|
|
| | | | | | | | | | | | | | | | | | | | | | | | Department of Mines, Industry Regulation and Safety |
| | | | Geological Survey of Western Australia |
| | | | | | | | | |
|
|
|
| | | Coonterunah Magmatic Event (PCCME) | AH Hickman | | | | | Event type | magmatic: intrusive and extrusive | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | igneous: large igneous province | Metamorphic facies | | Metamorphic/tectonic features | –– |
| | | Summary | The Coonterunah Magmatic Event, resulting from repeated mantle plume activity, formed the Warrawoona Large Igneous Province (LIP). The Coonterunah Magmatic Event commenced with eruption of the Coonterunah Subgroup although it is interpreted to encompass all ultramafic–mafic–felsic volcanic cycles of the of the 3530–3427 Ma Warrawoona Group. Because the cycles are not separated by more than about 15 Ma they were probably formed by separate pulses of plume activity within the evolution of a single plume. The eruption of felsic volcanic formations was closely contemporaneous with the intrusions of three granitic supersuites.
In each volcanic cycle, igneous activity commenced with the eruption of komatiite, followed by more widespread eruption of komatiitic basalt and tholeiite. In upper volcanic cycles of the group, eruption of thick tholeiite successions was followed by dacite and less commonly by rhyolite. Unlike the eruption of tholeiitic flood basalts which took place from numerous fractures in the crust (now represented by swarms of dolerite dykes), felsic volcanism was restricted to local felsic volcanic centres.
The exposed area of the East Pilbara Terrane is only 40 000 km², but allowing for Neoarchean and Proterozoic cover. The total area of the terrane is about 100 000 km². Between c. 3530 and 3427 Ma the Terrane was much larger because it included at least two sections of crust that were later separated as the Karratha and Kurrana Terranes during the East Pilbara Terrane Rifting Event.
The preserved stratigraphic thickness of the Warrawoona Group varies from 12 to 15 km, although the original stratigraphic thickness would have been greater. Erosional unconformities are present between some of the volcanic cycles. Assuming an average depositional thickness of 12 km, the total erupted volume of the Warrawoona Group is likely to have far exceeded 1 000 000 km³, readily meeting the accepted 100 000 km³ volume requirement for a large igneous province. | | | Distribution | The volcanic succession produced by the Coonterunah Magmatic Event is preserved in four subgroups of the Warrawoona Group: the Coonterunah Subgroup on NORTH SHAW, WODGINA, CARLINDI and SATIRIST; the Talga Talga Subgroup on MARBLE BAR, SPLIT ROCK, NORTH SHAW, COONGAN, MOUNT EDGAR and MUCCAN; the Coongan Subgroup on MARBLE BAR, MOUNT EDGAR, COONGAN, MUCCAN and SPLIT ROCK; and the Salgash Subgroup on MARBLE BAR, MOUNT EDGAR, MUCCAN, COONGAN, CARLINDI, TAMBOURAH, CORUNNA DOWNS, NULLAGINE and DE GREY. | | | Description | The Coonterunah Magmatic Event commenced abruptly at c. 3530 Ma and continued until c. 3427 Ma. The resulting volcanic succession is preserved in the four subgroups of the Warrawoona Group, in the following ascending stratigraphic order: the Coonterunah, Talga Talga, Coongan and Salgash Subgroups. The stratigraphic thickness of the Warrawoona Subgroup varies between 12 and 15 km. Presently preserved thicknesses are minimum depositional thicknesses, because the stratigraphic bases of the contemporaneous Coonterunah and Talga Talga Subgroups are not reserved due to granitic intrusion and shearing. Moreover, erosional unconformities in the succession indicate removal of parts of the succession.
