Abstract

The primary diagnostics for komatiite are chemical (CaO/Al2 O3 >1, MgO >9 percent, K2O <0.9); however, komatiites can only be meaningfully isolated and compared with other rock classes if the chemical diagnostics are coupled with textural criteria (for example, quench or spinifex texture) that establish the occurrence of komatiites as silicate melts. Examination of analyses of more than 20,000 rocks, using both the textural and chemical criteria, reveals that peridotitic komatiite (PK) is at present unknown from modern environments, and basaltic komatiite (BK) is rare. While it can be demonstrated that neither PK nor BK are reliable tectonic province indicators, the consistent association of Archean BK and PK with felsic volcanics argues against a modern sea-floor analog for their origin.

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