Triassic asymmetric subduction rollback in the southern New England Orogen (eastern Australia): the end of the Hunter-Bowen orogeny (original) (raw)
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Tectonophysics, 1994
The Adelaide, Lachlan and New England fold belts of eastern Australia record the continental growth of eastern Gondwanaland during the Palaeozoic. The New England Fold Belt (NEFB) represents a tectonic collage formed by subduction/accretion during the Late Paleozoic, but contains remnants of subduction-related rocks that date from the Cambrian. The Lachlan Fold Belt (LFB) developed inboard from the NEFB, initially as an amalgam of Proterozoic continental and Cambrian oceanic fragments that formed by rift and drift at the leading edge of eastern Gondwanaland. Convergent tectonism at N 500 Ma welded the fragments to the craton and formed the Adelaide fold belt. Oceanward dispersal of detritus across the LFB produced an overlap assemblage of quartzose Ordovician turbidites, and a new subduction zone developed at the eastern margin. The tectonic setting was similar to the modern Philippines plate of the western Pacific. Behind-the-arc, Silurian-Devonian convergent tectonics converted the 1700-2000~km-wide continental margin of the Proto-LFB into a-750~km-wide, thinskinned , fold-magmatic belt within 60 Ma. The driving force was delamination, which produced a ubiquitous basaltic underplate that generated: (1) regional low-P metamorphism; (2) local anticlockwise P-T-t paths and crustal-scale isobaric cooling; (3) voluminous syn-to late-tectonic granitoids, emplaced at rates approximately twice that of modern arcs; and (4) normal thickness crust, despite an average of N 60% shortening. Delamination occurred in two separate areas originally-1000 km apart, first in the eastern, then in the western part of the LFB. The LFB and its northern counterpart, the Thomson fold belt, represent approximately one-fifth of the Australian continent, and evolved from dispersed fragments into stable continental crust in N 300 Ma. Such rapid growth rates are typical of the 2.7-2.5 Ga and 1.9-1.7 Ga periods, when voluminous, widespread granitoids and large turbidite-dominated, low-P metamorphic belts were produced in settings that are not obviously subduction-related. Therefore, a similar process of rift-drift-delamination (RIDDEL tectonics) may have periodically operated throughout Earth history.
Chronological constraints on the Permian geodynamic evolution of eastern Australia
The New England Orogen in eastern Australia developed as a subduction-related orogen in the Late Devonian to Carboniferous, and was modified in the Permian by deformation, magmatism and oroclinal bending. The geodynamics associated with the development of the New England oroclines and the exact timing of major tectonic events is still enigmatic. Here we present new 40 Ar/ 39 Ar results from metasedimentary and volcanic rocks from the southern New England Orogen. Eight grains from four metasedimentary samples (Texas beds) that originated in the Late Devonian to Carboniferous accretionary wedge yielded reproducible plateau ages of~293, 280,~270 and~260 Ma. These results suggest a complex thermal history associated with multiple thermal events, possibly due to the proximity to Permian intrusions. Two samples from mafic volcanic rocks in the southernmost New England Orogen (Alum Mountain Volcanics and Werrie Basalt) yielded eruption ages of 271.8 ± 1.8 and 266.4 ± 3.0 Ma. The origin of these rocks was previously attributed to slab breakoff, following a period of widespread extension in the early Permian. We suggest that this phase of volcanism marked the transition from backarc extension assisted by trench retreat to overriding-plate contraction. The main phase of oroclinal bending has likely occurred during backarc extension in the early Permian, and terminated at 271-266 Ma with the processes of slab segmentation and breakoff.
