Intrusive rocks and plutonic belts of southeastern Alaska, U.S.A.

Abstract

Open-File Report 80-78 1980This r e p o r t i s p r e l i m i n a r y and has n o t been edited o r reviewed f o r conformity with Geological Survey standards and n o m e n c l a t u r e .NOW with Amax Exploration, Inc . , Denver, Colorado. ABSTRACT A v a i l a b l e i n f o r m a t i o n on t h e map d i s t r i b u t i o n , composition, and a g e s ofi n t r u s i v e r o c k s i n s o u t h e a s t e r n Alaska h a s been compiled and t h e r e s u l t s i n t e rp r e t e d t o i n d i c a t e t h e presence of s i x major and f i v e minor b e l t s . 2About 30 p e r c e n t of t h e 175,000 km of s o u t h e a s t e r n Alaska i s u n d e r l a i n by i n t r u s i v e igneous rocks. From west t o e a s t , t h e major b e l t s a r e : t h e F a i rweather-Baranof b e l t of e a r l y t o mid-Tertiary g r a n o d i o r i t e ; t h e Muir-Chichagof b e l t of mid-Cretaceous t o n a l i t e and g r a n o d i o r i t e ; t h e Admiralty-Revillagigedo p o r p h y r i t i c g r a n o d i o r i t e , q u a r t z d i o r i t e , and d i o r i t e b e l t of p r o b a b l e Cretaceous age; t h e Klukwan-Duke b e l t of c o n c e n t r i c a l l y zoned o r Alaskan-type ultramafic-mafic p l u t o n s of mid-Cretaceous age which i s mainly w i t h i n t h e Admiralty-Revillagigedo b e l t ; t h e Coast P l u t o n i c Complex t o n a l i t e s i l l of unknown, b u t perhaps mid-Cretaceous, age; and the Coast P l u t o n i c Complex b e l t I of e a r l y t o mid-Tertiary g r a n o d i o r i t e and q u a r t z monzonite.The minor b e l t s a r e d i s t r i b u t e d a s f o l l o w s : l a y e r e d gabbro complexes of i n f e r r e d mid-Tertiary a g e l i e w i t h i n and a r e probably p a r t of t h e FairweatherBaranof b e l t ; t h e Chilkat-Chichagof b e l t of J u r a s s i c g r a n o d i o r i t e and t o n a l i t e l i e s w i t h i n t h e Muir-Chichagof b e l t ; t h e S i t k o h Bay a l k a l i n e , Keadrick Bay pyrox e n i t e t o q u a r t z monzonite, and Annette and Cape Fox t r o n d h j e m i t e complexes, a l l i n t e r p r e t e d t o be of Ordovician ( ? ) a g e , form t h e c r u d e s o u t h e r n Southeast Alaska b e l t w i t h i n the Muir-Chichagof b e l t ; t h e Kuiu-Etolin v o l c a n i c -p l u t o n i c b e l t of mid-Tertiary a g e extends from t h e Muir-Chichagof b e l t eastward i n t o t h e Admiralty-R e v i l l a g i g e d o belt; and t h e B e h Canal b e l t of mid-t o l a t e T e r t i a r y g r a n i t e s l i e s w i t h i n and next t o t h e Coast P l u t o n i c Complex b e l t 11. I n a d d i t i o n , s c a t t e r e d maficu l t r a m a f i c b o d i e s occur w i t h i n t h e Fairweather-Baranof, Muir-Chichagof, and Coast P l u t o n i c Complex b e l t s . P a l i n s p a s t i c r e c o n s t r u c t i o n of 200-km r i g h t -l a t e r a l movement on t h e Chatham S t r a i t f a u l t does n o t s i g n i f i c a n t l y change t h e p a t t e r n of t h e major b e l t s , b u t does b r i n g mid-Tertiary v o l c a n i c -p l u t o n i c and Ord...

Preliminary reconnaissance geologic map of the Juneau, Taku River, Atlin, and part of the Skagway 1:250,000 quadrangles, southeastern Alaska

“…The Gravina belt as used here more or less corresponds to the Gravina belt as defined by Berg and others (1978), but the map distribution does not correspond because of newer information and differing interpretations. Brew and Morrell (1983); no isotopic age determinations are yet available but regional information suggests that these rocks in this map area are about 90 Ma, as are lithically similar, K-Ar dated rocks in the Tracy Arm-Fords Terror area to the southeast (Brew and Grybeck, 1984). As mapped, divided into:…”

“…named by Brew and Morrell (1983); located northeast of Coast Range megalineament (Brew and Ford, 1978). Regional aspects of this belt discussed by Brew and others (1976); Ford (1981, 1984c;Ford and Brew (1981); belt is currently interpreted to be 62-69 Ma on the basis of Pb-U determinations by G. E. Gehrels on zircons from rocks in this map area and in the Sumdum quadrangle to the southeast (Gehrels andothers, 1983, 1984).…”

“…Brew and Morrell (1983); age based on interpretation of K-Ar data (Loney and others, 1967). Part of the large complex of intermediate composition granitic and gabbroic rocks between the Sitkoh Bay and Peril Strait faults (Loney and others, 1975 Lanphere, oral communs., 1967Lanphere, oral communs., , 1983.…”

Creation of a full color geologic map by computer: A case history from the Port Moller project resource assessment, Alaska Peninsula: A section in <i>Geologic studies in Alaska by the U.S. Geological Survey, 1988</i>

“…1) is a long and narrow northwest-southeast-trending belt of eastward dipping orthogneiss sheets of Late Cretaceous to early Tertiary age. The belt forms the western part of the central zone of the informally named Coast plutonic-metamorphic complex (Brew and Ford, 1984a and b) for over 700 kilometers in southeastern Alaska Ford, 1981, 1984b;Brew and Grybeck, 1984;Brew and Morrell, 1983). Foliation in these concordant plutons parallels the northwest trend of the regional metamorphic fabric of their country rocks, as well as the intrusive contacts.…”

“…1). The pluton was mapped and informally named the Speel River pluton by Brew and Ford (1986), who correlated it with plutons in the Coast complex sill belt (Brew and Morrell, 1983) that are now collectively known as the great tonalite sill . Miller (1962) examined part of the pluton around Crater and Long lakes and referred to it as a quartz diorite intrusion.…”