Albany-Fraser Orogen Research Articles

Evolution of a crustal‐scale transpressive shear zone in the Albany–Fraser Orogen, SW Australia: 2. Tectonic history of the Coramup Gneiss and a kinematic framework for Mesoproterozoic collision of the West Australian and Mawson cratons

AbstractWithin the Albany–Fraser Orogen of southwestern Australia, the Coramup Gneiss is a NE–SW trending zone of high‐strain rocks that preserves a detailed record of orogenesis related to Mesoproterozoic convergence of the West Australian and Mawson cratons. New structural, metamorphic and U–Pb SHRIMP zircon age data establish that the Coramup Gneiss underwent high‐grade tectonism during both Stage I (c. 1290 Ma) and Stage II (c. 1170 Ma) of the Albany–Fraser Orogeny. Stage I commenced with c. 1300 Ma high‐T, low‐P M1a metamorphism during extension, and the formation of small‐scale ptygmatic folds within a subhorizontal S1a gneissosity. High‐P M1b metamorphism at c. 1290 Ma was accompanied by the transposition and shearing of S1a into a composite, shallow SE‐dipping S1b foliation, and the development of tight recumbent F1b folds with S1‐parallel axial surfaces and asymmetries indicating NW‐directed thrusting. The preservation of a similar P–T–time record in the Fraser Complex (NE of the Coramup Gneiss) is consistent with large‐scale, NW‐directed Stage I thrusting of the Mawson Craton margin over the south‐eastern edge of the West Australian Craton. Stage II tectonism in the western Coramup Gneiss involved high‐T, low‐P M2a metamorphism and the formation of subvertical SE‐dipping D2 shear zones, shallow SW‐plunging L2 mineral stretching lineations, and NW‐verging F2 folds with S2‐parallel axial surfaces. A synkinematic pegmatite dyke emplaced into a D2 shear zone yielded a U–Pb SHRIMP zircon age of 1168 ± 12 Ma. Kinematic indicators suggest a combination of pure shear flattening perpendicular to S2, and dextral simple shear. However, contemporaneous structures elsewhere in the Albany–Fraser Orogen are consistent with continued NW–SE convergence at craton‐scale during Stage II, and oblique compression in the Coramup Gneiss is attributed to the arcuate geometry of the orogen‐scale deformation front.

Evolution of a crustal‐scale transpressive shear zone in the Albany–Fraser Orogen, SW Australia: 1. P–T conditions of Mesoproterozoic metamorphism in the Coramup Gneiss

AbstractThe Albany–Fraser Orogen in southwestern Australia preserves an important thermo‐tectonic record of Australo‐Antarctic cratonic assembly during the Mesoproterozoic. New petrologic and thermobarometric data from the Coramup Gneiss (a 10 km wide zone of high strain rocks within the NE‐trending eastern Albany–Fraser Orogen) indicate at least two high‐grade metamorphic events during 1345–1140 Ma convergence and amalgamation of the West Australian and Mawson cratons. The first event (M1) involved c. 1300 Ma granulite facies metamorphism of the Coramup Gneiss (M1a: 800–850 °C, 5–7 kbar), followed by burial and recrystallization under high‐P conditions (M1b: 800–850 °C, c. 10 kbar) prior to high‐T decompression (M1c: 700–800 °C, 7–8 kbar) and the 1290–1280 Ma emplacement of Recherche Granite sills. The second event (M2) entailed high‐T, low‐P metamorphism within dextral D2 shear zones (M2a: 750–800 °C, 5–6 kbar), followed by fluid‐present amphibolite facies M2b retrogression. Subsequent sinistral D3 mylonites and pseudotachylites are considered contemporaneous with similar structures in the adjacent Nornalup Complex that postdate the c. 1140 Ma Esperance Granite. Our petrological and thermobarometric data permit two end‐member P–T‐time relationships between M1 and M2: (1) a single post‐M1b event involving continuous M1b–M1c–M2a–M2b cooling and decompression, and (2) a two‐stage post‐M1b evolution involving M1c metamorphism during the waning stages of an event unrelated causally or temporally to subsequent M2a metamorphism and D2 deformation. In a companion paper, new structural and U–Pb SHRIMP zircon data are presented to support a two‐stage P–T evolution for the Coramup Gneiss, with M1 and M2, respectively, reflecting thermo‐tectonic activity during Stage I (1345–1260 Ma) and Stage II (1215–1140 Ma) of the Albany–Fraser Orogeny.

