Polyphase deformation at the Harder Fjord Fault Zone (North Greenland)

Transcription

1 Geol. Mag. 138 (4), 2001, pp Printed in the United Kingdom 2001 Cambridge University Press 407 Polyphase deformation at the Harder Fjord Fault Zone (North Greenland) K. PIEPJOHN* & W. VON GOSEN *Geological Institute, University of Münster, Corrensstraße 24, D Münster, Germany Geological Institute, University of Erlangen, Schloßgarten 5, D Erlangen, Germany (Received 4 April 2000; revised version received 24 April 2001; accepted 4 May 2001) Abstract In North Greenland, the E W-trending Harder Fjord Fault Zone represents a major lineament which cuts through Cambrian to Silurian deep-water sediments of the Franklinian Basin over a distance of 300 km. On both sides of the fault zone, these successions were affected by two stages of folding (F1, F2) during Devonian to Early Carboniferous (Ellesmerian) deformation. No field evidence was found that the Harder Fjord Fault Zone was active prior to Ellesmerian folding. Early movements along the fault zone are indicated by post-ellesmerian sedimentation of coarse red-beds (Depot Bugt conglomerate) which represent the oldest of the Wandel Sea Basin sediments. They were probably deposited in narrow, fault-controlled (?)Late Carboniferous basins similar to those described from Svalbard. During Late Cretaceous times, 500 m thick fluvial and marine clastic sediments were unconformably deposited over the folded Cambro-Ordovician units. Although no direct field evidence suggests that sedimentation was controlled by displacements along the Harder Fjord Fault Zone, the intrusion of Upper Cretaceous mafic sills and dykes indicates a phase of important crustal extension related to reactivation of the fault zone during this period of time. This stage was followed by post-late Santonian (Eurekan) N S compression (D3) which affected the Franklinian Basin deposits, Wandel Sea Basin sediments and mafic intrusions. In general, it was concentrated along the Harder Fjord Fault Zone and probably caused the reactivation of pre-existing (?)Carboniferous and younger fault lines. The entire deformation and its timing are comparable with the Eurekan structures found at the Kap Cannon Thrust Zone in northernmost Greenland and are related to intracontinental compression prior to the separation of Svalbard from Greenland. 1. Introduction In North Greenland, the eastern part of the more than 2000 km long Lower Palaeozoic Franklinian Basin is exposed, and this exposure continues westwards into the Canadian Arctic Archipelago (Higgins et al. 1991; Trettin, 1991). The basin consists of a 8 km thick succession of Cambrian to Silurian strata and can be divided into a southern carbonate shelf platform and a northern deep-water trough (e.g. Dawes & Peel, 1981; Higgins et al. 1991; Trettin, 1991). Sedimentation in the Franklinian Basin was terminated by the Ellesmerian deformation (e.g. Trettin & Balkwill, 1979; Higgins, Friderichsen & Soper, 1981; Trettin, 1991) which is characterized by a northwards increase in deformation and metamorphism (e.g. Higgins & Soper, 1991). In the extreme north of North Greenland, three stages of deformation can be observed (e.g. Soper & Higgins, 1987, 1990, 1991a; von Gosen & Piepjohn, 1999). The E W- to NE SWtrending Ellesmerian structures can be traced towards the Canadian Arctic islands in the west (e.g. Trettin, 1989; Surlyk, 1991). On Barents Shelf in the east, they are represented by the structures of the Svalbardian deformation (e.g. Christie, 1964; Manby & Lyberis, * Author for correspondence: piepjoh@uni-muenster.de 1992; McCann, 2000; Piepjohn, 2000). The latest Devonian to earliest Carboniferous age of the Ellesmerian deformation on Devon Island (Mayr et al. 1998) and the post-late Famennian to pre-viséan age of the Svalbardian deformation on Spitsbergen (Piepjohn et al. 2000) suggest that the Ellesmerian deformation in North Greenland most likely took place at the Devonian Carboniferous boundary. The Ellesmerian deformation was followed by the deposition of a Carboniferous to Tertiary succession which is ascribed to the Wandel Sea Basin in North Greenland (e.g. Dawes & Soper, 1973; Håkansson & Stemmerik, 1984; Stemmerik & Worsley, 1989). Equivalent successions can be found on Svalbard (e.g. Håkansson & Stemmerik, 1984; Dallmann, 1999) and are known as the Sverdrup Basin deposits in Arctic Canada (Thorsteinsson & Tozer, 1970). Exposures of the Wandel Sea Basin are few and far between, with the principal outcrops found in the Wandel Hav Strike-Slip Mobile Belt, along the Kap Cannon Thrust Zone and the Harder Fjord Fault Zone (e.g. Stemmerik & Håkansson, 1991) which is the subject of this paper. Associated with the Late Cretaceous and Tertiary re-arrangement of the plate-tectonic configuration in the Arctic region and the openings of Labrador Sea, Baffin Bay, Eurasian Basin and the North Atlantic

