Stackebrandt, W.

Thiedig, F.

English

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Polarforschung 60 12): 96-98, 1990 (erschienen l v'ri )7. Young Teetonic Activities in theCoastal Ranges of Central Victoria LandBy Werner Stackebrandt* and Friedhelm Thiedig**INTRODUCTIONThe eharacter of parts of the Ross Sea area as a meridionally orientated rift system has been reeognized in reeentyears (Ross Sea Rift System, TESSENSOHN & WÖRNER 1991), At the same time, the morphogenesis oftheTransantarctie Mountains was estimated by fission track data and other methods to be younger than 50 my(FITZGERALD & GLEADOW 1990). The subsidence ofrift related grabens as weil as the uplift ofthe mountainranges adjacent to the west seem to have a uniform genetieal source. In addition, the morphogenesis ofthe N011hVictoria Land coastal ranges was explained to be the result of shoulder uplift in relation to the second phase ofthe Ross Sea rifting (ROLAND & TESSENSOHN 1987) which starred in the Upper Paleogene (COOPER et al.1987, HINZ & KRISTOFFERSEN 1987). Up to now, this interpretation is based mainly on geophysical datafrom the Ross Sea. Therefore, the study ofthe younger tectonic development in central North VictoriaLand wasone of the topics of the GANOVEX team in 1990/91.In this paper, we present preliminary results of these studies in the coastal region from Terra Nova Bay to LadyNewnes Bay as weil as between the Priestley and Larsen Glaciers (Fig. I). Methodieally, we foeus on fieldmeasurernents of fault and dike orientations, age relations of different dike generations, as weil as the characterand sense of motion on fault planes. Prior to the field studies, LANDSAT images and aerial photographs hadbeen analyzed. Since younger syngenetie sediments in the coastal ranges are missing, it is difficult to determinethe exact ages of the observed post-Ross tectonic events.FAULTZONESThe frequency and intensity of post-Ross faulting varies in the investigated area. Submeridionally oriented faultsexist both in the Terra Nova Bay and in the Lady Newnes Bay. The intensity ofNNE-SSW to NE-SW orientedfaults inereases to the north. In general, the faults represent brittle deformation in a high crustal level in anextensional environment. The outerops of the "Berliner Mauer" (proposed new name) at the narthern flank ofthe Aviator Glaeier (TIUEDIG & STACKEBRANDT this val.) show this character very clearly. NW and SEdipping faults ereating horst- and grabcn-structures or en echelon systems cut submeridionally oriented basalticdike swarms. If we assume a late Mesozoie to early Tertiary age of the basaltic dikes, then the faults should beof Cenozoic age. Another argument for a young age of these faults is their strong influence on the morphologyof the whole territory . This relation will be worked out in more detail. Ta the south, the exposures of rocks arepoorer. Many faults can be localized on aerial photos, but their age relations are unc1ear.Important fault zones seem to be rare in the investigated area. Possibly they were exposed to strong glacial erosionand are now eovered by glaciers. On the southem flank of the Priestley Glaeier the accompanying inventary ofa NW-SE trending regional fault was mapped. Ta the SE, this fault crosses Black Ridge and re-emerges againin the southem part of Gerlache Inlet. The same fault zone has been used by intrusions of younger basaltic veins.In the west, this normal fault displaces the Beacon peneplain by sorne hundreds of meters, whereas to the SE theintensity decreases rapidly. The relations to the Rennick graben (ROLAND & TESSENSOHN 1987, SKINNER1987) are currently under discussion.:;.Dr. Wcmer Stackcbrandt. Landesamt für Geowissenschaften und Rohstoffe Brandenburg. Stahnsdorfcr Damm 77,0-0-1532 Kleinmanchnow, FRG.** Prof. Dr. Fricdhelm Thicdig, Gcol.-Paläont. Institut, Universität Münster. Corrcnsstraße. 