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Exposed plate interface in the European Alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone

Urheber*innen

Bachmann,  R.
External Organizations;

/persons/resource/oncken

Oncken,  Onno
3.1 Lithosphere Dynamics, 3.0 Geodynamics and Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/glodnyj

Glodny,  Johannes
4.2 Inorganic and Isotope Geochemistry, 4.0 Chemistry and Material Cycles, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Seifert,  W.
External Organizations;

Georgieva,  V.
External Organizations;

Sudo,  M.
External Organizations;

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Zitation

Bachmann, R., Oncken, O., Glodny, J., Seifert, W., Georgieva, V., Sudo, M. (2009): Exposed plate interface in the European Alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone. - Journal of Geophysical Research, 114, B05402, B05402.
https://doi.org/10.1029/2008JB005927


https://gfzpublic.gfz-potsdam.de/pubman/item/item_238720
Zusammenfassung
We present observations from a continuous exposure of an ancient plate interface in the depth range of its former seismogenic zone in the central Alps of Europe related to Late Cretaceous-early Tertiary subduction and accretion of the South Penninic lower plate underneath the Adriatic upper plate. The material forming the exposed plate interface zone has experienced flow and fracturing over an extended period of time followed by syncollisional exhumation, thus reflecting a multistage evolution. Fabric formation and metamorphism, however, chiefly record the deformation conditions of the precollisional setting along the plate interface.We identify an unstable slip domain from pseudotachylytes occurring in the temperature range between 200 and 300_C. This zone coincides with a domain of intense veining in the subduction me´lange with mineral growth into open cavities, indicating fast, possibly seismic, rupture. Evidence for transient near-lithostatic fluid pressure as well as brittle fractures competing with mylonitic shear zones continues into the region below the occurrence of pseudotachylytes, possibly reflecting a zone of conditionally stable slip. The zone above the unstable slip area is devoid of veins but displays ample evidence of fluid-assisted processes similar to the deeper zone: solution-precipitation creep and dehydration reactions in the me´lange matrix, hydration, and sealing of the base of the upper plate. Seismic rupture here is possibly expressed by ubiquitous localized deformation zones. We hypothesize that trenchward sealing of parts of the plate interface as well as reaction-enhanced destruction of upper plate permeability is an important component, localizing the unstable slip zone. This relation may result from the competition of the pervasive, presumably interseismic, pressure solution creep destroying permeability and building elevated fluid pressure until the strength threshold is reached with seismic failure.