tectonic evolution of the chos malal fold and thrust belt neuquen basin argentina from u th he and fission track thermochronometry

estimates of plume height from infrasound for regional volcano monitoring abstract present efforts in volcano monitoring particularly in southeast asia rely on the combination of local data generally gathered at less than 100 km from the volcano and satellite remote sensing while this combination has its strengths there are still weaknesses that the use of ground based remote sensing data such as distant infrasound measurements could help alleviate infrasound offers tools for detecting and characterizing volcanic plumes independent of cloud cover and time of day larger volcanic eruptions generate infrasound that is related to the plume and offers a unique view into eruption dynamics within the context of monitoring past research has demonstrated that infrasound can be used to estimate source parameters such as the rate at which material is ejected from volcanic vents during eruptions these are key input parameters into empirical and numerical models to estimate the height of volcanic plumes atmospheric ash transport and dispersion here we demonstrate the use of remote infrasound in estimating the height of volcanic plumes including a case study on the may 30 2014 plume from the volcano sangeang api in indonesia we were able to determine the plume height using infrasound gathered from 2000 to over 5000 km distance from the volcano during the january 2020 eruption of taal volcano in the philippines this method was applied to remote infrasound recorded 1650 km to the east we show that our workflow can be implemented in near real time offering an effective tool for rapid plume height measurement including associated uncertainties when volcanic clouds are not visible from the ground or space

1600 1500 ma hotspot track in eastern australia implications for mesoproterozoic continental reconstructions mesoproterozoic a type magmatic rocks in the gawler craton curnamona province and eastern mount isa inlier form a palaeo curvilinear belt for reconstructed plate orientations the oldest igneous rocks in the gawler craton are the hiltaba granite suite c 1600 1575 ma the youngest in the mount isa inlier are the williams naraku batholiths c 1545 1500 ma the belt is interpreted as a segment of a hotspot track that evolved between c 1600 and 1500 ma this hotspot track may define a quasilinear part of australia s motion between 1636 and 1500 ma and suggests that australia drifted to high latitudes an implication of this interpretation is that australia and laurentia may not have been fellow travellers leading to the formation of rodinia a hotspot model for a type magmatism in australia differs from geodynamic models for this style of magmatism on other continents this suggests that multiple geologic processes may be responsible for the genesis of proterozoic a type magmas

lithospheric structures and possible processes in phanerozoic eastern australia from deep seismic investigations abstract the eromanga basin in eastern australia developed during four major episodes on the rifted eastern margin of the australian precambrian craton seismic reflection profiling together with coincident wide angle reflection refraction profiling indicates structures and compositions in the crust which are dominant in various depth ranges some structural features seem to be limited to the upper crust other deep reflection events and high crustal velocities predominate in the lower crust with mafic intrusion from upper mantle sources being one preferred interpretation these features emphasize the difference in structures and composition between the upper and lower parts of the crust yet other structural and deep reflection features are interpreted as being truly lithospheric in scale because they seem to have seismic expression right from the surface to the upper mantle similar interpretations are made for other continental regions indicating that lithospheric processes affect different depth ranges of the crust and upper mantle in a variety of ways any modelling of such processes in the lithosphere must lead to these quite different end results at appropriate depth ranges

seismic imaging of major tectonic features in the crust of phanerozoic eastern australia abstract crustal architecture can be recognised from seismic fabric characteristics and velocity information across phanerozoic eastern australia three major crustal sub divisions are identified from data in southern queensland they occur under west to east the nebine ridge taroom trough and new england fold belt with each crustal sub division having its own internal architecture but separated by major bounding structures geosutures these features are assessed against evolutionary models for the region the significant conclusions are as follows 1 1 the nebine ridge forms the southeastern part of the thomson fold belt but has a crustal architecture distinctly different from that under the central part of the fold belt tentatively supporting an evolutionary model involving fragmentation and eastward stretching and thinning of a precambrian australian craton the ridge crust has possibly been considerably altered by carboniferous plutonism and compressional events 2 2 between the nebine ridge and the crust under the taroom trough of the bowen basin there is a major low angle 5 10 geosuture the foyleview geosuture which extends from upper to lower crustal levels along a series of prominent horizons it was probably active during the major carboniferous tectonism which severely structured devonian basins west of the nebine ridge the geosuture forms the southeastern boundary of the thomson fold belt 3 3 the crustal architecture under the taroom trough has little obvious structure above an outstanding moho transition zone however the prominent meandarra gravity ridge striking along the trough axis highlights the possibility of high density mafic volcanics within the crust and the probability of a rift model being appropriate early in the trough s history the sedimentary basin architecture supports the concept of an early extensional history for the crust within a poorly defined n s trending strike slip regime 4 4 between the taroom trough and the new england fold belt we interpret a high angle geosuture extending through the crust the burunga mooki geosuture reactivation during late palaeozoic early mesozoic times produced a series of reverse faults along the uplifted eastern margin of the trough some of these structures are tentatively considered to be positive flower structures above deeper faults with strike slip movement the geosuture separates regions with distinctly different seismic fabrics and played an important role in the formation of the bowen gunne dah sydney basin system 5 5 within the new england fold belt crustal domains can be recognized associated with late palaeozoic oroclinal bending and early mesozoic trans tensional basins major oroclinal bending of the upper crust in the west of the fold belt is interpreted above a mid crustal detachment the texas detachment in the central part of the fold belt the seismic data support a trans tensional mechanism for the formation of triassic basins with steeply dipping bounding faults under the east of the fold belt an imbricate thrust stack accretionary wedge is clearly imaged above a mid crustal horizon the brisbane mid crustal detachment upper crustal deformation appears to have occurred above this detachment 6 6 from the nebine ridge to the coast the moho is clearly defined below a 3 km thick moho transition zone hast of the thomson fold belt the moho level is identified as a gently undulating feature at 36 38 km depth and probably re established after the major late palaeozoic tectonic events which formed the crust under the taroom trough and new england fold belt this contrasts with the middle palaeozoic lower crustal moho features which appear to be preserved under the thomson fold belt 7 7 the thickest crust under the nebine ridge about 44 km appears to be associated with lower crustal wedging from the east there is an apparent thinning of the non sedimentary crust under the deepest basin taroom trough of about 30 compared with the crust to the west and east no crustal thickening is evident in the region of oroclinal bending within the new england fold belt

