Definition card for: Foster Cliff Granite

State(s): NT,
Status of unit: Formal
Usage: Defined
Stratno: 33651

Reserved by: Scrimgeour I., Close D., Edgoose C. on: 27-JUL-99
Approved: Y
Approved by: on: 27-JUL-99

Name source: Foster Cliff, 25o35'8.9"S, 130o25'40"E, Petermann Ranges.

Unit history: Comprises part of the Olia Gneiss and unnamed metamorphosed granites of Forman (1966, 1972).

Constituents: Nill. Forms part of the Mantarurr Granite Suite.

Geomorphic expression: Low outcrops and rounded rocky hills. Rubbly slopes underlying quartzite scarps of Foster Cliff region and Butler Dome.

Type section locality: 1.5 km west of Foster Cliff 25o35'9.6"S, 130o24'39.2"E.

Extent: Occurs extensively throughout Olia Chain, particularly in regions up to 10 km west and south of Stevenson Peak, in the vicinity of Foster Cliff and extending 10-15 km southwest of Foster Cliff and a 4 x 4 km region centred 6 km northeast of Butler Dome, Petermann Rangeas.

Lithology: Foliated biotite granite which is typically finely porphyritic with abundant small phenocrysts of K-feldspar 2-5 mm in diameter. Locally the granite is equigranular and fine to medium grained. The mineralogy typically comprises quartz, K-feldspar, plagioclase, biotite, sphene, ilmenite and epidote, with secondary muscovite and accessory allanite. This granite is locally intruded by fine to medium grained leucogranites, and leucocratic veins and pegmatites.

Relationships and boundaries: Has contacts with the Kulu Granite which range from being sharp and intrusive to being apparently gradational. Has sharp intrusive contacts with the Utanta and Wala Wuru Granites. No consistent timing relationships are evident, although the presence of a diffuse early fabaric suggests that this may be the oldest granite in the Mantarurr Granite Suite. Is intruded by mafic dykes of the 800 Ma Amata Dyke Swarm and possibly also the 1078 Ma Alcurra Dyke Swarm.

Age reasons: Mesoproterozoic. Correlated (on the basis of geochemical similarities) with Kulu Granite which has a SHRIMP U-Pb zircon age of c.1168 +/- 14 Ma (M Fanning, pers. comm.)

Correlations: Geochemically and mineralogically similar to the Utanta Granite, Wala Wuru Granite and Kulu Granite. Similar age, but geochemically distinct from the Pottoyu and Umutju Granite Suites and Walal Granite on Petermann Ranges.

Proposed publication: Petermann Ranges 1:250 000 geological mapsheet Explanatory Notes.

Comments: Deformed and metamorphosed at 5-6 kbars and ~600-650oC during the c.560 Ma Petermann Orogeny.

Category: 2

Defn approved by: Beier P., Kruse P.D., Young D.N.

Proposer: Edgoose C.J., Close D.F., Scrimgeour I.R.