SM-ND AGE AND GEOCHEMISTRY OF GRANULITES FROM THE CENTRAL PART OF ANABAR SHIELD

Geochemistry and isotopic systems of Sm-Nd and Rb-Sr in rocks and minerals from the Daldyn series of Anabar Shield metamorphosed in granulite stage were studied. Petrochemical and isotope-geochemical data show that komatiites may serve as a pre-metamorphic substrate for metaultrabasites of the shield. As can be concluded from the contents and, distributions of petrogenic, rare earth and other immobile elements the toleiitic metabasites can be compared with modem basalts of spreading zones. Eight whole rock samples of toleiitic and subalkaline metabasites, metaultrabasites and plagiogneises define an isochrone (3085 +/- 75 m.y., epsilon(Nd)T = 3.1 +/- 1.4) corresponding to the age of the magmatic protolith eruption. Low initial Sr-87/Sr-86 values (less-than-or-equal-to 0.702) measured for three of these samples show their mantle sources or insignificant role of crustal material in their genesis. The age of regressive metamorphism of these rocks (1870 +/- 20 m.y.) is determined by using the Sm-Nd mineral isochrone for metabasites (pyroxene, plagioclase, garnet, WR).