2 408 K. PIEPJOHN & W. VON GOSEN Lomonosov Ridge Arctic Mid Ocean Ridge F r a m S t r a i t Figure 1. Overview map of the Arctic with locations of major Eurekan fault lines on Ellesmere Island, North Greenland and Spitsbergen, compiled after Dawes (1982), Mayr & De Vries (1982), Håkansson & Pedersen (1982), Soper & Higgins (1987), Perry & Fleming (1990), Okulitch (1991) and Dallmann et al. (1993). Ocean, the Tertiary Eurekan deformation (e.g. Thorsteinsson & Tozer, 1970; Soper, Dawes & Higgins, 1982) affected the Canadian Arctic, North Greenland and Svalbard. The Harder Fjord Fault Zone traverses almost all of North Greenland (Fig. 1) and can be traced from central Nansen Land in the west across Frederick E. Hyde Fjord and Hans Egede Land in the east (Fig. 2). In the Frigg Fjord area and along Frederick E. Hyde Fjord, it cuts through the Lower Cambrian to Silurian strata of the Franklinian Basin. The easternmost section of the fault zone in Hans Egede Land separates Lower Cambrian deep-water deposits in the north from Middle Proterozoic rocks in the south (Fig. 2). In the Frigg Fjord area, north of Midtkap and east of Depot Bugt, the fault zone consists of a tectonic mélange zone (Higgins, 1984; Håkansson, 1988; Bengaard & Henriksen, 1992). It contains Franklinian Basin deposits, (?)Upper Carboniferous red-beds, Upper Permian sediments, Upper Cretaceous clastic deposits and mafic intrusions as well as greenstones of uncertain age (e.g. Soper, Higgins & Friderichsen, 1980; Higgins, Friderichsen & Soper, 1981; Håkansson, Heinberg & Stemmerik, 1981, 1991; Parsons, 1981; Wagner, Soper & Higgins, 1982). To the west, the Harder Fjord Fault Zone is interpreted to continue into the Lake Hazen Fault Zone on Ellesmere Island (Fig. 1) (Christie, 1964; Higgins, Mayr & Soper, 1982; Håkansson & Pedersen, 1982). Similar long and linear fault zones are exposed on Svalbard (e.g. Billefjorden and Lomfjorden fault zones, Fig. 1). This contribution is based on mapping and structural analyses in six study areas in the central and eastern segments of the Harder Fjord Fault Zone. The structures of the observed deformational events and their cross-cutting relationships will lead us to an interpretative model of the tectonic history along the fault zone. Finally, the tectonic evolution will be discussed with respect to the plate-tectonic situation during Early Tertiary times.

3 Polyphase deformation in North Greenland 409 Figure 2. (a) Geological sketch map of the central and eastern parts of the Harder Fjord Fault Zone in Johannes V. Jensen Land and Hans Egede Land (for location see Fig. 1), modified from Bengaard, Henriksen & Hougaard (1986) and Henriksen (1992). Large frames and circles depict the locations of study areas with figures along the Harder Fjord Fault Zone north of Frigg Fjord and east of Depot Bugt. (b) Simplified stratigraphic chart of the rock units along the Harder Fjord Fault Zone in the study areas. 2. Stratigraphic outline of the rock units along the Harder Fjord Fault Zone 2.a. Franklinian Basin (Cambrian to Silurian) The oldest sedimentary units of the Franklinian Basin are represented by more than 1500 m thick siliciclastics, calcareous mudstones and dolomites of the Lower Cambrian Skagen and Paradisfjeld groups (Friderichsen et al. 1982) (Fig. 2b) along a narrow strip north of Midtkap and at the mouth of Frederick E. Hyde Fjord north of the Harder Fjord Fault Zone (Fig. 2a). They are overlain by m thick alternating mudstones and turbidites of the Lower Cambrian Polkorridoren Group (Fig. 2b) (Friderichsen et al. 1982; Higgins et al. 1991). The uppermost 400 m of this succession consist of the purple

4 410 K. PIEPJOHN & W. VON GOSEN Figure 3. (a) Geological map of the Harder Fjord Fault Zone east of Depot Bugt (for location see Fig. 2). (b) Simplified and schematic N S profile across the Harder Fjord Fault Zone, view to the east.

5 Polyphase deformation in North Greenland 411 Santon northern boundary fault Gletscher southern boundary fault Figure 4. Geological sketch map of the Santon Gletscher area northeast of Frigg Fjord and N S cross-sections through the Harder Fjord Fault Zone (for location see Fig. 2). and green Frigg Fjord mudstones (Fränkl, 1955; Dawes & Soper, 1973; Friderichsen et al. 1982). The Polkorridoren Group is widely exposed on both sides of the Harder Fjord Fault Zone (Fig. 2a) with mostly Frigg Fjord mudstones in the south and turbidites in the north (cf. Friderichsen et al. 1982; Surlyk, 1991; Bengaard & Henriksen, 1992). During late Early Cambrian to Early Ordovician times, m thick dark mudstones, cherts and turbidites of the Vølvedal Group (Fig. 2b) (Friderichsen et al. 1982; Surlyk & Hurst, 1984) were deposited on both sides of the present fault zone (Fig. 2a). They are overlain by m thick cherts and mudstones of the Amundsen Land Group with intercalated turbidites and conglomerates (Friderichsen et al. 1982) and m thick siliciclastic calcareous turbidites with subordi-

6 412 K. PIEPJOHN & W. VON GOSEN l o w e r u n i t u p p e r u n i t Figure 5. For legend see facing page.

