Application of low-grade metamorphic forces to a rock causes
- a decrease in rock density
- an increase in weathering
- an increase in rock volume
- an increase in rock density
- melting
The correct answer and explanation is:
The correct answer is: an increase in rock density.
Explanation:
Metamorphism is the process by which rocks undergo physical and chemical changes due to heat, pressure, and chemically active fluids. Low-grade metamorphism occurs at relatively low temperatures (150–450°C) and pressures. When low-grade metamorphic forces are applied to a rock, it undergoes changes that typically lead to an increase in density rather than a decrease.
Why does rock density increase?
- Recrystallization – During low-grade metamorphism, minerals within the rock start to recrystallize, forming a more compact and interlocking grain structure. This reduces pore spaces, making the rock denser.
- Compaction – Pressure forces mineral grains closer together, reducing the volume and increasing the overall density. This is particularly evident in rocks like shale transforming into slate.
- Loss of Volatiles – As temperature and pressure increase, certain volatile components like water and carbon dioxide are expelled from the rock, contributing to its densification.
Why Not Other Answers?
- Decrease in rock density – This is incorrect because metamorphism typically compacts the rock rather than making it more porous.
- Increase in weathering – Weathering occurs at the Earth’s surface, while metamorphism happens at depth under heat and pressure, reducing exposure to weathering forces.
- Increase in rock volume – While minerals can change and rearrange, volume usually decreases as the rock becomes more compact.
- Melting – Low-grade metamorphism does not reach temperatures high enough to cause melting, which occurs at much higher temperatures (>800°C).
Thus, low-grade metamorphism leads to increased rock density due to compaction, recrystallization, and the loss of volatile materials.
Now, I’ll generate an image to illustrate this process.
Here’s an illustration of the process of low-grade metamorphism, showing how sedimentary rock transforms into a denser metamorphic rock under heat and pressure. Let me know if you need any modifications!
