Question

The closure temperature represents the point when ________. A. a magma cools to the point where minerals begin to crystallize B. radioactive isotopes begin to decay C. isotopes are no longer free to move out of a crystal lattice D. the last remaining magma crystallizes

Answer 1

The closure temperature represents the point when isotopes are no longer free to move out of a crystal lattice.

Answer: Option C

Explanation:

The closure temperature can also be termed as blocking temperature. It is mostly used in radiometric dating. As the temperature decreases, below a certain point the isotopes may get freeze in their lattice positions. And there may be slowing of diffusion.

At the closure temperature, that rate of diffusion will be zero as the isotopes will be no longer free to move out of crystal lattice. So, this is termed as closure or blocking temperature. As the isotopes loose their ability to move, their concentration will remain fixed in their position leading to measurement of radiation dating.