|
|
| | | | | | | | | | | | | | | | | | | | | | | | Department of Mines, Industry Regulation and Safety |
| | | | Geological Survey of Western Australia |
| | | | | | | | | |
|
|
|
| | | North Pilbara Orogeny (PCN) | AH Hickman | | | | | Event type | tectonic: orogeny | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | orogen: collisional orogen | Metamorphic facies | | Metamorphic/tectonic features | –– |
| | | Summary | The 2955–2919 Ma North Pilbara Orogeny was the final tectonic event in the 300 my evolution of the Central Pilbara Tectonic Zone. Deformation was driven by collision between the Pilbara Craton and a plate converging from the northwest. As the northwestern plate was subducted under the northwestern Pilbara Craton the Mallina Basin was compressed and mafic and felsic igneous units of the Sisters Supersuite were intruded into it. The effects of the regional compression also extended west and east of the Mallina Basin.
Due to the regional extent of the North Pilbara Orogeny the thicknesses and rigidities of the crustal units affected by it varied. Consequently, the timing and styles of deformation differed across the northern Pilbara Craton, rendering it impossible to apply one particular deformation series to all areas of the region. In the northwestern Pilbara, three main stages are recognized, whereas in the eastern Pilbara only two stages are represented. Structural evidence indicates that convergence was partly oblique and that regional stress fields changed during the orogeny.
The first major structures in the Mallina Basin were northerly to northeasterly trending tight, upright and locally overturned folds that formed between 2955 and 2948 Ma. A steep axial plane schistosity cuts across refolded pre-2955 Ma folds. The second stage in the northwestern Pilbara took place between 2940 and 3930 Ma and produced major northeasterly trending, folds such as the Roebourne Synform and Prinsep Dome. The folds are oblique to regional-scale sinistral strike-slip faults and interpreted to be transpressional structures formed under compression from the north. The final stage of the orogeny in the northwestern Pilbara took place at c. 2920 Ma and involved dextral movement along pre-existing shear zones. This suggests a northwesterly to southeasterly compression. Additional local deformations are recorded in the Whim Creek area and in the Sholl Terrane.
| | | Distribution | Deformation and metamorphism of the North Pilbara Orogeny are widespread in the northwestern Pilbara Craton (Hickman, 2016) and extend well into western and northern parts of the east Pilbara Craton (Hickman, 2021). The 2954−2919 Ma Sisters Supersuite is contemporaneous with the orogeny, and intruded areas as far east as the Shaw Dome (TAMBOURAH and SPLIT ROCK) (Van Kranendonk et al., 2004, 2006). However, most deformation of the orogeny is preserved in the Central Pilbara Tectonic Zone, where the Croydon Group contains numerous large folds and shear zones. | | | Description | The North Pilbara Orogeny (Van Kranendonk et al., 2006) was a major event of deformation, metamorphism and granitic intrusion concentrated in the Central Pilbara Tectonic Zone (Hickman, 2016), but also extending west into the Karratha Terrane and east into the East Pilbara Terrane. The deformation and metamorphism of the orogeny were recognized from Geological Survey of Western Australia mapping in the 1970s (Hickman, 1981), but the event was not named. The timing of the event was interpreted to be c. 2950 Ma, based on the age of a widespread metamorphic event detected from Pb–Pb and Rb–Sr dating (Oversby, 1976). This interpretation has proved to be essentially correct.
Detailed geological mapping and extensive U−Pb zircon geochronology between 1995 and 2005 have provided far more data on the orogeny. A study of the Mallina Basin (Smithies et al., 2001) resulted in the conclusion that there are three phases of deformation in the Croydon Group. All available geochronology indicates that the northwestern Pilbara granitic intrusions of the Sisters Supersuite were emplaced between c. 2954 and 2924 Ma, whereas in the east Pilbara intrusion continued until c. 2919 Ma. Because deformation and granitic intrusion took place within the same tectonic setting, the age range of the supersuite closely approximates to the duration of the orogeny.
As a consequence of the regional extent of the North Pilbara Orogeny the thicknesses and rigidities of the crustal units affected were laterally variable, with the result that the timing and styles of deformation also varied. Hence, not a single particular deformation series applies across the entire northern Pilbara Craton. In the northwestern Pilbara, three main stages are recognized, whereas in the eastern Pilbara only two stages are represented. Structural evidence, including changes in the sense of movement along major strike-slip faults, indicates that convergence was oblique, but regional stress fields changed during the orogeny.
