Folds

Rationale: An isoclinal fold has limbs that are parallel or sub-parallel to each other due to uniform and intense compressive forces acting on the strata.

Rationale: An overturned fold is characterized by intense pressure that tilts one limb beyond the vertical plane, causing the younger strata to lie beneath older strata (inverted strata).

Rationale: When compressive forces are extremely strong and directional, the axial plane is pushed into a nearly horizontal position, producing a recumbent fold.

Rationale: A nappe is a large tectonic sheet or recumbent fold that has moved horizontally, often for kilometers, over underlying rock strata along low-angle fault planes.

Rationale: A monocline is a localized step-like bend in horizontal or gently dipping strata, typically caused by blind faulting in the basement rocks beneath.

Rationale: A fan fold (or fan-shaped fold) occurs when the crest of an anticline or trough of a syncline is compressed so severely that the strata spread outward in a fan configuration.

Rationale: A plunging fold is one whose axis dips downward into the earth at a specific angle (plunge), producing V-shaped or horseshoe-shaped outcrop patterns on geological maps.

Rationale: Due to upward arching and subsequent erosion, the oldest rock layers are exposed in the core of an anticline, whereas synclines preserve the youngest rocks in their core.

Rationale: Chevron folds exhibit characteristic zig-zag patterns with straight limbs and sharp, acute angular hinge zones, commonly developing in alternating hard and soft sedimentary beds.

Rationale: Fold mountains are formed by immense lateral compressional forces generated along convergent plate boundaries, leading to intense crustal shortening and folding.

Rationale: A symmetrical fold has equal limb inclination and balanced geometry relative to the vertical axial plane.

Rationale: Box folds (or conjugate folds) exhibit broad, flat crests or troughs bordered by steep limbs, giving them a distinct rectangular or box-like appearance.

Rationale: The axial plane is the imaginary surface that connects the hinge lines of all folded strata layers stacked one above another within a fold.

Rationale: Eroded plunging folds produce distinctive V-shaped or horseshoe patterns where the oldest beds close in the direction opposite to the plunge in anticlines.

Rationale: The Himalayas were formed by the collision of the Indian and Eurasian plates during the Cenozoic Era, representing classic Alpine-type fold mountains.

Rationale: Interlimb angle defines openness: open folds have wide interlimb angles (70 to 120 degrees), while closed folds have narrow angles (30 to 70 degrees).

Rationale: The fold axis or hinge line represents the line of maximum curvature along a folded stratum.

Rationale: Asymmetrical folds have unequal limbs and differing dip angles relative to the axial plane, reflecting directional stress.