7 Polyphase deformation in North Greenland 413 nate mudstones and chert-pebble conglomerates of the Silurian Peary Land Group (Hurst & Surlyk, 1982). Both groups are exposed northeast of Grønnemark and south of Frederick E. Hyde Fjord (Fig. 2a). 2.b. Wandel Sea Basin (Carboniferous to Tertiary) 2.b.1. Depot Bugt conglomerate Two fault-bounded narrow occurrences of red-beds are exposed east of Depot Bugt (Fig. 3a) and 4 km west of Santon Gletscher (the informal name of a glacier northeast of Frigg Fjord) (Fig. 4). They are introduced as the Depot Bugt conglomerate in this paper and consist of red to red-brown, sometimes grey, massive and unsorted conglomerates and sandstones. The conglomerates contain angular to subangular and some well-rounded pebbles, a centimetre to several decimetres in size. The clasts are mostly represented by black chert and subordinate polycrystalline quartz, resedimented red mudstone and sandstone. Typically, most of the pebbles are coated by iron hydroxide. In the Depot Bugt area, the conglomerates also contain pebbles of greenstone and quartzite. The bedding is indicated by thin and mostly lens-shaped layers of coarse, red to red-brown sandstones. West of Santon Gletscher, the red conglomerates are underlain by massive white and grey sandstones with intercalated conglomerate layers and dark grey siltstones. The age of the Depot Bugt conglomerate is difficult to prove because fossils have not been found. As the red-beds are not affected by Ellesmerian structures but by Eurekan thrust faults (see Section 3.a.3), their deposition took place within the post-early Carboniferous to latest Cretaceous time interval. Because the structural relations of the red-beds to the Upper Cretaceous deposits are unclear, the Depot Bugt conglomerate could possibly be latest Cretaceous in age. The absence of characteristic Upper Cretaceous white sandstone-pebbles in the red conglomerates and the red colouration itself, however, argue for a pre-late Cretaceous age. Post-Ellesmerian red-beds are only known from the base of the Late Carboniferous in North Greenland (Mallemuk Mountain Group) (Håkansson & Stemmerik, 1984; Stemmerik & Håkansson, 1989, 1991) and on Svalbard (Gipsdalen Group) (Gjelberg & Steel, 1981; Dallmann, 1999). Therefore, it is most likely that the Depot Bugt conglomerate is related to this stage of Late Carboniferous basin formation. 2.b.2. Permian deposits Northeast of Midtkap in central Frederick E. Hyde Fjord, a narrow occurrence of conglomerates, sandstones and carbonaceous shales is exposed in a small area along the Harder Fjord Fault Zone (Soper, Higgins & Friderichsen, 1980). The well-preserved floral content dates the deposits to the Late Permian (Wagner, Soper & Higgins, 1982). 2.b.3. Upper Cretaceous deposits Upper Cretaceous clastic deposits crop out in narrow, E W-trending strips within the fault zone in the Santon Gletscher area, at Depot Bugt (Figs 3, 4) (Soper, Higgins & Friderichsen, 1980; Håkansson, Heinberg & Stemmerik, 1981; Birkelund & Håkansson, 1983) and 20 km east of Depot Bugt (see Fig. 2). They can be divided into a sandstone-dominated lower unit and a siltstone-dominated upper unit (Fig. 5). The thickness of the entire succession can be broadly estimated to be in the range of at least 500 m in the Santon Gletscher profile, slightly more than the 400 m estimate of Håkansson, Heinberg & Stemmerik (1991). Soper, Higgins & Friderichsen (1980) and Håkansson, Heinberg & Stemmerik (1981) reported that the northern contact of the Cretaceous succession at Santon Gletscher is represented by a fault and that the top of the Cretaceous clastics faces northwards. However, our observations show that the contact between the folded Cambro-Ordovician Vølvedal cherts in the north and unfolded Upper Cretaceous deposits in the south is an angular unconformity. It is well exposed at the western margin of Santon Gletscher and in the valley 4 km west of Santon Gletscher (Figs 4, 5) and is characterized by an erosional, irregular surface which is overlain by a local, several-decimetre-thick basal breccia of chert clasts (up to 10 cm in diameter) which are derived from the directly underlying chert sequence. 2.b.3.a. Lower sandstone unit (pre-late Santonian) The most complete section of the lower sandstone unit is exposed at the western margin of Santon Gletscher. There, it can be divided into 60 m thick, massive white sandstones above the unconformity, 20 m thick grey silt- and sandstones and 25 m thick white sandstones at the top (Fig. 5). According to cross-bedding and the location of the unconformity in the north, the entire NNW-dipping sequence is steeply overturned. A similar succession is exposed at Depot Bugt with bioturbated white sandstones, well-bedded dark silt- and mudstones and again massive white sandstones (Fig. 3). In the outcrops 4 km west of Santon Gletscher and 20 km east of Depot Bugt, the upper white sandstones are not preserved, because they are probably cut-off by reverse faults. Figure 5. Tectonic sketch map of the Cambro-Ordovician chert sequence (Vølvedal Group) and the Upper Cretaceous clastic succession with mafic intrusions at the western margin of the Santon Gletscher (for location see Fig. 4). Note that the subvertical Upper Cretaceous deposits unconformably overlie the folded Cambro-Ordovician sediments in the north.

