<div>As a planet without plate tectonics, Mars has a fundamentally different setting to Earth, and yet we observe many familiar structural features at the surface. Mars is also home to the largest volcanoes in the Solar System, which are the spectacular surface expressions of an enormous, long-lived magmatic system underlying the region known as Tharsis. The many surface structures in the Tharsis region are an important record of the geologic and volcanic history of Mars. They can provide insight into the timing and nature of volcanic systems, which is important to investigations of past climate and potential habitability. This talk will explore how volcanism has driven formation of the structures we see on the surface of Mars and how this can help us answer important questions about the evolution of the red planet. The work presented is based on Dr Claire Orlov's PhD research conducted at the University of Leeds, UK. </div>

Lead isotope data from ore deposits and mineral occurrences in the Tasman Element of eastern Australia have been used to construct isotopic maps of this region. These maps exhibit systematic patterns in parameters derived from isotope ratios. The parameters include μ (238U/204Pb), as calculated using the Cumming and Richards (1975) lead evolution model, and the difference between true age of mineralisation and the Cumming and Richards lead isotope model age of mineralisation (Δt). Variations in μ coincide with boundaries at the orogen, subprovince and zone scales. The boundary between the Lachlan and New England orogens is accompanied by a decrease in μ, and within the Lachlan Orogen, the Central Subprovince is characterised by μ that is significantly higher than in the adjacent Eastern and Western subprovinces. Within the Eastern Subprovince, the Cu-Au-rich Macquarie Arc is characterised by significantly lower μ relative to adjacent rocks. The Macquarie Arc is also characterised by very high Δt (generally above 200 Myr). Other regions characterised by very high Δt include western Tasmania, the southeastern New England Orogen, and the Hodgkinson Province in northern Queensland. These anomalies are within a broad pattern of decreasing Δt from east to west, with Paleozoic deposits within or adjacent to Proterozoic crust characterised by Δt values of 50 Myr or below. The patterns in Δt are interpreted to reflect the presence of the two major tectonic components involved in the Paleozoic Tasman margin in Australia (cf., Münker, 2000): subducting proto-Pacific crust (Δt >150 Myr), and Proterozoic Australia crust (Δt < 50 Myr) on the over-riding plate. Proterozoic Australia crustal sources are interpreted to dominate the western parts of the Tasman Element and Proterozoic crust further to the west, whereas Pacific crustal sources are inferred to characterise western Tasmania and much of the eastern part of the Tasman Element. Contrasts in Δt between the Cambrian Mount Read Volcanics in western Tasmania and similar aged rocks in western Victoria and New South Wales make direct tectonic correlation between these rocks problematic.

The 2.1─1.79 Ga Trans-Australian and Canadian Trans-Hudson orogens preserve a common record of Himalayan-scale orogenesis and voluminous Cordilleran-style magmatism behind which turbidite-dominated sedimentary sequences evolved in a back-arc or retro-arc foreland setting. Successive cycles of subduction retreat and advance drove the orogenic process, culminating in continent-continent collision and closure of a shared and formerly contiguous ocean basin – the Paleoproterozoic Diamantina and Manikewan oceans. Cordilleran-style arc magmatism in proto-Australia commenced along the southern reaches of the Diamantina Ocean with emplacement of the 2005-1975 Ma Dalgaringa batholith along the leading edge of the Pilbara Craton (Gascoyne Province) before both it and its host craton docked against the Yilgarn Craton, resulting in the Glenburgh Orogeny. After a brief episode of post-kinematic granite magmatism from 1965─1945 Ma, tectonic activity switched to the opposing margin of the Diamantina Ocean in what is now northern Australia where a further three cycles of upper plate orogenesis and Cordilleran-style magmatism occurred from 1890─1850 Ma, 1840─1810 Ma and 1810─1760 Ma along a convergent continental margin extending from the Kimberley and Pine Creek regions southward through the Mount Isa domain into the eastern Gawler Craton. Batholiths developed along this margin include granites of both low and high Sr/Y composition with the more adakitic varieties interpreted to have been intruded during periods of enhanced asthenospheric upwelling accompanying the opening of one or more slab windows following slab breakoff, tearing and/or subduction of an actively spreading oceanic ridge. Terminal collision between the North and South Australian (Mawson) cratons at ca. 1790 Ma brought this succession of subduction-related events to a close, although neither this event nor the corresponding Trans-Hudson orogen need equate to final assembly of the Nuna supercontinent. Instead, the 1870 Ma peak in global compilations of magmatic and detrital zircon ages may be more simply interpreted as the result of elevated tectonism and magmatism along a Paleoproterozoic Cordilleran-style continental plate margin that was trans-continental in scale and continued uninterrupted from proto-Australia into northern Canada and beyond. <b>Citation:</b> G.M. Gibson, D.C. Champion, M.P. Doublier; The Paleoproterozoic Trans-Australian Orogen: Its magmatic and tectonothermal record, links to northern Laurentia, and implications for supercontinent assembly. GSA Bulletin 2024; doi: https://doi.org/10.1130/B36255.1

