the seismic structure of precambrian and early palaeozoic

etters 244 (2006) 44–57www.elsevier.com/locate/epsl

Earth and Planetary Science L

The seismic structure of Precambrian and early Palaeozoic terranesin the Lambert Glacier region, East Antarctica

A.M. Reading ⁎

Research School of Earth Sciences, Australian National University, Canberra, ACT, 0200, Australia

Received 29 August 2005; received in revised form 31 December 2005; accepted 16 January 2006Available online 13 March 2006

Editor: V. Courtillot

Abstract

The Lambert Glacier region of East Antarctica encompasses the proposed boundary between three of the ancient continents thatformed East Gondwana: Indo-Antarctica, the central East Antarctic Craton and a proposed extension of the Pinjarra Orogen ofAustralia. The only area of extensive rock exposure in central East Antarctica, it uniquely allows the seismic structure to be linkedto surface geology. New broadband seismic stations were established at the remote sites of the SSCUA deployment, which ranbetween the austral summers of 2002/2003 and 2004/2005. Recorded energy from distant earthquakes is used to calculate receiverfunction waveforms that are then modelled to deduce the seismic structure of the upper lithosphere.

The results of this study are two-fold. Firstly, seismic structure and crustal depth are determined beneath the Lambert Glacierregion providing constraints on its tectonic evolution. A significant contrast in crustal depth is found between the Northern andSouthern Prince Charles Mountains that may indicate the location of a major tectonic boundary. Secondly, baseline seismic receiverstructures are established for the Rayner, Fisher and Lambert terranes that may be traced beneath the Antarctic ice sheet in thefuture.© 2006 Elsevier B.V. All rights reserved.

Keywords: Lambert; East Antarctica; seismic structure; receiver functions; terranes

1. Introduction

The concept of East Antarctica as the ancientkeystone at the centre of the assembly of continentsforming Gondwana has been dramatically revised inrecent years in the light of new syntheses of geochro-nological data and geological observations from Africa,India, East Antarctica and Australia [1]. It is nowunderstood that former mobile belts run perpendicular to

⁎ Corresponding author. Tel.: +61 2 6125 3213; fax: +61 2 62572737.

E-mail address: [email protected].

0012-821X/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.epsl.2006.01.031

the modern-day Antarctic coastline. These belts may becorrelated with outcrops in continents that were joinedto East Antarctica within the supercontinent of Gond-wana, moreover, the edges of the belts act as ‘piercingpoints’ that precisely constrain the relation of thecontinents prior to break-up. Although there is reason-able outcrop exposure around the Antarctic coastline,the mountain ranges surrounding the Lambert Glacierare the only outcrop in the interior of East Antarctica andthus provide a window into understanding the assemblyof Gondwana and earlier supercontinents.

This study presents the first determinations of crustaland upper lithospheric structure in this part of the EastAntarctic interior using the techniques of broadband

mailto:[email protected]

http://dx.doi.org/10.1016/j.epsl.2006.01.031

45A.M. Reading / Earth and Planetary Science Letters 244 (2006) 44–57

earthquake seismology. Additionally, the correlation ofseismic structure with the terrane boundaries observedon the surface represents a significant advance in thelong-term goal of using earthquake seismology to tracemajor tectonic provinces beneath the ice.

1.1. Tectonic framework of the Lambert Glacier Region

The Lambert Glacier, the largest in East Antarctica,drains into southern Prydz Bay. It exploits a transten-sional basin that formed during the late Mesozoic duringthe breakup of Gondwana [2–4]. The location of (thefuture) Prydz Bay is shown (Fig. 1) in the context of theEast Gondwanan continents prior to break-up. Theregion encompasses a rare three-way junction betweenAncient, Grenville and Pan-African terranes and there isconsiderable ongoing debate concerning its likelytectonic evolution.

Ancient (>1600Ma, Archaean and Palaeoprotero-zoic) rocks are found in several locations across

Fig. 1. The location of Prydz Bay and the Southern Prince Charles Mountainsand the proposed sutures (grey shaded bands) including that between Indo-Anin Fig. 2. DML=Dronning Maud Land, M=Madagascar, EL=Enderby LMountains, PB=Prydz Bay, PEL=Princess Elizabeth Land, DG=DenmanTAM=Transantarctic Mountains, GC=Gawler Craton.

Antarctica including the Southern Prince CharlesMountains, which lie far inland, to the south of PrydzBay. Modern geochronological techniques have shownthat Grenville-age rocks (1190–980Ma, after the North-American orogen bearing this name [5]), exposed in awide band around the East Antarctic coast, fall into threedistinct age provinces [1]. It has also been establishedthat two, younger, Pan-African-age belts (650–500Ma[6]) truncate the Ancient and Grenville provinces [7].Ancient cratons and tectonic belts of both Grenville andPan-African ages may be correlated between Antarcticaand neighbouring continents in Gondwana: Africa, Indiaand Australia (Fig. 1) [8].

