Answer:
Based on the Wikipedia summary and search result [1], the appropriate word to fill in the blank in the question "_______will occur when continental collisions occur, thickening the crust and forcing some rocks to a depth where melting can take place" is "partial melting".
According to search result [1], partial melting is a process that occurs when thickening of the crust due to continental collision forces some rocks to a depth where melting can take place. This type of melting can lead to the formation of igneous rocks, including those that form intrusive bodies like plutons and batholiths.
It's worth noting that the Wikipedia summary also discusses the role of subduction in the formation of igneous rocks and the creation of the Earth's continental crust. When one tectonic plate, typically an oceanic plate, is subducted beneath another plate, the heat and pressure of the subduction zone can cause partial melting of the subducting plate. This magma can then rise to the surface and form a chain of volcanic islands or a larger landmass, eventually forming continental crust through a process called accretion.
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