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1.
AbstractThis paper summarises current knowledge on metamorphism within the entire New England Orogen (NEO) of eastern Australia. Rocks recording metamorphic assemblages characteristic of each of the three metamorphic facies series (high, medium and low P/T) have been identified within the orogen. These include high P/T blueschists and eclogites, mid P/T orogenic metamorphism and low P/T contact aureoles and sub-regional high-temperature–low-pressure (HTLP) metamorphism (regional aureoles). Metamorphism is described as it relates to six tectonic phases of development of the NEO that together comprise two major cycles of compression–extension. Medium–high-grade contact metamorphism spans all six tectonic phases while low-grade burial and/or orogenic metamorphism has been identified for four of the six phases. In contrast, exposure of high P/T eclogites and blueschists, and generation of sub-regional low P/T metamorphism is restricted to extensional phases of the orogen. Hallmarks of the orogen are two newly identified zones of HTLP metamorphism, the older of which extends for almost the entire length of the orogen.
- KEY POINTS
The orogen is dominated by low-temperature rocks while high-temperature amphibolite to granulite facies rocks are restricted to small exposures in HTLP complexes and contact aureoles.
Blueschist metamorphism falls into two categories; that associated with subduction during the Currabubula-Connors continental arc phase occurring at depths of ～13–30?km; and the other of Cambrian–Ordovician age, exposed within a serpentinite melange and associated with blocks of eclogite. The eclogite, initially from depths of ～75–90?km, appears to have been entrained in the deep crust for an extended period of geological time.
A comprehensive review of contact metamorphism in the orogen is lacking and as studies on low-grade metamorphism are more extensive in the southern part of the orogen than the north, this highlights a second research gap.
2.
R. A. Henderson C. L. Fergusson I. W. Withnall 《Australian Journal of Earth Sciences》2020,67(5):663-680
AbstractThe Charters Towers Province, of the northern Thomson Orogen, records conversion from a Neoproterozoic passive margin to a Cambrian active margin, as characteristic of the Tasmanides. The passive margin succession includes a thick metasedimentary unit derived from Mesoproterozoic rocks. The Cambrian active margin is represented by upper Cambrian–Lower Ordovician (500–460?Ma) basinal development (Seventy Mile Range Group), plutonism and metamorphism resulting from an enduring episode of arc–backarc crustal extension. Detrital zircon age spectra indicate that parts of the metamorphic basement of the Charters Towers Province (elements of the Argentine Metamorphics and Charters Towers Metamorphics) overlap in protolith age with the basal part of the Seventy Mile Range Group and thus were associated with extensional basin development. Detrital zircon age data from the extensional basin succession indicate it was derived from a far-field (Pacific-Gondwana) primary source. However, a young cluster (<510?Ma) is interpreted as reflecting a local igneous source related to active margin tectonism. Relict zircon in a tonalite phase of the Fat Hen Creek Complex suggests that active margin plutonism may have extended back to ca 530?Ma. Syntectonic plutonism in the western Charters Towers Province is dated at ca 485–480?Ma, close to timing of metamorphism (477–467?Ma) and plutonism more generally (508–455?Ma). The dominant structures in the metamorphic basement formed with gentle to subhorizontal dips and are inferred to have formed by extensional ductile deformation, while normal faulting developed at shallower depths, associated with heat advection by plutonism. Lower Silurian (Benambran) shortening, which affected metamorphic basement and extensional basin units, resulted in the dominant east–west-structural trends of the province. We consider that these trends reflect localised north–south shortening rather than rotation of the province as is consistent with the north–south paleogeographic alignment of extensional basin successions.
- KEY POINTS
Northern Tasmanide transition from passive to active margin tectonic mode had occurred by ca 510?Ma, perhaps as early as ca 530?Ma.
Cambro-Ordovician active margin tectonism of the Charters Towers Province (northern Thomson Orogen) was characterised by crustal extension.
Crustal extension resulted in the development of coeval (500–460?Ma) basin fill, granitic plutonism and metamorphism with rock assemblages as exposed across the Charters Towers Province developed at a wide range of crustal levels and expressing heterogeneous exhumation.
Protoliths of metasedimentary assemblages of the Charters Towers Province include both Proterozoic passive margin successions and those emplaced as Cambrian extensional basin fill.
3.
