Paul F. Carr

Proterozoic–Cambrian detrital zircon and monazite ages from the Anakie Inlier, central Queensland: Grenville and Pacific‐Gondwana signatures*

The Anakie Metamorphic Group is a complexly deformed, dominantly metasedimentary succession in central Queensland. Metamorphic cooling is constrained to ca 500 Ma by previously published K–Ar ages. Detrital‐zircon SHRIMP U–Pb ages from three samples of greenschist facies quartz‐rich psammites (Bathampton Metamorphics), west of Clermont, are predominantly in the age range 1300–1000 Ma (65–75%). They show that a Grenville‐aged orogenic belt must have existed in northeastern Australia, which is consistent with the discovery of a potential Grenville source farther north. The youngest detrital zircons in these samples are ca 580 Ma, indicating that deposition may have been as old as latest Neoproterozoic. Two samples have been analysed from amphibolite facies pelitic schist from the western part of the inlier (Wynyard Metamorphics). One sample contains detrital monazite with two age components of ca 580–570 Ma and ca 540 Ma. The other sample only has detrital zircons with the youngest component between 510 Ma and 700 Ma (Pacific‐Gondwana component), which is consistent with a Middle Cambrian age for these rocks. These zircons were probably derived from igneous activity associated with rifting events along the Gondwanan passive margin. These constraints confirm correlation of the Anakie Metamorphic Group with latest Neoproterozoic ‐ Cambrian units in the Adelaide Fold Belt of South Australia and the Wonominta Block of western New South Wales.

K‐Ar dating of Permian and Tertiary igneous activity in the Southeastern Sydney Basin, New South Wales

Abstract The southern part of the Sydney Basin of New South Wales is comprised mainly of Permian and Triassic marine to freshwater clastic sedimentary rocks. Within this sequence there are six latite extrusive units, several medium‐sized monzonite intrusions and a large number of small to medium‐sized basic to intermediate intrusions. Thin basaltic flows were extruded onto the Tertiary topographic surface. All of these rocks are relatively undeformed. Radiometric (K‐Ar) dating has previously been carried out on Mesozoic and Tertiary intrusions and flows of the southwestern portion of the Sydney Basin. However, relatively few Permian, and no post‐Permian, K‐Ar dates have been published for the southeastern portion of the basin. The present investigation provides nine K‐Ar dates from the latter area. Four extrusive and intrusive units have been confirmed as Permian in age (238 ± 6; 241 ± 4; 245 ± 6; and 251 ± 5 m.y.). Five post‐Permian (on stratigraphic criteria) intrusions yielded Tertiary ages (26.2 ± 3.0...

Origin, alteration and geochemical correlation of Late Permian airfall tuffs in coal measures, Sydney Basin, Australia

Abstract The Late Permian Illawarra Coal Measures of the southern Sydney Basin contain tuffs derived from altered pyroclastic airfall material. These units represent ideal stratigraphic time planes because, as the products of airfall volcanic ashes, they are distributed over wide areas in short periods of geological time. Geochemical correlation of the tuffs of the Illawarra Coal Measures with similar units in the stratigraphically equivalent Newcastle Coal Measures offers a unique opportunity to understand the temporal and spatial relations during deposition of coal-bearing units in the Sydney Basin. Thirty five core samples comprising 12 samples from each of the Burragorang and Farmborough Claystone Members and 11 samples from the Huntley Claystone Member were analysed for major and trace elements by X-ray fluorescence and instrumental neutron activation, and the results were subjected to stepwise discriminant analysis. The elements that served as the best discriminators between tuffs were, in order of atomic number, Ti, V, Sn, Hf and Th. Samples for basin-wide correlation were taken from thick interseam tuffs of the Newcastle Coal Measures and treated as unknowns in the discriminant model. The Burragorang Claystone Member shows a strong geochemical correlation with the Awaba Tuff, and the Farmborough Claystone Member correlates with the Warners Bay Tuff. The Huntley Claystone Member, however, has proved difficult to correlate with the Nobbys Tuff, the proposed stratigraphic equivalent in the Newcastle Coal Measures. Petrographic data for tuffs of the Illawarra Coal Measures indicate that they were deposited by airfall mechanisms and consist mainly of kaolinite and mixed-layer illite/smectite clays, quartz and plagioclase crystal fragments, lithic fragments and secondary calcite and siderite. Zr/TiO2 and Nb/Y ratios, tectonic discrimination diagrams and chondrite normalised REE patterns (La/Yb=3.3 to 11.9) are identical to those for tuffs of the Newcastle Coal Measures and are interpreted as being derived from magma that was calc-alkaline, rhyodacitic to rhyolitic in composition and derived from a continental volcanic-arc tectonic setting. The source of the tuffs is interpreted to be an active volcanic arc to the east of the present coastline (Currarong Orogen), but a lack of evidence from below the continental shelf makes it difficult to make concrete conclusions on its likely extent and composition.

