______~ O~C~E~A~N~O~LO~G~' C~A~A~C~T~A~,_'~9~8~1 ,~N~O_S~P__ ~~------
ArCIÎc Magnetic anomalie s Structure and plate tectonic l'laIe tccto ni C$ Sea flour s pre,*din~
• Arçtiqul.': Anomalies magnétiques evolution of the manne Arctic Tectonique des plaques OuverTure océanique as revealed by aeromagnetics
b l'. Vogt". C. Bernero • L. Kovacs' , p, Taylor" • Code 5110. Naval Research Laboratory, Washington, D.C. 20375. USA. b School of Geology and Geophy ~ iç ~. University of Oklahoma. Norman. Oklahoma 73019 . USA. < Code 922, Goddard Space flight Center, NASA. Greenbell . MD 10771. USA.
ABSTRA CT Over 400,000 km of low level acromagnetic data wcre collected by US Navy rescarch organiz.ations over the Arctic Basin a nd Grccnland-Norwegian Sea during the years 1972 10 1978. These data provide ncw co nstrainls on the cruslal structure and tcelonie evulu tion uf this vast region. Magnelic anomalies over continental fragments (Lomonosov Ridge and Chukchi 13 0rderland) are irregular, with local short-wavelength features indicating relatively shallow base ment. Long-wavelength a nomalies indicate deep base ment under mosl Arctic shclves exceplloclltty near coastlines. Conspicuously li neated a nomalies arc round only on Ihe wide east Greenland Shelf and to ;llesser e xtent along the Norwegian shelf ;lOd Barents Sea. Initial rifting belween Greenland a nd Scandinavia followed Il structural boundary separating the north-trcnding pre-rift anomalies on the Greenland side from more northeasterly trends on the Eurasian side . The nort hcrn part of the Greenland Sea began to open when the Hornsund tra nsform fault bcC;l me Il rifted margin. Howevcr , (rom the Bear IsI'lnd area south to the Grecnland-Senja F.Z., an oblique rift bcglill to open already in the early Tertia ry. Sca-fl oor spreading between SClIndina via and Greenla nd commenced about 58 m.y.b.p. during the reversed period preceding anomal y 24 . Sprellding between the Lomonosov Rid ge and Eurasia also began ;11 thi s time or poss ibly somewhal earlier. Anom;llies in the Lofoten Greenland Eurasiu basins are relati vel y linear a nd wcll-defincd despite the slow spreading rates (0.3 to 1 cm/yr half-rate). In the Greenl and Se O! oblique spreading, close-spaced transforms, and sediment input may explain the complex. ge nerall y undecipher&b le or non-existent anomulies there. A slight but persistent asymmelry has characlerized cruslal accretion in the Greenland-Norwegian Sea a nd Eurasia Busin : Ihe Eura nian flank of the plate boundary tends to exhibit fa stcr sprellding, greater depth . a nd reduced gravît y ll nu magne tic ilnornaly amplitudes, An exti nct spreading axis in the Canada Basin is indiC'lled by gravit y land magnetic data. A possible scen,nio is thal during the carly Crelaceous (' M ' _ magnetic re versai sequence) the Chukchi Borderland rifted away fro m the m;lrgÎn of Arcti c Canada al ong :, tmnsform fnu lt al ong the Alaskan North s10pe . Li near anomalies of possible spreading origin are found over some olhcr parts of the Canada Bllsin , the Makaroy Basin , ;Ind near the junction be lween the Lomonosov Rid ge and the Nort h American continental ma rgi n. Magnctic anomalies over the Alpha Ridge and parts of the adjacent basins are chaotic in trend and high in amplilU de. Direct correlation between basemcnt topognlph y and magnetic anomal y is found over parI of the Al ph;1 Ridge crest. The detailed acromagnetic d;lIa have nol se ttled the controvcrsy about the origin of the Alpha Ridge.
OO!//llui. AcUl. 19~1 . Procecdings 26'h Int ernmioMl Geological Congress. Gcology of oceans symposium, Paris. Jul y 7-17. 19KO. 25-40.
RÉSUME Structure el évolution tectonique globale de l'Arctique d'après des études aéromagnéliques.
400 000 km de levés aéromagnétiques à hasse altitude ont été effectués par les org:mismes de recherche de rus Navy sur le bassin Arcti que et les mers de Norvège et du Groënl and . au
25 P. VOGT. C. BERNERO. L. KOVACS . P. TAYLOR
cours des années 1972 à 1978. Ces données restreÎgnent les possibili tés dïnterprét:l tion de la structure crustale et de révolution tectonique de celle Vli~te région. Au-dessus des fragments continentau:>; (ride de Lomono~ov et bordure de Chuckchi). les anomalies magnétiques sont irrégulières. avec des ~ tru c ture s loc ~l le s de courte longueur d'onde qui trahissent la relati ve proximité du socle. Des anomalies de grande longueur d'onde indiquent la pré~ence d'un socle profond sous la majeure partie de la plate-forme Arctique . sauf l oc~lemenl près des côtes: Des anom:lJies re marquablementlinéltires ont été découvertes seulement sur la vaste plate-forme Est-Groën land et :o ur une moindre étendue le long de la plate-forme norvégienne et de la mer de l3 arenl Z. 1":1 séparation initiale entre le Groënland ct la Scandinavie a été guidée paf une limite structurale sé parant les anomalies pré-rift. alignées Nord-Sud. du côté du Groënland. de celles de rEurasÎe. dirigées plutôt Nord Est-Sud Ouest. La partie septentrionale de hl mer du Groënland a commencé à s'OU\'rÎr lorsqu'à la faille transforma nte de Homsund a succédé une véritable ouverture. Cependant. un rift oblique a commencé à fonct ionner. dès le début du Terti"ire. du sud de la zone de BC OrewlOl. Ada. 19K1. Acte, 26< Congrè~ International de Géologie. coll oque Géologie des océans. Pa ris. 7-17 JUIl. lYlSU. 2)-4U. INTRO DUCTI ON entire Arcti c Basin. Data compilations are also found in Grjjnl ie and Tillw:mi (1978) and Sweeney el al. (1978) : the During the period 1972 Ihrough 1978 sevcral US Navy latter report is a wbjcct-by-subject review. research organizations [Naval Research Laboralory(N RL). The prese nt pl.per begins \Vith the Eurasia Basin and Nuval Oceimographic Office (Navoce'lno). and Naval Ocea Greenland-Norwegian Sea. and emph'lsizes the post-mid nographie Re ~earc h a nd De"velopment Acli vi ty (Noroa)1 Prl leoçene plate tecto nic devclopment : the Canada B:tsin is collected a 10lal of aboul 400.000 km of low level aeroma di !>c usscd nexl. ~ince it now appears 10 have a sprellding gnetic d:\tll over the Arcti c Basin and Greenland-Norwegi:m origin . Followi ng cornes the Alpha Ridge. who ~ e n:\turc b SC~1. Typical truck :o pacings ranged from 10 to 15 km : the ~ ti Jl unknown. and fi na lJ y the magnetic characteri~t ic s of flight speed wa~ about 440 km/hr and the altitude 150 m to known or suspected continental crusi overflown during the 300 m above Ihe sea surface. A number of resellrch pu blica 1971- 1978 s tudie ~. tions have bcen based o n these aeromagnelic data (e.g. Vogt el al .. 