Characteristics of rare earth elements of lacustrine exhalative rock in the Xiagou Formation of Lower Cretaceous in Qingxi sag, Jiuxi basin

The exhalative rock occurring in the Xiagou Formation of Lower Cretaceous in Qingxi sag, Jiuxi basin is a sort of a rare lacustrine white smoke type, rich in ferrodolomites and albites. This paper introduces the geological background, mineral association, and lithology of the exhalative rock, and discusses its REE geochemical characteristics and connection with hydrothermal environment. It is shown that the exhalative rock has basal characteristics of hydrothermal depositional formation of LREE>HREE, with positive δCe and negative δEu, which is different from the characteristics of marine exhalative rock. Since the REE pattern and exceptional distribution of δEu and δCe are highly similar to the characteristics of alkalescent tholeiitic basalt in the same layer, the exhalative rock of Xiagou Formation is considered to be closely related to the origin of basalt in the same horizon. The fact that the amount of REE of exhalative rock decreases outwards indicates that exhalative rock in the Xiagou Formation may be connected with lacustrine hydrothermal convection circulation. © Higher Education Press and Springer-Verlag 2007.