Question

Sandstone beds above a magmatic body are domal in shape, while the beds below arc horizontal. The mae,:matic bod.v is a

• A. Batholith
• B. Laccolith
• C. Lopolith
• D. Sill

Answer 1

The Correct Option is B

The question asks us to identify the type of magmatic body that causes sandstone beds above it to appear domal (dome-shaped), while the beds below remain horizontal. Let's analyze each option and determine the correct answer.

1. Batholith: A batholith is a large plutonic rock formation, typically with a surface exposure greater than 100 square kilometers. It does not usually form domes; rather, it is a deep-seated and massive underground structure. Therefore, it does not fit the description of causing domal shapes in overlying strata.
2. Laccolith: A laccolith is a sheet intrusion (or concordant plutonic body) injected within or between sedimentary rocks. The pressure from the magma may cause the overlying beds to arch upwards, creating a domal structure while the strata beneath remain unaffected and horizontal. This matches the description given in the question.
3. Lopolith: A lopolith is another type of igneous intrusion, typically lens-shaped and concave upwards. It forms when magma sags the overlying strata; hence, it is more likely to result in a basin rather than a dome. This is inconsistent with the question's description.
4. Sill: A sill is a tabular sheet intrusion that occurs parallel to the existing rock. It does not create domal shapes as it does not deform the layers significantly. The intrusion occurs within horizontal strata, maintaining the existing structure.

Based on the above explanations, the correct answer is Laccolith. Laccoliths are known for creating domal structures in the sedimentary layers above them, while the layers beneath remain horizontal.