Publikationsdatum:
2017-04-04
Beschreibung:
We report a new type of ultramafi c pseudotachylyte that forms a fault- and injection-vein
network hosted in the mantle-derived Balmuccia peridotite (Italy). In the fault vein the pseudotachylyte
is now deformed and recrystallized into a spinel-lherzolite facies ultramylonite, made
of a fi ne (〈2 μm) aggregate of olivine, orthopyroxene, clinopyroxene, and spinel, with small
amounts of amphibole and dolomite. Electron backscattered diffraction study of the ultramylonite
shows a clear crystallographic preferred orientation (CPO) of olivine. The fault vein
pseudotachylyte overprints a spinel-lherzolite facies amphibole-bearing mylonite, indicating
that shear localization accompanying chemical reaction had taken place in the peridotite before
seismic slip produced frictional melting. The occurrence of amphibole in the host mylonite and
that of dolomite as well as amphibole in the matrices of ultramylonite and pseudotachylyte may
indicate that fl uid was present and had evolved in its composition from H2O-rich to CO2-rich
during ductile deformation with metamorphic reactions, which may account for the observed
rheological transition from ductile to brittle behavior. The spinel-lherzolite facies assemblage
in mylonites, P-T estimations from pyroxene geothermometry and carbonate reactions, and
the type of olivine CPO in deformed pseudotachylyte indicate that both the preseismic and the
postseismic ductile deformations occurred at ~800 °C and 0.7–1.1 GPa.
Beschreibung:
F. Seifert and Bayerisches
Geoinstitut (University of Beyreuth); Japan Society for the Promotion of Science
grant 17340159; Progetti di RilevanteInteresse Nazionale grant 2005044945 and a Progetti
di Eccellenza Fondazione Cassa di Risparmio di
Padova e Rovigo (CARIPARO) grant.
Beschreibung:
Published
Beschreibung:
607-610
Beschreibung:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Beschreibung:
JCR Journal
Beschreibung:
open
Schlagwort(e):
pseudotachylyte
;
peridotite
;
04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes
Repository-Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Materialart:
article
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