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Victoria provides the only well-exposed section across the southern part of the Lachlan Fold Belt and the easternmost Delamerides. Al-though the plate tectonic setting of this region in the Palaeozoic is still uncertain, the exposure provides important insights into its deposi-tional, magmatic and structural evolution from the Cambrian to the end o...
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Context 1
... the Bendigo Zone, the Kerrie Conglomerate between Lancefield and Gisborne (Figs 2, 4) is an entirely sedolithic braided stream deposit a few hundred metres thick, probably in a feeder channel to the Melbourne 'Trough' farther east. Its contact with underlying Upper Ordovician rocks is an angular unconformity. ...
Context 2
... the Melbourne Zone, there is a pronounced increase in structural complexity and cleavage development from west to east (VandenBerg & Gray 1988). In the west, the Silurian and Lower Devonian sediments have long, arcuate open folds, gen- erally 3-6 km apart (Fig. 4) above a decollement developed in shales at or near the top of the Ordovician. Below this, folds in the Ordovician sediments are tighter and more closely spaced, as in the Mornington Peninsula and at Sunbury (VandenBerg 1992). Cleavage is absent or confined to fold hinges. In the Upper Yarra region, in the east-central part of the zone, ...
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When did modern–style plate tectonics begin on Earth is not a consensus, but many authors suggest that it happened transitionally, from 3.0 to 2.5 Ga. This global geodynamical change, from plume–lid (vertical tectonics) to modern–style (horizontal tectonics), consequently, had a major impact on the nature of mineral systems, as mineral deposits rep...
Citations
... The geology of this area is dominated by sedimentary rocks, with a mix of sandstone, mudstone, and limestone formations [44,45]. The region is also home to some volcanic rock formations, including basalt and tuff [46,47]. The geological features of the Horsham region are part of the larger Murray Basin, which covers an area of over 1 million square kilometres and is a large sedimentary basin that covers a significant portion of southeastern Australia [43,48]. ...
The behaviour of unbound granular materials (UGMs) used in road construction is crucial in determining the longevity and performance of road pavement. Geotechnical analysis can assist engineers in selecting suitable materials and designing road pavements that meet industry standards. This paper presents the results of laboratory geotechnical tests conducted on unbound granular materials (UGMs) collected from three sites (Roses Gap, Rules East, and Polkemmet Road) in Horsham, Victoria, Australia. UGMs were investigated for their mechanical behaviour and suitability as subgrade materials for road pavements. The study utilised laboratory geotechnical tests, including particle size distribution (PSD), Atterberg limits, compaction (Proctor) test, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and repeated load triaxial (RLT) tests, to evaluate the physical and mechanical properties of the UGM samples. The study indicates that UGM samples collected from different locations displayed variations in their geotechnical properties, such as particle size distribution, water absorption, and CBR strength. Roses Gap samples showed weak cohesion properties, and significant vertical displacements after repeated triaxial tests. However, among the samples in this site, samples with higher clay content (RG21) demonstrated the most promise in triaxial tests. Similarly, the Rules East samples were found to be suitable for low-traffic subgrades due to their satisfactory CBR and RLT testing results, albeit with little cohesion from clay content. Out of three locations, Polkemmet samples were identified as potential subgrade applications, with PR12 being the top recommendation overall. It satisfied PSD, CBR, and RLT test conditions due to acceptable particle size in the largest range, highest CBR strength value, and lowest permanent displacement. The study's findings provide useful information for the design of road pavements using these materials and the characterisation of rural materials around the Horsham region for future use in various other contexts.
... The dating of the exposures at Ghin Ghin Road and Limestone Road, Yea, as Pridolian and Ludlovian respectively by Garratt andRickards (1984, 1987), , Rickards and Garratt (1990), and Rickards (2000) are contentious for a number of workers (Banks 1980;Cleal and Thomas, 1999 . Source: adapted from Moore et al. (1998: fig. 2). ...
