It is proposed to resume the Nain Anorthosite Project to pursue geochemical analysis of samples collected during the field phase of the project (1971-81) funded by NSF. The intervening time has been devoted to geochemistry of the Kiglapait Intrusion and to magma dynamics. Recent activities reaffirm that the anorthosite problem has major significance to the evolution of the earth's crust and mantle. Spectacular discoveries by members of this project show (1) that an apparent source enrichment event took place over a large area of Labrador about 2.3 Ga ago (Hamilton); (2) that Pb isotopes give wholerock and wholerock - feldspar alignments corresponding to 2.9 and 3.2 Ga, respectively, much older than the crystallization age of 1.3 Ga (Weis); and (3) that metamorphosed mafic rocks of the Adirondack region, New York, have almost identical major element trends to the calculated liquids of the Kiglapait Intrusion (Olson). None of these effects can be explained by crustal contamination, but instead carry valuable information on the nature and processes at the source. The 2.3 Ga enrichment event may extend across the boundaries of 3 or 4 structural provinces of the Canadian Shield. Trace element studies at contacts of the Nain anorthosite show the degree of interaction with crust, and allow evaluation of chilled margins as magma compositions. It is proposed to analyze country rocks and anorthosites in a 3-tier approach of x-ray analyses followed by rare-earth element analyses by neutron acti- vation, followed by a program of isotopic analyses for Nd and Pb. These will clarify and extend the current studies by giving essential details and constraining hypotheses. The work will have a major impact on the tectonic implications of anorthosites and their message about the mantle.