Zirconolite: A new U-Pb chronometer for mafic igneous rocks

Precise dates for mafic igneous events are essential for tectonic reconstructions and understanding mantle dynamics, mass extinctions, and paleoclimate. Zirconolite (CaZrTi2O7) is a uranium-bearing accessory mineral, found in a wide range of terrestrial and lunar rocks, that has been largely overlooked as a chronometer. In situ U-Pb geochronology of zirconolite from three dolerite intrusions in Western Australia demonstrates that it yields emplacement ages that are more precise than those obtained from coexisting zircon and baddeleyite. Dikes in the Stirling Range Formation give a zirconolite 207Pb/ 206Pb age of 1218 ± 3 Ma, indistinguishable from the less precise dates obtained from zircon (1215 ± 10 Ma) and baddeleyite (1217 ± 39 Ma) and coincident with dike emplacement in the adjacent craton margin and peak metamorphism in the Albany-Fraser orogen. Zirconolite from the 755 Ma Mundine Well dike swarm yields a 207Pb/206Pb age of 754 ± 5 Ma. Sills intruding the Proterozoic Manganese Group contain zirconolite crystals that give a 207Pb/206Pb age of 523 ± 14 Ma. Despite high U contents (550 ppm to 14,000 ppm) and greenschist facies metamorphism, zirconolite in these samples is apparently unaffected by loss of radiogenic Pb. Because of its remarkable properties for U-Pb geochronology, it may soon become the dominant tool for dating mafic igneous rocks as young as 500 Ma by ion microprobe, and thus will prove especially valuable in reconstructing Precambrian geologic history.

The Seismic Structure of Wilkes Land/Terre Adelie, East Antarctica and Comparison with Australia: First Steps in Reconstructing the Deep Lithosphere of Gondwana

A determination of the seismic structure of the crust and uppermost mantle of East Antarctica, in the region of Casey station, Wilkes Land and Dumont DUrville station, Terre Adelie is presented. High-fidelity waveforms from teleseismic earthquakes recorded at stations CASY and DRV (1996-2001) are used to calculate the seismic receiver function, the signal produced as energy passes through layers in the seismic velocity structure under the receiving station. The receiver functions are stacked to improve the signal-to-noise ratio and then modelled using an inverse algorithm to find the structure that best fits the observed waveform at each station. Inferences are made regarding the tectonic structure, in particular, the crustal thickness and character of the seismic Moho. The crustal thickness under Casey Station is found to be 30 km (+/- 2 km) with a fairly sharp Moho, considerably less than Dumont D'Urville Station, where the crustal thickness is 42 km, and there IS a significant low velocity region the deep crust. The structure of the Wilkes Land lithosphere is comparable to that of the Albany-Fraser Orogen, Western Australia, part of its conjugate margin. This places a new constraint on the relative position of East Antarctica and Australia in the reconstruction of Gondwana, and earlier, supercontinents. A recent reinterpretation of Antarctic geology proposes tectonic province boundaries trending perpendicular to the coast with counterparts in southern Australia. Seismic techniques, determining structure beneath regions with no surface exposure, are vital tools in testing such tectonic hypotheses, towards the reconstruction of Gondwana to full lithospheric depth.

Late Mesoproterozoic (ca1.2 Ga) palaeomagnetism of the Albany-Fraser orogen: no pre-Rodinia Australia-Laurentia connection

SUMMARY New palaeomagnetic data from metamorphic and mafic intrusive rocks of the Albany–Fraser orogen place Australia at high latitudes at ca 1.2 Ga, whereas existing data show that Laurentia occupied low latitudes at this time. No previous reconstructions linking Australia and Laurentia at ca 1.2 Ga are supported by our new data. The two continents moved independently during the early Grenville orogeny, although it is possible that late Mesoproterozoic convergence resulted in an AUSMEX configuration by 1070 Ma.

