© terra antartica publication

Terra Antartica2003, 10(3), 85-96

Aeromagnetic Anomaly Investigations along the Antarctic Coastbetween Yule Bay and Mertz Glacier

D. DAMASKE1, F. FERRACCIOLI2,3 & E. BOZZO2

1Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover - Germany2Dipartimento per lo Studio del Territorio e delle sue Risorse, Sez. Geofisica, Università di Genova,

V.le Benedetto XV 5, 16132 Genova – Italy3now at: British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET –UK

Received27 November 2002; accepted in revised form14 October 2003

Abstract - The GITARA VI aeromagnetic campaign was flown along a 1000 km long corridor between YuleBay and Mertz Glacier. We present total field aeromagnetic anomaly maps over the Lillie Glacier, OatesCoast and George V Coast survey areas. These new maps will provide further insight into the TransantarcticMountains and into the previously unexplored northernmost edge of Wilkes Subglacial Basin. The LillieGlacier anomaly map images contrasting magnetic anomaly signatures over the Admiralty Intrusives of theEverett Range and of Yule Bay. However, a discrete anomaly overlies the enigmatic rocks of Unger Islandand Surgeon Island, which presently lie adjacent to Yule Bay. The Oates Coast map reveals the mostremarkable linear magnetic anomaly of the survey: the Matusevich Anomaly. This linear anomaly reflectsGranite Harbour Intrusives and mafic/ultramafic rocks, associated with a major, but almost entirely buried,fault zone of the Wilson Terrane. Just west of the Matusevich Glacier, the highest-amplitude anomaly of thewhole survey overlies the Archangel Nunataks gabbro. Further west, along the extensively ice-coveredGeorge V Coast, two broad positive anomaly complexes are mapped. One overlies the Mawson Peninsulaand Scar Bluffs region; the second one is a coast-parallel feature located between Ninnis Glacier and MertzGlacier. Both these magnetic highs are located along the northern edge of the Wilkes Subglacial Basin andapparently lie adjacent to scarce rock outcrops of Jurassic Ferrar dolerites. We suggest that the anomalies inthe Mawson Peninsula/Scar Bluffs region may reflect thicker mafic Jurassic intrusions or maybe KirkpatrickBasalts, rather than previously hypothesised Precambrian rocks. This interpretation would imply that thePrecambrian East Antarctic Craton boundary could lie further west than previously inferred.

*Corresponding author([email protected])

INTRODUCTION

The GITARA VI aeromagnetic campaign wasperformed over George V, Oates, and Pennell Coastsduring the joint 1999-2000 German-ItalianGANOVEX VIII-I TALI A NTARTIDE XV Antarcticcampaign (Fig. 1). The general aim was to provide anew window upon crustal structure and tectonics ofthe northernmost Transantarctic Mountains and uponits “backside” component, which is stil l largelyunexplored. Over northern Victoria Land theaeromagnetic survey provides new geophysicalimaging of tectonic units involved in the RossOrogen. These tectonic units likely mark an EarlyPalaeozoic active margin of the East Antarctic Craton(Kleinschmidt & Tessensohn, 1987; Flöttmann &Kleinschmidt, 1991; Ricci et al., 1997; Finn et al.,1999; Ferraccioli et al., 2002). Over western OatesLand and George V Land the aeromagnetic surveyextends over the northernmost edge of the poorlyknown, yet controversial, Wilkes Subglacial Basin(Drewry, 1976; ten Brink et al., 1997; Ferraccioli et

al., 2001). We present new total field magneticanomaly maps and outline the possible geologicsources for the observed aeromagnetic anomalies.

SURVEY PARAMETERS, INSTRUMENTATIONAND DATA ACQUISITION

Survey parameters were chosen similar to earliersurveys conducted in the adjacent areas of NorthernVictoria Land (Bachem et al., 1989a,b; Damaske,1994; Bozzo et al., 1997a,b; Bozzo et al., 1999;Bozzo et al., 2002; Chiappini et al., 2002). As inthese surveys, a standard profile spacing of 4.4 kmwas selected as a compromise between an optimum inprofile spacing (which is also variable due to differentsource depths) and time available to cover an arealarge enough to allow a structural interpretation(Bosum, 1981; Damaske, 1989a). A tie-line spacing of22 km (i.e. a ratio of 1:5 to the profile spacing) waschosen to account for the special problem ofconducting aeromagnetic surveys at high magnetic

© Terra Antartica Publication

D. Damaske et al.86

latitudes, where considerable magnetic (time)variations are known (Maslanyj & Damaske, 1986;Damaske, 1989b; Damaske, 1993).

Survey altitude was at a constant barometric levelwithin the individual sections (Fig. 2). For the LillieGlacier area an altitude of 2730 m was chosen to beclear of the terrain across the entire area. The lines atthe Oates Coast and over the Wilson Hills were flownat 1715 m which was about the minimum elevationof the inland ice sheet in the southwestern corner ofthis survey section. For all other areas, extendingfrom the Matusevich Glacier across the Cook IceShelf to the Mertz Glacier, the survey level of 1425m was chosen for a close-to-surface survey, yetavoiding the turbulence from catabatic windscharacterising this area.

A Squirrel B2 helicopter was used to perform thesurvey. The aeromagnetic instruments consist of aCesium magnetometer in towed bird configuration

and a data acquisition system installed in the cabin ofthe helicopter. The position of the helicopter wasrecorded by a GPS-receiver. The overall accuracy forthe horizontal coordinates was estimated to about 20m throughout the survey. Differential GPS correctionswere available for most flights improving on thealtitude values and leading to a vertical accuracy ofless than 30 m.