The Influence of Palaeoenvironment and lava flux on the emplacement of submarine, near-shore Late Permian basalt lavas, Sydney Basin (Australia)

Abstract Lava flux and a low palaeoslope were the critical factors in determining the development of different facies in the Late Permian Blow Hole flow, which comprises a series of shoshonitic basalt lavas and associated volcaniclastic detritus in the southern Sydney Basin of eastern Australia. The unit consists of a lower lobe and sheet facies, a middle tube and breccia facies, and an upper columnar-jointed facies. Close similarities in petrography and geochemistry between the basalt lavas from the three facies suggest similar viscosities at similar temperatures. Sedimentological and palaeontological evidence from the sedimentary units immediately below the Blow Hole flow suggests that the lower part of the volcanic unit was emplaced in a cold water, shallow submarine environment, but at least the top of the uppermost lava was subaerial with some palaeosol development. The lower lobe and sheet facies was emplaced on a low slope (

Silurian and Early Devonian geochronology — a reappraisal, with new evidence from the Bungonia Limestone

The lower part of the Bungonia Limestone in the Bungonia-Marulan South area, N.S.W., has previously been dated as Ludlovian. New fossil localities from the upper part of the formation yield faunas including Scabriscutellum sp. cf. S. scabrum, Schizophoria, Eospirifer eastoni and Spathognathodus sp. cf. S. remscheidensis which indicate a Lochkovian age. The Bungonia Limestone is intruded by parts of the Marulan Batholith (398 ± 7m.y.) thus giving a minimum age for the Silurian-Devonian boundary. An appraisal of published data shows that there are 20 radiometric dates with good biostratigraphic control from Silurian and Early Devonian rocks. The relationship between the palaeontologically-based relative duration of Silurian and Early Devonian series and stages and the radiometric age of units confined to individual series or stages, provides an estimate of the age of the base of the following: Llandoverian 433 m.y.; Wenlockian 419 m.y.; Ludlovian 412 m.y.; Pridolian 405 m.y.; Gedinnian and Lochkovian 401 m....

REE geochemistry of Late Permian shoshonitic lavas from the Sydney Basin, New South Wales, Australia

Abstract Nine Late Permian shoshonitic lavas from the southern Sydney Basin have moderately fractionated rare-earth element (REE) patterns and are enriched in light REE (LREE). Petrographic and geochemical data accord with the lavas being related by low-pressure fractionation of plagioclase, olivine and clinopyroxene. Trace-element modelling on the basis of published partition coefficients and possible source compositions suggests that the shoshonitic magmas were generated by 10–15% partial melting of spinel lherzolite which had been enriched previously in LREE. Generation of the shoshonitic lavas in the Sydney Basin was not related directly to Benioff-zone magmatism but the enrichment of the source region in LREE may have been related to a pre-Late Permian subduction event. A compilation of REE data for shoshonitic volcanic rocks from a variety of geographic and tectonic settings indicates that there is no simple relationship between REE content and the thickness of continental crust above the source region.

