Temporal evolution of the Kerguelen plume: Geochemical evidence from approximate to 38 to 82 Ma lavas forming the Ninetyeast ridge - Discussion

In ''Temporal evolution of the Kerguelen plume: geochemical evidence from similar to 38 to 82 Ma lavas forming the Ninetyeast Ridge'' by F. Frey and D. Weis (1995), the literature geochemical data on the Ninetyeast Ridge are summarized, new trace element and isotopic data are presented, and isotope data on Ninetyeast Ridge lavas are compared with those of the Kerguelen Archipelago. Frey and Weis (1995) assume the composition of the Kerguelen plume source is nearly homogeneous and is the same as the youngest lavas of Kerguelen, in agreement with conclusions of some previous studies (Storey el al, 1988; Gautier et al. 1990; Weis et al. 1993). Class et al, (1993) concluded that the Ninetyeast Ridge-Kerguelen plume source has a unique composition based on evaluation of the isotopic evolution of plume-related lavas through time, but identified an entirely different composition for it (to be consistent with Frey and Weis, 1995, we call it Kerguelen plume instead of Ninetyeast Ridge plume). In this comment we review the two contrasting approaches to distinguishing the composition of the Kerguelen plume source. To simplify matters, we term the Kerguelen plume composition used by Frey and Weis (1995) and the others cited above as the ''static'' plume composition, and the one of Class et al. (1993) as the ''evolving'' plume composition. We discuss some of our concerns about the foundations for the ''static'' composition, considering in addition to Kerguelen data the constraints afforded by lavas from nearby Heard Island. Frey and Weis (1995) take strong issue with the interpretation of Class et al. (1993) and contend that the Kerguelen plume does not represent an ''evolving'' or ''aging'' plume source. We find their arguments to be unconvincing, calling for clarification on our part.