Geomagnetic activity on ground was monitored atvarious base stations set up on fast ice or glaciertongues close to the support vessel (which served asoperational base for the aeromagnetic survey) and onother sites within the different survey areas (Fig. 3 &Tab. 1). It was assured that survey flights took placepredominantly at times of a day when a relatively“quiet” magnetic field could be expected. Altogether26575 km of usable line data were collected over anarea of 83800 km2 (Fig. 2). The coastal region fromthe Mertz Glacier to Yule Bay, over a length of

Fig. 1 - Location of the GITARA VI aeromagnetic survey between Yule Bay and Mertz Glacier super-imposed upon a simplified tectonicsketch map. The inset shows the location of the aeromagnetic investigation with respect to continental-scale Antarctic tectonic elements.

Fig. 2 - Aeromagnetic flight lines for all new survey sections (solid lines). Grey shades indicate the location of previous aeromagneticsurveys over adjacent areas.

Aeromagnetic Anomaly Investigations along the Antarctic Coast between Yule Bay and Mertz Glacier 87

approximately 1000 km, was surveyed for the firsttime.

DATA PROCESSING AND MAPPING

After initial quality control (including removal ofspikes) data were corrected for time variations usingmagnetic base station recordings (Damaske et al.,2001). The second step in removing diurnal variationwas done by minimizing the differences at theintersections of profile and tie lines. This wasachieved with iterative “statistical levelling” using theprogram GEOSOFT-OASIS. To obtain crustalmagnetic anomalies, the total magnetic field valueshave to be reduced by their global and regionalcomponents. This was done by first computing theInternational Geomagnetic Reference Field (IGRF) atall survey points at the respective survey altitude andthen by subtracting these values from the survey’stotal field magnetic values. The IGRF 2000coefficients were used to calculate the reference fieldvalues for a mean date (15 January 2000) for allsurvey sections.

To remove residual high-frequency noise along theflight l ines a 10-point low pass filter (corresponding to approximately 440 m) was applied.No key “geological signal” was lost because thewavelength of the filter was set to be equal to thesmallest grid cell size adopted for map production.The data were gridded using the “random gridding”minimum curvature routine of the GEOSOFT

programme (Briggs, 1974). The grid mesh was 440 mx 440 m for the Lill ie Glacier and Oates Coastmagnetic anomaly maps and 880 m x 880 m for theGeorge V map.

ANOMALIES IN THE LILLIE GLACIER AREA

The Lill ie Glacier survey area is adjacent toprevious surveys (Damaske, 1990; Damaske & Finn,1996; Bozzo et al., 1999). It covers both the Bowersand the Robertson Bay zones (Finn et al., 1999),traditionally referred to as accreted terranes, separatedby the Leap Year Fault (e.g. Kleinschmidt &Tessensohn, 1987). The majority of the RobertsonBay terrane (or zone) is characterized by a broadmagnetic low (Fig. 4). There is no distinct higherfrequency magnetic feature which can be attributed tovery-low to low-grade metamorphic rocks of theRobertson Bay Group (Tessensohn et al., 1981;GANOVEX Team, 1987). This is consistent withmeasured low susceptibilities (0.0001 SI-units) overthese metamorphic rocks (Rossetti & Faccenna, pers.com., 2002).

The magnetic low stretches from the northwesterncorner of the survey area, offshore, to the AnareMountains onshore. It exhibits values in the range of-70 to -30 nT, and may be cross-cut by NW-SEmagnetic trends. Surprisingly, higher values (-30-0 nT) are found over the southeastern part of thesurvey area, which also features Robertson BayGroup metasediments (GANOVEX Team, 1987). AWNW-ENE oriented aeromagnetic lineament separatesthese two contrasting areas. This almost coast-parallellineament may indicate the existence of a hithertounrecognized fault or major contact within thebasement of the Robertson Bay zone.

The southern Robertson Bay zone, as defined byaeromagnetics, is cut by an elongated, almost E-Woriented, magnetic anomaly over the northern EverettRange. This 100 nT magnetic anomaly approximatelyoverlies Admiralty Intrusives of Late Devonian–EarlyCarboniferous age (GANOVEX Team, 1987; Fiorettiet al., 1997a). This aeromagnetic signature resemblesthe one observed over Admiralty Intrusives andassociated Gallipoli Volcanics of the SalamanderRange further south (Fioretti et al., 1997b; Bozzo etal., 1999; Ferraccioli et al., 2002). Indeed, high

Fig. 3 - Location of magnetic base stations in the aeromagnetic survey area. Abbreviations and full nomenclature for base stations arereported in table 1.

Tab. 1 - Location of magnetic base stations used to correct theGITARA VI aeromagnetic data for diurnal variations.

D. Damaske et al.88

magnetic susceptibilities in the range of 0.01-0.03 SI-units have been measured over some magnetite-richAdmiralty Intrusives (Bozzo et al., 1995; Fioretti &Lanza, 2000). Admiralty Intrusives within theRobertson Bay Zone are also mapped further to thenorthwest, in the area of Yule Bay (GANOVEXTeam, 1987), where the large Yule Batholith outcrops(Wyborn, 1981). However, the Yule Batholithproduces only a subtle indentation in the regionalmagnetic low (Fig. 4). Susceptibility measurementsperformed during the survey (Caneva, pers. com.,2000) agree with the new aeromagnetic evidence,which suggests that Admiralty Intrusives of theEverett Range are significantly richer in magnetitecontent compared to those of the Yule Batholith.

