Abstract:

The Yiwulüshan metamorphic core complex（YMCC） has typical three-layered structures: a metamorphic core, a middle ductile rheological bed and a cover bed of brittle deformation in the hanging wall. The middle ductile rheological bed is composed of the Mesoproterozoic and Neoproterozoic sedimentary rocks and is important part of the YMCC, distributing in the Eastern, Northern and Southern parts of YMCC. Middle ductile rheological bed was deformed by metamorphosed in lower greenschist facies, forming varied bedding rheological fabrics. The data of fluid inclusion analysis of the syntectonic quartz veins in the middle ductile rheological bed suggest a homogenization temperature of 150-170 ℃, density of 0.96-0.98 g/cm³, pressure of 40-50 MPa, and a depth of 5-6 km. According to these new data presented, the deformation of the middle ductile rheological bed must have occurred under a lower temperature environment in the upper crust level, mainly representing brittle-ductile deformation.

Key words: Yiwulüshan, metamorphic core complex, middle rheological bed, fluid inclusion, microstructure