Tahtsa-Twin Sisters-Francois Lake magmatic assemblage 

(Middle Jurassic to Early Cretaceous) 

(Central part of Canadian Cordillera, unit Jpf)

Occurs between latitudes 54 to 51  N in north-central British Columbia on the east side of the Coast Belt 
and consists chiefly of Jurassic and Cretaceous plutonic rocks. Also occurs between latitudes 50 to 52 N on 
east side of the Coast Belt where unit consists chiefly of minor volcanic and sedimentary rocks. The 
plutonic rocks of the unit are chiefly Middle to Late Jurassic granitic rocks that apparently post-date the 
accretion of the Stikinia terrane to the North American plate in the Late Jurassic (about 170 Ma). Magmatic 
assemblage widely distributed between the western Coast and eastern Omineca belts. Named by van der 
Heyden (1992) as part of the ancestral Coast Belt arc which is interpreted as the middle Mesozoic 
continental-margin arc of western North American. The oldest part of the assemblage may be equivalent to 
the Nelson plutonic suite and the youngest part of the assemblage may be equivalent to the Spences Bridge 
volcanic-plutonic belt. The assemblage may correlate in part with the Gravina-Nutzotin-Gambier volcanic-
plutonic-sedimentary belt. REFERENCES: Woodsworth and others, 1991; Wheeler and McFeely, 1991; 
van der Heyden, 1992; Monger and others, 1994.