WABS, 2019
The post-Lower Permian succession of the Perth Basin and Westralian Superbasin can be directly related to the plate tectonic evolution of the Gondwanan Super-continent. In the Late Permian to Albian the northern edge of Gondwana continued to break into microplates that migrated to the north and were accreted into what is today the southeastern Asia (Burma–China) region. These separation events are recorded as a series of stratigraphically distinct transgressions (corresponding to the initial stretching of the asthenosphere and acceleration of subsidence rates) followed by rapid regressions (when new oceanic crust was emplaced in thinned continental crust causing uplifts of large continental masses). Because the events are synchronous across large regions, and may be identified from specific log and seismic signatures, the intensity of stratigraphically related transgressive/regressive cycles varies, depending on the distance from the break-up centres and these cycles allow the ident...
Tectonic and Geodynamic Evolution of the Northern Australian Margin and New Guinea
ASEG Extended Abstracts
Rapid convergence between the Indo-Australian, Southeast Asian, and Pacific plates in the Cenozoic has resulted in a complex tectonic evolution of Australia's northern margin. A lack of available geologic data leads to large uncertainties, such as the timing of the Sepik collision with the New Guinea margin, currently constrained to sometime between 50 and 30 Ma. Previous work suggested a link between the Sepik collision and a voluminous fast seismic anomaly presently in the mantle beneath Lake Eyre. Following from previous work, this study uses coupled plate reconstruction and numerical geodynamic models to test 50 Ma and 30 Ma collision timings of the Sepik terrane, along with an upper extent back-arc basin, to further refine our understanding of the origin and trajectory of the slab beneath Lake Eyre and address uncertainties in the plate reconstructions. The results of mantle flow models indicate that the Eocene collision timing (~50 Ma) is more likely than an Oligocene collision (~30 Ma). In addition, dynamic topography results support previous suggestions that dynamic subsidence relating to the down-going Sepik slab has influenced the evolution of the Eyre Basin, with up to ~100 m of dynamic subsidence since ~20 Ma. However, further work is required to address numerical issues relating to rapid thermal diffusion of slab material, and to investigate reasonable trench retreat velocities for intermediate (~3000 km) subduction zone lengths. This work highlights the role of numerical experiments in understanding transient plate-mantle processes and their effect on basin evolution.
Tectonics, 2007
The Ross-Delamerian orogenic belt formed along the early Paleozoic active Pacific margin of the newly merged Gondwana supercontinent. In its northern-most segment in the Townsville region of northeastern Australia, we have identified a short contractional phase of the Delamerian orogeny in the Argentine Metamorphics postdating formation of a mafic breccia with a U-Pb zircon age of 500 ± 4 Ma. Contraction was followed by widespread inferred extensional deformation with formation of flat-lying foliation, domal features, and amphibolite grade and greenschist retrograde metamorphism all synchronous with latest Cambrian to Early Ordovician extensional backarc volcanism, sedimentation and intrusions. One of these intrusions gives a U-Pb zircon age of 480 ± 4 Ma. Foliation related to the extensional deformation is cross-cut by a late granodiorite dyke with a U-Pb zircon age of 461 ± 4 Ma. Late east-west contractional deformation affected the higher grade part of the assemblage. In contrast to the Ross-Delamerian orogenic belt in the Transantarctic Mountains and southeastern Australia, the orogenic belt in northeastern Australia was affected by a short episode of contraction at ∼495 Ma followed by long-lived backarc extension from ∼490 Ma to 460 Ma with subsequent contractional deformation.
Tectonic framework for the Cenozoic cratonic basins of Australia
Variations in the extent of Cenozoic marine inundation of Australia, as revealed by the distribution of marine and nearshore deposits, points to a tectonic regime involving three distinct modes of deformation. At the longest wavelengths (order 10 3 km), the continent has experienced southwest-up, northeast-down tilting with an amplitude of *300 m since the Late Eocene. We attribute this tilting to the dynamic topographic response to the northward motion of Australia towards the subduction realm of Indonesia and the western Pacific, as well as its passage across a complexly structured mantle. At short wavelengths (order 10 1 km), variations in elevation are associated with cumulative fault movements up to the order of 100 m. Fault-slip vectors are generally compatible with the prevailing in situ stress field and therefore can be allied to distant plate-boundary forcing. At intermediate wavelengths (order 10 2 km), undulations with amplitudes of the order of *100 m reflect, at least in part, lithospheric buckling due to relatively high levels of intraplate stress arising from plate-boundary forcing. Understanding the patterns of surface deformation associated with each of these deformation modes provides a tectonic framework against which the broader significance of the Australian Cenozoic record for such things as eustasy must be evaluated. M. Sandiford et al.
