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| | | | Geological Survey of Western Australia |
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| | | | AM Thorne, S Sheppard, SP Johnson, DMcB Martin, FJ Korhonen, and MTD Wingate | | | | | Event type | tectonic: intracratonic orogeny | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | orogen: intracratonic orogen | Metamorphic facies | | amphibolite: cordierite | amphibolite: staurolite | greenschist: undivided |
| Metamorphic/tectonic features | metatexitic; migmatitic; granoblastic |
| | | Summary | The 1030–955 Ma Edmundian Orogeny (Halligan and Daniels, 1964) is an intracratonic event that resulted in widespread deformation of the Edmund and Collier Groups (Bangemall Supergroup; Martin and Thorne, 2004). The orogeny largely resulted in north–south shortening that formed easterly to southeasterly trending, open to tight, upright folds and normal, reverse, and strike-slip faults (Martin et al., 2005). In the Edmund and Collier Groups, the Edmundian Orogeny consists of a localized D1e event, widespread easterly to southeasterly trending folds and associated faults (D2e), and northeasterly trending open folds (D3e).
The effect of the orogeny in the underlying basement was thought to be limited to formation or reactivation of discrete structures. However SHRIMP U–Pb geochronology of monazite and xenotime in thin sections of pelitic schists from the central Gascoyne Province, shows that greenschist to amphibolite facies metamorphism occurred between c. 1030 and 955 Ma (Sheppard et al., 2007). These data show that the Paleoproterozoic Gascoyne Province underwent an episode of intracontinental reworking concentrated in a northwesterly to southeasterly trending corridor during the Edmundian Orogeny. Therefore, the Edmundian Orogeny involved not only deformation and very low to low-grade metamorphism of the Edmund and Collier Group cover rocks, but also regional amphibolite facies metamorphism and deformation, granitic magmatism, and pegmatite intrusion in the Gascoyne Province between c. 1030 and 955 Ma. In the Gascoyne Province rocks, two main pervasive deformation events (D2e and D3e) are recognized, as well as an earlier fabric (D1e) preserved only in porphyroblasts.
| | | Distribution | The major structures that affect the Edmund and Collier Groups were formed during the Edmundian Orogeny (Martin and Thorne, 2004). In the northwestern part of the Capricorn Orogen, three deformation events are attributed to the Edmundian Orogeny. Of these events, D1e is a localized feature, whereas D2e and D3e affected the entire outcrop area of the two groups. Edmund and Collier Group rocks are divided into three structural zones referred to informally as the northeastern, central, and southwestern zones (Martin et al., 2005). The northeastern zone lies northeast of the Talga Fault and corresponds broadly to the Pingandy Shelf of Muhling and Brakel (1985). The central zone equates to the Wanna Syncline, an asymmetric southeasterly plunging synclinorium between the Talga Fault and the main Gascoyne Province outcrop to the southwest. The southwestern zone is represented by the more highly deformed rocks of the Mangaroon and Cobra Synclines.
The Edmundian Orogeny was also responsible for pervasive reworking along the northern margin of the Mutherbukin Zone in the central Gascoyne Province, including in the Nardoo Hills area in the northern part of the zone. Similar fabrics farther south probably formed during the older Mutherbukin Tectonic Event. Three deformation events are recognized in the Nardoo Hills area, but it is not clear how they relate to the events identified in the overlying Edmund and Collier Groups. Regional metamorphism associated with the Edmundian Orogeny in the Mutherbukin Zone ranges from greenschist to upper amphibolite facies (Sheppard et al., 2007).
| | | Description | The earliest deformation attributed to the Edmundian Orogeny in the Edmund and Collier Group rocks, D1e, consists of northwest-verging thrust faulting along the margin of a thick dolerite sill that intrudes the lower Edmund Group in the northwestern part of the Capricorn Orogen (Martin and Thorne, 2001). The main period of Edmundian deformation, D2e, produced east–west to southeast–northwest trending, generally upright open folds throughout the Edmund and Collier Groups. However, D2e folds may be tightened and inclined locally, particularly where associated with the major basement structures such as the Talga and Lyons River Faults, and in the Mangaroon and Ti Tree Synclines. Tight folding and steep dips along the southern limb of the Wanna Syncline are also related to D2e. The youngest of the Edmundian events, D3e, resulted in open northeast-trending upright folds. On a regional scale, these are responsible for plunge reversals in the F2e folds. The metamorphic grade in Edmund and Collier Group rocks is typically very low.
