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.
Answer
Why
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.
Why the others are wrong
- (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.
Concept
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.
Key facts
- 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.
Study next
Common traps
- 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.
Related PYQs
No directly related past PYQ was found.
Practice
- 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.