Amphiboles HFSEs

Amphibole HFSE characteristics are sensitive to the presence of Umenite and rutile. In MARID samples where rutile dominates over Umenite, Gregoire et al. (2002) note that K-richterites display large negative niobium and tantalum anomalies, whereas when Umenite dominates, these anomalies are positive. Nb/Ta ratios of amphibole vary from close to the PUM value (17.6) up to —25 (Figirre 23). Zr/Hf values are generally lower than the PUM value of 37 (Figure 23). Differences in HFSE contents between vein and disseminated amphibole (and mica) in spinel peridotites may be explained by a model in which Zr-Nb rich amphibole and mica crystallize close to, or within a melt vein in the mantle. The fractionated, chlorine-rich aqueous residual fluids from the evolved melt then crystallize low Zr-Nb, LREE-depleted amphibole or... 

Figure 17. Examples of etching units found in silicates and resulting from (a) the specific adsorption >l fluoride (teeth produced in the laboratory by treatment of hornblende with HF + HC1 solutions) mil (/>) localized chemical impmdies lens-shaped etch pits in augitc along amphibole exsolution l-imcMa boumlaries (likely l<> be pioduccd by specific adsorption of reactants on Al sites).

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