Late Ordovician island‐arc volcanic rocks, northern Capertee Zone, Lachlan Fold Belt, New South Wales

Late Ordovician (ca 450 Ma) units (Sofala Volcanics, Coomber Formation, Burranah Formation, Tucklan Formation) in the northern Capertee Zone of the northeastern Lachlan Fold Belt in central New South Wales are part of an extensive pile of mafic volcanic and volcaniclastic strata and associated shallow intrusions known collectively as the Molong volcanic province. Lavas and large clasts in volcaniclastic rocks comprise basalt (clinopyroxene‐phyric) and basaltic andesite (plagioclasephyric). Alteration mineral assemblages suggest prehnite‐pumpellyite to prehnite‐actinolite facies metamorphism. Geochemical data for samples with minimal alteration indicate shoshonitic affinity for these Ordovician magmatic rocks and are characterised by depletion of Ta, Nb, Zr, Ti and Y relative to Rb, Ba and K. Initial 87Sr/86Sr ratios and ϵNd values are similar to those reported from other Ordovician volcanic suites in the Molong volcanic province and indicate minimal crustal input. The geochemical and isotopic signature of these rocks indicates their genesis in a subduction‐related island‐arc setting.

Silurian volcanism in the wollondilly basin, eastern lachlan fold belt, new south wales

The Wollondilly Basin, east of Goulburn in the Southern Highlands of New South Wales, contains a mafic to silicic volcanic succession together with limestone and clastic deposits. The oldest unit, the Gundary Formation, includes clastic deposits, silicic pyroclastic flows, and mafic‐intermediate lavas and was emplaced, at least in part, in a terrestrial environment. Fresh hornblende separates from two samples of dacitic ignimbrite have an average K‐Ar age of 426 ± Ma (late Early Silurian). The mafic‐intermediate flows have a shoshonitic geochemical signature that reflects the nature of their source material. The Gundary Formation is in faulted contact with the marine Boxers Creek Formation which conformably underlies a Late Silurian turbidite unit, the Towrang Formation. Cessation of volcanic activity is reflected by decreasing input of volcanic detritus up section and the increase in detritus derived from uplifted Ordovician basement rocks. The succession demonstrates that rocks with shoshonitic affinity...

The early devonian tangerang formation of the marulan‐ windellama region, nsw — definition and palaeo‐environmental significance

The Early Devonian Tangerang Formation consists of a sequence of shallow marine conglomerate, limestone and shale interbedded with shallow marine and terrestrial volcaniclastic arenite, tuff and dacitic lava flows. Three distinctive members have been recognized within the formation, namely the Windellama Limestone Member, the Carne Dacite Member and the Aloes Tuff Member. Limestone is confined to the lower part of the formation in the south where it is overlain by an entirely shallow marine sequence of volcaniclastic arenite. The proportion of volcanic material increases northwards and includes fiamme and accretionary lapilli which are considered to represent ashflow and ashfall tuffs that accumulated, together with thick lava flows, on the flanks of subaerial dacitic volcanoes. These volcanoes were situated at the northern end of the Aloes Tuff Member and towards the top of the formation in the Marulan South area. In the south the Tangerang Formation unconformably overlies Ordovician strata and the prese...

Evolution of the early devonian bindook volcanic complex, wollondilly basin, eastern lachlan fold belt

The Early Devonian Bindook Volcanic Complex consists of a thick silicic volcanic and associated sedimentary succession filling the extensional Wollondilly Basin in the northeastern Lachlan Fold Belt. The basal part of the succession (Tangerang Formation) is exposed in the central and southeastern Wollondilly Basin where it unconformably overlies Ordovician rocks or conformably overlies the Late Silurian to Early Devonian Bungonia Limestone. Six volcanic members, including three new members, are now recognised in the Tangerang Formation and three major facies have been delineated in the associated sedimentary sequence. The oldest part of the sequence near Windellama consists of a quartz turbidite facies deposited at moderate water depths together with the shallow‐marine shelf Windellama Limestone and Brooklyn Conglomerate Members deposited close to the eastern margin of the basin. Farther north the shelf facies consists of marine shale and sandstone which become progressively more tuffaceous northwards tow...