loading page

Sandbox analogue experiments for subduction of trench-fill sediments beneath accretionary wedge and backstop
  • +2
  • Atsushi Noda,
  • Hiroaki Koge,
  • Yasuhiro Yamada,
  • Ayumu Miyakawa,
  • Juichiro Ashi
Atsushi Noda
National Institute of Advanced Industrial Science and Technology (AIST)

Corresponding Author:a.noda@aist.go.jp

Author Profile
Hiroaki Koge
National Institute of Advanced Industrial Science and Technology (AIST)
Author Profile
Yasuhiro Yamada
JAMSTEC Japan Agency for Marine-Earth Science and Technology
Author Profile
Ayumu Miyakawa
National Institute of Advanced Industrial Science and Technology (AIST)
Author Profile
Juichiro Ashi
The University of Tokyo
Author Profile

Abstract

We conducted sandbox analogue experiments for subduction of trench-fill sediments beneath accretionary wedge and backstop in order to explain how protoliths of high-pressure/low-temperature (HP-LT) metamorphic rocks are transported to high pressure environment. At accretionary-type subduction zones, it is commonly difficult that coarse-grained sandy trench-fill deposits subduct deeper than high pressure environment (>10 km in depth), because they are accreted at the shallower part of the wedge (<5 km) in association with stepping down of decollement due to progressive dewatering under the accretionary wedge. However, ancient exhumed accretionary complexes sometimes accompany with low-grade accretionary rocks from trench-fill turbidites and HP-LT metamorphic rocks including psammitic and even conglomeratic schists, whose provenance and depositional ages are similar to each other. Therefore, we need a model to explain growth of accretionary wedge and subduction of coarse-grained trench-fill sediments beneath the wedge at the same time. In this study, we attempt to identify an importance of seafloor roughness for transportation of trench-fill sediments to deep during subduction. For this purpose, we performed sandbox analogue experiments by using an unfixed rigid backstop on a subduction channel with the cases of smooth surface (Exp. A) and rough surface representing a seamount or ridge on subducting lower plate (Exp. B). The results of Exp. A showed progressive thickening of the accretionary wedge pushed the backstop down, meaning stepping down of the decollement and narrowing the subduction channel. On the other hand, Exp. B showed a subducting seamount lifted up the backstop, stepped up the decollement, and then widened the subduction channel. Subduction of a rigid material like seamounts is a possible mechanism to open subduction channels for transportation of terrigenous sediments from the trench to high-pressure condition. Significant sediment supply to the trench and rough surface of subducting oceanic plate are required to enable subduction of protolith of HP-LT metamorphic rocks and accretion of trench-fill sediments at the shallow part.