1978 : 1979 (1. b : 1981 : Kovacs. 1981 : K ov:;.c~ el al .. 1981 : PhilJips el al.• 198 1 : Ph illip ~. Tapscou. 1981 : Ber THE GREENLAND-NORWEGIAN SEA AND EURA nero. 198 1 : Taylor 1'1 lll .. 19K1 ). The pre ~ en[ paper is a SIA BAS INS synthesis of the plate tectonic and other geophyskal conclu sions drawn from this data bri se. Al though the dma have The Teniar}' opening of the GreenhlnJ-Norwegi;.n Se .. Hnd been or are being publishcJ elsewhcrc in one form or Eurasi:t Basin can now be reconstructed with considerable another. ail bU I Figure !> 1 and 4 arc ncw to this paper. For a precision (e.g .. Phillips. Tap~co u . 1981 : Tltl wani. Eldhohll. more detai led geoph ysical review of the Euril:.Îa Ba:.in ,.nd 1977 : Kristoffersen. Talwani . 1977 : Le Pichon et al .. 1977). Greenland-Norwegia n Sea the reader is referred to Vogt el As the geology :lIld geophysics of thi s area have been CIl. (1979 b) and Vogt 1'1 al. (1 981) respectively. Sweeney re viewed in ~omc detai! (Vogt l't lt/ .• 1978: 1979 b : 1981). (19HU) puhlished the mo ~ t recenl review 26 AEROMAGNETIC DATA AND AR CTIC EVOLUTION Figurt 1 Hallrym,,/r)' (O.J. 1.1. J. a"d 4 km ;saha/lu)• .fU I iu Iimi/5. Ulrd "a"'(5 ,,[ mtrjor aa.an·floor /" {lnf.:Nr{lhk fc/ll ures a/lll 5l'a5. Fn"" Vogl t r nI. (l979 b). A linealed a nomaly pattern is weJJ -developcd in most ridgcs with probably Ihickened oceanic cruslS and complex. lIeep-waler pariS of Ih is area and can be recogni zed eus il y high.amplilude magnelic anomalies (Fig, 8 and Feden et (II,. even in che less delailed Soviet data (Fig. 2.3). One 1979). Anolher magneticaJJ y eomplex area is the Grecnland exception is Ihe Yermak and Morris Jesup plateaus ("M " Sea from the Grecnl;tnd-Senjtr fractu re zone northward 10 and " Y" in Fig , 3) which appear 10 be Iceland-like aseismic the Eunrsia Basin. Anomalies are continuous only ovcr Figure 2 "Zebrll -l'I ripe" (zero-COII/OIlr) l'lUI" of I/"'SlIelie ImU/mlliO'$ i" lire A/'('Iic Ha sin IUld " nrll,em Greellllmd·No",'ef.:itur SNI , HII'rk denMes IIe1f(J/i"e Wrllrlllllil',f, lll/uJ mr US NIIV)'. SOI';el. wu/ $"mO' ü lllaJimr /I"",mllll""li(' 1111/11, SO"iel lllll! CII/illJi/llr , 'O/l/OltrS "'<'rI.' IUkell from Co ll's ct ni. (1978); US dma '''l'fl' Ilü/h-pan fi/ureJ 10 re",m't rt'Jlimw/ IGRF rO'$;dll/JI .~ U/lJ Jlum/JI ef/t(,b' (see Km'IIt's ctal. 19//1), No III/Cmp/ "'liS matll' 10 /Jdju$/ COlI / mirS al sun 'ey hlJund/Jrits. l'rrdl u5/1rl' "Jin'IIII/; ,url,y·· /1 - l, ... hidr 5ep/Jrares US-Catradlmr frol!! Sofier IIem IlluStre/le eo,·t!rll~, W/rere Jeralled Jmll sert 1J,·erl(J{lo/Jer./rs,f dewi/t'J d/Jlu. /Irt Ill//t'r ,,·tre tlimlllflltd. 27 P. VOGT, C. BERNERO, L. KOVACS. P. TAYLOR Figure: 3 Maglll'lif' liJlI'Mionj /md lir.ear oflselS or disruptiQl' s of magllerie anomal)' p"lIerlIS. Hused 011 Ctwadiau ship-btmle reSU11S ill Baffin Ba)' (JUr/il'OIl et .. 1.. 1979). Su .... "1 "~"bru-s lripe " ch"" of eas/em Elm.rsia Bas;1I (K"rasik, 1974; K"f(uik. Rotlrde,u\'enskii. 1977 ; Plrillips el at .. /981) alld US N".,y arrol/wlI'te tic dala (Vug/el al.. 1979a. b; K()I'(lcS 1981; Fedel! et al., 1979: IIlId Taylnr el al.. 1981). In ereenlllltd· Non-,'''g;all Sel'. 8(J.ffitr Bay. (J.ud Eum.fÎa Basin. dOl/ed alld lIumbered solid litres denute (J./Iumalie.t due 10 ua-flour spreadinf,( wld II/aguelic re"usals : diagotlally slriped liues lire fruCI/"t tmtts. lJal/ed lines labl'Iled K . M. (md N refer 10 age-dis/utlt'I' {Jlms fur Kolbeinsey. Mohns. uud NU/.se" Ridgl's (Fig. 4). BOl h pOSll;"1' (sulid) umi ",rlla/I"e (dashed) Iinea/iOtIS (J.re sho"," irt Amerasi(J. Bajin; l'ume muy be due /0 l'url)' Tuliar)' (md Mesozoic sea·flour S{JrelldinK (t.g., Fig. 9). Possible "ff(I(:lufe Wlles" afe slloll'll by dill8ouull)' s/riped liues. Unea, tJ.Iwmalii'S be/ie"i'd to be assoôllIed ",illl cOnliui'lUal cruSI are dellO/ed b)' ba"ed liues. Sm(J.1I "Y" /mJ ",\1" .ilww locariolls of Yi',,,,lIk auJ ,"' a"is JrS"P lIuismit' JI/Ille/III .•' ( ~èdi'u 0::1 al.. 1979). short d istances - sugge sting ~ large numbcr of transform st udying the reconst ru.:tions. Sorne major points ti re the faul ts - ,lnd in many parts of the ~ re ~. including segments following: 01' the present spreading axis (Knipovich Rid ge). arc absent al logether. Such magnetic smoolh zones may be due in pari 1) The Hne of initi al rifting was segmented into incipient 10 Ihermal effects caused by the rapid sedimentation or to spreading cenlers and transform faul lS (for reference purpo other processes related to the slow and oblique spreading ses these faul ts and several addition;:.1 points have been geometry (Vogl el al" 1978). Il is also likely that Knipovich marked by capital letlers in Fig. 7). The lellgth o f the segments is Iypically 200 to 400 km . comparable to the Ri dge hil s changed its configuration ~nd at Jeast parts of it have rnigrateJ or jumped eastwards. In spile of the close spacing between major fraclure zones in the equ.llorial Atlantic and elsewhere. sptlced aero.nagnetic data ~nd other information. the plule lectonic details for the Greenland Se .. have not been worked 2) There is only weak evidence 50 far for pre-rifl struCtu re .~ OUI. col inear with. and therefore perhllp:, helping lU 10clIlize the incipient fracture zones. One example is what we here cali Dy contrilst the Jinelltion pattern in the Greenl and. Lofoten. Ihe Scorcshy fracture 'Ione: ("C" in Fig. 7) whîch when and Eurasia basins is s traighlforw~.rd in Interpretation. extended southeastwards rorms the norlhcrn edge of the Sea-floor spreading began du ring the re\'ersed period before Shetland platform. and upon further extension. continues anomaJy 24. i.e. sometime during the lime 57-58 m.y.b.p. o n into a series of bends in the fault pattern west of the Viking the time scale of La Brecque e/ al.. 1977 (a nomilly 24 on Ihe Americ.m flank of Nansen Ridge is shown by a "u" in Graben. Farther north. the Barents and Greenland-Senja fracture zones ("G" and "F" in Fig. 7) extrapolate "nor Fig . 8 : the same anomaly in the Greenltlnd·Norwegian Sea thwestwards" ;nlO minor breaks in the pre-rift magnet;c is depicted in Fig. 6 !rnd 7). Although some plate kinematic anomal y p:lllern. Dikes a nd lines of volcllnic centers in the models predict modest pre-anomaly 25 movement of Green Faeroes and the British Isles (Noe-Nygaard , 1974) are land away from Eurasia (Sri vastavtl. 