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Home , Fold (geology), Fold and thrust belt

The Arctic Eurekan orogen: A most unusual -and-thrust belt

DECLAN G. DE PAOR DWIGHT C. BRADLEY* Department of & Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218 GLORIA EISENSTADT STEPHEN M. PHILLIPS

ABSTRACT displacement is not confirmed; rather, east- which halotectonic structures feature promi- The Eurekan orogen of north- vergent thrusts and dextral wrench faults typ- nently, especially on Axel Heiberg Island. ernmost North America differs from a stan- ify the system. We propose that the Eurekan tectonism between the Greenlandic dard fold-and-thrust belt in several respects. marked a change from tip propaga- and North American paleoplates has long been a It lacks a metamorphic-plutonic hinterland tion to pivotal tectonism as the North Atlantic source of controversy. Nares Strait, separating and wedge-shaped profile; instead, 2-km-high system penetrated the entire width of the northwest Greenland from Ellesmere Island, of southeast Ellesmere Island face Laurasian continent. was interpreted as a paleoplate boundary by the frontal thrust, whereas halotectonic poly- Taylor (1910) and Wegener (1915) (Fig. 3); gons, gentle warps, and subdued topography INTRODUCTION however, conflicts between geophysical models extend from Axel Heiberg Island in the center requiring as much as 400 km sinistral slip along of the system back to the Sverdrup Rim at its The Phanerozoic Innuitian fold belt (Trettin the strait (Carey, 1958) and geologic evidence rear. Clastic deposits are not located in a sin- and Balkwill, 1978), which extends for 1,500 for as little as 20-80 km of structural offset gle flexural foredeep but are distributed in km along North America's Arctic margin from across it (Kerr, 1980b; Dawes and Kerr, 1982; topographic lows amid several thrust sheets. Greenland to the Parry Islands, records two dis- Okulitch and others, 1988) have led many The age of the stratigraphy, amount of dis- tinct -building events (the Ellesmerian workers to invoke distributed through the placement, and intensity of strain all increase and Eurekan ) in two superimposed Eurekan orogen, not concentrated on a single cratonward, and the system's width-to-length sedimentary basins (the Franklinian and Sver- (Kerr, 1980a, 1981a, 1981b; Miall, 1981, ratio is anomalously high. drup Basins; Fig. 1). Proterozoic to 1983, 1984, 1985, 1986; Pierce, 1982; Hugon, 1983). Pitman and Talwani (1972), Kerr The orogen is attributed to Greenland's strata of the Franklinian Basin margin rest on (1980a), and Pierce (1982) suggested that the pivotal movement relative to North America, and are adjacent to rifted crystalline orogen might have formed near the pole of rota- which formed a braided Cenozoic plate basement of the Laurentian Shield. They were tion of Greenland relative to North America. In boundary in Ellesmere and Axel Heiberg Is- folded and faulted during mid-Paleozoic Elles- Jackson's (1985) alternative model, lands, not a single transform in Nares Strait merian orogenesis, which is not discussed here. along a cryptic zone in Nares Strait is as previously proposed. The three major Late Paleozoic extension and sedimen- invoked to accommodate displacement between strands of this braided system are the Parrish tation in fault blocks initiated the Sverdrup Greenland and North America. Glacier, Vesle Fiord, and Stolz thrusts. They Basin. Localized "Melvillian" extension was fol- die out toward a structural pole of rotation in lowed by basin-wide , Clearly, a structural and kinematic analysis of the south, whereas to the north, movement is generating a classic successor basin on thinned the Eurekan orogeny may help to explain its accommodated by a dextral transpression Franklinian crust. Sverdrup Basin is dominated features and resolve conflicting tectonic interpre- zone extending from Lake Hazen to northern by clastic rocks (Balkwill, 1978). Carbonates are tations. In this paper, we evaluate the Eurekan's Greenland. absent after the late Mesozoic, reflecting North potential role in solving the Nares Strait prob- America's drift toward cool northerly latitudes. Field studies on Ellesmere Island combined lem by addressing three questions: (1) Is the to times are characterized by with a regional synthesis of previous work style of deformation compatible with the pro- episodic basaltic volcanism and shallow-marine show that Eurekan deformation style is indic- posed plate configuration? (2) Does shortening to deltaic sedimentation, which kept pace with ative of pivotal tectonism, that the contrac- across the orogen tally with inferred displace- subsidence, in some cases extending beyond tion necessary to accommodate Greenland's ment of Greenland relative to North America? former basin margins. The overlying Eureka displacement is similar in magnitude to that (3) Is orogenesis on Ellesmere and Axel Heiberg Sound Group (Fig. 2) are broadly documented by Eurekan structures, and that Islands contemporaneous with paleomagnetic coeval with Paleogene "Eurekan" tectonism the ages of continental structures are compat- anomalies in Labrador Sea and Baffin Bay (for (Miall, 1985, 1986; Ricketts, 1987a, 1987b), ible with the paleomagnetic record of sea- example, Srivastava and Tapscott, 1986)? which inverted the to Tertiary floor spreading in Labrador Sea and Baffin In the summer of 1985, we undertook Sverdrup Basin and reactivated pre-existing El- Bay. Previously proposed sinistral strike-slip ground-based l:50,000-scale mapping and struc- lesmerian faults in underlying Proterozoic to tural studies in Ellesmere Island (De Paor and Franklinian strata. The resultant oro- others, 1985, 1986). Two further detailed sur- *Present address: U.S. Geological Survey, 4200 gen is an unmetamorphic fold-and-thrust belt in University Drive, Anchorage, Alaska 99508. veys of key areas were carried out by Eisenstadt

Geological Society of America Bulletin, v. 101, p. 952-967, 19 figs., July 1989.

952

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/7/952/3380699/i0016-7606-101-7-952.pdf by guest on 01 October 2021 Figure 1. The Innuitian orogen of northernmost North America. Map shows names referenced in the text. Major thrusts are (1) Parrish Glacier thrust, (2) Vesle Franklinian and Sverdrup Basins, major arches, fault and fold trends, and place Fiord-East Cape thrust, (3) Stolz thrust.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/7/952/3380699/i0016-7606-101-7-952.pdf by guest on 01 October 2021 1) Banks Basin

2) West Sverdrup Basin

3) Strand Fiord Basin

4) Remus Basin

5) Lake Hazen Basin

6) Judge Daly Basin

Wy^my/r^

Figure 2. Locations of Eureka Sound depocenters (after Miall, 1986).

