CHEMICAL WEATHERING-CAUSED MAGNETIC MINERALOGY CHANGES IN THE LATE MIOCENE TARIM DESERT STRATA

Desert strata consist of dune and interdune deposits and they have different magnetic properties. Contrasting magnetic properties of these two types of strata help to use magnetic parameters to reconstruct environmental evolution in these eco-fragile regions, but few has done so because of unclear mechanism of magnetic enhancement. Here we compared magnetic properties between dune and interdune strata of the late Miocene desert deposits in the northwestern Tarim Basin. We found interdune strata have enhanced magnetic properties mainly due to content increase of hematite and stable single-domain and smaller pseudo single domain magnetite in chlorite.This pattern is different from Chinese loess deposits in whether magnetic enhancement is accompanied with increase of superparamagnetic ferrimagnetic mineral content. We attribute this difference to less precipitation in the Tarim Basin so that chlorite cannot dissolve to product superparamagnetic ferrimagnetic grains.