J. McPhie K. J. Ehrig M. B. Kamenetsky J. L. Crowley V. S. Kamenetsky 《Australian Journal of Earth Sciences》2020,67(5):699-716
AbstractAcropolis is an Fe-oxide–copper–gold prospect ～20?km from Olympic Dam, South Australia, and marked by near-coincident gravity and magnetic anomalies. Prospective Fe-oxide–apatite?±?sulfide veins occur in Mesoproterozoic and Paleoproterozoic volcanic and granitoid host units beneath unmineralised sedimentary formations. We have produced a geological map and history of the prospect using data from 16 diamond drill holes, including LA-ICPMS and high-precision CA-TIMS ages. The oldest unit is megacrystic granite of the Donington Suite (ca 1850?Ma). A non-conformity spanning ca 250 My separates the Donington Suite and felsic lavas and ignimbrites of the Gawler Range Volcanics (GRV; 1594.03?±?0.68?Ma). The GRV were intruded by granite of the Hiltaba Suite (1594.88?±?0.50?Ma) and felsic dykes (1593.88?±?0.56?Ma; same age as the Roxby Downs Granite at Olympic Dam). The felsic dykes are weakly altered and lack Fe-oxide–apatite–sulfide veins, suggesting that they post-date the main hydrothermal event. If correct, this relationship implies that the main hydrothermal event at Acropolis was ca 1594?Ma and pre-dated the main hydrothermal event at Olympic Dam. The GRV at Acropolis are the same age as the GRV at Olympic Dam and ca 3–7 My older than the GRV exposed in the Gawler Ranges. The gravity and magnetic anomalies coincide with sections through the GRV, Hiltaba Suite and Donington Suite that contain abundant, wide, Fe-oxide veins. The GRV, Hiltaba Suite and Donington Suite are unconformably overlain by the Mesoproterozoic Pandurra Formation or Neoproterozoic Stuart Shelf sedimentary formations. The Pandurra Formation shows marked lateral variations in thickness related to paleotopography on the underlying units and post-Pandurra Formation pre-Neoproterozoic faults. The Stuart Shelf sedimentary formations have uniform thicknesses.
- KEY POINTS
Fe-oxide–apatite?±?sulfide veins are hosted by the Gawler Range Volcanics (1594.03?±?0.68?Ma), the Hiltaba Suite granite (1594.88?±?0.50?Ma) and Donington Suite granite (ca 1850?Ma).
The age of felsic dykes (1593.88?±?0.56?Ma) interpreted to be post-mineralisation implies that the main hydrothermal event at Acropolis was ca 1594?Ma.
The Gawler Range Volcanics at Acropolis are the same age as the Gawler Range Volcanics at Olympic Dam and ca 3 to 7 My older than the Gawler Range Volcanics exposed in the Gawler Ranges.
4.
AbstractThe Gangdese batholith, Tibet, records the opening and closing of the Neo-Tethyan ocean and the resultant collision between the Indian and Eurasian plates. The Mesozoic magmatic rocks play a crucial role in understanding the formation and evolution of the Neo-Tethyan tectonic realm. This study focuses on Jurassic intrusive rocks in the Xietongmen area of the southern margin of the Lhasa terrane adjacent to the Yarlung–Tsangpo suture. Zircon U–Pb dating yielded Middle Jurassic dates for ca 170?Ma hornblende gabbro and ca 173?Ma granodiorite intrusions. All of the samples are medium- to high-K calc-alkaline, and the majority are metaluminous and enriched in the large ion lithophile elements and depleted in the high-field-strength elements. This indicates the magma was generated in a subduction-related tectonic setting. The intrusive rocks have high and positive εHf(t) values (hornblende gabbro: 13.3–18.7; granodiorite: 14.2–17.6) that yield Hf model ages younger than 312?Ma. These new data, combined with the results of previous research, suggest that the Jurassic igneous rocks were derived from a metasomatised region of an asthenospheric mantle wedge. Extremely depleted Sr–Nd–Pb–Hf isotope compositions are similar to the Yarlung ophiolite and igneous rocks within other intra-oceanic island arcs. Together with the existence of sandstone that is identified as the product of the oceanic island arc environment, we suggest formation in an intra-oceanic island arc.
The new zircon U–Pb dating has yielded Middle Jurassic ages for the ca 170?Ma hornblende gabbro and ca 173?Ma granodiorite phases of the Xietongmen intrusion.
Jurassic igneous rocks formed from a metasomatised asthenospheric mantle wedge by northward subduction of the Neo-Tethys oceanic crust beneath the southern margin of the Lhasa terrane.
Late Triassic–Jurassic igneous rocks, which are characterised by highly depleted isotopic compositions within the Southern Lhasa sub-terrane, record residual intra-oceanic island arcs in the eastern Tethyan belt.
5.