Figure 3. Classic paleoplate reconstructions by (A) Taylor (1910) and (B) Wegener (1915) show a major sinistral strike-slip fault (now called the "Wegener fault") in Nares Strait. As much as 400 km of movement on this fault has been invoked to accommodate the Cenozoic drift of Greenland away from North America.

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and Phillips (unpub. data). Given limited logisti- Sverdrup Rim is distinguished from contrac- cal support, traverses were done on foot from tional Eurekan structures, the latter's map pat- base and fly camps; consequently, our field stud- terns are more coherent. ies are of a relatively detailed, localized nature and reveal many small-scale fabric indicators STYLE OF EUREKAN that were beyond the scope of previous DEFORMATION 1:250,000-scale surveys. Previous workers re- ported difficulties in taking compass readings so The Eurekan orogen differs from fold-thrust close to magnetic north, at a declination of belts such as the Appalachians in several re- about 89°W! Van Berkel (1988, personal com- spects (Fig. 8). First, the deformed zone's width- mun.) recorded magnetic excursions for 3 or 4 to-length ratio is much greater than normal. days during 1982 and 1983. We checked com- Eurekan thrusts extend about 700 km from pass settings daily against the Sun's shadow at Grantland to Baumann Fiord, where their dis- midnight (Fig. 4), but recorded no major excur- placements gradually drop to zero. Deformation sions or diurnal variations. extends 500 km across strike, dying out gradu- ally west of Cornwall Arch (Fig. 1). In contrast, CLASSIFICATION OF STRUCTURES the Appalachians are 3,700 km long but only 650 km at the widest. (This contrast may be less The Eurekan orogeny was the principal pe- striking if the northern Greenland thrust belt is riod of faulting, folding, and halotectonism in treated as a continuation of Eurekan structure; eastern Sverdrup Basin (Thorsteinsson and however, it has an opposite and may Tozer, 1970). Balkwill (1978) identified three be more easily explained as a local accommoda- phases of Eurekan deformation (Fig. 5): (1) up- tion structure at the termination of the left- lift and erosion over four intrabasinal arches lateral Wegener fault.) Second, there is no (Cornwall Arch, Princess Margaret Arch, Grant- elevated hinterland; not only is the topography subdued in the western part of the system, but land Uplift, and Sverdrup Rim), each sited on a Figure 4. Determination of magnetic decli- there are no roots of eroded mountains, and pre-existing Paleozoic structure; (2) map-scale nation at midnight (according to calculated open arches run from the halotectonic structures thrusting on Ellesmere and Axel Heiberg Is- Sun time). lands; (3) localized normal faulting. Subsequent of Axel Heiberg Island to Sverdrup Rim. Causal workers have confirmed the major division into compression or gravitational stresses could not have a source in the hinterland, as in other thrust phases 1 and 2 but have not attached regional (Miall, 1974) is preferable. Balkwill and Fox belts. Third, there is no foredeep indicative of significance to phase 3, although England (1987) (1982) described normal faults, magnetic anom- lithospheric flexure. In southeast Ellesmere Is- invoked or later deformation to explain alies, aligned evaporite domes, and modern land, 2-km-high cratonic mountains facing the geomorphological features. Miall (1981) pro- earthquake epicenters in a zone of intermittent frontal thrust form the highest peaks in eastern posed that Eureka Sound Group sedimentation Mesozoic to Holocene extension in western North America. Distal erosional products are developed in isolated basins separated by phase 1 Sverdrup Basin, whereas Soper and others distributed among several thrust sheets. Fourth, arches, a view supported by the gravity signature (1982) and Trettin and Parrish (1987) docu- stratigraphy becomes progressively older toward of Princess Margaret Arch (J. T. van Berkel, mented vulcanism in north the foreland, the opposite of standard age pro- 1988, personal commun.). Ricketts (1988), how- Greenland and north Grantland. Thus, interpret- gressions. Fifth, most thrust faults have both ever, attributed facies patterns to halokinetic dis- ing Sverdrup Rim as an extensional structure is hanging-wall and footwall folds; Schwerdtner turbance (Fig. 6) of an essentially unified sedi- fully compatible with its regional tectonic setting (1985, personal commun.) has described Eure- mentary basin (see Miall, 1988, for discussion). (Fig. 7). Rim uplift and erosion is attributable to kan faults as "underthrusts" rather than over- the fulcrum effect on down-to-basin listric nor- Although Balkwill's (1978) phase 1 includes thrusts. Sixth, displacement and strain are most mal faults, combined with rift shoulder uplift. 4.5 km of latest Cretaceous uplift and erosion of pronounced near the and dissipate to- Interpreting data from Meneley and others Sverdrup Rim, this does not necessarily imply ward the rear. lateral compression. It would be difficult to (1975) tectonically, the basal Permian uncon- transmit compressional through the least formity represents transition from Carboniferous Clearly, the lateral stresses responsible for deformed part of the Sverdrup Basin to the synrift tilting to Permian-Triassic subsidence and thrusting must emanate from the craton. In a southeast or through Canada Basin's shelf and sedimentation. At this stage, the rim occupied foreland thrust belt, this would be impossible— rise to the northwest, unless a landmass was the hanging walls of down-to-basin faults asso- undeformed platform extends in most cases for there during the Eurekan. The timing of sea- ciated with the opening of Sverdrup Basin to the hundreds of kilometers on the system's continen- floor spreading in Canada Basin is not accu- south. During the Cretaceous, Sverdrup Rim tal side. In the Eurekan case, however, we argue rately know, but Sweeney (1985) argued was an extensional structure of opposite ver- that the thrust belt is the plate boundary and that cogently for Early Cretaceous to Santonian (that gence, as the main crustal rift jumped to Canada the "foreland"was part of a separate Groenland- is, pre-Eurekan) rifting. Meneley and others Basin (Sweeney, 1985). Cenozoic clastics thus ie plate in Cenozoic times (Srivastava and (1975) presented the case against a Mesozoic rest unconformably upon rocks of progressively Tapscott, 1986). older age to the north. The unconformity is landmass prevenient to Canada Basin, and their A common problem in identifying Eurekan much earlier here than farther east, and ttie over- seismic data show normal faulting, not contrac- structures is the re-use of Ellesmerian faults. For lying Eureka Sound Group sediments are typical tion, in the rim. Therefore, an extensional expla- example, McWhae (1981) attributed dextral of an extensional margin (Miall, 1981). When nation of Sverdrup Rim and Storkerson Uplift transpressive structures in the pre-Ellesmerian

