Structural Geology and Tectonics
Structural Geology and Tectonics tests how rocks deform and how structures are shown on maps. Expect strike and dip, folds, faults, joints, unconformities, stress and strain, and plate-tectonic settings. Karnataka's N-S trending schist belts and granitic batholiths are useful local examples.
Core rules
- Strike is the compass direction of a horizontal line on a bedding plane; dip is the angle and direction of steepest descent.
- Anticlines have oldest beds in the core; synclines have youngest beds in the core.
- Faults show displacement; joints are fractures without visible displacement.
- An unconformity is a surface of erosion or non-deposition representing missing time.
- Stress types are compression, tension and shear; strain is the resulting deformation.
Worked example
A map shows symmetrical outcrop bands: shale in the centre, sandstone on both sides, then limestone outermost. Identify the structure. Reasoning: the youngest bed, limestone, lies outside the shale, so the oldest rock is in the centre. That geometry is an anticline. If limestone were in the centre, it would be a syncline.
Traps
- Do not confuse dip direction with strike; they are perpendicular.
- A fault is not a joint; displacement must be shown or inferred.
- An unconformity is not a conformable contact; it represents time missing.
- On a map, repetition of beds can be caused by folding or faulting; check symmetry and displacement.
Karnataka link
The Dharwar craton contains steeply dipping, N-S trending greenstone belts intruded by Closepet granite; these record Archean deformation, not modern plate-boundary rifting.