Lithology and the evolution of bedrock rivers in post-orogenic settings: Constraints from the high elevation passive continental margin of SE Australia

Understanding the role of lithological variation in the evolution of topography remains a fundamental issue, especially in the neglected post-orogenic terrains. Such settings represent the major part of the Earth's surface and recent modelling suggests that a range of interactions can account for the presence of residual topography for hundreds of millions of years, thereby explaining the great antiquity of landscapes in such settings. Field data from the inland flank of the SE Australian high-elevation continental margin suggest that resistant lithologies act to retard or even preclude the headward transmission of base-level fall driven by the isostatic response to regional denudation. Rejuvenation, be it episodic or continuous, is ‘caught up’ on these resistant lithologies, meaning in effect that the bedrock channels and hillslopes upstream of these ‘stalled’ knickpoints have become detached from the base-level changes downstream of the knickpoints. Until these knickpoints are breached, therefore, catchment relief must increase over time, a landscape evolution scenario that has been most notably suggested by Crickmay and Twidale. The role of resistant lithologies indicates that detachment-limited conditions are a key to the longevity of some post-orogenic landscapes, whereas the general importance of transport-limited conditions in the evolution of post-orogenic landscapes remains to be evaluated in field settings. Non-steady-state landscapes may lie at the heart of widespread, slowly evolving post-orogenic settings, such as high-elevation passive continental margins, meaning that non-steady-state landscapes, with increasing relief through time, are the ‘rule’ rather than the exception

New South Wales Vegetation Classification and Assessment: Part 2, plant communities of the NSW South-western Slopes Bioregion and update of NSW Western Plains plant communities, Version 2 of the NSWVCA database

This third paper in the NSW Vegetation Classification and Assessment series covers the NSW South-western Slopes Bioregion of 8.192 million hectares being 10% of NSW. A total of 135 plant communities, comprising 97 new communities and 38 previously described communities, are classified. Their protected area and threat status is assessed. A full description of the 135 plant communities is provided in a 400 page report, generated from the NSWVCA database, on the CD accompanying this paper. Eucalyptus-dominated grassy or shrubby woodlands and open forests are the main types of vegetation in the bioregion. The CD also contains a read-only version of Version 2 of the NSWVCA database that includes updated information on the plant communities previously published in Version 1 of the NSWVCA covering the NSW Western Plains. Six new communities are added to the Western Plains. The vegetation classification and assessment is based on published and unpublished vegetation surveys and map unit descriptions that are listed in the NSWVCA Bibliography on the CD, expert advice and extensive field checking. Over 80% of the native vegetation in the NSW South-western Slopes Bioregion has been cleared making it the most cleared and fragmented of the 18 IBRA Bioregions in NSW. Exotic plant species dominate the ground cover outside conservation reserves, state forests, roadsides and travelling stock reserves. As of September 2008 about 1.9% of the Bioregion was in 105 protected areas and 28 of the 135 plant communities were assessed to be adequately protected in reserves. Using NSWVCA Threat Criteria, 18 plant communities were assessed as being Critically Endangered, 33 Endangered, 29 Vulnerable, 25 Near Threatened and 30 Least Concern. Current threats include over-grazing, especially during drought, exotic species dominance of the ground cover, impacts of fragmentation on species persistence and genetic diversity and impacts of lower rainfall due to climate change. To address these threats, linking and enlarging vegetation remnants through revegetation (including regenerating native ground cover) is required. Some progress is being made through re-vegetation schemes driven by the NSW 2003 Natural Resource reforms, however, more incentive funding for landholders would accelerate the re-vegetation program

Sources and effects of fluids in continental retrograde shear zones: Insights from the Kuckaus Mylonite Zone, Namibia

Midcrustal rocks in retrograde metamorphic settings are typically H2O-undersaturated and fluid-absent and have low permeability. Exhumed continental retrograde faults, nonetheless, show evidence for the operation of fluid-mediated weakening mechanisms during deformation at midcrustal conditions. To explore the origin and effects of fluids in retrograde faults, we study the Kuckaus Mylonite Zone (KMZ), an exhumed crustal-scale, strike-slip shear zone in the southern Namibian Namaqua Metamorphic Complex. The KMZ deformed quartzofeldspathic migmatised gneisses at midcrustal retrograde conditions (450-480°C, 270-420 MPa) in the Mesoproterozoic, 40 Ma after granulite facies peak metamorphism at 825°C and 550 MPa. The mylonites contain fully hydrated retrograde mineral assemblages, predominantly adjacent to anastomosing high-strain zones, providing evidence of local H2O saturation and fluid presence during deformation. Whole rock and quartz vein δ18O values suggest that at least some of the fluids were meteoric in origin. The rocks across the shear zone retain the effect of different protoliths, implying little effect of fluid-rock interaction on whole rock major element chemistry. Together with a general scarcity of quartz veins, this suggests that fluid/rock ratios remained low in the KMZ. However, even small amounts of H2O allowed reaction weakening and diffusion-precipitation, followed by growth and alignment of phyllosilicates. In the ultramylonites, a fine grain size in the presence of fluids allowed for grain size sensitive creep. We conclude that the influx of even small volumes of fluids into retrograde shear zones can induce drastic weakening by facilitating grain size sensitive creep and retrograde reactions. In retrograde settings, these reactions consume fluids, and therefore elevated fluid pressures will only be possible after considerable weakening has already occurred. Our findings imply that the range of seismic styles recently documented at active retrograde transform faults may not require high fluid pressures but could also arise from other local weakening mechanisms