Early land plants with elongate sporangia held in the palaeobotanical archives of Museums Victoria were examined. The fossil plants are from Yea (?upper Silurian) and near Matlock (Lower Devonian) in central Victoria, and are of interest because they contribute to our understanding of the evolution of early land plants in a region in which research has been limited. Both Salopella australis and Salopella caespitosa were originally described over 30 years ago and this reinvestigation has resulted in the emending of the diagnosis of Salopella australis and the erection of a new morphotaxon Salopella laidae sp. nov. based primarily on differing branching architecture and sporangial morphology. Salopella laidae comes from Yea Formation and possesses regular isotomous branching over at least two orders of branching, terminating in elongate sporangia that are wider than their subtending axes, differing from S. australis, which possesses only one dichotomy emanating from at least two erect parallel parent axes with sporangia that are the same width as their subtending axes. A recently collected specimen of Salopella caespitosa was also examined and adds to our understanding of this taxon, which was previously only known from one specimen. Consideration is given to the possible sources of these early land plants based on other early land plants with a similar grade of organisation.
... The dating of the exposures at Ghin Ghin Road and Limestone Road, Yea, as Pridolian and Ludlovian respectively by Garratt andRickards (1984, 1987), , Rickards and Garratt (1990), and Rickards (2000) are continuous for a number of workers (Banks 1980;Cleal and Thomas, 1999 . Source: adapted from Moore et al. (1998: fig. 2). ...
McSweeney, F.R., Shimeta, J. and Buckeridge, J.S. 2021. Early land plants from the Lower Devonian of central Victoria, Australia, including a new species of Salopella. Memoirs of Museum Victoria 80: 169-181. Early land plants with elongate sporangia held in the palaeobotanical archives of Museums Victoria were examined. The fossil plants are from Yea (?upper Silurian) and near Matlock (Lower Devonian) in central Victoria, and are of interest because they contribute to our understanding of the evolution of early land plants in a region in which research has been limited. Both Salopella australis and Salopella caespitosa were originally described over 30 years ago and this reinvestigation has resulted in the emending of the diagnosis of Salopella australis and the erection of a new morphotaxon Salopella laidae sp. nov. based primarily on differing branching architecture and sporangial morphology. Salopella laidae comes from Yea Formation and possesses regular isotomous branching over at least two orders of branching, terminating in elongate sporangia that are wider than their subtending axes, differing from S. australis, which possesses only one dichotomy emanating from at least two erect parallel parent axes with sporangia that are the same width as their subtending axes. A recently collected specimen of Salopella caespitosa was also examined and adds to our understanding of this taxon, which was previously only known from one specimen. Consideration is given to the possible sources of these early land plants based on other early land plants with a similar grade of organisation.
... We were actually the first to establish that this pluton was Delamerian and an extension of the Glenelg Zone (Foster & Gleadow 1992) [i.e. before Moore et al. (1998) or Cayley & Taylor (1998 as referenced in VandenBerg (1999)] and not part of the Lachlan Orogen. We further stated this explicitly in Foster et al. (1996aFoster et al. ( , 1998. ...
... By the Middle to Late Devonian, much of the Lachlan Orogen had been deformed and intruded by granitoids and was characterised by an overlap sequence (Glen 1992) of mainly fluvial red-bed-style sedimentation with minor marine incursions. Post-orogenic magmatism (Gray & Foster 2004) was confined to the Howitt Province (O'Halloran & Gaul 1997;Moore et al. 1998), the Snowy Bluff volcanic rocks (Soesoo & Nicholls 1999) and the Central Victorian Magmatic Province in Victoria (Gray & Foster 2004), and narrow belts of limited extent in NSW, such the Dulladerry Volcanics (Raymond 1996;Pogson & Watkins 1998) and the Eden-Comerong-Yalwal Volcanic Zone (EVZ) (McIlveen 1974;Dadd 1992a;Giordano & Cas 2001). Arc volcanism was active farther to the east as a continuation of the Baldwin Volcanic Arc (Veevers 2000) or Calliope Arc Australian Journal of Earth Sciences (2011) 58, (209-222) ISSN 0812-0099 print/ISSN 1440-0952 online 2011 Geological Society of Australia DOI: 10.1080/08120099.2011.535563 ...
