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| | | | Geological Survey of Western Australia |
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| | | Capricorn Orogeny D1n/M1n (CCD1) | SP Johnson, S Sheppard, AM Thorne, and FJ Korhonen | | | | | Event type | deformation: transpressional | Parent event | | Child events | | Tectonic units affected | | Tectonic setting | orogen: intracratonic orogen | Metamorphic facies | | greenschist: chlorite | amphibolite: sillimanite |
| Metamorphic/tectonic features | foliated; gneissose; folded; schistose |
| | | Summary | The oldest tectonic fabric that can be attributed to the Capricorn Orogeny is referred to as D1n (and the corresponding mineral assemblage M1n). It is recognized in several structural and metamorphic zones in the Gascoyne Province, i.e. the southern Mooloo Zone, Paradise Zone, Errabiddy Shear Zone, Boora Boora Zone, and the Yarlarweelor Gneiss Complex, and in the Ashburton Basin in the northern part of the Capricorn Orogen. D1n structures in the Yarlarweelor Gneiss Complex were originally considered to be D2n structures and were correlated with a flat-lying fabric in rocks of the Bryah Group. However, it is now considered to be likely that these early fabrics formed during the 2005–1955 Ma Glenburgh Orogeny.
In most instances, the kinematics of D1n structures and precise pressure and temperature conditions of M1n are difficult to obtain due to multiple overprinting of tectonothermal events. In the Yarlarweelor Gneiss Complex, the Errabiddy Shear Zone, and the Bryah and Padbury Basins, D1n is represented by upright, close to isoclinal folds. The same types of structures are also assigned to D1n in the southern part of the Mooloo and Paradise Zones. The accompanying regional metamorphic grade in these units is greenschist facies, with the exception of the Yarlarweelor Gneiss Complex, where amphibolite facies metamorphism was widespread at this time. Similar structures and mineral assemblages were formed in the Boora Boora Zone at the northern end of the Gascoyne Province and in the Ashburton Basin at the same time. | | | Distribution | Structures that formed during the D1n event of the Capricorn Orogeny are present across the entire Capricorn Orogen and affect most tectonic units older than c. 1800 Ma. However, D1n deformation is most pervasive along the southern and northern margins of the orogen.
In the southern part of the orogen, large-scale upright folds and a pervasive schistosity were developed in the Mooloo and Paradise Zones, and the Yarlarweelor Gneiss Complex, whereas in the Bryah and Padbury Basins in the east and southeast, deformation is characterized by the development and reactivation of faults and shear zones (Occhipinti and Myers, 1999; Pirajno et al., 2000). These structures fold a layer-parallel foliation in metavolcanic rocks of the Bryah Basin that is regarded as having formed during the 2005–1955 Ma Glenburgh Orogeny (Pirajno et al., 2000).
Along the northern margin of the orogen, in the Boora Boora Zone of the Gascoyne Province on MAROONAH and UAROO and in the Ashburton Basin, deformation is characterized by intense tight to isoclinal folding with the development of a pervasive schistosity or foliation in higher-grade rocks (S1n). In the Ashburton Basin, Thorne and Seymour (1991) recognized three structural zones (Zones A, B, and C) based on the geometry of two sets of superposed structures (D1n and D2n). Zone A is dominated by large-scale open to tight folds and dextral wrench faults. Zones B and C are recognized on northeastern ULLAWARRA and CAPRICORN. Zone B is developed in the Ashburton Formation, northeast of the interpreted fault, striking west-northwest from about 1.2 km north of the Hearns Find gold prospect (Zone 50, MGA 500000E 7440000N) on CAPRICORN. It represents a relatively high-strain zone formed during D2n. Due to this, the recognition of D1n structures within Zone B is typically difficult because strong overprinting by D2n has resulted in the early cleavage (S1n) being coaxial, and commonly co-planar with the later fabric (S2n). Zone C occupies the remainder of the Ashburton Basin on ULLAWARRA and CAPRICORN, between the southwestern boundary of Zone B and the Edmund Group unconformity. It is distinguished from Zone B by its generally lower level of D2n strain leading to the better preservation of D1n structures and also by the presence of large-scale F2n folds and dextral wrench faults. Zone C also preserves evidence of D3n structures in the western Capricorn Range.