R. Abdullah U. Shaanan K. Lynn G. Rosenbaum 《Australian Journal of Earth Sciences》2020,67(2):153-173
AbstractCambrian deformation associated with the Delamerian Orogeny is most evident in the Delamerian Orogen (southwestern Tasmanides) but has also been documented in the Thomson Orogen (northern Tasmanides). The tectonic evolution of the Thomson Orogen in the context of the Delamerian Orogeny is poorly understood. In particular, tectonostratigraphic relationships between the different parts of the Thomson Orogen (Anakie Inlier, Nebine Ridge, and southern Thomson Orogen) are still unclear. New detrital zircon data from the Nebine Ridge revealed an age spectrum that is consistent with published geochronological data from the Anakie Inlier. These results, in conjunction with petrographic observations and the interpretation of geophysical data, suggest that along the eastern part of the Thomson Orogen, the?～?NNE-trending Nebine Ridge represents the southward continuation of the?～?N–S-trending Anakie Inlier. New detrital zircon geochronological data are also presented for metasedimentary rocks from both sides of the Thomson–Lachlan boundary. The results constrain the maximum age of deposition (Ordovician–Devonian), and show that both sides of the Thomson–Lachlan boundary received detritus from a similar provenance. This might suggest that the Thomson–Lachlan boundary did not play a major role as a crustal-scale boundary prior to the Devonian. We speculate that transpressional deformation along this?～?E–W boundary, during the Early Devonian, was responsible for disrupting the original belt that connected the Delamerian Orogen (Koonenberry Belt) with the eastern Thomson Orogen (Nebine Ridge and Anakie Inlier).
- Highlights
The Nebine Ridge is the southward continuation of the Anakie Inlier.
The Anakie Inlier and Nebine Ridge represent a northern segment of the Cambrian Delamerian–Thomson Belt.
～E–W-trending crustal-scale structures at the southern Thomson Orogen were active during Devonian.
6.
J. D. Clemens 《Australian Journal of Earth Sciences》2020,67(2):175-200
AbstractInformation, mainly from the granitic and silicic volcanic rocks in the Stawell, Bendigo and Melbourne structural zones in the state of Victoria, shows that the sources of both the S- and I-type rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with the sources of similar granitic rocks in the Melbourne Zone, consistent with the absence of the mainly Proterozoic Selwyn Block beneath most of the SBZ. Below a mid-crustal décollement in the SBZ, the crust is evidently highly variable and possibly includes thinned Proterozoic crust. There is geochronological evidence for ca 400 and ca 370?Ma granulite-grade metamorphic events here, and, after this double bout of metamorphism, and depletion in the silicic melt component, the constituents of the entire deep crust of the SBZ would have densities similar to those of overlying, much lower-grade Cambrian metabasaltic to boninitic rocks. Thus, granitic magmas may have formed here by partial melting of a variety of rock types, probably with back-arc affinities, with ages that may extend back to the Proterozoic. Therefore, the basement of the SBZ is unlikely to consist solely of thick ocean-floor rocks, as in some current interpretations.
- KEY POINTS
The sources of the Devonian granitic rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with those of the Melbourne Zone granites.
Two Devonian granulite-facies events left the melt-depleted deep SBZ crust with densities similar to those of overlying Cambrian metabasaltic rocks.
The SBZ Devonian granitic magmas probably formed by partial melting of heterogeneous Proterozoic to Cambrian arc-related crust, below the mid-crustal décollement.
7.
M. R. M. Ferguson K. Ehrig S. Meffre A. R. Cherry 《Australian Journal of Earth Sciences》2020,67(2):201-220
AbstractThe Hiltaba Suite intrusive rocks and penecontemporaneous Gawler Range Volcanics (GRV) comprise the 1590?Ma Gawler silicic large igneous province in the Gawler Craton, South Australia. Zircon is principally associated with Fe–Ti oxides and clusters of touching crystals in these rocks, including in the Roxby Downs Granite (RDG), host of the Olympic Dam iron oxide–copper–gold deposit, and in other intrusive rocks that comprise the Olympic Province. There has been no explicit evaluation and explanation of potential origins published for concentrations of zircon with Fe–Ti oxides (herein zircon-rich clusters) found in these and similar rocks of western North America and elsewhere. Here we use U–Pb geochronology, mineral morphologies and compositions, and insights from surface chemistry and liquid-bound particle interaction studies to investigate zircon-rich clusters and provide a model for their formation. U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590?Ma, so it is unlikely that there are significant xenocrystic zircon grains or that the zircons include significant inherited cores. The lack of pre-magmatic zircon, consistent intra-grain and inter-grain zircon compositional trends, the predominance of oscillatory zoned zircon with morphologies indicating growth from hot, evolved silicate melts, and the lack of evidence for zircon recrystallisation, indicates that zircon crystallised in the host GRV and RDG magmas. Variable zircon compositions within individual clusters does not support epitaxial nucleation of zircon on Fe–Ti oxides, but it is likely that some zircon grains grew from seed crystals formed by exsolution of Zr from Fe–Ti oxides. Aggregation of isolated, liquid-bound crystals is energetically favourable, and the grainsize discrepancy between larger crystals (Fe–Ti oxides, pyroxenes) and smaller accessory minerals (zircon, apatite) maximises the disparity in particle velocities and hence enhances the opportunities for collisions and adhesion between these crystals. We propose that zircon adheres to Fe–Ti oxides with greater ease and/or with greater bond strengths, than to other phases present in the parental magmas. It is possible that this association is related to interactions between zircon and Fe–Ti oxide surface sites with opposing charges, presuming the distance between phase surfaces is sufficiently small. The occurrence of small zircon grains within Fe–Ti oxides and both euhedral zircon and zircon with asymmetric growth zonation in contact with Fe–Ti oxides indicates that several processes are responsible for the high concentrations of zircon crystals in some Fe–Ti oxide clusters.
