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| | | | DMcB Martin | | | | | Event type | tectonic: accretionary orogeny | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | orogen: collisional orogen | Metamorphic facies | | Metamorphic/tectonic features | –– |
| | | Summary | The 2215–2145 Ma Ophthalmia Orogeny is the oldest recognized tectonic event within the Paleoproterozoic Capricorn Orogen, and is interpreted to record the accretion of the Glenburgh Terrane to the southern margin of the Pilbara Craton. Although the suture between these two cratonic blocks is not exposed, it is interpreted from reflection seismic data to be roughly coincident with the Lyons River Fault in the Gascoyne Province. The onset of deformation related to the Ophthalmia Orogeny is characterized by flexural subsidence of the southern margin of the Pilbara Craton, and deposition of the Turee Creek and Shingle Creek Groups in a foreland basin. This basin has been referred to as either the Turee Creek Basin or McGrath Trough, although the former is now the preferred nomenclature.
Deformation associated with the closure of the Turee Creek foreland basin was responsible for most of the regional and outcrop-scale folding that affects the underlying Hamersley and Fortescue Groups in the central part of the southern Pilbara region, as well as affecting the Turee Creek and Shingle Creek Groups. Two discrete periods of Ophthalmian folding have been recognised in the Hamersley Group based on fold style and overprinting relationships. However, five periods of Ophthalmian folding are recognized in the overlying Turee Creek Basin, where absolute timing with respect to dated mafic sills and dykes, and relative timing with respect to intrabasinal unconformities, suggests that all folding took place between c. 2208 and 2031 Ma. Metamorphism associated with the Ophthalmia Orogeny reaches a maximum of greenschist facies in the Fortescue Group, and is lower in younger parts of the succession. Deformation related to the Ophthalmia Orogeny decreases in intensity from south to north, along with a decrease in the age of the associated thermal affects. | | | Distribution | The physical effects of the Ophthalmia Orogeny are restricted to rocks older than c. 2031 Ma in the southern Pilbara region of Western Australia. This includes the Shingle Creek, Turee Creek, Hamersley and Fortescue Groups, although the thermal effects are much more widespread and extend far into the Pilbara Craton basement to the north (Rasmussen et al., 2005). Deformation can be traced via the presence of east–west and northwest–southeast trending folds that affect these stratigraphic units, although overprinting by co-axial folds and faulting related to the younger Capricorn Orogeny complicates interpretations in the southernmost part along the Nanjilgardy Fault System. The distribution of the Ophthalmia Orogeny can be traced through the presence of two distinctive sets of regional folds (e.g. Powell and Horwitz, 1994; Powell et al., 1999; Taylor et al., 2001), and more cryptically by the thermal effects as reflected in various isotopic systems (e.g. Blockley et al., 1980; Nelson et al., 1992; Alibert and McCulloch, 1993; Rasmussen et al., 2005). The older folds trend roughly east–west, are generally upright and open to tight, but with locally overturned steep-dipping limbs, and are known regionally as D2 folds (e.g. Powell et al., 1999; Taylor et al., 2001). Examples of regional D2 folds include the Jeerinah Anticline on FARQUHAR and JEERINAH, the Brockman and Hardey Synclines on HARDEY and ROCKLEA (Martin, 2020), the Wyloo Anticline on WYLOO and HARDEY, the Rocklea Anticline on ROCKLEA, the Turner Syncline on ROCKLEA and MOUNT LIONEL, the Milli Milli Anticline on MOUNT LIONEL and MOUNT BRUCE, the Turee Creek Syncline and Alligator Anticline on SNOWY MOUNT, the Weeli Wolli Anticline and Yandicoogina Syncline on MUNJINA and WEELI WOLLI, and the Wonmunna Anticline on GOVERNOR and OPHTHALMIA. The northwesterly trending regional D3 folds, also known as 'Panhandle folds' (e.g. Taylor et al., 2001; Dalstra, 2005, 2014), are of smaller wavelength and less obvious at the map scale