Abstract

Major and trace element analyses are presented for 30 amphibolites from the Grand Forks West Half quadrangle of British Columbia, Canada (N.T.S.1 82E/1, W 1/2). The amphibolites are part of the Grand Forks Group, a fault block of high-grade metamorphic rocks that is one of the southernmost extensions of the Shuswap Metamorphic Complex of southern British Columbia.

Samples were taken from amphibolites which are closely associated with metasedimentary rocks and from amphibolites which form sills in the metasedimentary succession, to see whether any significant chemical differences exist between the two groups. Given the presupposition that during metamorphism individual rock layers acted essentially as closed systems and that metasomatism did not occur to a significant degree, the chemical data were evaluated by the methods outlined by Evans and Leake (I960) and Leake (1964) and by Shaw and Kudo (1965). Both methods consistently indicate that all of the amphibolites analyzed are of igneous parentage and probably represent metamorphosed basic intrusions that have the composition of soda-rich basalt. The textural differences among schistose, lineated, and massive amphibolites of the Grand Forks quadrangle should then be attributed largely to processes related to the metamorphic and structural history of the rocks and not to primary structures.

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