Abstract:
The Iqe-Luofengpo eclogite-gneiss unit is situated in the western segment of the northern Qaidam marginal HP/UHP metamorphic belt. Microstructures and petrographic data suggest that eclogite and associated rocks underwent three stages of metamorphism and deformation related to subduction and subsequent exhumation. (1) Pre-eclogite facies stage. This stage is inferred from garnet cores with growth zoning and locally with “S”- or anti-“S”-shaped inclusion trails, consisting of epidote, amphibole and plagioclase, suggesting an asymmetrical rotational deformational strain of deformation fabrics related to subduction. (2) Eclogite-facies metamorphism and deformation stage. This stage is defined by oriented distribution of omphacite, phengite and zoisite around garnet, forming stretching lineation and foliation under eclogite-facies conditions. Lack of distinct asymmetrical fabrics indicates that the deformation under eclogite-facies conditions was coaxial. (3) Post-eclogite facies metamorphism and deformation stage. This stage is characterized by oriented distribution of amphiboles and plagioclase, and the deformation fabric mainly occurs in retrogressive eclogite (hornblendized eclogite) distributed around eclogite lenses and country rocks, which is in agreement with widespread regional amphibole-facies structure and is related to exhumation of HP/UHP rocks. The deformation and metamorphic evolution of eclogite and related rocks reflects the tectono-thermal history from the subduction to exhumation of the Iqe-Luofengpo eclogite-gneiss unit.