Just offshore of the Yule Bay Batholith a distinctpositive anomaly with a peak-to-peak amplitude ofabout 100 nT overlies both Unger Island and SurgeonIsland. Unger Island is made up of volcanic rocks,which have been related to Glasgow Volcanics of thedistant Bowers Terrane (Fig. 1) (Tessensohn et al.,1981) or to more local Gallipoli-volcanics, formingthe roof of the adjacent Yule Batholith (Tessensohn etal., 1996). Surgeon Island has been described as: a) a600 Ma granite-gneiss (Vetter at al., 1984),representing a possible remnant of the “SurgeonIsland Terrane” (Borg & DePaolo, 1991); b) as alarge gneissic xenolith of the Yule Batholith(Kleinschmidt et al., 1987); and c) as a GraniteHarbour Intrusive belonging to the distant WilsonTerrane (Tessensohn et al., 1996). The enigmaticgeology of both islands is very hard to reconcile withtheir present-day location amidst meta-sediments andAdmiralty Intrusives of the Robertson Bay Terrane(Roland & Henjes-Kunst, 2001; Fioretti et al., 2002).The Unger Island-Surgeon Island magnetic anomalymight now additionally reveal the presence of apreviously unsuspected subvolcanic mafic(?) intrusion.The Unger Island-Surgeon Island anomaly alsoappears to be located amidst a sharp step across twobroader NW-SE trending aeromagnetic highs locatedfurther offshore (Fig. 4).

The northern Bowers Mountains feature NW-SEtrending high-frequency anomaly chains, whichcontrast with the broad magnetic lows typical of theRobertson Bay terrane (or zone) (Fig. 4). Thenorthern Bowers Mountains anomalies appear to belocated at the western edge of the Robertson BayTerrane. Perhaps these anomalies mark the northernprosecution of the Millen Schist Belt, marking atectonic shear zone (Kleinschmidt & Tessensohn,1987), and possibly incorporating oceanic basementscraps at depth (Finn et al., 1999; Ferraccioli et al.,2002).

A NW-SE trending anomaly chain is imaged atthe edge of the survey. It was previously recognisedto extend along the eastern margin of the lowerRennick Glacier (Damaske & Bosum, 1993; Damaske& Finn, 1996). Recent interpretations suggest that

thick buried oceanic basement underlies the northernBowers Terrane and may cause this regionalaeromagnetic anomaly (Finn et al., 1999; Ferraccioliet al., 2002).

ANOMALIES OVER THE OATES COAST

Previous surveying over Oates Land clearlyimaged linear anomalies west of the Usarp Mountains(Fig. 5). Two-dimensional models of the anomaliesdid not lead to a unique geologic interpretation oftheir nature (Damaske & Bosum, 1993). It was noted,however, that the two high-frequency anomaly chainsover the entirely ice-covered region were on strikewith the Matusevich Glacier. Therefore they wereconsidered as part of a larger feature named the“Matusevich line”. This magnetic feature couldperhaps mark a major thrust fault, proposed to run inthe Matusevich Glacier and partially outcropping(Flöttmann & Kleinschmidt, 1991; Ferraccioli andBozzo, 1999; Finn et al., 1999). Hence it was one ofthe major targets of the GITARA VI survey to seewhether the “Matusevich line” did extend northwardto the Matusevich Glacier and was indeed a featureof regional tectonic importance.

Our new aeromagnetic anomaly map leaves nodoubt on the existence and regional character of thefeature we now call the “Matusevich Anomaly”(Fig. 5). It is the most linear and extended high-amplitude anomaly feature in all our coastal survey.Its amplitude ranges from 500 to 1000 nT. Theanomaly runs from the south - where it, indeed,continues the old “Matusevich line” - for about 110km to the north. The Matusevich Anomaly features asharp and straight eastern edge. A closer analysisreveals that the Matusevich anomaly is split intoseveral sections. A combined interpretation of theMatusevich anomaly patterns, geology and magneticsusceptibility data is presented by Ferraccioli etal.(this volume). It is suggested that the MatusevichAnomaly relates to Granite Harbour Intrusivesemplaced along the Exiles Thrust System and/or tomafic or ultramafic rocks, possibly representingremnants of a former suture zone in the westernWilson Terrane (Roland et al., 2001).

To the east a broad magnetic low dominates thearea over the Wilson Hills and Oates Coast towardsthe Rennick Glacier. To the east of the MatusevichGlacier high-frequency anomalies parallel the mainanomaly. They reach maximum amplitudes of 280 nT.These anomalies lie just east of the hills RinggoldKnoll-Thompson Peak-Mount Dalton (and just overthe eastern part of Celestial Peak), where rocks of theWilson Metamorphic Complex outcrop (Talarico etal., 2001). In line with this high-frequency anomalychain a 35 nT anomaly is detected over the HaraldBay region. Highly-magnetic ultramafic and maficmetamorphic rocks outcrop there (Talarico et al.,2001). This type of rocks is the source of the


Fig. 4 - Total field aeromagnetic anomaly map over the Lillie Glacier survey area.

Fig. 5 - Total field aeromagnetic anomaly map over the Oates Coast survey area. Note the prominent Matusevich Anomaly. RTD: RinggoldKnoll-Thompson Peak-Mount Dalton anomaly chain.

D. Damaske et al.90

observed high-frequency anomaly chains (see alsoFerraccioli et al., this volume). More scatteredanomalies can be found in the Wilson Hills magneticlow. Perhaps they may have similar sources.

To the west of the Matusevich Anomaly arelatively "flat", though more positive, magneticpattern is observed. One circular anomaly on thewestern flank of the Matusevich Anomaly deservesspecial attention. It is the strongest anomaly detectedso far from all the Ross Sea and Victoria Landaeromagnetic surveys. It reaches an amplitude of2460 nT. It can be correlated with a Granite Harbourgabbro outcrop of the southeasternmost ArchangelNunataks (Rolf & Henjes Kunst, 2001). Magneticsusceptibility measurements indicate high values up to0.072 SI-units over this mafic Granite HarbourIntrusive (Henjes-Kunst, pers. com. 2000; Talarico etal., this volume).

