Structural Geology and Tectonics
What the exam tests
Structural Geology and Tectonics tests the attitude of rock bodies (strike and dip), folds, faults, joints and unconformities, and the plate-tectonic setting of peninsular India and Kerala.
Core rules
- Strike is the compass direction of the line where a bed meets the horizontal; dip is the angle of steepest descent, measured perpendicular to strike, and must be reported with a dip direction.
- In an anticline the limbs dip away from the axis and the oldest beds lie in the core; in a syncline the youngest beds lie in the core.
- Normal faults form under extension, reverse faults under compression, strike-slip faults under horizontal shear.
- Unconformities record missing time: angular, non-conformity, disconformity, paraconformity.
- India forms part of the Indian plate, converging with Eurasia. Kerala lies on a passive rifted western margin, flanked by the Western Ghats escarpment and cut by lineaments such as the Achankovil shear zone.
Worked example
A bed crops out across 100 m of horizontal ground and dips 30°. True thickness t = width × sin(dip) = 100 × 0.5 = 50 m. Use the true dip and a width measured perpendicular to strike; an apparent dip measured in an oblique direction gives a thickness that is too large.
Traps
Reporting dip without direction. Confusing anticline and syncline map symbols - arrows point away from the core in an anticline. Calling a joint a fault; joints show no displacement. Treating an angular unconformity as a simple bedding plane.