Territory Stories

Woodgreen, Northern Territory : explanatory notes



Woodgreen, Northern Territory : explanatory notes

Issued by

Northern Territory Geological Survey


E-Publications; E-Books; PublicationNT; Australia 1:100 000 Geological Map Series




Australia 1:100 000 Geological Map Wood 5458; Australia 1:250 000 Geological MapAlcoota SF5310; Australia 1:250 000 Geological MapAlcoota SF5310

Map scale

1:100 000


Made available via the Publications (Legal Deposit) Act 2004 (NT); Available from GEMIS - Geoscience Exploration and Mining Information System




Geology; Georgina Basin; Arunta Region

Publisher name

Northern Territory Government; Northern Territory Government

Place of publication



1st ed.


Australia 1:100 000 Geological Map Series

File type







Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government



Related links

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/81885 [GEMIS]

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2 mylonitised Woodgreen Granite Complex (Figure20). The metamorphic grade of these shear zones is greenschist facies, with grade decreasing to the north. Further north within Woodgreen, steeply southsouthwestdipping reverse faults also truncate the Georgina Basin and juxtapose basement against it. These faults are part of a more extensive belt extending eastward into HUCKITTA, where they have been interpreted by Greene (2003) as reflecting reactivation and inversion of a normal fault system, due to the preferential preservation of Neoproterozoic rift sediments in the hangingwall. The faults are typically associated with monoclinal folds, and have steep to overturned bedding in the footwall, immediately adjacent to the fault. In Woodgreen, this style of tectonics is best seen by the development of an elongate asymmetric syncline situated in the footwall of an inferred northwesttrending thrust fault that juxtaposes Arunta Region granite (Mollie Granite Complex) with Georgina Basin rocks in the vicinity of Mollie Bluff. The limb adjacent to the fault displays locally steep to overturned strata. gEophySIcS Airborne Woodgreen is entirely covered by airborne geophysical (magnetic, radiometric, elevation) data, acquired by NTGS as part of the AlcootaAlice Springs survey in 1997. These data were acquired on northsouthoriented, 400 mspaced flight lines, with a nominal terrain clearance of 60 m. Nominal sampling intervals for the magnetometer and spectrometer (33 L NaI crystal detector) were 7 m and 80 m, respectively. Further specification details are available through the NTGS website www.minerals.nt.gov.au/ntgs and World Geoscience Corporation (1997). The magnetic field over Woodgreen ranges in intensity up to 900 nT and +700 nT either side of the nominal base level following IGRF removal. Mean and median TMI values for Woodgreen are also 00 nT or more below the nominal base level. This negative skew is due, at least in part, to a continentscale westnorthwesterly zone of low magnetic intensity passing through the sheet area, parallel to the Alice Springs Orogenyage shear zones indicated on the mapface (Mount Ida and Delny shear zones). The most extreme negative TMI values, in the vicinity of the Mount Ida Shear Zone in southeastern Woodgreen, may have a component sourced from nearsurface metamorphic units (Delny Metamorphics). However, a significant proportion of this feature is considered to arise from the geometric effects of crustalscale anomalies. Sources of the anomalies of greatest intensity (north and southeast of Mount Skinner) are concealed beneath significant thicknesses of Georgina Basin cover and thus are of uncertain affinity, but are presumably metamorphic rocks of the Aileron Province, possibly subunit LPgw3 of the Woodgreen Granite Complex. Magnetic features of the various mapped and interpreted units are discussed under their respective headings (see Stratigraphy). Details of observed radiometric signatures are similarly incorporated in the descriptions of mapped units; also noteworthy is the expression of many features of current and former drainage systems in the radiometric data. gravity The only gravity data on Woodgreen, additional to the national nominal kmspaced coverage of Geoscience Australia (25 stations), are a series of GPSlevelled 500 m and km stationspaced road and track traverses conducted for NTGS (Haines Surveys 2002). These latter data highlight several new features, including a high that is coincident with deeply sourced, northwesttrending linear features at Mount Dixon, and a low that is apparently associated with a granite intrusion south of Mount Skinner homestead. The data also demonstrate the lack of significant density contrast between Neoproterozoic basin fill and adjacent granitic basement at Mount Skinner. This is ascribed to well compacted fine siliciclastic and calcareous sediment in the former. Thus, significant thicknesses of preserved Centralian Superbasin successions will not necessarily have any gravity expression. Regional gravity characteristics include a range from 544 to 237 m/s2, with values broadly increasing from north to south. A low, encompassing the northeast and central east of Figure20. Woodgreen Granite Complex. Well developed SC fabric in mylonitised granite. 429200mE 7523264mN, 6 km NW of No 3 Bore. www.minerals.nt.gov.au/ntgs