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Penninic Austroalpine Subduction (Fossil Subduction Interface ('Cloud…
Penninic Austroalpine Subduction
Incremental strain reconstruction
i.e. how did plates move during Penninic-Austroalpine subduction
from vein formation sequence
overprinting relations btwn veins
opening directions of individual veins
Finite
strain
= total strain experienced by a body
(summation of incremental components)
from strain analysis of pebbles & extension veins
Engadine window limestone veins
Early stage:
Veins (1) open left-right
Later stage:
New veins open up-down
Older veins extended & boundinaged (less competent)
Fibrous calcite fills fractures in old veins to form protruding segments
Fibrous calcite composition with differing mechanical behaviour
Fossil Subduction Interface
Very narrow (cm-scale)
Not just interface accommodating strain
'Cloud of rocks' is deformed around actual interface
Surrounding rock above & below accommodates some strain
Rock closer to interface - increasingly deformed
hydrothermally altered / progressively more distorted
Africa atop, Europe on bottom
View through W 'frame' Engadine Window
Shows downdip thrust direction due to post-subduction folding
Pseudotachylite Veins
Found throughout
Austroalpine crystalline basement
Upper plate ~ amphibolite facies ?
Substantial volumes of molten rock
Along fossil plate interface above base of upper plate
Units in SZ
Upper plate: Austroalpine crystalline basement
Lower Plate: Penninic melange
Penninic Melange
Mess of blocks floating in soft mass
Matrix = flysch
= deep sea sediments deposited via gravitational events
Pseudotachylite Significance
Along fossil plate interface above base of upper plate
Delineate unstable slip region
within seismogenic coupling zone
Apulian /
Adriatic Plate
= small tectonic plate of primarily continental crust
Cretaceous - broke away from African Plate along large transform fault
Adriatic - usually refers to N portion plate
Austroalpine Nappes
= fragments of former continental shelf/slope of Apulian & Adriatic plate
Contain:
continental basement
sedimentary rocks deposited in these environments
Basement rocks - metamorphosed
Alpine metamorphism - low grade / none
Sed/volcanics - shallow marine limestones abundant (deposited on top)