than D2 folds, but are well-developed on the limbs of the Jeerinah Anticline and Brockman Syncline where they are also responsible for reorientation of the hinges of these folds into a more-northwesterly trend at their western extremity. Northwesterly trending D3 folds are less evident in the eastern Hamersley Basin, where they are mainly developed as outcrop-scale folds or as reorientations of D2 fold axes, such as in the Alligator Anticline on SNOWY MOUNT, or as upright open folds that are broadly coaxial with the D2 event and are attributed to progressive deformation (Cawood and Hollingsworth, 2002). The northernmost limit of Ophthalmian folding appears to be the Chichester Range, although hydrothermal monazite and xenotime ages attributable to the Ophthalmia Orogeny have been recorded as far north as the areas around Whim Creek and Marble Bar (Rasmussen et al., 2005). | | | Description | The Capricorn Orogen was originally interpreted to be the product of a single, protracted collision between the Pilbara and Yilgarn Cratons (Tyler and Thorne, 1990; Thorne and Seymour, 1991), which produced an older Ophthalmia fold belt and a younger Ashburton fold belt. The fold belt terminology has fallen out of favour since it was recognised that the Ashburton fold belt is the product of the 1820–1770 Ma Capricorn Orogeny, and that the Capricorn Orogen is the product of five orogenic events (e.g. Sheppard, 2004; Cawood and Tyler, 2004; Johnson et al., 2010). Also, it now appears that Ashburton-aged folds are rare or absent north of the Nanjilgardy Fault Zone, which probably acted as a strain barrier during the Capricorn Orogeny. Consequently, the 2215–2145 Ma Ophthalmia Orogeny (Rasmussen et al., 2005), which produced the Ophthalmia fold belt, is now recognised as the oldest tectonic event within the Capricorn Orogen (Powell and Horwitz, 1994; Powell et al., 1999), and is interpreted to record the collision of the Glenburgh Terrane with the southern margin of the Pilbara Craton (Sheppard, 2004; Martin and Morris, 2010; Johnson et al., 2010, 2011). Although the suture between these two cratonic blocks is not exposed, it is interpreted from reflection seismic data to be roughly coincident with the Lyons River Fault in the Gascoyne Province (Johnson et al., 2013). The onset of deformation related to the Ophthalmia Orogeny is characterised by flexural subsidence of the southern margin of the Pilbara Craton, and deposition of the Turee Creek and Shingle Creek Groups in a foreland basin. This basin has been referred to as either the Turee Creek Basin (e.g. Krapež, 1999) or McGrath Trough (e.g. Horwitz, 1982; Martin et al., 2000; Martin and Morris, 2010), although the former is now the preferred nomenclature (Martin, 2020).
Deformation associated with the closure of the Turee Creek Basin was responsible for most of the regional and outcrop-scale folding that affects the underlying Hamersley and Fortescue Groups in the central part of the southern Pilbara region, as well as affecting the Turee Creek and Shingle Creek Groups. Three discrete periods of regional-scale folding have been recognised in the Hamersley Group (e.g. Tyler, 1991; Powell and Horwitz, 1994; Taylor et al. 2001; Morris and Kneeshaw, 2011) based on fold style and overprinting relationships, which can be attributed to the Ophthalmia Orogeny. Five periods of Ophthalmian folding have also been identified in the overlying Turee Creek Basin, based on their relationship to intrabasinal unconformities (Martin, 2020). The oldest fold event to have affected the Hamersley and Fortescue Groups is the locally preserved D1 event, which is restricted to high-strain zones in specific stratigraphic horizons, and is refolded by later events. Although the absolute timing and tectonic significance of D1 is unclear, overprinting relationships and absolute timing with respect to dated mafic sills and dykes, and relative timing with respect to intrabasinal unconformities, suggests that the majority of the deformation associated with D2 and D3 took place between c. 2208 and 2031 Ma (Müller et al., 2005; Martin and Morris, 2010; Martin, 2020) and can be ascribed to the Ophthalmia Orogeny.