constraints and deception in the isotopic record the crustal evolution of the west musgrave province central australia abstract the hf and nd isotopic evolution of the musgrave province central australia is used to constrain the timing of crust formation and lithospheric organisation of proterozoic australia the dataset from this region challenges two widely held tenets of hf and nd isotope systematics namely that crust formation events can only be identified as periods when crystallisation ages correspond to model ages and that linear hf evolution arrays away from depleted mantle along crustal lu hf or sm nd slopes reflect reworking of the same source hf isotopes in musgrave province zircon crystals indicate two major crust formation events at c 1900 ma and at 1600 1550 ma although no juvenile rocks or crystals are known from c 1900 ma radiogenic addition into the crust at this time is required to account for consistent nd and hf evolution patterns which show no indication of an initially heterogeneous source oxygen isotopes in zircon grains confirm that much of the c 1900 ma hf isotopic signal is not compromised by mixtures furthermore the correspondence between mantle extraction and the commencement of reworking of archean material supports new crust generation at c 1900 ma and a coupling between lower and upper crustal processes the c 1900 ma timing of juvenile addition is dissimilar to that in the albany fraser and arunta orogens and may reflect continental arc development on the margin of a southern continent the general hf isotopic evolution trend of the musgrave province apparently reflects reworking from a dominant c 1900 ma source with some additional unradiogenic and radiogenic input through time however in the 1220 1050 ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle derived material intracontinental rifts and other regions with sustained very high temperature crustal recycling processes generate magmatic provinces with extreme hfse enrichment this can have a profound influence on isotopic evolution trends suppressing typical juvenile addition patterns isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within hfse enriched magmas without diverging isotopic signatures from apparent reworking trends in the musgrave province the crust had become so hfse enriched during the prolonged musgrave orogeny 1220 1150 ma that it was insensitive to mantle input which is estimated to have been as much as 85 during this event

crustal architecture and geodynamics of north queensland australia insights from deep seismic reflection profiling abstract a deep crustal seismic reflection and magnetotelluric survey conducted in 2007 established the architecture and geodynamic framework of north queensland australia results based on the interpretation of the deep seismic data include the discovery of a major west dipping paleoproterozoic or older crustal boundary considered to be an ancient suture zone separating relatively nonreflective thick crust of the mount isa province from thinner two layered crust to the east farther to the east a second major crustal boundary also dips west or southwest offsetting the moho and extending below it and is interpreted as a fossil subduction zone across the region the lower crust is mostly highly reflective and is subdivided into three mappable seismic provinces but they have not been tracked to the surface in the east the greenvale and charters towers provinces part of the thomson orogen have been mapped on the surface as two discrete provinces but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface and also extend northwards to beneath the hodgkinson province originally forming part of an extensive neoproterozoic cambrian passive margin continuation of the thomson orogen at depth beneath the hodgkinson and broken river provinces suggests that these provinces which formed in an oceanic environment possibly as an accretionary wedge at a convergent margin have been thrust westwards onto the older continental passive margin the tasman line originally defined to represent the eastern limit of precambrian rocks in australia has a complicated geometry in three dimensions which is related to regional deformational events during the paleozoic overall the seismic data show evidence for a continental margin with a long history paleoproterozoic to early mesozoic but showing only limited outward growth by crustal accretion because of a repeated history of overthrust shortening during repeated phases of orogenesis