In the eastern part of the survey area apronounced circular anomaly corresponds to a largemafic Granite Harbour intrusive of the Wilson Terrane(Rolf & Henjes Kunst, 2001). A broad positiveanomaly pattern continues to the south, as revealedalso by previous survey data (Damaske & Bosum,1993). Buried Granite Harbour Intrusives are thelikely source for this magnetic anomaly pattern to thesouth (Ferraccioli et al., 2002). Further east, the lower

Rennick Glacier anomaly (Damaske & Bosum, 1993;Finn et al., 1999; Ferraccioli et al., 2002) can now berecognized in figure 5 to extend considerably furtheroceanward.

ANOMALIES ALONG GEORGE V COAST

This aeromagnetic survey area stretches alongGeorge V Coast from the Matusevich Glacier in theeast to the Mertz Glacier in the west (Fig. 6). It is anarea largely devoid of outcrops and hence largelyunknown. The aeromagnetic survey is the onlycontinuous geophysical data set along this part of thecoast. This region is a key area since it features thenorthernmost outlet of the largely unexplored WilkesSubglacial Basin (Drewry, 1976; ten Brink et al.,1997; Ferraccioli et al., 2001).

The most outstanding features in the magneticanomaly map (Fig. 6) are two broad positive anomalycomplexes. One is located along the inferrednortheasternmost edge of the Wilkes Subglacial Basin,over the Mawson Peninsula, and Scar Bluffs region.The second corresponds to the western coastal part ofthe survey area, between Ninnis and Mertz Glacier,likely along the northwestern edge of the WilkesSubglacial Basin. A regional magnetic low separatesthese two areas. It extends from the Cook Ice Shelf

Fig. 6 - a) Total field aeromagnetic anomaly map over the George V Coast survey area. Boxes indicate the location of figures 7 and 8;b) Bedrock elevation map (modified from Lythe et al., 2000) showing that this survey section covers the northernmost edge (dashed line)of the Wilkes Subglacial Basin.


to Buckley Bay over a topographic high possiblyterminating the Wilkes Subglacial Basin to the north.

The prominent eastern anomaly complex might beevaluated in light of the few outcropping JurassicFerrar dolerites which intrude Beacon sediments atAnxiety Nunataks and Scar Bluffs (Roland et al.,2001). Figure 7 displays the area around the AnxietyNunataks and Scar Bluffs in further detail. Thiscontour map demonstrates that the anomaly complexdoes not directly overlie the outcrops of JurassicFerrar dolerite sills. The outcrops occur approximately10 km to the west and lie along the sharp N-Soriented western edge of the anomaly complex. Thespatial proximity to the Jurassic rocks and qualitativecomparisons with previously observed magneticanomaly signatures much further to the south, suggest

that the anomaly complex may relate to:a) significantly thicker portions of dolerite sills thanexposed to the west; b) to ice covered JurasssicKirkpatrick Basalts or; c) to thicker Jurassic maficfeeder bodies. Alternative explanations b) and c) areaddressed further in the discussion section. In thesurvey area the only other small outcrop of Jurassicdolerites is found at Horn Bluff. The regionalmagnetic anomaly map does not indicate acomparable magnetic anomaly signature with respectto the northeastern margin of the Wilkes SublacialBasin (Fig. 7). However, a closer look at the area(Fig. 8) and also inspection of individual profile linesreveal a high-frequency and low-amplitude magneticanomaly signature, which might be attributed torelatively thin dolerites outcropping at Horn Bluff.

Fig. 7 - Contour map over the Anxiety Nunataks and Scar Bluffs region showing that the outcrops of Jurassic Ferrar dolerite (red outline)lie west of the main magnetic anomaly complex of the Mawson Peninsula region. Contour interval 5 nT.

D. Damaske et al.92

The volume of magnetic rocks must be relativelysmall to explain the observed aeromagnetic signature.Horn Bluff and its associates, Organ Pipe Cliffs andan unnamed rock outcrop just south of Horn Bluff,may be the insular remnants of thin dolerite sillsoverlaying sedimentary rocks, likely Beacon rocks.

The broad magnetic low between Scar Bluffs andHorn Bluff lies along the northern edge of the WilkesSubglacial Basin. High-frequency anomaly chainsstriking WNW-ESE punctuate the regional magneticlow. The geological nature of these anomalies remainsenigmatic, because of the lack of coincident outcrop.Perhaps these anomalies are imaging mafic dykeswarms. Notably, close to the outcrops of Jurassicdolerites at Horn Bluff, these magnetic anomalylineaments disappear (Figs. 6 & 8).

A large and elongated anomaly (amplitudes closeto 500 nT), dominates the offshore area between theMertz and Ninnis Glaciers. It significantly differs instrike from the NW to NNW trending Matusevich andRennick anomalies (Fig. 6 vs. Figs. 5 & 4). However,the WNW-ESE trend of the magnetic anomaly is onstrike with a major fault system, running parallel tothe George V Coast, as identified with multi-channelseismic data, collected west of Mertz Glacier (DeSantis et al., 2002). A possible continuation of theanomaly west of the Mertz Glacier is indicated onone survey line terminating at 145 E. Highly-magnetic Precambrian rocks, with susceptibility valuesranging from 0.016 to 0.035 SI-units, are scattered inthe Mertz Glacier area (Talarico et al., 2001).

However, these rocks are located west of theaeromagnetic survey area. Therefore, it is not possibleto directly correlate the magnetic anomaly patternwith outcrop. This implies that magnetic sources otherthan Precambrian rocks cannot be ruled out either.

