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| | | | Geological Survey of Western Australia |
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| | | | HM Howard, RH Smithies, and R Quentin de Gromard | | | | | Event type | tectonic: accretionary orogeny | Parent event | _Top of Event list | Child events | | Tectonic units affected | | Tectonic setting | orogen: continental arc | Metamorphic facies | | Metamorphic/tectonic features | –– |
| | | Summary | The Mount West Orogeny is one of the oldest, widespread events in the west Musgrave Province for which there is direct evidence. The main expression of the Mount West Orogeny appears to be the magmatism that produced the 1345–1293 Ma Wankanki Supersuite. These granitic rocks form a significant component of the Tjuni Purlka Zone, and represent the most voluminous pre-1100 Ma magmatic component to the Mamutjarra Zone. However, the rocks are not known from the Walpa Pulka Zone or anywhere in the east Musgrave Province. The Ramarama Basin was initiated and evolved concurrently with the Mount West Orogeny and was the locus for deposition of the mainly sedimentary protoliths to the 1340–1270 Ma Wirku Metamorphics. | | | Distribution | Magmatic rocks generated during this event are grouped into the 1345–1293 Ma Wankanki Supersuite. These rocks form a significant component of the Tjuni Purlka Zone and represent the most voluminous pre-1100 Ma magmatic component of the Mamutjarra Zone. However, Wankanki Supersuite rocks are not known from the Walpa Pulka Zone or from the east Musgrave Province. The Ramarama Basin was initiated and evolved concurrently with the Mount West Orogeny and was the locus for deposition of protoliths to the 1340–1270 Ma Wirku Metamorphics (P_-_wm). | | | Description | The main expression of the Mount West Orogeny appears to be magmatism that produced the Wankanki Supersuite. Evidence for deformation during this event is uncommon, most likely overprinted by subsequent events such as the Musgrave Orogeny, Giles Event or Petermann Orogeny. Granitic rocks of the Wankanki Supersuite are typically strongly deformed and have been metamorphosed up to granulite facies. Migmatite in the most leucocratic granitic rocks is locally conspicuous. In lower-strain zones, the rocks are mainly porphyritic granodiorites and monzogranites, containing up to 15% (?primary) clinopyroxene and orthopyroxene, and late (?retrograde) hornblende.
The Wankanki Supersuite is dominated by rocks in the compositional range of monzogranite to syenogranite, although the full range includes rare tonalite and granodiorite. These are metaluminous, calc-alkaline, I-type rocks. On tectonic discrimination diagrams (e.g. Pearce et al., 1984), they consistently fall within the field for volcanic-arc granites, and in this respect they differ from all other granitic rocks in the west Musgrave Province (Smithies et al., 2010).
During the Mount West Orogeny, deposition of sediment into the Ramarama Basin produced the mainly siliciclastic sedimentary protoliths to the Wirku Metamorphics. Detrital zircon age data suggest the rocks were deposited after c. 1340 Ma (Evins et al., 2012). Banded paragneisses of the Wirku Metamorphics are present in all zones of the west Musgrave Province, mainly as rafts in granitic rocks of various ages. In the Tjuni Purlka and Mamutjarra Zones, the Wirku Metamorphics are hosted within rocks of the Wankanki Supersuite. Deposition of the protoliths to the Wirku Metamorphics, therefore, was almost entirely within the period of the Mount West Orogeny and the evolution of the Ramarama Basin was a response to that orogeny. Some samples of the Wirku Metamorphics contain zircon age components as young as c. 1270 Ma. These paragneisses are not in contact with granitic rocks of the Wankanki Supersuite and show that local sedimentary reworking continued after the currently recognized minimum age of the Mount West Orogeny.
