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| | | | Geological Survey of Western Australia |
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| | | Kuparr Tectonic Event (KU) | HNC Cutten and SP Johnson | | | | | Event type | deformation: strike-slip | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | orogen: intracratonic orogen | Metamorphic facies | | Metamorphic/tectonic features | –– |
| | | Summary | The 931–794 Ma Kuparr Tectonic Event is a newly identified period of brittle faulting and fault reactivation in the upper crustal siliciclastic sedimentary rocks of the Edmund and Collier Basins. The event is expressed by the development of centimetre-to metre-scale fault gouge or well-developed, millimetre-scale, slickenlines on discrete fault surfaces. The orientation of the slickenlines indicates a predominant transpressive sense of fault movement. The timing of movement is defined by K–Ar dating of authigenic illite clay from nine fault rock samples. One sample from the Mount Vernon Fault System, on the northern margin of the basins, yielded a date of c. 874 Ma. An additional eight fault rock samples from the Quartzite Well Fault System, which is more central to the Edmund and Collier Basins, including fault gouge from Abra drill core AB62, returned dates between c. 931 and 794 Ma. The known distribution of this event is currently restricted to the Mount Vernon and Quartzite Well Fault Systems from where the samples have been dated, however, Ar–Ar dating of Gascoyne Province basement rocks suggests this event is far more extensive. | | | Distribution | Expression of the 931–794 Ma Kuparr Tectonic Event in the upper crustal rocks of the Edmund and Collier Basins appears to be limited to transpressional fault movements on, at least, the Mount Vernon Fault System (MVFS) and Quartzite Well Fault System (QWFS) in the northern and central parts of the basins. The distribution of faults active during the event is difficult to define because, except by direct dating, they cannot be distinguished from coaxial structures active during the 1321–1171 Ma Mutherbukin Tectonic Event (Korhonen et al., 2015) and the 1026–954 Ma Edmundian Orogeny (Sheppard et. al., 2007). Dated samples reveal only very local movements on the Godfrey Fault of the MVFS. Movements associated with the Kuparr Tectonic Event is more evident in QWFS over a distance of 75 km, from faults on MOUNT EGERTON (Tom Hunts Fault), extending east onto MULGUL (Tony’s Fault, Quartzite Well Fault and Grove Fault) and on to CALYIE (Six Mile Creek Fault). | | | Description | The 931–794 Ma Kuparr Tectonic Event is a newly identified period of brittle faulting and fault reactivation in the upper crustal siliciclastic sedimentary rocks of the Edmund and Collier Basins. Although fault plane exposures in the Edmund and Collier Basins are not common, they occasionally do contain centimetre-to metre-scale fault gouge or show well-developed, millimetre-scale, slickenlines on discrete fault surfaces. The orientation of the slickenlines on slickenside surfaces of in situ rocks, indicates a predominant transpressive sense of fault movement. Most of the faults however, are characterized by offset ridges of steeply dipping sandstones separated by valleys filled with regolith, or as linear outcrops of massive vein quartz or quartz–ironstone breccia. Fault gouge is more commonly found in drill core, although the sense of movement is generally not observed.
Because many of the individual fault strands have been reactivated multiple times throughout the Proterozoic, movement during the Kuparr Tectonic Event has principally been identified by the K–Ar dating of authigenic illite clay from fault rock and slickenline samples, and so the known spatial extent of deformation across the Capricorn Orogen is limited by the number of dated samples. Older fault movements have been recorded by K–Ar dating during the 1321–1171 Ma Mutherbukin Tectonic Event and the 1026–954 Ma Edmundian Orogeny. | | | | | | Geochronology | | | Kuparr Tectonic Event | Maximum age | Minimum age | Age (Ma) | 931 | 749 | Age | Tonian | Tonian | Age data type | Inferred | | References | | |
| The age of faulting during the Kuparr Tectonic Event is currently constrained by K–Ar dating of authigenic illite clay in fault gouge and slickenlines developed within siliciclastic sedimentary rocks of the Edmund and Collier Groups. From the eastern part of the Edmund Basin the dated fault rock samples include whole rock samples that contain slickenlines on exposed fault surfaces, and the <2 µm size illite clay fraction that was extracted fault gouge samples contained within drill core (Abra Mining drill hole AB62). Sample collection was centred on the Mount Vernon Fault System (MVFS) along the northern margin of the Edmund Basin and the Quartzite Well Fault System (QWFS) more central to the basin.
A slickenline whole rock sample from the Godfrey Fault of the MVFS yielded a date of 874 ± 17 Ma (GSWA 189262), as well as some older dates of c. 1506, 1157 and 1171 Ma (Zwingmann et al., 2012). Samples from the QWFS indicated movement mostly during the Kuparr Event. A slickenline whole rock sample from Tony’s Fault yielded a date of 869 ± 19 Ma (GSWA 189270), and fault gouge samples from the main Quartzite Well Fault (GSWA 210013) and from Tom Hunts Fault (GSWA 210012) yielded dates of 931 ± 19 Ma and 799 ± 16 Ma, respectively. Additionally, five fault gouge samples from the Six Mile Creek Fault of the QWFS, were selected from drillcore AB62 close to the Abra deposit in the central part of the basin. The samples yielded dates of 914 ± 18 Ma (GSWA 189287), 880 ± 17 Ma (GSWA 189286), 813 ± 11 Ma (GSWA 189277), 797 ± 16 Ma (GSWA 189279), and 794 ± 16 Ma (GSWA 189278). These dates indicate individual movement events on the QWFS between c. 931 and 794 Ma.
A 960–820 Ma event was proposed by Occhipinti (2007) who applied ⁴⁰Ar/³⁹Ar dating of muscovite and biotite in the southern part of the Gascoyne Province, in basement rocks local to the Deadman Fault, to constrain greenschist facies metamorphism and the exhumation history. A wide range of dates were reported, and those between c. 960 and 820 Ma were identified as representing cooling through a closure temperature of 270–350°C. The robustness of this series of total fusion ages cannot be properly assessed, especially since many step-heated samples show sign of Argon disturbance.
| | | Tectonic Setting | The 931–794 Ma Kuparr Tectonic Event, marks a previously unidentified period of intracontinental reactivation within the upper crustal rocks of the Capricorn Orogen. The Orogen is the Proterozoic collisional zone between the Archean Pilbara and Yilgarn Cratons and has experienced over one billion years of subsequent reworking and reactivation (Johnson et al., 2017). The Kuparr Tectonic Event may correlate with an interpreted period of greenschist facies metamorphism and exhumation in the Gascoyne Province basement rocks (Occhipinti, 2007) although dating in the basement is not well constrained. | | | | References | Johnson, SP, Korhonen, FJ, Kirkland, CL, Cliff, JB, Belousova, EA and Sheppard, S 2017, An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization: Lithos, v. 268–271, p. 76–86. | Korhonen, FJ, Johnson, SP, Fletcher, IR, Rasmussen, B, Sheppard, S, Muhling, JR, Dunkley, DJ, Wingate, MTD, Roberts, MP and Kirkland, CL 2015, Pressure–temperature–time evolution of the Mutherbukin Tectonic Event, Capricorn Orogen: Geological Survey of Western Australia, Report 146, 64p. View Reference | 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 | 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. | Zwingmann, H, Wingate, MTD, Cutten, HN, Todd, AJ and Kirkland, CL 2012, 189218.1: siltstone fault-rock, Brumby Creek; Geochronology Record 1117: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference |
| | | | Recommended reference for this publication | Cutten, HNC and Johnson, SP 2022, Kuparr Tectonic Event (KU): 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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