197X : Phillips et lIl" examples of Paleocene structures with the righ t transform 1981). there is no magnetic or other direci evidence for such mO lion in the Greenhrnd-Norwegian Sea. However. if the trend. developed within continental crus!. But does th is small positive lineation near the Lomonosov Ridge is a volcano-tectonic trend refleet the Paleocene ~tress field or ~l!>o dceper, older continental st ruclUre~ ? This que:.lion spreading anomaly (Fig. 4. X). then the: separation of Lomo nosov Ridge from Eurasia occurred before S6 m.y.b.p. A rem ... in!> unanswered. curtographic<1l1y c,lreful reconstruction to the lime of 3) The incipient spreading axes in many cases parallel anomaly 24 - i.e. shortly afler spre'lding h'ld started _ is pre-rift !>tr uctures (Fig. 7). and thus may h~l ve bt:en conlrol ~ h own in Figure 7. Figure 6 is 11 reconSlruction 10 the lime led by them. One notable complication is the difference in of anomal y 13 (36 m.y.b.p.). Regional and temporal varia· structurtll Irend belween the Norwegian and Greenland lions in :.pre<1ding raie are shown in Figure 4. Regional sides of the rift. From C northward:. to H (Fig. 7). ,inti reçonMruetions and paleobalhymetry are shown in p;.rticularly from 0 10 F. structures on Greenland ,rnd ib Figure 5. Many inleresting observatio ns can be made by shelf Irend "north" whereas those on the Norwegian- 28 AEADMAGNETIC DATA AND AACTIC EVOLUTION ~ CL-r--~~~'T~~~~T'~~-'--,,-'~-r~=-o p. MIOCENE OllGOCENE EOCENE MAEST. AGE VS. DISTANCE TERTIARV CRET. . ~ ____~ ____-L ______L- ____~ ____~ ______L-~ __~ --" o 10 JO JO "" sa 60 10 "'.Y.a,p. Figure 4 Age ".1'. di.çla.rce plolS for Kolbein.'ie}', Mohl1 s. llI1d NOIrse.r ridge.f (stl' Fig, J). AI'crage spreadil1g halfrales are enlered alo/lg /lraplr segmelllS. NOIe Ihm if lil1 ear mlOmafy "X" ( Vogt ct ~I., 1979a, b) ;.1' of sM·floor spreadil1g I}'Pe, Ihe EUf/uia Basin beRan /() open ne/If lire Crelactol/s· Tertiary Rou,rdar}' (Wilhill stippled band), From Vogl, ct fil. (/981) /urd based 011 VOS' ct al. (1979 a, b, /980), uud Talwmli uud Eldholm (1977J. Figure 5 Poleobfllh)'me/ry al 42, JJ. 2(J. uml 9 m ,}' ,b,t" ",rd preSt'" bullr}''''elr)' in Cree,,'mrd·No""'J;im. Sea und Eurtuiu bllsh15. COIIIOl/ f,Ç ilr IOO',ç IIf "'l'fers lU 500 m illlen'u/. Damri/: Cfl/Sl ub"vl' st/l ll'l·el. m.d Jun Mayel! NidRe ut J3111.y.b.p. 29 P. VOGT. C. BERNERO, L. KQVACS , P. TAYLO R Figure 6 HUCIUS/Tllc/ioll 011 pO/ilf sureogr/lp/lk proje("lioll /0 fl/tolU/l/y 13 liml' (Jo m.y.h.p.). s!w,,·ülg major Il'elonir fealllru. maguf/h liuta/iOlls of 13/11:1.' mld aida. und II/aglle/ie llllo Harents shelf anu sueh structure!), a !), the Lofoten structural by li jump of the incipienl sprcading axb) or migrated high and NorwegÎlLn eo,lstnl struelUres from llbou t 61' to eastwards more gradually. In the laller case the continental MON trend ··northeast"·. T he Paleocene rifl axes from C to crust betwecn the Thulean volcanic" (KGH-K-S-H-S H) and F tend 10 foll ow the NorwegÎan. or · ·oorth-easterly" trenu. the Paleocene Tif! (A-B-C-D-E) would have been intruded producÎnB ,1 nmrked obliquencss between the structures in ;md partially covered by volcanic rocks .dighlly older than northcast Greenl,md. incluuing its shelL and the V~ring anomal y 24 but younger th::ln thc T hulean voleanic.... which Plateau csearpment and incipicnt Mohns Ridge (Fig. 7). lt are thern!),elves also not rn uch older th:tn anomaly 24. The t hu!), appc:,TS thal initial rifl ;ng followed a !)ol/lldar)' be tween graduai migrati on hypothesis is hard to provc sinee the two structur,tll y dissimilar province~ (wc note. howe\er. volcanic~ in question woulu bc found under generally thiek that · ·11o(\h·· or Grecnl:md trends are ,11!),o reprcsented tO Tertiary "nd Qualernary sediments. However. it i!. known sorne dcgree on the Eurasian side of the rift - forexnmple. that Faeroes volcanism did rnÎgrate in an eastward directÎon the Viking Graben. the central coa~t of Norway. the central (Noe-Nygaard. 1974). Cnledonian front. the TromsJol Ba!),i n. and the southern pari lntercstingly mosi Thulean vole:,nic lineament~ tend 10 of the Troms- Finnm;lrk fault zone). parai lei the NE or ··Norwegian·· ~truc tural trend. An 4) Thulean voJcllni sm (Noe-Nygaard. 1974). apparentl y eXlImple is the northern easi-Greenland vole;mics. from slightly olde r than anomal y 24. oceurred preferentially on south of Bontckoe I ~. (B) to Shannon Is. (S I-I ). ThÎ~ volea the Grcenland sidc of the line of initial rifting (Fig. 7). The nie lineament i~ closcJy pamllel to the V0ring Pl,ltea U present volcanÎç 30 AE AOMAGNETIC DATA AND AACTIG EVOLUTION Figure 7 f>% r-S ftrtogmpllic rI'CQrUIrUCf!cm / Q (/IrOlllfll)' 14/illllf (.56 m .y.h.p,) somr a/1er seo-/loor sprr:adill8 vtgwl. A/w mtlly 14 (md oldcr )'p"'adirl/;-lype wUlI/wlie,f /lfe vlflck (positi" e) wllereas pre- rift allomalies 011 ea)'t Oreellialld $lrelf are s/ippled. O/ller magne/le. Km,'i/)'. IIl1d slrucll/ml lilleu/luns. suvuerlt.' t ul/)' Terliury is neuru und Me.w:,oir e/.ri)' Tu/lfl f)' OllfcropS plOlled on ,.,t·ull s/ru r/iun fmm pl/hlica/IOIIS ine/lldinK tht follow;ng worts : EldhQl1Il and f'I,';ng (1 971), Eldholm (Jnd Sundr'o r (1980). EldllOl", alld T(l I"'(ln; (1977). Oa vrielsell alld Rumvers (1 979). CUirllUd et al. (1978). CrllnUr and Ta/"'uni (1978). Jllrgtnsen ulld Nm'res/ad (1 979). LurHn (1978). phl/Ups Ct al. ( 1981). Rm/lre.'ik (1979). S lIrld.·o( et Ill. (1 978; 1979). S ur/y !.: (1917). Suriy ~ et al. (1980). Ta/"'lIl1i (Illd Eldhalm (19 72 ; 1917) (Ill d TalJemus (1979). Larfi[e caf/ liai/mers A t1lrollgh J II/ark major olfse/s ur irreglllllri/ies in /rllet of jllilial brell!.: : P.P.Z" Filt rats PMe/lm: ZOIre .. S .F.Z . SlIl!Illl/ld F.Z ,,: O. J.M.F. Z .. Old Jmr Maye" F.Z." O.S. F.Z .. Orem/mld-Stnjo F.Z .: B.F.Z. . Bllrtlll .~ P. Z.; o/ld 1/. /".2 ., HortUllrrd E Z. A/o II g eas/ Gru lI/mld cOMI. smol/ mllitlll let/ers KCN dena/es KIl{l Cu .~ IIl Y Ho/m ; K . I( rmderdlugsslmq ; S. Sr:aresby S und ; B . Bml/e!.:"e Il/wul ; IIlId SH. ShwrruIII Islarrd. similar trend. There is 31 so 3 crude correspondence belwee n produced Ihe Greenland-Scotl and aseismic ridge. induding segments of the incipienl sprellding 3xis a nd segments of the pre ~ en l - da y Icelam! (Vogl. 1974 : see Vogt el al. • 19K1 for onshore voleanic linerunent!. : the southern pari of the review). A second. less polent Jan Mayen hO I spot is Faeroe-Shetland Escarprnent lies adjacent to the main bod y invoked 10 explain the outer V~r i n ); Plnteau and ilS escar of plateau basalu south of Scoresby Sund (S . Fig. 7) rllld pment. the EaSI Greenland volcallÎ cs from 1110 S H (Fig. 7) parallels the cOltstal dike swarm extending southwest from ,md . subsequcntly. such volcunocs as Vestcris lInd Eggvin S. The northertl part of the Faeroe-Shethmd Escnrpmcn1. banks (Vogi el (II .. 