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/7/952/3380699/i0016-7606-101-7-952.pdf by guest on 01 October 2021 Pe, magnetic TIMING OF EUREKAN DEFORMATION - epoch anomaly Phases (Balkwill, 1978) AXEL H E I B E R G, ELLESMER E ISLANDS P L PIACENZIAN I N O C conglomerate in NE Ellesmere E E ZANCLEAN phase O N (Wilson, 1976) E geomorphic features - T G MESSI N I AN M normal syntectonlc conglomerate Ellesmere E I TOR TO N I A N E (England, 1987) O SERHAVALL faulting Princess Margaret Arch N C LA N G HIAN E (Balkwill S Bustin, 1975; R E N BURDIGALIAN E Hills & Bustin, 1976) unconformity above AQUI TA N I A N T Eureka Sound Fm. , - O Ellesmere C H ATTIA N I ¿s P phase 2 (Riediger et at, 1984) A syntectonic conglomerate - A N RUPELIAN L E folding & Stolz Thrust, Lake Hazen Tertiary

R thrusting (Miall, 1984, 1985, 1986, 1988) in E E BARTONIAN footwall of O O Y C uplift of Princess Margaret Arch, Lake Hazen E G LUTETIAN main phase Fault N 21 / syntectonic conglomerate - Stolz Thrust E E of deformation ? (Christie & Y P R ES IA N Lake Hazen conglomerate N fluvial sedimentation Rouse, 1976) THANETIAN (Ricketts, 1987, 1988) E P C Judge Daly Basin syntectonic A E (Ricketts S Mclntyre, 1986) (Miall, 1985) L N MONTIAN conglomerate - E E phase 1 0 DANI AN 29 Judge Daly Basin fauna, flora in Eureka Sound Fm - MAASTRICHT (Mayr & De Vries, C uplift of I initiation of Eureka Sound U Bay Fiord, Ellesmere 1982) CAMPANIAN arches ! sedimentation R P (West et at., 1981) P E E •• 34 (Miall, 1986) R T I Cret. I Mag. Lull

Figure 5. Summary of evidence for timing of Eurekan orogeny on Axel Heiberg and Ellesmere Islands.

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Figure 6. Map pattern of wall-and- basin structure in Axel Helberg Island after Thorsteinsson (1971).

Devonian rocks of Bjorne Peninsula to the thrust and its numerous hanging-wall imbricates unconformably overlying Ellesmerian folds of Ellesmerian orogeny, but the upper Carbonifer- place Franklinian strata onto beds as young as Appalachian and style. The west- ous is displaced between Eids and Blue Fiords; the Tertiary Eureka Sound Group. Upper Pa- ernmost exposures of lower Paleozoic strata therefore, later reactivation occurred. We have leozoic and Mesozoic Sverdrup Basin sediments occur in its hanging wall, unconformably under- not examined this locality, and in the absence of are missing. Zone 1 structures display an arcuate lying Carboniferous fanglomerates of the Can- a detailed published study of mesoscale features shape in eastern and southern Ellesmere. Thor- yon Fiord Formation. Thus, the Mount James (see Okulitch, 1984), cannot attribute Bjorne steinsson (1974) attributed this to a salient that thrust juxtaposes the late Paleozoic faulted mar- Peninsula structures to either the Ellesmerian or wrapped around an initial bend in the Precam- gin of Sverdrup Basin with strata laid down dur- the Eurekan orogeny, if they are Ellesmerian, brian shield (see also Mayr and de Vries, 1982). ing the basin's thermal subsidence, beyond its then Kerr's interpretation of Cenozoic "pivotal Hugon (1983), however, proposed that the oro- bounding faults. transforms" needs re-evaluation. In Canon clinal bend was due to Eurekan sinistral shear of Osadetz (1982) mapped rocks of our zones 1 Fiord, a fault-bounded dextral transpressive en Ellesmerian structures. and 2 in the Grantland area of northern Elles- echelon fold pattern (Fig. 1) represents super- Zone 2 straddles the Mount James thrust. mere Island. In sections through the United posed Ellesmerian and Eurekan deformation Thin Mesozoic strata first appear in its footwall, States Range, he found an array of thin-skinned (S. M. Phillips, unpub. data). These two examples of undifferentiated Innuitian structures are important because they bound the oroclinal N W NORTH ELLEF RINGNES ISLAND bend discussed by Hugon (1983; see below). In certain circumstances, it may be possible to distinguish Eurekan structures on the basis of antecedent drainage patterns. For example, Fig- ure 9 illustrates striking patterns of antecedence in the Vesle Fiord-East Cape thrust system, which is obviously Eurekan because it cuts Ter- tiary strata. Elsewhere, where only the lower 7000 m Paleozoic is exposed, Eurekan thrusting can be SVERDRUP BASIN inferred from such drainage patterns. CANADA BASIN FAULT At the latitude of our map areas on Fosheim FAULT Peninsula, we identified the following zonation of Eurekan structures, from east to west 20 KM (Fig. 10). In zone 1, which extends west of the North Figure 7. Tectonic interpretation of a cross section drawn by Meneley and others (1975) American craton, the frontal Parrish Glacier through northern Ellef Ringnes Island.

