A powerful approach to the investigation of terrigenous sedimentary rocks is through combined study of petrography, major and trace element geochemistry, mineral chemistry and Nd- isotopic study. Such data provide critical evidence regarding the composition and mean age of he provenance. Using this approach, important constraints are provided for models of crustal composition, growth and evolution. Questions of tectonic setting and recycling history of sedimentary rocks can also be addressed. Isotopic evidence indicates that an important period of crustal growth occurred during the early Proterozic of North America at about 1.9-1.7 Ga. Evidence from Australia and Europe suggests this episode of crustal growth may have been of global significance. It is here proposed to examine the petrographical, geochemical and Nd-isotopic composition of two sedimentary sequences which were deposited at about this time, including the Chelmsford Formation (ca. 1.85 Ga) of the Sudbury region, Ontario and the Vadito - Ortega Groups (ca. 1.7 Ga) of northern New Mexico. The Chelmsford Formation is a proximal turbidite unit deposited in response to early development of the Penokean Orogeny. The Vadito - Ortega Groups are representative of sedimentary rocks deposited during crustal growth in southwestern U.S.A. at about 1.9 - 1.7 Ga. From this study, it will be possible to place important constraints on the nature of crustal growth and evolution during the early Proterozoic. Comparisons with crust-forming events at other times in earth history (particularly at the Archean - Proterozoic boundary) will help to test current models of crustal evolution.