1981). Two addiliolllli hOI spots have cast of wha! would later become the separme Jan Mayen been idcnlified weSI and north o f Greenland : in both cases Rid);e microcontinen1. corresponds to the moslly non-voleu Ihe carliest known activity is Paleocene as weil. T he Disko nic segment 8 -S of the Greenland nmrgin. The VI!1ring hot spot. now extinct. is credited wit h subllerial ~l s 'lll s of Platelw Escarpment parallels and corresponds to the voka Baffin Island (Cape Dyer) and Disko Island-Svartenhuk nie lineament B-S H. S H and E mark the northern limits of (Keen. Clilrke . 1974). Subsequenlly Ihis hot spot produced cast Greenland Thulean basalts and the outer Vôring the basement rise below Ihe Davis Straits. A variant o f the Phltcau , respecti vely. hot spot hypothesis is due 10 Talwani and Eldholm (1977) Hot spots provide one possible explanation for Ihe paltern who envisl.ge one extensive Icellind ho t spot responsible for of escrrrpments and Thulean vokanism. The Iceland hot the Iceland. Jan Mayen. and Disko Island volcanie provin spot , centered in the area around 8 . would have caused Ihe ce s. 80th hypolheses would allribute the cOncentration of VOICllllism from KGH to S on the Greenland coast. in Ihe initial FlIeroe-VJ1ri ng area VOI Cllllism on the Greenland plate Faeroes. along the Fr.crue·Shetl and EscH rpme nt . Hnd in the to the hot spots' initi:.1 locll1ion under Ih:11 plaie. British Terli,uy province. The sarne hot spot subsequenll y Off nnrther" Greenland the Yermak hot spot produced the 31 P. VOGT, C. BERNER a. L. KOVACS , P. TAY LO R Kap Wa ~ hin gto n basal ts, lower Tertülry tuff ~ on Spi hber Basin (Fig. 5). This is the firsl paleobathymetrie ehitrt for gen. the Yermak and Morris J e~up It ~e i s mic ridges (pla the Eurasia Basi n ; in the Greenland-Norwegütn Se;1 we Ceel teaus). and a h;gh magnetic-amplirude zone o n the late the charI!> in Figure 5 are somewhOit more acc urate Ihan the Terliary crust of Ihe Nansen Ridge (Feden elal., 1979). The rather simil ar one~ published by Grjjnlie (1979). in IXITI Yermak hot SpOI would ha ve been located in the area beca u ~e crustal ages cou Id be specified more aeeurateiy between point 1 and the Kap Washington basahs (C\V in from the delailed magnelÎ c data. but primarily becau<;e our Fig. 7). model ineorpor..lIes the effects of sedimenlation. As a first One difficul!y for the hOI spot hypolhesis in il S si mplesl approximation B~rnero assum ed thm the relatively sedi form is that Ihe Jceland. Jan Mayen. Oisko and Yermak hot ment-Slarved basins on Ihe American side of Ihe plll\e SpOIS 32 AE AQMAGNETIC DATA AND AACTIC EVOLUTION Fillu re 8 Rtsidua/ magn(/;c UlIQma/iu (positi,·t. block) p/OfftJ (.'/ung /light truds /.md .mpupostd on GEHCO bllfhyfltttric t'lw,., (Juhns"" el al.. 1979). Mnf.:nttic pralilts Io·t,... hiJ.:h-pun liI/l!!rtd 10 rtmarl' diurnal "orio/ions and Q/ha /ong-"·ol·tltnglll fGRr' 'tsidunls (Kol'acs el al .. 1981). L"II"rs " a " Ihrough "..," '''la /(} It/llu'I's discunl'd ln l U I. cruSI under the Amerasia fi :!sin formed by spre'lding sorne major transform fault În the opening of the Amerasia Basin. lime in the j ura s~ i c orcarly Cretaccous (Grantz l'lui.. 1979 ; Herron el al .. (1974) suggested that the Kolymski area. now Joncs, 1980: Churki n. Trexler. 1980). part of eastern SiberÎ'I. rift ed away from Arclic Canl.Ja and Despite an approxim'ile conse nsus on the timing, there subduction zone 10 the Roc ky Tt\(' Amt' rasia SpMnochasm models MountaÎn Laramidc Thrust. Grantz et al. (1979) favor an opcning geometry similar 10 Another North Slope tr:msform model i5 that of Joncs that originall y proposed by Carey (195l:1). AeeonJing to thb. (1980), who vicws the North Siopc margin ("Beauforl model in ib origin,ll rorm. the e ntiTe Amerasia Basin opened l..;lp tev (ault "') as originally a conlinu:tliun of the Tinlina as :1 roughly triangolltr-shapcd rifted basin with an ape" in fault. T he Alpha-f..l endeleev Ridge i!> proposed by Jone ~ to northwcstcrn CarHld ll . Gra ntz el (II. (1979) infe r li pole of have becn an active sprelldÎng center connecled to Ihe opcning at 69.1 "N. 130°5 W. According 10 this "Amerasia Beaufort-LuplCV tr:msform J uring the J ura s!> ic and E •., ly sphenochasm moder" both the Siberian-Alaskan and the Cret;J eeous. Subsequcntly, in the Lllle Cretaceous, righI C:madian continentl.1 nmrgins would lx: of the riflcd (Atlan laierai slrike Slip motion along lhe Kal tag !ault displaced the tic) Iypc, and any magnetic anomalÎes due to sea-floor Tintina from the postulatcd Be,lufort-L:lpte v (:luit by spreading should form a fan shaped pattern genemlly 500 km. The KlllIllg hmlt i! self continued along the Arctie pcrpcndicular to the LOlllono!>o v RiJgelEurHsi:l Basin. An Canadian margin. In the Jones (1980) mode!. the Canada ex ti net spreading a",is (fossir rift) "hould exi!> t in the miJdle Basin cruSI Wll S Icft unaffe Cled by these events and is of thi ~ fan-s hapcJ magnctie anomaly panern. Using only pi elured as alrcady exbling in the Permo·Triassic. Jones gravit y data, Granlz el (II. (1979) werc the fi rst tO identi fy an does not adress the arguments .. gainsl the Al pha Ri dl;e extinC I axis in the Canada Blisin. However. the geologic ;md having becn :t sprclldi ng center (e.g .. de Laurier, 1978). paleomagnetÎc evidcnce advanced by them ill ~ u pporl o f the Alllerasia sphe nochasm model (e.g .. Newman et (II .. 1977) has been questioned by Churkin and Tre"ler (1980). Th" l'acllie mlcruplale model Churkin and Trexlcr (1980) propose Ihat Ihe Arner:lsia Basin The North s l (l~ Ir llll.~ f tl rm mudels rcpresents a pari (or parts) of the Kulll (prolo- Pneifi e) plaie Scveral plate tec lo nie mo.lel5 have becn proposed in which wh ich was e ut off and isolated by complcx processes of thc Alaska·East Sibcrian conli ne nl al nm rgin aClcd li S a plme conve rgence and microplate aceretion. Thi s hypolhc- 33 P. VoGT. C. BERNERa. L. KQVACS. P. TAYLOR ~ i s makes no specific predictions about the geometry of Canadian side where the f1ight separation is comparable 10 oceanie crustal structures in the Cilnild~ Ba~in . However. anomaly wavelength (Fig. 9). The locations and trend~ of the authors' suggestion that the Alpha-Mendeleev ridges fraclUre zones offselting thc~e linealion.. are similarly rcpresent a fold bell caused by subnmrine collision be tween somewhal conjeclUral. Al though inlerprelations of the the Eurasia and Kula plates places sorne geomctric con· magnelie data of Figure 9 may vary in details (compare ,trainl~ on the types of structures (and perhaps magnelÎC Fig . 