The Comerong Volcanics are a Middle to Late Devonian bimodal sequence located in the southeastern Lachlan Orogen of NSW, Australia. Magmatism related to subduction was ongoing and located to the east of the continent during this period placing the Comerong Volcanics in a continental back arc setting. Mafic rocks in the Comerong Volcanics occur in three stratigraphically distinct units and range in composition from tholeiitic andesite to basalt. An inverse relationship between volume of erupted lava and degree of fractionation of the magma is evident from the base of the volcanic complex to its top. The lowermost mafic unit is the least voluminous and most fractionated and consists of flows with low Mg#, Ni and Cr and high incompatible trace element abundances. The overlying unit comprises both moderately and extremely fractionated basalt and is characterised by flows with a relatively high TiO2 content. Lavas in this unit can be divided into higher and lower-Ti types. The uppermost unit is the most voluminous and the least fractionated with relatively high MgO, Ni and Cr and low incompatible trace element abundances. Compositions are similar to the low-Ti lavas in the unit below. Trace element characteristics of all lavas suggest they were derived from a heterogeneously enriched source in the subcontinental lithospheric mantle. Enrichment of the source in LILE and depletion in Ti and Nb likely reflect earlier subduction in the orogen. The mafic rocks were erupted in a continental within-plate setting; a setting consistent with the field relationships.
... The rocks described in this paper have formerly been considered to be part of the Melbourne ''Trough''-a term used to refer to all the Ordovician to mid-Devonian rocks between the Cambrian Heathcote and Howqua À Wellington (now Governor Fault, see VandenBerg et al., 1995;Moore et al., 1998;Fig. 14. ...
... The good match between Ar/Ar deformation ages in the Stawell and Bendigo structural zones and the onset of Early Silurian Springfield -Wapentake -McAdam sandstone deposition in the Melbourne Zone points to the emergence of a new source region, lying within the Lachlan Fold Belt, with the Delamerides no longer providing sediments into the system. While the eastern limit of the Delamerides has long been uncertain (see, for instance, Gibson and Nihill, 1992;Fergusson and Coney, 1992;Glen et al., 1992a), dating and mapping have shown that it lies at the Moyston Fault (Cayley and Taylor, 1998;Moore et al., 1998), the western limit of the Stawell Zone (and of the Lachlan Fold Belt). The newly emergent source region provides a possible explanation for the bipolar nature of some of the Early Silurian palaeocurrents, which could have flowed parallel to a growing Early Silurian Stawell -Bendigo orogenic welt oriented NNE -SSW. ...
The Melbourne Zone comprises Early Ordovician to Early Devonian marine turbidites, which pass conformably upward into a mid-Devonian fluviatile succession. There are four pulses of Silurian to mid-Devonian deep-marine sandstone-dominated sedimentation: Early Silurian (late Llandovery), Late Silurian (Ludlow), earliest Devonian (Lochkovian) and late Early Devonian (Emsian). Two dispersal patterns have been defined using more than 1100 palaeocurrent measurements, mainly from sole marks and cross-laminations in graded beds, together with sandstone compositions. The older pattern, of Silurian to earliest Devonian age, contains the lowest three sandstone pulses. Palaeocurrents and provenance define a wedge of southwesterly derived sediment, of largely cratonic provenance, thinning eastward. This older dispersal pattern is part of an Early Ordovician to earliest Devonian east-facing passive continental margin succession. Palaeocurrents and provenance in the Emsian sandstone pulse comprise three patterns: (1) west- to southwesterly directed palaeocurrents associated with fine- to coarse-grained, locally conglomeratic, lithic sandstones containing a high proportion of volcanic detritus; (2) east- to northeasterly directed palaeocurrents associated with fine- to medium-grained quartz-lithic sandstones; (3) north- to northwesterly and south- to southeasterly directed palaeocurrents associated with fine- to medium-grained sandstones of variable lithic composition. The palaeocurrent and provenance pattern defines a NNW-elongate basin with a tectonically active eastern margin, and is similar to the coeval Mathinna basin of northeastern Tasmania. Both basins are part of the same system of wrench basins, which developed along the western side of the Wagga–Omeo Metamorphic Belt during the earliest Devonian to Middle Devonian. The change in tectonic setting in the earliest Devonian appears to have occurred during an interval of significant dextral translation of the eastern Lachlan Fold Belt towards the SSE along the Governor and associated fault zones.
... Stavely (e.g. Moore et al., 1998). Sedimentation in the area of the Adelaide Syncline and the greenstone belt was terminated by/during the Cambro-Ordovician Delamerian Orogeny. ...
