Sedimentary Basins related to Volcanic Arcs M08353 Basin Analysis

Reading - start with: Reading, H.G.: Sedimentary Environments 2nd edition. Tectonics & Sedimentation chapter by Mitchell & Reading 3rd edition. Volcaniclastics chapter by Orton, p. 549-

Volcanic arcs may develop... within oceanic lithosphere, where ocean floor subducts beneath ocean floor, and an island arc results, e.g. Lesser Antilles arc or at the edge of a continent, where oceanic lithosphere subducts beneath continental lithosphere, and a continental margin magmatic arc forms, e.g. Andes

Basins related to volcanic arcs fore-arc back-arc intra-arc All may be either submarine or subaerial, or may have marine & subaerial parts Much sediment is supplied from active arc.

Fore-arc basins Lie in the arc-trench gap, between volcanic arc and submarine trench range from small basins on trench slope to large basins (50 to 100 km wide, and > 500 km long) with thick fills (several km) Basins tend to become wider and shallower with time, partly because of accretion at trenches

fore-arc basins Sediment sources: volcanic arc outer arc longitudinally from a continent Tectonic style varies: compressional extensional strike-slip

Back-arc basins lie behind the magmatic arc often the site of extension & thinning of crust may overlie either ocean or continental crust oceanic back-arc basins are eventually subducted and destroyed, or preserved in thrust complexes related to ocean closure. back-arc basins on continental crust - more varied facies, because of terrigenous input; higher preservation potential.

Intra-arc basins Sedimentary basins within magmatic arcs, between volcanoes, or between older and younger belts of the arc Some are fault-bounded and subside rapidly. Faulting due to extension within arc, or flexure of lithosphere due to weight of volcano. With time, position of the arc migrates, and basins may change between intra-arc, back-arc and fore-arc.

Sediment supply and transport Sediment supply varies according to volcano behaviour, governed by magma viscosity and gas content. In deep water, explosive activity is suppressed by hydrostatic pressure. More silicic magmas in more evolved arcs - therefore greater explosive activity, more supply of pyroclastic sediment.

Sediment transport and deposition is controlled by: topography - both subaerial and submarine volcanic processes, especially eruption column height, direction of pyroclastic flows sediment transport systems - e.g. rivers, prevailing winds