Linking source and sedimentary basin: Detrital zircon record of sediment flux along a modern river system and implications for provenance studies

U/Pb analysis of detrital zircons from sands along the Frankland River in SW Australia reveal marked downstream changes in their age signatures that correlate with changing basement character. The Archean Yilgarn craton underlies the upper 70% of the river catchment (by area) and detrital zircons from sands in this region are characterized by a unimodal ∼2.7 Ga age signature. The lower part of the river catchment flows over the Mesoproterozoic Albany–Fraser orogen and input from this source results in progressive downstream masking of Yilgarn detritus so that in the most downstream samples this source constitutes only 25% of the detrital zircon age spectrum. The Frankland River age data indicate that the lower portions of the drainage system did not form a non-erosive pathway for sediment flux but rather basement lithologies were a continuing source of sediment yield. This probably reflects rejuvenation and incision of the lower reaches of the river system in response to a drop in baseline and possible sequestering of Yilgarn detritus in upstream reservoirs along the broad open mid-region valleys of the river system. These data emphasize that in ancient orogens, where the link between source and sample site is often not preserved, care needs to be exercised in relating detrital zircon age signature to interpretations of source distribution and paleogeographic reconstructions.

1.2 Ga thermal metamorphism in the Albany–Fraser Orogen of Western Australia: consequence of collision or regional heating by dyke swarms?

Compressive fabrics in the Late Palaeoproterozoic Mount Barren Group of the Albany–Fraser Orogen, southwestern Australia, record Mesoproterozoic collision between proto-Australia and proto-Antarctica. Petrographical evidence establishes that peak thermal metamorphism produced largely random growth of kyanite, staurolite, biotite, monazite and xenotime that overprinted those fabrics. SHRIMP U–Pb geochronology of xenotime and monazite yields an average age of 1205 ± 10 Ma. Thermal metamorphism therefore occurred at least 45 Ma after fabric formation, and was unlikely to have been caused by collision. Rather, thermal metamorphism overlapped with the emplacement of 1215–1202 Ma dyke swarms into the Orogen and the adjacent Yilgarn Craton, and was followed by emplacement of 1200–1180 Ma granites. Regional heating associated with mafic magmatism was the probable cause of thermal metamorphism, but previous proposals that the dyke swarms were the consequence of collision or extensional orogenic collapse cannot be substantiated. A regional thermal anomaly, craton-scale extension and adiabatic decompression melting of the asthenosphere are implied, but causal mechanisms such as a mantle plume or intracontinental rifting require substantiation from other parts of East Gondwana. The significant time gap between orogenic deformation and thermal metamorphism implies that metamorphism in many other orogens may not necessarily be due to compressive tectonics.

Proterozoic basement provinces of southern and southwestern Australia, and their correlation with Antarctica

Abstract Three Precambrian basement provinces extend from the southern coast of Australia into East Antarctica when reconstructed in a Gondwana configuration. These are, from east to west, the Mawson Craton, and the Albany-Fraser and Pinjarra Orogens. The Mawson Craton preserves evidence for tectonic activity from the late Archaean until the earliest Mesoproterozoic. It is exposed in the Gawler Craton of South Australia, the Terre Adélie and King George V Land coastline of East Antarctica, and the Miller Range of the central Transantarctic Mountains. It may form a significant part of the ice-covered East Antarctic Shield, although insufficient data are available to constrain its lateral extent. The Mawson Craton underwent late Palaeoproterozoic tectonism along its eastern margin (the Kimban Orogeny) and the occurrence of c. 1700Ma eclogites in the Transantarctic Mountains implies that this was, in part, a collisional event, although elsewhere it was characterized by low P/T metamorphism. The western margin of the Mawson Craton collided with a continental fragment comprising the Nawa Domain of the Gawler Craton, the Coompana Block and the Nornalup Complex of Western Australia at c. 1560Ma during the Kararan Orogeny. The western edge of the Nornalup Complex later collided with the Biranup and Fraser Complexes and Yilgarn Craton to form the Albany-Fraser Orogen during two stages of tectonism at c. 1350–1260 and 1210–1140Ma. The Pinjarra Orogen truncates the western margin of the Yilgarn Craton and Albany-Fraser Orogen, and contains allochthonous 1100–1000Ma gneissic blocks transported along the craton margin during at least two stages of Neoproterozoic transcurrent movement. It divides East Gondwana into Australo-Antarctic and Indo-Antarctic domains, which are distinct continental fragments with different Proterozoic histories that were juxtaposed by oblique collision at 550–500Ma during the assembly of Gondwana. The path taken by the Pinjarra Orogen beneath the Antarctic ice sheet is unknown, but it is of similar width and length to the East African Orogen, and must have been a fundamental Neoproterozoic boundary of critical importance to supercontinent assembly and breakup.