Metasediments in the three early Palaeozoic Ross orogenic terranes in northern Victoria Land and Oates Land (Antarctica) are geochemically classified as immature litharenites to wackes and moderately mature shales. Highly mature lithotypes with Chemical Index of Weathering values of ≥ 95 are typically absent. Geochemical and Rb-Sr and Sm-Nd isotope results indicate that the turbiditic metasediments of the Cambro-Ordovician Robertson Bay Group in the eastern Robertson Bay Terrane represent a very homogeneous series lacking significant compositional variations. Major variations are only found in chemical parameters which reflect differences in degree of chemical weathering of their protoliths and in mechanical sorting of the detritus. Geochemical data, 87Sr/86Sr t=490Ma ratios of 0.7120 - 0.7174, εNd,t=490Ma values of -7.6 to -10.3 and single-stage Nd-model ages of 1.7 - 1.9 Ga are indicative of an origin from a chemically evolved crustal source of on average late Palaeoproterozoic formation age. There is no evidence for significant sedimentary infill from primitive "ophiolitic" sources. Metasediments of the Middle Cambrian Molar Formation (Bowers Terrane) are compositionally strongly heterogeneous. Their major and trace element data and Sm-Nd isotope data (εNd,t=500Ma values of -14.3 to -1.2 and single-stage Nd-model ages of 1.7 - 2.1 Ga) can be explained by mixing of sedimentary input from an evolved crustal source of at least early Palaeoproterozoic formation age and from a primitive basaltic source. The chemical heterogeneity of metasediments from the Wilson Terrane is largely inherited from compositional variations of their precursor rocks as indicated by the Ni vs TiO2 diagram. Single-stage Nd-model ages of 1.6 -2.2 Ga for samples from more western inboard areas of the Wilson Terrane (εNd,t=510Ma -7.0 to -14.3) indicate a relatively high proportion of material derived from a crustal source with on average early Palaeoproterozoic formation age. Metasedimentary series in an eastern, more outboard position (εNd,t=510Ma -5.4 to -10.0; single-stage Nd model ages 1.4 - 1.9) on the contrary document stronger influence of a more primitive source with younger formation ages. The chemical and isotopic characteristics of metasediments from the Bowers and Wilson terranes can be explained by variable contributions from two contrasting sources: a cratonic continental crust similar to the Antarctic Shield exposed in Georg V Land and Terre Adélie some hundred kilometers west of the study area and a primitive basaltic source probably represented by the Cambrian island-arc of the Bowers Terrane. While the data for metasediments of the Robertson Bay Terrane are also compatible with an origin from an Antarctic-Shield-type source, there is no direct evidence from their geochemistry or isotope geochemistry for an island-arc component in these series.
... These two ages do much to enhance the appearance of diachronism but their use is of questionable validity. The Bushy Creek Tonalite is on the western side of the Moyston Fault, a region now regarded as part of the Adelaide Fold Belt deformed in the Cambrian–Ordovician Delamerian Orogeny (Moore et al. 1998). Its age compares well with the age of the oldest Delamerian granite in South Australia, the Encounter Bay Granite (K/Ar dated at 504 ± 8 and 495 ± 6 Ma) at Victor Harbor, 420 km farther northwest (Milnes et al. 1977). ...
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.
... Volcanism certainly overlapped with fluvial deposition of Late Devonian 'redbeds' in the Mansfield Basin (O'Halloran & Cas 1995). However, most of these volcanic rocks appear to be stratigraphically overlain by Late Devonian to Early Carboniferous sedimentary rocks (Moore et al. 1998) and their age also appears to be fairly well-constrained by good isotopic dating of the basal rhyolite (368.6 2.3 Ma) and top rhyodacite (367.1 2.3 Ma) in the Cerberean volcanic sequence (Williams et al. 1982). Approximately 230 km west of Bombala there are possible Carboniferous mafic lavas interbedded with the fluvial Mt Kent Conglomerate and the lower part of the overlying fluvial redbeds of the Snowy Plains Formation in the northeastern Avon Synclinorium of the Mt Howitt Province (Neilson 1976;Soesoo & Nicholls 1999). ...