East Antarctic geology and geochronology is consis-tent with a tectonic history of ocean closure andsubsequent plate-reorganisation with the following pro-posed account [9] relating directly to the region understudy. (1) Before 600Ma three continental blocks exist;one consisting of South America, Africa and DronningMaud Land, another consisting of Madagasgar, India and

related to their tectonic setting in a reconstruction of East Gondwana [8]tarctica and East Antarctica [9]. The rectangle represents the area shownand, MRL=Mac Robertson Land, SPCM=Southern Prince CharlesGlacier, BH=Bunger Hills, WI=Wilkes Land, MR=Miller Ranges,

46 A.M. Reading / Earth and Planetary Science Letters 244 (2006) 44–57

Enderby Land/Mac Robertson Land, and the third, theremaining parts of East Antarctica and Australia. (2) At590–560Ma, the African and Indian groups collide alongthe Mozambique Suture. (3) From 560Ma, subductionalong the African/Indian margin leads to convergencewith Antarctica/Australia. (4) At 535–520Ma, theAfrican/Indian continental group collides with theAntarctic/Australian group along the Kuunga Suture.This proposed suture runs west–east, to the north ofthe present-day Southern Prince Charles Mountains,and then turns north through Princess Elizabeth Land[10].

Fig. 2. Station locations of the SSCUA deployment and rock exposure locahave the same name as the station, they are not stated separately. MAW=Massif, CRES=Mt Cresswell, KOMS=Komsomolskiy Peak, WILS=WMountains, REIN=Reinbolt Hills, DAVI=Davis. Terrane boundaries are sholiterature (see text). Terrane names are given in upper case italics. Approxishown in Fig. 1. Basemap from Australian Antarctic Division.

Terrane boundaries in the Lambert Glacier region areshown (Fig. 2) with province names denoted by upper-case italics. The Rayner Terrane corresponds to theGrenville-aged region of Indo-Antarctica that becamepart of the Antarctic plate following collision along theproposed Kuunga Suture [10]. Within the Rayner, alongthe Mac Robertson coast near Mawson station, high-grade granulite facies gneiss, with large orthopyroxenegranite (charnockite) intrusions, is exposed [11]. TheNorthern Prince Charles Mountains, including JacklynPeak and Beaver Lake, are similar in lithology but alsoinclude upper amphibolite facies exposures and Permo-

lities in the Lambert Glacier and Prydz Bay regions. Where localitiesMawson, JACK=Jacklyn Peak, BVLK=Beaver Lake, FISH=Fisherilson Bluff, NMES=North Mawson Escarpment, GROV=Grovewn by dashed lines where they are constrained by published geologicalmate location in relation to the reconstructed Gondwana continents is


Triassic sediments [12]. The Fisher Terrane lies at thesouthern boundary of the Rayner and consists of moremafic volcanic rocks of much lower metamorphic grade[13,12]. On the east side of the Lambert Glacier, theMawson Escarpment preserves the boundary betweenthe Lambert and Ruker Terranes [14]. The LambertTerrane is characterised by Pan-African deformationwith upper amphibolite facies exposures near the NorthMawson Escarpment station. The extent of the LambertTerrane to the north and (possibly) the west is notconstrained by surface observations. The Ruker Terranecomprises Archaean granitic basement rocks andArchaean and Palaeoproterozoic metasediments [12].

The outcrops of the Prydz Bay coast consist of high-grade metamorphic rocks, intruded by granite plutons[11]. The outcrops record dominantly Pan-Africantectonism with relict Grenvillian metamorphism [15,16].Locations are shown in Fig. 2. At the southwest end ofsignificant rock exposure along this coast, the ReinboltHills are made up of Late Proterozoic granulites with twophases of later deformation and metamorphism [17].Moving eastwards, coarse-grained granite is exposed atLanding Bluff [11] and upper amphibolite to granulateparagneiss at the Larsemann Hills [18]. The Rauer Groupcontains both Archaean and Proterozoic components witha Pan-African metamorphic overprint [19]. At theeastward limit of exposed rock along the PrincessElizabeth Land coast lie the Archaean Vestfold Hills[11]. The Grove Mountains are an isolated group ofnunataks in the Princess Elizabeth Land interior. Theyconsist mainly of high-grade felsic gneisses intruded bythick granite sheets. In common with the Prydz Baycoastal exposures, metamorphism and emplacement ofgranite are likely to have Pan-African age associations[20].

1.2. Previous determinations of seismic structure inEast Antarctica

The seismic structure of the crust has beendetermined along two reflection/refraction lines cross-ing the Amery Ice Shelf [21,22] and interpreted andextrapolated in the light of reconnaissance aerogeophy-sical data [23] covering the wider Lambert Glacierregion [22]. The Moho is found to be 22–24km deepbeneath the Amery Ice Shelf, increasing to 30–34kmdeep on the flanks of what is interpreted as the LambertGraben.

Determinations of seismic structure using teleseismicdata include an examination of the crust and mantlebeneath the Lambert Glacier region of East Antarcticausing early reflections of P′–P′ (PKP–PKP) phases

from nuclear test sources in Novaya Zemlya recorded atNorth American seismic stations [24]. No regularreflecting horizons were found in the upper lithospherebut this early, novel study provides extends the coverageof the early active source work and provides someindependent determinations of the depth of seismicdiscontinuities observed in this study. Across centralEast Antarctica, the following previous estimates ofcrustal structure and Moho depth using receiver functionanalysis have been made: 36km at Syowa, EnderbyLand [25]; 42km at Mawson, Mac Robertson Land[25,26]; 30km at Vostok in the Antarctic interior [27];34km in the region between Vostok and the Transan-tarctic Mountains [28 and references therein].

