Territory Stories

Pine Creek orogen : field excursion guide. Chief Government Geologists Conference, 28 April - 2 May 2003

Details:

Title

Pine Creek orogen : field excursion guide. Chief Government Geologists Conference, 28 April - 2 May 2003

Creator

Ahmad, M; Lally, JH; Ahmad, M; Lally, JH

Issued by

Northern Territory Geological Survey; Northern Territory Geological Survey

Collection

E-Publications; E-Books; PublicationNT; NTGS Record; Australia 1:250 000 Geological Map Series Pine Creek SD5208

Date

2003; 2003

Location

Australia 1:250 000 Geological MapPine Creek SD5208; Australia 1:250 000 Geological MapPine Creek SD5208

Notes

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

Language

English

Subject

Geology; Pine Creek Orogen

Publisher name

Northern Territory Government; Northern Territory Government

Place of publication

Darwin

Series

NTGS Record; Australia 1:250 000 Geological Map Series Pine Creek SD5208

Volume

2003-003

File type

application/pdf

ISBN

724570608; 0724570608

ISSN

1443-1149; 1443-1149

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government; Northern Territory Government

License

https://creativecommons.org/licenses/by/4.0/; https://creativecommons.org/licenses/by/4.0/

Related links

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/82420 [GEMIS]; https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/82420

Parent handle

https://hdl.handle.net/10070/794266; https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/82420

Citation address

https://hdl.handle.net/10070/794285

Page content

9 for the formation of elongated basins and domes. The D5 deformation produced steeply plunging polyclinal kinks and drag folds associated with dextral movements along major faults. STOP DESCRIPTIONS Stop 1-1 Beestons Formation/Archaean unconformity Location: Rum Jungle Uranium Field 1:100 000 Special MGA 718100mE, 8559400mN Originally the Rum Jungle and Waterhouse "Granites" were thought to be concordant intrusions which had domed the Palaeoproterozoic metasediments of the Pine Creek Orogen (Sullivan and Matheson 1952, Malone 1962). However, no clear evidence of contact metamorphism was recorded, though quartz-tourmaline veins cut both granites and metasediments. In 1962, BP Ruxton and J Shields discovered an outcropping unconformity (Rhodes 1965), which showed beyond dispute that the Beestons Formation, the lowest stratigraphic unit in the Rum Jungle Region, lies unconformably on what Rhodes defined as the Rum Jungle Complex. Since then, French (1970) and Johnson (1974) have described several other exposures of the unconformity between granitic basement and Palaeoproterozoic metasediments. At most exposures, the unconformable contact is sheared and dips more steeply than 70 (Stephannson and Johnson 1976). However, at this locality, the contact is undeformed and dips southeast at about 40. The unconformity is exposed in three outcrops and can be traced for about 150 m (Figure 4). The unconformity surface is irregular and undulating, broadly concordant with the dip of the overlying sedimentary rocks (Eupene 1985). The basement at this locality is a massive, pink leucocratic coarse equigranular granite of the Rum Jungle Complex. The granite comprises microcline, quartz, plagioclase, biotite, sericite and minor fluorite. Thin, irregular fine-grained leucogranite dykes and quartz tourmaline veins are common, and the quartz has a characteristic pale blue opalescent colour. This granite has recently been dated by SHRIMP U-Pb zircon at about 2525 Ma (Ahmad et al in prep). The sedimentary rock in contact with the granite is poorly-sorted coarse to gritty arkose of the Beestons Formation. This arkose contains thin quartz pebble beds and lenses up to 3 m thick of chaotic clast-supported conglomerate, which is composed of angular white vein quartz fragments ranging up to 30 cm across in a gritty arkose matrix (Figure 5). Grains of blue opalescent quartz, like those in the granite basement, are common in the arkose. The arkose represents transgressive shallow water, possibly shoreline deposits, largely derived from the underlying granitic basement (French 1970). Inherited zircons from the arkose have been dated by SHRIMP 1. The age spectra ranges from 2500 Ma to 3615 Ma and is principally dominated by a mode between 2500 Ma and 2575 Ma (66% of grains). The weighted mean of the youngest six grains in the population yielded an age of 2506 14 Ma (Ahmad et al in prep), and this indicates that the sediment is derived entirely from the underlying granitic rocks. Figure 4. Geological map of the Beestons Formation/Archaean unconformity in the vicinity of Stop 1-1 (after Eupene 1985).


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