Palaeoproterozoic to Mesoproterozoic Geology of North Queensland

Australian GovernmentGeoscience AustraliaPalaeoproterozoic toMesoproterozoic Geology of NorthQueenslandIan Withnall (GSQ)Narelle Neumann, Lex Lambeck (GA)Townsville, 3 June 2009

Deep crustalseismic transectsMT ISAINLIERBB BURDEKIN BASINGCSP GRAVEYARD CK SUBPROVINCECCSP CAMEL CK SUBPROVINCETP THALANGA PROVINCECRP CAPE RIVER PROVINCEBP BARNARD PROVINCECOENINLIERYAMBOHODGKINSONINLIERBASINBPCRPGEORGETOWNINLIER TP CCSPGCSPBBCRPTPDRUMMONDBASININTRODUCTION• Georgetown Inlier (along with CoenInlier) contains the most easterlyProterozoic outcrops in Australia• Important to an understanding ofthe evolution of the continent andpossible configurations of Rodinia(e.g. SWEAT vs AUSWUS)• Most models for the evolution ofthe North Australian Cratonassume Georgetown to be a part ofit really explaining how it fits• Betts et al. (2002) inferred that theeastern margin of the NorthAustralian Craton was ocean-facingprior to the Mesoproterozoic(~1600-1500Ma) orogenesis, whichthey postulated was related to awest dipping subduction zone andcontinental collision due to dockingof the North American Craton at~1540Ma during formation ofRodinia.• Boger & Hansen (2004) speculatedthat the metamorphic evolution ofGeorgetown and some othercharacteristics suggest it wasaccreted to the NAC during theconstruction of Rodinia, rather thanhaving always been part of it.

Tasman LineCOENINLIERDeep crustalseismic transectsYAMBOINLIERHODGKINSONBASINGEORGETOWNINLIERMT ISAINLIERTasman Line

Structural Elements – Georgetown-Charters Towers regionOld Tasman LineTasman Line (Lynd Fault)Proterozoic fold beltPalaeozoic fold belts

50 kmSurface Geology – Georgetown region

Proterozoic Stratigraphic Units – Georgetown region50 km

Proterozoic Stratigraphic Units - Solid Geology – Georgetown region50 km

Palaeoproterozoic-Mesoproterozoic Stratigraphy – Georgetown regionCroydonVolc GroupYarman FmMalacura FmLanglovaleGroupLangdon River MdstRobertsonRiver SGpCandlow FmHeliman FmTownley FmLane Ck FmCorbett FmDead Horse MetabsltDaniel Creek FmBernecker Ck FmEtheridge GroupCobbold Metadoleriteamphibolitebiotite gneissEinasleigh MetamorphicsJuntalaMetsCassidy CkMetsorthogneisscalc-silicate gneissleucogneiss

Bernecker Creek Formation• Calcareous/dolomitic sandstone & siltstone• Abundant evidence of current activity – shallow water orturbidites??• MDA ~1844 Ma• major Archaean- earliest Palaeoproterozoic component(70%)

Bernecker Creek Formation• Calcareous/dolomitic sandstone & siltstone• Abundant evidence of current activity – shallow water orturbidites??• MDA ~1844 Ma• Major Archaean- earliest Palaeoproterozoic component(70%)201816Bernecker Creek Formation2007169002All; n=7314Number12108mda = 1844 ± 11 MaRelative probability64201500 1700 1900 2100 2300 2500 2700 2900Age (Ma)

Daniel Creek Formation• Very fine sandstone and siltstone/mudstone; locallycalcareous with concretions• Turbidites or shallow water??• MDA ~1695 Ma• major Archaean- earliest Palaeoproterozoic component(76%)

Daniel Creek Formation• Very fine sandstone and siltstone/mudstone; locallycalcareous with concretions• Turbidites or shallow water??• MDA ~1695 Ma• Major Archaean- earliest Palaeoproterozoic component(76%)201816Daniel Creek Formation2007169003All; n=81Number141210864mda = 1695 ± 13 MaRelative probability201500 1700 1900 2100 2300 2500 2700 2900Age (Ma)

Dead Horse Metabasalt• Aphyric tholeiitic metabasalt, local pillows andhyaloclastite; minor mudstone• Submarine emplacement• Magmatic age 1663±13Ma (Mike Baker, PhD, 2007)

