Question

A schematic deformation (D)-metamorphism (M)-time map of a metamorphic belt is shown below. The belt recorded two phases of deformation, D₁-D₂ and attendant schistosity, S₁-S₂ and metamorphism, M₁-M₂. The metamorphic minerals stable during these events are shown by solid lines. On the basis of this information, which of the following statement(s) is/are correct? 

• A. M₁ and M₂ events refer to regional and contact metamorphism, respectively.
• B. The S₁ schistosity developed as a crenulation cleavage.
• C. Garnet grew syntectonic with D₁.
• D. Andalusite grew during the waning phase of D₂.

Hint:

In metamorphic studies, it's important to distinguish between regional and contact metamorphism, with regional metamorphism occurring under high pressure and temperature, and contact metamorphism occurring due to the heat from an igneous intrusion.

Answer 1

The Correct Option is A, C

Step 1: Understanding the diagram and events.
- The diagram shows two deformation events (D₁ and D₂) with corresponding schistosity (S₁ and S₂), which are linked to two distinct metamorphic events (M₁ and M₂).
- M₁ typically corresponds to regional metamorphism, and M₂ corresponds to contact metamorphism, based on the context of the diagram and the minerals involved.

Step 2: Analyzing the options.
(A) M₁ and M₂ events refer to regional and contact metamorphism, respectively: Correct — M₁ corresponds to regional metamorphism, and M₂ corresponds to contact metamorphism as indicated in the diagram.
(B) The S₁ schistosity developed as a crenulation cleavage: This statement is incorrect, as S₁ is likely to correspond to the initial foliation, not a crenulation cleavage.
(C) Garnet grew syntectonic with D₁: This is unlikely, as garnet typically forms during metamorphism, which may not coincide exactly with deformation D₁.
(D) Andalusite grew during the waning phase of D₂: Andalusite typically forms at higher temperatures and pressures, and its growth would likely be associated with the later stages of metamorphism, not the waning of deformation.

Step 3: Conclusion.
The correct answer is (A) M₁ and M₂ events refer to regional and contact metamorphism, respectively.