Fold styles and overprinting relationships differ markedly between the east and west Hamersley Basin. East of about 118.5° longitude, broadly east–west trending, regional D2 folds are asymmetric, non-cylindrical, tight to elastica with overturned, steeply dipping limbs that are locally associated with small thrust faults, whereas D3 folds are open and upright and broadly coaxial with D2 (e.g. Cawood and Hollingsworth, 2002; Morris and Kneeshaw, 2011). These D3 folds have commonly been interpreted as Ashburton folds related to the Capricorn Orogeny (e.g. Powell et al., 1999), but they all predate the c. 2008 Ma Panhandle Dolerite (P_-_pa-od). West of 118.5° longitude, regional D2 folds tend to be open and upright and are non-cylindrical, forming large-scale dome-and-basin structures that are characteristic of the outcrop pattern of the western Hamersley Basin. In this area, D3 folds trend northwest and are responsible for outcrop-scale refolding of D2 fold limbs and larger scale reorientation of D2 fold axes. These folds are commonly referred to as 'Panhandle folds' and have been ascribed to a separate 'Panhandle orogeny' that is interpreted to post-date the Ophthalmia Orogeny and pre-date the Capricorn Orogeny (e.g. Taylor et al., 2001; Dalstra, 2014). Northwest-trending D3 folds also predate the c. 2008 Ma Panhandle Dolerite, and appear to be mostly restricted to the western Hamersley Basin, suggesting that they are instead a response to stress reorientation and progressive deformation during the Ophthalmia Orogeny.
Metamorphism associated with the Ophthalmia Orogeny reaches a maximum of greenschist facies in the Fortescue Group, and is lower in younger parts of the succession. The metamorphic grade within the Fortescue Group also increases from north to south, towards the orogenic front (Smith et al., 1982). A southward increase in the magnetite/hematite ratio of Hamersley Group BIFs has been ascribed to a higher metamorphic grade in the south, closer to the orogenic hinterland (Ewers and Morris, 1981). Deformation related to the Ophthalmia Orogeny decreases in intensity from south to north, along with a decrease in the age of the associated thermal affects (e.g. Rasmussen et al., 2005).
| | | | | | Geochronology | | | Ophthalmia Orogeny | Maximum age | Minimum age | Age (Ma) | 2215 | 2145 | Age | Paleoproterozoic | Paleoproterozoic | Age data type | Inferred | | References | | |
| The age of the Ophthalmia Orogeny can be constrained in terms of its relative age with respect to other dated units and events in the region, and by direct U–Pb dating of authigenic monazite and xenotime that are interpreted to have grown within the main cleavage. Direct dating indicates that metamorphic fluid flow related to the Ophthalmia Orogeny took place between c. 2215 and 2145 Ma (Rasmussen et al., 2005), although this age range does not include initiation of the Turee Creek Basin, which is interpreted to have formed in response to flexural loading of the Pilbara Craton in the orogenic foreland (Blake and Barley, 1992; Powell and Horwitz, 1994; Powell et al., 1999; Krapež, 1999; Martin et al., 2000; Martin and Morris, 2010).
The stratigraphic record of the onset of flexural subsidence in the Turee Creek Basin is controversial, but is widely regarded to have been initiated with the deposition of either the Boolgeeda Iron Formation or the Turee Creek Group. In both cases, the maximum age is constrained by the youngest depositional age within the Woongarra Rhyolite, which is c. 2444 Ma (GSWA 195892, Wingate et al., 2018), but may be as young as c. 2420 Ma (Martin, 2020). Within the Turee Creek Basin, sills belonging to the c. 2208 Ma Balgara Dolerite (Müller et al., 2005) were intruded during deformation of the Turee Creek Basin, as indicated by their relationship to local and regional unconformities (Martin and Morris, 2010; Martin, 2020). The minimum relative age is constrained by the fact that northwest-trending dykes of the c. 2008 Ma Panhandle Dolerite (Müller et al., 