In the Gascoyne Province, penetrative deformation and regional metamorphism up to amphibolite facies was concentrated in the Mutherbukin Zone. Two main pervasive deformation events (D2e and D3e) are recognized, as well as an earlier fabric (D1e) preserved only in porphyroblasts. The first of the pervasive events, D2e, produced a strong foliation that was associated with greenschist to amphibolite facies metamorphism (M2:M1 of Williams et al., 1983; Culver, 2001; Varvell, 2001). Within the Mutherbukin Zone, the grade of metamorphism ranges from greenschist facies in the south around Mount James, gradually increases to amphibolite facies in the northern part around the Nardoo Hills area, and rapidly decreases back to greenschist facies adjacent to the Ti Tree Syncline. The D3e event (D2 of Culver, 2001) is associated with retrogression of M2e assemblages at greenschist facies conditions (M3e). Structures produced during D3e consist of microscopic to megascopic, east-southeasterly trending upright folds (F3e) characterized by a crenulation schistosity parallel to the axial surfaces. These F3e folds plunge shallowly or moderately to the east-southeast and west-northwest, and define the major map-scale patterns. | | | | | | Geochronology | | | Edmundian Orogeny | Maximum age | Minimum age | Age (Ma) | 1026 ± 12 | 954 ± 12 | Age | Mesoproterozoic | Neoproterozoic | Age data type | Isotopic | | References | | |
| Five samples of schist were collected from the Pooranoo and Leake Spring Metamorphics in the Nardoo Well area of the central Gascoyne Province (GSWA 180911, 180918, 191970, 191975, 191977) for SHRIMP U–Pb monazite and xenotime dating. Three of the samples contain amphibolite facies assemblages, whereas the two most northerly samples (GSWA 191970, 191975) contain greenschist facies assemblages. The oldest date obtained was 1026 ± 12 Ma (GSWA 180911, SHRIMP U–Pb monazite) thus providing a maximum age for D1e/D2e (Sheppard et al., 2007). Additional dates were: 1005 ± 10 Ma (GSWA 180918, monazite), 1004 ± 8 Ma (GSWA 191977, monazite), 998 ± 8 Ma (GSWA 191970, xenotime), and 995 ± 6 Ma (GSWA 180918, xenotime) (Sheppard et al., 2007). The minimum age constraint for deformation (D3e) is provided by an undeformed dyke from the Thirty Three Supersuite that cross-cuts all of the Edmundian-age fabrics. This dyke has been dated at 954 ± 12 Ma (Sheppard et al., 2007). Farther south, where the Gascoyne River crosses the Cobra – Dairy Creek road on YINNETHARRA, discontinuous melt-filled pockets (10–100 cm long) are developed within strongly foliated metamonzogranite of the Durlacher Supersuite. The main L–S fabric in the metamonzogranites, which has been correlated with the 1321–1171 Ma Mutherbukin Tectonic Event, is cut by the shear zones. A sample of these melt-filled shear zones (GSWA 185945) yielded abundant, concentrically-zoned, igneous zircon cores that are overgrown by structureless, high-U rims interpreted to be of metamorphic origin. The cores yielded a date of c. 1650 Ma, whereas the metamorphic rims yielded a concordia age of 1000 ± 8 Ma (GSWA 185945, Wingate et al., 2010), indicating that the rims formed during the Edmundian Orogeny under middle to upper amphibolite facies conditions. | | | Tectonic Setting | Some previous studies attributed the Edmundian Orogeny to far-field reactivation of the Capricorn Orogen during the break up of Rodinia (Powell et al., 1994) and the assembly of Gondwana (Fitzsimons, 2003). In contrast, Myers et al. (1996) suggested that the Edmundian Orogeny resulted from the collision of the North and West Australian Cratons between c. 1300 and c. 1100 Ma. However, dolerite sills dated at c. 1070 Ma (Wingate, 2002) that intrude the Edmund and Collier Groups are also deformed into easterly trending folds. More recent advances in understanding the amalgamation history of the Rodinia supercontinent indicate that the collision of the eastern margin of Australia with Laurentia occurred at c. 1000 Ma (Li et