All subgroups contain volcanic cycles including komatiite, komatiitic basalt and tholeiite, and except for the Talga Talga Subgroup, all contain andesite, dacite and rhyolite. The ultramafic and mafic volcanism is interpreted to have been due to mantle plume activity (Arndt et al., 2001; Van Kranendonk et al., 2002, 2006, 2007a,b; Hickman, 2004, 2011, 2012; Hickman and Van Kranendonk, 2004, 2008, 2012; Smithies et al., 2005). The felsic volcanism is mainly explained by melting of basaltic crust, although fractionation of tholeiitic magmas is also likely (Champion and Smithies, 2007).
As in later plume-related magmatic events in the East Pilbara Terrane, such as the Kelly Magmatic Event and the Emu Pool Event, the Coonterunah Magmatic Event included intrusion of granitic rocks and eruption of felsic volcanic rocks. The granitic intrusions have the compositional range of tonalite–trondhjemite–granodiorite (TTG), which most workers have attributed to the partial melting of mafic crust (Glikson et al., 1987; Collins, 1993; Smithies et al., 2003, 2009; Champion and Smithies, 2007; Gardiner et al., 2017, 2018). Due to diapiric crustal reworking and younger granitic intrusion, preservation of the 3530–3490 Ma TTG units is uncommon and fragmented, but several intrusions have been dated between 3523 and 3496 Ma (Wiemer et al., 2018; Petersson et al., 2020). Felsic volcanic rocks in the Coucal Formation of the Coonterunah Subgroup have been dated between c. 3515 Ma (sample 70601, Buick et al., 1995) and c. 3498 Ma (GSWA 168995, Nelson, 2002). Geochemical data from the felsic volcanic rocks of the Coucal Formation suggest fractionation from tholeiitic parental magmas, variably contaminated by crustal material (Smithies et al., 2007).
Although the 3530–3490 Ma felsic igneous rocks of the East Pilbara Terrane are far less well preserved than contemporaneous mafic rocks, the geochronological record of detrital zircon ages in the Pilbara Craton reveals a major peak between 3530 and 3490 Ma (Hickman, 2021). Excluding detrital zircons from large Mesoarchean sedimentary basins (which might include zircons from outside the Pilbara Craton), the database contains 1087 detrital zircon ages between 3676 and 2923 Ma. There are 300 detrital zircon ages between 3535 and 3490 Ma, indicating a sudden commencement of widespread igneous activity.
A second indication of a major magmatic event commencing at c. 3530 Ma is provided by Lu–Hf isotope data from igneous, xenocrystic and detrital zircons dated between 3795 and 3400 Ma (SHRIMP U–Pb zircon method). For 123 zircons dated between 3795 and 3538 Ma, the maximum ƐHf value was calculated at +0.9 whereas 16 of 51 3538–3490 Ma zircons have ƐHf values between +2.0 and +6.0 (Hickman, 2021). These data indicate a substantial addition of felsic magma from juvenile sources from c. 3538 Ma onwards. However, the inclusion of moderately negative ƐHf values (to –2.9) within the 3538–3490 Ma group suggest mixed sources, implying some reworking of older crust (Hickman, 2021).
In summary, the Coonterunah Magmatic Event involved volcanism and igneous intrusion related to the arrival of a mantle plume beneath the Pilbara Craton at c. 3530 Ma. Lu-Hf isotope data suggest a mix of magma sources that included direct derivation from a depleted 3530 Ma mantle and partial melting of older crust. The abrupt change from chondritic to evolved ƐHf values prior to 3538 Ma to strongly positive ƐHf values from c. 3538 Ma onwards is analogous to a change that took place during rifting and breakup of the East Pilbara Terrane 300 Ma later. The c. 3235 Ma igneous zircons of the Cleland Supersuite have mainly chondritic to negative ƐHf values, whereas after the continental breakup of the East Pilbara Terrane many zircons of the 3199–3175 Ma Mount Billroth Supersuite record strongly positive ƐHf values. The analogy suggests that the Coonterunah Magmatic Event included not only plume-related melting of the mantle and the pre-3530 Ma Pilbara crust, but also deep rifting of the pre-3530 Ma crust.