| | | Description | Southern Capricorn Orogen
In the Paleoproterozoic Bryah and Padbury Basins large-scale, upright, tight to isoclinal prominent folds, including the Robinson Syncline and Livingstone Synform are assigned to D1n. Locally, a well-developed S1n crenulation cleavage is present in mafic and ultramafic schist of the Narracoota Formation and metasedimentary rocks of the Millidie Creek Formation. Pirajno et al. (2000) recorded that M1n (their M2) involved retrogression, metasomatism, and local hydrothermal alteration. Mineral assemblages formed during M1n were mainly noted in high-strain zones where the S1n schistosity is well developed. These include D1n shear zones south of the Robinson Syncline, where pervasive retrogression of metabasalts to actinolite–chlorite schist is observed (Pirajno et al., 1996). In addition, in the Mount Pleasant opencut mine, Pirajno et al. (2000) reported growth of albite porphyroblasts and the development of chlorite at the expense of biotite and epidote during M1n. Mafic and ultramafic rocks of the Narracoota Formation in the Bryah Basin typically have actinolite–tremolite(–talc–chlorite) assemblages indicative of greenschist facies metamorphism (Occhipinti and Myers, 1999). Higher grade metamorphism in M1n is recorded along the western edges of the Bryah and Padbury Basins adjacent to the Yarlarweelor Gneiss Complex (Pirajno et al., 2000). There, staurolite–andalusite–biotite–muscovite–quartz assemblages formed in rocks of the Padbury Group and indicate amphibolite facies metamorphism.
In the Yarlarweelor Gneiss Complex amphibolite layers cutting late Archean fabrics in the granitic gneisses, and coarse-grained metagranite and metapegmatite sheets emplaced during D1n, contain mineral assemblages and textures indicative of medium- to high-grade metamorphism. Most of the amphibolites are characterized by the assemblages green hornblende–andesine or green hornblende–andesine–clinopyroxene. Both have minor quartz and titanite. These assemblages are typical of regional metamorphism at middle to upper amphibolite facies (Bucher and Frey, 2002). Amphibolite gneisses from the area between Red Peak Bore, Morris Bore, and Jubilee Bore along the southern edge of MARQUIS have a polygonal or amoeboid granoblastic texture, and assemblages of brown hornblende–labradorite–clinopyroxene–iron oxide minerals or clinopyroxene–labradorite–green hornblende–iron oxide minerals (Sheppard and Swager, 1999). The assemblages and textures are consistent with local higher grade metamorphism at the transition between amphibolite and granulite facies (Bucher and Frey, 2002). Sheets of coarse-grained granite and pegmatite that are folded about F1n may show gneissic fabrics. Development of almandine and domains of feldspar and quartz with amoeboid and granoblastic polygonal textures imply medium- to high-grade metamorphism. Granitic and calc-silicate gneisses of the complex have mineral assemblages and textures indicative of medium- to high-grade metamorphism. However, it is not always possible to confidently separate the effects of late Archean metamorphism from those of M1n.
Within the Errabiddy Shear Zone, Archean granitic gneisses of the Yarlarweelor Gneiss Complex and metasedimentary rocks of the Camel Hills Metamorphics are folded about upright F1n folds. The F1n structures fold the migmatitic pelitic gneisses, including the leucosomes and diatexite melts of the Quartpot Pelite. These F1n folds were the dominant structures developed during D1n in the Errabiddy Shear Zone. The F1n folds range from close (in areas of moderate D1n strain) to isoclinal (in zones of high D1n strain). Pelitic schist and gneiss at the northern end of the outcrop of Quartpot Pelite on ERRABIDDY commonly contain a steeply dipping crenulation cleavage, which plunges parallel to the F1n folds. The plunge of F1n folds ranges from shallow to steep towards the east-northeast to northeast or west-southwest to southwest. The limbs of F1n folds are commonly marked by a strong foliation, or in some places, by a gneissic banding. Thicker layers of calc-silicate gneiss and amphibolite in the northeastern part of ERRABIDDY commonly define fold hinges with amplitudes of up to 200 m. In the southwestern corner of ERRABIDDY and the southeastern corner of LANDOR, east-northeasterly trending shear zones with associated tight to isoclinal, mesoscopic upright folds deform the Narryer Terrane. These folds are correlated with pervasive F1n folds in the Yarlarweelor Gneiss Complex and Camel Hills Metamorphics. Northeasterly plunging folds commonly have a ‘Z’ sense of asymmetry consistent with a dextral sense of shear, i.e. north block to the east-northeast. Locally, an intersection lineation plunges parallel to the F1n folds. Porphyroclasts show reversals in sense of shear around some F1n fold axes, indicating that an early lineation has been folded. Small-scale, Type 2 refolded fold structures (Ramsay, 1967) produced by interference between Archean F2 and F1n are widespread.