Abstract: Compressional deformation is a common phase in the post-rift evolution of passive margins and rift systems. The central-west Western Australian margin, between Geraldton and Karratha, provides an excellent example of a strain gradient between inverting passive margin crust and adjacent continental crust. The distribution of contemporary seismicity in the region indicates a concentration of strain release within the Phanerozoic basins which diminishes eastward into the cratons. While few data exist to quantify uplift or slip rates, this gradient can be qualitatively demonstrated by tectonic landforms which indicate that the last century or so of seismicity is representative of patterns of Neogene and younger deformation. Pleistocene marine terraces on the western side of Cape Range indicate uplift rates of several tens of metres per million years, with similar deformation resulting in sub-aerial emergence of Miocene strata on Barrow Island and elsewhere. Northeast of Kalbarri near the eastern margin of the southern Carnarvon Basin, marine strandlines are displaced by a few tens of metres. A possible Pliocene age would indicate that uplift rates are an order of magnitude lower than further west. Relief production rates in the western Yilgarn Craton are lower still - numerous scarps (e.g. Mount Narryer) appear to relate individually to <10 m of displacement across Neogene strata. Quantitative analysis of time-averaged deformation preserved in the aforementioned landforms, including study of scarp length as a proxy for earthquake magnitude, has the potential to provide useful constraints on seismic hazard assessments in a region containing major population centres and nationally significant infrastructure.

Tectonic geomorphology along the continental margin of Western Australia indicates the presence of an approximately 2000 km long zone of dextral-oblique neotectonic faults and folds referred to as the Western Australian shear zone (WASZ). The WASZ reoccupies older rift related structures that initially formed during periods of continental-scale fragmentation in the Paleozoic and Mesozoic Eras. Reactivation in the WASZ is coincident with late Neogene reorganization of Australia’s plate boundaries and realignment of the intraplate stress field. Neotectonic deformation in the southern WASZ is dominated by transpressional inversion within the extended crustal domain between Australian oceanic crust to the west and non-extended Australian continental crust to the east. The WASZ appears to accommodate differential motion expressed as dextral transpression between oceanic and non-extended continental tectonic blocks—or micro-plates.

Detrital zircon age patterns are reported for sandstones from the mid-Permian-Triassic part of the accretionary wedge forming the Torlesse Composite Terrane in Otago, New Zealand and from the early Permian Nambucca Block of the New England Orogen, eastern Australia. In Otago, the Triassic Torlesse samples have a major (64%) age group of Permian-Early Triassic components ca. 240, 255 and 280 Ma, and a minor age group (30%) with a Precambrian-early Paleozoic range (ca. 500, 600 and 1000 Ma). In Permian sandstones nearby, the younger group is diminished (30%), and the older group also contains a major (50%) and unusual, Carboniferous group (components at ca. 330-350 Ma). This trend is similar in sandstones from the Nambucca Block, an early Permian extensional basin in the southern New England Orogen, in which Permian zircons are now minor (<20%), and the age patterns are also dominated (40%) by similar Carboniferous age components, ca. 320-350 Ma.

Vertical stress is one of the three principal stresses and is an important parameter in geomechanical studies that are focussed on the prediction of pore pressure, fracture gradients, and wellbore stability. Variations of the vertical stress magnitude can be attributed to variations in lithology or diagenetic history, localised uplift, and overpressures caused by disequilibrium compaction. This study uses wellbore data from 102 open-file petroleum wells to characterise vertical stress within the onshore Canning Basin of north-western Australia. Vertical stress magnitudes are interpreted from density logs and checkshot data and at 1 km depth below the ground surface range from 20.5 MPa km-1 to 25.0 MPa km-1 with a mean value of 22.1 MPa km-1 (s.d. = 1.0 MPa km-1). Significant variation is evident within the calculated stress magnitudes, and when presented spatially, three regions of elevated vertical stress are identified: the Barbwire Terrace, the Devonian Reef Complexes of the northern Lennard Shelf, and the Mowla Terrace. Lithology, abnormal pore pressures, and tectonic uplift are investigated as potential mechanisms of the observed variation. Although abnormal pore pressures are identified, no direct correlation between overpressured areas and elevated vertical stress magnitudes is observed. The Canning Basin has an extensive history of uplift; however, there is little evidence for significant recent inversion. While uplift is likely to exert some influence over vertical stress magnitudes in the Canning Basin, the primary cause is interpreted to be lithological; areas of elevated vertical stress magnitude are also areas where thick intervals of carbonate sediments are present. Appeared in The APPEA Journal 59, pages 364-382, 17 June 2019