Crustal residence history and garnet Sm–Nd ages of high-grade metamorphic rocks from the Windmill Islands area, East Antarctica

Nd whole-rock data from the Windmill Islands area yield early Proterozoic to middle Archaean Nd model ages. These crustal residence times are consistent with regional correlations with other parts of Antarctica (Bunger Hills, Denman Glacier area) and the Albany-Fraser Orogen of south-western Australia during the Mid-Proterozoic and thus support reconstructions with a continuous Mid-Proterozoic orogen in these areas. The new Nd isotope data provide strong evidence that no age boundary exists between the higher- and lower-grade parts of the Windmill Islands area, and that the metamorphic complex represents a single terrane with a common crustal history. The data support the notion of a time-link between the occurrence of intrusive charnockites (C-type magmas) and high-grade metamorphism. The magmatic rocks and orthogneisses in the area are interpreted to have a mixed source consisting of older crustal components, i.e. older sediments (ca. 3.2–2.6 Ga) and a younger mafic component (ca. 1.9 Ga). Two garnet Sm–Nd isochrons yield ages of 1156±17 Ma and 1137±2.5 Ma and are identical to SHRIMP U–Pb results on monazite from these samples. A garnet Sm–Nd age of 1123±13 Ma for the Ford granite is significantly younger than the SHRIMP U–Pb zircon age for this sample. The difference relates to the different closure temperature of each isotopic system and is thus interpreted as initial cooling after granulite facies metamorphism.

Did late Palaeoproterozoic assembly of proto-Australia involve collision between the Pilbara, Yilgarn and Gawler Cratons? Geochronological evidence from the Mount Barren Group in the Albany–Fraser Orogen of Western Australia

The Mount Barren Group, which crops out on the southern margin of the Yilgarn Craton, has been considered an allochthonous synorogenic sequence to a Mesoproterozoic (1300 Ma) collision between southwestern Australia, southeastern Australia and eastern Antarctica during assembly of East Gondwana. Reassessment of its stratigraphic geometry confirms the historical perspective that nonconformable and faulted contacts are preserved on autochthonous Archaean orthogneiss of the Yilgarn Craton, emphasising that it is not an allochthonous sequence. SHRIMP UPb dating of early diagenetic xenotime establishes a Late Palaeoproterozoic (1696±7 Ma) depositional age for the Mount Barren Group, thereby negating a Mesoproterozoic synorogenic origin. The Mount Barren Group now correlates in time with strike-slip sequences in the Capricorn Orogen approximately 1000 km to the north, and which were a post-collisional response to ∼1750 Ma sinistral transform collision between the Pilbara and Yilgarn Cratons. SHRIMP UPb detrital-zircon geochronology of the Mount Barren Group, therefore, has an important role in establishing if Pilbara–Yilgarn transform collision were either independent of or a component in the Late Palaeoproterozoic assembly of a proto-Australian continent. Detrital-zircon age-data from four samples of different sandstone beds in the Mount Barren Group define complex age spectra composed of seven significant provenance age-subpopulations. Comparison to age spectra from provinces with a possible geotectonic link to the Yilgarn Craton indicates that either the Pilbara Craton or the Gawler Craton was the source terrain. A barrier to a dispersal-system link to the Pilbara Craton points to the Gawler Craton as the source, a provenance link that was also made for the now-redundant 1300 Ma scenario. The 1696±7 Ma depositional age and zircon provenance analysis support a contentious hypothesis involving coeval collisions between the Pilbara–Yilgarn and Yilgarn–Gawler Cratons during assembly of a proto-Australian continent some 500–400 million years earlier than envisaged by other reconstructions.

