b'The Australian continent: A geophysical synthesisFeatureinclude rocks older than 3700 Ma in Western Australia andThe eastern seaboard, including Tasmania, is a patchwork of 3100 Ma in the Gawler Craton of South Australia. The oldestPaleozoic metamorphic, sedimentary and igneous rocks. These zircon crystals yet found on the Earth, dating back to 4400 Ma,rocks are revealed, as highlands, due to the rift-flank uplift occur in Proterozoic conglomerates within the Yilgarn Craton ofgenerated by opening of the Tasman and Coral seas which Western Australia. In contrast, recent volcanic activity in bothfinished around 80 Ma.northeast and southeast Australia has left distinct volcanicThe Flinders Ranges, a Y-shaped region of uplifted edifices, with the latest eruptions in the southeast at aboutNeoproterozoic sedimentary rocks in South Australia, attest 4600 BCE. to the influence of regional compression across the Australian Around 80% of Australia is covered by extensive MesozoicPlate. Across northern Australia, large areas of mostly and younger sedimentary rocks and regolith (beige areas inProterozoic metasedimentary rocks occur in the Kimberley, Pine Figures4 and 5). These cover rocks indicate the general tectonicCreek, Macarthur and Mt Isa areas. These basins were filled with stability of much of the continent from Mesozoic times to thevast sandsheets during a time when the Earths land surface Present. was devoid of the stabilising influence of life, and became the The underlying Australian continental crust was accreted incontainers for major base metal and uranium mineral systems.three major supercontinent cycles, each building about one- These simplified geological province boundaries provide a third of the continental area from the Archean cratons in theuseful summary of the main features of the solid geology, as can west to the Phanerozoic provinces in the east (Huston et al.be seen from Figure 6.2012). Disparate Archean crustal elements were assembled intoIn subsequent sections [of The Australian Continent: A three major cratonic zones in the Proterozoic. Geophysical Synthesis], these province outlines are used in The West Australian, the North Australian and the Southcombination with the major crustal boundaries dataset, Australian elements were formed by 1830 Ma, and theseillustrated in Figure 7, as an overlay on many of the geophysical cratonic elements were joined to the Rodinian supercontinentimages.by 13001100 Ma. The configuration of these Archean materialsThe two sets of boundaries provide a convenient reference is indicated in Figure 3, which shows a simplified map of solidframe for comparison of geophysical datasets. They also help to geological provinces, along with the surrounding and linkingprovide a tie between the distribution of geophysical properties Proterozoic belts. and the different classes of geological environments.Since the Proterozoic, there has been a set of deformationKorsch and Doublier (2016) have developed a dataset of cycles in central Australia culminating in the Alice Springsmajor crustal boundaries, based on the occurrence of crustal-Orogeny around 400 Ma. These events occurred awayscale breaks in the extensive continental coverage of seismic from plate boundaries and involved extension as well asreflection profiles. Such features are often inferred to be compression, although their precise history remains difficultrelict sutures between different crustal blocks and hence to unravel from the geologic record. Much evidence ofmark changes in crustal properties. The boundaries have deformation is left in the central Australian crust, whichbeen extended away from the seismic profiles with the aid features significant Moho topography and an associatedof geological information (e.g., outcrop mapping, drill hole gravity signal. sampling, geochronology, isotopes) and geophysical imagery The fold belt structures of the Phanerozoic Tasman Element(e.g., gravity, aeromagnetic, magnetotelluric).comprise the eastern third of Australia, which was accretedThe dataset is built from rather heterogeneous materials onto the eastern margin of the Precambrian cratons inand so the various boundary lines have different levels a number of stages (see, e.g., Collins and Vernon 1992;of confidence. In particular, in regions covered by thick Rosenbaum 2018). The Delamarian Orogen at around 500 Masedimentary successions, the locations of some crustal formed part of a much larger belt of accretion along theboundaries are not at all well constrained. It is likely that some eastern margin of Gondwana. This was followed by at leastsignificant boundaries may be missed under cover in the two further periods of accretion that added the LachlanNorthern Territory, where little deep seismic reflection work Orogen and the New England Orogen to the Australia has been undertaken.Antarctic land mass.The break-up of Gondwana, through a series of rifting eventsNevertheless, this crustal boundary dataset provides a useful from about 180 Ma, resulted in the formation of the passivereference frame for comparison of geophysical datasets.margins around Australia, with the formation of the Coral and Tasman seas in the east, the Southern Ocean in the south andCrustal agethe Indian Ocean in the west (Huston et al. 2012). These rift events created the accommodation space for the late PaleozoicThe accessible rocks at the Earths surface provide one facet and Mesozoic sedimentary basins that host most of Australiasof the nature of the continent, but the middle and lower crust hydrocarbon resources. remain hidden. Fortunately studies of isotopic tracers such as There has been significant subsequent volcanism; in thesamarium-neodymium (Sm-Nd) provide a way to exploit felsic Mesozoic, Australia was the continental margin of theigneous rocks across the continent to map the development of subducting Pacific Plate and subsequently a set of chains ofthe crust over time (Champion 2013).hotspot-related volcanism have developed through easternThis work has established a database of Sm-Nd isotopic data, Australia. The eastern margin of Australia has been influencedand associated metadata, for >2650 samples of Australian by sea floor spreading in the Tasman Sea from80 Ma and alsorocks. Results have been compiled for a range of lithologies, by back-arc spreading in the Coral Sea. including felsic and mafic igneous rocks, sedimentary rocks, as 43 PREVIEW APRIL 2019'