Fluid inclusions in xenoliths yield evidence for fluid evolution in peralkaline granitic bodies at Pantelleria (Italy)

Fluid inclusions are rare in peralkaline granitoid xenoliths entrained in volcanic units at Pantelleria, Italy, suggesting that the shallow magma bodies in this peralkaline center do not develop extensive hydrothermal systems. Only one of the samples studied, an alkali-feldspar granite xenolith, contains abundant fluid inclusions in quartz. Four types of aqueous fluid inclusions are distinguished: Type I brines, including early, highly saline, NaCl-bearing inclusions (T(h L) = 508-560-degrees-C; salinity = 60-68 eq. wt.% NaCl) that occur in random groups (Type Ia) and late, NaCl-bearing inclusions (T(h L) = 386-450-degrees-C; salinity = 37-45 eq. wt.% NaCl) along secondary healed fractures (Type Ib); Type II vapor-rich aqueous inclusions (T(h V) > 600-degrees-C) associated with Type Ia inclusions; Type III biphase (L + V) aqueous inclusions (T(h L) = 360-390-degrees-C) along secondary healed fractures; and minor Type IV high-density biphase (L + S) brines. The earliest fluids to be trapped (T > 600-degrees-C) are represented by vapor-rich inclusions (Type II), which suggest boiling of the fluid phase. No coexisting brines were trapped, however, as all brines were trapped at temperatures below 560-degrees-C. High-salinity fluid phases circulated in the system down to temperatures of about 380-degrees-C, suggesting prolonged endogeneous fluid circulation in the shallow intrusive body that was the source for the xenolith. In contrast to the cooling history of many shallow-level granitic bodies, there is no evidence of pervasive circulation of low-temperature ( < 300-degrees-C), low-salinity fluids of largely meteoric origin