Regional correlation of Mesoproterozoic structures and deformational events in the Albany–Fraser orogen, Western Australia

Geologic mapping and meso- and microstructural analysis of a previously unstudied area in the western part of the Mesoproterozoic Albany–Fraser orogen, Western Australia, leads to a correlation of deformational events along the exposed length of the orogen. The earliest deformational event (D 1) accompanied granulite-facies metamorphism and is characterized by a locally preserved subhorizontal foliation and associated recumbent folds. This event is interpreted to record northwest–southeast contraction. The second event (D 2) produced a subvertical, east-northeast-striking foliation and variably plunging, upright folds. Northwest-vergent folds (toward 333°) and sparse kinematic indicators suggest southeast-up tectonic transport with a dextral component of movement. A third deformational event (D 3) is manifested by a conjugate set of mylonitic to cataclastic shear zones with a dominant, dextral set oriented at 105° and a subordinate, sinistral set oriented at 010°. The bisector of the average orientations for the shear zones is 325°, consistent with northwest–southeast shortening. Like the D 2 structures, the D 3 structures may represent deformation in a dextral transpressive setting. D 4 structures include two subvertical joint sets, one oriented at 355° and the other at 105°. All structures are similar in geometry and kinematics to structures near Albany, which have been constrained to 1190–1170 Ma (Precambrian Res., 59 (1992) 95), as well as structures east of Esperance that are associated with a major tectonothermal event at 1345–1260 Ma (Precambrian Res., 102 (2000) 155). Additional geochronological data, particularly from the Western Albany–Fraser orogen, are needed to resolve this apparent discrepancy. There is a near one-to-one correlation in lithology, structural style, metamorphic grade, kinematics, and possibly timing of deformational events between the Albany–Fraser orogen and the Bunger Hills of East Antarctica, supporting the previously suggested ties between these two areas. Marked dissimilarities, however, in model T DM ages, U–Pb zircon dates, kinematics and timing of deformation, and timing of metamorphism between the Albany–Fraser orogen and the Oaxacan Complex of southern Mexico raise serious doubts regarding the viability of Rodinia reconstructions that juxtapose those two Mesoproterozoic terranes.

Juvenile lithospheric mantle enrichment and the formation of alkaline ultramafic magma sources: Re–Os, Lu–Hf and Sm–Nd isotopic systematics of the Norseman melnoites, Western Australia

Several 850-Ma melnoites occur in the Norseman region at the southeastern margin of the Archaean Yilgarn Craton, Western Australia. Major, trace element and Rb–Sr, Sm–Nd and Re–Os isotopic data from whole rocks and Re–Os and Lu–Hf isotopic data from mineral separates, including Mg-ilmenite macrocrysts and groundmass magnetite, are used to characterise their mantle source. Compositions of whole rocks and groundmass phlogopite and clinopyroxene show that although these rocks contain abundant Mg-ilmenite macrocrysts, they are not kimberlites. Macrocryst Mg-ilmenite geochemistry, coupled with the paucity of lithospheric mantle minerals, suggests that these macrocrysts are early-formed phenocrysts rather than xenocrysts. Mg-ilmenite geochemistry and estimated fO 2 are correlated with proximity to the cratonic margin, suggesting that the melnoite source was laterally heterogeneous on a scale of ∼100 km. Whole rock initial ε Nd values and 87Sr/ 86Sr ratios range from +3.3 to +5.4 and from 0.70181 to 0.70307, respectively, and Mg-ilmenite initial ε Hf values range between −4.8 and +1.7. These data are consistent with the interpretation that the mantle source experienced the time-integrated enrichment of incompatible elements. Initial 187Os/ 188Os ratios for the uncontaminated on-craton melnoites, ilmenites and magnetites are radiogenic and range from 0.2133 to 0.2599 ( γ Os=+76 to +115), whereas initial 187Os/ 188Os ratios for the Mg-ilmenite at the cratonic margin are significantly more radiogenic ( 187Os/ 188Os=0.3918 and 0.4338; γ Os=+223 and +258). In contrast, the Lu–Hf isotopic data from Mg-ilmenite do not vary at the level of analytical uncertainty obtained between the on-craton and craton margin samples, suggesting the decoupling of Re and incompatible element enrichment through the 100-km section. The Lu–Hf, Sm–Nd and Re–Os isotopic systems also yield Mid-Proterozoic (1000–1400 Ma) model ages that are indistinguishable from the age of the Albany–Fraser Orogen (1100–1300 Ma) which truncates the Yilgarn craton at its southern margin. It is postulated that this episode of plate collision provided the necessary components (e.g. pyroxenites–websterites), via intra-mantle melt addition, to the lithospheric mantle to produce the observed geochemical and isotopic features in the melnoite source. This study highlights the ability of the Re–Os isotopic system, as opposed to the Lu–Hf and Sm–Nd isotopic systems, to fingerprint juvenile lithospheric mantle enrichment events and has important implications for the generation of ocean island-like Nd and Hf isotopic signatures in kimberlites and carbonatites.