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STANDARD FOLD & THRUST BELT

Figure 9. Arrows point to locations of possible antece- dent drainage patterns on the

High < — STRAIN — > Low hanging wall of the Vesle Fi- ord-East Cape thrust system, Fosheim Peninsula. EUREKAN THRUST BELT

No Hinterland! No Foredeep !

Youngest Low < — STRAIN — > High

Figure 8. Differences between a standard thrust belt and the Eurekan thrust system. See text for discussion. i. CONTOURS 1000-3000 FT.

RIVERS/LAKES

Figure 10. Four zones of Eurekan structures. Zone 1: Proterozoic-Iower Paleozoic strata in thrust sheets, Eureka Sound strata in footwall . No Mesozoic sedi- ments exposed. Zone 2: Thrusting exposes both Sverdrup Basin and Frank- linian Basin strata. 50 km Zone 3: Sverdrup Basin sedi- ments thrust over the Eureka Sound Group. Franklinian strata not exposed. Zone 4: Broad warps, halotec- tonic and halokinetic structures.

thrust faults overlapping laterally in en echelon folding, halotectonic, and halokinetic structures, style, with a consistent 2-3 km depth to dé- extending from Axel Heiberg and Ellef Ringnes collement. He dated their movement as middle Islands to Sverdrup Rim and including Corn- and identified the Grantland Forma- wall Arch (see Gould and De Mille, 1964; tion as an important décollement horizon. Hig- Thorsteinsson, 1974; Nassichuk and Davis, gins and Soper (1983), however, argued that 1980). Salt-cored diapirs and wall-and-basin surface faults steepen into a dextral flower struc- structures of zone 4 were studied by Schwerdt- ture at depth. ner and Clark (1967), Schwerdtner and Osadetz Zone 3 extends across the Vesle Fiord and (1983), van Berkel (1986), and van Berkel and Stolz thrust sheets as far as Princess Margaret others (1983, 1984). Schwerdtner (1986) made Arch on Axel Heiberg Island, about 200 km west of the frontal thrust. Sverdrup Basin strata are faulted against the Eureka Sound Group, but underlying Franklinian beds are never exposed. Figure 11. Locations of detailed maps in Zone 4 is a 350-km-wide tract of broad open Figures 12 and 13.

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EH TERTIARY Eureka Sound Group

ES3 CRETACEOUS Kanguk, Hassel, Christoph er, Isachsen Fms.

• TRI ASSIC Heiberg Schei Björne Fms.

EU PERMIAN

ESI CARBONIFEROUS

Fault • Thrust

^ Diki N o t mapped

O measurements

84 W 83 W o 2 6 Vesle Fiord Area km

Figure 12. Detailed map of Vesle Fiord area shows reinterpretation of high-angle faults as reverse faults and locations of slickenside striations plotted in Figure 14.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/7/952/3380699/i0016-7606-101-7-952.pdf by guest on 01 October 2021 79' QUATERNARY "ION Mt. James Area m TERTIARY Eureka Sound Qroup

ES3 CRETACEOUS Kanguk^assel, Christopher, Isachsen F m s.

E3 PERMIAN/ CARBONIFEROUS Canyon Fiord Fm.

• TO DEVONIAN OKse Bay, Blue Fiord, Eids, Cape Phillips, Allen Bay Fms. Cornwallis Group Eleanor River, Baumann Fiord Fms.

Fault Thrust

O Slickenside measurements Not mapped 83'25'W 82*30 W

Figure 13. Detailed map of Mount James area showing locations of slickenside striatums, arrays, and minor folds plotted in Figures 14 and 15B.

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an important distinction between salt intimately N associated with thrusting in east Axel Heiberg and purely gravitational salt diapirs mainly in the west. To test the hypothesis that geophysically re- quired displacement of North America and Greenland was distributed as sinistral shear throughout the Eurekan fold-thrust belt, possi- bly along braided fault networks visible on Ca- nadian Geological Survey maps, we analyzed two areas of the Fosheim Peninsula, central Ellesmere Island, in detail (Figs. 11-14). In both areas, slickenside lineations were measured to evaluate fault movement directions (no over- printing of slickenlines was observed; curved lines were recorded only at one location). To test for oblique movement on thrusts, one imbri- cate west of Mount Low was subjected to de- tailed analysis. Measurements of en echelon vein arrays and minor fold axes were collected in the hanging wall (Fig. 15). Fault and slick lineations are plotted, following the method of Hoeppener (1955) whereby each point on the net represents the pole to the fault plane, and the line through the point is a fragment of the great circle con- taining the pole and the (an arrow in- dicates the direction of hanging-wall movement, where determined). The advantage of this plot- ting method is that fault orientation and slip data plot at a single point. The data show that the azimuth of slip is generally east-west, regardless Figure 14. Equal-angle plot of fault poles and senses of displacement (see text for details and of fault-plane orientation. Slip is approximately discussion). Arrows indicate direction of hanging-wall movement. normal to regional thrust traces, albeit with a ±30° spread reflected in conjugate map-scale caused little contraction; he estimated 40 km ments are about one tenth of their trace length, patterns that offset folds and dikes both total shortening from the wavelength-to-arc- yields 62 km displacement on these major faults. dextrally and sinistrally on western Axel Hei- length ratio of folds. McWhae (1981) calculated Note that stratigraphic separation diagrams may berg and central Ellesmere Islands. Dip slip on displacements in two parallel sections. The yield a false impression of total displacement north-south-striking planes, strike slip on east- southern one yielded 20 km shortening, the because of the occurrence of unconformities in west-striking planes, and oblique slip on planes northern one 40 km; however, neither section some sections, especially in zones 1 and 2. of intermediate orientation all imply eastward extended across the full width of the orogen. displacement of the thrust system. An important Further displacement estimation is illustrated Okulitch (1982) reinterpreted many normal observation is the absence of north-south sinis- by a study of the Vesle Fiord thrust, Fosheim faults of Thorsteinsson and Tozer's map in tral strike-slip faults. The orientations of minor Peninsula. Previous workers showed this as a southern Ellesmere as thrusts, thus augmenting fold axes in Ordovician carbonates (Fig. 15B) flat-on-flat fault (Fig. 16A), but we found the inferred contractional displacements. He es- are consistent with east to southeast thrusting. hanging-wall (Fig. 16B) and footwall folds. By timated 25%~50% shortening for both Ellesmer- Meso-scale vein arrays have sinistral sigmoidal observing the East Cape thrust's structural relief ian and Eurekan deformation, which would geometry. A 60° scatter of axial orientations across Canon Fiord, it is evident that as much as amount to 50 to 100 km of total displacement if about a moderately plunging southeasterly mean 15 km of displacement could have occurred extrapolated. Ricketts' (1987a) section shows 55 suggests that the veins were formed prior to under the central thrust sheet. Movement on the km shortening, assuming a décollement in the hanging-wall displacement and rotation. They Parrish Glacier-Scoresby Bay system may be upper Paleozoic and omitting reacti- may be Ellesmerian in age. In summary, we even greater because Okulitch (1988, personal vated Melvillian extensional faults (see De Paor cannot eliminate the possibility of some sinistral commun.) identified 20 km displacement on and Eisenstadt, 1987; Eisenstadt and De Paor, displacement along major faults in central Scoresby Bay thrust. Van Berkel (1988, personal 1987). Ellesmere, but the data do not establish such a commun.) considered the movement on Stolz hypothesis convincingly and are everywhere Our field studies in central Ellesmere, com- thrust to be somewhat less, about 10 km. Com- compatible with simple east-vergent thrusting. bined with the previous work of Schwerdtner bined with 40 km shortening estimated from and his students in Axel Heiberg, show that fold wavelength-to-arclength ratios by Balkwill there are three major thrust sheets in the Eure- (1978), 50-100 km contraction across the AMOUNT OF SHORTENING kan thrust system: the Stolz sheet, the Vesle Eurekan system can be accounted for, with a Fiord-East Cape sheet, and the Parrish Glacier- displacement gradient increasing to the east. Balk will (1978) considered that movement Scoresby Bay sheet (Fig. 1). Elliott's (1977) Displacement in the fold-and-thrust belt is there- on steep reverse faults of the Eurekan orogen "bow-and-arrow" rule, whereby fault displace- fore on the order of magnitude required by geo-