9 of Ihis paper with Fig. 2 of Taylor el al.. 1981). the anomalies) in the area of these ridges. Furthermore , if first-order magnetie tcctoni c fabric of the southern Canada oceanic crust now in the Amerasia Ba ~ in was formed in the Basin nevertheless now appears delinealcd. Pacifie substantially to Ihe south. the magnetic anomalies The age of the magnelic IÎneations is still uncertain ahhough wuuld probably exhibit grealer skewness and lower ampli· the probable Jurassic or Early Cretaceous age of the ba~in tude Ihan would be expected if Ihis crust h;ld formed ~t high makes il very Iikely thatthe lineations represent part of the latiludes. Keathley (M) series of geomagncl1c reversais. The Keathley reversais (Vogt. Einwich. 1979) occurred in the period 11 0 to 155 m.y.b.p. (laIe Callovian 10 mid·Aplian). so the age of the Canada 'lasin crust probably lies somewhere within this AEROM AGNETIC TESTS interval. This would be consiSlent witb age~ independently deduced from borcholc dala and surface geology (e.g .. Keeping in mind the h ypo t hè~e~ outlined above. consider Granlz el a/" 1979). Taylor el {lI. (1981) proposed tlO now the acromagnetie data as a possible leSI (Fig. 2, 3. and identificillion for the Canada Basin anomaly pattern. 8·10). A~ discussed by Taylor el al. (198 1). Ihere are in the Acçording 10 them the spreading lasted approximately (rom Amer.tsia Basin al least IWO areas of linear magnelic 15] m.y.b.p. (anomaly M·25) to 127 m.y.b.p. (anomal y anomalies. suggeslive of sea-noor spreadingand geomagne M-12), or late Jurassic to carly Cretaceous. Certainly other lic reversais: the southern Canada Bilsin and Ihe centml correlations wilh the Keathley Sequence are possible. For Makarov Basin (Siberia or Fletcher Aby s~al Plain). example. if the axial magnetic low (Fig. 9) represenls the ln the soulhern Canada Basin anomalies with ilmplitudc ~ of reversed inlerval M·3 the Canada Basin could have bcKun 10 il few hundred rIT peak·to·trough. Iypical for Mesozoic form in the early Crelaccous. il time favored on geotogical oceanic cruSI formed in mid · or hi gh.latitudes. strikc north grounds by Sweeney (1980). In any case, the existence of in the central parts of the basin but morc northeastcrly in the spreading-type Iineations rules out lhe suggestion of Herron marginal zones (Fig. 9). The northerly trend is çonvincingly el (JI. (1974) who Ihought the basin was formed during a time exhibiled by a broad magnetic negative flanked by two of few or no reverSlils (180·150 m.y.b.p.). Wherctls ,j narrower highs. The bro..'ld neg,lti"e was suggesled 10 Keathley O.. i·Serie ~) age for the Canada Ilasin crust i5 represent a fossil axis of sea·floor spreading (Taylor el al" probable. we cannol be cerlain Ihat the obscrved l in eation~ 1981): limiled gravit y data from air-lifted ice-floc ~ Iation ~ do nOI belong 10 a more ancient reversaI sequence. ilS reveal li .... 25 10 + 50 mgal Free·Air high (Fig. la) çoinci· implied by the model of Jones (1980). ding with the main. central segment of the extlnct aXI' The somewhal fan·shaped anomaly pattern in the cenlrfl J indieated in Figure 9. The exiMence of this gravil y anomaty Canada Basin (Figs 9. la) .md extinct axis is consistent with lends credence to the sugge5ted extinct axis. Presumabl y the Amerasia Sphenoch;lsm Model (Carcy. 1958 : Grantz el the ba scment topography responsible for the gravit y high a/. , 1979: Taylor el al .. 1981). However. there i~ no lies entircly buried bclow thick ~cdimcnt~ known tu exi ~ t magnetic or olher evidence for a cOirlillllOliorr of Ihis pattern bclow the Camlda Aby~ s[1 1 rlain (Grant:l. el al .. 1979). northw'lrd towards and across the Alpha-r.,·lendeleev RidBC Lineations on eilher side o f the cxtinCI central rift zone (Fig. 8). Admiuedly the aeromagnetic f1ight !racks nOrlh of become more northeasterly in trend. paralteling the North· 76 Q N run parallel or sub·p;\nlllcJ to any such pallern and wind Ridge and the Ca nadian margin. The northea ~ terl y therefore are poorly ~ uit ed tu tC ~ 1 the Amerasia ~p heno · anomaly trend is ~omewhat deOOI~ble. p~rtkularl y on tbe chasm model in ilS original form. Of course. if the At phn Fij;ure 9 /...... Residrurl ",agut/Ir Iinta(;'mS.l·ul;I;f$ud "(lrrtlU/if/1l ...... - linu and /ranl,·tr~r fraefllfu (dlJlud) and nl/nel spt(ldi"l1 axis (Ihid: lint) in Canada Ba~i" . Ba/Ir }"' ...... IIIf lrie ron/Ours in IIItIUS. Su alsa Ta )lur el al (1981). 34 AE AOM AGNETIC DATA AND ARCTIC EVOLUTION Figure 10 GrUl'il )' me fJ)· " rf'm e '!l .~ (d oh") {m d 25 mgal F ree-A ir fU lOm"/}' cmll()lIrs. Su/id ,,/Id da.dlfd fill es (Ire mugI/fa ,· wlfJmu/)' cor rflm ;ul/ s uml /l rtI/iond jm" /lires jfl!m Figure 9. OUlltymelric Cflli /O/IU ill me/ers. Set a lso TUY/fl r el ,,1. (/981). Ridge is continental in nature, the fa n-shaped pattern would Borderland block had begun to move away, along a North be expected to continue only to the boundary betwee n this Siope transform fault (e-S., Herron et al., 1974), the plate ridge and the Canada Basin crust (e .g. Sweeney, 1980 ; kinematic pallern changc:d and the axis of spreading became Johnson et al .. 1978). It is al so possible that such a reoriented to its present oblique co nfigurati on (Fig. 9 , la). continuatio n once ex isted but WOlS subsequently overprinted Although we prefer this interpretation - implied by the or erased by the tectonie or vo[canie proeesses that formed lineations and fracture zones proposc:d in Figure 9 a nd 10 - the Alpha-Mendeleev Ri dge. more detailed aerom.,gnetie dat., are needed to establish We have not yet criticalJ y examined the skewness and bc yo nd doubt the pattern of 'Inomalies along the margins of amplitudes of the Canada Basin magnetie lineations (Fig. 9) the Canada Basin. as a test for the Pacifie microplate hypothesis. However. Anoma[y amplitudes are not low throughout the Canada whe n a lJ owance is made for 4 to 5 km sed imen ts in the Basin but increase irregularl y as the Alpha-Me ndeleev central Canada Basin (Grantz et ai. , 1979). the low anomal y Ridge tS approached from the sout h. It is uneertain how the amplitudes observed Ihcrc (150 10 250 nT peak-Io-Irough) extinct spreading axis continues northward beyond the area resemble those of Keathle y anomalies in the western Nort h of Figures 9 a nd la. It was suggested thm the lineations At lantic, present latitude 30"_35G (Vogt . Einwich , 1979) and extending towards the lower right from point "' i" (Fig. 8) paleo -Iatitude 20"_ 25G N (Irving. 