8 414 K. PIEPJOHN & W. VON GOSEN Over a distance of 110 km, the lithologies of the deposits in all four outcrop areas can be directly compared. The white sandstones are especially characteristic for the lower sandstone unit along the Harder Fjord Fault Zone. The latter contain centimetre- to decimetre-thick conglomerate layers with clasts of black chert and polycrystalline quartz and layers with single pebbles of black chert. The age of the lower sandstone unit is probably Late Cretaceous, which is indicated by relics of plants in the basal white sandstones at Depot Bugt. There, the lower sandstone unit possibly represents the lower part of the Herlufsholm Strand Formation (Håkansson, Heinberg & Stemmerik, 1981). 2.b.3.b. Upper siltstone unit (late Santonian) The upper siltstone unit at the western margin of Santon Gletscher consists of at least three, up to 100 m thick, packages of dark grey siltstones which are separated by a 30 m thick layer of sandy siltstones and a 15 m thick, massive white sandstone unit (Fig. 5). The uppermost part of the succession is represented by at least 140 m thick, grey sandstones with thin siltstone layers. The entire sequence is steeply inclined to the south. Only the southernmost sandstones are overturned (Fig. 5). East of Santon Gletscher (Fig. 4), the upper siltstone unit consists of dark grey and black siltstones with intercalated massive, monotonous grey sandstones. According to cross-bedding and graded bedding, the entire sequence is in an upright position and gently dips approximately to the SSW. Further east, the E W-trending strip of Cretaceous strata wedges out (Fig. 4). The upper siltstone unit is late Santonian in age, as dated by well-preserved inoceramids in the southern part of the Santon Gletscher profile (Håkansson, Heinberg & Stemmerik, 1981, 1991; Håkansson, 1988). 2.b.4. Mafic intrusions (Late Cretaceous) Along the Harder Fjord Fault Zone, the Palaeozoic Paradisfjeld Group, Frigg Fjord mudstones and Vølvedal cherts as well as the lower and upper units of the Upper Cretaceous succession are truncated by mafic sills and dykes. Two generations of intrusions can be observed in the Santon Gletscher profile; the older generation is represented by centimetre- to tensof-metres-thick sills. They are mostly injected parallel or at small angles to the bedding of the Upper Cretaceous clastics and mostly strike ENE WSW (Fig. 5). The sills are cross-cut by several-metres-thick, almost vertical, approximately NW SE-trending and partly irregular dykes. In general, the sills record a higher degree of alteration compared with the crosscutting dykes. Northwest of Frigg Fjord, up to 40 m thick, E Wtrending greenstone bodies are exposed within the Harder Fjord Fault Zone. Estrada (1998) pointed out that there are no significant petrological and geochemical differences between these greenstones and the sills and dykes. The author suggested that the greenstones originally represented E W-trending dykes which were mechanically fragmented and brecciated during the Eurekan deformation. The intrusion of the mafic dykes in North Greenland took place during a long time interval between 103 Ma (Manby et al. 1998) and the extrusion of the Kap Washington volcanics at the Cretaceous Tertiary boundary (64 ± 3 Ma: Larsen, 1982; Estrada, Höhndorf & Henjes-Kunst, 1998). In the studied outcrop areas, a post-late Santonian (post-83 Ma) phase of intrusion is indicated, as some of the sills and dykes cut through the upper Santonian upper siltstone unit. This observation does not exclude the possibility that some of the mafic intrusions along the Harder Fjord Fault Zone pre-date the late Santonian sedimentation. 2.b.5. Lower Tertiary sediments at Depot Bugt An isolated occurrence of undeformed Lower Tertiary sediments has been described from an E W-trending valley at Depot Bugt (Croxton et al. 1980). During our work in the Depot Bugt area, we could not find outcrops of these deposits. 3. Structural architecture of the Harder Fjord Fault Zone 3.a. Western segment between Nornegæst Dal and Santon Gletscher area In the 25 km long western segment between the valley north of Nornegæst Dal and Santon Gletscher, the Harder Fjord Fault Zone consists of two major boundary faults (Fig. 2). The northern boundary is represented by a subvertical fault which separates Polkorridoren mudstones and turbidites in the north from Vølvedal cherts in the south (Figs 4, 6a, 7b, 8). The southern boundary also consists of a subvertical fault zone and separates Vølvedal cherts in the north from Frigg Fjord mudstones in the south in the Nornegæst Dal area. There, competent greenstones and mafic intrusions are additionally involved in the southern boundary zone and are faulted against incompetent Frigg Fjord mudstones (Figs 6, 7b, c). In the Santon Gletscher area, the southern boundary is marked by a steeply S-dipping reverse fault which carried the Frigg Fjord mudstones towards the north over the Depot Bugt conglomerate (Fig. 4 profile A A ) and Upper Cretaceous deposits (Fig. 4 profiles B B, C C ). Between both boundary faults, the Harder Fjord Fault Zone consists of a narrow, 250 to 350 m wide strip which can be traced from the valley north of Nornegæst Dal in the west to Santon Gletscher in the east. This strip contains Vølvedal cherts which are overlain by Upper Cretaceous deposits in the Santon Gletscher area. In addition, fault-bounded red-beds of

