Geology Department

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Geology 110 Syllabus

POLYPHASE DEFORMATION

FoldsFabric

I. POLYPHASE DEFORMATION - rocks affected by more than one phase of deformation

A. Phase - large as orogeny and smaller ones associated with an orogenic event

1. Fabric analysis (Sander, 1930's), look at fabrics to determine what happened when

2. Crustal conditions exposed in fabric

Dx = deformation event or phase (phases)

Fx = folding

Lx = lineation

Sx = foliation/cleavage

Mx = metamorphism

II. DISCLAIMERS:

A. Relative timing of deformation:

e.g., F1, F2, F3 are not necessarily related to "periods of interkinematic quiescence" F1 - on, off - quiescence, turn on F2 , etc... however, know that F1, F2, F3 etc... could form due to single phase i.e., multiple folds do not necessitate a series of discrete events

B. Fold correlations:

1. F1 may not be the same F1 in another area

2. F1, F2, F3 determined in one outcrop may not correlate to another

III. REFOLDED FOLD PATTERNS - Ramsay 1967

A. Type 1 - fold interference patterns (basins and domes) form due to F1 and F2 are upright

B. Type 2 - boomerangs and mushrooms

1. Start with overturned fold

2. Superimpose upright F2 fold

C. Type 3 -hook pattern

1. Fold hinges are coaxial (=), earlier hinge surface is folded