Mechanism and mode of albitization of detrital feldspar in the Devonian Padeha Formation, Eastern Alborz, Iran

The Early to Middle Devonian Padeha Formation in the Eastern Alborz includes a thick terrestrial synrift succession of white to purple sandstone, conglomerate and shale. The Lower sandstone unit is characterized by submature quartzarenite, subarkose and arkose. The sandstones have been examined using scanning electron and hot- cathodoluminescence microscopy to study the albitized detrital feldspars. Detrital K-feldspar is the major feldspar that has been partly albitized throughout the study sandstone. The textural variation is considerable, including vein-like, blocky, and patchy forms. Probable sodium sources for albitization include smectite to illite or chlorite transition, diabase sills, detrital albite dissolution, and replacement of detrital sodium plagioclases by authigenic minerals. From comparison with other basins worldwide, a temperature estimate of 75–130°C for the mesodiagenetic albitization is inferred, suggesting a burial depth of 2000-5500 m based on a thermal burial model for the basin. The model suggests that the temperature at the base of the Padeha Formation did not exceed 150°C, constraining conditions for albitization.