Albitization of K-feldspar grains in Proterozoic arkoses and greywackes from southern Sweden.

Detrital K-feldspar grains have been replaced by euhedral crystals of albite in Upper Proterozoic arkoses and greywackes of the Visingso group in S Sweden. The albite, which formed late in burial diagenesis, replaced the K-feldspar by dissolution-precipitation rather than by solid-state diffusion. Calcite, quartz and TiO₂ crystals are commonly found in dissolution voids on the K-feldspar, while iron oxides occur between and as coatings around the albite crystals. The albitization may be due to an increase in aNa⁺/aH⁺ ratio in pore solutions (K⁺ released from the K-feldspar is fixed as authigenic illite or consumed in late-diagenetic transformation of kaolinite and mixed-layer illite-smectite into illite) and T (<150oC). Albitization by dissolution-precipitation processes is enhanced by relatively low porosity and permeability encountered in late-burial environments. In such environments, K-feldspar might decompose into Si-Al chains rather than into individual ions. (Author's abstract) -J.M.H.