13. PROCESSES OF VOLCANICLASTIC SEDIMENTATION DURING THE EARLY GROWTH STAGES OF GRAN CANARIA BASED ON SEDIMENTS FROM SITE 953 1Steven Carey,2 Tony Maria,2 and Winton Cornell 3 |
ABSTRACTSite 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 sand- to 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. |
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