Chemical evolution and origin of granites in the Lachlan Fold Belt

The author has been involved in studying the granites of the Lachlan Fold Belt (LFB) since 1963 with this being the main focus of his scientific studies since 1973. This thesis brings together many of the publications that have arisen from that work and those 20 papers that are being submitted for examination are listed in Section 1 (pp. 2-3) and are bound together at the back of this volume. A complete list of the 114 publications for which this writer is an author is given in Section 10 (pp. 43-51). That list is comprehensive and again includes the 20 papers being examined. The remaining 94 papers are listed in support of the candidacy. Among those other papers, 37 deal with various aspects of granite studies, both in the LFB and elsewhere, and the remainder with a variety of geological and geochemical subjects

Impact of the 2019-20 Mega-Fires on the Greater Blue Mountains World Heritage Area, New South Wales

The 2019-20 ‘Black Summer’ mega-fires burnt an unprecedented 79% of the Greater Blue Mountains World Heritage Area, which is more than three times greater than the area burnt in any of the previous 48 fire seasons. The fires were not proportionally more severe than previous large fires but their huge scale meant that an unprecedented 29% of the World Heritage Area was burnt at high to extreme severity. The fires were particularly extensive and severe in parts of the World Heritage Area that are rarely burnt by wildfires, notably in cooler areas over 1000 m in the south-west. The vegetation type least impacted by the fires was grassy woodland, an important bird habitat, of which 48% was burnt. However, grassy woodland covers less than 2% of the World Heritage Area and extensive areas of grassy woodland were burnt elsewhere in 2019-20. Rainforest and shrubby wet sclerophyll forest in sheltered gullies have played an important role in past fires as unburnt fauna refuges but were unusually heavily impacted in 2019-20, with 82% and 79% burnt, respectively. The fauna and flora of the World Heritage area are likely to eventually recover from the Black Summer fires if this was an exceptional event that will not recur for many decades. However, a change in the Australian fire regime to more frequent, more extensive, more severe wildfires as a result of climate change has long been predicted. If the Black Summer fires are a harbinger of this change, the long-term impact on the environment and biota of the World Heritage Area would be catastrophic

Magmatic and hydrothermal evolution of the browns creek intrusive complex and associated gold mineralisation

The Browns Creek Au-Cu deposit near Blayney, New South Wales, consists skarnhosted, magmatically derived and structurally controlled mineralisation. The deposit is hosted by altered Blayney Volcanics and Cowriga Limestone. The skarn alteration is a result of the intrusion of the Carcoar Granodiorite, which is <1 member of the Browns Creek Intrusive Complex. Other members of this complex are the Long Hill Phase of the Carcoar Granodiorite, the Mine Dyke Group and the PostMineralisation Intrusives. The Mine Dyke Group has been responsible for the mineralisation. The Carcoar Granodiorite is 430.4 ± 4.7 Ma old (based on U-Th-Pb dating teclmiques on zircons). This date is around 15 Ma older than previously determined ages for this intrusive. The granodiorite is a multiple phase intrusive. The most notable phase is the cumulate Long Hill Phase. This mafic phase was previously believed to be a separate intrusive body to the granodiorite. Greater abundances of iron, magnesium and lower abundaces of aluminium and potassium are consistent with the Long Hill Phase representing a cumulate phase of the Carcoar Granodiorite. Other elements show similar abundances to the granodiorite. Several forms of alteration are associated with the intrusion of the Carcoar Granodiorite. The granodiorite has marblised the Cowriga Limestone Member and hornfelsed the Blayney Volcanics. The dominant alteration assemblage is the skarn metasomatisation, visible at the mine and other pockets along the contact of the Carcoar Granodiorite with the country rock. The orebody has formed close to the contact of the Carcoar Granodiorite with the Blayney Volcanics and the marblised Cowriga Limestone Member. A complex structural corridor had previously formed. Three dominant structural trends can be identified in the vicinity of the mine north-south, northwest and northeast. The north-south structural trend was the first to be activated in this area. This has created Abstract v a structural fabric that was reactivated by later structural movements. The northwest structural trend has resulted in the juxtaposition of the Carcoar Granodiorite with the Cowriga Limestone Member. Regional scale, northeast structures have controlled the dilation of pre-existing north-south structures. This has facilitated the emplacement of the Mine Dyke Group and hence the mineralisation. The Mine Dyke Group is a series of dykes that predominantly lie within the ore zone. The dykes are mostly granitic in composition and range from aplites to pegamatites. They are mostly oriented north-south and some show evidence of intruding along north-south oriented faults and shears. The dykes have intruded synto post-mineralisation and two were dated using U-Th-Pb techniques on zircons. These analyses yielded ages of 430.0 ± 5.4 Ma and 432.3 ± 4.9 Ma. The Mine Dyke Group is the phase of the Browns Creek Intrusive Complex that is associated with mineralisation. As the Carcoar Granodiorite predates the mineralisation, the ages of the Mine Dyke Group in conjunction with the Carcoar Granodiorite can be utilised to obtain a date for the mineralisation event. The three dates give a mean age of 431 ± 3 Ma for this event. The orebody is cross-cut by a late intrusive body identified in the latter part of the mine's operation. The Post-Mineralisation Intrusive is quartz monzodioritic to granodioritic in composition and is slightly more mafic than the Carcoar Granodiorite. It has intruded after the formation of the ore body and is not associated with any mineralisation. There is a slight amount of skarn alteration that is observed with this intrusion, overprinting the pre-existing skarn and mineralisation