Please enable JavaScript.
Coggle requires JavaScript to display documents.
Calla Portal/ D'Agulles (Sigma clast (Tail = asymmetric wrt mylonitic…
Calla Portal/ D'Agulles
Shear zone network
Cala Portal / D'Agulles
Major shear zone where bay pronounced
(preferentially eroded to form inlet)
Pegmatite
abuts mouth of bay
Sigmoid shape
on hill / headland adjacent indicates top-to-the-right shear sense
Cap de Creus Shear Sense
Top to the right
Sigma
clast
Tail = asymmetric wrt mylonitic foliation
Stair-
stepping
geometry
Tails located either side of reference line - do not cross it
Asymmetry - result of rotational deformation
Sigmoid shape on hill / headland adjacent
Indicates
TOP TO THE RIGHT
shear sense
Shear zone networks
Where shear zones exceed critical scale they connect with others
--> Form km-scale SZ networks
Probably typical for middle crust
Shear zones
interact kinematically
within these networks
Asymmetry of Mylonite Structures
Useful for evaluating shear zone:
Sense of shear
Degree of coaxiality (rotation)
Especially useful in SZ if you cannot see margins
Shear
Bands
Mylonitic
foliation (S)
form along X-Y plane of strain ellipsoid
foliation(S) curves in & out of shear surfaces (C)
Shear surfaces (C)
form parallel to shear zone walls as strain accumulates
early deformation - cut across foliation
continual deformation - shear bands & foliation near parallel
(indistinguishable?)
C'
New, oblique shear bands (C') form
Backrotate CS foliation which is now termed 'S'
If strain is high enough
Shear sense indicators
Sigma clasts - asymmetry
Shear band - deflection sense of mylonitic foliation
Stretching lineations
Alignment of quartz crystal c-axes
Long axes of deformed grains
oriented oblique to main foliation
Angle btwn lineation & mylonitic foliation
Allows inference shear sense/rotation
Form in mineral aggregates that dynamically recrystallise during deformation