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| Titel |
The Pietra Grande thrust (Brenta Dolomites, Italy): looking for co-seismic indicators along a main fault in carbonate sequences |
| VerfasserIn |
Alfio Vigano, Simone Tumiati, Silvana Martin, Manuel Rigo |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076922
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| Zusammenfassung |
| At present, pseudotachylytes (i.e. solidified frictional melts) are the only unambiguous
geological record of seismic faulting. Even if pseudotachylytes are frequently observed along
faults within crystalline rocks they are discovered along carbonate faults in very few cases
only, suggesting that other chemico-physical processes than melting could occur (e.g. thermal
decomposition). In order to investigate possible co-seismic indicators we study the Pietra
Grande thrust, a carbonate fault in the Brenta Dolomites (Trentino, NE Italy), to analyse field
structure, microtextures and composition of rocks from the principal slip plane, the fault core
and the damage zone.
The Pietra Grande thrust is developed within limestones and dolomitic limestones of Late
Triassic-Early Jurassic age (Calcari di Zu and Monte Zugna Formations). The thrust,
interpreted as a north-vergent décollement deeply connected with the major Cima Tosa thrust,
is a sub-horizontal fault plane gently dipping to the North that mainly separates the
massive Monte Zugna Fm. limestones (upper side) from the stratified Calcari
di Zu Fm. limestones with intercalated marls (lower side). On the western face
of the Pietra Grande klippe the thrust is continuously well-exposed for about 1
km.
The main fault plane shows reddish infillings, which form veins with thicknesses
between few millimetres to several decimetres. These red veins lie parallel to the
thrust plane or in same cases inject lateral fractures and minor high-angle faults
departing from the main fault plane. Veins have carbonate composition and show
textures characterized by fine-grained reddish matrix with embedded carbonate
clasts of different size (from few millimetres to centimetres). In some portions
carbonate boulders (dimension of some decimetres) are embedded in the red matrix,
while clast content generally significantly decreases at the vein borders (chilled
margins).
Red veins are typically associated with cohesive cataclasites and/or breccias of the fault zone.
Host and fault rocks are locally folded, with fold axes having a rough E-W direction
compatible with simultaneous thrust activation, suggesting deformation under brittle-ductile
conditions. A late brittle deformation is testified by near-vertical fractures and strike-slip
faults (WNW-directed) intersecting the whole thrust system.
Field structure, microtextures, chemical and mineralogical compositions of host rocks,
cataclasites and breccias are analysed. In particular, red veins are carefully compared with the
very similar Grigne carbonate pseudotachylytes (Viganò et al. 2011, Terra Nova, vol. 23,
pp.187–194), in order to evaluate if they could represent a certain geological record of
seismic faulting of the Pietra Grande thrust. |
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