On a continental scale, deeper lithospheric structurehas been determined using surface waves [29–33]. Thecontrast between the shallower, warmer lithosphere ofWest Antarctica and the deeper, colder lithosphere ofEast Antarctica is evident in all these studies. Thechallenge of determining surface wave structure at aresolution that shows detail within East Antarctica isbeginning to be addressed through deployments oftemporary broadband instruments.

1.3. Aims of the SSCUA deployment and scope of thisstudy

The SSCUA deployment aims to extend the coverageof seismic structure into the interior of Mac RobertsonLand (West of the Lambert Glacier) and PrincessElizabeth Land (East of the Lambert Glacier) towardsa better understanding of this key region in Gondwana(Fig. 2). Use of remote broadband seismic recording andreceiver function analysis presented in this study allowsa regional-scale investigation of the seismic structurewithout the need for large-scale, costly refraction lines.The depth of the Moho and other seismic discontinuitiesmay be used to compare and contrast deep crustalstructure in relation to the main geological terranes (e.g.[34]). In addition, the determined crustal structures formbaseline information in tracing the path of main tectonicunits beneath the Antarctic ice-sheet. The broadbanddata are also suitable for the determination of wider-scale structure using surface-wave methods that are thesubject of further work.

2. Data and methods

2.1. Data collection

Remote stations of the SSCUA seismic deploymentwere installed at locations shown (Fig. 2). Beaver Lake


(BVLK) station was installed in January 2002 during theinitial ‘pilot’ year of field activity and retrieved duringthe austral summer of 2004/2005. Other stations weredeployed for shorter time intervals: Jacklyn Peak(JACK) January 2003–December 2003, Fisher Massif(FISH) December 2003–January 2005, Mount Cress-well (CRES) November 2002–December 2003, GroveMountains (GROV) December 2003–January 2005,North Mawson Escarpment (NMES) December 2002–January 2005 and Reinbolt Hills (REIN) January 2003–December 2003. Site access was generally by fixed-wing aircraft, operating from Davis station or thePCMEGA field camp at Mount Cresswell, landing onthe adjacent glacier and moving equipment to the rockby sledge. Helicopters were an alternative means ofaccessing the more northerly sites and REIN station wasaccessed only by helicopter. Stations were also deployedat Komsomolskiy Peak (KOMS) and Wilson Bluff(WILS). It was not possible to reach these stations, andhence retrieve data, owing to aircraft operationalproblems (2004/2005 austral summer). At the time ofwriting these problems are unresolved and data retrievalis not be possible in the foreseeable future. Thesestations are therefore not included in the analysispresented in this paper.

Each remote station consisted of a high-fidelitybroadband seismic sensor (Guralp CMG-ESP, compacttype) that was buried in moraine adjacent to outcroppingrock. The station at Mount Cresswell was buried in iceowing to extensive crevassing which prevented accessto the nunatak from the aircraft landing area. Theseismic data was recorded using Nanometrics ‘Orion’seismographs which employ data cartridges with aninternal heating facility. Timing was controlled using asmall GPS receiver. Three 53W photo-voltaic (‘solar’)panels were used to maintain power in three 76A h sealedgel-type batteries. The batteries, voltage regulator,seismometer ‘break-out’ box and seismograph werehoused in a large insulated case. Seismic recordinggenerally ceased in late April when the solar panels couldno longer supply sufficient power to maintain the batteryvoltage required by the seismograph (10.8V). Moststations resumed recording in October when the longerhours of day-light on the solar panels raised the batteryvoltage above the restart voltage on the seismograph(11.8V).

The station at Davis operated successfully fromDecember 2003 using a Guralp CMG-40T sensor andNanometrics Orion seismograph on mains power. Theseismic station at Mawson is installed in a 10-m deepvault and operated on a permanent basis by GeoscienceAustralia.

2.2. Receiver function methods

Receiver functions provide a means of determiningthe S-wave structure of the crust and uppermost mantleimmediately beneath the recording station—exploitingenergy from distant earthquakes. The P-wave codaincludes information on the seismic discontinuities thatdefine this structure (e.g. theMoho) in the form of energythat has converted fromP- to S-wave as it travels upwardson the last part of its path from source to receiver (Fig. 3).This converted S-wave energy may be extracted from 3-component data by deconvolving the radial, horizontalcomponent with the vertical component in the frequencydomain [35,36]. In this work, receiver functions arecalculated [37] and then stacked to produce a compositereceiver function with improved signal-to-noise ratio.Stacks are made using receiver functions from all back-azimuths with the inherent assumption that the structurebeneath the station is sufficiently close to 1-D for thisapproximation to be valid. Departures from this situationare discussed as they arise.

2.3. Inversion for structure

The relationship between the receiver functionwaveform and the seismic structure giving rise to thiswaveform is very non-linear. In this work, an adaptive,non-linear inversion technique that searches the param-eter space using the efficient Neighbourhood Algorithm[38] is used. The 1-D model structure is found whichcorresponds to the synthetic receiver function that mostclosely fits (by a least squares measure) the observedreceiver function. Departures of the best-fit syntheticreceiver function from the observed receiver function inreconnaissance-level work are generally due to 3-Dstructure which can only be investigated with a muchlonger station deployment and earthquakes at a range ofback-azimuths. Reverberant structure may also lead tosome parts of the wave-forms which cannot be fitted,since reverberant ray paths are not included in the 1-Dmodelling. Nevertheless, a best-fit, 1-D, S-velocitymodel (as derived in this study) remains an excellentstarting point from which to investigate the deep crust.