Dead Horse Metabasalt• Aphyric tholeiitic metabasalt, local pillows andhyaloclastite; minor mudstone• Submarine emplacement• Magmatic age 1663±13Ma (Mike Baker, PhD, 2007)

Corbett Formation• Predominantly mudstone, rare sandstone• Deep waterMDA ~1785 Mamajor Archaean- earliest Palaeoproterozoic component(48%)

Corbett Formation• Predominantly mudstone, rare sandstone• Deep water• MDA ~1785 Ma• Major Archaean- earliest Palaeoproterozoic component(48%)201816Corbett Formation2007169004All; n=7314Number12108mda = 1785 ± 11 MaRelative probability64201500 1700 1900 2100 2300 2500 2700 2900Age (Ma)

Lane Creek Formation• Mudstone and siltstone, commonly carbonaceous;minor fine-grained sandstone; rare limestone• Deep water• MDA ~1786 Ma• major Archaean- earliest Palaeoproterozoic component(30%)

Lane Creek Formation• Mudstone and siltstone, commonly carbonaceous;minor fine-grained sandstone; rare limestone• Deep water• MDA ~1786 Ma• Diminishing Archaean- earliest Palaeoproterozoiccomponent (30%)1412MDA = 1786 ± 6 MaLane Creek FormationIWGT550All; n=84Number10864Relative probability201700 1900 2100 2300 2500 2700 2900 3100207/206 Age

Cobbold Metadolerite• Mostly sills of metadolerite and metagabbro• Restricted to units up to & including Lane Creek Formation

Cobbold Metadolerite• Mostly sills of metadolerite and metagabbro• Restricted to units up to & including Lane Creek Formation• Magmatic age 1656±2Ma for (leucogabbro intruding LaneCreek Formation)

Cobbold Metadolerite• Mostly sills of metadolerite and metagabbro• Restricted to units up to & including Lane Creek Formation• Magmatic age 1656±2Ma for (leucogabbro intruding LaneCreek Formation)

Townley Formation• Mudstone, siltstone, locally carbonaceous; minor finegrainedsandstone, commonly with rip-up clasts• Deep water?• MDA ~1649 Ma• Diminished Archaean- earliest Palaeoproterozoiccomponent (27%)• Contact with Lane Creek Formation unremarkable

Townley Formation• Mudstone, siltstone, locally carbonaceous; minor finegrainedsandstone, commonly with rip-up clasts• Deep water?• MDA ~1649 Ma• Diminishing Archaean- earliest Palaeoproterozoiccomponent (27%)• Contact with Lane Creek Formation unremarkable; noobvious unconformity201816Townley Formation2007169005All; n=6614Number12108mda = 1649 ± 5 MaRelative probability64201500 1700 1900 2100 2300 2500 2700 2900Age (Ma)

Heliman Formation• Mudstone and siltstone, locally carbonaceous; abundantsiliceous siltstone and fine-grained sandstone, commonlywith mudclasts• Deep water???• MDA ~1655 Ma• Minor Archaean- earliest Palaeoproterozoic component (8%)

Heliman Formation• Mudstone and siltstone, locally carbonaceous; abundantsiliceous siltstone and fine-grained sandstone, commonlywith mudclasts• Deep water???• MDA ~1655 Ma• Minor Archaean- earliest Palaeoproterozoic component (8%)201816mda = 1655 ± 3 MaHeliman Formation2007169006All; n=7714Number121086Relative probability4201500 1700 1900 2100 2300 2500 2700 2900Age (Ma)

Candlow Formation• Mudstone, siltstone, commonly carbonaceous - up to 10% TOC –and pyritic; abundant mudclast sandstone• Local gypsum moulds & rare stromatolites• Conflicting interpretationsDeep water (Lambeck)Shallow water, possibly lacustrine (Draper)

Langdon River Mudstone• Laminated mudstone, commonly carbonaceous and pyritic (redgreyin outcrop)• Probably deep water• Sampled for SHRIMP MDA, but data not available

Palaeoproterozoic-Mesoproterozoic Stratigraphy – Georgetown regionCroydonVolc GroupYarman FmMalacura FmLanglovaleGroupLangdon River MdstRobertsonRiver SGpCandlow FmHeliman FmTownley FmLane Ck FmCorbett FmDead Horse MetabsltDaniel Creek FmBernecker Ck FmEtheridge GroupCobbold Metadoleriteamphibolitebiotite gneissEinasleigh MetamorphicsJuntalaMetsCassidy CkMetsorthogneisscalc-silicate gneissleucogneiss