Zircon is principally associated with Fe--Ti oxides in 1.59 Ga Gawler Range Volcanics (GRV) and Roxby Downs Granite (RDG)
U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590?Ma
Zircon compositions and morphologies indicate that zircon crystallised in the host RDG and GRV magmas and suggest recharge, reheating and mixing occurred in these magmatic systems
Seed crystals, aggregation and surface chemical affinities contributed to the strong association of zircon and Fe–Ti oxides
8.
AbstractThe shape and structural development of the box-like Parrabel Dome (PD) within the Hastings Block is poorly understood because it has only been weakly cleaved, complexly folded and extensively faulted in comparison to the adjoining blocks. Better characterising this block will provide important controls on the tectonics of the southern New England Orogen. The structural development of the PD and southern Hastings Block (SHB) provides evidence of the degree of rotation, translation and deformation of the Hastings Block, a key terrane within the southern New England Orogen. A major decollement under the Hastings Block–Nambucca Block was suggested to facilitate south-directed deformation caused by the developing Coffs Harbour Orocline. The orientation of bedding and the stratigraphic facing of some fault blocks within the northern Hastings Block (NHB) are consistent with development of the PD, while other fault blocks indicate significant disruption of the NHB prior to, during and after dome development. A deep-seated fault is suggested by the gravity worm analysis consistent with the boundary zone between the PD, NHB-Yarrowitch Block and the east-dipping and younging sequences in the SHB. The eastern limb of the PD underwent clockwise rotation after formation. Fault blocks have been rotated and translated within a restraining bend as the NHB moved post-PD formation northwest along the interface between the NHB and SHB.
- KEY POINTS
The Hastings Block was translated and rotated into its current position from the southeastern end of the Tamworth Belt.
Gravity worm data indicate a boundary between northern and southern Hastings Block.
The Hastings and Nambucca blocks have been detached from the basement Gondwana rocks.
Fault block analysis within the Parrabel Dome, northern Hastings Block indicates relocation of some blocks by faulting.
9.
T. J. Munson S. W. Denyszyn J. M. Simmons M. Kunzmann 《Australian Journal of Earth Sciences》2020,67(3):321-330
AbstractAn interpreted CA–IDTIMS age of 1642.2?±?3.9?Ma for a volcanogenic tuffaceous siltstone from the previously undated Fraynes Formation of the Birrindudu Basin in the northwestern Northern Territory enables a rigorous chronostratigraphic correlation to be made with the economically important Barney Creek Formation of the southern McArthur Basin. This result supports previous interpretations that these geographically widely separated formations are probably linked in the subsurface. It also establishes the stratigraphic interval encompassing the Fraynes and Barney Creek formations as a potential target for greenfields base metals and petroleum exploration programs across the greater McArthur Basin.
- KEY POINTS
A new interpreted CA–IDTIMS age provides a chronostratigraphic link between the Fraynes Formation of the Birrindudu Basin and the economically important Barney Creek Formation of the southern McArthur Basin.
The Fraynes and Barney Creek formations are probably linked in the subsurface.
This stratigraphic level is a potential target for greenfields base metals and petroleum exploration across the greater McArthur Basin.
10.