Geologic framework and tectonic evolution in Western Victoria, Australia
Tectonophysics, 1992
The Stawell Zone is interpreted to be part of the eastern extension of the Adelaide Fold Belt into Victoria. The Cambro-Ordovician turbidite sequence of the Stawell and Glenelg zones rests on a pile of Late Proterozoic metavolcanic rocks, rather than Cambrian metavolcanic units that are characteristic of the Lachlan Fold Belt. Early deformation events, D 1-D 3, in the Stawell Zone pre-date granite emplacement and were synchronous with regional fold-forming events that accompany thrust movements along discrete detachment surfaces. The thrust system follows a NE-SE-trending strike, with an E-directed translation of the tectonic units. The steep (≈ 60°) predominantly W-dipping thrusts represent high-strain zones localised in relatively weak Cambro-Ordovician quartz-rich turbidites, that are sandwiched along the boundaries of the Late Proterozoic metavolcanics. Overprinting the early thrust system are D 4-D 6 deformation events that include reverse, strike-slip and normal faults. The Grampians extensional basin, overlying the Late Proterozoic to Ordovician sequence, records a significant change in the tectonic regime operating during the Late Silurian-Early Devonian. It has been subjected to a Middle Devonian compressional deformation event, D 4, with the development of thrust and fold structures. This deformation is also superimposed on the thrusted and folded (D 1 to D 3) sequence to the east of the Grampians half-graben, producing further thrusts. A gradual change from a NE-SW to a N-S stress field produces oblique strike-slip faults. Normal faults of probably Early Cretaceous age transect the entire sequence. The Proterozoic-Cambrian sequence has been affected by a low- P/high- T, mid-greenschist facies regional metamorphic event. Peak-metamorphic conditions have been inferred from metavolcanic rocks and mafic units; derived from a strongly differentiated tholeiitic suite at Stawell. These have been calculated to be 1.7 ± 0.7 (2 σ) kbar and 450 ± 20 (2 σ)° C. The advective heat input necessary to create this low- P/high- T metamorphic event is attributed to penetrative deformation and strain partitioning between the crust and the mantle lithosphere which in turn causes crustal thickening, associated compression, and the observed D 1 to D 3 structures on the surface.
Precambrian Research, 2017
Interpretation and modelling of high resolution regional geophysical data of the central Leichhardt River Fault Trough in the Mount Isa Inlier are used to determine the timing of a major basin inversion event following the development of the ca 1780-1740 Ma Leichhardt Superbasin. Inversion of the Leichhardt Superbasin formed the regional north-south trending Leichhardt Anticline during east-west shortening. The limbs of the anticline are overprinted by several eastwest trending wedge-shaped, non-magnetic sub-basins filled with ca 1710 Ma Calvert and Isa superbasin successions. These relationships suggest inversion of the Leichhardt Superbasin occurred between ca 1740 and 1710 Ma. The event is also known to have affected the northern and eastern North Australian Craton. The scale of the inversion suggests it was a significant event that we have defined as the Leichhardt Event. This event requires a major tectonic driver to the east of the North Australian Craton, possibly the accretion of a micro-continental ribbon to the east of the Mount Isa Inlier. The results of this study have implication for paleogeographic reconstruction of the Australian continent during the formation of Nuna because eastern North Australian Craton faced an ocean at ca 1740-1720 Ma. The results also challenge the significance and intensity of crustal shortening associated with the ca 1600-1500 Ma Isan Orogeny throughout the western Mount Isa Inlier.