Age of metamorphism in the high-grade rocks of Sri Lanka

Abstract:

Controversy concerning the age of regional granulite-grade metamorphism in Sri Lanka stems from the fact that different isotopic systems apparently record different events. Published isotopic data show that zircons from igneous and sedimentary protoliths experienced considerable Pb-loss at 550 Ma and that new growth of zircon, monazite, rutile and garnet between 539 ± 6 and 608 ± 3 Ma probably dates near-peak metamorphic conditions. A granulite of igneous origin from the Kataragama klippe in southern Sri Lanka yielded discordant ion microprobe data that suggest emplacement of the protolith at 1770-1880 Ma. Thus a Rb-Sr whole-rock age of 1930 ± 130 Ma from the same suite is unlikely to reflect isotopic homogenization during granulite formation. This and other best-fit lines are interpreted as a memory effect in the Rb-Sr isotopic system that provides approximate ages for the gneiss protoliths, not for the high-grade metamorphism. -from Authors

Año de publicación:

1993

Keywords:

Fuente:

scopus