Abstract:

The components and deformation characteristics of Archaean rocks in Xiaoheishan area, southern Liaoning were studied through the field investigation and microscope observation. The Archaean rocks are composed of supracrustal rocks, gneisses and metamorphic mafic veins，which appears as enclaves in Xiaoheishan metamorphic plutons. The supracrustal rocks consist of biotite granulite and banding hornblende magnetite quartzite. The gneisses are composed of banding hornblende biotite plagioclase gneisses and banding hornblende plagioclase gneisses, their protolith was tonalite. Metamorphic mafic veins consist of plagioclase amphibolite and hornblendite. After supracrustal rocks deposited, into which the tonalite intruded, and then mafic veins intruded into the supracrustal rocks and tonalite （gneisses）. Plagioclase amphibolite contains enclaves of hornblendite. The Archaean rocks underwent two episodes of deformation. The first episode of deformation formed folds (DF₁), foliations (DS₁) in parallel with axial-plane of the folds and lineations (DL₁). The second episode of deformation only formed inclined plunging folds (DF₂) by superposed folding without foliations and lineations. Deformation sequence, features of structure and deformation in the Archaean metamorphic rocks show that the two episodes of the deformations should occurred in the setting of middle tectonic level. The first deformation formed nappe structures, and the second episode formed Ⅲ type superposed folds by horizontal compressing in the same direction.

Key words: southern Liaoning, Xiaoheishan area, Archaean, rock components, deformation sequence, tectonic