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The Arctic Eurekan Orogen: a Most Unusual Fold-And-Thrust Belt

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The Arctic Eurekan Orogen: a Most Unusual Fold-And-Thrust Belt The Arctic Eurekan orogen: A most unusual fold-and-thrust belt DECLAN G. DE PAOR DWIGHT C. BRADLEY* Department of Earth & 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 Tertiary 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 Cenozoic tectonism between the Greenlandic dard fold-and-thrust belt in several respects. orogeny 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 rift system penetrated the entire width of the northwest Greenland from Ellesmere Island, mountains 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 mountain-building events (the Ellesmerian workers to invoke shear distributed through the placement, and intensity of strain all increase and Eurekan orogenies) in two superimposed Eurekan orogen, not concentrated on a single cratonward, and the system's width-to-length sedimentary basins (the Franklinian and Sver- fault (Kerr, 1980a, 1981a, 1981b; Miall, 1981, ratio is anomalously high. drup Basins; Fig. 1). Proterozoic to Paleozoic 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 Precambrian 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, subduction lands, not a single transform in Nares Strait merian orogenesis, which is not discussed here. along a cryptic suture zone in Nares Strait is as previously proposed. The three major Late Paleozoic extension and evaporite 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 Mesozoic sedimentation, 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 Triassic to Cretaceous 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 sediments (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 Carboniferous 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 Devonian 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. 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 THE ARCTIC EUREKAN OROGEN 955 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 vergence 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.
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