The first event of the North Pilbara Orogeny took place between c. 2955 and c. 2948 Ma. Major folds in the Mallina Basin include the Powereena and Croydon Anticlines. Smithies et al. (2001) classified these as D2 structures, whereas they were assigned to D6 in the more regional interpretation of Hickman (2016). An associated steep axial plane schistosity (S6) cuts across refolded D5 folds between the Satirist Monzogranite and Nunyerry Gap. In the Whim Creek greenstone belt, Krapež and Eisenlohr (1998) described folds and thrusts affecting the lower part of the Bookingarra Group and Hickman (2016) assigned these to D7.
The second major deformation of the orogeny (D3, Smithies et al., 2001; D8, Hickman, 2016) was widespread across the northwestern Pilbara and produced major northeasterly trending folds, such as the Roebourne Synform, Prinsep Dome, Cleaverville Syncline, Bradley Syncline and Whim Creek Anticline. These folds are obliquely oriented to major sinistral strike-slip faults and shear zones, and are transpressional folds formed under compression from the north or north-northwest. Large folds of this generation in the eastern Pilbara Craton include the John Bull Syncline in the Pilbara Well greenstone belt and the Goldsworthy Syncline in the Goldsworthy greenstone belt. In the Mallina Basin. The age of these structures has been estimated at 2940−2930 Ma (Smithies et al., 2001; Hickman, 2016).
An apparently local third event of deformation is present in the Sholl Terrane east and west of the Maitland Shear Zone (Hickman, 2001). Here, a steeply inclined tectonic foliation (S9, Hickman, 2016) cuts northeasterly trending D8 folds. The eastern side of the Cherratta granitic complex is dominated by the northerly to southerly striking S9. Some shear zones within the area deformed by D9 include granites, containing zircons dated at c. 2944 and c. 2925 Ma. This suggests that the third event in the orogeny took place at c. 2930 Ma (Hickman, 2016).
The final stage of the orogeny took place at c. 2920 Ma and included dextral movement on pre-existing major shear zones. (D10, Hickman, 2016). U−Pb zircon dating close to the Sholl Shear Zone has revealed a metamorphic disturbance event at about 2920 Ma (GSWA 118976, Nelson, 1997; Krapež and Eisenlohr, 1998). Dextral strike-slip movement of 30 to 40 km is shown on geological maps of the Caines Well granitic complex and the Whim Creek greenstone belt (Hickman and Smithies, 2000; Hickman, 2001). Dextral movement on the east-northeasterly striking shear zone indicates northwesterly to southeasterly compression at c. 2920 Ma.
Deformation related to the North Pilbara Orogeny has also been described from the Lalla Rookh − Western Shaw Structural Corridor (Zegers, 1996; Van Kranendonk and Collins, 1998; Zegers et al., 1998; Van Kranendonk, 1998, 2000, 2003, 2008; Van Kranendonk et al., 2002, 2006; Hickman, 2021) and the Tabba Tabba Shear Zone (Beintema et al., 2001; Smithies et al., 2002; Beintema, 2003; Hickman, 2016, 2021). Both these major structures contain evidence of major sinistral strike-slip movement between 2940 and 2930 Ma, although this movement is now interpreted to have taken place along deep crustal fractures formed dating the 3280−3165 Ma East Pilbara Terrane Rifting Event (Hickman, 2021).
Van Kranendonk and Collins (1998) identified the Lalla Rookh − Western Shaw Structural Corridor as a corridor of linked fold structures and shear zones, developed in response to c. 2950 Ma sinistral transpression. The timing of the compression and deformation was subsequently revised to between 2940 and 2930 Ma (Van Kranendonk et al., 2002; Van Kranendonk, 2008). The structural corridor is exposed over a northerly to southerly strike length of approximately 150 km and varies in width from a single shear zone between the Carlindi and Muccan Domes to 35 km between the Shaw and Yule Domes. The western boundary fault is the Lalla Rookh − Western Shaw Fault, whereas along the western margin of the Shaw granitic complex the eastern boundary fault is the Mulgandinnah Shear Zone.
The Tabba Tabba Shear Zone defines the southeastern boundary of the Central Pilbara Tectonic Zone. The zone is up to 3 km wide and contains intensely faulted and sheared intrusive, volcanic and sedimentary rocks. In the northeast it is represented by the Pardoo Fault and in the far southwest it is the faulted northwestern margin of the Pilbara Well greenstone belt. Structural studies of the TTSZ have reported evidence of a major c. 2940 Ma strike-slip movement (Beintema et al., 2001, 2003; Hickman et al., 2001; Smithies et al., 2002; Beintema. 2003). Mesoscopic structures, such as C−S fabrics and rotated feldspar phenocrysts, indicate sinistral displacement. Additionally, northwesterly plunging mineral and stretching lineations indicate normal movement consistent with the juxtaposition of the Croydon Group in the Mallina Basin against Paleoarchean rocks of the East Pilbara Terrane to the southeast.