In the Errabiddy Shear Zone on southeastern LANDOR and southwestern ERRABIDDY, Sheppard and Occhipinti (2000) recorded steeply dipping shear zones that they interpreted as part of D1n. Within these shear zones amphibolites comprise green hornblende–andesine–quartz–ilmenite, consistent with metamorphism in the amphibolite facies (Bucher and Frey, 2002). However, at that stage the 2005–1960 Ma Glenburgh Orogeny had not been identified. More recent work on northern ERONG and southern LANDOR by Occhipinti and Reddy (2004) and Occhipinti (2004) indicates that D1n fabrics in pelitic rocks were accompanied by widespread development of greenschist facies mineral assemblages: muscovite and chlorite after sillimanite and biotite, and chlorite or chloritoid after garnet.
In the Glenburgh Terrane in the southern part of the Gascoyne Province, the most widespread D1n structures are upright, open to close, shallowly to moderately plunging folds and a pervasive easterly trending foliation. These mesoscopic folds are common in the Halfway Gneiss and the Mumba Psammite in the southern part of the Mooloo Zone, and also include macroscopic folds south of Dunnawah Well in the Paradise Zone. In the Paradise Zone, the D1n foliation is typically subparallel to the regional structural trend (D1g) established during the Glenburgh Orogeny. A c. 1810 Ma biotite–muscovite granite plug in the central-eastern part of GLENBURGH contains a weak foliation. This also applies to sheets of a similar granite to the north, dated at c. 1820 Ma, that intruded subparallel to ?D2g fold-axial surfaces locally developed in the Dalgaringa Supersuite. Northerly trending Glenburgh Orogeny fabrics (D1g and D2g) dated at 2005–1950 Ma in the Carrandibby Inlier on DAURIE CREEK suggest that in the southwestern corner of GLENBURGH, the main effect of the Capricorn Orogeny was to rotate earlier fabrics developed during the Glenburgh Orogeny into easterly trending structures.
In the southern part of the Mooloo Zone, the Halfway Gneiss forms an elongated easterly trending dome that is interpreted as a regional-scale D1n antiform refolded about a northerly trending axis. In the Mumba Psammite, in the central-northern part of GLENBURGH and just north of the Dalgety Fault (Paradise Zone), well-developed, small-scale D1n folds and S1n crenulations deform an earlier S2g bedding-parallel fabric. The S1n foliation is well developed in the southern part of the Mooloo Zone on GLENBURGH, particularly in sheets of the 1810–1805 Ma Dumbie Granodiorite, which commonly contains a pervasive L–S or L-tectonite fabric and is only rarely folded. Many of the rocks show evidence of recrystallization under greenschist facies conditions. This low-grade metamorphic overprint is more pervasive (and dynamic) in the Mooloo Zone than in the Paradise Zone (Occhipinti and Sheppard, 2001). Higher grade assemblages formed during the Glenburgh Orogeny in the Moogie Metamorphics are partially or wholly overprinted by greenschist facies assemblages. The Mumba Psammite now comprises chloritoid-bearing schist, quartzofeldspathic schist, and quartzite. Quartzofeldspathic schist consists mostly of sericite and quartz, with minor amounts of biotite and feldspar. Chloritoid-bearing schist consists of a variety of assemblages, including quartz–sericite–chloritoid(–chlorite) schist, quartz–magnetite–sericite–chloritoid(–chlorite) schist, and chloritoid–quartz–sericite schist. Chloritoid-bearing schist locally contains relict porphyroblasts of garnet. Accessory minerals commonly include opaque minerals and tourmaline. Sericite commonly forms fine-grained aggregates with minor quartz, which may represent pseudomorphs of a higher grade mineral. Chloritoid, although in places aligned in the foliation of the rock, typically forms clumps and splays and exhibits a ‘bow-tie’ texture. The chloritoid ranges from colourless to pale green or bright blue. Of the calc-silicate gneisses, the amphibole- and diopside-rich gneisses are partly or wholly replaced by assemblages of actinolite–tremolite, epidote, albite, calcite, and titanite. Forsterite and clinohumite are commonly partly serpentinized in the marbles.
