The contribution of geochronology to understanding the Paleozoic geological history of Australia

Williams, Ian S.; Pulford, A.

doi:10.1080/08120090802097401

Cited by 20 publications

(13 citation statements)

References 243 publications

(240 reference statements)

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“…Both are consistent with a Gondwana source (Veevers, 2000;Veevers et al, 2006). It has been argued that this source is represented by the central Gondwanan orogenic belt formed by collision of West and East Gondwana (Maidment et al, 2007;Williams and Pulford, 2008) and referred to as the "Transgondwanan Supermountain" (Squire et al, 2006). Alternatively, a source has been proposed closer to the site of deposition in the ice-covered hinterland of East Antarctica, and therefore not directly observable (Veevers andSaeed, 2008, 2011).…”

supporting

confidence: 65%

Proto-Pacific-margin source for the Ordovician turbidite submarine fan, Lachlan Orogen, southeast Australia: Geochemical constraints

Offler

Fergusson

2016

Sedimentary Geology

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The Early Palaeozoic proto-Pacific Pacific margin of Gondwana was characterised by a huge turbidite submarine fan with abundant clastic detritus derived from unknown sources within Gondwana. These deposits are widespread in the Lachlan Orogen of southeast Australia and include the Ordovician Adaminaby Group. Here we show that the mudstones and sandstones of the Adaminaby Group have chemical compositions that indicate the detritus in them was derived from a felsic, continental source similar in composition to Post Archean Australian Shales (PAAS). Chondrite normalised REE patterns showing LREE enrichment, flat PAAS normalised patterns and elemental ratios La/Sc, Cr/Th, Cr/V, Th/Sc and Th/U, have been used to support this interpretation. The dominance of quartz, and to a lesser degree plagioclase and biotite in the sandstones, suggests that the source was mainly granodioritic to tonalitic in composition. Th/Yb and Ta/Yb ratios indicate that the source was probably calc-alkaline, continental and shoshonitic. In addition, the presence of detrital muscovite, low-grade metamorphic and felsic volcanic clasts, demonstrates that a lowgrade metamorphic terrane and volcanic arc contributed to the detritus observed in the samples. The presence of well-rounded zircons and tourmalines, very high Zr contents, high Zr/Sc and higher Cr/V ratios in some samples particularly in the Shoalhaven River area, indicate that some of the detritus was recycled.SiO2 versus (Al2O3 + K2O + Na2O) plots suggest the source areas experienced conditions varying from humid/semihumid to semi-arid. Textural features and weathering trends of samples from all locations follow a curved pathway on Al2O3 -(CaO* + Na2O) -K2O (ACNK) diagrams, and indicate that the clays formed from weathering had been K-metasomatised prior to penetrative deformation. Chemical indices of alteration (CIA) reveal that even the freshest sandstones are altered and others are moderately to strongly altered. Discrimination diagrams involving major, trace and REE strongly support a collisional/continental volcanic arc setting that was substantially eroded to produce the plutonic detritus observed in the sandstones. The collisional setting accords with that proposed previously by other authors who suggested that it developed during the Delamerian Orogeny, resulting in the uplifted source areas providing detritus that inundated the backarc and forearc sites of the Macquarie Arc. Some of the detritus, however, may have been derived from a continental arc that existed in the late Cambrian along the margin of the Ross Orogen. Based on palaeocurrent analyses in previous studies and shoshonitic signature of the detritus, it is proposed that the Cambrian volcanics along the eastern active margin of Gondwana provided much of the detritus in the Adaminaby Group. Zircons with the Grenvillian signature suggest that some detritus were also derived from the Ross Orogen. Discrimination diagrams involving major, trace and REE strongly support a collisional/continental volcanic arc setting...

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supporting

confidence: 65%

Proto-Pacific-margin source for the Ordovician turbidite submarine fan, Lachlan Orogen, southeast Australia: Geochemical constraints

Offler

Fergusson

2016

Sedimentary Geology

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“…Extensive studies have shown that the Lachlan Orogen forms part of the cratonisation history of the eastern margin of the Australian continent (Foster et al, 1999;Glen, 2005;Gray and Foster, 2004;Williams and Pulford, 2008). Further, subduction models for the Lachlan Orogen are well supported (Collins, 2002;Fergusson and Frikken, 2003;Foster and Gray, 2000;Foster et al, 1999;Gray, 1997;Gray and Foster, 1998;Prendergast, 2007;Prendergast et al, 2011;Spaggiari et al, 2004), with subduction being active from at least 460-440 Ma.…”

Section: Lachlan Orogenmentioning

confidence: 96%

Underplated seamount in the Narooma accretionary complex, NSW, Australia

Prendergast

Offler

2012

Lithos

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“…The Paleozoic Lachlan Orogen formed during cratonisation of the eastern margin of the Australian continent (Offler et al 1998;Foster et al 1999;Glen 2005;Williams & Pulford 2008) through accretion along multiple subduction zones (Gray 1997;Foster et al 1999;Foster & Gray 2000;Collins 2002;Spaggiari et al 2004).…”

Section: Geological Settingmentioning

confidence: 98%

⁴⁰Ar/³⁹Ar and K–Ar ages: early Paleozoic metamorphism and deformation in the Narooma accretionary complex, NSW

Prendergast

Offler

Phillips

et al. 2011

Australian Journal of Earth Sciences

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White micas in slates from an imbricated sequence of deformed turbidites, and clast-in-matrixmelanges that form the Narooma accretionary complex at Batemans Bay, record apparent 40 Ar/ 39 Ar whole rock ages in the range 450 to 500 Ma, with intermediate-temperature average ages of 471 + 13 Ma and 476 + 11 Ma (2 standard deviations). By contrast, two K-Ar whole rock ages are 430.9 + 8.6 Ma and 449.2 + 9.0 Ma. Fractions (52, 3-5 and 10-20 mm) from the same samples show a progressive increase in age with grainsize (52 mm ¼ 413.1 + 8.3-404.7 + 8.1 Ma; 3-5 mm ¼ 417.1 + 8.3 Ma; 10-20 mm ¼ 434 + 8.6-437.5 + 8.8 Ma 2 standard deviations). The older whole rock 40 Ar/ 39 Ar ages are attributed to recoil loss of 39 Ar. The cleavage forming event is believed to have occurred at *460-440 Ma (Upper Ordovician to Lower Silurian). The finest fractions possibly record a younger thermal event at approximately 413 Ma. Kü bler Index values obtained from the Wagonga and Adaminaby Groups indicate lower epizonal (greenschist facies) metamorphic conditions. b 0 lattice parameter values (x ¼ 9.033; n ¼ 21) are characteristic of the intermediate pressure facies series.Assuming a temperature of approximately 3008C and P ¼ 4 kb suggests a depth of burial of approximately 15 km was reached by these rocks and that a geothermal gradient of 208C/km operated during subduction.

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The contribution of geochronology to understanding the Paleozoic geological history of Australia

Cited by 20 publications

References 243 publications

Proto-Pacific-margin source for the Ordovician turbidite submarine fan, Lachlan Orogen, southeast Australia: Geochemical constraints

Proto-Pacific-margin source for the Ordovician turbidite submarine fan, Lachlan Orogen, southeast Australia: Geochemical constraints

Underplated seamount in the Narooma accretionary complex, NSW, Australia

⁴⁰Ar/³⁹Ar and K–Ar ages: early Paleozoic metamorphism and deformation in the Narooma accretionary complex, NSW

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The contribution of geochronology to understanding the Paleozoic geological history of Australia

Cited by 20 publications

References 243 publications

Proto-Pacific-margin source for the Ordovician turbidite submarine fan, Lachlan Orogen, southeast Australia: Geochemical constraints

Proto-Pacific-margin source for the Ordovician turbidite submarine fan, Lachlan Orogen, southeast Australia: Geochemical constraints

Underplated seamount in the Narooma accretionary complex, NSW, Australia

40Ar/39Ar and K–Ar ages: early Paleozoic metamorphism and deformation in the Narooma accretionary complex, NSW

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⁴⁰Ar/³⁹Ar and K–Ar ages: early Paleozoic metamorphism and deformation in the Narooma accretionary complex, NSW