An example of structural and metamorphic relationships in the Musgrave orogenic belt, central Australia

Abstract

The western Musgrave Ranges are broadly divided into three groups of metamorphic rocks. A central granulite‐facies core is bounded on the north by rocks of amphibolite grade and on the south by rocks transitional between the granulite and amphibolite facies. Faults trending east‐west separate the three groups of rocks. The detailed structural relationships between the granulites and the lower grade rocks are described and discussed. The granulites are structurally relatively simple and are characterised by the presence of a strong southwesterly‐plunging, mineral‐streaking lineation. In marked contrast, the transitional rocks are more complexly folded on a macroscopic scale and they also have a well‐developed mineral lineation plunging to the southeast. These two lineation orientations are considered to be directions of maximum elongation. The amphibolite‐facies rocks are also complexly folded and at least two lineations related to different phases of deformation have been recognized. A suite of foliated and lineated dolerite dykes which occurs throughout the area inherited their fabric during a period of intense deformation and recrystallization, which resulted in the development of numerous mylonite zones. It is suggested that the granulite‐facies rocks may represent a suite of cover rocks which have been thrust in a northerly direction over a pre‐existing amphibolite‐facies basement.