resolving the nature and geometry of major fault systems from geophysical and structural analysis the palmerville fault in ne queensland australia abstract the palmerville fault in northeastern queensland australia forms a major terrane bounding structure that probably had a major influence on the evolution of the adjacent palaeozoic hodgkinson province the northernmost part of the tasman fold belt system in eastern australia the nature and subsurface expression of the palmerville fault remain poorly constrained and models for contrasting geometries exist in addition to structural field and microscopic observations we have combined results from multi scale wavelet edge analysis worming forward modelling of regional magnetic and gravity data and geochemical data sets to develop an improved understanding of the nature and subsurface geometry and depth extent of the palmerville fault results from worming suggest a steeply dipping geometry for the palmerville fault based on constraints from field observations and worming we have generated a number of sections across the palmerville fault and forward modelled their magnetic and gravity response to compare with the observed magnetic and gravity response our results show that the palmerville fault represents a steeply eastward dipping structure that may become listric at depth suggesting the presence of proterozoic basement underneath the hodgkinson province our findings suggest that the palmerville fault was a first order normal fault that controlled early middle palaeozoic basin development in the hodgkinson province subsequently the fault acted as a mid crustal decollement zone accommodating basin inversion in the hodgkinson province during the late palaeozoic these results provide important constraints on the tectonic evolution of the hodgkinson province in northeastern australia and importantly demonstrate the strength of combining geological observations with geophysical analysis in particular multi scale wavelet edge analysis in resolving the surface geometry and evolution of major fault systems especially in areas of low data density

a seismic refraction study of the quilpie trough and adjacent basement highs eromanga basin eastern australia abstract the jurassic cretaceous eromanga basin in eastern australia is a relatively undisturbed sedimentary sequence covering the devonian quilpie trough and the early palaeozoic canaway ridge and cheepie shelf seismic refraction recording across these three features with additional reflection gravity and well information has been used to determine the velocity structure to a depth of 10 km the thickness of the eromanga basin sequence along the traverse varies between 1 1 and 1 4 km with p wave velocities ranging from 2 0 to 3 8 km s the maximum thickness of the underlying quilpie trough is about 3 8 km but the base of the trough is hard to define the velocities in this devonian sequence range from 4 0 to 5 0 5 5 km s two small bodies with a velocity of 4 0 4 5 km s occur immediately below the eromanga basin sediments on the canaway ridge and the cheepie shelf they may be remnants of devonian sediments on an erosion surface the velocities within the ordovician basement are less below the canaway ridge than under the cheepie shelf and quilpie trough they reach 6 0 km s at 7 km depth below the ridge at 4 km depth under the shelf and at an intermediate depth under the trough from gravity modelling the density of the basement to the quilpie trough increases at a depth of about 7 km this may be related to volcanics found in the basement further north the canaway ridge has a lower density than the cheepie shelf or the basement of the quilpie trough relative vertical movement between these three features may in part be related to these density differences

geomorphic evidence for plio quaternary compression in the andean foothills of the southern neuquen basin argentina the southern central andes foothills are made of imbricate thick and thin skinned fold and thrust belts they were formed during cretaceous and miocene compressive periods by successive eastward propagation episodes of the orogenic front we analyze remnant terraces and alluvial deposits of the neuqun river and its tributaries to study the plio quaternary tectonic regime in the southern neuqun basin topographic profiles of remnant terraces show a crustal scale tens of kilometers anomaly above the chihuido south anticline this anomaly is accompanied by sedimentary aggradations downstream and upstream of the anticline another anomaly in the terrace profiles correlated with a knickpoint in the current neuqun river is observed farther east near aelo we interpret these anomalies to be the consequence of a plio quaternary uplift of the chihuidos and aelo anticlines folding and surface faulting of plio quaternary alluvial deposits show that this uplift is concomitant with the reactivation of the miocene orogenic front and of the predominantly thin skinned agrio fold and thrust belt from these data we infer that the southern neuqun basin is still shortening under a compressive stress regime and that the andean orogenic front is migrating farther to the east extensional features in the study area correspond mainly to thin skinned gravitational gliding resulting from crustal uplift thus we argue that the tectonic compressive regime is preserved in the southern neuqun basin throughout the plio quaternary though the slab may have steepened during this period

southern patagonian plateau basalts and deformation backarc testimony of ridge collisions abstract the distribution and volume of tertiary patagonian plateau basalts and the evolution of the patagonian fold and thrust belt between 46 and 49 s appear to be closely tied with ridge trench interactions along the continental margin to the west eocene plateau basalts south of 43 s are associated with a gap in the eocene arc and can be related to a proposed collision of the aluk farallon ridge against the trench at this time eruptions of late miocene to recent plateau basalts between 46 and 49 s can be related to time transgressive slab windows in the underlying mantle generated by the collision of segments of the chile ridge at 10 14 ma and 6 ma the principal deformation in the patagonian fold and thrust belt predates the eruption of the basalts and also appears to be related with late miocene ridge collision comparison of plateau basalts related to the collision of the three distinct ridge segments suggests that the volume of basalt erupted increases with the length of the collided ridge segment almost all eocene to recent plateau basalts between 46 and 49 s have oib like ocean island basalt trace element signatures showing that the mantle source region changed little with time plateau basalts with more arc like signatures appear to be contaminated by continental crust relative melting percentages inferred from the trace element chemistry of the plateau basalts correlate with volumes of erupted basalt implying spatial and temporal changes in temperatures in the mantle source that can be correlated with slab windows