Examination of the ensemble of possible models thatclosely fit the observed receiver function enables trade-offs between parameters and other non-unique aspects ofthe procedure to be addressed. In previous studies, it hasbeen possible to compare discontinuity depths determinedusing receiver functions and the Neighbourhood Algo-rithm with those obtained using active source seismicrefraction at the same location [39]. Such comparisonsshow that receiver functions analysis is a realistic, low-

Fig. 3. Sketch showing how a 1D seismic structure may be derivedfrom a teleseismic earthquake: (a) simplified Earth structure andincoming earthquake energy; (b) simplified radial receiver functioncalculated from three-component data; (c) the corresponding derivedseismic velocity profile (reproduced from [26] with permission fromthe Geological Society of London).


cost alternative and that careful use of the non-linearNeighbourhood Algorithm allows robust determinationsof structure to be made in remote locations.

3. Seismic structure

3.1. Observed receiver functions

Events that occurred during the deployment and aresuitable for receiver function analysis are shown for oneof the remote stations, NMES, and the year-roundstation DAVI (Fig. 4). These were located at anepicentral distance of 30–80° from the station andrecorded with a good signal-to-noise ratio. Observedreceiver function stacks are shown (Fig. 5) for stationsof the SSCUA deployment together with the permanentstation, MAW, at Mawson. The short arrows indicate theconverted waveform due to the seismic discontinuity atthe Moho. Where there is some debate about whichdiscontinuity corresponds to the Moho, alternatives areshown and discussed later in the text. On some stationstacks, the converted waveform due to the Mohodiscontinuity is clear (e.g. REIN), in others (e.g.FISH) it is of lower amplitude. In the case of a loweramplitude conversion, the arrows have been assignedafter carefully viewing receiver functions from individ-ual events together with the stacks shown. Theconversion due to the Moho can be generally be seenon individual receiver functions and is therefore a robustfeature of the stack, even though it is a relatively lowamplitude feature.

The amplitude of noise preceding the main P arrival(at 0s), together with the number of events in each stackprovides a measure of the reliability of the receiverfunction stacks. Noisiest is JACK, with only two eventsin the stack (due to the loss of one horizontal componenta few weeks after installation). The noise at REIN andMAW is due to their coastal locations. MAW inparticular is exceptionally windy. The stations in theAntarctic interior generally produced a better stack (incomparison to MAW) from a smaller number of receiverfunctions that were recorded over a shorter time period.

The receiver function stack for MAW shows severalhigh-amplitude conversions within the first 5s indicat-ing several strong discontinuities within the crust. Thepeak most likely to correspond to the seismic Moho is at4.8s. The stack for station JACK shows a similarlyreverberant structure with a Moho arrival at 4.9s. BVLKshows a strong discontinuity at 3.6s and a smalleramplitude conversion at 5.2s. The observed receiverfunction stack for station FISH shows a markedlydifferent character, with more subdued discontinuities instructure in the upper crust and a low-amplitude Mohoconversion at 4.4s. The rather different appearance ofthe receiver function at CRES is due to the station beinglocated on ice and shows a Moho conversion at 3.9s.

Fig. 4. Distribution of earthquakes recorded during the SSCUAdeployment at: (a) NMES, an example of a remote station; (b) DAVI,the year-round station. Earthquakes are indicated by open circles, thestation by an open triangle and the approximate raypath between themby the solid lines.


On the east side of the Lambert Glacier, towards thenorth end of the Mawson Escarpment, NMES shows aMoho conversion at 3.2s, and the station in the GroveMountains, GROV, shows a very reverberant structurewith a Moho conversion at 4.8s. On the margin of PrydzBay, the station at Reinbolt Hills, REIN, shows a clearMoho conversion at 3.9s while the record from Davis,DAVI, shows little discontinuity in the upper crust and aMoho conversion at 4.6s.

3.2. The effect of an ice-layer

Synthetic receiver functions demonstrating theeffects of an ice-layer are shown (Fig. 6). Fig. 6ashows the synthetic receiver function for a Moho at35km deep, Fig. 6b substitutes a layer of sediment/regolith with a base at 5km. An ice layer of increasingdepth (0.5, 1.0, 1.5 and 2.0km) takes the place of someof this sediment/regolith in Fig. 6c–f. The receiverfunction for the simple one-layer crust and Mohodiscontinuity shows a conversion at 3.9 s. Thecorresponding phase arrives later, at 4.6s, with thesubstitution of the upper 5km of crust with material oflower seismic velocity. The ice layer gives rise to abroad, complex pulse following the initial P-wavearrival. Beneath CRES, the ice thickness is known tobe 1.30–1.33km from ice-radar measurements [40]which matches well to a synthetic intermediate to thoseshown in Fig. 6d and e.

