THE LATE ARCHEAN HISTORY OF THE WYOMING PROVINCE AS RECORDED BY GRANITIC MAGMATISM IN THE WIND-RIVER RANGE, WYOMING

The Wyoming province, a small, ca. 500 000 km(2) Archean craton, is th e most southwestern of the Archean provinces in North America. It is c omposed primarily of Late Archean potassium-rich granitic rocks. In co ntrast to many other Archean provinces, rocks of tonalite-trondhjemite affinity are rare over most of the province and are restricted to roc ks older than 2.8 Ga. Field, petrologic, geochemical and isotopic stud y of the Late Archean granites exposed in the Wind River Range have al lowed us to identify at least four periods of potassic calc-alkalic ma gmatism at similar to 2.8, 2.67, 2.63 and 2.55 Ga. Granitic rocks of t hese ages appear to be widespread across the Wyoming province. The old est calc-alkalic granites of the Wind River Range, emplaced at ca. 2.8 Ga, appear to be derived predominantly from pre-existing crust. Howev er, Nd isotopic data suggest that these granites cannot be the product solely of partial melting of older tonalitic gray gneisses. During at least two other periods of plutonism, at 2.67 and 2.63 Ga, generation of the Wind River Range batholiths involved the incorporation of subs tantial amounts of isotopically juvenile material, either from deplete d mantle or young continental crust. The information presented below, as well as data available from elsewhere in the Wyoming province, is i nterpreted to suggest that the Wyoming province, unlike other Archean cratons, is not composed of a tectonic amalgamation of smaller, exotic terranes. Although the Wyoming province did experience crustal additi on in Archean time, it was not by lateral accretion, but by incorporat ion of mantle-derived melts into large granitic batholiths. (C) 1998 E lsevier Science B.V.