Micro- to macroscale strain partitioning in granulite facies rocks: Mt.Hay block, central Australia

Abstract

Experimental work on the strength of single phases has been used to infer the strengths of the upper and lower crust and mantle. Dislocation creep in plagioclase is commonly inferred to approximate the rheology of the lower crust. Recent work suggests that diffusion-accommodated grain-boundary sliding in plagioclase may be an important deformation mechanism in naturally deformed lower crust. One way to constrain rheology is through field and petrographic studies of naturally deformed systems, such as the Mt. Hay block in central Australia. These rocks demonstrate strain partitioning from the micro- to macroscale and provide an opportunity to study the relationships between structures of different scales. Field work shows map-scale fabric contrasts (lineation dominant versus equal foliation and lineation) between the geographic domains in the Mt. Hay block. At the outcrop scale, plagioclase-rich domains shape defines both foliation and lineation. Microstructural studies also show the partitioning of strain between lithologic domains. These show that plagioclase has different microstructures in different lithologic layers. This suggests different deformation mechanisms are active depending on plagioclase content, which may control variations in meso- and macroscale fabric. EBSD analyses of plagioclase in these different domains will evaluate the importance of dislocation creep in this context.