Zircons from two igneous and two sedimentary units in the Bombala area of southeastern New South Wales have been examined by the sensitive high resolution ion microprobe (SHRIMP) to establish a timeframe in which to interpret these rocks. Previous studies have correlated these rocks with Late Devonian units of the south coast, solely upon the basis of stratigraphy and lithology as palaeontological evidence was absent. The two igneous units are the Hospital Porphyry and Paradise Porphyry occurring beneath the sedimentary units. Both give a Frasnian age that can be correlated with the Boyd Volcanic Complex. The sedimentary samples are from the basal and upper sections of the Rosemeath Formation, a fluvial 'redbed' consisting of conglomerate, coarse sandstone, and associated red siltstone and mudstone. Detrital zircons from the basal conglomeratic section at Kilbrechin indicate a dominant provenance from local Silurian granites and volcanics and a maximum depositional age that can be correlated with the Frasnian-Famennian Merrimbula Group. However, detrital zircons from the upper coarse sandstone section of the Rosemeath Formation at Endeavour Lookout challenge the positive correlation trend with a lack of Silurian-age grains and a presence of grains ranging from Late Devonian to Early Carboniferous in age. These results imply either that the south coast correlation is not valid for the upper sequences, or that the Merrimbula Group sequences also extend upward into the Carboniferous. The general coarseness of the Rosemeath Formation also suggests a relatively local provenance. No Early Carboniferous source is known in the immediate vicinity suggesting that Early Carboniferous igneous activity in this region of the Lachlan Orogen may have been more extensive than is currently realised.
... At large scales (deposit and district-size studies ), high-resolution magnetic and gravity data are often useful in defining structures directly related to mineralization (e.g., strike-slip faults—Isles et al, 1989; Henley and Adams, 1992; kimberlite dikes—Mckinlay et al., 1997; folds—Whiting, 1986). On the other hand, at smaller scales, geophysical data help elucidate the regional geologic framework, mainly by defining major compositional boundaries or structural zones that may be favorable environs for mineralization (e.g., Gunn et al., 1997a, b; Jaques et al., 1997; Leclair et al., 1997; Moore et al., 1998). Here we investigate the utility of regional gravity and magnetic data in understanding the distribution of large ore deposits , concentrating on epithermal and porphyry precious and base metal deposits and sediment-hosted gold deposits in the western United States cordillera. ...
Upgraded gravity and magnetic databases and associated filtered-anomaly maps of western United States define regional crustal fractures or faults that may have guided the emplacement of plutonic rocks and large metallic ore deposits. Fractures, igneous intrusions, and hydrothermal circulation tend to be localized along boundaries of crustal blocks, with geophysical expressions that are enhanced here by wavelength filtering. In particular, we explore the utility of regional gravity and magnetic data to aid in understanding the distribution of large Mesozoic and Cenozoic ore deposits, primarily epithermal and porphyry precious and base metal deposits and sediment-hosted gold deposits in the western United States cordillera. On the broadest scale, most ore deposits lie within areas characterized by low magnetic properties. The Mesozoic Mother Lodge gold belt displays characteristic geophysical signatures (regional gravity high, regional low-to-moderate background magnetic field anomaly, and long curvilinear magnetic highs) that might serve as an exploration guide. Geophysical lineaments characterize the Idaho-Montana porphyry belt and the La Caridad-Mineral Park belt (from northern Mexico to western Arizona) and thus indicate a deep-seated control for these mineral belts. Large metal accumulations represented by the giant Bingham porphyry copper and the Butte polymetallic vein and porphyry copper systems lie at intersections of several geophysical lineaments. At a more local scale, geophysical data define deep-rooted faults and magmatic zones that correspond to patterns of epithermal precious metal deposits in western and northern Nevada. Of particular interest is an interpreted dense crustal block with a shape that resembles the elliptical deposit pattern partly formed by the Carlin trend and the Battle Mountain-Eureka mineral belt. We support previous studies, which on a local scale, conclude that structural elements work together to localize mineral deposits within regional zones or belts. This study of mineral deposits of the western United States demonstrates the ability of magnetic and gravity data to elucidate the regional geologic framework or structural setting and to contribute in locating favorable environments for hydrothermal mineralization.