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Figure 15A. Photograph of minor folds in Ordovician Eleanor River Formation, Figure 15B. Equal-area plot of minor fold hanging wall of thrust imbricate just west of Mount Low. Location of sample area is marked in and en echelon vein axes pictured in Figures Figure 13. 15A and 15C. Orientation and rotation sense of vein arrays and fold axes is consistent with north-northwest to south-southeast compres- sion associated with thrusting.

with the Beaufort Formation of the Arctic Coastal Plain unconformably overlying deform- ed Eureka Sound sediments and therefore con- sidered the onset of Beaufort sedimentation to mark the end of Tertiary orogenesis. Recent field studies, however, have revealed deforma- tion of conglomerates assigned to the Beaufort Formation (Balkwill and Bustin, 1975; Bustin, 1982). Either deformation continued during Beaufort sedimentation or the assignment of sed- iments to the Beaufort Formation needs re- evaluation. Tozer (1956) defined the Beaufort Formation between Banks and Meighen Islands, an area of low topographical relief and low Figure 15C. Line drawing of en echelon vein array in hanging wall of thrust imbricate. Veins strain, quite distinct from the intensely deformed are from same locality as folds pictured in Figure 15A. eastern Sverdrup Basin. Comparative palynol- ogy leads to a correlation with the upper Mio- cene/lower Pliocene Kougarok Formation of physical models, especially considering that ments, it is essential to consider the timing of Alaska (Hills and Ogilvie, 1970). A Miocene or north-south extension across Lancaster Sound Beaufort Formation and Eureka Sound Group Pliocene age for deformed Beaufort Formation and Jones Sound can accommodate significant sedimentation. If synorogenic sediments are of was supported by Roy «and Hills (1972). Hills counterclockwise movement of Greenland Neogene age, as suggested in the past, then the and others (1974), Hills and Matthews (1974), (Pierce, 1982; A. D. Miall, 1988, personal associated deformation is too recent to correlate and Hills and Bustin (1976) attributed north- commun.). with plate movements in Labrador Sea and Baf- south floral variations to latitudinal rather than fin Bay. The age of syn- and post-orogenic sedi- age differences. An alternative explanation, im- TIMING OF EUREKAN mentation in Ellesmere Island, however, is open plying an earlier age, is presented below, DEFORMATION to dispute. however. In order to assess the relationship between Early workers (for example, Tozer, 1956) Tozer (1963), Thorsteinsson (1971), and Eurekan orogenesis and causal plate move- recognized undeformed sediments correlative Balkwill and Bustin (1975) recorded cobble