2005; Martin, 2020) post-date all folding that is attributable to the Ophthalmia Orogeny. Furthermore, the poorly preserved Wooly Formation (Martin, 2020), which has a maximum depositional age of 2031 ± 6 Ma (Müller et al., 2005), does not appear to have been affected by Ophthalmian deformation. These relative constraints suggest that the full range of deformation related to the Ophthalmia Orogeny may span the interval from c. 2420 to ≥2031 Ma, which includes the main metamorphic event at 2215–2145 Ma, as well as an older cryptic event at 2430–2400 Ma (Rasmussen et al., 2005; Fielding et al., 2017). | | | Tectonic Setting | Significant recent advances have been made in the understanding of the tectonic evolution of the northern margin of the Capricorn Orogen, which was originally thought to be the product of a single protracted collision between the Pilbara and Yilgarn Cratons (e.g. Tyler and Thorne, 1990; Thorne and Seymour, 1991). This interpretation suggested southwards-directed subduction beneath the Yilgarn Craton formed a peripheral foreland basin on the southern margin of the Pilbara Craton, mainly recorded by the Wyloo and Capricorn Groups (Ashburton Basin). Subsequent work by Blake and Barley (1992) and Krapež (1999) invoked subduction beneath the Pilbara Craton and formation of the Turee Creek Basin as a retroarc foreland basin. Although no unequivocal record of a magmatic arc of the correct age has yet been found south of the Pilbara Craton, two important lines of evidence point to its potential existence. The first is the identification of a bimodal large igneous province related to BIF deposition in the Hamersley Group (Barley et al., 1997), represented by the Woongarra Rhyolite and coeval dolerite sills in the Weeli Wolli Formation, and the second is the significant contribution of volcaniclastic material to the shales of the Hamersley Group (e.g. Pickard et al., 2002; Trendall et al., 2004). This interpretation was extended by Martin and Morris (2010), who showed that the Cheela Springs Basalt and cogenetic Balgara Dolerite could have been derived from a subduction-modified mantle source. In the absence of evidence for an alternative collisional architecture, the Turee Creek Basin is widely regarded as a retro-arc foreland basin (e.g. Blake and Barley, 1992; Powell and Horwitz, 1994; Martin et al., 2000; Martin, 2020), and this collision has recently been interpreted to have involved the accretion of the Glenburgh Terrane to the southern margin of the Pilbara Craton during the Ophthalmia Orogeny (Sheppard, 2004; Martin and Morris, 2010; Johnson et al., 2011). Although there is no exposed suture zone, regional reflection seismic data has imaged a major south-dipping structural corridor in the middle to lower crust of the Capricorn Orogen (the Lyons River Fault) that separates two seismically distinct crustal blocks (Johnson et al., 2013). Additionally, the age, oxygen and hafnium isotopic composition of xenocrystic zircons within younger granitic rocks in the northern part of the Gascoyne Province identify a source region deep in the crust that could have formed within an Ophthalmian-aged magmatic arc (Johnson et al., 2017a,b). These data support the original interpretation of south-directed subduction of the Pilbara Craton.
Alternative interpretations dispute the tectonogenetic relationship between the Turee Creek and Shingle Creek Groups, instead favouring an extensional tectonic setting for the Shingle Creek Group (e.g. Krapež, 1999; Taylor et al., 2001; Müller et al., 2005; Krapež et al., 2017) following an interpreted hiatus of c. 370 Ma. The foreland basin interpretation has also been disputed by Van Kranendonk et al. (2015) who instead interpret an extensional intracratonic setting for the basal Turee Creek Group. | | | | References | Alibert, C and McCulloch, MT 1993, Rare earth element and neodymium isotopic compositions of the banded iron formations and associated shales from Hamersley, Western Australia: Geochimica et Cosmochimica