Chemical weathering of crystalline rocks in contrasting climatic conditions using geochemical proxies: An overview

Weathering profiles of granitoid rocks from the Sila Massif (southern Italy) have been studied to characterize weathering processes that affect this area. Chemical weathering indices of the Sila Massif weathered granitoids were compared to those of different areas of the world characterized by different climates (Malaysia, Puerto Rico, Georgia, China, Nigeria, Colorado, Switzerland, and Sweden) to decipher their weathering characteristics. The geochemical indices show values of CIA (Chemical Index of Alteration) ranging from 55 to 97, CIW (Chemical Index of Weathering) ranging from 60 to ~100, PIA (Plagioclase Index of Alteration) ranging from 55 to ~100, WIP (Weathering Index of Parker) ranging from 7 to 64 and RR (Ruxton Ratio) ranging from 2.14 to 3.96. All these geochemical proxies closely resemble each other and show variations mainly related to the different climatic and tectonic settings. Malaysia and Puerto Rico granitoids showing high CIA values (respectively 97 and 95 on average) underwent very intensive chemical weathering alteration; Georgia, China and Nigeria showing medium-high CIA values (respectively 86, 90 and 92 on average) underwent moderate-intensive chemical weathering alteration; southern Italy and Colorado granitoids showing medium-low CIA values (68 on average) underwent moderate-weak chemical weathering alteration, whereas Switzerland and Sweden granitoids showing low CIA values (respectively 58 and 55 on average) underwent weak chemical weathering alteration. Those values are mainly related to the climatic conditions in term of temperature and precipitation of each area. CIA vs. climate histograms display a shift towards higher CIA values with increasing of warm-humidity (‘tropical’) conditions, whereas granitoids weathered under conditions inferred to be cold-arid-polar climate show lower CIA values.