Northern Capricorn Orogen
During the mapping of the Ashburton Basin the structural evolution of this part of the orogen could not be reconciled with that along the southern margin (Thorne and Seymour 1991). Hence, the two regions were described separately with different structural nomenclature, defined as the ‘Ashburton Fold Belt’ with the structural notations D1a/ash/M1a/ash, D2a/ash/M2a/ash, and D3a/ash/M3a/ash. However, more recent mapping across the entire orogen, combined with high-precision geochronology has demonstrated that the three events recognized in the Ashburton Basin are equivalent to the D1n, D2n, and D3n events recognized in the south. Hence, the older terminology and structural notations have now been abandoned.
Most of the evidence for the D1n deformation comes from Zone C. This is based on the presence of rare F1n folds and the recognition of two closely spaced cleavages (S1n and S2n) that are present in the Ashburton Formation, but not in the unconformably (angular) overlying Capricorn Group, which carries only the S2n cleavage (Thorne and Seymour, 1991). In many outcrops, the early S1n cleavage is developed subparallel to the bedding and probably represents the remnants of attenuated tight to isoclinal fold limbs. S1n is commonly crenulated by S2n at a low angle making the two particularly difficult to differentiate in the field. As the metamorphic grade increases in southwestern parts of Zone C, the S1n fabric develops into a metamorphic schistosity. In the Capricorn Range, e.g. localities around Zone 50, MGA 493300E 7412000N, the marked angular unconformity at the base of the Bywash Formation provides clear evidence that the Ashburton Formation was folded prior to deposition of the Capricorn Group. At Mount Blair, on adjacent TUREE CREEK, the basal unconformity of the Capricorn Group dips north at 50° due to D2n folding. The S1n cleavage in the underlying Ashburton Formation dips 15–45° south, whereas bedding dips (and youngs) southward at 0–30°. Rotation of bedding and S1n to their pre-D2n orientation indicates that the tight F1n fold was characterized by a steeply southward-dipping axial surface. An example of F1n minor folds that have been refolded during D2n is preserved north of Koonong Pool at AMT556, Zone 50, MGA 492918E 7418481N. Here, a pair of small-scale F1n folds with ‘S’ and ‘Z’ vergence are preserved on the southern and northern limbs, respectively, of a westerly plunging, downward facing F2n anticline.
Throughout most of the Ashburton Basin, metamorphic grade is low. However, grade and schistosity gradually increase towards the west and southwest. Northeast of the Edmund Group unconformity, the nature of the transition suggests that many psammites and pelites represent metamorphosed Ashburton Formation rocks. Thorne and Seymour (1991) note that much of the Ashburton Basin is characterized by the mineral assemblage quartz–chlorite–muscovite(–sericite) in pelitic and psammitic rocks. On northern ULLAWARRA, medium-grade metamorphosed equivalents of the Ashburton Formation are represented by quartz–muscovite–biotite–cordierite–andalusite–garnet schist (P_WYa-mh), indicating medium-grade metamorphic conditions. Textural evidence suggests that porphyroblastic minerals (biotite, andalusite, cordierite, and garnet) grew during and after the D1n deformation event, overgrowing a quartz, muscovite, and chlorite groundmass. The metamorphic schistosity (S1n) is typically deformed by F2n folds and crenulation cleavage.
The oldest fabric in the metamorphic rocks in the Boora Boora Zone of the Gascoyne Province (MAROONAH and UAROO) is a regionally extensive foliation or gneissic layering (S1n). This fabric is parallel or subparallel to lithological layering. The gneissic layering is commonly accentuated by minor pegmatite banding. Associated with the gneissic layering are widespread, small-scale isoclinal folds (F1n) that are best developed in the foliated and gneissic metagranodiorite and metatonalite (P_-MO-mggn). These folds are locally refolded by upright F2n folds to form Type 3 fold interference structures (Ramsay, 1967). Around the Monte Carlo mine (Zone 50, MGA 351370E 7450100N), a megascopic, isoclinal F1n fold is refolded about a megascopic F2n fold to form a Type 3 interference structure.