Geochronology in the eastern Kaapvaal Craton of southern Africa indicates that the Onverwacht Group also originated at c. 3530 Ma, which might be interpreted to suggest that the Coonterunah Magmatic Event also affected the Kaapvaal Craton. At 3530 Ma the Kaapvaal Craton was probably on an adjacent part of the same continental crust. | | | | | | Geochronology | | | Coonterunah Magmatic Event | Maximum age | Minimum age | Age (Ma) | 3530 | 3427 | Age | Paleoarchean | Paleoarchean | Age data type | Inferred | | References | | |
| The maximum age of the Coonterunah Magmatic Event coincides with the maximum deposition ages of the Coonterunah and Talga Talga Subgroups at c. 3530 Ma (Van Kranendonk et al., 2007a,b; Hickman, 2012; Hickman and Van Kranendonk, 2012). This age estimate is based on the presence of a large detrital zircon age component dated between c. 3530 and c. 3490 Ma in sedimentary formations of the East Pilbara Terrane (Hickman, 2021). Additionally, U–Pb zircon dating of felsic volcanic and granitic rocks in the East Pilbara Terrane confirms magmatic activity between 3523 and 3496 Ma. Geochronology on felsic volcanic rocks in the Coucal Formation (central formation of the subgroup) provided dates of 3515 ± 3 Ma (Buick et al., 1995) and 3518 ± 4 Ma (Green, 2001). A sample of gneissic granodiorite in the Muccan Dome was dated at 3523 ± 2 Ma (sample 18APPB05, Petersson et al., 2020).
The minimum age of the event coincides with the minimum depositional age of the Panorama Formation. A date of 3427 ± 2 Ma (GSWA 168913, Nelson, 2001) was obtained from dacite in the eastern part of the Kelly greenstone belt. This date is very reliable because it is supported by several very similar dates from felsic volcanic rocks of the Panorama Formation. | | | Tectonic Setting | Commencing at c. 3530 Ma, the Coonterunah Magmatic Event commenced the evolution of a volcanic plateau on top of 3800–3540 Ma sialic crust. This underlying crust was probably at least 30 km thick and had evolved in several stages, with peaks of magmatic activity between 3760 and 3700 Ma, at c. 3650 Ma, and from 3590 to 3570 Ma (Hickman, 2021). The Coonterunah Magmatic Event began with the eruption of the Coonterunah and Talga Talga Subgroups of the Warrawoona Group between c. 3530 and 3490 Ma. The composition of these subgroups and of the subsequent Coongan and Salgash Subgroups is consistent with mantle plume activity.
The ages of detrital zircons in Paleoarchean and Mesoarchean sedimentary rocks of the east Pilbara indicate a major eruption at c. 3530 Ma after about 30 Ma of minimal magmatic activity. Lu–Hf isotope data indicate that igneous activity between 3800 and 3540 Ma was mainly sourced from partial melting of older crust, possibly with additions from a chondritic mantle, magma generated during the Coonterunah Magmatic Event included substantial juvenile input from a depleted mantle. This change is analogous to the one which took place at c. 3220 Ma during the continental breakup of the East Pilbara Terrane when a sudden influx of juvenile magma contributed to the generation of the Mount Billroth Supersuite (Hickman, 2021). The implication is that the Coonterunah Magmatic Event was likely triggered by extension, deep rifting and possibly partial breakup of the pre-3530 Ma crust. This would be consistent with the arrival of a major mantle plume, such as the one which resulted in eruption of the Warrawoona Group.