9 Polyphase deformation in North Greenland 415 Figure 6. Profile north of Nornegæst Dal, ~7 km WNW of the end of Frigg Fjord (for location see Fig. 2). (a) Schematic N S profile depicting the general situation in the outcrop and the location of the main faults of the Harder Fjord Fault Zone (see text for further explanations). (b) Simplified block sketch of two stages of Early Palaeozoic Ellesmerian folding (F1, F2) affecting the cherts and quartzitic sandstone layers of the Cambro-Ordovician Vølvedal Group (see (a) for location). Post-Ellesmerian (Eurekan) reverse faults cut through the fold structures. the Depot Bugt conglomerate are exposed in the southern part of the strip in the valley 4 km west of Santon Gletscher (Figs 4, 8). 3.a.1. Profile north of Nornegæst Dal North of Nornegæst Dal, about 7 km WNW of the end of Frigg Fjord (see Fig. 2), a N S-trending valley exposes a profile across the Harder Fjord Fault Zone. In the northern part, a 250 m wide strip of Vølvedal cherts is separated by steep faults from Frigg Fjord mudstones on both sides (Fig. 6a). The cherts are intensely folded by at least two generations of folds. F1 folds several metres in size are tight to nearly isoclinal with the axes steeply plunging to the west (Figs 6b, 7a). They are folded around open to tight second generation folds (F2) on a tens-of-metres scale with approximately E W- to NE SW-striking B2 fold axes. S1 and S2 fracture cleavage planes are related to the respective fold generations and fan around the hinge zones. Both fold generations are cross-cut by mostly northwards-inclined brittle D3 reverse faults (Figs 6b, 7a). Within thicker fault zones, duplex structures are developed. Together with slickensides on the fault planes they indicate N- and S-directed transports of the hanging walls. In the southern part of the profile, a thick body of greenstones is separated from the Frigg Fjord mudstones by steep faults. Both mudstones and greenstones are affected by intense C3 shearing. Another greenstone body is juxtaposed along a S- dipping D3 thrust fault zone and now represents a wedge-shaped and fault-bounded relic within the Vølvedal chert sequence (Fig. 6a).

10 416 K. PIEPJOHN & W. VON GOSEN Figure 7. For legend see facing page.

11 Polyphase deformation in North Greenland 417 stream Figure 8. Geological sketch map of the Harder Fjord Fault Zone in the valley 4 km west of Santon Gletscher (for location see Fig. 4). 3.a.2. Profile south of Grønnemark About 3 km northwest of the end of Frigg Fjord (see Fig. 2), intensely folded cherts of the Vølvedal Group are exposed in a NNW SSE-trending canyon south of Grønnemark. In the north, they are separated from Lower Cambrian Polkorridoren turbidites and mudstones by S-dipping faults (Fig. 7b). The southern boundary to the Frigg Fjord mudstones is represented by an almost vertical fault zone (Fig. 7b,c). In the central and southern parts of the 300 m long outcrop, three massive greenstone bodies are juxtaposed against the Vølvedal cherts and Frigg Fjord mudstones along vertical faults (Fig. 7c). In the Vølvedal cherts, the deformation is dominated by open to tight folds which are partly combined with accommodation faults. The fold axes strike ENE WSW and are comparable with the F2 folds in the Vølvedal Group north of Nornegæst Dal. Fracture cleavage planes (S2) fan around the fold hinges. The Vølvedal cherts as well as the F2 fold structures are partly cross-cut by high-angle reverse Figure 7. (a) Lower hemisphere stereographic plots (equal area) of fabric elements in cherts of the Cambro-Ordovician Vølvedal Group in the profile north of Nornegæst Dal, ~7 km WNW of Frigg Fjord. (b) Geological sketch map of the outcrop situation at Grønnemark, ~3 km NNW of the end of Frigg Fjord (for location see Fig. 2). (c) Ellesmerian folding in the Cambro-Ordovician Vølvedal cherts and Eurekan brittle faulting in the cherts and along the boundaries of greenstone bodies and Frigg Fjord mudstones in the canyon at Grønnemark.

12 418 K. PIEPJOHN & W. VON GOSEN Figure 9. For legend see facing page.

