Amelia Creek: a Proterozoic impact structure in the Davenport Ranges, Northern Territory

Abstract

The Amelia Creek impact structure is located in Australia's Northern Territory in folded Palaeoproterozoic strata of the Davenport Ranges (20°51'S, 134°53′E). An impact origin is confirmed by presence of unequivocal shatter cones with apices that point upwards, and by planar microstructures in quartz grains from target sandstones of the Hatches Creek Group. Aeromagnetic, advanced spaceborne thermal emission and reflection radiometer (ASTER), and X-band synthetic aperture radar (X-SAR) images show an area of anomalous deformation in which smooth regional trends are disrupted by arcuate features at a 10 km radius to the north and south of the shock-metamorphosed rocks. However, no arcuate forms are apparent to the east and west of these shocked rocks, and instead, large south-southwest-trending faults are present about 6 km away on both sides. Despite pervasive shatter coning, typical of the central region of complex impact structures, no structural uplift is apparent, but instead the shocked rocks lie at the southern toe of a north-northeast-trending syncline. These shatter cones overprint and post-date the Palaeoproterozoic regional deformation, and thus, the impact structure has not been refolded and its abnormal form is likely due to pre-existing structure in the target rocks and/or an oblique impact. Small pockets of undeformed Late Neoproterozoic and Middle Cambrian strata are exposed in palaeovalleys in the central region of the structure, constraining the time of the impact to the Proterozoic.