Where the Wirku Metamorphics show less well-developed gneissic banding, original sedimentary layering is preserved and is locally continuous. The original sedimentary rocks were dominantly arkosic sandstones, although mudstone (now pelite) and quartz-rich sandstone (orthoquartzite) interlayers also occur. Locally, fine-grained granofelsic units have yielded unimodal, or near unimodal, 1330–1300 Ma zircon age distributions that strongly contrast with the complex age distribution patterns typically found in other components of the Wirku Metamorphics. These granofelsic units are geochemically similar to granitic rocks of the Wankanki Supersuite and suggest that felsic volcanism contributed to the fill of the Ramarama Basin (Evins et al., 2012.). Volcanic layers in the Wirku Metamorphics occur in both the Mamutjarra Zone and the Tjuni Purlka Zone, but are absent from the Walpa Pulka Zone.
| | | | | | Geochronology | | | Mount West Orogeny | Maximum age | Minimum age | Age (Ma) | 1345 | 1293 | Age | Mesoproterozoic | Mesoproterozoic | Age data type | Inferred | | References | | Kirkland et al. (2010) | Kirkland et al. (2010) |
| | Kirkland et al. (2012) | Evins et al. (2012) |
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| The crystallization age-range of the Wankanki Supersuite is constrained to between 1345 ± 7 Ma (GSWA 194393, Kirkland et al., 2010) and 1293 ± 9 Ma (GSWA 183726, Kirkland et al., 2012). Approximately 20 samples have been dated within this range, and most dates fall within a narrow range of c. 1326 to 1312 Ma (White et al., 1999; Kirkland et al., 2008, 2009; Smithies et al., 2009; Howard et al., 2011).
Detrital zircon age spectra from the Wirku Metamorphics reveal distinct age trends for each of the three tectonic zones. Wirku Metamorphics of the Walpa Pulka Zone contain a main 1650–1530 Ma detrital zircon age component dominated by a c. 1570 Ma zircon mode. More varied and slightly more pelitic lithologies in the Tjuni Purlka Zone contain a main c. 1590 to 1280 Ma detrital zircon age component centred on c. 1500 Ma, and with significant modes around c. 1560, 1410 and 1360 Ma. Samples from the Mamutjarra Zone are characterized by zircon derived from younger 1345–1293 Ma Wankanki Supersuite magmatism. Wirku Metamorphics from the Latitude Hills area in the southeast part of the Tjuni Purlka Zone yield unique spectra with two main Proterozoic detrital zircon modes at 1820–1700 and 1550–1400 Ma, as well as an Archean component as old as c. 3100 Ma (Evins et al., 2012; Howard et al., 2015). | | | Tectonic Setting | Magmatic rocks formed during the Mount West Orogeny (Wankanki Supersuite) show geochemical and Nd-isotopic characteristics that suggest continental-arc magmatism (Giles et al., 2004; Betts and Giles, 2006; Smithies et al., 2010; Howard et al., 2011; Kirkland et al., 2012). Nd- and Hf-isotope trends neither support nor contradict this interpretation as they can also be explained by recycling of pre-existing radiogenic Musgrave basement, with no additional contribution from a mantle (wedge) source, although this point may simply reflect isotopic similarities between pre-existing Musgrave basement and any supposed subduction-modified mantle source. Nevertheless, it is possible that the arc-like signature of the Wankanki Supersuite is inherited through partial melting of compositionally primitive 1950–1550 Ma Musgrave Province basement, perhaps in a post-accretionary setting.
The Mount West Orogeny broadly coincides with Stage I of the Albany–Fraser Orogeny and emplacement of the 1330–1276 Ma Recherche Supersuite (White, 1997; Smithies et al., 2010; Spaggiari et al., 2014). Magmatism associated with the Albany–Fraser (Stage I) Orogeny (Recherche Supersuite) differs from the Wankanki Supersuite in that it involved a much higher proportion of mafic (tholeiitic) magmas, and although the felsic magmas are calc-alkaline, they are typically also distinctly more Fe-rich (ferroan in the terminology of Frost et al., 2001) than the Wankanki Supersuite, have distinctly less radiogenic Nd-isotopic compositions, and the majority fall into the within-plate field on tectonic discrimination diagrams. The Recherche Supersuite is ascribed to a syn- to post-accretionary tectonic setting (Spaggiari et al., 2014).