13 Polyphase deformation in North Greenland 419 faults (D3) which dip to the north or south (Fig. 7c). They are accompanied by conjugate sets of small-scale reverse faults which also displace the boundary between the greenstone and the cherts in the centre of the profile (Fig. 7c). 3.a.3. Profile 4 km west of Santon Gletscher In the valley 4 km west of Santon Gletscher (Fig. 4), the following ENE WSW-striking rock units are exposed across the Harder Fjord Fault Zone (Fig. 8). The area north of the fault zone consists of steeply SSE-dipping turbidites and Frigg Fjord mudstones of the Polkorridoren Group. To the south, folded cherts of the Vølvedal Group crop out within a 300 m wide strip and are unconformably overlain by subvertical Upper Cretaceous deposits. The next narrow zone to the south contains red-beds of the (?)Upper Carboniferous Depot Bugt conglomerate. Finally, folded Frigg Fjord mudstones mark the southern boundary of the Harder Fjord Fault Zone. The structures within the Polkorridoren Group north of the Harder Fjord Fault Zone can clearly be assigned to the Ellesmerian deformation. The vergence of a second-order fold indicates that the Frigg Fjord mudstones in the north and underlying turbidites in the south are located on the thick overturned short limb of a NNW-vergent, hundreds of metres in scale, Ellesmerian F2 fold structure (Fig. 9, top profile, left) which is cut off by the northern boundary fault of the Harder Fjord Fault Zone. The Vølvedal cherts further south are intensely folded by at least two generations of folds, comparable with the situation in the profile north of Nornegæst Dal (Fig. 9 top profile right). Tight to isoclinal F1 folds from a decimetre to several metres in size are accompanied by a planar, axial-plane S1 cleavage. Different orientations of the B1 fold axes are a result of second generation folds (F2) which, on a scale of tens of metres, overprinted the entire sequence around E W- to NE SW-trending axes (Figs 9 top profile right, 10a). Within silty layers, an S2 crenulation cleavage is developed or is replaced by C2 shear planes in chert layers. The folded chert sequence is cross-cut by N-dipping reverse and thrust faults which are accompanied by C3 shear planes (Fig. 10a). The faults cut through both generations of folds (F1, F2), and slickensides indicate S-directed transports of the hanging walls. The Frigg Fjord mudstones south of the Harder Fjord Fault Zone are dominated by a penetrative S2 axial plane cleavage fabric which is related to open F2 folds around ENE WSW-striking axes (Figs 9 bottom profile, 10b). Equivalents of the F1 folds in the north could not be found. The D2 fabric elements are crosscut by densely spaced, N- and S-dipping C3 shear planes (Figs 9 bottom profile, 10b) which crenulate the older planar fabrics. Near the contact to the Depot Bugt conglomerate in the north, a zone of several S-dipping reverse faults and intensely sheared and cleaved mudstones is exposed (Fig. 9 bottom profile). There, S2 cleavage planes in the mudstones are folded on a centimetre scale around E W axes and cross-cut by C3 shear planes. The F3 folds, C3 shear planes and reverse faults are related to the ~80 S-dipping southern boundary fault of the Harder Fjord Fault Zone which carried the Frigg Fjord mudstones northwards over the Depot Bugt conglomerate. The (?)Upper Carboniferous Depot Bugt conglomerate north of the Frigg Fjord mudstones is affected by (conjugate sets of) shear planes, cleavage planes and mostly S-directed reverse faults (Fig. 10c). Intense shearing and reverse faulting within the black siltstones in the southernmost part of the outcrop are related to a S-directed reverse fault at the base of a white sandstone unit (Fig. 11c). The structures are similar to the C3 shear planes and reverse faults in the Franklinian deposits on both sides of the Harder Fjord Fault Zone. The subvertical Cretaceous sediments are affected by N- and S-dipping conjugate sets of C3 shear planes and mostly N-dipping reverse faults (Figs 9 middle profile, 10d, 11a,b). The latter cut across the basal unconformity and underlying Vølvedal cherts (Fig. 11a). Within the Cretaceous strata, the intersection lineations (δ3) strike ENE WSW to ESE WNW (Fig. 10d). C3 shear planes are accompanied by single, small-scale thrust and reverse faults which also displace the mafic intrusions (Fig. 11a). Shearing and S- directed thrust faulting increase southwards. Duplex structures on a decimetre to metre scale confirm the top-to-the-south sense of displacement (Fig. 11b). The mafic intrusions record comparable C3 shear planes and thrust fault fabrics. As in the Depot Bugt conglomerate, no fold structures were found within the Cretaceous sediments. 3.a.4. Santon Gletscher The dark grey and well-bedded cherts of the Vølvedal Group below the Cretaceous unconformity are affected by intense folding on a scale up to several tens of metres. The folds are combined with shear planes Figure 9. Simplified and schematic N S cross-section summarizing the situation along the N S-trending valley 4 km west of Santon Gletscher (for location of profile see Fig. 8). The upper profile through the Lower Cambrian Polkorridoren turbidites and the Cambro-Ordovician Vølvedal cherts is not to scale. Note the isoclinal Ellesmerian F1 folds refolded by E W-trending F2 folds in the chert sequence. The profile sketch also depicts the main fabric elements within Frigg Fjord mudstones of the Polkorridoren Group (lower profile) just to the south of the inferred, main high angle reverse fault of the Harder Fjord Fault Zone.

14 420 K. PIEPJOHN & W. VON GOSEN Figure 10. Lower hemisphere stereographic projections (equal area) of fabric elements from the different units in the profile along the valley 4 km west of Santon Gletscher (a d) and in the Santon Gletscher area (e h) (for location see Fig. 8). (a) Lower Cambrian turbidite sequence (Polkorridoren Group) and Cambro-Ordovician chert sequence (Vølvedal Group) north of Harder Fjord Fault Zone, (b) Lower Cambrian Frigg Fjord mudstones (Polkorridoren Group) south of Harder Fjord Fault

