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TitlePossible mechanism of mud volcanism at the prism-backstop contact in the western Mediterranean Ridge Accretionary Complex
AuthorKioka, A; Ashi, J; Sakaguchi, A; Sato, T; Muraoka, S; Yamaguchi, A; Hamamoto, H; Wang, K; Tokuyama, H
SourceMarine Geology vol. 363, 2015 p. 52-64,
Alt SeriesEarth Sciences Sector, Contribution Series 20140139
Mediapaper; on-line; digital
File formatpdf
AreaMediterranean Sea
Lat/Long WENS 15.0000 35.0000 40.0000 30.0000
Subjectsvolcanology; mud volcanoes; pressure; vitrinite reflectance; fluid migration; submarine features; Mediterranean Ridge
Illustrationslocation maps; bathymetric profiles; 3-D models; photographs; histograms; graphs; diagrams
ProgramWestern Canada Geohazards Project, Public Safety Geoscience
AbstractThe EasternMediterranean seafloor has numerousmud volcanoes,most ofwhich formawell-defined beltwithin the Mediterranean Ridge (MedRidge) accretionary complex. However, mud volcano fields in the western MedRidge are less well known as those in the central and eastern MedRidge. This study investigates material cycling and fluid migration within the westernMedRidge. We propose a possible ascent style of the ejecta forming the Médée-Hakuho Mud Volcano (MHMV) in the western MedRidge by applying the vitrinite reflectance technique to ejecta samples. First, we model the 2-D thermal structure in the western MedRidge, taking into account frictional heating on the plate interface, to help estimate the source depth of the MHMV ejecta. The result suggests an effective coefficient of friction of around 0.01, and a temperature of about 160 ± 15 °C along the plate interface at a distance of ~180 kmfromthe deformation front, the location of the seaward toe of the Aegean backstop. Second,we evaluate the source depth of theMHMV ejecta using vitrinite reflectance in conjunctionwith the modeled thermal structure. The results suggest that the ejecta matrix showing vitrinite reflectance values of ~0.6% was subjected to a temperature of around 85 °C, corresponding to a depth of approximately 5 km below the seafloor (kmbsf), whereas older clasts of Aptian or earlier age, with vitrinite reflectance values of ~0.6-1.0%, are derived from much deeper depths. Most of the clasts are considered to have been lifted to the depth of 5 kmbsf as a result of underplating at the toe of a rigid backstop that had developed below MHMV after underthrusting related to plate subduction. At that depth, fluid pressures that are dramatically increased because of underplating promote the ascent of fluid-rich sediments and entrain clasts along an existing fault in the accretionary wedge.
Summary(Plain Language Summary, not published)
Pore fluid pressure along subduction zone megathrusts is one of the most important parameters affecting earthquake generation. It is difficult to study in situ the level of the fluid pressure, but mud volcanoes produced by the elevated pore fluid pressure in some places provide rare opportunities. This work is focused on a case study of a mud vocano site at the Hellenic subduction zone. The results help us understand similar processes in other subduction zones, including places where mud volcanoes are rare or absent, such as Cascadia.