DISCUSSION

SUBGLACIAL GEOLOGY AT THE NORTHERNEDGE OF THE WILKES SUBGLACIAL BASIN

Although the subglacial geology and tectonicorigin of the Wilkes Subglacial Basin in thehinterland of the Transantarctic Mountains (Fig. 9) isvery poorly constrained, it is the centre of severalspeculations and controversies. The basin wasoriginally hypothesised to be a major sedimentarybasin related to continental rift ing within EastAntarctica (Drewry, 1976; Steed, 1983). Later modelsfor the Wilkes Subglacial Basin predicted Cenozoicflexure of thick East Antarctic Craton lithosphereinduced by Transantarctic Mountains uplift, andargued against a major sedimentary basin in theregion (Stern & ten Brink, 1989; ten Brink & Stern,1992; ten Brink et al., 1997). More recently, gravityanomalies along the ITASE traverse at 75° S (Fig. 9)have been modelled to hypothesise possible broadcrustal extension rather than simple flexure, at leastbeneath part of the Wilkes Subglacial Basin(Ferraccioli et al., 2001). High-frequency magnetic

Fig. 8 - Contour map over the Horn Bluff region revealing a high-frequency anomaly pattern, interpreted to reveal relatively thin JurassicFerrar dolerite sills (red outline marks the outcrops). Contour interval 5 nT.


anomalies along the traverse (Fig. 9) have beenspeculatively interpreted as Jurassic rocks related tothe Ferrar Large Igneous Province (Elliot et al.,1999), perhaps extending from the TransantarcticMountains to the entirely ice-covered WilkesSubglacial Basin region (Ferraccioli et al., 2001).

The new aeromagnetic map along the George VCoast (Fig. 6) can be used to discuss the possiblesubglacial geology at the northernmost edge of theWilkes Subglacial Basin. The Mawson Peninsula andScar Bluffs region, which appears to be located at thenortheasternmost edge of the Wilkes Subglacial Basin,is now recognized as featuring high-amplitudemagnetic anomalies. These anomalies are obviouslyunrelated to sedimentary rock and are also unlikely to

be caused by the thin Jurassic Ferrar dolerite sillssuch as those detected at Horn Bluff (compareFigs. 6, 7 & 8). Hence, we put forward here two newpossibilities, which could be subsequently testedquantitatively with magnetic modelling, i.e.: a) buriedJurassic Kirkpatrick Basalt or, b) Jurassic maficfeeder bodies (Fig. 9). Hypothesis a) arises byconsidering that similar aeromagnetic anomalies havebeen imaged over 500 km further south (Fig. 9), andrelated to Kirkpatrick Basalt rocks preserved fromerosion in graben or pull-apart-like structures,interpreted along the eastern margin of the WilkesSuglacial Basin (Ferraccioli & Bozzo, 2003).Hypothesis b) arises by considering that high-amplitude aeromagnetic anomalies -detected 1000 km

Fig. 9 - Schematic geologic element map compiled from regional magnetic interpretation over a bedrock elevation map (modified fromLythe et al., 2000) for the Wilkes Subglacial Basin-Transantarctic Mountains. Both the linear aeromagnetic anomaly over the MatusevichGlacier, attributed to Ross-age rocks (Ferraccioli et al., this volume), and the previously detected aeromagnetic lineament system in theReeves Glacier area (Bosum et al., 1989; Ferraccioli and Bozzo, 1999; Ferraccioli et al., 2002; Ferraccioli and Bozzo, 2003) are shown.Note inferred Jurassic mafic intrusions, Kirkpatrick Basalt and Ferrar Dolerite rocks. We display the edge of the Precambrian Craton aspossibly lying close or at the western margin of the Wilkes Subglacial Basin. Heavy white line: GITARA VI survey; Dash-dot line: ITASEtraverse; black line: aeromagnetic lineament.

D. Damaske et al.94

south of our survey- delineate a mafic(?) Jurassicfeeder body at Butcher Ridge (Fig. 9). This feederbody is located close to the enigmatic hinterland ofthe Transantarctic Mountains (Wilson et al., 1999;Behrendt et al., 2002).

WHERE IS THE EAST ANTARCTIC CRATONBOUNDARY?

A significant open question in this sector ofAntarctica regards the location of the boundarybetween the Precambrian East Antarctic Craton andthe Ross Orogen (Roland et al., 2001). Prior to ourinvestigation a prominent aeromagnetic lineamentsystem was detected west of Reeves Glacier (Fig. 9),approximately 350 km to the south of the presentsurvey area (Bosum et al., 1989). It was originallyinterpreted to image the buried East Antarctic Cratonboundary (Bosum et al., 1989; Roland, 1991). Morerecently the aeromagnetic anomalies along thislineament system have been re-interpreted asreflecting Ross-age magmatic arc rocks, in partsoverlain by Jurassic Ferrar Group rocks (Ferraccioli &Bozzo, 1999; Ferraccioli et al., 2002; Ferraccioli &Bozzo, 2003). If this aeromagnetic boundary isspeculatively projected towards the Oates Coast, itcould perhaps lie in the Matusevich Glacier(Ferraccioli & Bozzo, 1999) or west of it, along155° E (Ushakov, 1960; Roland, 1991). Both areasare now crossed by the new aeromagnetic survey(Figs. 5 & 6). Hence, the craton boundary problemcan be re-discussed from a more robust aeromagneticperspective than previously possible. The newaeromagnetic anomaly map over Oates Land certainlyreveals a prominent linear anomaly over theMatusevich Glacier (Fig. 5). The sources of theanomalies over the Matusevich Glacier, however, areunlikely to represent Precambrian shield rocks.Rather, the anomalies are interpreted to reflect highly-magnetic Granite Harbour arc rocks, andmafic/ultramafic basement rocks of Ross-age, whichpartially outcrop (Ferraccioli et al., this volume). TheGranite Harbour Intrusives were affected by westwarddirected ductile thrusting of Ross-age along the ExilesThrust system (Flöttmann & Kleinschmidt, 1991;Roland et al., 2001).

