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| | | Edmundian Orogeny D3e/M3e (CED3) | S Sheppard, SP Johnson, FJ Korhonen, and MTD Wingate | | | | | Event type | deformation: undivided | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | orogen: intracratonic orogen | Metamorphic facies | | Metamorphic/tectonic features | –– |
| | | Summary | The D3e event in the Gascoyne Province produced east-southeasterly trending upright folds that dominate the map patterns in the northern part of the Mutherbukin Zone. Folding was associated with low-grade metamorphism and retrogression of M2e assemblages. | | | Distribution | Structures and mineral assemblages related to the D3e event may have been developed across the width of the Mutherbukin Zone, although precise age contraints are available only on some fabrics close to the Ti Tree Shear Zone. Along the northern edge of the zone, adjacent to the Ti Tree Syncline, the S3e cleavage in the basement rocks is broadly parallel to structures in the Edmund Group within the syncline. | | | Description | 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. The metasedimentary rocks of the metamorphosed Edmund Group and Pooranoo Metamorphics show a systematic northward decrease in metamorphic grade, towards the Ti Tree Syncline. In low-grade areas of the Nardoo belt, near the Ti Tree Syncline, the Pooranoo Metamorphics are typically fine-grained rocks comprising mainly slate and phyllite. The rocks have a pervasive cleavage (S3e), which is axial planar to kilometre-scale folds in the Pooranoo Metamorphics and metamorphosed Edmund Group, and broadly parallel to structures in unmetamorphosed Edmund Group rocks within the Ti Tree Syncline.
The D3e event is associated with retrogression of M2e assemblages at greenschist facies conditions (M3e). In the Nardoo Hills area Culver (2001) and Varvell (2001) documented growth of chlorite and biotite porphyroblasts during M3e (M2 of Culver, 2001). They noted the presence of isograds marking the appearance of chlorite and biotite, and suggested that the grade of M3e increases towards the ‘Guran Gutta granite’, as does the intensity of deformation. However, our mapping suggests that the Gurun Gutta granite cuts S3e. Along the northern edge of the Mutherbukin Zone, adjacent to the Ti Tree Syncline, the typical assemblage in the slaty rocks of the Pooranoo Metamorphics is chlorite–muscovite–quartz(–albite–magnetite). The magnetite commonly forms small black porphyroblasts up to 2 mm long. The rocks have a pervasive, planar, continuous cleavage (S3e). There is probably only a small contrast in metamorphic grade between the Pooranoo Metamorphics at this locality and Edmund Group rocks in the Ti Tree Syncline. | | | | | | Geochronology | | | Edmundian Orogeny D3e/M3e | Maximum age | Minimum age | Age (Ma) | 995 | 954 | Age | Neoproterozoic | Neoproterozoic | Age data type | Inferred | | References | | |
| There are no direct ages for the D3e/M3e event, although some constraints are provided by ages of the D2e/M2e event and by the intrusion of rare-element pegmatites that cut D3e structures. A maximum age for D3e is provided by the youngest SHRIMP U–Pb monazite or xenotime date for the D2e/M2e event of 995 ± 6 Ma (Sheppard et al., 2007). Metasedimentary rocks in the Nardoo Hills area are cut by a suite of rare-element pegmatites, which were intruded during or after D3e (Hardy, 1992; Sheppard et al., 2007). A rare-element pegmatite (UWA 117154; site ‘U’ of Trautman, 1992) was sampled for SHRIMP U–Pb geochronology by Sheppard et al. (2007). This pegmatite forms a saddle ‘reef’ in the hinge zone of a regional-scale F3e antiform. The pegmatite plunges parallel to the plunge of the antiform, and is undeformed on the exposed southern limb of the antiform; these features indicate that the pegmatite probably intruded during D3e (Hardy, 1992; this work). A coarse monazite crystal several millimetres in size was separated and analysed. The monazite contains inclusions of quartz, a Th-silicate mineral surrounded by radial fractures, and clusters of xenotime. Seven analyses of the monazite produced a weighted mean ²⁰⁷Pb*/²⁰⁶Pb* date of 954 ± 12 Ma (Sheppard et al., 2007), which provides a minimum age for D3e/M3e. | | | 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. | Hardy, A 1992, The structural and metamorphic setting of the Yinnetharra pegmatites in the Nardoo Hill area, Gascoyne Complex, Western Australia: The University of Western Australia, Perth, Western Australia, BSc (Hons) thesis (unpublished). | 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. | 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. | Trautman, RL 1992, The mineralogy of the rare-element pegmatites of the Yinnetharra pegmatite belt, Gascoyne Province, Western Australia: The University of Western Australia, Perth, Western Australia, BSc (Hons) thesis (unpublished). | 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. | 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 |
| | | | Recommended reference for this publication | Sheppard, S, Johnson, SP, Korhonen, FJ and Wingate, MTD 2022, Edmundian Orogeny D3e/M3e (CED3): 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 09 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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