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| | | Capricorn Orogeny D3n/M3n (CCD3) | S Sheppard and SP Johnson | | | | | Event type | deformation: undivided | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | orogen: intracratonic orogen | Metamorphic facies | | Metamorphic/tectonic features | crenulated; faulted; retrogressed |
| | | Summary | The third tectonic fabric that can be attributed to the Capricorn Orogeny is referred to as D3n, and the corresponding mineral assemblage, M3n. This fabric is recognized only in the Limejuice Zone where D2n gneissic fabrics and foliations are folded about upright local- to regional-scale close to tight folds. A well developed crenulation cleavage is developed parallel to the macroscopic F3n fold axial traces. | | | Distribution | D3n deformation is only present in the Limejuice Zone. However, the presence of metamorphic zircon rims within quartzites of the Moogie Metamorphics in the Mutherbukin Zone dated at c. 1770 Ma suggest that this zone may have also been affected by D3n deformation and metamorphism. | | | Description | In the Limejuice Zone, pelitic and psammitic schists of the Leake Spring Metamorphics are folded about upright, close to tight folds (F3n). A crenulation schistosity is commonly formed parallel to the axial surfaces of the folds; this upright schistosity (S3n) crenulates a millimetre- to centimetre-scale compositional layering (S2n). Associated metamorphic assemblages (M3n), which comprise muscovite–chlorite–quartz(–magnetite) in pelitic rocks and quartz–muscovite(–chlorite) in psammitic rocks, have almost completely replaced M2n assemblages. | | | | | | Geochronology | | | Capricorn Orogeny D3n/M3n | Maximum age | Minimum age | Age (Ma) | 1784 | 1772 ± 6 | Age | Paleoproterozoic | Paleoproterozoic | Age data type | Inferred | | References | | |
| There are no direct age constraints on the timing of D3n deformation and metamorphism. In the Limejuice Zone, D2n gneissic fabrics and foliations within both the Middle Spring Granite and schists of the Leake Spring Metamorphics are folded around F3n folds indicating that F3 folding occurred after c. 1784 Ma (the younger age constraint for D2n).
Metamorphic zircon rims on detrital grains from a quartzite (GSWA 187403) sampled from northwestern YINNETHARRA in the Mutherbukin Zone have been dated at 1772 ± 6 Ma (Wingate et al., 2010). This age is considerably younger than that obtained for the D2n episode and so it is possible that it records deformation associated with D3n; however, no structures can be confidently linked to this period metamorphic zircon growth. | | | Tectonic Setting | The Capricorn Orogeny has been widely, although not universally, attributed to oblique collision of the Archean Yilgarn and Pilbara Cratons, following the model of Tyler and Thorne (1990) and Thorne and Seymour (1991). Since then, it has been recognized that some structures previously attributed to the Capricorn Orogeny belong to the older Ophthalmia and Glenburgh Orogenies (Powell and Horwitz, 1994; Occhipinti and Sheppard, 2001), although modifications of the earlier interpretation prevail (e.g. Evans et al., 2003). Krapež (1999) and Krapež and Martin (1999) considered that the Capricorn Orogeny reflected deformation along a sinistral transcurrent megashear, although little evidence was advanced to support this interpretation. Some objections to the interpretation of the Capricorn Orogeny as reflecting oblique collision of the Yilgarn and Pilbara Cratons were raised by Sheppard (2004, 2005) and Sheppard et al. (2010), who interpreted the orogeny as reactivation in an intracontinental setting.