P. J. Hatherly 《Australian Journal of Earth Sciences》2020,67(2):243-263
AbstractFor the past 200?years, there have been numerous investigations and much speculation concerning the formation of the dramatic valleys of the Blue Mountains of NSW. In this paper, further evidence for the uplift and erosional history of the Blue Mountains is obtained from longitudinal river profiles, detailed mapping of the Rickabys Creek Gravel on the Lapstone Structural Complex and consideration of the topographical position of Miocene basalts. Knickpoints on the main rivers flowing east from the Great Dividing Range are identified and interpreted to be due to uplift events linked to the northward movement of the Australian continent over mantle inhomogeneities. At the Lapstone Structural Complex on the eastern range front, the occurrence of the Rickabys Creek Gravel and the nature of the over-steepened reaches on the rivers and streams crossing the Complex, suggest a more recent ongoing phase of uplift and antecedent river erosion. The Miocene basalts provide evidence of this landscape 20–15?Ma. Their locations with respect to the current rivers and ridges are interpreted to show additional evidence for recent uplift that has resulted in the formation of the Lapstone Structural Complex. It is suggested that this uplift commenced 10–5?Ma when the contemporary compressive stress field was established.
- KEY POINTS
Longitudinal profiles for major rivers in the Blue Mountains are consistent with a model of initial Cretaceous uplift followed by further Cenozoic uplift associated with dynamic topography.
Mapping of Rickabys Creek Gravel within the Lapstone Structural Complex suggests the presence of antecedent rivers.
Within the Lapstone Structural Complex, stream profiles, gravels and nearby outcrops of Miocene basalts are interpreted to indicate a third phase of uplift, possibly since 10?Ma.
11.
S. J. Craven 《Australian Journal of Earth Sciences》2017,64(3):401-418
Detrital zircon from the Carboniferous Girrakool Beds in the central Tablelands Complex of the southern New England Orogen, Australia, is dominated by ca 350–320 Ma grains with a peak at ca 330 Ma; there are very few Proterozoic or Archean grains. A maximum deposition age for the Girrakool Beds of ca 309 Ma is identified. These data overlap the age of the Carboniferous Keepit arc, a continental volcanic arc along the western margin of the Tamworth Belt. Zircon trace-element and isotopic compositions support petrographic evidence of a volcanic arc provenance for sedimentary and metasedimentary rocks of the central Tablelands Complex. Zircon Hf isotope data for ca 350–320 Ma detrital grains become less radiogenic over the 30 million-year record. This pattern is observed with maturation of continental volcanic arcs but is opposite to the longer-term pattern documented in extensional accretionary orogens, such as the New England Orogen. Volcanic activity in the Keepit arc is inferred to decrease rapidly at ca 320 Ma, based on a major change in the detrital zircon age distribution. Although subduction continues, this decrease is inferred to coincide with the onset of trench retreat, slab rollback and the eastward migration of the magmatic arc that led to the Late Carboniferous to early Permian period of extension, S-type granite production and intrusion into the forearc basin, high-temperature–low-pressure metamorphism, and development of rift basins such as the Sydney–Gunnedah–Bowen system. 相似文献
12.
R. P. Bourman D. Banerjee S. Buckman D. K. Panda A. P. Belperio 《Australian Journal of Earth Sciences》2020,67(5):627-647
AbstractQuaternary alluvial and colluvial sediments infill major river valleys and form alluvial fans and colluvium-filled bedrock depressions on the range fronts and within the Mount Lofty Ranges of southern Australia. A complex association of alluvial successions occurs in the Sellicks Creek drainage basin, as revealed from lithostratigraphy, physical landscape setting and optically stimulated luminescence (OSL) ages. Correlation of OSL ages with the Marine Oxygen Isotope record reveals that the alluvial successions represent multiple episodes of alluvial sedimentation since the penultimate glaciation (Marine Isotope Stage 6; MIS 6). The successions include a penultimate glacial maximum alluvium (Taringa Formation; 160?±?15?ka; MIS 6), an unnamed alluvial succession (42?±?3.2?ka; MIS 3), a late last glacial colluvial succession within bedrock depressions (ca 15?ka; MIS 2) and a late last glacial alluvium (ca 15?ka; MIS 2) in the lowest, distal portion of Sellicks Creek. In addition, the Waldeila Formation, a Holocene alluvium (3.5?±?0.3?ka; MIS 1), and sediments deposited during a phase of Post-European Settlement Aggradation (PESA) are also identified. The age and spatial distribution of the red/brown successions, mapped as the Upper Pleistocene Pooraka Formation, directly relate to different topographic and tectonic settings. Neotectonic uplift locally enhanced erosion and sedimentation, while differences in drainage basin sizes along the margin of the ranges have influenced the timing and delivery of sediment in downstream locations. Close to the Willunga Fault Scarp at Sellicks Creek, sediments resembling the Pooraka Formation have yielded a pooled mean OSL age of 83.9?±?7?ka (MIS 5a) corroborating the previously identified extended time range for deposition of the formation. Elsewhere, within major river valleys, the Pooraka Formation was deposited during the last interglacial maximum (128–118?ka; MIS 5e). In general, alluviation occurred during interglacial and interstadial pluvial events, while erosion predominated during drier glacial episodes. In both cases, contemporaneous erosion and sedimentation continued to affect the landscape. For example, in the Sellicks Creek drainage basin, which lies across an actively uplifting fault zone, late glacial age sediments (MIS 2) occur within the ranges and near the distal margin of the alluvial fan complex. OSL dating of the alluvial successions reported in this paper highlights linkages between the terrestrial and marine environments in association with sea-level (base-level) and climatic perturbations. While the alluvial successions relate largely to climatically driven changes, especially in major river valleys, tectonics, eustasy, geomorphic setting and topography have influenced erosion and sedimentation, especially on steep-sloped alluvial fan environments.
