The structural geology of the western margin of the Entia Dome, Harts Range, eastern Arunta Inlier

Abstract

The study area is located within the eastern Harts Ranges, approximately 150 km ENE of Alice Springs in the Proterozoic Arunta Inlier, central Australia. Detailed geological mapping at a scale of 1:12 500 has included lithologies of the Entia Gneiss Complex within the Entia Dome, the Irindina supracrustal assemblage and the Bruna Gneiss (terminology after Ding and James, 1985). The 'basement' lithologies of the Entia Gneiss Complex have undergone at least three repeated, generally isoclinal, recumbent folding events and peak (upper amphibolite facies) metamorphism prior to intrusion of the Bruna Gneiss. The metapelitic lithologies of the Irindina supracrustal assemblage ('cover') have been subject to at least one isoclinal folding event prior to its juxtaposition with the 'basement'. Emphasis is on the Bruna Gneiss, interpreted as a variably mylonitised orthogneiss that was emplaced along a wide ductile shear zone that separated the 'cover' and 'basement'. This study subdivides the Bruna Gneiss into two lithologies on the basis of field and microstructural observations and strain analysis: the structurally lower granitic gneiss and the overlying (much thinner) megacrystic gneiss. The megacrystic gneiss, previously described as mylonite derived from the granitic gneiss, is interpreted as having been intruded independently from the bulk of the Bruna (ie granitic) Gneiss, and has undergone less complex deformation relative to the granitic gneiss.