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conglomerate overlying Eureka Sound sedi- ments in Gibs Fiord, Axel Heiberg, and sug- gested syntectonic derivation from the west during uplift of ancestral Princess Margaret Arch. Picea banksii spruce cones in these sedi- ments were taken to prove a Miocene or later age, implying a Miocene phase of Eurekan de- formation. Ricketts and Mclntyre (1986), how- ever, re-evaluated the palynology of Axel Heiberg's synorogenic deposits and suggested a middle (phase 2) age, contemporaneous with the uppermost unit of the Eureka Sound Group. In the Yelverton Bay area, northernmost Ellesmere Island, Wilson (1976) assigned unfos- siliferous fault-related coarse conglomerates overlying Eureka Sound Formation to the Beau- fort Formation, purely on the basis of lithologi- cal similarity to P. banksii-bt&nng conglomer- Figure 16A. View to the southwest of Sawtooth Mountains. Vesle Fiord thrust places ates in Axel Heiberg and the Arctic Coastal Permian strata on Tertiary Eureka Sound Group and appears to be a flat-on-flat fault. Plain, hundreds of kilometers away. Because Ricketts and Mclntyre (1986) reassigned the P. banksii-bc&x'mg Axel Heiberg conglomerates to middle Eocene, the argument for Neogene deformation in northern Ellesmere Island no longer holds. Blackadar (1954) reported the discovery by G. Hattersley-Smith of a conifer cone from Eu- gene Glacier, northeast of Lake Hazen, north- eastern Ellesmere Island. On the advice of W. L. Fry, he dated the host strata as Miocene. Osa- detz (1982), however, re-examined the evidence and concluded that this date was based on an erroneous view that arenaceous Tertiary sedi- ments were automatically Paleogene and ru- daceous sediments Neogene in age. D. C. MacGregor (in Christie, 1964) reassigned these beds to the Paleocene-. Christie (1976) described Tertiary of Eureka Sound Formation in the footwall of the Lake Hazen fault and assigned them to the Oligocene-Miocene. Later re-examination by Christie and Rouse (1976), however, suggested that the palynofacies were Eocene. Figure 16B. Closer examination reveals a hanging-wall on Vesle Fiord thrust. In southeastern Ellesmere Island, Riediger Figure in foreground for scale. and others (1984) described "Beaufort" con- glomerates apparently unconformably overlying the Eureka Sound Group as postorogenic, ex- plaining local folds as products of ice push. The P. banksii cones is dubious. Hills and Bustin for morphological variations at sea level, the decameter scale of folding, however, strongly (1976) noted that the Axel Heiberg P. banksii same argument may support a pre-Miocene age suggests a tectonic origin. specimens had basal tapers resembling those of for cones in sediments shed off thrust sheets. The use of the name "Beaufort Formation" treeline species from . As specimens from Given the current height of the Princess Mar- for rocks of such widely contrasting tectonic en- intermediate locations on Ellef Ringnes Island garet Range, for example, the mountains from vironment is a potential source of much confu- and Meighen Island were associated with plant which these sediments were shed could have ex- sion. We propose that the name be restricted to macrofossils that suggested proximity to the tree- ceeded the treeline, which is a surface rising to rocks of the Arctic Coastal Plain and that syn- line, they suggested that floral differences be- the south and not just a line at sea level on the orogenic sediments associated with faults at tween Banks and Axel Heiberg Islands reflected map, and so the Axel Heiberg specimens may Stolz, Lake Hazen, Parrish Glacier, Judge Daly environmental stress associated with the treeline, have been thrust up through the "tree-plane" Promontory, and Yelverton be assigned to the not age differences. Because latitude-controlled long before the islands drifted past the sea-level Eureka Sound Group. Dating by the presence of environmental stress has been held accountable treeline. The environmental stresses revealed by

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the Axel Heiberg specimens may be pre- wall ramp , and ending during Eureka never intended this gap to be interpreted as Miocene (spruce cones are present throughout Sound Group deposition in the Paleocene. From ocean crust; on page 207, they stated: the Tertiary) and therefore attributable to con- the mainly distal nature of the latter sediments, it tractional deformation accompanying extension is evident that most faults terminated as blind In the extreme northwest of Greenland the narrow and in Baffin Bay and Labrador Sea. thrusts underlying ramp anticlines with a wide shallow strait separating it from Ellesmere Island is shown widened to 400 km, it would have been more The relative ages of continental deformation gently arched topographic expression. realistic to regard Ellesmere Island as part of Green- in the Arctic Archipelago versus sea-floor land, on to which it fits closely, and to have displaced spreading in Labrador Sea and Baffin Bay are The Question of Distributed Sinistral Shear it with Greenland. We did not do this as we were critical to the interpretation of Eurekan tecton- doubtful where to draw the limits of the block and did not wish to become involved in arbitrary assumptions ism. Balkwill (1978) dated phase 1 (Late Hugon (1983) suggested that the bend in the about an area not closely connected with our main Cretaceous to late Paleocene) and phase 2 (mid- Innuitian orogen in central Ellesmere Island theme. Eocene to early Miocene) using lithostratigraph- could have resulted from Eurekan sinistral shear ic evidence of pre-, syn-, and post-tectonic of the Ellesmerian fold belt. No southerly con- On the basis of paleomagnetic studies, Srivas- sedimentation and palynological data available tinuation of this , however, is evident tava (1985) stated that at anomaly 25 time, the at the time. Miall (1985) documented progres- in the Precambrian basement, and this model present coastlines of Greenland and Ellesmere sive deformation in Judge Daly Basin during does not resolve the plate reconstruction prob- Island were separated by 150 km, following the phases 1 and 2 of the Eurekan orogeny and lem, for upon restoring the Innuitian fold belt, standard paleomagnetic practice by which found that alluvial fans were overridden by their cratonic crustal areas of Devon Island and main- coastal gaps and overlaps are used as indicators own source at the close of phase 1. Phase 2 is land Canada overlap. The distributed shear zone of general regions of compression and , now thought to be no younger than early Oligo- would lie too far to the west to serve as a substi- respectively. Many workers, however, inter- cene by Ricketts and Mclntyre (1986) and Miall tute for discrete movement in Nares Strait and preted Bullard's and Srivastava's gaps as an ex- (1986), and the above discussion is consistent could accommodate only part of the total dis- panded seaway in Nares Strait (Fig. 17), and with this. placement required by geophysical models. Jackson (1985) has gone so far as to suggest that Furthermore, Jackson and Halls (1988) found as much as 400 km of oceanic crust could have DISCUSSION no evidence of distributed shear in their paleo- been subducted under Ellesmere Island during magnetic analysis of the eastern Sverdrup Basin. the Tertiary. Jackson and Koppen (1985) lent Eureka Sound Group and further support to this theory, invoking a "cryp- tic suture" to explain the narrowness of the su- Paleocene Tectonism The Question of Subduction ture zone, and Wilson (1988) cited Nares Strait in Nares Strait as an example of ridge subduction parallel to the Two of Balkwill's phase 1 arches form a co- coastline. The proposal that as much as 400 km herent pair. The Cornwall Arch lies north of In his famous fit of the continents around of oceanic crust was subducted under eastern Boothia Uplift—a structure which probably was the North Atlantic, Sir Edward Bullard left a Ellesmere Island is herein rejected on several active in the Paleozoic (Miall, 1986). It is herein gap between northwestern Greenland and the grounds. (1) Because the match of interpreted as an accommodation structure for North American plate in the vicinity of the pres- across the strait is such that strike-slip move- the orogen's westernmost buried thrust. The an- ent Nares Strait. Bullard and others (1965) cestral Princess Margaret Arch is interpreted as a hanging-wall anticline of the Stolz thrust. Its structural position east of the present topograph- ic feature (the Princess Margaret ) is attributable to postorogenic erosion of the mountain front. It was probably higher than the Cornwall Arch. On Ellesmere Island, an arch topographically expressed as the Sawtooth Mountains defines a hanging-wall anticline atop the Vesle Fiord thrust. Because the oldest beds exposed are upper Paleozoic, it is not possible to say whether the fault also represents a reacti- vated Ellesmerian structure. Farther southeast, thrusting intensifies toward a salient in the Pre- cambrian foreland. Thrusts invariably cut Eu- reka Sound sediments and could be phase 1 or phase 2 structures. Tilting and folding of western thrust faults over eastern ones suggest a foreland progression. Phase 1 of the Eurekan orogeny may be attributed to contractional deformation, Figure 17. Early Cretaceous reconstruction, showing present-day coastlines, assuming that commencing in the Campanian-Maastrichtian, all late Mesozoic and Cenozoic displacement between Greenland and North America is ac- with reactivation of Paleozoic arches as hanging- commodated along Nares Strait (after Srivastava and Tapscott, 1986).

