Sedimentary Basins related to Volcanic Arcs

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Sedimentary Basins related to Volcanic Arcs

• M08353 Basin Analysis

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Reading - start with

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

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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

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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.

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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 gt 500 km long)
  with thick fills (several km)
• Basins tend to become wider and shallower with
  time, partly because of accretion at trenches

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fore-arc basins

• Sediment sources
• volcanic arc
• outer arc
• longitudinally froma continent

• Tectonic style varies
• compressional
• extensional
• strike-slip

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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.

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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.

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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.

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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