- KEY POINTS
Luminescence dating of the Sellicks Creek alluvial fan complex reveals that sedimentation occurred predominantly during the later stages of glacial cycles accompanying lower sea-levels than present.
Luminescence dating confirms that the stratigraphically lower portions of the Pooraka Formation are beyond the range of radiocarbon dating.
Upper Pleistocene alluvial fan sedimentation at Sellicks Creek correlates with pluvial events in southeastern Australia.
13.
The Wongwibinda Metamorphic Complex (WMC) is a high‐temperature, low‐pressure (HTLP) belt in the southern New England Orogen. It is characterized by a high metamorphic field gradient exposed in variably metamorphosed siliceous turbidites. The Abroi Granodiorite and the Rockvale and Tobermory adamellites, S‐type granitoids of the Hillgrove Plutonic Suite, intrude the metaturbidites. Six samples of metaturbidite were studied from an ～3 km long field traverse. Integrated petrography, mineral chemistry, and mineral equilibria modelling indicate a peak metamorphic temperature of 350–450 °C in the lowest grade rocks and ～660 °C in the highest‐grade rocks. Maximum pressure does not exceed 3.5 kbar anywhere, implying a maximum depth of 12 km and indicating an average vertical gradient of at least 55 °C km?1, though our calculations suggest this is not linear. Metamorphic isograds show no apparent relationship with distance to the exposed margins of the Hillgrove Suite granitoids. Electron microprobe U–Th–Pb monazite data indicate a date of 296.8 ± 1.5 Ma for the thermal peak of the HTLP metamorphism. Laser ablation inductively coupled plasma mass spectrometry indicates a zircon U–Pb crystallization age of 290.5 ± 1.6 Ma for the Abroi Granodiorite, confirming that the pluton post‐dates the peak HTLP metamorphism. Consequently, magmatic advective heat transfer from depth via emplacement of a large volume of granitoid is unlikely to be the key local driver of the high‐grade metamorphism. It is concluded that published evidence of an extensional geodynamic setting around the Carboniferous–Permian boundary supports conductive heat transfer as the key driver of HTLP metamorphism for the WMC. It is not possible to exclude magmatic advective heat transfer via emplacement of mantle derived basaltic magmas in the deeper crust. 相似文献
14.
J. J. Veevers 《Australian Journal of Earth Sciences》2013,60(4):385-408
The Quaternary beach sand of SE Australia, driven northward by southern swell, contains zircons with dominant U–Pb ages of 700–500 Ma, model ages (TDMc) of 2.2 Ga to 1.0 Ga, and ?Hf of +12 to –30, indicating a host rock type of granitoids with alkaline affinity. These properties match those of detrital zircons in the Middle Triassic (ca 240 Ma) Hawkesbury Sandstone (TDMc of 2.1 to 1.0 Ga, ?Hf of +8 to –40, alkaline granitoids) and the Ordovician (ca 460 Ma) turbidites and ca 430 Ma S-type granitoids of the Lachlan Orogen (T2DM of 2.0 to 1.0 Ga, ?Hf of +5 to –30), all of which are identified as proximal provenances. Superimposed are the ca 400 Ma zircons in beaches in the south backed by the 420–375 Ma I-type Bega Batholith, and ca 350 Ma and ca 250 Ma zircons in the north backed by the New England Orogen. The Ordovician turbidites, part of a deep-sea super-fan, were fed by the detritus of the exhumed 700–500 Ma Transgondwanan Supermountains atop the East African–Antarctic Orogen. At the same time, the ancestral Gamburtsev Subglacial Mountains of East Antarctica probably contributed a subsidiary fan of 700–500 Ma sediment. Primary zircons aged 600–500 Ma in igneous and metamorphic rocks in Australia and the ancestral Transantarctic Mountains are minor contributors of the Australian sediments. The properties of the 700–500 Ma primary zircons in the East African–Antarctic Orogen are traceable through the first-cycle Ordovician turbidite and intruding second-cycle granite, and younger sediment, such as the third-cycle Triassic Hawkesbury Sandstone and the third-cycle beach sand. The sand at the northern terminus of the coastal system off Fraser Island spills over the shelf edge into the Tasman Abyssal Plain to reflect in miniature the deep-sea depositional environment of the Ordovician. 相似文献
15.
