b'Education matters The Coral Sea, located on theBy rede\x1dning the COB for the northern northeastern margin of Australia in theand southern margin of the Coral Sea, southwest Paci\x1dc, is currently used as ait was found that chron 27 (o) is not type example of a marginal sea that haspresent on the sea\x1boor between the undergone successive rifting events. ThePapuan Plateau and the Queensland most recent extensional history consistsPlateau, although it is present further of three overlapping extensionalwest at the Cato Trough. This indicates megacycles occurring each in thethat sea\x1boor spreading began \x1drst Triassic (R1), Jurassic-Early Cretaceousbetween the Mellish Rise and the (R2), and the Late Cretaceous (R3),Queensland Plateau at 61.4 Ma, and followed by sea\x1boor spreading fromthen propagated westward, rather 61.2-52 Ma. Despite its use as a typethan beginning simultaneously across example, its polyphased extensionalthe entire region. Sea\x1boor spreading history prior to sea\x1boor spreading hasbetween the Papuan Plateau and the not been well modelled due to limitedQueensland Plateau began as late as availability of geological samples and59 Ma, up to 3.6 Ma later than originally geophysical data. thought. The region was believed to have experienced anomalously fast In this study, a new time-evolvingsea\x1boor spreading at the beginning deforming plate tectonic reconstructionwhich eventually slowed. This has been was developed using GPlates to describeresolved by bringing the COBs outboard; the main rifting events involved inthe newfound absence of chron 27 the evolution of the Coral Sea, and to(o) insinuates a slower initial rate of describe the pre-rift positions of thespreading that increased with time.various basins and continental plateaus in the region. This was achieved viaA rotation for the opening of the a palinspastic restoration approach,Queensland and Townsville Troughs wherein the continent-ocean boundariesduring the Jurassic rift was constructed, (COBs) and unstretched continental crustwith a common pole of rotation to locations (UCCLs) were revised from athe southwest of the junction of theLarge-scale folding is less evident at synthesis of published seismic, gravity,troughs. This pole of rotation coincidedKoppio or Kookaburra Gully.magnetic and crustal thickness data,with the structural lineaments as and from recovered samples from RVdescribed in the literature, and forA combined interpretation of magnetic Investigator voyage IN2019_V04. the \x1drst time, a plate model has beenand resistivity data from airborne developed to describe the formation ofelectromagnetic data (TEMPEST) has Deforming models overcome thethese structures during the Jurassic rift.revealed an electromagnetic anomaly limitations of rigid plate models byThe results provide some insight intoat both Koppio and Kookaburra Gully. providing a more comprehensive historythe evolution of the eastern GondwananInterpretation of these data showed of deformation by tracking changesmargin and an understanding of thekilometre-scale tight-isoclinal folding in the deforming region, de\x1dned bydeformation associated with multiphasestructures within an interpreted the COB and UCCL through time. Forrift systems. subunit of the Cook Gap Schist. example, changes in crustal thickness,Mineralisation is on the flanks of the strain rate and tectonic subsidence in theClaire Mortimers, University of Westernfolds, not the hinge zone.deforming region can be tracked basedAustralia: Using geophysics to explore on rotations allocated to each margin. for graphite in southern Eyre Peninsula inAn interpretation of high-resolution South Australia. Loupe ground TEM survey over the A focused deformation model, whichKoppio deposit identi\x1ded a sequence centres the deformation aroundThe southern Eyre Peninsula in Southof Middleback Jaspillite, Cook Gap the rift axis, was implemented forAustralia is host to several occurrencesSchist and Donington Suite gneisses. the Cretaceous rift. This uses a jointof \x1bake graphite of which only the UleyInterpretation of these data suggests optimisation approach to assesses thedeposit has signi\x1dcant production.that graphitic strata within the Cook best combination of parameters relatedMinor deposits occur at KoppioGap Schist is tightly-isoclinally folded at to the deforming region which bestand Kookaburra Gully. All knownthe scale of a few hundred metres. An matches the present-day crustal thicknessoccurrences of graphite in the areaextension of the graphitic stratigraphy and topography. Palaeobathymetryare in the Paleoproterozoic Cook Gapwas interpreted to the west of the reconstructions from the Cretaceous toSchist (biotite-\x1bake graphite schistsurvey area. Parasitic folds identi\x1ded the present-day were developed based onand quartzite) and structural controlin the Koppio adit, suggest that the derived tectonic subsidence from theof mineralisation has been postulated.the Koppio lode is a part of a larger deforming model. Key \x1dndings includeOutcrop in the region is sparse. fold sequence extending westward. de\x1dning the pre-Jurassic position of theConversely, no folding structures were Queensland and Townsville Troughs andRegional scale interpretation ofinterpreted from the TEM survey over pre-Cretaceous position of the PapuanGeological Survey of South AustraliaKookaburra Gully.Plateau, Louisiade Plateau and Mellishaeromagnetic data successfully Rise. Further, palaeobathymetry since themapped the regional geologyPetrophysical investigations of magnetic Cretaceous has been modelled at thisconfirming the Uley deposit occurssusceptibility and galvanic resistivity region for the \x1drst time. in the nose of a regional scale fold.measured low values within subunits 33 PREVIEW DECEMBER 2023'