Cala Portal/ D'Agulles
Kinematic Data
SZ network Morphology
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
Shear sense indicators
Sigma clasts - hill/headland asymmetry
Shear band - deflection sense of mylonitic foliation
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 braided SZ networks
Accommodated plate motion @ depth - Probably typical for middle crust
Shear zones work together / interact kinematically to accomodate deformation @ Cap de Creus
Cap de Creus Shear Sense
Top to the right
Stereonets
Great circle = mylonitic foliation
Poles = stretching lineation
3 stereonets: W, Central, E sections SZ
measured in individual SZs
(corresponding to foliation)
Kinematic
SZ Data
Three shear zones make up this braid/network
Comprises 3 shear zones
Dominant shear zone dip ~45-80° (NE)
Stretching Lineations
Shear sense variable :
East sz: Dominantly top-to-SE
NW dipping sz: Top-to-NW (weak signal)
Top-to-SE =
Most robust
i.e. nothing rotates beyond this
All segments evolving toward mature/stable top-to-SE shear sense
Top to NW segments = Rotating
to try & assume stable top-to-SE orientation
NW dipping shear zones tend to exhibit top-to-NW shear sense
Orientation ~ consistent
Shear sense dominantly top-to-SE
Dip direction - highly variably
Cross Section of Cala D'Agulles SZ
Looking into mvmt/stretching direction
LHS: Steep vertical dextral shear zone joins
RHS: Narrower sinistral SZ
dextral - top to right etc
Complex deformation in unit between
Delta clast - tourmaline aggregate
Delta
Clast
Top-to-SE shear sense indicator
Tourmaline aggregate
- Clast rolling along sheared margin
- Recrystallises & tail dragged around as rotates
Stair stepping
Direction tail rotated
At margin between
- high grade metapelite
- highly deformed pegmatite
Tourmaline
= common in pegmatite
Collect elements unused in pegmatite
~effectively waste buckets
Stair stepping direction on asymmetric clasts
Strain Partitioning
Folding in less deformed domains between braided shear zones
Fold axes & axial planes = steeply dipping
Orientations variable - suggests folds largely formed independently