al., 2008 and references therein), a time coincident with the Edmundian Orogeny recorded here in the West Australian Craton. In most Rodinia reconstructions (i.e. Pisarevsky et al., 2003; Li et al,., 2008) the western margin of the West Australian Craton faces an open ocean, so if these configurations are correct, the Edmundian Orogeny must be a response to far-field plate stresses related to Rodinia assembly along the eastern margin of Australia. However, it is possible that the Edmundian Orogeny formed in response to plate collision/accretion along the western margin of the West Australian Craton and that current models of Rodinia are incomplete (Johnson, 2013). Uplift of the southern Capricorn Orogen between c. 950 and c. 850 Ma (Occhipinti, 2004, 2007) has been linked to collision of the Kalahari Craton with the western margin of Australia along the Pinjarra Orogen (Occhipinti, 2004). The Northampton and Mullingarra Inliers in the Pinjarra Orogen are interpreted to be allochthonous terranes, derived from the Albany Fraser Belt (Ksienzyk et al., 2007, 2012) that were metamorphosed at granulite and amphibolite facies, respectively at c. 1080 Ma, and intruded by granites at c. 1070 Ma. The inliers were thought to have been emplaced in their present position relative to the Yilgarn Craton in the Neoproterozoic (Fitzsimons, 2003) although, because they contain undeformed dolerites of the Mundine Well Dolerite, emplacement must have occurred prior to dolerite intrusion at c. 755 Ma. The metamorphism in the central Gascoyne Province is a minimum of 40 Ma younger than that in the Northampton Inlier. However, a pegmatite from the Northampton Inlier has been dated at 989 ± 2 Ma (Bruguier et al., 1999), suggesting that there could be other tectonothermal events in the Pinjarra Orogen coeval with the metamorphism and magmatism dated here (see also Ksienzyk et al., 2007). A comparison of the age of detrital zircons from metasedimentary rocks of the Northampton Inlier with similar, possibly correlative packages from the Maud Belt of Antarctica, reveals different ages suggesting that the Kalahari Craton – West Australian Craton association may not be valid (Ksienzyk et al., 2007). | | | | References | Bruguier, O, Bosch, D, Pidgeon, RT, Byrne, DI and Harris, LB 1999, U-Pb chronology of the Northampton Complex, Western Australia - evidence for Grenvillian sedimentation, metamorphism and deformation and geodynamic implications: Contributions to Mineralogy and Petrology, v. 136, p. 258–272. | Culver, KE 2001, Structure, metamorphism and geochronology of the northern margin of the Gurun Gutta Granite, Central Gascoyne Complex, Western Australia: Curtin University of Technology, Perth, Western Australia, BSc (Hons) thesis (unpublished), 126p. | Fitzsimons, ICW 2003, Proterozoic basement provinces of southern and southwestern Australia, and their correlation with Antarctica: Geological Society, London, Special Publications, v. 206, p. 93–130. | Halligan, R and Daniels, JL 1964, Precambrian geology of the Ashburton Valley Region, north-west division, in Annual report for the year 1963: Geological Survey of Western Australia, p. 38–46. View Reference | Johnson, SP 2013, The birth of supercontinents and the Proterozoic assembly of Western Australia: Geological Survey of Western Australia, Perth, Western Australia, 78p. View Reference | Ksienzyk, AK, Jacobs, J, Boger, SD, Kosler, J, Sircombe, KN and Whitehouse, MJ 2012, U-Pb ages of metamorphic monazite and zircon from the Northampton Complex: Evidence of two orogenic cycles in Western Australia: Precambrian Research, v. 198–199, p. 37–50. | Ksienzyk, AK, Jacobs, J, Kosler, J and Sircombe, KN 2007, A comparative provenance study of the late Mesoproterozoic Maud Belt (East Antarctica) and the Pinjarra Orogen (Western Australia): Implications for a possible Mesoproterozoic Kalahari-Western Australia connection, in Antarctica: a keystone in a changing world - online proceedings of the 10th international