Geologic map of southeastern Alaska

Abstract

Open-Fi le Report 84-886This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature.*~n c h o r a~e ,

Reconnaissance geology and U-Pb geochronology of the west flank of the Coast Mountains between Juneau and Skagway, southeastern Alaska

“…The main plutons in the Coast Mountains can be divided into several suites of differing age, composition, and intrusive style (Buddington and Chapin, 1929;Barker et al, 1986;Brew, 1988;Gehrels et al, 1991b;Gehrels and Berg, 1992) (Fig. 2).…”

“…This body was originally reported to intrude strata of the Gravina belt (Berners Formation of Knopf, 1911), but Redman (1984) reported that the contact is at least locally nonconformable. This conclusion has been controversial because strata of the Gravina belt are Upper Jurassic-Lower Cretaceous (Berg et al, 1972), and most plutons along the west flank of the Coast Mountains are mid-Cretaceous in age (Brew and Morrell, 1983;Gehrels and Berg, 1992).…”

“…100-90 Ma) plutons that occur elsewhere along the west flank of the Coast Mountains (see compilations of Brew and Morrell, 1983;Brew, 1988;Gehrels and Berg, 1992). Rather, the body appears coeval with (1) younger 224…”

“…(2) diorite-granodiorite plutons that intrude the Alexander terrane in southeast Alaska (see Brew and Morrell, 1983;Gehrels and Berg, 1992) and the Wrangellia terrane to the north in Yukon (Dodds and Campbell, 1988); and (3) zoned ultramafic bodies that occur just west of the Coast Mountains for the length of southeastern Alaska (Taylor, 1967;Saleeby, 1992). Parts of the Mount Kashagnak pluton northwest of Haines (Fig.…”

Oceanic Pb-isotopic sources of Proterozoic and Paleozoic volcanogenic massive sulfide deposits on Prince of Wales Island and vicinity, southeastern Alaska

“…), in addition to other, more radiogenic rocks in the fluid-reaction path that would account for the variation in Pb ratios. Such a close link to older source rocks is particularly evident for the Niblack deposit, which notably is hosted by felsic metavolcanic and tuffaceous metasedimentary rocks that resemble the lithologic sequence in the Wales Group (Gehrels and Berg, 1992;Maas and others, 1995). Detrital zircons dated by U-Pb Pb ratios for Ordovician mantle from primitive intraoceanic arcs in Newfoundland (Swinden and Thorpe, 1984;Swinden, 1996) and for Devonian mantle from a primitive island arc associated with massive sulfide deposits in the Klamath Mountains, Calif. (Shasta; Doe and others, 1985).…”