# Distributed deformation along the subduction plate interface: insights from fossil examples and mechanical implications

Hugues Raimbourg, Vincent Famin, Giulia Palazzin, Asuka Yamaguchi, Yujin Kitamura

► To cite this version:

Hugues Raimbourg, Vincent Famin, Giulia Palazzin, Asuka Yamaguchi, Yujin Kitamura. Distributed deformation along the subduction plate interface: insights from fossil examples and mechanical implications. 20th EGU General Assembly, 2018, Vienne, Austria. pp.14897. hal-03552811

HAL Id: hal-03552811

https://hal.science/hal-03552811

Submitted on 2 Feb 2022

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>
<figure><img src="image_2.png" /></figure>

# Distributed deformation along the subduction plate interface: insights from fossil examples and mechanical implications

Hugues Raimbourg (1), Vincent Famin (2), Giulia Palazzin (1), Asuka Yamaguchi (3), and Yujin Kitamura (4)

(1) Institut des Sciences de la Terre, UMR 7327, Université d'Orléans, Orléans, France (hugues.raimbourg@univ-orleans.fr),

(2) Laboratoire Géosciences Réunion, IPG UMR 7154, Université de La Réunion, Saint-Denis de la Réunion, France, (3)

Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan, (4) Graduate School of Science and Engineering, Kagoshima University, Kagoshima, Japan

Many recent geophysical and geodetic observations in subduction zones have unraveled the diversity of the deformation of the plate interface. Such mechanical complexity is commonly interpreted in the framework of friction mechanics, from experimental and theoretical approaches based on rate-and-state friction laws. Alternately, the deformation along the plate interface can be studied using naturally-deformed structures in fossil subduction zones. We will show in this work the results obtained in the Shimanto Belt in Japan, the fossil equivalent to the deep domains of the modern margin, the Nankai accretionary prism. In particular, we focused on domains of the Shimanto Belt considered as tectonic mélanges, which concentrated a large proportion of the strain resulting from plate differential motion. Several tectonic slivers of mélanges, emplaced at different periods, are intercalated with units where deformation is less intense and where the original sedimentary layering is preserved. In contrast, mélanges have a block-in-matrix structure, where cm- to tens-of-meter scale lenses, constituted of sandstone or basalt, are embedded in a shale matrix. Mélanges are pervasively deformed, with the development of a phyllosilicate-rich foliation and the preferential flattening of the lenses parallel to the foliation. Furthermore, mélanges incorporate a dense network of quartz veins and quartz-filled shear bands, with a consistent direction of motion. At the thin-section scale, the elementary processes governing deformation within the mélanges involve a combination of fracturing, dissolution and precipitation to form quartz veins, along with slip on a network of µm- to mm-scale phyllosilicate-rich shear bands. At the larger scale of the whole tectonic mélange units, the shear bands can be interpreted as a top-to-the-trench shear along the subduction plate interface, at temperatures in the range 150-250°C, typically of the order of the seismogenic zone. Consequently, mélange units can be considered as large shear zones that accommodated at depth the plate differential motion over their whole thickness. Such type of large shear zones, where the strain is distributed over a thickness of at least tens of meters, contrasts with narrow faults or pseudotachylytes, where strain is localized over a few centimeters. While the localized endmember of deformation is well accounted for by friction laws, the distributed endmember of deformation is not, although it constitutes an appropriate candidate for domains of the plate interface where deformation is aseismic. To describe the whole range of the deformation modes occurring along the plate interface, more complete models should therefore incorporate a larger variety of elementary deformation processes, in particular pressure solution, as able to accommodate the strain.