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Subduction of trench-fill sediments beneath an accretionary wedge: insights from sandbox analogue experiments
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  • Atsushi Noda,
  • Hiroaki Koge,
  • Yasuhiro Yamada,
  • Ayumu Miyakawa,
  • Juichiro Ashi
Atsushi Noda
National Institute of Advanced Industrial Science and Technology, National Institute of Advanced Industrial Science and Technology

Corresponding Author:[email protected]

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Hiroaki Koge
National Institute of Advanced Industrial Science and Technology, National Institute of Advanced Industrial Science and Technology
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Yasuhiro Yamada
JAMSTEC, JAMSTEC
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Ayumu Miyakawa
Geological Survey of Japan, AIST, Geological Survey of Japan, AIST
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Juichiro Ashi
University of Tokyo, University of Tokyo
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Abstract

Ancient exhumed accretionary complexes are sometimes associated with high-pressure–low-temperature (HP–LT) metamorphic rocks, such as psammitic schists, which are derived from sandy trench-fill sediment. At accretionary margins, sandy trench-fill sediments are rarely subducted to the depth of HP metamorphism because they are commonly scraped off at the frontal wedge. This study uses sandbox analogue experiments to investigate the role of seafloor topography in the transport of trench-fill sediment to depth during subduction. The experiments were conducted with a detached, rigid backstop to allow a topographic high (representing a seamount) to be subducted through a subduction channel. In experiments without topographic relief, progressive thickening of the accretionary wedge pushed the backstop down, leading to a stepping down of the décollement, narrowing the subduction channel, and underplating the wedge with subducting sediment. In contrast, in experiments with a topographic high, the subduction of the topographic high raised the backstop, leading to a stepping up of the décollement and widening of the subduction channel. These results suggest that the subduction of topographic relief is a possible mechanism for the transport of trench-fill sediment from the trench to HP environments through a subduction channel. A sufficient supply of sediment to the trench and topographic relief on the subducting oceanic plate might enable trench-fill sediment to be accreted at various depths and deeply subducted to become the protoliths of HP–LT metamorphic rocks.
01 Aug 2020Published in Geosphere volume 16 issue 4 on pages 953-968. 10.1130/GES02212.1