Crustal scale ductile fault systems in the Arunta Inlier, central Australia

Abstract

Detailed geologic observations along three 100 km long traverses across the Early Proterozoic Arunta Inlier, central Australia, indicate that Paleozoic ductile shear zones are organized into crustal scale structural systems which control the map pattern and distribution of metamorphic zones. Two provinces can be distinguished: 1. (1) a southern one where shear zones form a series of hinterland dipping and south verging, imbricate reverse faults in the west (Redbank area), grading eastward into a foreland dipping duplex in the Arltunga Nappe Complex. Directly north of this complex, flat lying Paleozoic south-directed, ductile shear affects a large portion of the crust, a point which has been underestimated so far. 2. (2) The northern province is characterized by both south and north dipping shear zones showing reverse motion to produce a crustal-scale “pop-up” structure, presumably resulting from a more coaxial deformation history. Strike-slip shear zones become predominant in the eastern part of this province. Stratigraphic and cross-cutting relationships indicate that the southern systems developed first; the northern systems probably developed in response to the lock-up stages of overthrusting in the southern province. One important result of this work is that the distribution of granulite facies rocks and major geophysical anomalies throughout the Arunta Inlier is best explained by their position relative to the Paleozoic ductile fault systems described above. There is no need to invoke extensive Proterozoic uplift of these lower crustal materials.