Reconnaissance geologic map of the Bradfield Canal quadrangle, southeastern Alaska

Combined description of map units and correlation of map units for the Petersburg-Wrangell area 1:63,360-scale geologic maps, southeastern Alaska

“…The following three units in the Bradfield Canal quadrangle are interpreted in this report to be closely related, and the second two are revised from the interpretation given by Koch and Berg (1996). This reinterpretation was done on the basis of the field relations and compositional similarities and on the available geochronologic information.…”

“…K-Ar determinations by M. A. Lanphere, U.S. Geological Survey, (written communs., 1981; reported in Brew and others, 1984;and Douglass and others, 1989, p. 64) interpreted to be applicable to the whole suite are as follows: Koch and Berg, 1996). Some of these units are also described in the section on the Brew and Morrell (1983); rocks interpreted to be 100-118 Ma on the basis of their similarity to dated rocks elsewhere (Lanphere and Eberlein, 1966;Himmelberg and Loney (1995) Douglass and others, 1989, p. 65).…”

“…Smith, U.S. Geological Survey, unpub. data, cited by Koch and Berg, 1996). intense and shows no consistent structural trends.…”

“…This reinterpretation was done on the basis of the field relations and compositional similarities and on the available geochronologic information. The original unit names and map symbols used by Koch and Berg (1996) biotite more abundant than hornblende, and invariably chioritized, abundant zoned (An38-An2s) subhedral plagioclase; and myrmekite intergrowths are ubiquitous.…”

Reconnaissance geologic map of the Petersburg B-1 quadrangle, Southeastern Alaska

“…The alternative was to assign the same metamorphic age to these plutons, but that is equally inadequate because not all of them show metamorphic features. The belt was informally named by Brew and Morrell (1983) and is described by Burrell (1984abc); preliminary K-Ar determinations by M. A. Lanphere (U.S. Geological Survey, written communs., 1981Survey, written communs., , 1982 interpreted to be applicable to the whole suite are as follows: Koch, oral commun., 1982;Koch and Berg, 1996). As mapped in this quadrangle, divided into: Ktoc Garnet-Biotite Tonalite and Minor GranodioriteNonfoliated, crowded-plagioclase rock; inequigranular to porphyritic; very fine-to medium-grained; C.I.…”