Properties of Magma — Volatiles and Types (UPSC Prelims PYQ 2001)

Consider the following statements:

1. Most magmas are a combination of liquid, solid and gas.
2. Water vapour and carbon dioxide are the principal gases dissolved in a magma.
3. Basaltic magma is hotter than the silicic magma.
4. The magma solidified between sedimentary rocks in a horizontal position is known as dike.

Which of these statements are correct?

1. I, II and III
2. II, III and IV
3. I and IV
4. I, II and IV

Explanation

Option (a) is correct

• Most magma consists of a mixture of liquid molten material, solid mineral crystals, and dissolved gases, making Statement I correct. Water vapour and carbon dioxide are the major gases commonly present in magma, so Statement II is also correct. Basaltic magma has lower silica content and generally possesses higher temperatures than silicic magma, making Statement III correct. However, Statement IV is incorrect because magma that solidifies horizontally between sedimentary rock layers is called a sill, whereas a dike is a vertical or steeply inclined intrusion cutting across rock layers.

Answer: (a) I, II and III