P-T path of UHP meta-granites from the Dabie Shan (China) displaying dehydration melting during exhumation (Modified after Xia et al. 2010). The phengite dehydration melting curve (stippled) is shown for a pelitic bulk rock composition (after Vielzeuf and Holloway 1988). The wet granite solidus is after Huang and Wyllie (1981) and Holtz et al. (2001) and the second critical point is extrapolated by Hermann et al. (2006) from the critical curve of Bureau and Keppler (1999). The compositional character of the fluid phase above the second critical point follows the definition of Hermann et al. (2006) (for details see text and caption of Fig. )
Partial melting may occur during decompression in felsic rocks
exhumed from these depths (see Fig. 10.7).
2010; Fig. 10.7) and in the Greenland Caledonides (Lang and
All of these fluid phases are supercritical over a large range of
P-T conditions (Figs. 10.7, 10.8).
2008; Figs. 10.4, 10.7, 10.8).
However, experimental data at 30 ± 5 Kbar and 700 ± 50°C,
concerning the second critical point for meta-pelitic or
meta-granitic rocks, suggest that (supercritical) transitional
fluids can be expected in continental crust, which has suffered UHP
conditions in relatively cold subduction zones (Figs. 10.4,
10.7; also see Hermann et al.
Thus polyphase solid inclusions are construed to be remnants of
transitional fluids or hydrous silicate melts derived by
dehydration melting of the subducting host rock under UHP
conditions in both cold and hot subduction zones (Fig. 10.7).
2009) and may lie very close or even in the field where
transitional fluids are to be expected (Fig. 10.7).
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