1. Announcements Field trip to Tanque Verde this Saturday
Announcements Field trip to Tanque Verde this Saturday! 8:00 AM departure; loading dock

2. In brittle regime: joints, tensile fractures, shear fractures (faults
In brittle regime: joints, tensile fractures, shear fractures (faults!), pressure solution (cleavage development)- deformation mechanisms depend on pressure! What about deformation in the deeper crust?

3. Today: Foliations, stretching lineations, and tectonites- deformation in the deeper crust (D&R, pp ; )

4. "General" definition: Foliation: Penetrative (at outcrop and microscopic scale) and parallel planar fabric elements in a rock. "Structural geologist's" definition: Planar fabric is secondary and due to mineral recrystallization and/or plastic behavior during deformation at elevated temperatures

5. phyllitic structure is a type of foliation

6. Schistosity: coarser grained fabric- also a foliation

7. Gneissic structure: Compositional banding produced during deformation.

8. Migmatite: Compositional banding due to in-situ partial melting
Migmatite: Compositional banding due to in-situ partial melting. Swirly appearance

9. In a conglomerate, flattened pebbles may define a foliation- "flattening fabric"

10. Flattening of strong layers surrounded by weak layers may cause strong layers to "neck" and form boudins.

11. more boudins

12. Boudins in 3-D

13. Mylonitic foliation: Forms due to grain-size reduction by a mix of brittle and plastic deformation in shear zones
brittle deformation of feldspar porphyroclasts
plastic deformation of quartz "ribbons" and mica

14. Coarse-grained mylonitic augen gneiss
Coarse-grained mylonitic augen gneiss. The large porphyroclasts are called augen ("eyes")

15. A strongly mylonitized rock- note the extremely fine grain size due to "pulverization" during shearing

16. Lineation: penetrative linear fabric
Lineation: penetrative linear fabric. We will focus on those that are related to deformation.
How does it differ from other linear structures we have talked about, like slickenlines on a fault surface?
Types of lineations:
1) Intersection
2) Crenulation
3) Mineral
4) Stretching

17. Intersection lineation: Intersection of two planar features- an "apparent" lineation in that there is no fabric that is linear.
e.g., intersection between cleavage and planar surface

18. Crenulation lineation: Intersection between fold hinges and foliation

19. Mineral lineation: preferred alignment of minerals due to deformation and/or recrystallization during deformation

20. Stretching lineation: elongation of minerals due to "stretching" deformation

21. Stretched
calcite

22. Lineation defined by stretched pebbles in a conglomerate

23. Tectonites: Rocks that are pervaded by foliation and/or lineation- flowed in solid state
S: Schistosity (foliation) only due to flattening- no lineation
L: Lineation only, due to unidirectional stretching/ constriction
LS: Foliation and Lineation, related to noncoaxial strain- shearing

24. Strain ellipse and tectonites
S-tect = S1= S2 > S3 (coaxial)
L-tect = S1 > S2 = S3 (coaxial)
LS-tect = S1 > S2 > S3 (non-coaxial)

25. What kind of tectonite is this?
Coaxial (pure shear) or non-coaxial strain?
L-tectonite
Coaxial
What is it?

26. What kind of tectonite is this?
Coaxial vs. non-coaxial?
L-S tectonite
non-coaxial

27. S-C fabrics- occur in L-S tectonites and serve as excellent sense-of-shear indicators
S-Surfaces- planes of schistosity/foliation (flattening)
C-Surfaces- planes of maximum shear "shear bands"
C comes from cisaillement, French for shear

28. When studying S-C fabrics- must look perpendicular to lineation!

29. S-C fabrics and the strain ellipse

30. First step- find shear bands (C-surfaces)
Second step- find flattening planes (S-surfaces)
Third step- sense of shear from strain ellipse!
left-lateral sense of shear

31. Practice!
top to right sense of shear S C

32. For fine-grained mylonites- S-C fabrics can be studied using a microscope

33. Saturday's field trip to Tanque Verde Wash (Redington Pass area)
A look at deformation in a shear zone related to the Catalina detachment

34. Hypothesis for evolution of metamorphic core complexes including the Catalina-Rincon core complex and detachment system.

35. Next Lecture: Shear zones and shear sense indicators Please read (D&R, pp. 493-551)

36. Important terminology/concepts
foliation
gneissic structure
migmatite
boudins
mylonites
augen gneiss
lineation (intersection, crenulation, mineral, stretching)
tectonites (L, S, L-S)
tectonites and strain ellipsoid
S-C fabrics and sense-of-shear
Structural evolution of metamorphic core complexes