Acta, v. 57, p. 187–204. | Barley, ME, Pickard, AL and Sylvester, PJ 1997, Emplacement of a large igneous province as a possible cause of banded iron-formation 2.45 billion years ago: Nature, v. 385, p. 55–58. | Blake, TS and Barley, ME 1992, Tectonic evolution of the Late Archaean to Early Proterozoic Mount Bruce megasequence set, Western Australia: Tectonics, v. 11, p. 1415–1425. | Blockley, JG, Trendall, AF, de Laeter, JR and Libby, WG 1980, Two "anomalous" isochrons from the vicinity of Newman, in Annual report for the year 1979 edited by Brown, WC: Geological Survey of Western Australia, Perth, Annual Report 1979, p. 93–96. View Reference | Cawood, PA and Hollingsworth, DA 2002, Resolution of the subsurface structure of the Hamersley Province by multi-channel seismic reflection: MERIWA Project M282: Minerals and Energy Research Institute of Western Australia, Report 228. | Cawood, PA and Tyler, IM 2004, Assembling and reactivating the Proterozoic Capricorn Orogen: Lithotectonic elements, orogenies, and significance: Precambrian Research, v. 128, p. 201–218. | Dalstra, HJ 2005, Structural controls of bedded iron ore in the Hamersley Province, Western Australia — An example from the Paraburdoo Ranges, in Iron Ore 2005, Fremantle, 19–21 September: Australian Institute of Mining and Metallurgy; Conference proceedings vol. 8, p. 49–55. | Dalstra, HJ 2014, Structural evolution of the Mount Wall region in the Hamersley province, Western Australia and its control on hydrothermal alteration and formation of high-grade iron deposits: Journal of Structural Geology, v. 67, p. 268–292, doi:10.1016/j.jsg.2014.03.005. | Ewers, WE and Morris, RC 1981, Studies on the Dales Gorge Member of the Brockman Iron Formation, Western Australia: Economic Geology, v. 76, p. 1929–1953. | Fielding, IOH, Johnson, SP, Zi, J, Rasmussen, B, Muhling, JR, Dunkley, DJ, Sheppard, S, Wingate, MTD and Rogers, JR 2017, Using in situ SHRIMP U-Pb monazite and xenotime geochronology to determine the age of orogenic gold mineralization: An example from the Paulsens Mine, southern Pilbara Craton: Economic Geology, v. 112, p. 1205–1230. | Horwitz, RC 1982, Geological history of the early Proterozoic Paraburdoo Hinge Zone, Western Australia: Precambrian Research, v. 19, no. 2, p. 191–200. | Johnson, SP, Korhonen, FJ, Kirkland, CL, Cliff, JB, Belousova, EA and Sheppard, S 2017, From subduction magmatism to cratonization: An isotopic perspective from the Capricorn Orogen, in GSWA 2017 extended abstracts: promoting the prospectivity of Western Australia: Geological Survey of Western Australia, Record 2017/2, p. 9–13. View Reference | Johnson, SP, Korhonen, FJ, Kirkland, CL, Cliff, JB, Belousova, EA and Sheppard, S 2017a, An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization: Lithos, v. 268–271, p. 76–86. | Johnson, SP, Sheppard, S, Rasmussen, B, Wingate, MTD, Kirkland, CL, Muhling, JR, Fletcher, IR and Belousova, E 2010, The Glenburgh Orogeny as a record of Paleoproterozoic continent-continent collision: Geological Survey of Western Australia, Record 2010/5, 54p. View Reference | Johnson, SP, Sheppard, S, Rasmussen, B, Wingate, MTD, Kirkland, CL, Muhling, JR, Fletcher, IR and Belousova, EA 2011, Two collisions, two sutures: punctuated pre-1950 Ma assembly of the West Australian Craton during the Ophthalmian and Glenburgh Orogenies: Precambrian Research, v. 189, no. 3–4, p. 239–262, doi:10.1016/j.precamres.2011.07.011. | Johnson, SP, Thorne, AM, Tyler, IM, Korsch, RJ, Kennett, BLN, Cutten, HN, Goodwin, J, Blay, OA, Blewett, RS, Joly, A, Dentith, MC, Aitken, ARA, Holzschuh, J, Salmon, M, Reading, A, Heinson, G, Boren, G, Ross, J, Costelloe, RD and Fomin, T 2013, Crustal architecture of the Capricorn Orogen, Western Australia and associated metallogeny: Australian Journal of Earth Sciences, v. 60, no. 6–7, p. 681–705, doi:10.1080/08120099.2013.826735. | 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, Müller, SG, Fletcher, IR and Rasmussen, B 2017, A tale of two basins? Stratigraphy and