| | | | | | Geochronology | | | North Pilbara Orogeny | Maximum age | Minimum age | Age (Ma) | 2955 | 2919 | Age | Mesoarchean | Mesoarchean | Age data type | Inferred | | References | | |
| Geological evidence Geological evidence indicates that the North Pilbara Orogeny was closely contemporaneous with intrusion of the Sisters Supersuite. The maximum age of the Sisters Supersuite is indicated by a date of 2954 ± 4 Ma (GSWA 142935, Nelson, 2000) on hornblende granodiorite of the Indee Suite. Other granitic intrusions of the Indee Suite have been dated between c. 2954 and 2945 Ma (reviewed by Hickman, 2016).
A second line of evidence on the maximum age of the orogeny is based on the existence of an erosional unconformity between the Whim Creek Group and the Bookingarra Group on the northwestern margin of the Mallina Basin. This unconformity, first recognized by Pike and Cas (2002), is evidence of deformation and erosion between deposition of these groups. U–Pb zircon dating of a sedimentary unit in the Cistern Formation at the base of the Bookingarra Group suggests a maximum depositional age of 2964 ± 6 Ma (GSWA 142949, Nelson, 2000; age re-calculated by Huston et al., 2002) and the true depositional age might be substantially younger. The Kialrah Rhyolite of the Bookingarra Group has been dated at three localities and has an average age of c. 2945 Ma (see Kialrah Rhyolite). Syndepositional VMS mineralization in the Cistern Formation and Rushall Slate has been dated at c. 2950 Ma (Huston et al., 2002). The Cistern Formation unconformity is interpreted to be the same age as an unconformity within the Croydon Group in the central trough of the Mallina Basin (Hickman, 2016). Smithies et al. (2001) previously suggested this unconformity was formed at c. 2955 Ma.
The minimum age of the North Pilbara orogeny approximates to the age of dextral strike-slip movement on the Sholl Shear Zone. U−Pb zircon dating close to the Sholl Shear Zone has revealed a metamorphic disturbance event at about 2920 Ma (GSWA 118976, Nelson, 1997; Krapež and Eisenlohr, 1998). The minimum age of the Sisters Supersuite is indicated by a date of 2919 ± 3 Ma (GSWA 142883, Nelson, 1998), which is interpreted also to provide the best estimate of the minimum age of the North Pilbara Orogeny. | | | Tectonic Setting | The deformation, metamorphism and granitic intrusion during the North Pilbara Orogeny is interpreted to be directly related to plate collision and subduction on the northwestern margin of the Pilbara Craton (Hickman, 2016). Early stages of the orogeny included strike-slip faulting and transpressional folding, with local areas of extension and sedimentary deposition (Smithies et al., 1999, 2001). However, by c. 2920 Ma the Mallina Basin had become entirely closed as a result of the complete amalgamation of underlying plates of Paleoarchean continental crust and the basin had been converted into a mature orogenic belt. | | | | References | Beintema, KA 2003, Geodynamic evolution of the west and central Pilbara Craton: A mid-Archean active continental margin: Geologica Ultraiectina, Utrecht University, Utrecht, The Netherlands, PhD thesis (unpublished), 248p. | Beintema, KA, de Leeuw, GAM, White, SH and Hein, KAA 2001, Tabba Tabba shear: A crustal-scale structure in the Pilbara Craton, WA, in Extended Abstracts — 4th International Archaean Symposium, Perth, 24–28 September 2001 edited by Cassidy, KF, Dunphy, JM and Van Kranendonk, MJ: AGSO (Geoscience Australia), Record 2001/37, p. 285–287. | Hickman, AH 1981, Crustal evolution of the Pilbara Block, in Archaean Geology: Second International Symposium, Perth 1980 edited by Glover, JE and Groves, DI: Geological Society of Australia, Special Publication 7, p. 57–69. | Hickman, AH 2001, Geology of the Dampier 1:100 000 sheet: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 39p. View Reference | Hickman, AH 2016, Northwest Pilbara Craton: A record of 450 million years in the growth of Archean continental crust: Geological Survey of Western Australia, Report 160, 104p. View Reference | 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 Smithies, RH 2000, Roebourne, WA Sheet SF 50-3 (2nd edition): Geological Survey of Western Australia, 1:250 000 Geological Series. View Reference | Hickman, AH, Smithies, RH, Pike, G, Farrell, TR and Beintema, KA 2001, Evolution of the West Pilbara granite–greenstone terrane and Mallina Basin, Western Australia — a field guide: Geological Survey of Western