76 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



WESTERN ASSEMBLAGE TRANSITIONAL ASSEMBLAGE 

 3 4 12 



"Hi 



EASTERN ASSEMBLAGE 

 5 6 



liOGEOSYNCUNe 



INFERRED FORI OF GEOSYNCUNE BEFORE SHORTENING IN ANTLER OROGENY 



Fig. 6.9. Stratigraphic sections of pre-Late Mississippian rocks in north-central Nevada. Repro- 

 duced from Roberts ef a/., 1958. 1, Hot Springs Range; 2, Osgood Mountains; 3, Battle Moun- 

 tain; 4, northern Shoshone Range; 5, Cortez Mountains; 6. Roberts Mountains; 7, Eureka. 



limestone and greenstone masses. A number of large intrusive bodies 

 have been noted in the east-west belt of argillite; and these, together 

 with the overlapping Cenozoic rocks, effectively prevent the recognition 

 of contacts and the determination of stratigraphic relationships. The beds 

 are Pennsylvanian in age, because of Fusulina fossils found in the lime- 

 stones. Reds younger than Pennsylvanian may have been included in the 

 formation as mapped (Gilluly, 1937). 



The whole formation is provisionally considered marine. The tuffaceous 

 argillite, the tuff, and the tuffaceous limestone all clearly attest notable 

 pyroclastic contributions to the formation, and it is highly probable that 

 cherts so numerous and thick as those in this formation may be considered 

 evidence of igneous contribution also. 



The association of limestone with volcanic materials may have no 

 genetic significance, but a dependency is suspected because volcanism 



might have raised the temperature of the sea and hence decreased the 

 solubility of the lime (Gilluly, 1937). 



The Clover Creek greenstone overlies the Elkridge argillite and con- 

 sists of altered volcanic flows and pyroclastic rocks, with subordinate con- 

 glomerate, limestone, chert, and argillite. It is known to extend as far 

 eastward as the Snake River Canyon, and is therefore probably the same 

 as the "Permian volcanics" of several areas in eastern Idaho. It is at least 

 4000 feet thick (Gilluly, 1937). 



The effusive rocks in order of abundance are quartz keratophyre ( lava- 

 bearing albite), quartz keratophyre tuff, and meta-andesite. Fossils col- 

 lected from the formation betray a Permian age. 



The marine limestone and associated fossiliferous tuffs demonstrate a 

 marine origin for part of the formation, at least. The type of albitization 

 which most of the volcanic rocks have undergone is common in demon- 

 strably submarine volcanic rocks, and the association here with marine 

 limestone suggests rather strongly that the Clover Creek greenstone is in 

 large part of submarine origin. 



Northern Washington and Southern British Columbia. Where the 

 Okanogan River crosses the international boundary, extensive areas of 

 pre-Tertiary rocks are found. The pre-intrusives (pre- Jurassic) meta- 

 morphic rocks are called the Anarchist series; they crop out in the 

 Okanogan Range adjacent to the Okanogan Valley on the west and exten- 

 sively in the Okanogan highlands on the east. According to Krauskopf 

 ( 1939) neither the top nor the bottom of the Anarchist series has been 

 found, but at least 10,000 feet of beds exist. They can be divided rather 

 vaguely into three divisions. The lower consists chiefly of gray to jet black 

 phyllites with some interbedded quartzite and a little chlorite schist; the 

 middle consists of limestone, massive quartzite, graywacke, conglomerate, 

 some phyllite, and to the north and east of much greenstone; the upper 

 consists for the most part of greenstone with some interbedded phyllite 

 and quartzite. The albite in the greenstones of the upper division suggests 

 a correlation with the keratophyres of eastern Oregon. 



Regional metamorphism has converted the original sedimentary and 

 volcanic rocks to a typical chlorite zone assemblage. Near some of the 

 plutonic bodies higher-grade contact metamorphism has been superim- 