detrital zircon provenance of the Paleoproterozoic Turee Creek and Horseshoe Basins of Western Australia: Precambrian Research, v. 294, p. 67–90. | Martin, DMcB 2020, Geology of the Hardey Syncline — The key to understanding the northern margin of the Capricorn Orogen: Geological Survey of Western Australia, Report 203, 62p. View Reference | Martin, DMcB and Morris, PA 2010, Tectonic setting and regional implications of ca. 2.2 Ga mafic magmatism in the southern Hamersley Province, Western Australia: Australian Journal of Earth Sciences, v. 57, no. 7, p. 911–931. | Martin, DMcB, Powell, CMcA and George, AD 2000, Stratigraphic architecture and evolution of the early Paleoproterozoic McGrath Trough, Western Australia: Precambrian Research, v. 99, p. 33–64. | Morris, RC and Kneeshaw, M 2011, Genesis modelling for the Hamersley BIF-hosted iron ores of Western Australia: A critical review: Australian Journal of Earth Sciences, v. 58, p. 417–451, doi:10.1080/08120099.2011.566937. | Müller, SG, Krapež, B, Barley, ME and Fletcher, IR 2005, Giant iron-ore deposits of the Hamersley province related to the breakup of Paleoproterozoic Australia: new insights from in situ SHRIMP dating of baddeleyite from mafic intrusions: Geology, v. 33, no. 7, p. 577–580, 4p., doi:10.1130/G21482.1. | Nelson, DR, Trendall, AF, de Laeter, JR, Grobler, NJ and Fletcher, IR 1992, A comparative study of the geochemical and isotopic systematics of late Archaean flood basalts from the Pilbara and Kaapvaal cratons: Precambrian Research, v. 54, p. 231–256. | Pickard, AL 2002, SHRIMP U-Pb zircon ages of tuffaceous mudrocks in the Brockman Iron Formation of the Hamersley Range, Western Australia: Australian Journal of Earth Sciences, v. 49, no. 3, p. 491–507. | 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. | Powell, CMcA, Oliver, NHS, Li, ZX, Martin, DMcB and Ronaszeki, J 1999, Synorogenic hydrothermal origin for giant Hamersley iron oxide ore bodies: Geology, v. 27, no. 2, p. 175–178, doi:10.1130/0091-7613(1999)027<0175:SHOFGH>2.3.CO;2. | Rasmussen, B, Fletcher, IR and Sheppard, S 2005, Isotopic dating of the migration of a low-grade metamorphic front during orogenesis: Geology, v. 33, p. 773–776. | 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 | Smith, RE, Perdrix, JL and Parks, TC 1982, Burial Metamorphism in the Hamersley Basin, Western Australia: Journal of Petrology, v. 23, no. 1, p. 75–102, doi:10.1093/petrology/23.1.75. | Taylor, D, Dalstra, HJ, Harding, AE, Broadbent, GC and Barley, ME 2001, Genesis of high-grade hematite orebodies of the Hamersley Province, Western Australia: Economic Geology, v. 96, no. 4, p. 837–873, doi:10.2113/gsecongeo.96.4.837. | Thorne, AM and Seymour, DB 1991, Geology of the Ashburton Basin, Western Australia: Geological Survey of Western Australia, Bulletin 139, 141p. View Reference | Trendall, AF, Compston, W, Nelson, DR, de Laeter, JR and Bennett, VC 2004, SHRIMP zircon ages constraining the depositional chronology of the Hamersley Group, Western Australia: Australian Journal of Earth Sciences, v. 51, no. 5, p. 621–644. | Tyler, IM 1991, The geology of the Sylvania Inlier and the southeast Hamersley Basin: Geological Survey of Western Australia, Bulletin 138, 108p. 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. | Van Kranendonk, MJ, Mazumder, R, Yamaguchi, KE, Yamada, K and Ikehara, M 2015, Sedimentology of the Paleoproterozoic Kungarra Formation, Turee Creek Group, Western Australia: A conformable record of the transition from early to modern Earth: Precambrian Research, v. 256, p. 314–343. | Wingate, MTD, Lu, Y, Kirkland, CL and Johnson, SP 2018, 195892.1: rhyodacite, Woongarra Pool; Geochronology Record 1453: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference |
| | | | Recommended reference for this publication | Martin, DMcB 2022, Ophthalmia Orogeny (OP): 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 14 January 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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