3.3. Results of inversion for structure

Best-fit structures, found using the NeighbourhoodAlgorithm, are shown in Figs. 7, 8 and 9. If the Moho isnot modelled as a clear step in the S-velocity profiles(the broad white lines) then it is interpreted as the baseof the velocity-gradient-zone in the lower crust. Thereceiver function stack from MAW (Fig. 7) reveals abest-fit seismic structure with several crustal disconti-nuities and a Moho at 44km (±2km) depth. Thestructure beneath JACK is similar, showing markeddiscontinuities at 12km, 20km and the Moho at 39km.Beneath BVLK, the best-fit structure shows a discon-tinuity at 14km and at 30km with a moderately broadtransition at 40–44km deep. The interpretation of thesediscontinuities is discussed in Section 4. Beneath FISH(Fig. 8), the structure shows slight discontinuitiesrepresenting small changes in seismic velocity, and theMoho in the best-fit model is at 42km (±2km) depth.CRES shows a dramatic change in deep structure with aMoho at 33km (±2km) deep. Upper crustal structurebeneath this station is overwhelmed by the part of thereceiver function due to the ice-layer and is notsignificant. The Moho beneath NMES is at a similardepth, 34km (±2km) and shows relatively lowvelocities in the upper crust. Some reverberations areseen at 8–9s on the NMES receiver function that are notmodelled as part of the 1-D structure and have not,therefore, been matched by the synthetic waveform. Theunsatisfactory fit of the waveform around 5s is likely tobe due to the influence of 3-D structure in the crust thatis not accounted for in the parameterisation investigated

Fig. 5. Stacked receiver functions (observed) from stations shown in Fig. 2. The number of events in each stack is indicated below the station code andthe arrival due to conversion at the Moho is indicated with an arrow. Where there is some debate as to which discontinuity is to be interpreted as theMoho, two arrows are shown.


Fig. 6. Synthetic receiver functions showing the effects of an ice layer.Layer thicknesses/depths are given and seismic S-wave velocities areas follows: ice, 1.5–2.0km s−1; sediment, 2.5–3.0km s−1; crustalbasement, 3.0=3.8km s−1; mantle, 4.4km s−1.


using the Neighbourhood Algorithm. The major featuresof the observed waveform are accounted for and thedetermination of Moho depth is sufficiently robust forthis reconnaissance-scale survey. The receiver structurebeneath GROV (Fig. 9) is highly reverberant withseveral discontinuities in a relatively low-velocity crustand a Moho at 38km (±2km) depth. The negativeamplitudes of the waveform at 2.5s and after 6.5s areagain due to reverberations, not low-velocity layers, andhave not been matched by the synthetic. Again, theMoho depth determination is sufficiently robust tojustify the conclusions made in this work. BeneathREIN, the Moho is very sharp at 30km (±2km) depth,resulting in a good match between the observed andsynthetic Moho pulse at this station. Beneath DAVI, abest-fitting crustal structure with a broad high-velocity-gradient zone above a Moho at 36km depth is found.

4. Discussion

4.1. Depth of Moho and seismic discontinuities withinthe crust

A summary of Moho depths determined in this studyis shown (Fig. 10) together with the Moho depthsdetermined from earlier reflection/refraction work[22,21] and two of the inferred discontinuities fromearlier teleseismic data [24]. The locations of thereflection/refraction lines, which were shot toward thenortheast, are also shown but extrapolated depths in thesouthern part of the Lambert Glacier region [22] are not,since the determinations of structure from receiverfunction analysis provide much stronger controls.

The Rayner Terrane stations show modelled Mohodepths of 44 (±2) km and 39km for MAW and JACKrespectively that are similar to the earlier result of 42kmat MAW [25]. We take the intermediate value of 42kmas the characteristic Moho depth for the Rayner Terrane.The slight disparity between the receiver functiondetermination of Moho depth at JACK and the depthdetermined in the earlier reflection/refraction work [21]is probably related to problems associated with depthdetermination over dipping interfaces in unreversedseismic lines. The receiver function from Beaver Lakestation, BVLK, shows a sharp interface at 30km deepthat is interpreted as the Moho [22] and is also the mostlikely interpretation in this study. It is possible that broadtransition over the depth interval of 40–44km is astructure related to the base of the crust on the westernside of the major fault bounding the Lambert transten-sional basin (also referred to in various studies as theLambert rift or graben). Beaver Lake is close to thisfault, possibly located over the fault at depth and the 1Dapproximation of structure may be an oversimplificationfor this station. The 40–44km broad transition couldalso be a sub-horizontal structure in the upper mantlepossibly related to underplating or collision tectonicprocesses. Station FISH, in the Fisher Terrane appearsto contrast significantly with the stations in the RaynerTerrane (MAWand JACK) in the simplicity of its crustalstructure even though the Moho depth is similar.

Between FISH and CRES (33km), the difference inMoho depth is striking. It is likely that the southernboundary of the Fisher Terrane represents a significanttectonic boundary. The similarity of Moho depth atCRES and NMES (34km), across the Lambert Glacier inthe north Mawson Escarpment, is consistent with theLambert Terrane underlying both stations. In thisproposed interpretation, the Lambert Terrane extendswestward, across the axis of the present-day Lambert

Fig. 7. Best-fit receiver functions and corresponding S-wave velocity models for stations of Mac Robertson Land. Upper plots: solid line=observedreceiver function, broken line=synthetic. Lower plots: heavy white line=best-fit model, fine grey lines=other models searched, fine blacklines= limits of models searched.

Fig. 8. Best-fit receiver functions and corresponding S-wave velocity models for stations in the central Lamber Glacier region.


