Question

Which one of the following is the CORRECT sequence of igneous rocks with increasing SiO2 content?

• A. basalt → komatiite → dacite → andesite
• B. dacite → basalt → komatiite → andesite
• C. basalt → dacite → andesite → komatiite
• D. komatiite → basalt → andesite → dacite

Hint:

To remember the sequence of igneous rocks based on SiO2 content, think of the order as moving from less viscous (komatiite, basalt) to more viscous (andesite, dacite) with increasing silica.

Answer 1

The Correct Option is D

Step 1: Understand the Composition of Igneous Rocks.
Igneous rocks are categorized based on their silica (SiO2) content. The higher the SiO2 content, the lighter the color and the more viscous the magma. The typical sequence from low to high SiO2 content is:
- Komatiite: Very low SiO2 content (about 40-45%).
- Basalt: Low SiO2 content (about 45-55%).
- Andesite: Intermediate SiO2 content (about 55-65%).
- Dacite: High SiO2 content (about 65-75%).
Step 2: Sequence the Rocks.
Following the increasing SiO2 content from low to high: \[ \text{komatiite} \rightarrow \text{basalt} \rightarrow \text{andesite} \rightarrow \text{dacite} \] Thus, the correct answer is (D). Final Answer: \[ \boxed{\text{komatiite} \rightarrow \text{basalt} \rightarrow \text{andesite} \rightarrow \text{dacite}} \]