A. P. Fan S. N. Sun Z. Zhang S. De J. D. N. Nenzhelele 《Australian Journal of Earth Sciences》2020,67(3):361-377
AbstractLongstanding debates on the tectonic setting and provenance of the Lower Cretaceous Lingshandao Formation have hindered basin analysis and tectonic studies of the collision of the Yangtze Craton and the North China Craton, and thus the evolution of the Sulu Orogen. Thin-section analysis, identification of rock particles, cathodoluminescence, heavy minerals and trace-element analysis have, in addition to field investigations, been applied to reconstruct the source area and transport pathways of the sediments that build the Lower Cretaceous Laiyang Group on the Lingshan Island, western Yellow Sea. These analyses indicate that the Laiyang Group consists mainly of material derived from a recycled orogen and from transitional continental sediments. The Laiyang Group on Lingshan Island has been sourced from igneous and metamorphic rocks. Comparing analyses of detrital minerals with rocks from surrounding areas leads to the conclusion that the main source area is the Sulu Orogen that supplied sediment to rift basin rather than a residual basin between the Yangtze Craton and the North China Craton.
A recycled orogenic belt is the source area for the Laiyang Group on Linshan Island.
Felsic metamorphic and igneous rocks form the most probable sources.
The rift basin was filled by sediments supplied from the Sulu Orogen on both sides.
16.
G. C. Young R. L. Dunstone P. J. Ollerenshaw J. Lu B. Crook 《Australian Journal of Earth Sciences》2020,67(2):221-242
AbstractEdenopteron, with a lower jaw some 48?cm long, and total length perhaps exceeding 3 m, is the largest Devonian lobe-fin known from semi-articulated remains. New material described from the type locality (Boyds Tower, south of Eden) includes three slightly smaller articulated skulls and jaws, and additional bones of the shoulder girdle. Another articulated skull roof, shoulder girdle and palate is described from a second locality (Hegarty Bay), about 10?km south of Boyds Tower. Both localities represent the upper part of the Worange Point Formation, of late Famennian age (uppermost Upper Devonian). The new morphological evidence supports a close relationship to the tristichopterids Mandageria and Cabonnichthys, from the slightly older (Frasnian, Upper Devonian) fossil fish assemblage at Canowindra, New South Wales. Features of the shoulder girdle (supracleithrum, anocleithrum) suggest that Edenopteron is more closely related to Mandageria than Cabonnichthys. Eight characters are used to define a tristichopterid subfamily Mandageriinae, to which Notorhizodon from the Middle Devonian of Antarctica is also referred. The Mandageriinae is endemic to East Gondwana (Australia–Antarctica). In combination with possibly the most primitive tristichopterid, Marsdenichthys from the Frasnian of Victoria, these distributions implicate East Gondwana as a likely place of origin for the entire group. This relates to the major but unresolved question of a possible Gondwana origin for all the land vertebrates (tetrapods).
An endemic Gondwanan sub-group (Mandageriinae) of the Devonian fishes closest to land animals (tetrapodomorph tristichopterids) is confirmed.
Retention of primitive features (e.g. accessory vomers) points to an earlier origin of the Mandageriinae in East Gondwana, consistent with the Victorian occurrence of another primitive tristichopterid (Marsdenichthys).
Edenopteron is confirmed from a second south coast fossil site, and new characters indicate its closest relative is Mandageria from Canowindra, NSW.
Congruent evidence of older Gondwanan occurrences in other groups (basal tetrapodomorphs, rhizodontids, canowindrids), and previously dismissed trace fossil evidence (Grampians trackways), implicate South China and East Gondwana as the likely place of origin for all land vertebrates.
17.