symposium on Antarctic earth sciences edited by Cooper, Alan and Raymond, C, Santa Barbara, California, USA, 26 August - 1 September 2007; USGS Open-File Report 2007–1047. | Li, ZX, Bogdanova, SV, Collins, AS, Davidson, A, Waele, B, Ernst, RE, Fitzsimons, ICW, Fuck, RA, Gladkochub, DP, Jacobs, J, Karlstrom, KE, Lu, S, Natapov, LM, Pease, V, Pisarevsky, SA, Thrane, K and Vernikovsky, V 2008, Assembly, configuration, and break-up history of Rodinia: A synthesis: Precambrian Research, v. 160, no. 1–2, p. 179–210, doi:10.1016/j.precamres.2007.04.021. | Martin, DMcB, Sheppard, S and Thorne, AM 2005, Geology of the Maroonah, Ullawarra, Capricorn, Mangaroon, Edmund, and Elliott Creek 1:100 000 sheets: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 65p. View Reference | Martin, DMcB and Thorne, AM 2001, Another Jillawarra-style sub-basin in the Bangemall Supergroup - implications for mineral prospectivity, in Geological Survey of Western Australia annual review 1999–2000 edited by Day, L and Reddy, DP: Geological Survey of Western Australia, Perth, p. 31–35. View Reference | Martin, DMcB and Thorne, AM 2004, Tectonic setting and basin evolution of the Bangemall Supergroup in the northwestern Capricorn Orogen: Precambrian Research, v. 128, no. 3–4, p. 385–409. | Muhling, PC and Brakel, AT 1985, Geology of the Bangemall Group: The evolution of a Proterozoic intra-cratonic sedimentary basin: Geological Survey of Western Australia, Bulletin 128, 266p. View Reference | Myers, JS, Shaw, RD and Tyler, IM 1996, Tectonic evolution of Proterozoic Australia: Tectonics, v. 15, p. 1431–1446. | Occhipinti, SA 2004, Tectonic evolution of the southern Capricorn Orogen, Western Australia: Curtin University of Technology, Perth, Western Australia, PhD thesis (unpublished), 220p. | Occhipinti, SA 2007, Neoproterozoic reworking in the Paleoproterozoic Capricorn Orogen: Evidence from ⁴⁰Ar/³⁹Ar ages: Geological Survey of Western Australia, Record 2007/10, 41p. View Reference | Pisarevsky, SA, Wingate, MTD, Powell, CMcA, Johnson, SP and Evans, DAD 2003, Models of Rodinia assembly and fragmentation: Geological Society, London, Special Publications, v. 206, no. 1, p. 35–55, doi:10.1144/GSL.SP.2003.206.01.04. | Powell, CMcA, Preiss, WV, Gatehouse, CG, Krapež, B and Li, ZX 1994, South Australian record of a Rodinian epicontinental basin and its mid-Neoproterozoic breakup (~700 Ma) to form the Palaeo-Pacific Ocean: Tectonophysics, v. 237, p. 113–140. | Sheppard, S, Rasmussen, B, Muhling, JR, Farrell, TR and Fletcher, IR 2007, Grenvillian-aged orogenesis in the Palaeoproterozoic Gascoyne Complex, Western Australia: 1030–950 Ma reworking of the Proterozoic Capricorn Orogen: Journal of Metamorphic Geology, v. 25, p. 477–494. | Varvell, CA 2001, Age, structure and metamorphism of a section of the Morrissey Metamorphic Suite, Central Gascoyne Complex, Western Australia: Curtin University of Technology, Perth, Western Australia, BSc (Hons) thesis (unpublished), 209p. | Williams, SJ, Williams, IR, Chin, RJ, Muhling, PC and Hocking, RM (compilers) 1983, Mount Phillips, Western Australia: Geological Survey of Western Australia, 1:250 000 Geological Series Explanatory Notes, 29p. View Reference | Wingate, MTD 2002, Age and palaeomagnetism of dolerite sills of the Bangemall Supergroup on the Edmund 1:250 000 sheet, Western Australia: Geological Survey of Western Australia, Record 2002/4, 48p. View Reference | Wingate, MTD, Kirkland, CL, Sheppard, S and Johnson, SP 2010, 185945.1: pegmatite lenses in metamonzogranite, Yinnetharra Homestead; Geochronology Record 901: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference |
| | | | Recommended reference for this publication | Thorne, AM, Sheppard, S, Johnson, SP, Martin, DMcB, Korhonen, FJ and Wingate, MTD 2022, Edmundian Orogeny (CE): 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 March 2022. | | | | | 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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