Basing on the data on the correlation of carbon and non-radiogenic nob
le gas isotopes in the mantle reservoirs a new genetic criteria of the
metamorphic fluid is presented. Modeling calculations indicate that t
he C/Ar-36 ratio of the metamorphic fluids in the continental crust mu
st be below 10(10) the latter known as a mantle value. The study of na
tural samples such as high carbon bearing sedimentary rocks, Precambri
an sandstones, and amfibolite facies rocks of the Notozero complex (No
rthern Karelia) has provided the experimental confirmation of the calc
ulated parameters of the crustral metamorphic fluids. The causes and r
esults of carbon and noble gas isotopic fractionation in the fluid pha
se in the process of vlatile capture from natural waters and within th
e subsequent diagenesis is studied.