Australia, Record 2001/16, 65p. View Reference | Huston, DL, Sun, S-S, Blewett, R, Hickman, AH, Van Kranendonk, MJ, Phillips, D, Baker, D and Brauhart, C 2002, The timing of mineralization in the Archean North Pilbara Terrain, Western Australia: Economic Geology, v. 97, p. 733–755. | Krapež, B and Eisenlohr, B 1998, Tectonic settings of Archaean (3325–2775 Ma) crustal–supracrustal belts in the West Pilbara Block: Precambrian Research, v. 88, p. 173–205. | Nelson, DR 1997, 118976.1: porphyritic dacite, Cherratta Road – Nickol River crossing; Geochronology Record 433: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 1998, 142883.1: foliated porphyritic syenogranite dyke, South of Mulgandinna Hill; Geochronology Record 352: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 2000, 142935.1: hornblende granodiorite, Wallareenya Homestead; Geochronology Record 322: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 2000, 142949.1: metasandstone, Whim Creek; Geochronology Record 299: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Oversby, VM 1976, Isotopic ages and geochemistry of Archaean acid igneous rocks from the Pilbara, Western Australia: Geochimica et Cosmochimica Acta, v. 40, no. 7, p. 817–829. | Pike, G and Cas, R 2002, Stratigraphic evolution of Archaean volcanic rock-dominated rift basins from the Whim Creek Belt, west Pilbara Craton, Western Australia, in Precambrian sedimentary environments: a modern approach to ancient depositional systems edited by Altermann, W and Corcoran, P: Blackwell Science, Oxford, UK, International Association of Sedimentologists, Special Publication 33, p. 213–234. | Smithies, RH, Champion, DC and Blewett, RS 2002, Geology of the Wallaringa 1:100 000 sheet: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 27p. View Reference | Smithies, RH, Hickman, AH and Nelson, DR 1999, New constraints on the evolution of the Mallina Basin, and their bearing on relationships between the contrasting eastern and western granite–greenstone terranes of the Archaean Pilbara Craton, Western Australia: Precambrian Research, v. 94, p. 11–28. | Smithies, RH, Nelson, DR and Pike, G 2001, Development of the Archaean Mallina Basin, Pilbara Craton, northwestern Australia; a study of detrital and inherited zircon ages: Sedimentary Geology, v. 141–142, p. 79–94. | Van Kranendonk, MJ 1998, Litho-tectonic and structural components of the North Shaw 1:100 000 sheet, Archaean Pilbara Craton, in Geological Survey of Western Australia annual review 1997–98 edited by Johnston, JF and Nowak, IR: Geological Survey of Western Australia, Perth, p. 63–70. View Reference | Van Kranendonk, MJ 2000, Geology of the North Shaw 1:100 000 sheet: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 86p. View Reference | Van Kranendonk, MJ 2003, Geology of the Tambourah 1:100 000 sheet: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 57p. View Reference | Van Kranendonk, MJ 2008, Structural geology of the central part of the Lalla Rookh – Western Shaw structural corridor, Pilbara Craton, Western Australia: Geological Survey of Western Australia, Report 103, 29p. View Reference | Van Kranendonk, MJ and Collins, WJ 1998, Timing and tectonic significance of Late Archaean, sinistral strike-slip deformation in the Central Pilbara Structural Corridor, Pilbara Craton, Western Australia: Precambrian Research, v. 88, no. 1–4, p. 207–232, doi:10.1016/s0301-9268(97)00069-7. | 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, Bagas, L, Williams, IR and Farrell, TR 2004, Event stratigraphy applied to 700 million years of Archean crustal evolution, Pilbara Craton, Western Australia, in Geological Survey of Western Australia Annual Review 2003–04 edited by Geological Survey of Western Australia, Perth, Western Australia, p. 49–61. View Reference | Zegers, TE 1996, Structural, kinematic, and metallogenic evolution of selected domains of the Pilbara granite–greenstone terrain: Geologica Ultraiectina, Utrecht University, Utrecht, the Netherlands, PhD thesis (unpublished), 208p. | Zegers, TE, de Keijzer, M, Passchier, CW and White, SH 1998, The Mulgandinnah shear zone; an Archean crustal scale strike-slip zone, eastern Pilbara, Western Australia: Precambrian Research, v. 88, p. 233–248. |
| | | | Recommended reference for this publication | Hickman, AH 2024, North Pilbara Orogeny (PCN): 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 28 May 2024. | | | | | 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 |
|
| |
|
|