Late Proterozoic-Cambrian Metamorphic Basement of the Alexander Terrane on Long and Dall Islands, Southeast Alaska
Late Proterozoic-Cambrian metamorphic basement of the Alexander terrane on Long and Dall Islands, southeast Alaska GEORGE E. GEHRELS Department of Geosciences, University of Arizona, Tucson, Arizona 85721 ABSTRACT much of southeast Alaska and parts of coastal Previous Work British Columbia, southwestern Yukon, and Geologic and U-Pb (zircon) geochrono- eastern Alaska (Fig. 1; Berg and others, 1972; Buddington and Chapin (1929) mapped the logic studies demonstrate that Long Island Gehrels and Saleeby, 1987a). In contrast to the shorelines of Dall and Long Islands in recon- and southern and central Dall Island are un- relatively nondeformed Ordovician through naissance fashion and published the first geo- derlain in large part by upper Proterozoic- Triassic strata that characterize much of the logic map and descriptions of the area. Various Lower Cambrian metamorphic rocks of the Alexander terrane, Long and Dall Islands are U.S. Geological Survey workers have studied Wales Group. The group comprises a lower underlain in large part by upper Proterozoic- parts of Dall and Long Islands, but only the assemblage of predominantly metadacite, Lower Cambrian metamorphic rocks. These northern part of Dall Island has been described metamorphosed to amphibolite and green- older rocks apparently served as the metamor- in published reports (Condon, 1961; Eberlein schist facies, and an upper assemblage of phic basement for the widespread Ordovician and others, 1983). These reports, combined with lower-grade basaltic metavolcanic rocks, and younger strata. investigations on southern Prince of Wales Is- thick marble layers, and interlayered calcare- land (Herreid and others, 1978; Gehrels and Sa- ous metadacite, marble, metapelite, and met- leeby, 1986, 1987a, 1987b), provided the agraywacke.
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