ژيوشيمي عناصر اصلي ماسه سنگ هاي سازند لالون در مقطع باهمو، ايران مركزي: با نگرشي بر سنگ مادر، شرايط هوازدگي قديمه و جايگاه زمين ساختي

Geochemistry of Lalun sandstones in Bahmoo section, Central Iran: Implications for source rock, paleoweathering, and tectonic setting

Major elements composition of 12 sandstone samples from Early Cambrian Lalun Formation in Bahmoo section, Poshte Badam block, Central Iran, has been investigated to determine their provenance, tectonic setting, and paleoweathering. The major elements composition are comparable to average upper continental crust and show that only Na20 content depleted relative to UCC, due to post depositional processes or lack of Na-palagioclase bearing source rocks .The CIA and PIA values (chemical index of alteration and plagioclase index of alteration) for these sandstones and the A-CN-K diagram represented intermediate degrees of weathering in main body of formation and intense weathering in top quartzite. These evidences propose trend of climate change from semi arid to humid during deposition of the Lalun Formation. In addition, the index of compositional variability (ICV) of the sandstones suggests that the recycling of top quartzite was intense. The geochemical data and use of discrimination diagrams support a quartzose and felsic source and a passive margin tectonic setting for these sandstones. Similarly, the amounts of their major elements are in consistent with a passive-margin setting.