Proterozoic Stratigraphic Units - Solid Geology – Georgetown region50 km

Langlovale Group• Malacura Sandstone (dominantly feldspathic sandstone – shallowmarine or proximal turbidite?)• Yarman Formation (dominantly mudstone with sandy intervals(distal to proximal turbidite – prodelta?)• Unconformable on Etheridge Group and overlain by CroydonVolcanic Group• MDA~1625Ma• Very minor Archaean- earliest Palaeoproterozoic component (1%)Malacura SandstoneYarman Formation

Langlovale Group• Malacura Sandstone (dominantly feldspathic sandstone – shallowmarine or proximal turbidite?)• Yarman Formation (dominantly mudstone with sandy intervals(distal to proximal turbidite – prodelta?)• Unconformable on Etheridge Group and overlain by CroydonVolcanic Group• MDA~1625Ma• Very minor Archaean- earliest Palaeoproterozoic component (1%)

Langlovale Group• Malacura Sandstone (dominantly feldspathic sandstone – shallowmarine or proximal turbidite?)• Yarman Formation (dominantly mudstone with sandy intervals(distal to proximal turbidite – prodelta?)• Unconformable on Etheridge Group and overlain by CroydonVolcanic Group• MDA ~1625Ma• Very minor Archaean- earliest Palaeoproterozoic component (1%)• Intruded by 1550Ma Esmeralda Supersuite201816mda = 1625 ± 5 MaMalacura Sandstone2007169009All; n=73Number141210864Relative probability201500 1700 1900 2100 2300 2500 2700 2900Age (Ma)Yarman Formation

Palaeoproterozoic-Mesoproterozoic Stratigraphy – Georgetown regionCroydonVolc GroupYarman FmMalacura FmLanglovaleGroupLangdon River MdstRobertsonRiver SGpCandlow FmHeliman FmTownley FmLane Ck FmCorbett FmDead Horse MetabsltDaniel Creek FmBernecker Ck FmEtheridge GroupCobbold Metadoleriteamphibolitebiotite gneissEinasleigh MetamorphicsJuntalaMetsCassidy CkMetsorthogneisscalc-silicate gneissleucogneiss

Proterozoic Stratigraphic Units - Solid Geology – Georgetown region50 km

Croydon Volcanic Group• Dominated by almost flat-lying sheets of felsic ignimbrite• Undeformed and unmetamorphosed• Intruded by comagmatic granites of the Esmeralda Supersuite• Both granites and volcanics contain abundant graphitic enclaves– presumably derived from the Etheridge Group at depth• Geochemically peraluminous and reduced – S-types or I-typesmodified by assimilation?• Conventional U-Pb zircon age of 1552Ma

Proterozoic Stratigraphic Units - Solid Geology – Georgetown regionInorunie Basin50 km

Inorunie Group• Unconformably overlies the Croydon Volcanic Group• Largely quartzose, micaceous fluviatile sandstone• Undeformed and unmetamorphosed• Only age constraints are relationships with Croydon VolcanicGroup and overlying Permian volcanic rocks – could beNeoproterozoic to early Palaeozoic

Palaeoproterozoic-Mesoproterozoic Stratigraphy – Georgetown regionCroydonVolc GroupYarman FmMalacura FmEsmeraldaSupersuiteLanglovaleGroupForsaythSupersuiteLangdon River MdstRobertsonRiver SGpCandlow FmHeliman FmGreenschistTownley FmLane Ck FmCorbett FmDead Horse MetabsltDaniel Creek FmBernecker Ck FmEtheridge GroupCobbold MetadoleriteAmphibolite -granulitebiotite gneissamphiboliteEinasleigh MetamorphicsAmphiboliteJuntalaMetsCassidy CkMetsorthogneisscalc-silicate gneissleucogneiss

Proterozoic Stratigraphic Units - Solid Geology – Georgetown region

Migmatitic graniteBiotite gneissEinasleigh Metamorphics• Psammopelitic gneisses (biotite & calc-silicate types); common mafics; rareleucogneiss (feldspathic psammite?) –> migmatite and anatectic granite• Previously correlated with lower part of Etheridge Group – gradationalboundary - may be partly true, but geochemistry and zircons suggestprovenance differences• Upper amphibolite to transitional granulite metamorphismCalc-silicate gneissLeucogneissLeucogneiss