the australian central eromanga basin project an introduction abstract the australian bureau of mineral resources is carrying out a major multidisciplinary program of geological and geophysical studies in southwestern queensland in cooperation with the geological survey of queensland the project is aimed at providing information on the regional structure and depositional history of the central eromanga basin and the underlying adavale cooper and galilee basins the information being obtained is particularly relevant to a better understanding of the petroleum prospectivity of the area the program includes geophysical surveys involving 1400 km of new six fold cdp seismic reflection coverage on regional traverses up to 400 km long crossing the main structural elements of the area gravity measurements along all new seismic reflection traverses refraction surveys along two major east west and north south traverses and magnetotelluric soundings along the same major east west traverse landsat imagery studies are providing new perspective on many regional structures when used in conjunction with seismic and gravity information wireline logs and synthetic seismograms are being used with the new seismic data to re examine stratigraphic correlations palynologic and lithologic studies are underway to assist in determining depositional environments source rock maturation hydrological and geochemical studies are providing information on the generation and migration of hydrocarbons a significant feature of the program is the extension of the recording time of all new reflection data to 20 s to obtain good quality deep crustal reflection information comparable to that obtained on cocorp programs in the united states the reflection data is being interpreted with the refraction gravity and magnetotelluric data to investigate the relationship of deep crustal and upper mantle features to the sedimentary basins in the central eromanga basin area

three dimensional structural model of the rhourde el baguel field algeria the rhourde el baguel field located in the ghadames basin is one of the largest oil fields in algeria it produces oil from fractured cambrian sandstones at subsea depths of 2300 3070 m the structure is reinterpreted as a compressive fold related to two reverse faults which cut and deform a preexisting normal fault the structure formed during three main episodes of deformation 1 triassic to liassic extension resulting in normal faults having significant throw 2 middle jurassic flowage of liassic salt resulting in low amplitude structures in this unit and 3 austrian early cretaceous compression resulting in a basement involved fault propagation fold the revised structural model explains the complex fault patterns and anomalous thickness variations of units observed in a number of deep wells on the west flank of the structure the model has been used to sidetrack some existing deep wells into locations within the field and to optimize the location of new wells in the field

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

three dimensional seismo tectonics in the po valley basin northern italy the po valley northern italy is a composite foreland foredeep basin caught in between the southern alps and northern apennine mountain belts by integrating the 3d structural model of the region with the public earthquake dataset the seismo tectonics of the basin is shown at different scales of observation the three dimensional geo volumeis used to reviewthe seismicity around the region and validate the structure earthquake association for such a complex tectonic framework despite the overall uncertainty due to the original data distribution quality as well as the crustal scale model dimension the direct correlation between structures and seismicity a confirms the po valley region as an active tectonic system and b allows the whole structural architecture to be revised by a unique three dimensional perspective and approach this study also indicates that 3d methodology is a powerful tool for better understanding of highly complex seismo tectonic situations at both regional and local scales

late paleo mesoproterozoic plate margin deformation in the southern gawler craton insights from structural and aeromagnetic analysis abstract the integration of structural analysis of outcrop and aeromagnetic interpretation has revealed a complex tectonic evolution for the southern gawler craton that reflects the regional tectonic signal during the late paleo to early mesoproterozoic results suggest that exposures at yarlbrinda hill comprise the margin of a highly deformed st peter suite pluton emplaced within the southwestern gawler craton at ca 1611 ma d 1 at outcrop records east to northeast directed ductile thrusting regionally this deformation overprints north south trending dextral yarlbrinda shear zone fabrics within ca 1622 ma st peter suite granite and ca 1690 1670 ma tunkillia suite granite progressive east to northeast directed thrust movements led to exhumation of the deformed ca 1611 ma granite d 2 deformation is recorded by the brittle reactivation of first generation mylonitic fabrics accompanied by cataclasis alteration and pseudotachylite development d 3 records a switch to northwest southeast shortening which led to the folding and tear faulting of the d 1 2 shear zone a switch to extension and subsequent rotations of the principle stress axes led to hiltaba suite granite emplacement and contemporaneous faulting under east west extension during d 4 and west northwest east southeast extension during d 5 deformation of ca 1622 ma st peter suite granite is consistent with movement on the yarlbrinda shear zone and requires the st peter suite to have been emplaced into or adjacent to the ca 1690 1670 ma tunkillia suite prior to shear zone activity and on the overriding plate during subduction d 1 d 3 deformation is constrained by the emplacement of ca 1580 ma hiltaba suite granite and correlates with the wartakan orogeny in the southeastern gawler craton and the olarian orogeny in the curnamona province a 52 disparity between the shortening directions in these respective areas suggests different degrees of mesoproterozoic rotation which likely aided the formation of an intervening basin province the remnants of which are presently preserved in the mount painter inlier the record of convergent deformation is geochronologically constrained to a 30 myr period and places this region of the central gawler craton near a late paleoproterozoic convergent plate margin prior to a period of transient extension beginning at ca 1580 ma the continental scale signal of tectonic events can be recognized at the outcrop scale highlighting the importance of detailed outcrop studies in sparsely exposed areas

