Question

Choose the correct combination(s) of textural features of magmatic rocks with corresponding petrological processes from the following.

• A. ophitic texture in dolerite - peritectic crystallization
• B. perthite in granite - slow subsolidus cooling
• C. spinifex texture in komatiite - eruption of ultramafic lava
• D. orthopyroxene rim around olivine in peridotite - eutectic crystallization

Hint:

Magmatic textures such as perthitic and spinifex textures are important indicators of the cooling history and crystallization processes of igneous rocks.

Answer 1

The Correct Option is B, C

Step 1: Understanding the question.
This question asks about the relationship between magmatic textures and the processes that create them. Textures like ophitic and perthite are linked to specific petrological processes.
Step 2: Analyzing the options.
(A) ophitic texture in dolerite - peritectic crystallization: Incorrect — Ophitic texture in dolerite typically forms due to slow cooling in shallow intrusions, and is not associated with peritectic crystallization.
(B) perthite in granite - slow subsolidus cooling: Correct — Perthite forms during slow cooling, particularly in granitic rocks, through exsolution of two feldspar phases.
(C) spinifex texture in komatiite - eruption of ultramafic lava: Correct — Spinifex texture is characteristic of rapidly cooling ultramafic lava flows such as komatiites, where large crystals of olivine are surrounded by finer-grained material.
(D) orthopyroxene rim around olivine in peridotite - eutectic crystallization: Incorrect — This texture is typically the result of fractional crystallization in a cooling magma, not eutectic crystallization.
Step 3: Conclusion.
The correct answer is (B), (C), as these combinations correctly link magmatic textures with the petrological processes responsible for their formation.