High-strain deformation zones accommodate much of the strain during orogenic shortening through localised weakening. However, once a weakened zone develops, it should inhibit the formation of wide high-strain zones (hundreds of metres to kilometres across), making their origin contentious. We address this problem by studying the 100–300 m-wide, garnet–biotite-rich Cattle Water Pass shear zone in the intracontinental Alice Springs Orogen, central Australia. Microstructural features, including cuspate grain shapes, low dihedral angles, ‘string of beads’ textures and thin elongate grains of plagioclase and quartz, indicate deformation in the presence of melt. Quantitative crystallographic orientation data show three-dimensional plagioclase connectivity and limited quartz and ilmenite deformation in highly modified samples, consistent with syn-deformational melt crystallisation. Whole-rock geochemistry and major-, trace- and rare earth element variations demonstrate that deformation occurred in an open system, buffered by fluxing melt. Cathodoluminescence textures and local chemical variations in feldspar and biotite further support melt–rock interaction during deformation. Variably hydrated domains across the shear zone suggest spatially heterogeneous melt flux. The magnitude of rheological weakening caused by syn-deformational melt fluxing precludes formation of the entire high-strain zone in a single event; instead, the melt–rock reacted domains must reflect multiple episodes of melt ingress, reaction and egress. The absence of cross-cutting relationships indicates that each event preserved earlier domains, with new strain localising along weaker interfaces or in adjacent, less-strained regions. We propose a model in which successive melt pulses progressively widen the shear zone as the melt conduit network expands.

Tectonic and geomorphological histories and dynamic topography of the eastern margin of the Australian continent have long been debated. In this paper, an attempt is made to bring together geological evidence and geophysical modelling of terrestrial landscape evolution to uncover the origins of the partially exposed bedrock surfaces on the continental shelf of the southeast Australian margin in New South Wales. New information from high-resolution LiDAR sea-bed mapping of the nearshore and inner shelf and other sources have stimulated a re-examination of an earlier model of continental shelf planation by marine abrasion. We show how terrestrial processes of erosion and deposition through the Cenozoic, along with periods of volcanic activity, and subsequent marine erosion, have together influenced the history of the shelf. Interactions between fluvial and marine processes operating throughout different stages during the evolution of the continental margin show that the shelf bedrock surface is a compound planation feature on a passive continental margin subject to variable phases of uplift and subsidence over at least the past 100 Ma.

During the late Paleozoic glacial ice extended from Antarctica across most of the Australian part of Gondwana. Maximum ice thickness over Antarctica was ∼5400–8000 m and over central Australia 2700–4000 m. Asselian to Sakmarian warming led to in situ down wasting of ice, producing thick successions of proglacial sediments. Subsequent marine transgression penetrated along the southern lowland from the (now) southeast of the continent, but not into the Pedirka and Cooper basins. Early Jurassic subsidence in the central part of the Australian plate initiated development of the Eromanga Basin and fluviatile sedimentation. From the latest Jurassic to Early Cretaceous climate became progressively colder (Frakes Thermal Minimum), punctuated by two major glaciations and a lesser late Aptian event that are coincident with global cold intervals. Glacial debris was deposited along southern margins of the Eromanga Basin. Marine influence commenced in the latest Jurassic(?) to earliest Valanginian, followed by at least 14 transgressions and regressions in the Valanginian to early Cenomanian. Regression from the interior of the continent by the early Cenomanian led to fluvial to lacustrine conditions. Higher rainfall and temperature in the Late Cretaceous to early Paleocene promoted deep weathering. A drainage divide existed between the central part of the continent and the Eucla Basin. Subsidence in the late Paleocene initiated fluvial to lacustrine deposition in the Lake Eyre Basin. Climate during the ensuing late Paleocene to early Eocene in the central part of Australia was warmer than the south where cool temperate, high-rainfall conditions prevailed. Deposition during the middle Eocene to late Eocene spread over a large part of the interior of the continent in an endorheic drainage system akin to the Okavango delta in Botswana. Climate in the interior had become monsoonal, whereas along the southern coastal region conditions were moist, warm temperate fostering prolonged weathering and widespread silicification in the interior, a process probably extending into the Oligocene. By the early Neogene climate was warmer and drier in the interior, drainage was poor and rainfall strongly seasonal with high evaporation rates producing saline and carbonate-rich lakes. In the early to middle Miocene episodic subsidence in the Lake Eyre Basin, along with mild uplift along the southern basin margin and/or falling lake levels, led to stream rejuvenation.

