Shaping the Australian crust over the last 300 million years: Insights from fission track thermotectonic imaging and denudation studies of key terranes

Abstract

Apatite fission track thermochronology is a well-established tool for reconstructing the lowtemperature thermal and tectonic evolution of continental crust. The variation of fission track ages and distribution of fission track lengths are primarily controlled by cooling, which may be initiated by earth movements and consequent denudation at the Earth's surface and/or by changes in the thermal regime. Using numerical forward-modelling procedures these parameters can be matched with time-temperature paths that enable thermal and tectonic processes to be mapped out in considerable detail. This study describes extensive Australian regional fission track datasets that have been modelled sequentially and inverted into time-temperature solutions for visualisation as a series of timeslice images depicting the cooling history of present-day surface rocks during their passage through the upper crust. The data have also been combined with other datasets, including digital elevation and heat flow, to image the denudation history and the evolution of palaeotopography. These images provide an important new perspective on crustal processes and landscape evolution and show how important tectonic and denudation events over the last 300 million years can be visualised in time and space. The application of spatially integrated denudation-rate chronology is also demonstrated for some key Australian terranes including the Lachlan and southern New England Orogens of southeastern Australia, Tasmania, the Gawler Craton, the Mt Isa Inlier, southwestern Australian crystalline terranes (including the Yilgarn Craton) and the Kimberley Block. This approach provides a readily accessible framework for quantifying the otherwise undetectable, timing and magnitude of long-term crustal denudation in these terranes, for a part of the geological record previously largely unconstrained. Discrete episodes of enhanced denudation occurred principally in response to changes in drainage, base-level changes and/or uplift/denudation related to far-field effects resulting from intraplate stress or tectonism at plate margins. The tectonism was mainly associated with the history of continental breakup of the Gondwana Supercontinent from Late Palaeozoic time, although effects related to compression are also recorded in eastern Australia. The results also suggest that the magnitude of denudation of cratonic blocks has been significantly underestimated in previous studies, and that burial and exhumation are significant factors in the preservation of apparent 'ancient' features in the Australian landscape.

Standardless fission-track dating of the Durango apatite age standard

“…The familiar worldwide recent exhumation is then an artefact due to a methodological imperfection rather than a consequence of selecting the annealing model of Laslett et al (1987). It also implies that normalizing fossil-track lengths to a personal initial length (zero-length), either that of induced tracks (Ketcham et al, 2009; or that of fossil tracks considered not to have experienced significant geological annealing (Gunnell et al, 2003;Kohn et al, 2002;, has unpredictable effects on the thermal histories.…”

Major shear zones of southern Brazil and Uruguay: escape tectonics in the eastern border of Rio de La plata and Paranapanema cratons during the Western Gondwana amalgamation

“…The K-Ar ages obtained for fine fractions are slightly older in the Itariri Shear Zone, between 395 and 425 Ma, than those of the Cubatão Shear Zone, between Fission-track dating of apatites resulted in important information on the thermal-tectonic evolution of the Cubatão-Itariri Shear System and the Mongaguá and Registro terranes, specifically on the low-temperature thermal history, supplying records of the main exhumation events. The uplift of the South-American continent coastal region, associated with the uplift phase of the process that culminated with the continental rupture and opening of the Atlantic (Gallagher et al 1995;Amaral et al 1997;Hackspacher et al , 2004aKohn et al 2002;Tello Sáenz et al 2003;Godoy et al 2006;Hackspacher and Tello Sáenz 2006;Hackspacher et al 2008), is recorded by apatite fission tracks with ages around 120 Ma in rocks of the crystalline basement of the Paraná Basin eastern border (Godoy et al 2006). Similar values were obtained in the Registro and Mongaguá domains affected by the Cubatão Shear Zone.…”

Transcontinental Cainozoic paleovalleys of Western Australia

“…During the period of highly positive water balance (110-45 Ma), erodibility is calibrated using a minimum estimate of the amount of total incision, which corresponds to the present depth local relief, from valley floors to nearest interfluves. Accordance of elevations along the interfluves indicates that little dissection has taken place on ridgelines, which have therefore experienced areal diffuse erosion which in the Australian interior typically occurs at rates of 2-5 m/My (Fujioka et al, 2014;Kohn et al, 2002;Nott and Roberts, 1996;Struck et al, 2015). The paleovalleys experienced systematic sediment filling in the Middle Eocene (Alley et al, 2009;de Broekert and Sandiford, 2005).…”