An assessment of the determination of depositional ages for precambrian clastic sedimentary rocks by U–Pb dating of detrital zircons

Methodologies for the determination of depositional ages for clastic sedimentary rocks by ion microprobe U–Pb analysis of their detrital zircon populations are described. Provided there has been no sample contamination or disturbance of the U–Pb system, the youngest igneous crystallization dates obtained on detrital zircons from a sedimentary rock sample will provide a maximum age for sediment deposition. Maximum depositional ages so obtained are comparable to minimum ages determined from the dating of cross-cutting dykes, or of metamorphic or diagenetic minerals, but a significant advantage of this approach is that detrital zircons are virtually ubiquitous in clastic sedimentary rocks. The advantages and limitations of this approach are demonstrated in case studies of sedimentary rocks from the Archaean Yilgarn Craton, the Mesoproterozoic Albany–Fraser Orogen and the Neoproterozoic Officer Basin of Australia. These examples demonstrate that the probability that maximum deposition ages based on the dating of detrital zircons are close to the time of sediment deposition is influenced by the lithological characteristics of the sediment samples, with the best results obtained from lithologies with the widest possible provenance range represented in their detrital zircon populations. Due to difficulties in matching wide provenance ranges to particular source areas, lithologies that are suited to maximum depositional age determinations are not necessarily suited to provenance studies. The approach will find applications particularly in studies of sedimentary basins that lack volcanic or intrusive rocks amenable to radiometric dating.

Provenance record of a rift basin: U/Pb ages of detrital zircons from the Perth Basin, Western Australia

Abstract U/Pb dating of 588 detrital zircons by ion microprobe from Lower Triassic, Permian and lower Paleozoic sandstone samples from the Perth Basin yield ages ranging from Archean to early Paleozoic. The detrital age spectrum of Lower Triassic samples differ from underlying units in lacking Archean and post-Mesoproterozoic detritus. The Archean Yilgarn craton has previously been envisaged as the main source of detritus in the Perth basin. The bulk of the detritus, however, is of Mesoproterozoic age, which together with the overall broad spectrum of age ranges within individual samples indicates that the detritus was derived from multiple sources. Potential source regions recognized include the Yilgarn craton, the Mesoproterozoic Albany Fraser Orogen, the Meso- to Neoproterozoic Leeuwin complex of the Pinjarra orogen, and probably also the late Mesoproterozoic Northampton complex of the Pinjarra orogen. In addition, source terranes possibly associated with Greater India and East Antarctica, which originally formed the western and southern margins of the basin, may have also contributed detritus accounting for the input of material whose age cannot be related to the known age ranges in currently exposed bounding source blocks. The multi-sourced nature of the detritus suggests the Perth basin was not a simple half-graben structure down stepping to the west but contained a variety of uplifted blocks with an overall longitudinal supply of detritus from the south. The distribution of exposed source blocks changed dramatically at the start of the Triassic with the cessation of input from Archean and Neoproterozoic source regions. The differing age spectra between Triassic and Permian strata and between Late Permian and older sequences suggest any reworked detritus is of extra-basinal origin and not related to intra-basin erosion of underlying rock units. Potential sources for this reworked multicycle detritus are the metasedimentary sequences within the bounding source terranes.

Geochronological constraints for a two-stage history of the Albany–Fraser Orogen, Western Australia

