Supplement to: Pertsev, Nikolay N; Boronikhin, V A (1983): Secondary K-feldspar in basalts at Deep Sea Drilling Project Hole 504B and the problem of K-feldspathization in oceanic basalts. In: Cann, JR; Langseth, MG; Honnorez, J; Von Herzen, RP; White, SM; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 69, 589-591, https://doi.org/10.2973/dsdp.proc.69.132.1983
Basalts from some holes of the Deep Sea Drilling Project contain secondary K-feldspar which forms pseudomorphs after calcic (〉76% An) Plagioclase cores, whereas Plagioclase of rims and microlites (68-74% An) remains unaltered. In basalts of Hole 504B two such grains with relics of Plagioclase in the central parts of phenocysts were recovered. The composition of the Plagioclase rims and of non-replaced phenocrysts is An79-81; the composition of relics is An83. The An and Ab contents of the K-feldspar is higher than in K-feldspar from altered basalt in Hole 418A in the Atlantic Ocean near the Bermuda Rise. Replacement of plagioclases by K-feldspar evidently is caused by oxygen-rich nearbottom sea water penetrating into basalts. The temperature interval of K-feldspathization is probably in the range 30 to 80°C, more-calcic Plagioclase being replaced by K-feldspar at higher temperatures.
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