1979). White thi s observli mil )' belong to the M-Series (Vogt el (li" 1979 a ) and tio n is in qualitati ve agreement with a large-seale northward thcrefore fOT m a contin uat io n wit h the southe rn Ca nada displaeeme nt of Canada Basin crust (Churki n, Trexler_ Basin anomalies . Additional data arc ncedcd to establish the 1980) there are many other fa ctors that influence magnetie re lation between these anom;ll y patterns. anom.,ly ampli tudes (e.g" Vogt el (II .. 1979 li . h ). Further more , the existence o f ~ l fossil spreading r.:e ntcr between the Chukehi borderhlOd 35 P. VOGT,C. BERNERa, L. KOVACS , p , TAYLOR now_exlinct axis roughly bisecting this basin during the time generated oceanic pla teau. like Ihe Shalsky Ri se and Ontong period 80 to 47 m.y,b.p . (a nomal y 19 10 34) at a half-rale of Java Plmeau in the PacifÎ\.:. or the Greenland-lceland-Faeroe O.!'!5 clll/Yr. The observed fan-shaped anomaly panern Ridge. Azore~ Plateau. or Rio Gnmde Ri se in the Atlantic. (Fig. 8) would then mcan that the amount of opening Ali these features have d imensions of the same magni tude decreased from the Siberian side toward the North Ameri as thal of the Alpha Ridge (4()O km x 800 km , with il can side. If tht: Alpha-Mendeleev Ridge was !>ome type of topographie lmomaly of about 3.5 km with respect to subduction zone (Herron et al.. 1974 ; Churkin. Trexler. average C ret aceou~ oceanic crusl). 1980). the Makarov Basin may have becn its corresponding 4) The Alpha Ridge could also have origi naled by plaie back-arc basin. The proposcd accreting plaIe boundary W,tS convergence (Herron el {II" 1974). perhaps like Japan or the connected to the Labrador-Baffin rift and the Greenland Lord Howe Rise (Taylor. 19711). The limited M~ i ~mic refrac Norwegian Sea rift in sorne way not yet underslOod. tion data (Hunkins. 1% 1 ; 1962) do not support Ihis hypo One difficuhy with the Taylo r el al. (1981) hypothesis is thllt thesis. and no arc-like ros ~ il trench or volcanic chalns arc one of the most prominent positi ve Iineations (jUSI 10 the [dt apparent from existing data . The existence of a median of point "8" in Fig. 8) follows ,1 line of seamounts (the rift-like va lley (Vogt el al .. 1979 a ) is also unexplained by Marvin Seamounts. previously referred to as the Marvin this hypothesis. unless the valley is reinterpreted as a fossi! SPUT; see Sobczak. 1977). The magnetic lineati on may trench or ,Iburtive intchlrC spreading eenle r. The onl:lppinfl therefore be a topographie or structural effect rather than a relationship be lween Makarov Basin sediments and the sea-floor spreading lineation. il could be that the Marvin Alpha Ridge seems more in line with the "spreadi ng ce nter" Seamounts represent the summits of rift mountains than with the "subducti on I.o ne " hypolhesis ( O ~ten~o. associated with the extinct Makarov Basin axis. now largely Wold. 1977). buried under thick sediments (Ostenso, Wold. 1977 ; Blasco 5) The Alpha Ridge could repre!>ent a region of plate el ul .. 1979). However, this is unallractive because the compression and deformation nOI like eil her an Andean or scamounts and assoeialed anomal y do not correspond to an an island-arc type convergence zonc. This is a purely ad hoc axis of symmetry either for the entire lineation pallern or hypothesis since no such convergence I.one has elsewhere for the Makarov Basin. Another difficult y with Ihe interpre been idenlified in an oceanic aren. tation of the Makarov Basin as a simple rifted basin is the grcat difference betwecn the topography, magnetic anoma 6) T hc Alpha Ridge could represent ., ~ ub s idcd, perhaps lies, and crustal struct ure of the Alpha-Mendeleev and thinned shield (Ki ng el (I/.. 1966). The long-wavelength Lomonosov ridges. If these two (ea tures are fragments of a magnetic anomaly over the Alpha Ridge is similar to what is once continuous continental massif (Johnson el al .. 1978; observed over continental shield s (Cole !> el ,,1 .. 1978). Sweene y. 1980) o ne should expecl sorn e geophysical simila Again. the subsided shield hypothesis is inconsistent with rities between them. sparse seismic refraclion ,md surface wave studies (l'Iun kins. 1961 ; 1962) and it doe!> not explain Ihe ex istence of a crestl,1 vll ll ey. THE ALPHA-MENDELEEV RIDGE 7) T he aerornagnctic dulu do nOI rc veal simple line,lI ions of the sea-floor spreading type. In the best-known part of the Alpha Ridge crest the "centr<11 vil lley" and flanking ridges The Alpha-Mendeleev Ridge complex has becn the object of correlate with a magnctic lo\'.' (""" in Fig.!'!) flanked by much speculation over the last decude (e.g .. Vogt, Ostenso. highs (Vogt el (/1" 1979 (l). Thc!>e observ:Hions suggest that 1970; Vogt. Avery, 1974 ; Herron el (l /" 1974 ; Swt!ency. a highly magne ti zed (norm.rl pola rit y) ba~ementlOpo gr;t ph y 1980). Sinee the US Nnvy aeromagnetic datn extend ol1ly to - r;tther than bands of ahernating polarity - is responsible the junction betwecn the Al pha and Mendelee\' ridges. we fur the ohscrved llnorn alics (the IWO sharp. ell ee"elOtI shall only discuss the Alpha Ridge here . However. it may magnetic low~ below point" e" in Figure 8 may represent weil be that the two fealUre!> "re o lll~ one. in which ca .. .: the exceptiona! strips of reversed polarity,. The rnagnetic following discussion also applÎes 10 the Mendeleev Ridge. anomaly pllttern is not inconsistent with the hypothesîs that The origin of even the Alpha Ri dge still remains conjectural the Alpha Ridge i ~ an occanic plateau - an ancient Iceland despite the large volume of ncw detailcd acromagnetic data - formed during li long periml of normal pol,lrity such as (Fig. 8). which rcveal irregular anomalie !> of hÎgh amplitude the mid-Cretaceou<;. Magneti c anomalic!> on !celand (lnd the (500 to over 1.000 nT peak to trough and var i ou~ irregular 10 Ice land-Faeroe Ridfle also exhibit gre,ll irregularity a nli high sublinear patterns (Fi g. 3). We summarize our Inferences amplitude!