Preserved within the Glenelg River Complex of SE Australia is a sequence of metamorphosed late Neoproterozoic-early Cambrian deep marine sediments intruded by mafic rocks ranging in composition from continental tholeiites to mid-ocean ridge basalts. This sequence originated during breakup of the Rodinia supercontinent and is locally host to lenses of variably sheared and serpentinised mantle-derived peridotite (Hummocks Serpentinite) representing the deepest exposed structural levels within the metamorphic complex. Direct tectonic emplacement of these rocks from mantle depths is considered unlikely and the ultramafites are interpreted here as fragments of sub-continental lithosphere originally exhumed at the seafloor during continental breakup through processes analogous to those that produced the hyper-extended continental margins of the North Atlantic. Subsequent to burial beneath marine sediments, the exhumed ultramafic rocks and their newly acquired sedimentary cover were deformed and tectonically dismembered during arc-continent collision accompanying the early Paleozoic Delamerian Orogeny, and transported to higher structural levels in the hangingwalls of west-directed thrust faults. Thrust-hosted metasedimentary rocks yield detrital zircon populations that constrain the age of mantle exhumation and attendant continental breakup to be no later than late Neoproterozoic-earliest Cambrian. A second extensional event commencing ca. 490 Ma overprints the Delamerian-age structures; it was accompanied by granite magmatism and low pressure-high temperature metamorphism but outside the zone of magmatic intrusion failed to erase the original, albeit modified, rift geometry. This geometry originally extended southward into formerly contiguous parts of the Ross Orogen in Antarctica where mafic-ultramafic rocks are similarly hosted by a deformed continental margin sequence.

In plate boundary regions moderate to large earthquakes are often sufficiently frequent that fundamental seismic parameters such as the recurrence intervals of large earthquakes and maximum credible earthquake (Mmax) can be estimated with some degree of confidence. The same is not true for the Stable Continental Regions (SCRs) of the world. Large earthquakes are so infrequent that the data distributions upon which recurrence and Mmax estimates are based are heavily skewed towards magnitudes below Mw5.0, and so require significant extrapolation up to magnitudes for which the most damaging ground-shaking might be expected. The rarity of validating evidence from surface rupturing palaeo-earthquakes typically limits the confidence with which these extrapolated statistical parameters may be applied. Herein we present a new earthquake catalogue containing, in addition to the historic record of seismicity, 150 palaeo-earthquakes derived from 60 palaeo-earthquake features spanning the last > 100 ka of the history of the Precambrian shield and fringing extended margin of southwest Western Australia. From this combined dataset we show that Mmax in non-extended-SCR is M7.25 ± 0.1 and in extended-SCR is M7.65 ± 0.1. We also demonstrate that in the 230,000 km2 area of non-extended-SCR crust, the rate of seismic activity required to build these scarps is one tenth of the contemporary seismicity in the area, consistent with episodic or clustered models describing SCR earthquake recurrence. A dominance in the landscape of earthquake scarps reflecting multiple events suggests that the largest earthquakes are likely to occur on pre-existing faults. We expect these results might apply to most areas of non-extended-SCR worldwide.

The Tasman Frontier region includes c. 3,000,000 sq km of seabed that is thought to be underlain by crust with continental affinities: the Lord Howe Rise, Bellona Trough, Challenger Plateau, Dampier Ridge, Middleton Basin, Fairway Basin, New Caledonia Trough, Norfolk Ridge System, Reinga Basin, and deep-water parts of Taranaki and Northland basins. We have compiled and interpreted c. 100,000 line km of archival seismic reflection data. Using seismic stratigraphy tied to Deep Sea Drilling Project (DSDP) wells, we identify a tectonic and stratigraphic event that we refer to as the 'Tectonic Event of the Cenozoic Tasman Area' (TECTA). This Middle Eocene to Late Oligocene event involved regional uplift followed by 1-2 km of tectonic subsidence of topographic highs, and >2 km of tectonic subsidence in the New Caledonia Trough. Strata below the TECTA reflector (or seismic unit in some places) are locally folded or reverse faulted. We present seismic-stratigraphic evidence that numerous islands were transiently created by uplift on the Lord Howe Rise during the TECTA event. We suggest that the underlying cause of the TECTA event was initiation of the subduction system that has since evolved into the Tonga-Kermadec system. Note: Abstract for initial submission; acceptance to be confirmed.