A difficulty in advancing our understanding of the Capricorn Orogeny is the extensive nature of later Paleoproterozoic and Neoproterozoic reworking of the orogen. These reworking events have obliterated many of the fabrics, kinematic indicators, and mineral assemblages that formed during the Capricorn Orogeny. In the Errabiddy Shear Zone, Occhipinti et al. (2004) and Reddy and Occhipinti (2004) have shown that deformation related to the Capricorn Orogeny probably reflects dextral transpression. Along the northern margin of the Capricorn Orogen, Thorne and Seymour (1991) interpreted the Ashburton Basin as a foreland basin to collision between the Yilgarn and Pilbara Cratons, with uplift of the Gascoyne Province and thrust stacking to the south of the basin. This model was based in large part on the sedimentology of the Ashburton Formation and, even if the orogeny does not reflect continent–continent collision, it clearly involved substantial compression and uplift of the Gascoyne Province. | | | | References | Evans, DAD, Sircombe, KN, Wingate, MTD, Doyle, M, McCarthy, M, Pidgeon, RT and van Niekerk, HS 2003, Revised geochronology of magmatism in the western Capricorn Orogen at 1805-1785 Ma: Diachroneity of the Pilbara-Yilgarn collision: Australian Journal of Earth Sciences, v. 50, no. 6, p. 853–864. | Krapež, B 1999, Stratigraphic record of an Atlantic-type global tectonic cycle in the Palaeoproterozoic Ashburton Province of Western Australia: Australian Journal of Earth Sciences, v. 46, p. 71–87. | Krapež, B and Martin, DMcB 1999, Sequence stratigraphy of the Palaeoproterozoic Nabberu Province of Western Australia: Australian Journal of Earth Sciences, v. 46, no. 1, p. 89–103, doi:10.1046/j.1440-0952.1999.00692. | Nelson, DR 2004, 169086.1: biotite monzogranite, Boora Boora Bore; Geochronology Record 117: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Occhipinti, SA and Sheppard, S 2001, Geology of the Glenburgh 1:100 000 sheet: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 37p. View Reference | Occhipinti, SA, Sheppard, S, Passchier, C, Tyler, IM and Nelson, DR 2004, Palaeoproterozoic crustal accretion and collision in the southern Capricorn Orogen: The Glenburgh Orogeny: Precambrian Research, v. 128, p. 237–255. | Powell, CMcA and Horwitz, RC 1994, Late Archaean and Early Proterozoic tectonics and basin formation of the Hamersley Ranges, in Excursion Guidebook 4: 12th Australian Geological Convention: Geological Society of Australia. | Reddy, SM and Occhipinti, SA 2004, High-strain zone deformation in the southern Capricorn Orogen, Western Australia: Kinematics and age constraints: Precambrian Research, v. 128, p. 295–314. | Sheppard, S 2004, Unravelling the complexity of the Gascoyne Complex, in GSWA 2004 extended abstracts: promoting the prospectivity of Western Australia: Geological Survey of Western Australia, Record 2004/5, p. 26–28. View Reference | Sheppard, S 2005, Does the ca. 1800 Ma Capricorn orogeny mark collision of the Yilgarn and Pilbara Cratons?, in Supercontinents and Earth Evolution Symposium 2005 - program and abstracts edited by Wingate, MTD and Pisarevsky, SA: IGCP 509 inaugural meeting, Fremantle, Western Australia, 26-30 September 2005: Geological Society of Australia and Promaco Conventions Pty Ltd, Canning Bridge, WA; GSA Abstracts no. 81, p. 29. | Sheppard, S, Bodorkos, S, Johnson, SP, Wingate, MTD and Kirkland, CL 2010, The Paleoproterozoic Capricorn Orogeny: Intracontinental reworking not continent-continent collision: Geological Survey of Western Australia, Report 108, 33p. View Reference | Thorne, AM and Seymour, DB 1991, Geology of the Ashburton Basin, Western Australia: Geological Survey of Western Australia, Bulletin 139, 141p. View Reference | Tyler, IM and Thorne, AM 1990, The northern margin of the Capricorn Orogen, Western Australia — an example of an early Proterozoic collision zone: Journal of Structural Geology, v. 12, p. 685–701. | Wingate, MTD, Kirkland, CL, Bodorkos, S, Groenewald, PB and Sheppard, S 2010, 187403.1: quartzite, Robinson Bore; Geochronology Record 862: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference |
| | | | Recommended reference for this publication | Sheppard, S and Johnson, SP 2022, Capricorn Orogeny D3n/M3n (CCD3): 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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