Alkali gabbro fragments in Sudbury breccia have been misinterpreted as potash-enriched greywacke. Because of differing proportions of arenaceous and argillaceous components, greywackes vary widely in chemical composition. However, on plots of SiO2/Al2O3 against TiO2, greywacke-argillites fall along a hyperbolic sorting curve. Alkali gabbro fragments fall well off the curve. The distinction between the two rock types is supported by other chemical data.

You do not currently have access to this article.