The Paleoarchean volcanic plateau was progressively thickened by volcanism and granitic intrusion related to mantle plume activity, and it was periodically deformed by gravity-driven vertical deformation (Hickman, 2021). The Paleoarchean size of the plateau is unknown owing to the two events of continental breakup at c. 3220 Ma and between 2775 and 2501 Ma that left only a c. 100 000 km² fragment of the original East Pilbara Terrane. However, volcanism related to mantle plumes can extend across areas greater than 1 000 000 km², and suggested stratigraphic correlations between the Pilbara and Kaapvaal Cratons, imply magmatic events on the scale of large igneous provinces. | | | | References | Arndt, N, Bruzak, G and Reischmann, T 2001, The oldest continental and oceanic plateaus: geochemistry of basalts and komatiites of the Pilbara Craton, Australia, in Mantle plumes: their identification through time edited by Ernst, RE and Buchan, KL: Geological Society of America, Special Paper 352, p. 359–387. | Buick, R, Thornett, J, McNaughton, N, Smith, JB, Barley, ME and Savage, MD 1995, Record of emergent continental crust ~3.5 billion years ago in the Pilbara Craton of Australia: Nature, v. 375, p. 574–577. | Champion, DC and Smithies, RH 2007, Geochemistry of Paleoarchean granites of the East Pilbara Terrane, Pilbara Craton, Western Australia: implications for early Archean crustal growth, in Earth's oldest rocks edited by Van Kranendonk, MJ, Bennett, VC and Smithies, RH: Elsevier B.V., Burlington, Massachusetts, USA, Developments in Precambrian Geology 15, p. 369–410. | Collins, WJ 1993, Melting of Archaean silicic crust under high aH2O conditions: genesis of 3300 Ma Na-rich granitoids in the Mount Edgar Batholith, Pilbara Block, Western Australia: Precambrian Research, v. 60, p. 151–174. | Gardiner, NJ, Hickman, AH, Kirkland, CL, Lu, Y, Johnson, T and Zhao, J 2017, Processes of crust formation in the early Earth imaged through Hf isotopes from the East Pilbara Terrane: Precambrian Research, v. 297, p. 56–76, doi:10.1016/j.precamres.2017.05.004. | Gardiner, NJ, Hickman, AH, Kirkland, CL, Lu, Y, Johnson, TE and Wingate, MTD 2018, New Hf isotope insights into the Paleoarchean magmatic evolution of the Mount Edgar Dome, Pilbara Craton: Implications for early Earth and crust formation processes: Geological Survey of Western Australia, Report 181, 41p. View Reference | Glikson, AY, Davy, R, Hickman, AH, Pride, C and Jahn, B 1987, Trace elements geochemistry and petrogenesis of Archaean felsic igneous units, Pilbara Block, Western Australia: Bureau of Mineral Resources, Geology and Geophysics (Geoscience Australia), Record 1987/030, 63p. | Green, MG 2001, Early Archaean crustal evolution: evidence from ~3.5 billion year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia: University of Sydney, PhD thesis (unpublished), 277p. | Hickman, AH 2004, Two contrasting granite–greenstones terranes in the Pilbara Craton, Australia: Evidence for vertical and horizontal tectonic regimes prior to 2900 Ma: Precambrian Research, v. 131, p. 153–172. | Hickman, AH 2011, Pilbara Supergroup of the East Pilbara Terrane, Pilbara Craton: Updated lithostratigraphy and comments on the influence of vertical tectonics, in Geological Survey of Western Australia annual review 2009–10 edited by Bower, R and Johnston, J: Geological Survey of Western Australia, p. 50–59. | Hickman, AH 2012, Review of the Pilbara Craton and Fortescue Basin, Western Australia: Crustal evolution providing environments for early life: Island Arc, v. 21, p. 1–31. | Hickman, AH 2021, East Pilbara Craton: a record of one billion years in the growth of Archean continental crust: Geological Survey of Western Australia, Report 143, 187p. View Reference | Hickman, AH