Fig. 9. Best-fit receiver functions and corresponding S-wave velocity models for stations in Princess Elizabeth Land.


glacier, at least as far as CRES seismic station (on ice,approximately 15km northwest of Mt. Cresswell nuna-tak). Regional scale magnetic and gravity anomaly maps[23] show notable changes across the approximate regionof the boundary between the Fisher and Lambert Terranesand generally support the interpretation of contrast inMoho depth as indicating a major tectonic boundary.

The receiver function determination of Moho depthbeneath station REIN (30km) is in agreement with thereflection/refraction results. At this point the activesource line runs almost parallel to the strike of the gentleMoho dip and there is no problem with accepting thisdepth estimate from the unreversed line. The differencein character of the lower crust (low seismic velocitybeneath REIN, high seismic velocity beneath NMES)suggests that the deep crust beneath REIN is not relatedto that which underlies NMES, i.e. the northern extent ofthe Lambert Terrane lies south of REIN. The Mohodepth from the receiver function at GROV beneath theGrove Mountains (38km) shows a distinct contrast toNMES. The discontinuity depths inferred from theteleseismic observations close to NMES (25km) andGROV (49km) [24] provide an independent confirma-tion that such a contrast exists. The contrast mayindicate a significant tectonic boundary, or the GroveMountains block may be showing structure attributableto more extensive intrusive activity and underplating.The available magnetic anomaly map changes to lower

resolution over the Grove Mountains and henceprovides no further insight while the (Bouger) gravityanomaly map mostly reflects changes in ice-loading[23]. Beneath DAVI, the Moho depth determined in thisstudy is 36km. The complexity of outcrop geologybetween REIN and DAVI, together with the regionalscale magnetic anomaly map [23], suggests that thePrydz Coast is an amalgamation of smaller blocks suchthat there is no single significant tectonic or terraneboundary between the two stations.

Crustal features and Moho depths may be preservedthroughout very long periods of geological time [34],but later influences on crustal structure must also beconsidered. It is arguable that the shallower crustaldepths seen at BVLK, CRES, NMES and REIN are dueto crustal thinning associated with the failed transten-sional Lambert basin. However, the reflection/refractionresults [21,22] suggest that the major faults boundingthe ‘rift’ are within the current bounds of the mainLambert Glacier. The only station that might show someinfluence from a linear ‘rift’ is therefore BVLK. It ispossible that the axis of the transtensional basin curveswestward at the latitude of the Mawson Escarpment.This scenario provides an alternative explanation for theshallow crustal depth observed at CRES, although REINand NMES would not be affected [22] and the receiverfunction structure characterising the Lambert Terraneremains appropriate.

Fig. 10. Summary of Moho depths determined in this study and comparison with depths determined in earlier work [22,24]. The approximate locationof the single-channel seismic lines [21,22] which constrain the depth contours near the northern Amery Ice Shelf are shown by A–A′ and B–B′.


Erosion and uplift/subsidence processes may also besignificant in producing apparent structural boundaries,especially if uplift/subsidence occurs in a heterogenousmanner across the terrane under analysis. At the presenttime, uplift is occurring at a negligible rate across theLambert Glacier region [41]. Two phases of denudation,Permo-Triassic and Early Cretaceous, have beenquantified in the Northern Prince Charles Mountains[3]. The total denudation is of the order of 2–3km awayfrom the Lambert Glacier, but may be close to 10kmnear Beaver Lake. Should heterogenous uplift or crustalthinning have been significant earlier in the tectonichistory of the region then contrasts in crustal structureand Moho depth alone may falsely imply a tectonic

boundary. In this case complementary geological andgeophysical techniques might show a terrane to becontinuous across such an apparent boundary.

4.2. Tectonic implications

This study has revealed a major tectonic boundarybetween FISH and CRES and similarities in structurebetween CRES and NMES. These observations areconsistent with the location of the proposed suture ofIndo-Antarctica and the Antarctic craton. The LambertTerrane could therefore represent a major featureassociated with this suture—it follows the location ofthe broad grey-shaded band to the north of the Southern


Prince Charles Mountains (Fig. 1). Trans-tensionalextension along the axis of what is now the LambertGlacier appears to have initiated at the eastern margin ofthe Rayner Terrane and extended southward, cuttingthrough the Lambert Terrane/suture where it turns totrend east–west and terminating close to the contactwith the Ruker Terrane.

4.3. Seismic structure and terrane characterisation

The following seismic structures form a basis fortracing the extent of the terranes further beneath theAntarctic ice sheet in future studies. The Rayner Terraneis characterised by a Moho depth of approximately42km and significant seismic discontinuities in theupper and mid-crust (e.g. 10km and 26km at JACK).The Fisher Terrane also shows a crustal depth of 42kmand a more uniform increase of seismic velocitythroughout the crust. The Lambert Terrane is charac-terised by a shallow Moho depth of approximately34km with a single discontinuity (at approximately12km) in the upper crust.

5. Summary

The depth of the crust to the west of the LambertGlacier is approximately 42km with shallower crust atapproximately 34km occurring south of the FisherTerrane. East of the Lambert Glacier crustal depths arebetween 34 and 30km. Beneath Davis, the crust is alittle deeper, at 36km and further inland, beneath theGrove Mountains, 38km. It is likely that a majortectonic boundary exists between the Northern andSouthern Prince Charles Mountains that extends acrossthe axis of the Lambert basin. Seismic structurescharacteristic of the Rayner, Fisher and Lambert Terranehave been determined which may be used to tracetectonic provinces beneath the ice.