The previously inferred craton boundary at 155° E(Ushakov, 1960; Roland, 1991) can now berecognized as relating, at least spatially, to thenortheastern edge of the Wilkes Subglacial Basin(note Ushakov’s boundary at 155°E in Fig. 6). Wehave discussed the hypothesis that the sources ofmagnetic anomalies at the northeastern edge of theWilkes Subglacial Basin could relate to Jurassicmagmatism, rather than to unexposed Precambrianshield rocks. The aeromagnetic map along George VCoast suggests that highly magnetic rocks, which mayspeculatively relate to the East Antarctic Craton itself

(Talarico et al., 2001), appear to be located muchfurther west than originally proposed by Bosum et al.,(1989). Hence, we now hypothesise that the cratonboundary could lie closer to the western margin ofthe Wilkes Subglacial Basin, rather than closer to itseastern margin (Fig. 9). This hypothesis would alsoagree with magnetic modelling results along theITASE traverse (Ferraccioli et al., 2001).

CONCLUSIONS

We have presented the first results of anaeromagnetic anomaly investigation carried out alongthe previously unexplored Antarctic coast betweenYule Bay and Mertz Glacier. These results aresummarised below:- Admiralty Intrusives of the Everett Range produce

a positive magnetic anomaly. In contrast the YuleBay pluton is marked by a subtle magnetic low.Presently offshore Yule Bay, the Unger Island-Surgeon Island anomaly, reveals a possiblesubvolcanic intrusion.

- Granite Harbour Intrusives and perhaps mafic andultramafic basement rocks cause the prominentMatusevich Anomaly imaged over Oates Land.The Archangel Nunataks gabbro, also assigned tothe Granite Harbour Intrusives, causes the mostintense anomaly of the whole survey.

- Ferrar-related igneous rocks may be revealed bythe anomalies of the Scar Bluffs/Anxiety Nunataksregion, along the northeastern flank of the WilkesSublglacial Basin. However, these anomalies differfrom those mapped over Horn Bluff, where thinFerrar sills outcrop.

- The boundary of the Precambrian East AntarcticCraton could lie much further west than proposedfrom some previous aeromagnetic interpretations.

Acknowledgements- This paper is a contribution of thejoint German-Italian GANOVEX VIII-ITALI ANTARTIDE XVExpedition 1999-2000. Logistic and financial support wasprovided by BGR and PNRA. The Italian contribution tothis paper was funded within the BACKTAM geophysicalprogramme. D. Moeller (BGR) and G. Caneva(DIP.TE.RIS) are thanked for technical assistancethroughout the survey. M. Chiappini (INGV) isacknowledged for aeromagnetic data quality control andarchiving during Leg 2 of the expedition. Special thanks aredue to the aeromagnetic survey pilots of the HelicopterNew Zealand team. F. Ferraccioli acknowledges both aDIPTERIS/PNRA research grant (2001/02) on the WilkesSubglacial Basin/Transantarctic Mountains region and BASfor their support to continue previously initiated work. Thereviewers Ash Johnson and Emanuele Lodolo are gratefullyacknowledged for providing constructive suggestions, whichimproved an earlier version of the MS.


REFERENCES

Bachem H.-C., Bosum W., Damaske D. & Behrendt J.C., 1989a.Planning and Execution of the GANOVEX IV AeromagneticSurvey in North Victoria Land, Antarctica. GeologischesJahrbuch, E38, 69-80.

Bachem H.-C., Damaske D., Dumas B. & Heimes F.-J., 1989b.Aircraft Navigation in North Victoria Land, Antarctica.Geologisches Jahrbuch, E38, 59-68.

Behrendt J.C., Damaske D., Finn C.A., Kyle P. & Wilson T.J.,2002. Draped Aeromagnetic Survey in TranasantarcticMountains Over the Area of the Butcher Ridge IgneousComplex Shows Extent of Underlying Mafic Intrusion.Journalof Geophysical Research, B8, 10.1029/2001JB000376.

Borg S.G., DePaolo D.J., 1991. A tectonic model of the AntarcticGondwana margin with implications for southeastern Australia:isotopic and geochemical evidence. Tectonophysics, 196, 339-358.

Bosum W., 1981. Anlage und interpretation aeromagnetischervermessungen im rahmen der erzprospektion. GeologischesJahrbuch, E20, 363.

Bosum W., Damaske D., Roland, N.W., Behrendt, J.C. & Saltus,R., 1989. The GANOVEX IV Victoria Land/Ross Seaaeromagnetic survey: interpretation of the anomalies.Geologisches Jahrbuch, E38, 153-230.

Bozzo E., Caneva, G., Capponi, G., & Colla A., 1995. Magneticinvestigations of the junction between Wilson and BowersTerranes (northern Victoria Land, Antarctica), AntarcticScience, 7, 149-157.

Bozzo E., Caneva G., Colla A., Damaske D., Ferraccioli F.,Gambetta M., Meloni A. & Moeller H.D., 1997a. Totalmagnetic anomaly map of Victoria Land (central-southern part),E. Bozzo and D. Damaske, (eds.), Antarctic Geomagnetic1:250 000 map series, Museo Nazionale dell’Antartide- Sez.Scienze della Terra, Siena, Italy, Ministero dell’Università edella Ricerca Scientifica e Tecnologica- Programma Nazionaledelle Ricerche in Antartide, Sheets A-B.

Bozzo E., Ferraccioli F., Gambetta M., Caneva G., Damaske D.,Chiappini M. & Meloni A., 1997b. Aeromagnetic regionalsetting and some crustal features of central-southern VictoriaLand from the GITARA surveys. In: C.A. Ricci (ed.), TheAntarctic Region: Geological Evolution and Processes, TerraAntartica Publication, Siena, 591-596.

Bozzo E., Ferraccioli F., Gambetta M., Caneva G., Spano M.,Chiappini M., & Damaske D., 1999. Recent progress inmagnetic anomaly mapping over Victoria Land (Antarctica) andthe GITARA 5 survey, Antarctic Science, 11 (2), 209-216.