and Van Kranendonk, MJ 2004, Diapiric processes in the formation of Archaean continental crust, east Pilbara granite–greenstone terrane, Australia, in The Precambrian Earth: tempos and events edited by Eriksson, PG, Altermann, W, Nelson, DR, Mueller, WU and Catuneanu, O: Elsevier, Amsterdam, The Netherlands, Developments in Precambrian Geology 12, p. 54–75. | Hickman, AH and Van Kranendonk, MJ 2008, Archean crustal evolution and mineralization of the northern Pilbara Craton — a field guide: Geological Survey of Western Australia, Record 2008/13, 79p. View Reference | Hickman, AH and Van Kranendonk, MJ 2012, Early earth evolution: evidence from the 3.5 – 1.8 Ga geological history of the Pilbara region of Western Australia: Episodes, v. 35, no. 1, p. 283–297, doi:10.18814/epiiugs/2012/v35i1/028. | Nelson, DR 2001, 168913.1: dacite, Gallop Well; Geochronology Record 225: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 2002, 168995.1: altered rhyolite, Farrel Well; Geochronology Record 163: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Petersson, A, Kemp, AIS, Gray, CM and Whitehouse, MJ 2020, Formation of early Archean granite–greenstone terranes from a globally chondritic mantle: insights from igneous rocks of the Pilbara Craton, Western Australia: Chemical Geology, v. 551, article no. 119757, doi:10.1016/j.chemgeo.2020.119757. | Smithies, RH, Champion, DC and Cassidy, KF 2003, Formation of Earth's early Archaean continental crust: Precambrian Research, v. 127, p. 89–101. | Smithies, RH, Champion, DC and Van Kranendonk, MJ 2009, Formation of Paleoarchean continental crust through infracrustal melting of enriched basalt: Earth and Planetary Science Letters, v. 281, no. 3, p. 298–306. | Smithies, RH, Champion, DC, Van Kranendonk, MJ and Hickman, AH 2007, Geochemistry of volcanic rocks of the northern Pilbara Craton, Western Australia: Geological Survey of Western Australia, Report data package 104. View Reference | Smithies, RH, Van Kranendonk, MJ and Champion, DC 2005, It started with a plume — early Archaean basaltic proto-continental crust: Earth and Planetary Science Letters, v. 238, no. 3–4, p. 284–297. | Van Kranendonk, MJ, Hickman, AH, Smithies, RH and Champion, DC 2007a, Paleoarchean development of a continental nucleus: the East Pilbara Terrane of the Pilbara Craton, Western Australia, in Earth's oldest rocks edited by Van Kranendonk, MJ, Bennett, VC and Smithies, RH: Elsevier B.V., Burlington, Massachusetts, USA, Developments in Precambrian Geology 15, p. 307–337. | Van Kranendonk, MJ, Hickman, AH, Smithies, RH, Nelson, DN and Pike, G 2002, Geology and tectonic evolution of the Archaean North Pilbara terrain, Pilbara Craton, Western Australia: Economic Geology, v. 97, p. 695–732, doi:10.2113/gsecongeo.97.4.695. | Van Kranendonk, MJ, Hickman, AH, Smithies, RH, Williams, IR, Bagas, L and Farrell, TR 2006, Revised lithostratigraphy of Archean supracrustal and intrusive rocks in the northern Pilbara Craton, Western Australia: Geological Survey of Western Australia, Record 2006/15, 57p. View Reference | Van Kranendonk, MJ, Smithies, RH, Hickman, AH and Champion, DC 2007b, Secular tectonic evolution of Archaean continental crust: Interplay between horizontal and vertical processes: Terra Nova, v. 19, p. 1–38. | Wiemer, D, Schrank, CE, Murphy, DT, Wenham, L and Allen, CM 2018, Earth's oldest stable crust in the Pilbara Craton formed by cyclic gravitational overturns: Nature Geoscience, v. 11, no. 5, p. 357–361, doi:10.1038/s41561-018-0105-9. |
| | | | Recommended reference for this publication | Hickman, AH 2021, Coonterunah Magmatic Event (PCCME): 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 23 June 2021. | | | | | 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 |
|
| |
|
|