This interpretation of the Cambrian–Ordovician history of the southern Tasmanides on mainland Australia examines: (i) the Selwyn Block of central Victoria; and (ii) the Delamerian Arc, stretching from Victoria into South Australia, and then into far northwestern NSW. The zig-zag belt of Delamerian arc volcanics may have existed with gaps from ca 540 Ma in Victoria (Stavely Arc), but the 510–500 Ma upper part that formed during regional ca 515 to 500 Ma extension is best known. This extension generated back-arc rift basins west of, and rift volcanics on the site of the old arc. Destruction/inversion of these rift basins at ca 500 Ma, reflects the main Delamerian Orogeny. From 510 Ma, the outboard Selwyn Block had migrated northwest towards the east Gondwana margin from a location in a marginal sea between that margin and an inferred east-dipping subduction zone. It had collided with the 518–510 Ma fore-arc of that subduction zone, with ophiolite obduction over by 510 Ma. The Selwyn Block, with overthrust ophiolites preserved in the Heathcote Fault Zone and Governor Fault Zone, remained outboard of Gondwana in open ocean, covered by basalt, chert and shale, with the last two distal from the continental margin, from ca 510 to 450 Ma until it was accreted along with the Bendigo basin at ca 443 Ma. The Selwyn Block is thus interpreted as a submarine plateau. In contrast, the West Tasmania Terrane is a continental block that was accreted at ca 500 Ma. This accretion removed an obstacle to the deposition of the turbidites into marginal ocean basins either side of the Selwyn Block from ca 500–490 Ma to 443 Ma.

Numerous features, predominantly encountered upon the undersides of bedding planes and interpreted to be of biogenic origin, are described from the Sirbu Shale Member of the Upper Vindhyan Group, central India. Some of the features display surface trail-like or horizontal undermat burrow-like characteristics typically associated with microbial mats. Other features suggest the presence of macroscopic metazoans displaying bilateral symmetry or characteristics arguably of locomotion or of frondose origin, one strongly reminiscent of the fossil/trace fossil Bunyerichnus. Newly dated to ca 852 Ma (mid-Tonian Period), and thereby pre-dating the famed Ediacaran Biota by some 270 million years, these features are analogous to various biogenic structures from other stratigraphic horizons globally that, in places, extend back into the Paleoproterozoic Era. Additionally, geochemical proxies indicate oxygenated redox conditions prevailed within the Vindhyan Basin, which likely assisted these organisms to develop motility. However, whether these biogenic trail-like features reflect a subdued state and prolonged ‘slow burn’ of pre-Ediacaran evolution within an oxic enclave of an otherwise global anoxic ocean, or an early evolutionary flourish within an isolated, oxygenated intracratonic basin within the Rodinia Supercontinent remains to be determined.

The impact of volcanic eruptions on the sedimentary filling process of a rift basin is not only the premise for reasonably explaining the binary filling characteristics of volcanic and sedimentary rocks in a rift basin, but also the key geological basis for hydrocarbon reservoir prediction. Based on a large amount of three-dimensional seismic, logging and lithology data, we estimated the volcanic eruption period, volcano distribution and sedimentary facies distribution in the Changling faulted depression in the Songliao Basin. Then we assessed the influence of volcanic eruptions on the type of sedimentary fill, the distribution of sedimentary facies and the spatial stacking of sedimentary strata. This study revealed that during the rapid rifting stage, the Changling faulted depression experienced four phases of volcanic eruptions. The lithology, scale and spatial distribution of volcanoes were directly related to the activity and location of the basement faults in this area, reflecting the control that basement fault activity had on the volcanic eruptions. The stacking form and eruption scale of volcanic rocks played a substantial role in the paleogeomorphology of the basin, which in turn affected the form of the source channel in the basin, causing changes in the sedimentary facies type, spatial distribution and changes in spatial overlapping patterns of sediments. Moreover, the differences in location and delivery methods of volcanic debris complicate the structure and reservoir properties of the sandstone.

