Study On The Structural Movement Of Dabashan Tectonic Belt And The Trace Elements And REEs Of The Fluids

The tectonic Framework of Dabashan was fianally formed after Indosinian movement and Yanshan movement. Subduction and collision of south and north Dabashan took place during the Indosinian movement,and during the Yanshan movement intracontinental orogenesis took place in Dabashan area. Two paleotectonic stress fields in Dabashan area during Mesozoic have been obtained By the field and indoor study: NE-SW compression and NW-SE compression. NW-SE compression took place during the Indosinian movement and Yanshan movement and the characters of stress field were:σ1 (40°∠2°),σ3 (175∠88°) NW-SE compression were later than NE-SW compression,its characters of stress field were:σ1 (143°∠1°),σ3 (267°∠88°).According to different characters of structural deformation,from NE to SW,Dabashan can be divided into 4 different structural deformation belts:thrust-nappe structural belt, The basement detachment structural belt, cap rock decollement structural belt and forland depression structural belts.There are different tectonic styles in different structural belt. From NE to SW, the patten of deformations are from ductile to brittle and the strength and depth of deformations decrease gradually.Trace elements and REEs of calcite veins filled in fractrures in Dabashan Tectonic belt have been analyzed.The wall-rocks had single origin,indicating the stable sedimentary environment. REEs showed positive Eu anomaly, which indicated environment of the formation of the calcite vein was reductive.The fluids flowed during the NE-SW compression were mainly from wall-rocks,mixing with another kind of fluid with high Ba and Rb and low∑REE and La/Yb. The fluids flowed during the NW-SE compression were mainly from wall-rocks,too,and also mixing with another kind of fluid with high Ba and Rb and low∑REE and La/Yb.