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A B S TR A CT Metasedimentary gneisses show a rapid change in grade within a 10-km-wide low-P/high-T regional aureole at Mt Stafford, Arunta Block, central Australia. Migmatites occur in all but the lowermost of five metamorphic zones, which are characterized by: (1) muscovite-quartz schist; (2) andalusitecordierite-K-feldspar granofels with small melt segregations; (3) spinel-sillimanite-cordierite-K-feldspar migmatite; (4) garnet-orthopyroxene-cordierite migmatite and minor diatexite; and (5) biotite-cordieriteplagioclase diatexite that shows a transition to granite. A subsolidus unit comprising interbedded sandstone and siltstone is equivalent to bedded migmatite, the main rock type in Zones 2-4. Mesoscopic textures and migmatite classification of this unit vary with grade. In Zone 2, metatexite is developed in siltstone layers that are separated by quartz-rich, unmelted metapsammite layers. Melt segregation was less efficient in Zones 3 and 4, where the dominant migmatite layering is a modified bedding. High proportions of melt were present in Zone 4, in which schlieren migmatite is transitional between bedded migmatite and metapelite-sourced diatexite. The preservation of sedimentary structures and coexistence of melt reactants and products in Zone 4 metapelite imply that melting proceeded in situ without substantial migration of melt. Zone 5 biotite-cordierite-plagioclase diatexite carries rafts of bedded migmatite with strongly resorbed edges, as well as large K-feldspar and quartz augen. This unit of comparatively Ca-rich migmatites is inferred to have been formed by the mixing of locally derived and injected granitic melt.

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The Australian continent is actively deforming in response to far-field stresses generated by plate boundary interactions and buoyancy forces associated with mantle dynamics. On the largest scale (several 10 3 km), the submergence of the northern continental shelf is driven by dynamic topography caused by mantle downwelling along the Indo-Pacific subduction system and accentuated by a regionally elevated geoid. The emergence of the southern shelf is attributed to the progressive movement of Australia away from a dynamic topography low. On the intermediate scale (several 10 2 km), low-amplitude (c. 100-200 m) long-wavelength (c. 100-300 km) topographic undulations are driven by (1) anomalous, smaller-scale upper mantle convection, and/or (2) lithospheric-scale buckling associated with plate boundary tectonic forcing. On the smallest scale (10 1 km), fault-related deformation driven by partitioning of far-field stresses has modified surface topography at rates of up to c. 170 m Ma 21 , generated more than 30-50% of the contemporary topographic relief between some of Australia's highlands and adjacent piedmonts, and exerted a first-order control on long-term (10 4 -10 6 a) bedrock erosion. Although Australia is often regarded as tectonically and geomorphologically quiescent, Neogene to Recent tectonically induced landscape evolution has occurred across the continent, with geomorphological expressions ranging from mild to dramatic.

We digitize surface rupture maps and compile observational data from 67 publications on ten of eleven historical, surface-rupturing earthquakes in Australia in order to analyze the prevailing characteristics of surface ruptures and other environmental effects in this crystalline basement-dominated intraplate environment. The studied earthquakes occurred between 1968 and 2018, and range in moment magnitude (Mw) from 4.7 to 6.6. All earthquakes involved co-seismic reverse faulting (with varying amounts of strike-slip) on single or multiple (1–6) discrete faults of ≥ 1 km length that are distinguished by orientation and kinematic criteria. Nine of ten earthquakes have surface-rupturing fault orientations that align with prevailing linear anomalies in geophysical (gravity and magnetic) data and bedrock structure (foliations and/or quartz veins and/or intrusive boundaries and/or pre-existing faults), indicating strong control of inherited crustal structure on contemporary faulting. Rupture kinematics are consistent with horizontal shortening driven by regional trajectories of horizontal compressive stress. The lack of precision in seismological data prohibits the assessment of whether surface ruptures project to hypocentral locations via contiguous, planar principal slip zones or whether rupture segmentation occurs between seismogenic depths and the surface. Rupture centroids of 1–4 km in depth indicate predominantly shallow seismic moment release. No studied earthquakes have unambiguous geological evidence for preceding surface-rupturing earthquakes on the same faults and five earthquakes contain evidence of absence of preceding ruptures since the late Pleistocene, collectively highlighting the challenge of using mapped active faults to predict future seismic hazards. Estimated maximum fault slip rates are 0.2–9.1 m Myr-1 with at least one order of uncertainty. New estimates for rupture length, fault dip, and coseismic net slip can be used to improve future iterations of earthquake magnitude—source size—displacement scaling equations. Observed environmental effects include primary surface rupture, secondary fracture/cracks, fissures, rock falls, ground-water anomalies, vegetation damage, sand-blows / liquefaction, displaced rock fragments, and holes from collapsible soil failure, at maximum estimated epicentral distances ranging from 0 to ~250 km. ESI-07 intensity-scale estimates range by ± 3 classes in each earthquake, depending on the effect considered. Comparing Mw-ESI relationships across geologically diverse environments is a fruitful avenue for future research.

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Within 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 AlbanyFraser 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.

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