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...