Bozzo E., Ferraccioli F., Chiappini M., Damaske D. & BehrendtJ.C, 2002. Recent progress towards the compilation of anintegrated magnetic anomaly map of the Ross Sea sector ofAntarctica. In: Gamble J.A., D.N.B. Skinner, S. Henrys (eds.)Antarctica at the close of a millenium. Proceedings of the 8th

International Symposium on Antarctic Earth Sciences, RoyalSociety of New Zealand Bulletin, 35, SIR publishing, 629-634.

Briggs J.C., 1974. Machine contouring using minimum curvature,Geophysics, 39, 39-48.

Chiappini M., Ferraccioli F., Bozzo E. & Damaske D., 2002.Regional compilation and analysis of aeromagnetic anomaliesfor the Transantarctic Mountains-Ross Sea sector of theAntarctic. Tectonophysics, 347, 121-137.

Damaske D., 1989a. Spatial resolution of the aeromagnetic flightgrid-North Victoria Land, Antarctica. Geologisches Jahrbuch,E38, 91110.

Damaske D., 1989b. Geomagnetic activity and its implications forthe aeromagnetic survey in North Victoria Land. GeologischesJahrbuch, E38, 41-57.

Damaske D., 1990. Technical description of the 1:250,000 Maps ofthe Anomalies of the Total Magnetic Field Lower RennickGlacier, North Victoria Land, Antarctica. - AeromagneticSurvey During the Expedition GANOVEX V 1988/89. - 2maps, pp.11, BGR, Hannover.

Damaske D., 1993. Layout, Execution, and Data Processing of theAeromagnetic Survey in the Lower Rennick Glacier Area,North Victoria Land, Antarctica. Geologisches Jahrbuch, E47,

115-138.Damaske D., & W. Bosum, 1993. Interpretation of the

aeromagnetic anomalies above the lower Rennick glacier andthe adjacent polar plateau west of the USARP Mountains.Geologisches Jahrbuch, E47, 139-152.

Damaske D., 1994. Aeromagnetic Surveys over the TransantarcticMountains and the Ross Sea Area. Terra Antartica, 1, 503-506.

Damaske D. & Finn C., 1996. Explanatory Notes on the 1:250,000Maps of the Anomalies of the Total Magnetic Field, BowersMountains, Antarctica. - Aeromagnetic Survey During theExpedition GANOVEX VI 1990/91. - 1 map, pp.10, BGR,Hannover.

Damaske D., Bozzo E., Moeller D., Ferraccioli F. & Chiappini M.,2001. A New Aeromagnetic Survey along Pennel, Oates andGeorge V Coasts (East Antarctica). Terra Antartica Reports, 5,1-12.

Drewry D.J., 1976. Sedimentary basins of the East Antarctic Cratonfrom geophysical evidence. Tectonophysics, 36, 301-314.

Elliot D.H., Fleming TH., Kyle P.R., Foland K.a., 1999. Long-distance transport of magmas in the Jurassic Ferrar LargeIgneous Province, Antarctica. Earth and Planetary ScienceLetters, 167, 89-104.

Ferraccioli F. & Bozzo E., 1999. Inherited crustal features andtectonic blocks of the Transantarctic Mountains: anaeromagnetic perspective (Victoria Land - Antarctica). Journalof Geophysical Research, 104, 25297-25319.

Ferraccioli F., Coren. F, Bozzo E., Zanolla C., Gandolfi S., TabaccoI. & Frezzotti M., 2001. Rifted(?) crust at the East AntarcticCraton margin: gravity and magnetic interpretation along atraverse across the Wilkes Subglacial Basin region. Earth andPlanetary Science Letters, 197, 407-421.

Ferraccioli F., Bozzo E. & Capponi G., 2002. Aeromagnetic andgravity constraints for an early Paleozoic subduction system ofVictoria Land, Antarctica. Geophysical Research Letters, 29,10.1029/2001GL014138.

Ferraccioli F. & Bozzo E., 2003. Cenozoic strike-slip faulting fromthe eastern margin of the Wilkes Subglacial Basin to thewestern margin of the Ross Sea Rift: an aeromagneticconnection. Intraplate Strike-Slip Deformation Belts(Storti, F.,Holdsworth R.E., & Salvini F., eds). Geological Society,London, Special Publications, 210, 109-133.

Finn C., Moore D., Damaske D. & Mackey T., 1999. AeromagneticLegacy of early Paleozoic subduction along the Pacific marginof Gondwana. Geology, 27, 1087-1090.

Fioretti A.M., Visona’ D., Cavazzini G., & Lombardo B., 1997a.Devonian magmatism: implcations for the evolution ofnorhern Victoria Land, Antarctica, and correlation withsoutheastern Australia and northeastern Tasmania. In: C.A.Ricci (ed.), The Antarctic Region: Geological Evolution andProcesses, Terra Antartica Publication, Siena, 293-296.

Fioretti A.M., Cavazzini G., & Visona’ D., 1997b. AdmiraltyIntrusives in the southern Bowers Terrane: the Collins Peakpluton. Comparisons with the Salamander Granite Complex,northern Victoria Land, Antarctica. In: C.A. Ricci (ed.), TheAntarctic Region: Geological Evolution and Processes, TerraAntartica Publ., Siena, 287-292.

Fioretti A.M., & Lanza R., 2000. Preliminary paleomagneticresults from the Devono-Carboniferous Admiralty Intrusives(northern Victoria Land, Antarctica). Terra Antartica, 7, 657-664.

Fioretti A.M., Capponi G., Black L.P., Varne R., & Visona’ D.,2002. Inherited zircon pattern of Surgeon Island granite:evidence for Proterozoic crust at the eastern end of northernVictoria Land (Antarctica), paper presented at Gondwana 11.Christchurch N.Z. 26-30 Aug. 2002.