Acknowledgements

Brian Kennett, Seismology Group Leader, andtechnical staff at RSES/ANSIR (Australian NationalSeismic Imaging Resource) are warmly thanked for theirsupport of this work. Logistics provided by AustralianAntarctic Division are greatly appreciated. Particularthanks to Mike Woolridge and many others at AADKingston and Davis Station for support over severalfield seasons. Recording equipment was made availablethrough a grant from the ANU Major EquipmentCommittee and support provided through an AAS(Australian Antarctic Science) grant (Project #2303).

References

[1] I.C.W. Fitzsimons, Grenville-age basement provinces in EastAntarctica: evidence for three separate collisional orogens,Geology 28 (2000) 879–882.

[2] S.D. Boger, C.J.L. Wilson, Brittle faulting in the Prince CharlesMountains, East Antarctica: cretaceous transtensional tectonicsrelated to the break-up of Gondwana, Tectonophys 367 (2003)173–186.

[3] F. Lisker, R. Brown, D. Fabel, Denudation and thermal historyalong a transect across the Lambert Graben, northern PrinceCharles Mountains, Antarctica, derived from apatite fission trackthermochronology, Tectonics 22 (2003) 1055, doi:10.1029/2002TC001477.

[4] H.M.J. Stagg, J.B. Colwell, N.G.Direen, P.E.O'Brien, B.J. Brown,G. Bernardel, I. Borissova, L. Carson, D.B. Close, Geologicalframework of the continental margin in the region of the AustralianAntarctic Territory, Geoscience Australia Record 2004/25.

[5] T. Rivers, Lithotectonic elements of the Grenville Province:review and tectonic implications, Precambrian Res. 86 (1997)117–154.

[6] J.J. Veevers, Pan-Africa is Pan-Gondwanaland: oblique conver-gence drives rotation during 650–500Ma assembly, Geology 31(2003) 501–504.

[7] I.C.W. Fitzsimons, A review of tectonic events in the EastAntarctic Shield and their implications of Gondwana and earliersupercontinents, J. Afr. Earth Sci. (2000) 3–23.

[8] I.C.W. Fitzsimons, Proterozoic basement provinces of south-western Australia, and their correlation with Antarctica, in: Y.Yoshida, B.F. Windley, S. Dasgupta (Eds.), Proterozoic of EastGondwana: Supercontinent Assembly and Breakup, Spec. Publ.-Geol. Soc. Lond., vol. 206, 2003, pp. 93–130.

[9] S.D. Boger, C.J. Carson, C.M. Fanning, J.M. Hergt, C.J.L.Wilson, J.D. Woodhead, Pan-African intraplate deformation inthe northern Prince Charles Mountains, East Antarctica, EarthPlanet. Sci. Lett. 195 (2002) 195–210.

[10] S.D. Boger, J.McL. Miller, Terminal suturing of Gondwana andthe onset of the Ross-Delamerian Orogeny: the cause and effectof an Early Cambrian reconfiguration of plate motions, EarthPlanet. Sci. Lett. 219 (2004) 35–48.

[11] R.J. Tingey, The Geology of Antarctica, Oxford Monographs onGeology and Geophysics, Oxford University Press, UK, 1991.

[12] E.V. Mikhalsky, J.W. Sheraton, A.A. Laiba, R.J. Tingey, D.E.Thost, E.N. Kamenev, L.V. Fedorov, Geology of the PrinceCharles Mountains, Antarctica, AGSO—Geoscience Australia,Canberra, Bulletin, vol. 247, 2001.

[13] S.D. Boger, C.J. Carson, C.J.L. Wilson, C.M. Fanning,Neoproterozoic deformation in the Radok Lake region of thenorthern Prince Charles Mountains, East Antarctica; evidence fora single protracted orogenic event, Precambrian Res. 104 (2000)1–24.

[14] S.D. Boger, C.J.L. Wilson, C.M. Fanning, Early Paleozoictectonism within the East Antarctic craton: the final suturebetween east and west Gondwana? Geology 29 (2001) 463–466.

[15] P.H.G.M. Dirks, C.J.L. Wilson, Crustal Evolution of the EastAntarctic mobile belt in Prydz Bay: continental collision at500Ma? Precambrian Res. 75 (1995) 189–207.

[16] I.C.W. Fitzsimons, The Brattstrand Paragneiss and the SostreneOrthogneiss: a review of Pan-African Metamorphism andGrenvillian Relics in Southern Prydz Bay, in: C.A. Ricci (Ed.),The Antarctic Region: Geological Evolution and Processes, TerraAntartica Special Publication, 1997.

http://dx.doi.org/10.1029/2002TC001477


[17] G.T. Nichols, R.F. Berry, A decompressional P–T path, ReinboltHills, East Antarctica, J. Metamorph. Geol. 9 (1991) 257–266.

[18] C.J. Carson, C.M. Fanning, C.J.L. Wilson, Timing of theProgress Granite, Larsemann Hills: additional evidence forEarly Palaeozoic orogenesis within the east Antarctic Shieldand implications for Gondwana assembly, Aust. J. Earth Sci. 43(1996) 539–553.

[19] S.L. Harley, I. Snape, L.P. Black, The evolution of a layeredmetaigneous complex in the Rauer Group, East Antarctica:evidence for a distince Archaean terrane, Precambrian Res. 89(1998) 175–205.

