SPECTROSCOPIC DATA ON COEXISTING PREHNITE-PUMPELLYITE AND EPIDOTE-PUMPELLYITE

X-ray absorption spectra in the Fe K near-edge region (XANES) and Fe-5 7 Mossbauer spectra were collected on two Fe-rich pumpellyite specimen s from low-grade metamorphosed spilitic rocks from the Keweenaw Penins ula, northern Michigan, and on prehnite and epidote coexisting with pu mpellyite. Spectroscopic data for prehnite, presented for the first ti me, are discussed in light of the pseudosymmetry of its structure. The data clearly show the prevailing role of Fe3+ in the crystal chemistr y of the paragenetically associated Ca-silicates. This is in agreement with the overall oxidizing. conditions typical of the low-grade metam orphic environment and the mineral assemblages characteristic of alter ation zones in basaltic rocks as described by petrological analyses.