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ments exceeding 50 km have been disputed by many (in Dawes and Kerr, 1982, for example), normal movements of several hun- dred kilometers are even harder to reconcile. It is difficult to justify a suture, albeit cryptic, when Figure 18. In a simple two- it must pass through a steep-walled 25-km gap plate system, shortening or sub- between matching regions of Precambrian duction shown by the stippled shield. (2) Jackson (1985) suggested that the area on one side of the pole of oceanic crust was created in the Silurian and rotation is accompanied by ex- subducted in the Tertiary. There is no Silurian tension or creation of new oce- compression of the Archean craton in mainland anic crust on the opposite side. Canada to counterbalance the proposed exten- At points 1, 2, 3, and 4, the sion in Nares Strait, north of the ocean's pole of angular velocities are equal, but rotation. Furthermore, compared with modern tangential displacements are not. examples, the oceanic crust would have been extremely old (350 m.y.) when subducted and would have survived the intervening late Pa- leozoic Ellesmerian orogeny along its passive margins. (3) It is unlikely that 400 km of oce- anic crust, including a ridge, could have been subducted without metamorphic or volcanic trace. Kovacs and others (1986) failed to find Rockall rift at anomaly 34, and the subsequent gence on one side of the pole must be accom- magnetic data to support the presence of any propagation of a crustal crack along the Labra- modated by convergence on the opposite side volcanic activity in the area. (4) At its southern dor Trough and Baffin Bay. By anomaly 24 (Fig. 18). Although angular rotations are con- end, Nares Strait is too straight and steep walled time, the rift system had penetrated through stant for all small circles centered on the rotation to accommodate a low-angled structure (a most of the total width of the Laurential conti- pole, tangential displacements are not; rather, number of thrust faults and a possible lateral nental block. De Paor (1987) proposed that it they are too small to detect near the pole and ramp occur farther north; A. V. Okulitch, 1988, became energetically feasible for the crust to increase rapidly away from it. Because of such personal commun.). pivot about a temporarily stationary pole of ro- ever-increasing displacement, thrusts on the tation, with consequent thrusting and thickening convergent side of the pole cannot continue for A Mechanical Model of Eurekan Orogenesis of Sverdrup Basin and its attenuated lithosphere great distances along strike but must be termi- north of the pivot point. Such pivotal motion nated by wrench structures—hence the unusual Kerr (1980a), Miall (1981), and Pierce may be likened to the common experience of aspect ratio of the Eurekan orogen and its north- (1982) suggested an arcuate in the cutting a plank or a tree with a saw; after pene- ern termination in the Lake Hazen transpres- Arctic Islands coeval with rifting of Labrador trating most of the wood's width, propagation of sional zone Sea and Baffin Bay during the latest Cretaceous. the saw cut is replaced by gravitational bending Pierce (1982) redrew the Bullard reconstruction of the remainder. In the case of Earth's crust, CONCLUSIONS for the Canadian Arctic region showing a gap in pivotal movements must become jammed after a the map ornamentation through Axel Heiberg, certain amount of crustal overlap has occurred. We confirm that the Eurekan orogeny is cap- southern Ellesmere Island, and eastern Devon Furthermore, the total rift length of the mid- able of accommodating the rifting in Labrador Island. We support this view, identify the loca- Atlantic system was at this stage close to its Sea-Baffin Bay. Its style is consistent with this tion of the distributed plate boundary, and pro- stable limit (a great-circular rift cannot exceed interpretation—indeed, no other explanation for pose a mechanical explanation for its pivotal 180° on a sphere of constant volume). As the the orogen is evident. The amount of shortening tectonic style. Atlantic system lengthened, it was inevitable is adequate to permit on the order of 50-100 km that a realignment of plate driving forces would Oceans have their origins in intracratonic rift of contraction across Nares Strait. The timing take place. This was marked by the initiation of systems of relatively small initial size. A mid- has been a subject of much confusion; in fact, rifting at anomaly 21 east of Greenland, which ocean ridge of 180° length can spread indefi- there is no incompatibility between Eurekan then became a separate plate. Continued rifting nitely if it is accompanied by subduction zones. orogenesis and the oceanic paleomagnetic rec- in Labrador Trough is compatible with mainly A passive ocean, however, cannot open without ord. Further work will address the detailed normal contraction across Nares Strait (Srivas- lateral propagation, as documented by an in- restoration of pre-Eurekan paleogeography as tava, 1985; Miall, 1981). Strong support for this crease in magnetic anomaly length within de- an essential step toward understanding the un- model has come from the paleomagnetic data of creasing age in present oceans. Tip propagation derlying Paleozoic structure. Jackson and Hall (1988). Similar conclusions in the North Atlantic system began at the ends of Recently, refined geophysical models (Srivas- have been independently drawn by A. V. Oku- Blake's anomaly (J2) and proceeded to both tava and Tapscott, 1986) have reduced wrench litch (1988, personal commun.). north and south. Numerous jumps occurred, the displacements between Greenland and North most important for our studies being the aban- In a simple two-plate system wherein the pole America to 120 km, much of which is presumed donment of the Gulf of Mexico, the failure of the of rotation lies along the plate boundary, diver- to have been distributed through sinistral shear

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the Arctic Institute of North America, and the Elliott and Balk Funds (Department of Earth & Planetary Sciences, Johns Hopkins University).

