Answer to Question 1
The pressures for depths between 1520 km equate to between 47 kb (Figure 6.2). In this pressure range, we would expect to see kyanite and/or sillimanite in the metamorphic rocks (Figure 6.18). With a normal geothermal gradient of 25oC/km (Figure 6.5), the temperature at 1520 km would be between 375o and 500oC, which is in the kyanite stability field (Figure 6.18). So, the regional metamorphic rocks would contain kyanite but contact metamorphic rocks, which should be closer to the outcrops of igneous rocks, could contain sillimanite because they formed at higher temperatures (Figure 6.5 and 6.18).
Answer to Question 2
The transfer of atoms from one part of a crystal to another part of the crystal or an adjacent crystal. It changes the size and shape of existing minerals but does not produce new ones. Large grains are able to grow and fit tightly together, often suturing to form a mosaic of large grains. In cementation, grains are not greatly altered by the precipitation in the pore spaces, and you would expect to see a difference between sedimentary grain size and precipitated crystal size.
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