Peralkaline magmatic systems can host significant enrichment in high-field-strength elements (HFSE) (e.g. HREE, Zr, Nb, Ta), potentially yielding large-tonnage resources. Primary enrichment is interpreted to result from low-degree melting of a metasomatised mantle source followed by extensive fractional crystallisation. Secondary processes may modify resource potential, but primary magmatic enrichment remains critical, highlighting the importance of investigating these systems from source and tectonic setting through to emplacement. To understand controls on HFSE enrichment, we combined field mapping, petrography, geochemistry, isotopic analysis and geochronology to investigate an alkali basalt to peralkaline rhyolite suite in central Queensland consisting of the Alton Downs Basalt and Mount Hedlow Trachyte. The suite comprises a widespread magmatic field of basaltic lava flows, shallow mafic intrusions and felsic cryptodomes emplaced contemporaneously in the Late Cretaceous at ca 77 Ma. Geochemical trends and restricted isotopic compositions suggest derivation from a common mafic parent magma with minimal crustal assimilation. Fractionation progressed through plagioclase- to alkali feldspar-dominated assemblages, producing felsic endmembers evolving towards relative HFSE enrichment and agpaitic indicators (e.g. aenigmatite), or less HFSE enrichment and miaskitic assemblages (e.g. zircon, monazite). Sm–Nd isotopic compositions (ƐNd(77Ma) = 6.07 to 7.34) indicate a depleted mantle source distinct from younger, plume-related elements of the Eastern Australia Volcanic Province. Trace-element enrichment in the most primitive basalts relative to MORB is consistent with a continental rift setting, which may ultimately relate to northward propagation of Gondwana breakup and development of failed rifts along the Queensland margin. Felsic rocks did not reach the extreme degrees of fractionation interpreted for more strongly HFSE-enriched suites in central Queensland (e.g. southern Peak Range Volcanics), and this may be the main limiting factor resulting in modest HFSE content. More fractionated bodies may exist at depth and would be more prospective.

The ∼150 km-wide Narooma Accretionary Complex can be traced north from East Gippsland (Victoria) to under the Sydney Basin (New South Wales). Its formation is related to westward convergence along the Paleozoic paleo-Pacific plate boundary, which drove the initial late Ordovician Benambran deformation (D1) of the Cambrian ocean-floor basalts and Ordovician turbidites on the east Gondwanan margin. These Ordovician turbidites, which were deposited in a deep-sea trench outboard of Gondwana before and during the Benambran Orogeny, were further deformed (D2) during a progressive clockwise mega-folding event during the evolution of the Lachlan Orocline. This produced intercalated allochthonous sheets of Upper Ordovician turbidites (Adaminaby Group), interlayered with chert, pelagic mudstone and Cambrian ocean-floor basalt. F1 recumbent folds and mélanges juxtaposed different allochthonous units with different ages and rheological properties. As the accretionary wedge developed, off-scraped and underplated ocean-floor basalt, chert and turbidite were stacked along megathrusts or décollements as seaward-verging folds and thrust sheets and incorporated into the turbidite package. At the same time, the Macquarie Arc was split along strike-slip faults and juxtaposed against the Adaminaby Group. The Macquarie Arc became a dynamic backstop during further westward convergence. During D2, north–south-trending, east-verging F2 folds and orogen-parallel coaxial prolate boudins developed. Cratonisation of the accretionary complex in the Tabberabberan Orogeny (ca 385–370 Ma) was followed by exhumation, strike-slip faulting, kinking, reactivation of faults and the formation of Late Devonian–Carboniferous rift basins.