[20] X. Liu, Z. Zhao, Y. Zhao, J. Chen, X. Liu, Pyroxene exsolution inmafic granulites from the Grove Mountains, East Antarctica:constraints on Pan-African metamorphic conditions, Eur. J.Mineral. 15 (2003) 55–65.

[21] R.G. Kurinin, G.E. Grikurov, Crustal structure of part of EastAntarctica from geophysical data, in: C. Craddock (Ed.),Antarctic Geoscience, University of Wisconsin Press, Madison,1982, pp. 895–901.

[22] L.V. Fedorov, G.E. Grikurov, R.G. Kurinin, V.N. Masolov,Crustal Structure of the Lambert Glacier Area from GeophysicalData, in: C. Craddock (Ed.), Antarctic Geoscience, University ofWisconsin Press, Madison, 1982, pp. 931–936.

[23] D.E. Thost, G. Leitchenkov, P.E. O'Brien, R.J. Tingey, P.Wellman, P. Wellman, A.V. Golynsky. Geology of the LambertGlacier-Prydz Bay Region, East Antarctica. Geoscience Aus-tralia, map (1998).

[24] R.D. Adams, Reflections from discontinuities beneath Antarc-tica, Bull. Seismol. Soc. Am. 61 (1971) 1441–1451.

[25] M. Kanao, A. Kubo, T. Shibutani, H. Negishi, Y. Tono, Crustalstructure around the Antarctic margin by teleseismic receiverfunction analyses, in: J. Gamble, D.N.B. Skinner, S. Henrys(Eds.), Antarctica at the Close of a Millennium, . Bull.-R. Soc. N.Z., vol. 35, 2002, pp. 485–491.

[26] A.M. Reading, Investigating the deep structure of terranes andterrane boundaries: insights from earthquake seismic data, in:A.P.M. Vaughan, P.T. Leat, R.J. Pankhurst (Eds.), TerraneProcesses at the Margins of Gondwana, Spec. Publ.-Geol. Soc.Lond., vol. 246, 2005, pp. 293–303.

[27] M. Studinger, G.D. Karner, R.E. Bell, V. Levin, C.A. Raymond,A.A. Tikku, Geophysical models for the tectonic framework ofthe Lake Vostok region, East Antarctica, Earth Planet. Sci. Lett.216 (2003) 663–677.

[28] J.F. Lawrence, D.A. Wiens, A.A. Nyblade, S. Anandakrishnan, P.J. Shore, D. Voight, Upper mantle thermal variations beneaththe Transantarctic Mountains inferred from teleseismic S-waveattenuation, Geophys. Res. Lett. 33 (2006) L03303, doi:10.1029/2005GL024516.

[29] G. Roult, D. Rouland, J.P. Montagner, Antarctica II: Upper-mantle structure from velocities and anisotropy, Phys. EarthPlanet. Inter. 84 (1994) 33–57.

[30] M.H. Ritzwoller, N.M. Shapiro, A.L. Levshin, G.M. Leahy,Crustal and upper mantle structure beneath Antarctica andsurrounding oceans, J. Geophys. Res. 106 (2001) 30645–30670.

[31] S. Danesi, A. Morelli, Structure of the upper mantle under theAntarctic Plate from surface wave tomography, Geophys. Res.Lett. 28 (2001) 4395–4398.

[32] A. Morelli, S. Danesi, Seismological imagine of the Antarcticcontinental lithosphere: a review, Glob. Planet. Change 42 (2004)155–165.

[33] A. Sieminski, E. Debayle, J-J. Leveque, Seismic evidence fordeep low-velocity anomalies in the transition zone beneath WestAntarctica, Earth Planet. Sci. Lett. 216 (2003) 645–661.

[34] A.M. Reading, B.L.N. Kennett, B. Goleby, Seismic structure ofthe Yilgarn Craton, Western Australia, Aust. J. Earth Sci. 50(2003) 427–438.

[35] C.J. Ammon, The isolation of receiver effects from teleseismic Pwaveforms, Bull. Seismol. Soc. Am. 81 (1991) 2504–2510.

[36] S. Stein, M. Wysession M, An Introduction to Seismology,Earthquakes, and Earth Structure, Blackwell Publishing Ltd, 2003.

[37] T. Shibutani, M. Sambridge, B. Kennett, Genetic algorithminversion for receiver functions with application to crust anduppermost mantle structure beneath Eastern Australia, Geophys.Res. Lett. 23 (1996) 1829–1832.

[38] M.S. Sambridge, Geophysical inversion with a neighbourhoodalgorithm: I. Searching a parameter space, Geophys. J. Int. 138(1999) 479–494.

[39] A.M. Reading, B.L.N. Kennett, Lithospheric structure of thePilbara Craton, Capricorn Orogen and northern Yilgarn Craton,Western Australia, from teleseismic receiver functions, Aust. J.Earth Sci. 50 (2003) 439–445.

[40] Neal Young, Volkmar Damm, personal communication (2005).[41] P. Tregoning, P.J. Morgan, R. Coleman, The effect of receiver

firmware upgrades on GPS vertical timeseries, Cahiers duCentre Européen de Géodynamique et de Séismologie, 23(2004) 37–46.

http://dx.doi.org/10.1029/2005GL024516

the seismic structure of precambrian and early palaeozoic

Documents