15 Polyphase deformation in North Greenland 421 fanning around the hinge zones and are similar to the F2 folds in the profiles north of Nornegæst Dal, at Grønnemark and in the valley 4 km west of Santon Gletscher. The B2 fold axes plunge W to WSW, and extension joints and fracture planes are oriented perpendicular to them (Fig. 10e). The folded Vølvedal cherts and irregularly intruded Cretaceous dykes are cross-cut by brittle shear planes (C3) (Fig. 12 top profile left) which dip gently to the north and south (Fig. 10e) and indicate N S compression. The overlying Cretaceous succession does not record any fold structure. The sandstones and siltstones are cross-cut by cleavage and shear planes (S3/C3) which mostly dip approximately to the NNW or SSE and partly represent conjugate sets (Fig. 12). They are comparable to those in the cherts of the Vølvedal Group below the unconformity in the north. Within dark siltstones, C3 shear planes are replaced by conjugate S3-fracture cleavage planes creating a pencil cleavage fabric. The C3/S3 planes also cut through the mafic dykes and sills (Fig. 12). The latter are sheared along the boundaries and to a variable extent also in the central parts. In the upper siltstone unit, the orientation of the S3 cleavage is partly different (Figs 5, 10g). However, the intersection lineation (δ3) between bedding (S0) and cleavage/shear planes (S3/C3) has a fairly constant E W to ENE WSW trend over the entire profile (Fig. 10f,g). East of Santon Gletscher, the bedding (S0), cleavage planes (S3) and intersection lineations (δ3) in the upper siltstone unit strike ESE WNW (Fig. 10h). The folded Vølvedal cherts and overlying Upper Cretaceous sediments in the Santon Gletscher area were together rotated southwards into a vertical to overturned position (Figs 4, 5, 11a, 12). Additionally the rotation of the underlying chert sequence is indicated by the present S-directed vergence of the F2 folds in the Vølvedal cherts (Fig. 4 profile B B ) which does not correspond to the regional N-vergence of the Ellesmerian fold structures. Rotating the Cretaceous pile of rocks along with the Vølvedal cherts back into its initial horizontal position, however, would restore the N-vergence of the Ellesmerian folds in this block. This would fit with the overall picture of the Ellesmerian fold geometries depicted by Soper & Higgins (1987), among others. 3.b. Eastern segment in northern Hans Egede Land 3.b.1. Depot Bugt The Harder Fjord Fault Zone just to the east of Depot Bugt consists of a 100 m wide strip of tectonic slices and imbricates which are bounded by E W-trending, slightly curved and S-dipping thrust and reverse faults (Fig. 3). Their orientation as well as slickenside lineations, for example, on a steeply S-dipping (~80 ) reverse fault cutting through the Cretaceous succession in the eastern part of the outcrop, indicate N-directed reverse movements of the hanging walls perpendicular to the fault zone. In the western part of the outcrop, S-dipping lens-shaped imbricates contain two thin slices of red Polkorridoren mudstones which are separated by imbricates with red-beds of the Depot Bugt conglomerate and mafic sills. The redbeds are intensely sheared along S-dipping C3 shear planes which can be related to the imbricate faults. In the upper part of the imbricate zone, 20 m thick grey and red Depot Bugt conglomerates are thrust northwards over the Polkorridoren mudstones (Fig. 3). 3.b.2. Easternmost exposure of the Harder Fjord Fault Zone The deformation in the easternmost outcrop of the Harder Fjord Fault Zone 20 km east of Depot Bugt is characterized by mostly N-directed reverse faults and by gently NNE-dipping C3 shear planes affecting Cretaceous sandstones and a 10 m thick mafic sill (Fig. 13a). Within the siltstones, the shear planes are replaced by conjugate sets of S3 fracture cleavage planes creating a pencil cleavage fabric. The planes dip to NNE and SSW, and the intersection lineations (δ3) strike approximately NW SE (Fig. 13c). In addition, the deposits as well as the sill are truncated by SSWand NNE-dipping reverse faults (Fig. 13a). Similar to the Santon Gletscher profile, the Upper Cretaceous strata are rotated into a vertical position. Further east, the Upper Cretaceous deposits wedge out. There, the Harder Fjord Fault Zone probably continues as a single fault between the Franklinian Skagen and Paradisfjeld groups in the north and the Middle Proterozoic Independence Fjord Group in the south (Fig. 2). This outcrop is the only one along the Harder Fjord Fault Zone in which we found fabric elements indicating lateral displacements; the entire Cretaceous sequence at this locality is cross-cut by four sets of strike-slip fault planes and shear planes (Fig. 13d). We interpret the N S-trending dextral planes and the NNE SSW-trending sinistral planes (which displace the sill in the Polkorridoren Group, Fig. 13b) as strikeslip transfer planes resulting from N S to NE SW compression (D3). The ESE WNW-trending sinistral planes and E W-trending dextral planes are more or less parallel to the fault zone and could indicate two different stages of post-late Santonian lateral displacements. Unfortunately, the interpretation re- Zone, (c) (?)Upper Carboniferous Depot Bugt conglomerate, (d) Upper Cretaceous clastic succession within the Harder Fjord Fault Zone, (e) Cambro-Ordovician chert sequence (Vølvedal Group) north of the Cretaceous succession, (f ) Upper Cretaceous sediments in the lower sandstone unit, (g) upper siltstone unit west of Santon Gletscher and (h) east of Santon Gletscher.

16 422 K. PIEPJOHN & W. VON GOSEN Figure 11. For legend see facing page.

