Question

Intrusion of a 10-meter thick dolerite dyke into a boron-rich quartz-garnet-biotite-muscovite-chlorite schist developed a visible symmetric baked zone. Which of the following minerals can develop in this baked zone, 2 meters away from the margin of the dyke?

• A. Orthopyroxene
• B. Clinopyroxene
• C. Amphibole
• D. Tourmaline

Hint:

Amphibole is a common product of metamorphism around hot intrusions, such as dolerite dykes, due to its formation in intermediate to high-grade metamorphic conditions.

Answer 1

The Correct Option is C

Step 1: Understanding the baked zone.
The baked zone refers to the area around the dyke where the temperature increases due to the intrusion of hot magma. This high temperature can cause the metamorphism of the surrounding rocks, leading to the formation of new minerals
. The type of minerals formed depends on the chemistry of the host rock and the temperature of the intrusion.

Step 2: Analyzing the mineral formation.
- Orthopyroxene (Option A) forms in high-temperature, low-pressure conditions and is typically found in igneous rocks, not in metamorphic rocks of this type.
- Clinopyroxene (Option B) also forms at high temperatures but is more typical of igneous rocks formed in mafic conditions.
- Amphibole (Option C) is a common metamorphic mineral that forms in intermediate to high-grade metamorphic conditions, particularly when schists are subjected to heat during contact metamorphism, such as around the intrusion of a dolerite dyke.
- Tourmaline (Option D) is a common mineral in pegmatitic environments and is not typically associated with the temperature conditions of a baked zone around a dolerite dyke.

Step 3: Conclusion.
Given the conditions of metamorphism due to the intrusion of the dolerite dyke, the mineral that would most likely develop in the baked zone is amphibole. Therefore, the correct answer is (C).
\[ \boxed{\text{Amphibole}} \]