Flöttmann T. & G. Kleinschmidt, 1991. Opposite thrust systems innorthern Victoria Land, Antarctica: Imprints of Gondwana’sPaleozoic accretion.Geology, 19, 45-47.

GANOVEX TEAM, 1987. Geological Map of North Victoria Land,Antarctica, 1:500 000, Explanatory Notes. GeologischesJahrbuch, B66, 7-79.

Kleinschmidt G. & Tessensohn F., 1987. Early Paleozoic westwarddirected subduction at the Pacific margin of Antarctica. In:G.D. McKenzie (ed.), Gondwana Six: Structure, tectonics, and

D. Damaske et al.96

geophysics, Amer. Geophys. Union, Geophys. Monogr. Series,40, 89-105.

Kleinschmidt G., Tessensohn F. & Vetter U., 1987. Paleozoicaccretion of the Pacific margin of Antarctica. Polarforschung,57, 1-8.

Lythe M.B., Vaughan D.G. & the BEDMAP Consortium: BEDMAP- bed topography of the Antarctic, 1:10,000,000 scale map,Cambridge, British Antarctic Survey, 2000, BAS (Misc)9.

Maslanyi M.P. & Damaske D., 1986. Lessons regardingaeromagnetic surveying during magnetic disturbances in polarregions. British Antarctic Survey Bulletin, 73, 9-17.

Ricci C.A., Talarico F. & Palmeri R., 1997. Tectonothermalevolution of the Antarctic Paleo-Pacific active margin ofGondwana: a northern Victoria Land perspective. In: C.A.Ricci (ed.), The Antarctic Region: Geological Evolution andProcesses, Terra Antartica Publication, Siena, 213-218.

Roland N.W., 1991. The boundary of the East Antarctic craton onthe Pacific margin. In: M.R.A. Thomson, J.A. Crame, and J.W.Thomson,Geological Evolution of Antarctica, Cambridge Univ.Press, New York, 161-165.

Roland N.W. & Henjes-Kunst F., 2001. The Unger Island volcanics,Northern Victoria Land (Antarctica): related to the CambrianGlasgow Volcanics or the Devonian-Carboniferous Gallipoli-type extrusives?. Terra Antartica Reports, 5, 67-70.

Roland N.W., Henjes-Kunst F., Kleinschmidt G. & Talarico F.,2001. Petrographical, geochemical and radiometricinvestigations in Northern Victoria Land, Oates Coast andGeorge V Coast: towards a better understanding of plateboundary processes in Antarctica. Terra Antartica Reports, 5,57-65.

Rolf C. & Henjes-Kunst, 2001. Paleomagnetic investigations. TerraAntartica Reports, 5, 51-56.

Steed R.H.N., 1983. Structural interpretation of Wilkes Land,Antarctica. In: R.I. Oliver, P.R. James & J.B. Jago (eds.),Antarctic Earth Science, Cambridge University Press, NewYork, 567-572.

Stern. T.A & ten Brink, U.S. 1989. Flexural uplift of theTransantarctic Mountains. Journal of Geophysical Research, 94,10 315-10 330.

Talarico F., Armadillo E., & Bozzo E., 2001. Antarctic rock

magnetic properties: new susceptibility measurements in OatesLand and George V Land, Terra Antartica Reports, 5, 45-50.

Tarlowski C., Milligan P.R. & Mackey T., 1996. Magnetic anomalymap of Australia (second edition): Canberra, AustralianGeological Survey Organisation, 1996, scale 1:5 000 000.

ten Brink U.S. &. Stern T., 1992. Rift flank uplifts and hinterlandbasins: comparison of the Transantarctic Mountains with theGreat Escarpment of Southern Africa. Journal of GeophysicalResearch,97, 569-585.

ten Brink U.S., Hackney R.I., Bannister S., Stern T.A, MakovskyY. 1997. Uplift of the Transantarctic Mountains and thebedrock beneath the East Antarctic ice sheet. Journal ofGeophysical Research, 102, 27 603-27 621.

Tessensohn F., 1979. Passive “Gondwanische” und aktive“Pazifische” Tektonik der Antarktischen Platte. - ClausthalerGeologische Abhandlungen, 30, 164-191.

Tessensohn F., Duphorn K., Jordan H., Kleinschmidt G., Skinner,D.N.B., Vetter U., Wright T.O. & Wyborn D., 1981. GeologicalComparison of Basement Units in North Victoria Land,Antarctica. Geologisches Jahrbuch, B41, 31-88.

Tessensohn F., Kreuzer H., Henjes-Kunst F., Kleinschmidt G., &Vetter U., 1996. Geological map of the Yule Bay Quadrangle,Victoria Land, Antarctica- 1:250000, GIGAMAP Series, BGR,Hannover.

Vetter U., Lenz H., Kreuzer H. & Besang C., 1984. Pre-Rossgranites at the Pacific margin of the Robertson Bay Terrane,North Victoria Land, Antarctica. Geologisches Jahrbuch, B60,363-369.

Wilson T., Csatho B, Damaske D., Finn C., Behrendt J.C., Bell R.& Ferraccioli F., 1999. Transantarctic Mountainsaerogeophyisical research activities (TAMARA): a progressreport, Paper presented at 8th International Symposium onAntarctic Earth Sciences, Wellington 5-9 July 1999.

Wyborn D., 1981. Granitoids of north Victoria Land, Antarctica-field and petrographic observations. Geologisches Jahrbuch,B41, 229-249.

Ushakov S.A., 1960. Some features of the structure of KingGeorge V coast and Oates coast according to geophysical data,Inf. Bulletin of the Soviet Antarctic Expedition, 18, 11-14.

© terra antartica publication

Documents