Review of the Proterozoic evolution of the Grenville Province, its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians

In recent years, a rapidly expanding database, especially in sensitive high-resolution ion microprobe (SHRIMP) geochronology, has led to signifi cant advances in understanding of the Precambrian tectonic evolution of the Grenville Province, including its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians. Based upon this information, we review the geochronology and tectonic evolution of these regions and signifi cant similarities and differences between them. Isotopic data, including Pb isotopic mapping, suggest that a complex belt of marginal arcs and orogens existed from Labrador through the Adirondacks, the midcontinent, and into the southwest during the interval ca. 1.8–1.3 Ga. Other data indicate that Mesoproterozoic inliers of the Appalachians, extending from Vermont to at least as far south as the New Jersey Highlands, are, in part, similar in composition and age to rocks in the southwestern Grenville Province. Mesoproterozoic inliers of the Appalachian Blue Ridge likewise contain some lithologies similar to northern terranes but exhibit Nd and Pb isotopic characteristics suggesting nonLaurentian, and perhaps Amazonian, affi nities. Models invoking an oblique collision of eastern Laurentia with Amazonia are consistent with paleomagnetic results, and collision is inferred to have begun at ca. 1.2 Ga. The collision resulted in both the ca. 1190–1140 Ma Shawinigan orogeny and the ca. 1090–980 Ma Grenvillian orogeny, which are well represented in the Appalachians. Several investigators have proposed that some Amazonian Mesoproterozoic crust may have been tectonically transferred to Laurentia at ca. 1.2 Ga. Data that potentially support or contradict this model are presented. mwr206-02 page 1