1. ABSTRACT
Komatiitic basalts are ultramafic rocks formed from volcanic liquids containing less than
18 wt.% magnesium oxide that can be linked, spatially, geochemically and texturally to
komatiites. Archean komatiites and komatiitic basalts are critical to models of early Earth’s
mantle evolution. Major and trace elements in these rocks are poorly preserved due to early sub-
seafloor alteration with superimposed regional metamorphism: in particular the alkali, alkaline
earths, and other elements with low valence numbers. Current analytical methods focus on
analyzing whole rock, fresh olivines and melt inclusions to evaluate elemental concentrations
and for petrogenetic studies. Although these methods establish elemental concentrations, REE,
Sr, Na and Ba should be better represented by evaluating trace elements in fresh augites from
komatiitic basalts, which contain moderate levels of trace element concentrations that olivines
lack.
In this study trace elements were analyzed within samples from two different formations
(Mendon and Weltevreden) within the Barberton Greenstone Belt, South Africa. These samples
contain fresh augites from komatiitic basalts and were analyzed using LA-ICP-MS.
Results suggest that REE in augites from the freshest komatiitic basalts closely match the
predicted values calculated from bulk rock analyses when distribution coefficients and Rayleigh
fractionation are taken into account. Zr and Ti, exhibit anomalies within the augites that
correspond to anomalies found in bulk rock data. This supports the contention that both the REE
and HFSE remain a closed system within these rocks. However, Na, Sr and Ba were mobilized
within the bulk rock during alteration. Values for Na are particularly difficult to establish from
bulk rock data. Even when they are nearly constant within a suite of flows, their values are far

2. from those predicted from augite analyses. Sr has negative anomalies in these rocks, and this is
confirmed to be a trait acquired from the magmas through augite analyses.
These data confirm two important components of komatiite petrogenesis: 1) fractionation of
a high pressure phase to modify the HFSE, and 2) assimilation of felsic material during crustal
ascent. Important radiogenic systems, such as Rb-Sr, Nd-Sm, and Lu-Hf, should be evaluated
using augite proxies from single mineral SIMS, LA-ICP_MS, or mineral separations.