There are generally strong temporal links between the Musgrave, Madura and Coompana Provinces and Albany–Fraser Orogen, but whole-rock geochemistry and isotope data from all these regions indicate significant differences in their evolution and respective basements. These provinces represent juvenile crustal remnants of Proterozoic Australia, while the Albany–Fraser Orogen is dominated by evolved material (Smithies et al., 2015; Spaggiari and Smithies, 2015; Kirkland et al., 2017). The early stages of the Musgrave Province, and of the Madura and Coompana Provinces (Eucla basement), are interpreted to reflect the evolution of oceanic lithosphere of the Mirning Ocean that originated around 1950–1900 Ma (Kirkland et al., 2017; Spaggiari and Smithies, 2015; Spaggiari et al., 2015). However, the Albany–Fraser Orogen is interpreted as the Proterozoic modification of the Archean Yilgarn Craton continental margin. Only minor amounts of evolved material are present in the Madura Province consistent with the interpretation of a hyperextended margin that evolved into an ocean–continent transition (Spaggiari et al., 2015; Kirkland et al., 2017). The evolution of the Mirning Ocean and successive oceanic arcs formed within it reflect plate tectonic processes between the West Australian Craton (WAC) and the South Australian Craton (SAC) dominated by extension and juvenile crust production during subduction.
In a broad sense, both the Wankanki and Recherche Supersuites may reflect the final stage in the Proterozoic amalgamation of central and southern Australia (e.g. Giles et al., 2004; Betts and Giles, 2006; Smithies et al., 2010). | | | | References | Betts, PG and Giles, D 2006, The 1800-1100 Ma tectonic evolution of Australia: Precambrian Research, v. 144, p. 92–125. | Evins, PM, Kirkland, CL, Wingate, MTD, Smithies, RH, Howard, HM and Bodorkos, S 2012, Provenance of the 1340-1270 Ma Ramarama Basin in the west Musgrave Province, central Australia: Geological Survey of Western Australia, Report 116, 39p. | Frost, BR, Barnes, CG, Collins, WJ, Arculus, RJ, Ellis, DJ and Frost, CD 2001, A geochemical classification for granitic rocks: Journal of Petrology, v. 42, no. 11, p. 2033–2048. | Giles, D, Betts, PG and Lister, GS 2004, 1.8 - 1.5-Ga links between the North and South Australian Cratons and the Early-Middle Proterozoic configuration of Australia: Tectonophysics, v. 380, p. 27–41. | Howard, HM, Smithies, RH, Kirkland, CL and Quentin de Gromard, R 2015, The burning heart — the Musgrave Province, in GSWA 2015 extended abstracts: promoting the prospectivity of Western Australia: Geological Survey of Western Australia, Record 2015/2, p. 28–30. View Reference | Howard, HM, Werner, M, Smithies, RH, Evins, PM, Kirkland, CL, Kelsey, DE, Hand, M, Collins, AS, Pirajno, F, Wingate, MTD, Maier, WD and Raimondo, T 2011, The geology of the west Musgrave Province and the Bentley Supergroup - a field guide: Geological Survey of Western Australia, Record 2011/4, 116p. View Reference | Kirkland, CL, Smithies, RH, Spaggiari, CV, Wingate, MTD, Quentin de Gromard, R, Clark, C, Gardiner, NJ and Belousova, EA 2017, Proterozoic crustal evolution of the Eucla basement, Australia: Implications for destruction of oceanic crust during emergence of Nuna: Lithos, v. 278, p. 427–444. | Kirkland, CL, Smithies, RH, Woodhouse, A, Wingate, MTD, Howard, HM and Belousova, EA 2012, A multi-isotopic approach to the crustal evolution of the west Musgrave Province, in GSWA 2012 extended abstracts: promoting the prospectivity of Western Australia: Geological Survey of Western Australia, East Perth, WA, Record 2012/2, p. 30–31. View Reference | Kirkland, CL, Wingate, MTD and Bodorkos, S 2008, 183496.1: orthogneiss, Mount West; Geochronology Record 747: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Kirkland, CL, Wingate, MTD, Bodorkos, S and Smithies, RH 2009, 183492.1: K-feldspar porphyritic granite, Mount West; Geochronology Record 757: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Kirkland, CL, Wingate, MTD and Evins, PM 2010, 194393.1: granitic gneiss, Ngaturn; Geochronology Record 920: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Kirkland, CL, Wingate, MTD and Smithies, RH 2012, 183726.1: leucogranitic