280 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



Fig. 17.17. Structural map of part of the border of the Colville batholith. Reproduced from 

 Waters and Krauskopf, 1941. 



variable but well-foliated migmatitic gneisses ( magmatic injection and re- 

 placement) characterized by severe granulation of the constituent min- 

 erals. Over broad zones this rock is a mylonite (crushed and rolled-out 

 streaky powder); locally recrystallization has produced types resembling 



metamorphic granulites. That the crushing was protoclastic (localized 

 along the contact) and not due to regional metamorphism following the 

 solidification of the batholith, is proved by the relations with the wall 

 rocks and by the widespread cementation of the broken materials by films 

 and stringers of undeformed quartz and microcline. 



Along the contact between the approximately contemporaneous Oso- 

 yoos and Colville batholiths occurs a narrow belt of heterogeneous syenite 

 with highly complicated internal structure. This is believed to be a hybrid 

 rock formed by the action of magmas and emanations from both batho- 

 liths upon a thin septum of wall rock. 



The Coast Range Batholith and Related Structures. The Coast Range 

 batholith extends for more than 1100 miles from Fraser River in British 

 Columbia northwestward into Yukon Territory. See Figs. 17.13 and 17.18. 

 From Vancouver to Skagway on the mainland, the batholith forms the 

 backbone of the Coast Range and is exposed either at the shore fine or a 

 short distance inland. Outlying dikes, stocks, and batholiths believed to 

 be of the same general period of intrusion as the main batholith and 

 genetically allied to it are found locally on Vancouver Island and the 

 Queen Charlotte Islands, and abundantly throughout most of the Alex- 

 ander Archipelago. The Coast Range batholith is the largest on the North 

 American continent, aside possibly from certain ones of Precambrian age. 



It is widest south of Skeena River in British Columbia, where it reaches 

 110 miles east and west. In southeastern Alaska, it is 35 to 60 miles wide. 



Buddington ( Buddington and Chapin, 1929 ) discusses the batholith in 

 southeastern Alaska in respect to six approximately parallel belts, namely, 

 the border zone east of the Coast Range batholith, the Coast Range batho- 

 lith of the mainland, the Wrangell-Revillagigedo metamorphic belt, the 

 Prince of Wales-Chicagof belt, the Kuiu-Heceta belt, and the Dall- 

 Baranof belt. See map, Fig. 17.19. 



The eastern border zone is conspicuous for its absence of contact 

 metamorphism on a regional scale. Even local metamorphism is meager. 

 The border zone rocks are closely folded; argillaceous rocks have been 

 changed to slaty types, and locally andesitic volcanic rocks to greenstone; 

 but there is practically no phyllite and no crystalline schist away from the 

 immediate contact of the intrusive bodies. 



