| Abstract: | It is well known that a great deal of fluid wasreleased during subduction of oceanic crust, resulting in arcmagmatism, quartz veining and metamorphic mineralizationof syn-subduction. In contrast, the process of continentalsubduction is characterized by the relative lack of fluid andthus no arc magmatism has been found so far. During exhu-mation of deep-subducted continental crust, nevertheless,significant amounts of aqueous fluid became available fromthe decomposition of hydrous minerals, the decrepitation ofprimary fluid inclusions, and the exsolution of structuralhydroxyls. This kind of metamorphic fluid has recently at-tracted widespread interests and thus been one of the mostimportant targets in deciphering the geological processesconcerning metamorphism, magmatism and mineralizationin collisional orogens. A large number of studies inlvolvingstable isotopes, fluid inclusions and petrological phase rela-tionships have been accomplished in past a few years withrespect to the mobility and amount of metamorphic fluid inUHP metamorphic rocks from the Dabie-Sulu orogenic belt.The results demonstrate that the fluid activity during theexhumation of deep-subducted continental crust has the fol-lowing effects: (1) amphibolite-facies retrogression due topervasive fluid flow; (2) formation of HP quartz veins withineclogites due to channelized fluid flow; and (3) partial melt-ing of overlying crustal rocks due to focused fluid flow, pro-ducing syn-exhumation magmatism within the orogenic belt.In particular, the aqueous fluid released by decompressionexsolution of hydroxyl from UHP minerals is characterizedby low salinity and is capable of resulting in pervasive andchannellized flow. Therefore, the intensive study of fluid ac-tivity during exhumation of UHP metamorphic rocks can notonly provide insight into geodynamic processes that occurredin continental collisional belts, but also shed light on under-standing of crust-mantle recycling and relevant magmatismin subduction zone setting. |