Einasleigh Metamorphics• Psammopelitic gneisses (biotite & calc-silicate types); common mafics; rareleucogneiss (feldspathic psammite?) –> migmatite and anatectic granite• Previously correlated with lower part of Etheridge Group – gradationalboundary - may be partly true, but geochemistry and zircons suggestprovenance differences• Upper amphibolite to transitional granulite metamorphism• Age constraints‣ 1700Ma SHRIMP on detrital zircons in leucogneiss (epiclastic sediments froma felsic igneous source – Black & others, 2005)Complex provenance forleucogneiss in the western areaRelatively simple zircon populations in leucogneiss in theLyndhurst area suggesting a 1565Ma metamorphic eventoverprinting a single ca 1700Ma igneous provenance

Einasleigh Metamorphics• Psammopelitic gneisses (biotite & calc-silicate types); common mafics; rareleucogneiss (feldspathic psammite?) –> migmatite and anatectic granite• Previously correlated with lower part of Etheridge Group – gradationalboundary - may be partly true, but geochemistry and zircons suggestprovenance differences• Upper amphibolite to transitional granulite metamorphism• Age constraints‣ 1700Ma SHRIMP on detrital zircons in leucogneiss (epiclastic sediments froma felsic igneous source – Black & others, 2005)‣ ~1690Ma SHRIMP on zircons from gneissic granite gives minimum age~1675Ma SHRIMP on zircons from amphiboliteintruding 1695Ma granite gneiss

Einasleigh Metamorphics• Psammopelitic gneisses (biotite & calc-silicate types); common mafics; rareleucogneiss (feldspathic psammite?)• Previously correlated with lower part of Etheridge Group – gradationalboundary - may be partly true, but geochemistry and zircons suggestprovenance differences• Upper amphibolite to transitional granulite metamorphism• Age constraints‣ 1700Ma SHRIMP on detrital zircons in leucogneiss (epiclastic sediments froma felsic igneous source – Black & others, 2005)‣ ~1690Ma SHRIMP on zircons from trondhjemitic gneissic granite‣ ~1675Ma SHRIMP on zircons from amphibolite intruding 1695Ma granitegneiss

Einasleigh Metamorphics• Psammopelitic gneisses (biotite & calc-silicate types); common mafics; rareleucogneiss (feldspathic psammite?)• Previously correlated with lower part of Etheridge Group – gradationalboundary - may be partly true, but geochemistry and zircons suggestprovenance differences• Upper amphibolite to transitional granulite metamorphism• Age constraints‣ 1700Ma SHRIMP on detrital zircons in leucogneiss (epiclastic sedimentsfrom a felsic igneous source – Black & others, 2005)‣ ~1690Ma SHRIMP on zircons from trondhjemitic gneissic granite‣ ~1675Ma SHRIMP on zircons from amphibolite intruding 1695Ma granitegneiss‣ Detrital ages of both biotite and calc-silicate paragneisses, have beenobtained, but need more interpretation - spread of ages between ~1670 and3240 Ma, with no big groups – some clusters between 1700 and 1900 Ma and2300 and 2600

Proterozoic solid geology – Georgetown region, showing granitoidsForsayth Forsayth Batholith BatholithMigmatitic granitoidEsmeralda Esmeralda SupersuiteSupersuiteForest HomeTrondhjemite

Mesoproterozoic Granitoids• Forest Home Supersuite –– biotite trondhjemite –– no magmatic zircon butxenocrysts with cores ~1650Ma• Migmatitic (nebulitic) granitoids with abundant restite in the EinasleighMetamorphics – SHRIMP ages of ~1560Ma• Lighthouse Supersuite – irregular gneissic to pegmatitic leucogranite – U-Pbmulti-grain TIMS ages ~1560Ma• Forsayth Supersuite – locally deformed, peraluminous S-type granitesdominated by grey porphyritic muscovite-biotite granite – U-Pb multi-grainTIMS ages ~1550Ma• Esmeralda Supersuite – undeformed peraluminous S-type (or I-type graniteswith significant assimilation) granite intruding and comagmatic with theCroydon Volcanic Group

