Correlation coefficient patterns and their interpretation in three basaltic suites

Single stage magmatic fractionation processes result in igneous rock suites in which correlation coefficients between pairs of elements are generally high. The Tertiary lavas of E. Iceland are used as an illustration of this type of behaviour. When a second process such as fractionation at a different pressure, wall-rock assimilation, or mixing with a different magma, occurs, correlation coefficients are altered in a predictable way if the process and the chemical characteristics of the participating rocks, minerals and liquids are known. A computer program has been devised to simulate complete correlation coefficient matrices for any desired two- or multi-stage process e.g. fractional crystallisation coupled with contamination. Basaltic suites from Mahabaleshwar, India and the Rooi Rand, southern Africa show correlation coefficient patterns characteristic of multi-stage evolution, and these are interpreted with the aid of computer simulation. The Mahabaleshwar suite shows clear evidence of contamination by a granitic component. The Rooi Rand rocks however remain problematic.