When a rock is fluid-free, rehydration reactions never occur, unless free water is supplied externally or retrograde breakdown of hydrous minerals occurs, as hydrous minerals such as lawsonite and talc contain large amounts of water (Palin et al. 2014).
Firstly, rehydration reactions generally require an external supply of water or breakdown of hydrous minerals sufficient to produce low-temperature hydrous minerals (e.g., Yardley et al. 2014; Vitale Brovarone and Beyssac 2014; Palin et al. 2014).
While the breakdown of hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous minerals provides an additional water source.
The processes involved the breakdown of iron minerals in a source rock by the action of groundwater and the formation of thin films of iron oxide (hematite), which coloured the rocks red.
Therefore, dehydration melting can be caused not only by the breakdown of hydrous minerals but also by the exsolution of structural hydroxyl from NAMs.
With subduction of crustal rocks to mantle depths, the majority of water is released in the form of molecular water through breakdown of hydrous minerals.
In addition, the breakdown of hydrous minerals such as low-Mg amphibole, biotite, and phengite may have provided the high Nb/Ta fluids for rutile growth (Gao et al. 2014).
Likewise, the growth of metamorphic and anatectic garnets is primarily dictated by the breakdown of hydrous minerals such as amphibole, biotite, epidote, lawsonite, phengite, and zoisite at subsolidus and supersolidus conditions, respectively (e.g., Baxter and Caddick 2013; Li et al. 2014; Zhou et al. 2014).