gneiss, Michael Hills; Geochronology Record 1046: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Pearce, JA, Harris, NBW and Tindle, AG 1984, Trace element discrimination diagrams for the tectonic interpretation of granitic rocks: Journal of Petrology, v. 25, p. 956–983. | Smithies, RH, Howard, HM, Evins, PM, Kirkland, CL, Kelsey, DE, Hand, M, Wingate, MTD, Collins, AS, Belousova, E and Allchurch, S 2010, Geochemistry, geochronology, and petrogenesis of Mesoproterozoic felsic rocks in the west Musgrave Province, Central Australia, and implications for the Mesoproterozoic tectonic evolution of the region: Geological Survey of Western Australia, Report 106, 73p. View Reference | Smithies, RH, Howard, HM, Evins, PM, Kirkland, CL and Wingate, MTD 2009, New insights into the geological evolution of the west Musgrave Complex, in GSWA 2009 extended abstracts: promoting the prospectivity of Western Australia edited by Geological Survey of Western Australia: Geological Survey of Western Australia, Record 2009/2, p. 19–22. View Reference | Smithies, RH, Spaggiari, CV and Kirkland, CL 2015, Building the crust of the Albany-Fraser Orogen; constraints from granite geochemistry: Geological Survey of Western Australia, Report 150, 49p. View Reference | Spaggiari, CV, Kirkland, CL, Smithies, RH and Wingate, MTD 2014, Tectonic links between Proterozoic sedimentary cycles, basin formation and magmatism in the Albany-Fraser Orogen, Western Australia: Geological Survey of Western Australia, Report 133, 63p. | Spaggiari, CV, Kirkland, CL, Smithies, RH, Wingate, MTD and Belousova, EA 2015, Transformation of an Archean craton margin during Proterozoic basin formation and magmatism: the Albany–Fraser Orogen, Western Australia: Precambrian Research, v. 266, p. 440–466, doi:10.1016/j.precamres.2015.05.036. | Spaggiari, CV and Smithies, RH (compilers) 2015, Eucla basement stratigraphic drilling results release workshop: extended abstracts: Geological Survey of Western Australia, Perth, Record 2015/10, 70p. View Reference | White, RW 1997, The pressure-temperature evolution of a granulite facies terrain, western Musgrave Block, central Australia: Macquarie University, Sydney, New South Wales, PhD thesis (unpublished), 256p. | White, RW, Clarke, GL and Nelson, DR 1999, SHRIMP U-Pb zircon dating of Grenville-age events in the western part of the Musgrave Block, central Australia: Journal of Metamorphic Geology, v. 17, p. 465–481. |
| | | | Recommended reference for this publication | Howard, HM, Smithies, RH and Quentin de Gromard, R 2020, Mount West Orogeny (MW): Geological Survey of Western Australia, WA Geology Online, Explanatory Notes extract, viewed 05 August 2025. <www.dmp.wa.gov.au/ens> |
| | | This page was last modified on 29 January 2020. | | | | | Grid references in this publication refer to the Geocentric Datum of Australia 1994 (GDA94). Locations mentioned in the text are referenced using Map Grid Australia (MGA) coordinates, Zones 49 to 52. All locations are quoted to at least the nearest 100 m. Capitalized names in text refer to standard 1:100 000 map sheets, unless otherwise indicated. WAROX is GSWA’s field observation and sample database. WAROX site IDs have the format ‘ABCXXXnnnnnnSS’, where ABC = geologist username, XXX = project or map code, nnnnnn = 6 digit site number, and SS = optional alphabetic suffix (maximum 2 characters). All isotopic dates are based on U–Pb analysis of zircon and quoted with 95% uncertainties, unless stated otherwise. U–Pb measurements of GSWA samples were conducted using a sensitive high-resolution ion microprobe (SHRIMP) in the John de Laeter Centre at Curtin University, Perth, Western Australia. Digital data related to WA Geology Online, including geochronology and digital geology, are available online at the Department’s Data and Software Centre and may be viewed in map context at GeoVIEW.WA. | | | Further details of geological publications and maps produced by the Geological Survey of Western Australia are available from: Information Centre Department of Mines, Industry Regulation and Safety 100 Plain Street EAST PERTH, WA 6004 Telephone: +61 8 9222 3459 Facsimile: +61 8 9222 3444 |
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