A large body of magmatic material that cools in the deeper depth of the Earth's crust and develops in the form of large domes is known as
- (a)Batholiths.
- (b)Lacoliths.
- (c)Lopoliths.
- (d)Phacoliths.
Correct — A, Batholiths. A batholith is a very large mass of magma that solidifies deep within the crust, forming huge dome-like bodies of intrusive (plutonic) rock such as granite. They are exposed at the surface only after long erosion strips away the overlying rock, revealing large granite domes and uplands.
- (b)Lacoliths. — A laccolith is a smaller intrusion with a flat base and a domed top that arches up the overlying strata — much smaller than a deep-seated batholith.
- (c)Lopoliths. — A lopolith is a large saucer- or basin-shaped intrusion that sags downward in the middle — not a large dome.
- (d)Phacoliths. — A phacolith is a small lens-shaped intrusion that forms in the crests and troughs of folded strata, not a great dome cooling at depth.
Intrusive (plutonic) igneous landforms form when magma cools below the surface. They differ by size and shape: batholiths are the largest, deep dome-like masses; laccoliths are flat-based, dome-topped; lopoliths are saucer-shaped sagging bodies; phacoliths are lens-shaped bodies in folds. Sills and dykes are sheet-like intrusions.
The clues 'large', 'deeper depth' and 'large domes' point straight to a batholith. The distractors are the other named intrusive forms, distinguished mainly by shape and scale.
- A batholith is a very large, deep-seated dome-like body of intrusive rock (often granite).
- It becomes visible only after prolonged erosion of overlying rock.
- Laccolith = flat base with domed top; lopolith = saucer-shaped; phacolith = lens in folds.
- Sills (horizontal) and dykes (vertical) are sheet-like intrusions.
'Large' + 'deep' + 'domes' identifies the batholith among the intrusive forms.
- Confusing a laccolith (small, flat-based dome) with a large batholith.
- Mixing intrusive (below surface) with extrusive (volcanic) landforms.
Asked by describing an intrusive body's size/shape and asking for its name, or by matching intrusive forms to diagrams.
No directly related past PYQ was found.
- practice — not a real PYQ
A flat-based, dome-topped igneous intrusion that arches up the overlying strata is a
- (a)Batholith
- (b)Laccolith
- (c)Dyke
- (d)Sill
Answer(b) Laccolith — smaller than a batholith, with a domed top.
- practice — not a real PYQ
A horizontal sheet-like igneous intrusion between rock layers is called a
- (a)Dyke
- (b)Sill
- (c)Batholith
- (d)Lopolith
Answer(b) Sill — a concordant, horizontal sheet intrusion.