Geochemistry of Mesozoic Intrusions, Quesnel and Stikine Terranes

The re cord of arc magmatism is wide spread in the Ca na dian Cor dil lera (e.g., Armstrong, 1988; Woodsworth et al., 1991), par tic u larly in the Quesnel and Stikine ter ranes, where plutonic rocks re lated to Me so zoic arcs host most of the por phyry-style min eral de pos its in the Cor dil lera (An der son, 1985; Woodsworth et al., 1991; McMillan et al., 1995; Fig 1). Iso to pic char ac ter iza tion of arc rocks is a pow er ful tool for dis tin guish ing source and con tam i na tion sig na tures of mag mas, and has di rect ap pli ca tions to de vel op ing eco nomic and tec tonic mod els for Me so zoic magmatism. De spite the im por tance of the plutonic hostrocks, there is a lack of re li able and com plete geo chem i cal and ra dio genic iso tope com po si tions for these in tru sions in south ern Brit ish Co lum bia. Pre vi ous geo chem i cal stud ies have em pha sized the vol ca nic units, par tic u larly the Late Tri as sic to Ju ras sic (?) Nicola Group (Schau, 1970; Preto et al., 1979; Mortimer, 1987; Smith et al., 1995). Ef fec tive use of ra dio genic iso tope geo chem is try re quires knowl edge of the ab so lute age of in di vid ual sam ples, and iden ti fi ca tion of tem po ral suites of in tru sions from dif fer ent re gions. Poor age con straints on the Nicola Group and its com plex struc tural style (Schau, 1970; Preto, 1979) have hin dered wide spread ap pli ca tion of de tailed stud ies (e.g., Preto et al., 1979; Mortimer, 1987; Smith et al., 1995), par tic u larly those in volv ing Sr and Nd iso topes. Pub lished Sr and Nd iso tope com po si tions are available for a number of scattered intrusions (Ghosh, 1995), which provides an important basis for further geochemical study.