early tectonic evolution of the thomson orogen in queensland inferred from constrained magnetic and gravity data abstract the crustal architecture as well as the kinematic evolution of the thomson orogen in queensland is poorly resolved because the region is concealed under thick phanerozoic sedimentary basins and the basement geology is known from limited drill holes combined potential field and seismic interpretation indicates that the thomson orogen is characterized by prominent regional ne and nw trending structural grain defined by long wavelength and low amplitude geophysical anomalies the smooth magnetic signature is interpreted to reflect deeply buried source bodies in the mid to lower crust short wavelength positive magnetic features that correlate with negative gravity anomalies are interpreted to represent shallower granitic intrusions they appear to be focused along major fault zones that might have controlled the locus for magmatism the eastern thomson orogen is characterized by a prominent ne structural grain and orthogonal faults and fold interference patterns resulting in a series of troughs and highs the western thomson orogen consists of a series of nw trending structures interpreted to reflect reverse faults sedimentation and basin development are interpreted to have initiated in the neoproterozoic to early cambrian during e w to ene wsw extension possibly related to the rodinia break up this extensional event was followed by late cambrian shortening recorded in the maneroo platform and the diamantina river domain which possibly correlates with the delamerian orogeny renewed deposition and volcanism occurred during the ordovician and may have continued until late silurian resulting in thinned proterozoic basement crust and extensive basin systems that formed in a distal continental back arc environment our interpretation places the thomson orogen to the west of the neoproterozoic passive margin preserved in the anakie inlier the region is likely to represent the internal extensional architecture during the rodinia break up that has been subsequently extensively modified by multiple extensional basin forming events and transient episodes of crustal shortening and basin inversion

source of the lachlan fold belt flysch linked to convective removal of the lithospheric mantle and rapid exhumation of the delamerian ross fold belt during the cambrian ordovician the paleo pacific margin of gondwana underwent a rapid transition from a site of convergent deformation delamerian ross orogeny to one of sedimentation during which the thick turbiditic sequences of the adjacent basal lachlan fold belt were deposited laser probe 40 ar 39 ar data show that the synkinematic 523 486 ma mid crustal i and s type granites and metamorphic country rocks of the delamerian fold belt were rapidly cooled at 490 485 ma coincident with the intrusion of a suite of high level postkinematic a type granites and gabbros ca 497 481 ma 40 ar 39 ar data on detrital muscovites from the basal sections of the lachlan fold belt provide information on exhumation rather than cooling but yield an age pattern 507 480 ma identical to that of the delamerian fold belt demonstrating that this was the source of the sediments the combined data require that some 15 km of exhumation occurred very rapidly 5 15 mm yr 1 coincident as implied by overlapping ages with the cessation of convergent deformation and partial melting to form the postkinematic magmas this scenario implies a causative link which we infer to have been convective removal of lithospheric mantle following orogenic thickening the model is analogous to the tertiary uplift of the india asia orogen which provided the sediment source for the bengal fan our results suggest that similar processes were important in the evolution of mountain belts at least as far back as the early phanerozoic

multi scale integrated structural and aeromagnetic analysis to guide tectonic models an example from the eastern musgrave province central australia abstract in many polydeformed precambrian provinces the understanding of their tectonic history is limited by insufficient exposure which leads to difficulty in developing links between local and regional architecture and results in poorly constrained models of their regional scale architecture high resolution aeromagnetic data allows interpretation and modelling at a scale comparable to structural mapping and by integrating these methods these links can be developed with high confidence as an example we integrate structural mapping aeromagnetic data interpretation and 3d magnetic inversions in a multi scale structural analysis of the polydeformed eastern musgrave province in central australia deformation during the ca 1200 ma musgravian orogeny is characterised by an originally northeast trending structural grain defined by shear zones and tight to isoclinal folds at all scales 3d magnetic inversion models of syn to post musgravian granites indicate that this structural grain is predominantly west dipping this architecture suggests that a northeast oriented fold and thrust belt developed as a result of northwest southeast compression in central australia during the musgravian orogeny the next deformation event is characterised by an array of originally east southeast trending shear zones that truncate and offset the musgravian structural grain with apparent dextral displacements of up to 1 km these shear zones are commonly co located with mafic and granitic dykes suggesting a dilational origin and they are interpreted to have initiated under northeast southwest extension during the ca 1080 ma giles event the architecture of these two mesoproterozoic events was later extensively overprinted by two deformation events during the pan african aged ca 550 ma petermann orogeny the first is characterised by the widespread reactivation of mesoproterozoic structures resulting in a network of shear zones of variable orientation and the second is characterised by the development of crustal scale transpressional shear zones motion on which has caused the rotation of lithospheric blocks and the reorientation of prior structural trends by up to 90 collectively the architecture of these two events suggests broadly north south crustal shortening in central australia as an intraplate response to gondwana assembly this example demonstrates that the integration of structural geology with aeromagnetic interpretation and modelling can be used to develop high confidence links between local and regional structures these links permit the derivation of better constrained models of major tectonic events particularly in regions where outcrop is poor and the structural architecture is complex