S. J. Craven 《Australian Journal of Earth Sciences》2018,65(2):191-207
The high-temperature–low-pressure Wongwibinda Metamorphic Complex of the southern New England Orogen is bound by S-type granite plutons of the Hillgrove Supersuite to the north, east and south. New U–Pb geochronology of five samples of the Hillgrove Supersuite demonstrates that plutonism in the complex involved two pulses: ca 300 Ma and ca 292 Ma. This indicates that plutonism partially overlaps the age of high-T–low-P metamorphism (296.8 ± 1.5 Ma), but also postdates it. Zircon grains identified as xenocrysts based on age (≥310 Ma) have U–Pb–Hf isotopic character that largely overlaps detrital grains in the host Girrakool Beds, indicating that accretionary complex crust is the likely source of these xenocrysts. The 176Hf/177Hf initial character for zircon for the ca 300 Ma plutons (three samples) is less radiogenic than those in the ca 292 Ma plutons (two samples). The progression in 176Hf/177Hf initial character for zircon infers an increasing mantle component in the Hillgrove Supersuite with time. These data are evidence of a rift tectonic setting, where mantle-derived magmas are predicted to more readily migrate to shallower crustal levels as the crust thins and becomes hotter. Additionally, early episodes of partial melting in the system melt-depleted the metasedimentary sources, thus reducing the S-type component as anatexis progressed. The evolution of the Hillgrove Supersuite coincides with a period of early Permian slab roll back and extension accompanied by crustal rifting and thinning, leading to high-T–low-P metamorphism, anatexis and S-type granite production and the development of rift basins such as the Sydney–Gunnedah–Bowen system. 相似文献
18.
C. L. Fergusson P. F. Carr C. M. Fanning T. J. Green 《Australian Journal of Earth Sciences》2013,60(6):857-866
The Anakie Metamorphic Group is a complexly deformed, dominantly metasedimentary succession in central Queensland. Metamorphic cooling is constrained to ca 500 Ma by previously published K–Ar ages. Detrital‐zircon SHRIMP U–Pb ages from three samples of greenschist facies quartz‐rich psammites (Bathampton Metamorphics), west of Clermont, are predominantly in the age range 1300–1000 Ma (65–75%). They show that a Grenville‐aged orogenic belt must have existed in northeastern Australia, which is consistent with the discovery of a potential Grenville source farther north. The youngest detrital zircons in these samples are ca 580 Ma, indicating that deposition may have been as old as latest Neoproterozoic. Two samples have been analysed from amphibolite facies pelitic schist from the western part of the inlier (Wynyard Metamorphics). One sample contains detrital monazite with two age components of ca 580–570 Ma and ca 540 Ma. The other sample only has detrital zircons with the youngest component between 510 Ma and 700 Ma (Pacific‐Gondwana component), which is consistent with a Middle Cambrian age for these rocks. These zircons were probably derived from igneous activity associated with rifting events along the Gondwanan passive margin. These constraints confirm correlation of the Anakie Metamorphic Group with latest Neoproterozoic ‐ Cambrian units in the Adelaide Fold Belt of South Australia and the Wonominta Block of western New South Wales. 相似文献
19.
A. M. Piechocka J.-W. Zi C. J. Gregory S. Sheppard B. Rasmussen 《Australian Journal of Earth Sciences》2013,60(7):973-990
AbstractUnlike many Phanerozoic orogens, where the primary effects of orogenic events can be easily determined, Precambrian orogens are commonly characterised by repeated tectonothermal events making it challenging to decipher the geological history. The Capricorn Orogen is a complex Precambrian intraplate orogen located within the West Australian Craton that has been subjected to four separate reworking tectonic events between 1820 and 900?Ma. Although direct U–Pb ages for metamorphism have been obtained for the younger events, there is only limited geochronological data for the oldest event, the 1820–1770?Ma Capricorn Orogeny. This is primarily because of multiple episodes of deformation and metamorphism overprinting and obscuring the original tectonic fabrics and destroying metamorphic chronometers. In this study, we use in situ U–Pb monazite and xenotime geochronology, from a feldspathic metasandstone, a quartz–muscovite–chlorite–garnet pelitic schist, a quartz–muscovite–tourmaline schist and a garnet–biotite–plagioclase pelitic gneiss, to obtain the first direct age constraints for metamorphism during the Capricorn Orogeny in the northern Gascoyne Province. Metamorphism was synchronous with the 1820–1775?Ma magmatism in the northern part, and possibly in the southern part, of the Gascoyne Province. Furthermore, our results hint at a late stage hydrothermal fluid event at ca 1750–1730?Ma, post-dating the magmatism in the northern Gascoyne Province. 相似文献
20.
AbstractThe Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study.
- KEY POINTS
U–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters.
(U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters.
Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin.