Ordovician and Silurian history of the southeastern part of the Lachlan Geosyncline

Crook, Keith A. W.; Bein, J.; Hughes, R.J.; Scott, Paul

doi:10.1080/14400957308527903

Cited by 45 publications

(19 citation statements)

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“…Recent mapping shows that this Llandovery quartz‐rich turbidite and mudstone unit is much more widespread than formerly thought ( Lewis et al 1994 ; Fergusson 1998). At Quidong, it is this unit that was deformed, together with underlying Ordovician rocks, during the ‘Quidongan Orogeny’ of Crook et al (1973) , confirming that the Quidongan and Benambran are the same event.…”

Section: Deformation and Magmatism— Diachronous Or Episodic?mentioning

confidence: 83%

“…In large part this is because earlier workers were unaware of the existence of Early Silurian sedimentary rocks in the region. Ramsay and Vandenberg (1986) pointed to the poor age control then available for the type area and stated it could not be distinguished from the Quidongan Orogeny of Crook et al (1973) . Vandenberg (1978) first suggested a somewhat later age than generally accepted—towards the end of the Llandovery.…”

Section: Deformation and Magmatism— Diachronous Or Episodic?mentioning

confidence: 99%

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Timing of orogenic events in the Lachlan Orogen

Vandenberg

1999

Australian Journal of Earth Sciences

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A substantial database of 40Ar/39Ar ages, collected recently from micas in western and central Victoria, has been used in several recent papers as support for continuous, diachronous deformation across western and central Victoria lasting through much of the Early Palaeozoic. This paper reviews these ages, together with field evidence collected over the last ten years. It provides an alternative interpretation, that mica growth and overgrowth in western Victoria was not continuous but episodic, occurring at ca 455 Ma, 440 Ma and 425 Ma, with little or no mica growth recorded from between these times. These ages have been obtained from mica in regional cleavage, crenulation cleavage and in quartz veins, and from across the entire width of the Stawell and Bendigo structural zones of western Victoria. A sharp change in mica ages occurs at the Mt William Fault, east of which no mica growth older than about 380 Ma is recorded. Several ages used in support for diachronous deformation are not related to deformation: an 40Ar/39Ar age of 417 Ma from Chewton is from the aureole of a Devonian granite, and an age of 410 Ma from the Melbourne Zone is shown to contain a substantial amount of inherited mica. If it is accepted that mica growth can be used to date deformation, then the 40Ar/39Ar ages indicate episodic, not continuous, deformation in western Victoria (Stawell and Bendigo Zones). The sharp decrease in the deformation age in the Melbourne Zone, east of the Mt William Fault, agrees well with field evidence that shows continuous sedimentation in the Melbourne Zone in the period (Ordovician to mid‐Early Devonian) during which the Stawell and Bendigo zones were undergoing deformation. Some correlation also exists between the 40Ar/39Ar ages from western Victoria and well‐constrained deformational events in the eastern Lachlan Orogen. The pattern of deformation has important corollaries in any model that attempts to understand what drives the deformation. While plate convergence must be the ultimate driving force, the pattern is quite inconsistent with deformation of a crust that was being drawn pro‐ gressively into subduction zones, as proposed in recently published models. Rather, the observed pattern suggests that deformation happened in several very brief events, probably on semi‐rigid plates.

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Section: Deformation and Magmatism— Diachronous Or Episodic?mentioning

confidence: 83%

Section: Deformation and Magmatism— Diachronous Or Episodic?mentioning

confidence: 99%

Timing of orogenic events in the Lachlan Orogen

Vandenberg

1999

Australian Journal of Earth Sciences

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“…Upper Ordovician to Lower Silurian units occur in the basal parts of the Tumut Trough and Canberra-Yass Basins and are deep marine quartz and lithic turbidites of the Bumbolee Creek Formation around Tumut, the Mundoonen Sandstone near Yass and the Murrumbateman Formation, Black Mountain Sandstone and State Circle Shale at and north of Canberra ( Figure 3) (Crook et al 1973;Basden 1990;Abell 1991;Colquhoun et al 2003). Late Benambran deformation separates Upper Ordovician to Lower Silurian units from overlying Upper Silurian units of the Canberra-Yass Basin and this break is also developed in the Tumut region (Stuart-Smith et al 1992).…”