Proterozoic structural domains & solid geology – Georgetown regionEINASLEIGH SUBPROVINCEGILBERT FOLD BELTSAVANNAHPROVINCECROYDON PROVINCECLARAVILLE PROVINCE

Deformation & metamorphismGilbert Fold beltRegional studies have suggested the following eventsD1• mainly E-W folds with strong cleavage/foliation• dominant regional structures;• lower greenschist to amphibolite metamorphism• usually thought to be ~1590Ma, based on SHRIMP dates from Dargalong areafarther north.D2• approx N-S folds superimposed on E-W structures,• restricted to E half of outcrop area;• multiple mesoscopic fabrics;• most workers have associated D2 with peak amphibolite facies metamorphismand emplacement of Forsayth Supersuite (S-type anatectic granites) andcommon metamorphic zircon growth at 1550-1560MaD3 - E-W folds, restricted to central part of areaLater open folds, possibly early Palaeozoic

Robertson River areaDeformation & metamorphismHowever, detailed microstructural (FIA analysis of porphyroblasts) & CHIMEdating of monazite from the Robertson River area give a somewhat differentpicture (Cihan & others, JCU)Porphyroblasts containing FIA1 to FIA3, overgrew a S1/S2 matrix foliationFIA1 and FIA2 related to early N-S shortening associated with monazite dated at1625±15 MaFIA3 related to E-W shortening associated with monazite dated at 1586±6 MaThermobarometry indicates pressure increased progressively to 6-7kb duringFA1 to FA3S3 – a flat lying fabric associated with matrix monazite dated at 1564±8 MaProbably related to decompression and exhumationFIA4 related to NW-SE shortening associated with monazite dated at 1542±8 MaAssociated with lower pressure-high temperature metamorphism at 3-4kbS4 younger fabric associated with with monazite dated at 1512±5 Ma

Einasleigh MetamorphicsStructural history not well constrainedDeformation & metamorphismMultiple foliations, including an early composite layer-parallel foliation, on whichare superimposed broadly E-W and N-S regional foldsExtensive migmatite terrains grading into anatectic granite with SHRIMP zirconpopulations of ~1560Ma (magmatic?) and 1568, 1595 and 1617Ma inheritanceMetamorphic zircons at 1552Ma in amphibolite and mafic granulite and ~1560Main leucogneiss and paragneiss; inferred to date D2/M2Work by Quinton Hills (Monash) suggests that 1675Ma amphibolite postdates amigmatitic layering – amphibolite at Einasleigh also appears to postdate and earlyfoliationTherefore Einasleigh Metamorphics or part thereof may be basement to the restof the Etheridge Group

Deformation & metamorphismLanglovale Group (Savannah or Kowanyama Province?)• Unconformable on Etheridge Group – truncates major E-W folds• Open folding with E-W shortening (D2 in Etheridge Group?), but no cleavage• Unconformably overlain by Croydon Volcanic Group and intruded by EsmeraldaSupersuite• Not metamorphosed (except contact metamorphism by Esmeralda Supersuite)• Relationships and zircon MDA indicate older than 1550Ma and younger than1625Ma• Tentatively considered part of Savannah Province (best developed in CoenInlier), but could be Kowanyama Province that lies in subsurface betweenGeorgetown & Mt IsaCroydon Province• Not metamorphosed• Dominated by almost flat-lying sheets of felsic ignimbrite

Deformation & metamorphismReconciling the regional analysis and SHRIMP dating with the JCU detailed studiesis difficult, but allowing for the statistics for the CHIME dates being somewhatrubbery, the following is a possibility• Possible metamorphic and deformation pre-1675Ma (post 1690Ma?) in theEinasleigh Metamorphics• D1 - N-S shortening at ~1620Ma• D2 – E-W shortening at ~1590Mamedium P-T metamorphism• Uplift and retrogressive metamorphism sometime between 1590 and 1560Ma• D3 - NW-SE shortening and low pressure-high temperature metamorphism at1560-1550Ma, associated with main metamorphic zircon growth andemplacement of Forsayth Batholith and Croydon Volcanic Group and EsmeraldaSuite• D4 – possibly 1510Ma• Subsequent Palaeozoic events