24, D-4400 MÜnster, FRG.96B a y~ Undifferentiafed t-tetomccpbicso Granite Harbour IntrusivesBeacon SupergroupQ Mefbourne VutcanitesN 0 v aTe r r a2010oIDA VI DFig. 1: Orientation of basaltic dikcs in thc coastal ranges of central North Victoria Land.Geology simplified aftcr CARi\tIIGNANI ct al. (1988) andGANOVEX Team (1987). For dircction of dip reduce givcn maxirnum by 90° anticlockwisc.Abh.I: Orientierungbasaltisoher Gänge im zentralenVierortaland. Das Einfallen der Gänge erhältman, wenn vom dargestelltenStreich-Maximum90° gegen den Uhrzeiger-Sinn abgezogen werdenIn the same area satellite images show numerous NE-SW trending normal faults. According to field observationsin the central part of the Priestly Glacier, these faults are often accompanied by intensively jointed zones reachingseveral tens of meters in width. Slickenslide striations impley a dominant sinistral sense of motion. Thetransformation of joints and faults to open cracks points toward a young morphogenesis of the mountains alonga NE-SW oriented axis. Typical examples for open cracks were found likewise in the southern part of theEisenhower Range and in the vicinity of the Tinker Glacier to the north.97DIKESThe coastal region of the investigated area is eharaeterized by frequent dike intrusions. To the south of TerraNova Bay, aeidie dikes frequently oeeur (Tarn Flat, Mt. Crummer, south of Drygalski Ice Tongue(KLEINSCHMIDT & MATZER this vol.). However, in the northern part near Lady Newnes Bay basaltie dikesare dominant. By observing the erosseutting relations of the different dike types the following time sequence ofintrusive aetivity has been derived: (i) elikes of the late Ross eycle (lamprophyres, pegmatites and aplites: thesewere not further eonsidereel) and (ii) dikes of the post Ross eycle, i.e. from old to young: altereel basalts - rhyolites-daeites - fresh basalts.The strike elireetion of the dikes varies (Fig. I). Both types ofbasaltie elikes follow mainly submerielional to NE-SW orienteel zones, whereas the aeielie dikes, which reaeh often more than 10m in width, are aligneelpreelominantly along E-W direetions. The intrusion of dacites is often eonneeted with a dextral sense of shearing.Dextral shear movements south of the Drygalski Ice Tongue (KLEINSCHMIDT & MATZER THIs vol.) wereobviously ereateelby the sarne regional stress fieleI. On the other hand, the intrusion of the younger basaltie dikesis predominantly eonneeted to a sinistral sense of shearing. Later on, normal faulting dominates. The inereaseof basaltie sills anelelikesfrom the inland towards the Ross Sea points to a close eonneetion bctwcen the generationof graben struetures within the Ross Sea and the erustal wielening in the eoastal ranges of North Vietoria Land.Gooel examples for this relationship exist espeeially in the northern part of the investigateel area (Tinker, Aviatoranel Parker glaeiers).A more eletaileel interpretation of the fielel data, including an evaluation of satellite images anel aerial photos,will be given later. Another stuely, whieh ineludes new raeliometrie elata as weIl as the petrography of the dikesis plannecl.ACKNOWLEDGMENTSWe are greatly indebted to F. Tessensohn and G. Kleinsehmielt for making available our Antaretie stuelies in avery historie time in Germany. The projeet was finaneially supporteel by the Deutsehe Forsehungsgemeinsehaft(DFG).ReferencesCo 0 per, A. K., Da v e y , F. J. & Be h r c n d t , J. C. (1987): Seismic stratigraphy and structurc of thc Victona Land Basin. westcrn RossSea, Antarcrica.. In:The AntarcticContincmal Margin:Geology andGcophysics of Ihe WesternRoss Sca.- CircumPacific Council fürEnergyand Mineral Rcsourccs. EarthSei. Sero SB: 27-65, Hauston.Fit z g c r a I d , P.G. & G 1e a d 0 w J. W. (1988): Fission-trackgeochronology. teerenies and srtucture of the Transantarette Mountains in northemVictoria Land, Antarctica> Chem. Geol. 73: 169-198.Hin z K. & Kr i s ! 0 f f e rs e n , Y. (1987): Antarctica. Recent advances in rhc undersranding of the Contineutal Shelf.. Geol. Jb. E37: 3~54.R 0 1a n d , N. W. & Tc s sen s 0 h n, F. (1987); Rennick Paulting - an carly phase of Ross Sea Rifting.. Geol. Jb. B66: 203~229.Ski n n er, D. N. B. (1987); TetT3 Nova Bay and Deep Freezc Range - the scuthem allochthonous borderof North Victoria Land, Antarctica.. Mem.Soc. Geol. Itaiiana 33: 41-58.Te s s e n s 0 h n , F. & W ö r n er, G. (1991); The Ross Sea Rift System (Antarctica) - structure, evolution and analogues.. In: Thomson, M.R.A ..Cramc, J.A. & Thomson, J.W. (eds.), Gcological evolution of Antarctica.. Cambridgc University Press: 273-277, Carnbridge.98

7. Young Tectonic Activities in the Coastal Ranges of Central Victoria Land

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