The grade of M1n in the Boora Boora Zone is difficult to estimate because most of the metamorphosed rocks are granitic in composition and because of widespread overprinting by M2n assemblages. Granitic gneisses have locally preserved anhedral granular and amoeboid textures, suggesting medium- to high-grade metamorphism. Calc-silicate rocks are composed of augite/diopside, zoisite, titanite, plagioclase, and quartz. Mafic rocks on northern MAROONAH with only a weakly developed S2n fabric have assemblages of blue-green hornblende, plagioclase, and minor quartz, accompanied by polygonal textures. Locally, mafic rocks are epidote amphibolites with plagioclase of oligoclase composition and no chlorite. Collectively, these assemblages are consistent with amphibolite or epidote–amphibolite facies metamorphic conditions during M1n.
Metasedimentary rocks in the Boora Boora Zone show a considerable range in M1n metamorphic grade. Metasedimentary rocks at the southern end of a very large pluton of muscovite–biotite granite on MAROONAH show no evidence of having been metamorphosed at more than low or very low grade. However, along strike to the northwest, metasedimentary rocks around the Laura prospect (Zone 50, MGA 361387E 7424532N) contain the M1n assemblage of muscovite, biotite, garnet, ?andalusite, and quartz. Textures indicate that porphyroblasts of garnet and ?andalusite grew at the same time or after S1n, and were partly or wholly replaced by chlorite and sericite during M2n. The M1n assemblages here are consistent with lower amphibolite facies metamorphic conditions (Spear, 1993). Farther to the northwest, about 8 km northwest of Horse Well (Zone 50, MGA 348340E 7432470N), pelitic rocks contain small domains of biotite, quartz, and muscovite with mats of fibrolite (sillimanite) in the muscovite, implying upper amphibolite-facies conditions (Spear, 1993). The increase in grade to the northwest suggests that the metamorphic isograds are perpendicular to the dominant D2n structural grain, and that the isograds are likely to have been folded. | | | | | | Geochronology | | | Capricorn Orogeny D1n/M1n | Maximum age | Minimum age | Age (Ma) | 1813 ± 8 | 1800 | Age | Paleoproterozoic | Paleoproterozoic | Age data type | Isotopic | | References | | Nelson (1998a) | Nelson (1998a) | Nelson (1998a) |
| | Nelson (2001) | Evans et al. (2003) | Wingate et al. (2017a) | Wingate et al. (2017b) |
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| Geochronological constraints on the age of D1n vary according to the tectonic unit, and the structural domain or zone within a given tectonic unit in which the structures are present. Although each dated fabric is the earliest attributable to the Capricorn Orogeny within a given area, it is possible that with variations in imposed strain, the earliest fabric in a given area may be diachronous across the orogen. With this caveat in mind, the constraints on D1n are as follows.
In the Bryah Basin, there are effectively no geochronological controls on the age of D1n. In the Yarlarweelor Gneiss Complex, intrusions of coarse-grained metagranite and metapegmatite (P_-MO-mgmp), one of which was dated at 1813 ± 8 Ma (Nelson, 1998a), are interpreted to have intruded during the D1n event (Occhipinti et al., 1998; Occhipinti and Myers 1999; Sheppard and Swager 1999). A younger limit for D1n is provided by a U–Pb SHRIMP zircon date of 1808 ± 6 Ma (GSWA 142851, Nelson, 1998b) on the Kerba Granite, which is discordant to D1n structures (Sheppard and Swager, 1999).
In the Glenburgh Terrane of the southern Gascoyne Province, the only effective constraints on the age of D1n come from the southern part of the Mooloo Zone. Here, foliated and deformed Dumbie Granodiorite, which is dated at 1811 ± 6 Ma, 1810 ± 9 Ma, and 1804 ± 5 Ma (Nelson 1998a,b; Wingate et al., 2011), are cut by undeformed, massive plutons and dykes of the Scrubber Granite. The oldest of them is dated at 1800 ± 7 Ma (Nelson, 2001). At one locality on southern PINK HILLS (SPJPKH000927, Zone 50, MGA 453174E 7235217N), medium-grained, seriate to porphyritic Dumbie Granodiorite is locally strongly deformed with the production of gneissic fabrics. This rock is included as rafts and inclusions within fine-grained, slightly porphyritic, and only weakly deformed Dumbie Granodiorite. A lower strain portion of the medium-grained granodiorite gneiss (Wingate et al., 2011) has been dated at 1804 ± 5 Ma, and the intrusive finer-grained undeformed granodiorite at 1810 ± 9 Ma (GSWA 159996, Nelson, 2000). These age and field relationships suggest that parts of the Dumbie Granodiorite, at least in the southern part of the Mooloo Zone, were syntectonic with respect to the D1n event.