Section: Tumut Trough Canberra-yass and Ngunawal Basinsmentioning

confidence: 94%

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Fergusson

2010

Australian Journal of Earth Sciences

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“…Biostratigraphic investigations by Talent (1965) in Victoria, and Packham (1969a, b, 1987), Webby (1976; Webby 1987) and Crook et al . (1973) in New South Wales, established the gross stratigraphic framework of the Lachlan Orogen (see also Talent et al .…”

Section: Review Of Approaches To Eastern Australia Tectonic Evolutionmentioning

confidence: 98%

Tectonic evolution of the Lachlan Orogen, southeast Australia: historical review, data synthesis and modern perspectives

2004

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The Lachlan Orogen, like many other orogenic belts, has undergone paradigm shifts from geosynclinal to plate-tectonic theory of evolution over the past 40 years. Initial plate-tectonic interpretations were based on lithologic associations and recognition of key plate-tectonic elements such as andesites and palaeo-subduction complexes. Understanding and knowledge of modern plate settings led to the application of actualistic models and the development of palaeogeographical reconstructions, commonly using a non-palinspastic base. Igneous petrology and geochemistry led to characterisation of granite types into 'I' and 'S', the delineation of granite basement terranes, and to nonmobilistic tectonic scenarios involving plumes as a heat source to drive crustal melting and lithospheric deformation. More recently, measurements of isotopic tracers (Nd, Sr, Pb) and U-Pb SHRIMP age determinations on inherited zircons from granitoids and detrital zircons from sedimentary successions led to the development of multiple component mixing models to explain granite geochemistry. These have focused tectonic arguments for magma genesis again more on plate interactions. The recognition of fault zones in the turbidites, their polydeformed character and their thin-skinned nature, as well as belts of distinct tectonic vergence has led to a major reassessment of tectonic development. Other geochemical studies on Cambrian metavolcanic belts showed that the basement was partly backarc basin-and forearc basin-type oceanic crust. The application of 40 Ar-39 Ar geochronology and thermochronology on slates, schist and granitoids has better constrained the timing of deformation and plutonism, and illite crystallinity and b o mica spacing studies on slates have better defined the background metamorphic conditions in the low-grade parts. The Lachlan deformation pattern involves three thrust systems that constitute the western Lachlan Orogen, central Lachlan Orogen and eastern Lachlan Orogen. The faults in the western Lachlan Orogen show a generalised east-younging (450-395 Ma), which probably relates to imbrication and rock uplift of the sediment wedge, because detailed analyses show that the décollement system is as old in the east as it is in the west. Overall, deformation in the eastern Lachlan Orogen is younger (400-380 Ma), apart from the Narooma Accretionary Complex ( ca 445 Ma). Preservation of extensional basins and evidence for basin inversion are largely restricted to the central and eastern parts of the Lachlan Orogen. The presence of dismembered ophiolite slivers along some major fault zones, as well as the recognition of relict blueschist metamorphism and serpentinite-matrix mélanges requires an oceanic setting involving oceanic underthrusting (subduction) for the western Lachlan Orogen and central Lachlan Orogen for parts of their history. Inhibited by deep weathering and a general lack of exposure, the recent application of geophysical techniques including gravity, aeromagnetic imaging and deep crustal seismic reflection profiling ...

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Ordovician and Silurian history of the southeastern part of the Lachlan Geosyncline

Cited by 45 publications

References 10 publications

Timing of orogenic events in the Lachlan Orogen

Timing of orogenic events in the Lachlan Orogen

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Tectonic evolution of the Lachlan Orogen, southeast Australia: historical review, data synthesis and modern perspectives

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