Palaeoproterozoic-Mesoproterozoic Stratigraphy – Georgetown regionCroydon VolcGroupYarman FmMalacura Fm~1786Ma~1785MaEsmeraldaSupersuiteLangdon River MdstRobertsonRiver SGp1663±13MaCandlow FmLanglovaleGroup ~1625MaHeliman FmTownley FmLane Ck FmCorbett FmDead Horse MetabsltDaniel Creek FmBernecker Ck FmD3 1550-1560Ma~1655Ma~1550Ma~1650MaCobbold Metadolerite1656±2Mabiotite gneissEtheridgeGroupForsaythSupersuiteD1/D2 1620-1590Maamphibolite1675±3MaEinasleigh Metamorphics~1550-1560MaMagmatic ageMax dep ageJuntalaMetsCassidy CkMets~1695Ma~1845Ma1685-1695Maorthogneisscalc-silicate gneissleucogneiss~1705Ma

Deep crustalseismic transectsTasman LineCOENINLIERYAMBO HODGKINSONINLIER BASINOther ProterozoicInliers – northernGeorgetown(Dargalong)GEORGETOWNINLIERMT ISAINLIERTasman Line

Other Proterozoic Inliers – northern Georgetown (Dargalong)Dargalong Metamorphic GroupFig Tree GraniteMcDevitt MetamorphicsLane Creek Formation

Other Proterozoic Inliers – northern Georgetown (Dargalong)•McDevitt Metamorphics– Laminated to thin-bedded metapelites & subordinate meta-sandstone,quartzite & mafic sills– No isotopic constraints, but lithologically like Corbett and Lane CreekFormations in the Etheridge Group– Intruded by Fig Tree Hill Granite (part of Forsayth Supersuite)•Dargalong Metamorphic Group– Migmatitic gneiss, augen gneiss, amphibolite, schist, quartzite and minorcalc-silicate gneiss– Isotopic constraints• Mylonitised granodioritic to tonalitic gneisses; 1586±5Ma and 1580±4Ma(Blewett et al., 1998)Note that these are orthogneisses and ages probably reflect anatexis andpeak of metamorphism – therefore original age of paragneisses is stillunknown

Tasman LineCOENINLIEROther ProterozoicInliers – YamboDeep crustalseismic transectsYAMBOINLIERHODGKINSONBASINGEORGETOWNINLIERMT ISAINLIERTasman Line

Other Proterozoic Inliers – YamboOswald SchistSaraga SchistChuka QuartziteChelmsford GneissPombete GneissArkara GneissPalmerville FaultHodgkinson Province

Other Proterozoic Inliers – Yambo•Yambo Metamorphic Group– Divided into 13 metamorphic units– High-grade metasedimentary and meta-igneous rocks– Sedimentary protoliths inferred to be fine-grained siliciclastic rocks– Isotopic constraints (Blewett et al., 1998)• Mafic granulite – zoned zircon with an age of 1586±4Ma interpreted to bean igneous age• Sericite-garnet gneiss – igneous zircon modified by metamorphismgives an age of 1585±6Ma• Granodioritic gneiss; rims at 1576±5Ma and cores at 1581±8Ma and1636±13Ma• Mylonitic granitic gneiss with a complex spectrum of zircon ages; rimsat 1579±4Ma (metamorphic age) and youngest group of cores 1642±7MaNote again that these are orthogneisses and ages probably reflect anatexisand peak of metamorphism – therefore original age of paragneisses isstill unknown

COENINLIEROther ProterozoicInliers – CoenTasman LineDeep crustalseismic transectsYAMBOINLIERHODGKINSONBASINGEORGETOWNINLIERMT ISAINLIERTasman Line

Other Proterozoic Inliers – Coen•Newberry Metamorphic Group– Divided into 3 named units– High-grade metasedimentary and meta-igneous rockssimilar to Yambo Metamorphic Group– Sedimentary protoliths uncertain– Isotopic constraints (Blewett et al., 1998)• Felsic gneisses; ages of 1564±12Ma and 1561±15Maare probably metamorphic ages• Cores in one sample yield an age of 1638±9Ma•Coen Metamorphic Group– Divided into 4 metamorphic units– Schist, gneiss and lesser quartzite; lacks orthogneissand mafic rocks of Newberry and Yambo MetamorphicGroups– Isotopic constraints (OZCHRON)• Feldspathic gneiss has zircons with zoned igneousrims of 1554±4Ma (possibly in situ partial melting)with cores at ~1585, ~1700 and 1770Ma