In the northern part of the Capricorn Orogen, the maximum age for D1n can be loosely constrained by the igneous crystallization age of the youngest deformed and oldest undeformed intrusions, and the age of felsic volcanic horizons above and below the regional-scale Ashburton Formation — Capricorn Group unconformity. In the Boora Boora Zone the youngest granitic rock which carries the S1n fabric, a foliated metagranodiorite from MAROONAH, is dated at 1794 ± 9 Ma (P_-MO-mggn; GSWA 169087, Nelson, 2004a), whereas the oldest undeformed granitic pluton, a seriate to porphyritic monzogranite from UAROO, is dated at 1796 ± 3 Ma (P_-MObo-ggpb; GSWA 216528, M. Wingate, 2018, written comm., 12 May). In the Ashburton Basin, the minimum age for D1n is provided by SHRIMP U–Pb zircon crystallization ages of 1796 ± 9 Ma (GSWA 169885, Wingate et al., 2014) and 1786 ± 5 Ma (Krapez and McNaughton, 1999) for the Boolaloo Granodiorite (P_-MObo-ggpb) that intrudes the Ashburton Formation and truncates the S1n fabrics. Felsic volcanic and volcaniclastic units below the regional-scale unconformity have provided several SHRIMP U–Pb zircon dates. A thick felsic volcaniclastic sandstone and siltstone unit within the Ashburton Formation on CAPRICORN yielded a SHRIMP U–Pb zircon age of 1806 ± 9 Ma (GSWA 148922, Nelson, 2004b). On the other hand, felsic volcaniclastic units within the upper part of a thick mafic and felsic volcanic sequence within the Ashburton Formation on BOGGOLA yielded SHRIMP U–Pb zircon dates of 1829 ± 5 Ma (Sircombe, 2003) and 1834 ± 4 Ma (GSWA 219592, M. Wingate, 2018, written comm., 12 May). The June Hill Volcanics, which are stratigraphically equivalent to the Ashburton Formation, also carry a prominent S1n fabric. Evans et al. (2003) obtained a SHRIMP U–Pb zircon crystallization age of 1799 ± 8 Ma from a pumice-breccia sandstone of the June Hill Volcanics on the 1:250 000 sheet WYLOO. Above the regional unconformity, felsic volcanic and volcaniclastic units of the Koonong Member (P_-CPbk-fn) of the Bywash Formation have yielded SHRIMP U–Pb crystallization ages of 1804 ± 7 Ma (Hall et al., 2001), 1800 ± 7 Ma (GSWA 219522, Wingate et al., 2017a), and 1801 ± 6 Ma (GSWA 219526, Wingate et al., 2017b). These felsic volcanic units only carry the S2n cleavage. The similarity in dates of felsic volcanic horizons above (i.e. the Capricorn Group at c. 1800 Ma) and below (i.e. the June Hill Volcanics at c. 1799 Ma) the regional unconformity suggest that uplift and isoclinal folding during the D1n event must have taken place within a very short time frame of 5–6 million years.
Despite the potential regional diachroneity of the onset and duration of deformation and metamorphism across the Capricorn Orogen, the minimum constraints for the D1n event are fairly precise and consistent, suggesting that regional-scale folding, faulting, and metamorphism were complete by c. 1800 Ma.
| | | 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 this interpretation was published, 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 (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 brought forward to support this interpretation. Some objections to the interpretation of the Capricorn Orogeny to reflect an oblique collision of the Yilgarn and Pilbara Cratons were raised by Sheppard (2004, 2005) and Sheppard et al. (2010), who interpreted the orogeny as a reactivation in an intracontinental setting.