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Glacier thrusts. northern Ellesmere Island: Geological Survey of Canada Paper 76- 1C. p. 153-156. Dawes, P. R., and Kerr, J. W„ eds., 1982, Nares Strait and the drift of Green- land: A conflict in plate : Meddelelser om Granland, Geo- science 8, p. 1-392. De Paor, D. G., 1987, Mechanics of pivotal motion between plates [abs.]: EOS (American Geophysical Union Transactions), v. 68, n. 44, p. 1474. zones in the Arctic Islands. At least 100 km of probably extended along the basin axis, rejuve- De Paor, D. G., and Eisenstadt, G., 1987, Stratigraphic and structural conse- displacement normal to the Nares Strait has nating Paleozoic crustal weaknesses in the quences of fault reversal: An example from the Franklinian Basin. Ellesmere Island: Geology, v. 15, p. 948-949. been called for, however, leading some workers direction of the Hazen Trough. In the Early De Paor, D. G, Bradley, D„ Eisenstadt, G„ and Phillips, S. M„ 1985, Struc- tural development of central Ellesmere: Geological Society of America to invoke a west-dipping subduction zone under Cretaceous, the rifting axis jumped north to the Abstracts with Programs, v. 17, p. 560. Ellesmere Island. Our field studies along with Canada Basin and evolved into a small ocean, De Paor, D. G„ Bradley, D„ Phillips, S. M„ and Eisenstadt, G„ 1986, Interplay of thrust and dextral wrench tectonics in the Eurekan orogeny: Implica- map interpretation of adjacent areas reveal a whereas Sverdrup Basin continued to subside tions for plate movement directions [abs.]: Geological Association of Canada-Mineralogical Association of Canada annual meeting, complex combination of extensional, easterly and to accumulate sediments rapidly, with v. II, p. 62. overthrust, and dextral wrench faulting consist- minor igneous activity. Eisenstadt, G., and De Paor, D. G., 1987, Evidence for fault reversal during of the Franklinian Basin, Ellesmere Island: Geological Society ent with geophysical models. East Ellesmere is The Cenozoic plate boundary of northern- of America Abstracts with Programs, v. 19, p. 653. Elliott, D., 1977, Some aspects of the geometry and mechanics of thrust bells: considered part of Greenland, whereas west most North America passed through Ellesmere Canadian Society of Petroleum Geology, Annual Seminar Publication Axel Heiberg is rigidly attached to North Amer- Island and not simply through the Nares Strait. Notes, 8th, University of Calgary Continuing Education Department, v. 1, p. 2. ica; the intervening paleo-plate boundary lies in Displacements were taken up principally on England, J., 1987, Glaciation and the evolution of the Canadian high arctic landscape: Geology, v. 15, p. 419-424. an imbricate zone dominated by the Parrish three networks, the Stolz, Vesle Gould, D. 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V., Jr., 1974, A preliminary list of fossil plants from the Beaufort Formation, Meighen Island, District of Franklin: Thrusts die out toward the Eurekan orogeny's plate boundary from Ellesmere east to northern Geological Survey of Canada Paper 74-IB, p. 224-226. Greenland. Hills, L. V., and Ogilvie, R. T., 1970, Picea banksii n. sp. Beaufort Formation structural pole of rotation south of Baumann (Tertiary), northwestern Banks Island, Arctic Canada: Canadian Jour- and Vendom Fiords; beyond that point, exten- nal of Botany, v. 48, p. 457-464. Hills, L. V., Klovan, J. E., and Sweet, A. R., 1974, Juglans eocinerea n. sp.. sional tectonics prevail. Dextral wrench move- ACKNOWLEDGMENTS Beaufort Formation (Tertiary), southwestern Banks Island, Arctic Can- ada: Canadian Journal of Botany, v. 52, p. 65-90. ments intensify from Cañón Fiord shear zone Hoeppener, R., 1955, Tektonik im Schiefergebirge: Geologische Rundschau, north to Lake Hazen, culminating in an offshore We thank A. Miall, A. Okulitch, J. T. van v. 44, p. 26-58. Hugon, H., 1983, Ellesmere-Greenland foldbelt: Structural evidence for left- transform fracture zone that continues through Berkel, and H. Balkwill for their insightful re- lateral shearing: , v. 100, p. 215-225. Jackson, H. R., 1985, Nares Strait—A suture zone: Geophysical and geological North Greenland to Svalbard. Palinspastic resto- views and comments. This research was funded implications: Tectonophysics, v. 114, p. 11-28. ration of Ellesmere Island (Fig. 19) and adjacent by the American Chemical Society's Petroleum Jackson, H. R., and Koppen, L., 1985, The Nares Strait gravity anomaly and its implications for crustal structure: Canadian Journal of Earth Science, regions shows that the shape of the Sverdrup Research Fund (17526-G2) and the National v. 22, p. 1322-1328. Jackson, K. C., and Halls, H. C., 1988, Tectonic implications of paleomagnetic Basin is in part a result of tectonic deformation Science Foundation (EAR86-18620). 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F., 1985, Comments about the age of the Canada Basin: Tectono- MANUSCRIPT RECEIVED BY THE SOCIETY MARCH 18,1988 — 1984, Compressive and near dextral continental physics, v. 114, p. 1-10. REVISED MANUSCRIPT RECEIVED DECEMBER 12,1988 transform faults within the Arctic Platform, southeastern Ellesmere Is- Taylor, F. B., 1910, Bearing of the Tertiary mountain belt on the origin of the MANUSCRIPT ACCEPTED DECEMBER 15,1988

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