Based on structural, petrographic and geochronological work (SHRIMP zircon, monazite and rutile), the Mesoproterozoic Albany–Fraser Orogeny is divided into two discrete thermo-tectonic stages, between c. 1345 and 1260 Ma (Stage I) and c. 1214 and 1140 Ma (Stage II). The existence of a two-stage history is confirmed by the discovery of 1321±24 Ma detrital zircons and 1154±15 Ma metamorphic rutiles in metasedimentary rocks from Mount Ragged. The detrital zircons demonstrate that the Mount Ragged metasedimentary rocks unconformably overly, and were derived from, Stage I basement. Metamorphic rutile formed as a consequence of overthrusting by high-grade early-Stage II rocks along an inferred NE-SW striking structure (the Rodona Fault). This interpretation is supported by zircon geochronology, which demonstrates that granulite facies metamorphism on the northwestern side of the structure predates that on the southeastern side by ∼100 Ma. Rocks to the northwest record a low-grade imprint relating to the younger (Stage II) event. The two-stage thermo-tectonic history of the Albany–Fraser Orogen correlates with adjacent Grenville-age orogenic belts in Australia and East Antarctica, implying that Mesoproterozoic Australia assembled in two stages subsequent to the amalgamation of the North Australian and West Australian cratons. Initial collision between the combined West Australian–North Australian craton and the South Australian–East Antarctic continent at c. 1300 Ma was followed by intracratonic reactivation affecting basement and cover at c. 1200 Ma. Two comparable and contemporaneous compressional orogenies controlled the formation of the Kibaran Belt in Africa and the Grenville Belt in Canada, suggesting that tectonic events in Mesoproterozoic Australia follow a similar pattern to that recognised for Rodinia amalgamation world-wide.

Provenance of detrital zircons on the Western Australia coastline—Implications for the geologic history of the Perth basin and denudation of the Yilgarn craton

Research Article| October 01, 1999 Provenance of detrital zircons on the Western Australia coastline—Implications for the geologic history of the Perth basin and denudation of the Yilgarn craton K. N. Sircombe; K. N. Sircombe 1Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia Search for other works by this author on: GSW Google Scholar M. J. Freeman M. J. Freeman 2Land Access Unit, Department of Minerals and Energy, 100 Plain Street, East Perth, Western Australia 6004, Australia Search for other works by this author on: GSW Google Scholar Geology (1999) 27 (10): 879–882. https://doi.org/10.1130/0091-7613(1999)027<0879:PODZOT>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation K. N. Sircombe, M. J. Freeman; Provenance of detrital zircons on the Western Australia coastline—Implications for the geologic history of the Perth basin and denudation of the Yilgarn craton. Geology 1999;; 27 (10): 879–882. doi: https://doi.org/10.1130/0091-7613(1999)027<0879:PODZOT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The age distributions of four detrital zircon samples from Western Australia placer deposits are found to be dominated by Neoproterozoic and Mesoproterozic ages; this outcome challenges a long-held assumption about derivation from the nearby Archean Yilgarn craton. The dominant ages are consistent with derivation from Proterozoic orogens marginal to the Yilgarn craton, including the Pinjarra orogen and Leeuwin block to the west and the Albany-Fraser orogen to the south. The results suggest that these marginal orogens were preferentially uplifted in the Jurassic-Cretaceous rifting event that formed the Perth basin and subsequently dominated the sedimentary contribution to this basin. These sediments have since been recycled to form the modern beach-sand placer deposits that reflect their non-Archean provenance despite proximity to the Yilgarn craton. The lack of a sedimentary contribution from the Yilgarn craton to the Perth basin implies that peneplanation was complete before the Mesozoic and that denudation rates have been minimal ever since. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Proterozoic tectonic framework and metal deposits of southwestern Australia

Abstract The Proterozoic tectonic evolution and metal deposits of southwestern Australia reflect a dynamic history of repeated aggregation and dispersal of continental fragments. This contrasts with previous interpretations that much of Australia was part of a Proterozoic supercontinent in which all orogenic activity and metallogenesis was ensialic. Southwestern Australia contains a wide range of sedimentary and intrusive rocks that span the whole of Proterozoic time. They occur in four Proterozoic orogens and as cover sequences on one of the orogens and on an adjacent Archaean craton. Each Proterozoic orogen formed during one of three episodes of continental collision, which occurred in the Early, Middle and Late Proterozoic. The oldest deposits (Hamersley Group) occur on the Archaean Pilbara Craton and are dominated by banded iron formations containing major supergene enriched hematite-goethite ores. Following Early Proterozoic rifting, the Archaean Pilbara and Yilgarn cratons collided and amalgamated forming the intervening Capricorn Orogen between 2.0 and 1.6 Ga. Granite with associated minor Mo, W, Bi, Pb and U mineralisation is abundant in the vicinity of the suture. Sedimentary rocks from passive continental margins and foreland basins, together with basalt, gabbro and serpentinite from oceanic or arc environments were folded and thrust outwards onto the margins of the adjacent cratons, and locally contain prominent Au, Cu and Pb mineralisation. Middle Proterozoic sedimentary rocks (Bangemall Group) that unconformably overlie the Capricorn Orogen contain significant deposits of PbCuAg and Mn. The Middle Proterozoic Albany-Fraser Orogen is dominated by huge thrust sheets of high-grade gneiss and granite reflecting another episode of continental collision along the southern margin of Western Australia. Exposed Proterozoic rocks of the Pinjarra Orogen are high-grade gneiss and granite that appear to have been involved in Late Proterozoic continental collision. The Paterson Orogen comprises Early, Middle and Late Proterozoic components that were also involved in Late Proterozoic continental collision. It contains major deposits of AuCu, CuPbZn and U.