deep crustal reflection results from the central eromanga basin australia abstract from 1980 to 1982 deep seismic reflection profiles were recorded across the central eromanga basin in eastern australia to study the regional structure stratigraphy and geological history of the eromanga basin and infra basins the reflection data were recorded to 20 s to obtain additional information on the nature and structure of the crust below the sediments and their relationship to the development of the basins the seismic sections show good quality reflections from the deep crust as well as from the sedimentary layers based on the character strength coherence continuity and spatial distribution of the reflections the sections can be divided into four zones the tope zone between 0 and 2 5 s shows fairly uniform coherent and continuous events which correlate with the mesozoic and late palaeozoic sediments the zone from 2 5 to 8 s 4 to 22 km does not show any primary reflections and is interpreted as the highly deformed metasedimentary and metavolcanic rocks of the early palaeozoic thomson orogen underlying the sediments without any recognisable reflection or diffraction patterns in this zone it is difficult to say whether the faulting and folding observed in the sediments extend into the upper crustal basement the deeper zone of numerous reflection segments between 8 and 12 5 s 22 to 36 km is interpreted as thin laminae of alternating low and high velocity intermediate and basic rocks and correlates with the lower crust bounded by refraction velocity discontinuities the lowest zone of no reflections below 12 5 s corresponds with the upper mantle the reflection character and thickness as well as the refraction velocity structure of the crust under the central eromanga basin area are significantly different from those of the precambrian crust under the georgina basin to the northwest it is proposed that the crust under the eromanga basin is extensionally attenuated crust which had been intruded by sills of basaltic melt from the underlying asthenosphere

detrital zircon ages in neoproterozoic to ordovician siliciclastic rocks northeastern australia implications for the tectonic history of the east gondwana continental margin u pb detrital zircon ages in variably metamorphosed dominantly fine grained clastic successions are used in northeastern australia to identify two major successions along the east gondwana margin the older succession is of probable late neoproterozoic age and is considered part of a passive margin associated with rifting at c 600 ma most detrital zircons have ages in the range 1000 1300 ma and were probably derived from an extension of a late mesoproterozoic 1050 1200 ma orogenic belt from the central australian musgrave complex located 1500 km to the west no evidence has been found for 600 800 ma rifting of a rodinian supercontinent and therefore it is suggested that breakup must have occurred well outboard of the present early palaeozoic east gondwana margin the younger succession is of early palaeozoic age and contains the distinctive 500 600 ma detrital zircon signature that is widespread in east gondwana in addition to some samples with ages in the range 460 510 ma consistent with local igneous sources the younger succession is related to the active margin of gondwana that developed on the former passive margin in a back arc setting and the source of 510 600 ma zircons is considered to be a composite of rift related and back arc volcanic sources

mid crustal detachments controlling basin deformation ramp synforms in southwestern queensland abstract deep seismic data from the adavale basin region of southwestern queensland suggest that westward carboniferous movement of the upper crust over mid crustal ramps was responsible for the present day geometry of two synforms containing devonian sediments we interpret the troughs as hanging wall synforms formed by sub vertical simple shear within the upper crust during down dip movement over the ramp one of these structures the quilpie trough in the southern adavale basin is an asymmetric trough interpreted to be an extensional ramp syncline it overlies a west dipping ramp in the boundary between the seismically non reflective upper crust and the seismically reflective lower crust formation of this basin by the relative movement of the upper crustal thomson fold belt over the mid crustal ramp is postulated the significant asymmetry of the trough suggests that lower crustal extension by pure shear may have occurred during upper crustal translation the other structure the westgate trough contains two palaeozoic sequences we propose that the devonian lower sequence is in a ramp syncline formed by folding of the sediments in a conveyor belt style mechanism during a translation of the upper crust the upper sequence is interpreted as a ramp basin in which sediments were deposited in the synform as it developed deep seismic reflection data from the central eromanga basin region indicate that relative horizontal translation can occur between the upper and lower crust on mid crustal detachments the geometry of the synforms suggests that above these detachments crustal deformation has a sub vertical simple shear style whereas the lower crust below the detachments seems to deform in a pure shear style recognition of relative movement of tens of kilometres on mid crustal detachments is important for our understanding of basin geometry and development in the central eromanga basin

