BEHAVIOR OF MINOR ELEMENTS IN THE PROCESS OF FORMATION OF A WEATHERING PROFILE ON GRANITES

It has been shown that the ancient weathering profiles on granite mass ifs in West Siberia and state of South Carolina, USA, developed in acc ordance with the model for the Korzhinskii infiltration metasomatic co lumn. There are grounds to believe that the process run with the volum e being constant; unaltered granites were replaced by weathered rocks along the sharp boundary; with plagioclase completely replaced by kaol inite, orthoclase may remain intact. Under the conditions of sufficien tly intense drainage the kaolinite zone of the weathering profile lost up to 40% Si, nearly all alkalies and alkaline earths, more than 50% U, Be, and Zn, 20-50% lanthanides (except Ce); only hydrolyzate elemen ts left in place such as: Al and Ti, Zr and I-IF, Nb and Ta, Th and Ce . Under the conditions of hindered drainage some elements removed from the kaoline zone precipitated in the lower part of the profile where plagioclase is already lost but illite-accompanied orthoclase still re mained; here, along with rare alkalies, about a half of lanthanides in volved into migration were retained at the alkaline barrier, their rat ios being insignificantly changed. In the upper part of the profile hy drolysis processes led to precipitation of Fe and Mn hydroxides, proba bly, supplied from sediments overlying the crust of weathering; As, Sb , Co, Ni, Be, B, Mo, and Pb accumulated on hydroxides. Typical feature s of the infiltration metasomatic column may be veiled by outliers rem ained between zones of fracture, as well as by processes of redistribu tion of chemical elements. When the crusts of weathering developed on granites are subjected to denudation, the quartz is brought to sands, thus <<diluting>> the minor element concentration, while the accessory minerals chiefly enrich silty fractions. Thus, differences in chemica l composition of sandstones and aleuropelites originate from nothing e lse but weathering processes.