Which of the following changes do not typically occur in rock as it is subjected to metamorphism?

(2 answers are correct)

Question

Which of the following changes do not typically occur in rock as it is subjected to metamorphism?

(2 answers are correct)

BlackTom AI · Accepted Answer

We are asked to identify which changes do NOT typically occur in rock during metamorphism, and there are two correct choices.

Option 1: 'new elements can be created through metamorphism' — This is not a typical metamorphic outcome. Metamorphism involves recrystallization and redistribution of existing minerals and elements under heat and pressure, but it does not create new chemical elements. Elemental composition remains the same overall, so this statement is inaccurate for describing metamorphic processes.

Option 2: 'mineral crystals can become aligned perpendicular to the stress field' — Metamorphism commonly produces preferred orientation or foliation as minerals recrystallize under directional stress. The familiar result is alignment parallel to the direction of maximum compression (or along the shortening direction), not perpendicular to the stress field. Therefore, stating perpendicular alignment mischaracterizes the usual fabric development, making this a not-typical change.

Option 3: 'mineral crystals can shrink due to metamorphism' — Grain size change is a nuanced outcome of metamorphism. While recrystallization often leads to growth or coarsening in some minerals, creating larger and cleaner crystals, there are cases where grains can become smaller or more complex due to dynamic recrystallization and subgrain formation. However, a general, everyday description of metamorphism emphasizes grain growth and recrystallization rather than universal shrinking. In the context of typical metamorphic trends, this option is generally considered not a standard, expected outcome, so it can be regarded as not typical.

Option 4: 'mineral crystal chemistry can change by reconfiguring constituent atoms' — This is a well-established metamorphic effect. Under heat and pressure, minerals can undergo isochemical or metasomatic reactions that rearrange their crystal structure or even alter their composition within solid solution, leading to changes in crystal chemistry. This is a common metamorphic phenomenon and should be considered a typical change.

Option 5: 'mineral crystals can enlarge' — Grain growth is a common metamorphic outcome, especially during recrystallization under elevated temperatures, leading to larger, more stable crystals. Therefore, this is a typical change and not a 'do not typically occur' change.

In summary, the changes that do not typically occur during metamorphism are: Option 1 (new elements created) and Option 3 (mineral crystals shrinking). The other options describe changes that are consistent with metamorphic processes (Option 4) or with typical metamorphic outcomes (Option 5), while Option 2 misstates the orientation pattern expected under directional stress.

Which of the following changes do not typically occur in rock as it is subjected to metamorphism? (2 answers are correct)多项选择题

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