structural evolution of the permian triassic cooper basin australia relation to hydrocarbon trap styles the structural and depositional history of the cooper basin in eastern central australia has revealed that the basin is a mildly compressional structural depression controlled by northwest trending and northeast trending pre permian basement features pronounced pre permian compressions are indicated by northeast trending major structures the gidgealpa merrimelia innamincka and murteree nappacoongee trends detailed chronostratigraphic facies analysis with closely spaced palynological control of the patchawarra formation revealed that two pronounced phases of uplift occurred during the sakmarian the major intrabasin highs were rejuvenated during these tectonic events as documented by crestal unconformities middle and upper patchawarra unconformities evidence of each event is dominantly tectonic in character with similar depositional patterns over these highs related to each event these events are also recognizable in midflank areas and basin margins with contemporaneous deposition in deeper parts of the basin results from this research show potential for future hydrocarbon discoveries within structural stratigraphic and structural stratigraphic traps in the cooper basin various trap styles are closely associated with faults unconformities and lateral facies changes lowside fault closures onlap plays and unconformity traps are expected to be well copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received february 22 1995 revised manuscript received august 6 1996 final acceptance november 12 1996 2geological survey of western australia 100 plain street east perth wa australia 6004 e mail n apak dme wa gov au 3national centre for petroleum geology and geophysics ncpgg university of adelaide thebarton campus university of adelaide sa 5005 australia 4santos ltd 101 grenfell street adelaide sa 7000 australia the authors wish to thank the cooper basin consortium group of companies for permission to publish this paper the drafting staffs at santos ltd and geological survey of western australia gswa are sincerely thanked for their efforts in preparing figures this paper is dedicated to the memory of bill stuart

early devonian gedinnian nonmarine strata present in a rapidly subsiding basin in far western new south wales australia abstract the nonmarine early devonian mt daubeny formation represents sediment deposited principally from sheet floods and braided streams and partly perhaps in shallow temporary lakes the formation locally 6 km thick is chiefly composed of pale red coarse arenite and minor conglomerate in the north and west and varicoloured fine arenite and siltstone in the southeast ten lithofacies are identified and described during basin subsidence a mountain range is inferred to have been progressively uplifted to the west and erosion of this range provided the sediment which formed the formation palaeocurrents suggest the presence of a number of convex upward structures which grew eastwards and these are interpreted to be terminal fans in the south a composite fan extended much further eastwards than fans in the north causing a ponding effect and local southward flow near the northern margin of the southern fan apparent permanency of position of the probable terminal fans indicates that the positions of the feeding streams also had some permanency implying that an antecedent drainage pattern developed within the mountain range because desiccation structures are rare and pedogenic carbonate is absent the basin is considered to have developed within a humid environment with much infiltration of runoff water the immature arenites indicate partial derivation from acid and intermediate volcanoes and major derivation from late precambrian to cambrian strata of low to medium metamorphic grade

crustal architecture across phanerozoic australia along the eromanga brisbane geoscience transect evolution and analogues abstract the crustal architecture across phanerozoic australia has been established from seismic data along an 1100 km long east west transect the eromanga brisbane geoscience transect this has enabled a better understanding of deep structures and processes that have controlled the development of major sedimentary basin systems it has shown that crustal dynamics throughout geological history have played an important role in the development of these sedimentary basins and that structures developed during the early palaeozoic have influenced and continue to influence basin systems the transect crosses three major basement provinces of the tasman orogenic system in eastern australia the thomson northern lachlan and new england orogens the basement geology in the transect region has until now been only poorly understood because it is largely obscured by the mesozoic cover rocks of the eromanga surat and clarence moreton basins the transect interpretation has firmly identified crustal scale ramp structures multiple intra crustal detachment surfaces strike slip fault architecture lower crustal magmatism underplating mono remobilisation and intra crustal terranes in the geological reconstructions of southern queensland the boundaries between the orogens the foyleview and burunga mooki geosutures have been identified as lithospheric scale structures that have influenced the evolution of the tasman orogenic system as a whole

new seismic reflection results in the central eromanga basin queensland australia the key to understanding its tectonic evolution abstract regional seismic traverses were recorded from 1980 to 1982 by the bureau of mineral resources geology and geophysics as part of a major multidisciplinary program aimed at studying the geological evolution of the central eromanga basin area and its petroleum potential six fold cdp reflection data were obtained to 20 s reflection time on 1400 km of traverses up to 400 km long crossing the main structural features of the area additional seismic reflection information to complement the study was obtained from 2300 km of older mainly single coverage analogue data which was transcribed to digital format and reprocessed the central eromanga basin area has a complex history and contains four phanerozoic potentially hydrocarbon bearing basins each separated by unconformities i e the devonian adavale basin the late carboniferous to triassic cooper and galilee basins and the jurassic cretaceous eromanga basin the seismic results are being interpreted with the aid of synthetic seismograms from key wells to provide information on the extent nature and relationship of these basins the quality of the reflection data from the devonian sequence is generally very good and these data are proving to be most useful in the study thick devonian sediments were deposited over a wide area well beyond the present confines of the adavale basin and its associated troughs intensive folding and faulting accompanied by major basement uplift including the canaway ridge in the centre of the area took place during the mid carboniferous kanimblan orogeny this was followed by a period of erosion which truncated the devonian sequence and resulted in separation of the adavale basin from the other devonian troughs in the area the preliminary seismic results give some indication also of the extent and nature of the cooper and galilee basins sediments these are generally thin in the central area and thicken to the west and east respectively where coal measures produce good lithologic and seismic markers gentle folding and minor faulting apparent in the seismic reflection sections from the overlying eromanga basin sequence have resulted mainly from basement uplift and minor movements along pre existing faults continuing into the late mid tertiary and possibly from some compaction of the thick sedimentary section the seismic information is also assisting in studies of the petroleum potential of the area providing information particularly on structuring timing and depth of burial of the prospective sediments

