Han, ZZ; Gao, LH; Yang, RC; Fan, AP; Song, DF; Cai, GG; Li, CH; Chen, JY
According to the components and stability of the clastic heavy minerals, the tectonic evolution of the studied area can be classified into two stages:the stable heavy mineral period and unstable-stable heavy mineral period. Firstly, the period of the steady heavy mineral corresponds to the Eocene(Es3) ,during which the assemblage of stable heavy minerals is dominate, and the average of stability coefficient, ZTR factor, zircon and titania is 80. 54%, 45. 88%, 44. 1% and 14.79% respectively. While in the unstable and stable stage, the content of heavy minerals are low,indicating a situation of smooth tectonic activity. Secondly, the period of the unstable-stable heavy mineral corresponds to the Oligocene (Es2 to Ed) ,during which the assemblage of unstablestable heavy minerals are domination, and the average content of the epidote, pyroxene+ amphibole, and garnet is 20. 39%, 3. 87% and 19. 48% respectively, indicating a situation of intense tectonic activity. From Eocene to Oligocene, the stable factor and ZTR index were declining gradually, suggesting the increasing of intensity of tectonic movement, and the Es 2 being the important tectonic transition. The law of longitudinal distribution of the heavy minerals and the structural evolution of Liaohe Basin are homologous. The stable period can be divided into two stages:the extend-ebbing period of the Lower Es3 with weak to gentle structural activity and the ascend-reversion of the Upper Es3 with intensive structural activity. Unstable-stable period can be divided into the extend-ebbing period of the Es2 with gentle structural activity, the ascend-reversion of the Es1 with intensive structural activity, the extend-ebbing period of the early-mid Ed with gentle structural activity and the clockwise period of the Late Ed with intensive structural activity. According to analysis of hematite and limonite from the sandstone, it is considered that the weather of the depositional stage is dry in Upper Es3 ,Es 2 and Ed2 with higher content of heavy minerals, and moist in Lowe Es3 ,Es1 ,Ed3 and Ed1 with lower content of heavy minerals.