Other Proterozoic Inliers – Coen•Holroyd Group– Divided into 5 named units– Fine to medium-grained clastic sediments becomingmore pelitic to east– Some mafic rocks with MORB-like geochemistry– Isotopic constraints (OZCHRON)• Laminated slate has a MDA of 1560±22Ma with a widerange of older ages up to ~3300Ma• Phyllite has a MDA of 1550±10Ma with other agegroups at ~1593, ~1639 1696 and ~1750Ma• Zircon rims in a gneiss sample have an age of1430±10Ma•Edward River Metamorphic Group– Divided into 5 named units– Similar siliciclastic sedimentary rocks to Holroyd Group– No isotopic constraints•Sefton Metamorphics– Schist, quartzite, phyllite, greenstone, marble, calcsilicatesand ironstone– MDA zircon age of ~1200Ma – probably Neoproterozoic toCambrian

Correlations between InliersEtheridge Province – deposited between 1700and ~1620Ma; with multiple deformation eventsaccompanied by metamorphism from 1620 to1550Ma•Forsayth SubprovinceEtheridge Group (including EinasleighMetamorphics & McDevitt Metamorphics)•Yambo SubprovinceDargalong, Yambo, Newberry & CoenMetamorphic GroupsSavannah Province – MDA of ~1550-1560Ma sounconformable on Etheridge Province; possiblemetamorphism around 1430Ma and in Silurian-DevonianHolroyd & Edward River MetamorphicGroupsLanglovale Group (deposited in interval 1625-1550Ma) may be part of the Savannah Provinceor could be Kowanyama Province (unknownrocks in subsurface between Mt Isa andGeorgetown)

Correlating Georgetown and Mt Isa Successions?????????LanglovaleGroupUpperEtheridgeLowerEtheridge

Correlating Georgetown and Mt Isa Successionsε N d• Deposited after ~1625 Ma-1-2• Dominated by Proterozoicdetrital agesPrimitivesignature• Deposited after ~1655 Ma-3• Dominated by Proterozoicdetrital agesMDA 1658Ma-1Toole Ck-2-5-5KuridalaMDA 1670MaMt NornaLlewellyn CkEvolvedsignature-4-8-8-8• Deposited between ~1700 Maand ~1660 Ma• Dominated by ArchaeanearliestPalaeoproterozoicdetrital ages

Correlating Georgetown and Mt Isa Successions10080MountMountIsaIsaInlierInlierLeichhardt Superbasin 100Leichhardt SuperbasinMount Mount Isa Isa Inlier Inlier7 samples;7 samples;n=466n=466EasternEasternSuccessionSuccessionlowstandlowstand66samples;samples;n=419n=41980Number6040Relative probabilityNumber6040Relative probability2020020Georgetown Inlierlower Etheridge Group3 samples; n=227060Georgetown InlierUpper upper Etheridge Group3 samples; n=216 n=21650Number1510Relative probabilityNumber4030Relative probability2051001500 1700 1900 2100 2300 2500 2700 2900Age (Ma)01500 1700 1900 2100 2300 2500 2700 2900Age (Ma)

Correlating Georgetown and Mt Isa SuccessionsMaximum depositional ages for the Etheridge Group are similar to those ofthe Soldiers Cap and Mt Isa Groups and deformation events appear tocorrelate BUT ……•The provenance of the lower Etheridge Group is very different to any Mt IsaInlier Proterozoic sediments.•The provenance of the upper Etheridge Group is similar to Mount Isa Inlier,but requires an E-W event between ~1660 and 1640 Ma to bring these terranestogether.Other differences between Georgetown and Mt Isa:•Normal geothermal gradient (clockwise P-T-t with superimposed high templowpressure event) vs dominantly high geothermal gradient (anti-clockwiseP-T-t) (e.g. Boger & Hansen, 2004; Cihan et al., 2006; Rubenach 1992)•Intensity of N-S folding decreases westwards towards Mt Isa•E-W vs N-S directed structural grain (e.g. O’Dea et al., 1997)•S-type vs I- and A-type magmatism at ~1555 Ma (e.g. Black & McCulloch, 1990;Wyborn et al., 1992)•Any rigorous geodynamic model needs to take these differences intoaccount