The geochemical characteristics of light metasedimentary rock for Gaojian Group and their geologic implication in the southwest Hunan.

Gaojian Group is light metasedimentary rock, which is mainly composed of me tamudstone and schist. The original rocks tend to be more abundant in fine- grained sediments. The metamorphism affected a little change of the chemica l components. The Chemical Index of Alteration (CIA) of Gaojian Group is si milar (avg. CIA = 75). Illite, muscovite and smectite, mainly are the chemi cal weathering minerals. Intermediate and felsic igneous provenances for li ght metasedimentary rock of Gaojian Group are shown using major element geo chemistry of the Gaojian Group. Most trace elements in the group are deplet ed relative to the composition of average crust. It is similar to the chara cteristics of the assemblages among Cu, Zn, Co, Ti, Cr and et al. elements and the shapes of the REE pattern in the Southern and Northern Xiangxinan. However, some elements (e. g. Au, Ag, As, Sb, Sr, Ba) were differentiated b y sedimentary environment. The values of Sr/Ba and delta Ce may imply that Gaojian Group deposiy in the half-deep and deep sea reducing environment.