A difficulty in advancing the 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) showed 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. In large part, this model was based 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 | Bucher, K and Frey, M 2002, Petrogenesis of metamorphic rocks: Springer Verlag, Berlin, 341p. | 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. | Hall, CE, Powell, CMcA and Bryant, J 2001, Basin setting and age of the Late Palaeoproterozoic Capricorn Formation, Western Australia: Australian Journal of Earth Sciences, v. 48, no. 5, p. 731–744. | 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. | Krapež, B and McNaughton, NJ 1999, SHRIMP zircon U-Pb age and tectonic significance of the Palaeoproterozoic Boolaloo Granodiorite in the Ashburton Province, Western Australia: Australian Journal of Earth Sciences, v. 46, p. 283–287. | Nelson, DR 1998a, 142849.1: foliated coarse-grained monzogranite, northeast of White Well; Geochronology Record 365: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 1998b, 142851.1: recrystallized monzogranite, Kerba Pool; Geochronology Record 367: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 2000, 159996.1: biotite monzogranite, Claypan Bore; Geochronology Record 231: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 2001, 168939.1: biotite monzogranite, Trickery Bore; Geochronology Record 209: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 2004a, 169087.1: foliated biotite granodiorite, Minga Springs; Geochronology Record 44: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Nelson, DR 2004b, 148922.1: crystal–vitric tuff, Koonong Pool; Geochronology Record 249: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Occhipinti, SA 2004, Tectonic evolution of the southern Capricorn Orogen, Western Australia: Curtin University of Technology, Perth, Western Australia, PhD thesis (unpublished), 220p. | Occhipinti, SA and Myers, JS 1999, Geology of the Moorarie 1:100 000 sheet: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 20p. View Reference | Occhipinti, SA and Reddy, S 2004, Deformation in a complex crustal-scale shear zone: Errabiddy Shear Zone, Western Australia, in Flow processes in faults and shear zones edited by Alsop, GI, Holdsworth, RE, McCaffrey, KJW and Hand, M: The Geological Society of London, Special Publication 224, p. 229–248. | 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, Nelson, DR, Myers, JS and Tyler, IM 1998, Syntectonic granite in the southern margin of the Palaeoproterozoic Capricorn Orogen, Western Australia: Australian Journal of Earth Sciences, v. 45, p. 509–512. | Pirajno, F, Adamides, NG, Occhipinti, SA, Swager, CP and Bagas, L 1996, Geology and tectonic evolution of the Early Proterozoic Glengarry Basin, Western Australia, in Geological Survey of Western Australia annual review 1994-95 edited by Mikucki, JA: Geological Survey of Western Australia, Perth, Western Australia, p. 71–80. View Reference | Pirajno, F, Occhipinti, SA and Swager, CP 2000, Geology and mineralization of the Palaeoproterozoic Bryah and Padbury Basins, Western Australia: Geological Survey of Western Australia, Report data package 59. View Reference | 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. | Ramsay, JG 1967, Folding and fracturing of rocks: McGraw-Hill, New York, USA, Series in Earth and Planetary Sciences 160, 568p. | 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 | Sheppard, S and Occhipinti, SA 2000, Geology of the Errabiddy and Landor 1:100 000 sheets: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 37p. View Reference | Sheppard, S and Swager, CP 1999, Geology of the Marquis 1:100 000 sheet: Geological Survey of Western Australia, 1:100 000 Geological Series Explanatory Notes, 21p. View Reference | Sircombe, KN 2003, Age of the Mt Boggola volcanic succession and further geochronological constraint on the Ashburton Basin, Western Australia: Australian Journal of Earth Sciences, v. 50, p. 967–974. | Spear, FS 1993, Metamorphic phase equilibria and pressure-temperature-time paths: Mineralogical Society of America, Monograph, 799p. | 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 and Johnson, SP 2011, 188975.1: biotite metatonalite, Dalys Bore; Geochronology Record 980: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Wingate, MTD, Kirkland, CL, Thorne, AM and Johnson, SP 2014, 169885.1: biotite granodiorite, Stuarts Well; Geochronology Record 1208: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Wingate, MTD, Lu, Y and Fielding, IO 2017a, 219522.1: felsic volcanic rock, Koonong Pool; Geochronology Record 1369: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference | Wingate, MTD, Lu, Y, Fielding, IO and Johnson, SP 2017b, 219526.1: felsic volcanic rock, Bali Lo deposit; Geochronology Record 1370: Geological Survey of Western Australia, <www.dmpe.wa.gov.au/geochron>. View Reference |
| | | | Recommended reference for this publication | Johnson, SP, Sheppard, S, Thorne, AM and Korhonen, FJ 2022, Capricorn Orogeny D1n/M1n (CCD1): 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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