substrate controlled ichnofacies along a marine sequence boundary the intra valanginian discontinuity in central neuquen basin argentina abstract the intra valanginian discontinuity in the neuquen basin argentina marks a dramatic sea level fall within lower cretaceous strata and can be mapped for tens of kilometers both along depositional strike and dip in the proximal region of the lowstand configuration the subaerial segment of the sequence boundary is demarcated by alluvial conglomerates basal mulichinco formation onto deep marine black shales vaca muerta formation in the distal marine realm the time equivalent marine sequence boundary separates black shales and marls beneath from shallow marine carbonate deposits above this paper documents and discusses substrate controlled trace fossils demarcating the marine sequence boundary across more than 30 km in a proximal distal transect in order to shed light onto processes affecting the sea floor during the generation biogenic modification and preservation of this regionally extensive omission surface the downdip expression of the marine sequence boundary is well exposed across a 20 km long strike oriented outcrop everywhere in this region the discontinuity is demarcated by robust thalassinoides with well defined walls and circular cross sections suggesting that the marly substrate was relatively firm during excavation the burrow system is filled with bioclasts of echinoids and bivalves not present in underlying strata up to pebble size intraclasts that were eroded from the underlying succession and authigenic minerals glauconite phosphates this trace fossil suite illustrates the glossifungites ichnofacies the updip expression of the marine sequence boundary in the study area was recorded in a cored well located about 20 km from the outcrops as in the distal region a first generation of passively filled thalassinoides excavated into a firm marly substrate is attributed to the glossifungites ichnofacies however this suite is cross cut at the top by gastrochaenolites and other unidentified borings bored intraclasts also occur above the omission surface this trace fossil suite represents the trypanites ichnofacies the intra valanginian discontinuity records a complex history after the onset of the dramatic sea level fall extensive erosion and exhumation of previous sediments as well as early cementation combined to produce different types of substrates during the generation of the omission surface firmgrounds and hardgrounds colonization of firm substrates probably started firstly in proximal regions when relative sea level was still falling during early transgression firmgrounds were occupied in distal regions and borers colonized the hardgrounds developed in proximal regions thus the surface demarcates a composite surface involving a sequence boundary plus a transgressive surface draped in turn by a mixing of sediments suggesting siliciclastic starvation the generation and preservation of the features associated with the intra valanginian discontinuity are thought to result from the combination of a ramp type pre existing morphology coupled with a high amplitude sea level fall and a relatively deep marine setting prior to the formation of the omission surface

three dimensional structural modeling and its application for development of the el porton field argentina the el portn field located in the neuqun basin belongs to one of the largest oil and gas trends of argentina fields in the area produce oil from middle cretaceous fluvial and eolian porous sandstones at about 600 m 1968 ft below sea level the field structure is described as a triangle zone located in front of the neuqun fold and thrust belt that was formed during the andean orogeny by a combination of tight detachment folds and fault propagation folding the structure has a basal detachment through the contact between the evaporites of the auquilco formation and the shales of the vaca muerta formation the upper detachment corresponds to the salt layers of the huitrn formation the structure was reactivated by basement fault inversion that produced tightening of the preexisting geometry and backthrusts that increased the structural complexity a three dimensional 3 d structural model has been constructed using 3 d seismic data and well information to plan new horizontal wells in steeply dipping to overturned limbs through 50 60 m 164 196 ft of productive reservoir avoiding pilot and sidetrack wells the results of the modeling have made the company consider as a priority the 3 d structural model building procedure for the development of fields located in fold and thrust belts

aeromagnetic gradiometer program of the geological survey of canada during the past two decades the geological survey of canada aeromagnetic survey group consisting of geophysicists electronic engineers technicians and computer scientists developed the aeromagnetic gradiometer technique for mineral exploration the same group ran the aeromagnetic survey program in canada perhaps the largest such continuing aeromagnetic survey program in the world in 1973 fabrication commenced on an inboard vertical gradiometer system on the gsc queenair aeromagnetic survey aircraft during the period 1978 1981 a number of experimental gradiometer surveys were carried out by the geological survey of canada to demonstrate the efficacy of the aeromagnetic gradiometry technique as a geologic mapping tool in mineral exploration programs because of a need for aeromagnetic gradiometer surveys in the topographically rugged gaspe peninsula of quebec the gsc began in 1983 to foster the development of helicopter borne gradiometer systems through r and d contracts four companies responde