New structural studies in the Walker Fault Zone of eastern Arnhem Land
are integrated with basin-wide reconnaissance observations, made to
refine models for the structural evolution of the McArthur Basin and
provide new insights into the nature of metal logenetical ly important
pre-inversion phases of the basin's evolution. At least five principal
events may be identified during the Proterozoic: The Tawallah Group and equivalents were deposited throughout the
McArthur Basin during an extensional event. Rifting of an incipient
Batten Trough occurred at this time, in a terrain characterised by
orthogonal, linked extensional faults. Uplift and erosion of the Tawallah
Group accompanied continuing extension and was penecontemporaneous
with continuing deposition of the overlying Parsons Range Group, within
a precursor to the Walker Trough. Dt (of the Walker Fault Zone) relates to a new rifting event,
penecontemporaneous with deposition of the McArthur Group and its
equivalents in the Walker and Batten Troughs. This rifting accompanied
dextral strike-slip faulting along northerly-trending bounding faults, as a
result of northwesterly-directed oblique extension, leading to pull-apart
basins. D2 inversion of the Batten and Walker Fault Zones pre-dates deposition
of the Roper Group. In the proposed model WNW-ESE directed
shortening (D2.), accompanied by folding and thrusting, and by local
development of cleavage in the Walker Fault Zone, is seen to be followed
by northerly-trending sinistral faulting (D2b), about a SE to ESE-directed
compression. D3 is basin-wide and post-dates the Roper Group. It is characterised by
conjugate faulting and folding about ENE to NE-directed compression.
The latest Proterozoic event to be identified (D4) comprises widespread north-trending strike-slip dextral faulting of Roper Group, coupled with
N-S directed thrusting across the Urapunga Fault Zone and Murphy Inlier
This is accompanied by late dextral reactivation of NNW to
NNE-trending faults in the Walker and Batten Fault Zones.