplete ervation of erupted products and the inability to access the earlie posits. During Ocean Drilling Program (ODP) Leg 157, four s (953, 954, 955, and 956) were drilled into the volcaniclastic apro Gran Canaria island in an attempt to recover the sedimentary re of submarine growth and subaerial emergence and activity. island was selected because of its well-characterized subaerial v nic history and the great compositional diversity of erupted prod (Schmincke, 1982, 1993). One of the major objectives of Leg was to examine the various evolutionary stages of Gran Cana detail from its inception on the seafloor to its present subaerial figuration (Schmincke et al., 1994). Much is known about the volumes and compositions of eru products from the subaerial volcanic activity of Gran Can (Schmincke, 1993). Principal features include two major phase felsic volcanism in the middle Miocene and a third, less volumino Pliocene episode. The most voluminous phase occurred betwee and 13.4 Ma and involved eruption of trachyte, peralkaline rhyol and alkali basalts (Mogán Formation). Much less is known abou pre-Mogán history of the island, when the rates of volcanic acti are inferred to be high and much of the shield-building stage was ing place. Recovery of volcaniclastic sediments of this age surro 1Weaver, P.P.E., Schmincke, H.-U., Firth, J.V., and Duffield, W. (Eds.), 1998. Proc. ODP, Sci. Results, 157: College Station, TX (Ocean Drilling Program). 2Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, U.S.A. scarey@gsosun1.gso.uri.edu 3Department of Geosciences, University of Tulsa, Tulsa, OK 74104, U.S.A. eir ich proDethe resdes of ord he lcacts 57 in ned ia of s, 14.0 s, the ity aknding Gran Canaria provides an excellent opportunity to investigate stage of the island’s history and to develop a complete reconstru of the island’s evolution. In this paper we present a study of the volcaniclastic dep comprising Unit V of Site 953. This unit has been correlated to pre-Mogán stage of volcanism in the Canary Islands based o stratigraphic position and composition (Shipboard Scientific Pa 1995). The work focuses on the lithology and sedimentology of deposits with the objective of constructing a model for the origin emplacement of volcaniclastic sediment on the island flanks.

Processes of volcaniclastic sedimentation during the early growth stages of Gran Canaria based on sediments from Site 953