Isotopic evidence on the age and origin of the Fraser Complex, Western Australia: a sample of Mid-Proterozoic lower crust

SmNd, RbSr and Pb isotopic data have been obtained for a variety of samples from within and around the Fraser Complex, a large (> 400 × 30 km) composite body of metagabbro which is a major component of the Proterozoic Albany-Fraser Orogen. Granites to the north and east of the complex and a granite sheet near its centre have SmNd model ages ( t DM) of ∼2000 to ∼ 2300 Ma, similar to values recorded in the western portion of the orogen. SmNd data for Fraser Complex gabbros scatter significantly on an isochron plot, but well-preserved igneous minerals extracted from one sample give 1291 ± 21 Ma with initial ϵ Nd = -1.3 ± 0.2. RbSr for the biotite-rock pair gives a cooling age of 1268 ± 20 Ma with initial 87Sr/ 86Sr≈0.706. Slices cut from a mixed gneiss/ amphibolite zone of ductile deformation and retrogression along the western margin of the complex give a ∼ 1300-Ma Pb/Pb date for final tectonic emplacement. Intrusion, granulite-facies metamorphism and upper-crustal tectonic emplacement of the complex were probably all achieved within ≤ 30 Ma. SmNd and RbSr characteristics of the western deformation zone suggest flushing by large volumes of fluid derived from a moderately depleted mantle source (ϵ Nd ≈ + 2.4; ϵ Sr, ≈ − 5 at 1300 Ma). The precursors to the Fraser Complex could have been derived from the same (or a similar) source at ∼ 1900 Ma.

Timing of plutonism in the Proterozoic Albany Mobile Belt, southwestern Australia

Abstract Zircon U-Pb ages for two adamellites from the Albany Mobile Belt, in the Albany-Fraser Orogen of southwestern Australia, fall within the range 1174 ± 12 Ma and are interpreted as dating post-tectonic granite emplacement in the belt. Slightly younger K-Ar ages on hornblendes from granulite and amphibolite facies metamorphic rocks from the southern part of the belt are interpreted as cooling ages recording uplift associated with the closing stages of orogeny and granite emplacement. A U-Pb age of 1289 ± 10 Ma for zircons from an enderbitic gneiss adjacent to the 1177 ± 12 Ma old Albany Adamellite is interpreted as dating the emplacement of the granodioritic parent of the gneiss, probably during granulite facies metamorphism. This, together with a previously reported Rb-Sr age of ∼ 1300 Ma for the granulite facies metamorphism in the northeast section of the Albany-Fraser Orogen, suggests that granulite facies conditions were widespread in the orogen at ∼ 1300 Ma. Previous Sm-Nd results suggest that the granitoids were derived from ∼ 2000 Ma old crust. So far no older zircon xenocrysts, which could support this model, have been found in the granitoids.

Precambrian tectonic evolution of part of Gondwana, southwestern Australia

Southwestern Australia has a long dynamic Precambrian history of crustal fragmentation and aggregation by continental collision and accretion. This interpretation contrasts with the widely held belief that most of Australia was part of a Proterozoic supercontinent in which all tectonic, magmatic, and metamorphic activity was intracontinental. The Pilbara and Yilgarn cratons are two quite different fragments of Archean continental crust that collided to form the Capricorn orogen between 2000 and 1600 Ma. The Albany-Fraser orogen formed along the southern margin of the Yilgarn craton during another major continental collision at 1300 to 1100 Ma. Rifting removed the northeastern part of these combined cratons and orogens between 1100 and 700 Ma. Subsequent continental collision along this rifted margin formed the Paterson orogen at 700 to 600 Ma. Therefore, the assembly of this considerable part of Gondwana may not have been completed until about 600 Ma.