>. about the Al pha Ridge under the fOllow ing ten points: 1) The thick cover of sedi ment (400·1 .200 m). the recovery 8) However. neither b the magnetic pattern tlver the Alph,l of Eocene and Maaslrichtü.n sediment from the ridge crest. Ridge necesSlJril y inconsistent wilh the "compres sion/subduction I.o ne" (Herron el al" 1974 ; Churkin. and the absence of sei~m icit y ail ru le out the hypothe ~is th,.t the Alpha Ridge is an active plate boundary of any type. or a Trexlcr. 19HO) and "~ubsi ded shield " (King el (I I .. 1966) hypothcses. One should expcct anomalies evell over a Tertiary axis of sea-floor spreadîng (de Laurier, 1':17~ ). complex îmbri cate subductiOn zone toexhibit sorne regiona! 2) The shallow present bnsement deplh (2.900 .:.. 500 m lineation) çorresponding tO volcanic arcs. trcnches, back after Îso~tatic correction for sediment loading; de Laurier. arc basins. and remnant arcs. No such regionlll banding b 1978) rules OUI the hypothe~i ~ that the Alpha Ridge i ~ a observed. If. on the other hand. the Alpha Ridge b Il typÎcr,1 aecretion axis extinct since Mesozoic or earlier ~ ub !>i ded shi eld. one should e xpect !>ome m:lgnetic similarilY times. because subsequent thermal subsidence would have to adjacent. presumably o nce contiguous continental essentially reduecd the initial "ddge" form to zero. This fragme11l s such a~ the Chukchi Plateau, the Lomono~ov point has been made repeatedly in the literalUre (Vogt. Ridge. and Ellesmere b land . However. Figure ~ a~ weil il!> el al .. Avery. 1974; Herron 1974 ; de Laurier. 1978). Soviet (Kanlsik, 1974) :lnd Canlldian d,lta (Coles el (I I •• 1978) 3) The age and shaJJow basement deptn do not rule out the ~how lillie or no similarilY belween rnflgnet ic anomalies of hypothesis that the Alpha Ridge is an ancien! hot ~pOt the Alpha Ridge and those over adjacent cOOlinental 36 AEAOMAGNETIC DATA AND AACTlC EVOLUTION fnlgments. Only at "c(' (Fig. 8) i ~ a magnetic anomal y ln view of the wide variation in crustal :.ge. composition ;md round IhM carries the Alpha Ridge trend across the conti structure of continental çrust. the variety in magnetic nental shelf loward the coast of Ellesmere bland. expression of shelves and continental fragments is not surprising (Fig. 6-9). 9) Cardul examination of the anomllly pattern (Fig. 8) suggeSls a set of parullel "fracture zones" disrupting the On the wide shelf cast of northern Greenland. remarkably anomalies along a !rend parallello 170"W . roughl y the same linear anomalies strike nO fth la north-northeast . parallel ta trend as the Mendeleev Ridge and Chukchi BorderlamJ adjacenl coastal topography and inl and structures including (Fig. 3). The fractures . if real, extend from the Makarov the Caledonian Front (Fig. 7). T he anomaly sources lie Basi n across the Alpha Ridge and into the northern Canada buried up to la km below sea level according 10 our Basin. The Ire nd of the " fractures" is significantl y oblique magnclic source depth calcul ations. The eaSI Greenland to the topographic fracture trend (parullel to 142°W) inferred shelf is there{ore underlain bya Ihick sediment-filled OO sin. by Hall (1973) from scauered ice-island and submarine The anom:\lies presumably refiecl magnetization contrasts soundings. Il is uncertain whether the sublle trends in the wit hin rocks of Caledonian and/or Pre-Cambrian age. II is magnetic data reprcsenltrue transforrn faulls. Several line;\f not known whether there are correlati ve seismi c structures anomalies extending towards the lower right Crom poi", ,. (' and gravit y anomalies. The cast Greenland shelf anomali es (Fig. 8) parullel the "fracture" trend. arc nOlably oblique to the trend of Paleocene rifting except in li small area betwecn the Barents fracture zone (BFZ : Apart from the suggested " fractures". the magnetic anoma poi nt G in Fig. 7) and the Greeniand-Senj'I F.Z. lies over th e Alph:\ Ridge and adjacent parts of the Clmada Basin are generall y at least subparallelto the regional strike Less regular palterns of magnelic lineations lie along the of thal ridge. Overall the patlern is quite chaoti c and Norwegian margin and in the western Barents Sc:! (Fig. 7). lineations of di verse trends can be found (Fig. 3.8). How Correlations with gra vi t y anomalies and seismically deter ever. track spacing is in some areas too wide to permit mined structures :.re the exception rather than the rule. reliable correlation of shorler-wavelength anomalies from However, the magnetic anomalies do generally parallel the one track to Ihe next : furlhermore , lineations paraUe!to the other geophysical trends lInd coastal structures. lInd proba Irac ks wcre fihered from the datu set 37 P. VOGT, C. BERNERO . L. KOVACS , P. TAYLOR were once colinear, their present displacement (250 km) ,;nomalies may be associated with the boundary between allesting tO the cumulative sinistral displacement of Elles continental and oceanic crust. mere Ishmd with respect to Greenland. Three difficulties with this Interpretation are ; 1) a 150 km gap remains The Alaska continental margin .md shelf was overflown on only a few flights. and the orientation of the tracks is between 0 and n even after the lineations are brought into alignment; 2) the tineation III-II may be an ;tTt ifact of unf,lVOnlble for detecting anomalies paraJle!ing the marsin fortuitous arrangement of the irregular, high arnpl ilUde (Fig. 9). The anomalies are low in amplitude and long in anomalies associated with Ihe Morris Jesup Rise; and wave lenglh , consistent with seismic studies tha t indieatc at 3) independent evidence for a displacement of this magni least 4 to 8 km of sediments (Grantz el al.. 1979). tude is inconcl usive (Brook. 1980). A magnetic smooth zone is found over mueh of the Lincoln Sea (w in Fig. 8) and appears to be associated wilh a CONCLUSION seaward extension of the N~;res Strait (Wegener) transform fault. Magnetic source depths are about 5 10 10 km (Kovacs. 1981 ). but the type of crust below this marginal smooth zone The large volume of new aeromagnetic data from high-Iati is unknown. If this smooth zone (w) describes the ex te nt of tude ocean basins has now been mil ked for the more transform mot ion at sea. then the zone of shear must be straightforward concl usions. Even without additionaJ geo much wider (100-200 km) than the Narcs Slrait portion of physÎCa l data. the plate tcclOnic evolUlion of the Greenland the fault. Norwegian Sea and Eurasia Basin is now re.tsonably weil The Lomonosov Ridge was overflown along a short section established. Frustrating complexities remain . for eX 38 AEROMAGNETIC DATA AND AReTle EVOLUTION REFERENCES Bf:rMf'l) C.. 1981. Terliary paleobathymetry of thl' Joneo; P. 8 ., 1980. Evidence from Can.'1da and Alaska On plate NorwegianiGtel'nland Sl'a and Eur:.sia Basin of the Arctic OCelln. tectonic evolulion of the Arctic Ocean Basin. Na/urt. 285, 215.217. M. Sri. Tlrtsir. Uni.'. OMo/w mo. J .., r&ellHo F., Nllvrt!itad T., 1979. Mai n structural clements and Bla_ S. M., Hornhllid B. 1)., 1.ltwl5 C. F. M., 1979. Preliminary sedimenU!.ry ~ u ecess ion on the shelf ouuide Nordland ( Norway). resulls of surficial geology and geomorphology slUdies of the Norwegi .. n Sc:a Symposium. No' ...'. Pf'I . Soc .• Oslo. NSSllI , 1.20. Lomonosov Ridge , Central Arctic B:.sin. in : CUITent research. Part C, Gw/. SUT\! . Can .. 79·1C. n·83. KIIT1lSlk A. l'II .• 1974. Yevrazisikii bassein ee\"erno~o ledovitogo okeana ~ po:dtsii tektoniki plit, in : PrQblmri Ge%gii Polynornikll Rrook J . N., 1980. Nares Suait debate ends with no bUL Oeotillles. Oblasltl Ztmli. Leningrad. Nidra. 24.31. 25 , 21·2). Carey S. W., 1958 The orocline concept in gcotcctonics, R. Soc. KlltIIslk A. M., R o~ hd es t ~ensk l S. 5.,1977. Struktura osi razraSHl . Tasmania Pop . Pmc .. 119 , 255·288. Iliya okeanicheskovo dna i l.akonomernosti yeyo formirovaniya (na primery riftovio 7.0ny severo·atl antÎCheskovo melabasseina). in : Churkln M .• Trellier J . Il .. 1980. Circum·Arctic plate aecretion. Osno~nie rll'ogtnfZo. edÎted by N. A. Logachev. Novosibirsk. isolating pMt of a Pacifie pl ate to faTm the nucl l'us of the Arctie Nauka.167· 175. Basin , E(lrrii Platrel. Sei. Ltl/ .. 411 , 3.'i6-362. Kllrulk A. M., Gutrc:vlch N. 1., l\.lIIsolov V. N .. Shcht loHIAOV V. G., Cole$ R. L., Hann. tord W., l''oin~ G. V .• 1978. M"Gnetic anomalies 1971. Sorne fl'alUre S of the deep structure and genesis of the and the evolution of the Arctie. in : An·tk Gtoplrys. Rev .. edited by Lomonosov Ridge based on dau< of ai rbornc magneti c s urvey ~, J. F. Sweeney. Pub. E"rth Physics Br.tneh. Dept. Energy. Mines IInll Re sources. Ollilwa. Canada, 4S, 51-66. Geolh. Me'ody rUl l'edkl l ' a,ktike (in Ru ssian). 6, 9.19. de l ..a ur ~ r J .. 1978. The Alphll Rill ge i ~ not a sprl'ading centre. in : Ku n M. J ., Clarke D. H.• 1974. Tertiary basahs of Barrin Bay : Artlie Gtoplrys. Rtv .. ellited by J . F. SWl'l'ncy. Earth Physics eochemicaJ evidence for a fo~ s il hm·spot. in : GeodYllamics QI Branch. EnerilY Mines and Re sources Canlida. Ottawa. Canada. lee/and and the Nonh Allan/le Arca. editcd by L. Kristjansson. 454, 87·90 . Oordrecht , Holland. O. Reidel Publ. Co .. 127· 137. Eldholm O., E"'lnS J ., 1971. Marine geoph ysical survey in the Kln k E. R., Zllttz J., Alldredkt L. R., 1966. Magnetic data on the soulhwl'Slern Barents Sea, J. Geophys. Rts. 76. 3832·3841. structure of the central ArctÎc region. Geo/. Soc. Am. Bull., 77, 619-646. Eldholm O., Sund"or E., 1980. The continental margins of the No",,·egian·Greenland Sea: Recent results and Olltstanding pro Kovaa L. C., 1981. MOlion along Narcs Suait recorded in the hlems. Philos. Tran,. R. Soc. London. 294. 77·86. Lincoln Sea : aeromasnclic evidenee. submincd for publi cation. Eldhllim O .• Talwanl M., 1977. Sediment dislribotionand struclural KO"lIa L. C., Pilgu R., VOllt P. N., Taylor p. T., Johnson G. L., framework of the Harent! Sea, GeaI. Soc. A.m . Bul/ .• 88. 1015·1029. 1981. Aeromagnetic and teetonic c hart of the ArClic Ocean rcgion. Geol. Suc. Am. Map Su., in press. Feden R. Il .. Vogt P. R., .·~ m l n ll H . S .• 1979. Magnetic and bathymetrie evidenc!: for Ihe " Yermak" hot spot northwest of Krilitoffersen V ., T.I... a",] M .• 1977. Extinct triple junction south of Svalbard in the Arctic 8 asin, Eanh Planer. Sei. Lm .. 4, 18-38. Greenland and the Tertiary motion of Greenland rdative to North America. Gco/. Soc. Am. Hull .. 88, 1037·1049. G a br ~lst n R. H., Kamlleril l. B., 1979. Fracturl' pal1erns in Norway from Landsat hnagcry : results anll potential use:, Norwcgian $ca LarBrecque J . L.. Kent O. V .. Cande S. C., 1977. Revised magnetic Symposium . Oslo. Norw. Soc .. N55n3, 1-2 8. polarity lime SCille for late Cretaceolls and CcnOl!oic time , Gtology. "t'. 5, Ho-33'. Galraod H., Jacquarl (i., Auberlln F., fl.euzart P., 1978. The Jan Mayen Rid~ : synlhesis of Geological kn owlcdge and new dala. Larsen H. C., 197H. Offshore cont inuation of East Greenland dyke Oc~ano/ . A. rta. l , 3. 33'·358. swarm and North At lantic Ocean formation. Nature. 174, 220-223. Grantz A., EIUrdm S., OInler 1). A., 1979. Geology and ttetonic Le Plchun X. , Sibuet J . C. , .·ranchelea u J ., 1977. The fit of the development of the continental margin north of Alaska. Tee/ono continent s around Ihe North Atlantic OCl'an. Teetrlnopilysie.f. 3H , p/ly$Îcs. 59, 263-291. 169·209. Gr.,nlie C; ., 1979. TertiHry palcogl'ography of the Norwegian· Mioster J . B., Jordlln T. H ., Un8. l'r e~e nt ·day plate motions. J . Greenland Sea , Norsk ra/orins/. Skr., 170, .9-61. GeQplrys. Res., 83, S33 1·53S • . Gr/il nl le G., TlIl wll nl M .. 1978. Geophysieal atlas: Norwl'gian· Ne "'lII l1n G. W., Mull C. G. , Wlltklns N. U., 1977. NOTlhern Ala~ka Greenland Seu. Vema Re s. Ser., vol . • . Lamonl-Doherty Geol. paleomilGnetism. pl:.te rotation, and teclonics (abstr.). A/u~' ko Geol. Obs .• New York. 26 p. Soc. Symp .• AnehorrlKC. A/o.fka, 16-19. HIIII J . K., 1973. Geophysical evidence ror ancient sea·floor sprea· Not·Nygurd A., 1974. Ceno1.oic to Recent volcanis lTl in and around ding from Alphll Corllillera and Mendeleyev Ridge . in : Are/ie the North Atlantic Ba ~ in . in : Tht 39 P VOG T.C. BERNERO. L. KOVACS. P. TAYLOR Kupptl H. O., Mdl~ndt~ A. G .. 1976. Free-air gravit y anomal~ T.)lor t'. T ., Koucs L. C .. Vogt P. R .• Johnwn G. I... 19111. map of the ea~te r n Chukchi and southern Beaufon Sca~. USGS l)elailed aerornagnetie in,e~ l ii;a t ion of the Arctic Basin. 2. J. Map MF-1I1S. G~ophys. Ru .. in prc: s~. Sobuak 1.. W., 1977. Bathymelry of the Arctic Ocean north of 8S !'>o VOIII P. H., 1974. The Icelllnd phenomenon : imprints of a hot 'pol latitude. TutnnophYlin. .42. n7·T13. on the ocean cr u ~t and implication) for flow below the plates. in . Geodyltumics of iceland alld Ih" NOf/h Atlantic ur~u. C'dited by Sriusta'·. S. P .. 1918. E\'olution of the Labr.. dor Se 40