17 Polyphase deformation in North Greenland 423 mains unclear because no cross-cutting relationships between the four different sets of planes could be detected. 4. Discussion and synthesis of structural evolution 4.a. Pre-Devonian Although the Harder Fjord Fault Zone as mapped is clearly a post-ellesmerian structure (Soper & Higgins, 1987), its early history is still a matter of debate. Surlyk, Hurst & Bjerreskov (1980), Surlyk & Hurst (1983, 1984) and Hurst & Surlyk (1983, 1984) suggested that the fault zone already controlled the platform margin in Early Cambrian times. In contrast, Soper & Higgins (1987, 1991b) pointed out that the position of the lineament does not coincide with the facies changes in the Lower Cambrian sediments which define the trough platform transition. In the study areas the almost identical Frigg Fjord mudstones on both sides of the Harder Fjord Fault Zone indicate that it was not active during Early Palaeozoic times because no effect on sedimentary facies in the Franklinian Basin could be observed. 4.b. Devonian to Early Carboniferous (Ellesmerian deformation) The earliest observable structures in the rock units in the vicinity of the Harder Fjord Fault Zone are related to two stages of deformation (D1, D2) of the Franklinian Basin sediments. As the F1 and F2 fold structures and related cleavage planes (S1, S2) do not affect the Wandel Sea Basin deposits or do not pass through the unconformity into the overlying Cretaceous sediments, their Ellesmerian age is evident. This is supported by irregularly injected post-upper Santonian mafic dykes with chilled margins in the Vølvedal cherts cutting across S2 cleavage planes and F2 fold structures (Fig. 12 top profile left). Dawes & Soper (1973, 1979), Soper, Higgins & Friderichsen (1980), Higgins, Soper & Friderichsen (1985) and Soper & Higgins (1987, 1990) recognized three Ellesmerian fold generations in Johannes V. Jensen Land. Along the Harder Fjord Fault Zone, the observed structures in the study areas can be attributed to the first two events (D1, D2), as the third Ellesmerian folding is restricted to the north coast of North Greenland (e.g. Soper & Higgins, 1991b). The first deformation D1 is characterized by tight to isoclinal F1 folds on a decimetre to several metre scale with related S1 cleavage planes. The orientations of the B1 fold axes do not coincide with the overall ENE WSW trend of the Ellesmerian structures and can be compared with W- and S-directed imbricate thrusts south of the Harder Fjord Fault Zone southwest of Frigg Fjord (Fig. 2). Håkansson & Pedersen (1982) and Pedersen (1986) interpreted these structures as being related to the Caledonian orogenic belt in Kronprins Christian Land (eastern North Greenland) during the Early to Middle Devonian Vølvedal orogeny and suggested large-scale (?about 700 km), pre-ellesmerian sinistral strike-slip displacements along the fault zone during that time. In this case, the northernmost parts of North Greenland would represent a terrane and the Harder Fjord Fault Zone a terrane boundary (Soper & Higgins, 1991b). This would also imply a reactivation of the lineament during the subsequent Ellesmerian deformation with a concentration of compressional structures parallel to the supposed terrane boundary. This is inconsistent with our observations in the field which show (a) that the same stratigraphic successions crop out on either side of the present fault zone and (b) that there is no evidence for a concentration of Ellesmerian structures along the fault zone. On the contrary, the NNWvergent, hundreds of metres in scale F2 folds and associated D2 structures affected the Polkorridoren and Vølvedal groups on either side of the Harder Fjord Fault Zone to the same extent, suggesting that it was still inactive at that time. This is supported by Soper & Higgins (1991b), who found no evidence that the fault zone, as now seen, was in existence during the Ellesmerian deformation. The differing D1 structures and S- and W-directed imbricate thrusts can probably be related to S-directed Ellesmerian thrusts at similar stratigraphic levels found all the way along the Ellesmerian front in North Greenland, because there is no evidence for Caledonian or Ellesmerian deformation in the 200 km wide strip of Palaeozoic platform sediments between Kronprins Christian Land and Frigg Fjord (Soper & Higgins, 1985, 1987, 1990). 4.c. (?)Upper Carboniferous In the field, indications for initial movements along the Harder Fjord Fault Zone are outlined by the (?)Upper Carboniferous red-beds of the Depot Bugt conglomerate west of Santon Gletscher and east of Depot Bugt. The coarse conglomerates with boulders up to a decimetre in size were deposited during an episode of intense uplift and erosion possibly caused by tectonic Figure 11. Profile sketches of the outcrop situation in the valley 4 km west of Santon Gletscher (for locations see Fig. 8). (a) Upper Cretaceous sediments with an unconformable contact to the Cambro-Ordovician Vølvedal cherts in the north. Note Eurekan C3 shear planes and small-scale faults cutting across the basal unconformity and the mafic intrusions. (b) Eurekan C3 shear planes and S-directed reverse fault planes within Upper Cretaceous sediments and mafic intrusions. Note intense faulting in the grey-black siltstones with the formation of duplex structures. (c) Sandstones and conglomerates of the (?)Upper Carboniferous Depot Bugt conglomerate with intensely sheared grey-black siltstones in the southern part of the outcrop.

18 424 K. PIEPJOHN & W. VON GOSEN Figure 12. Simplified and schematic N S cross-section through the Cambro-Ordovician chert sequence (Vølvedal Group) and Upper Cretaceous clastic succession along the western margin of Santon Gletscher (see text for explanation). movements. The cherts in the Depot Bugt conglomerate are probably derived from the Vølvedal Group on both sides of the fault zone. These observations and the long lateral continuation along strike, parallel to the present fault zone, indicate that the early Harder Fjord Fault Zone could have been a post-ellesmerian rift with narrow, possibly graben-like, basins with coarse infills of red-beds (Fig. 14a). This development

19 Polyphase deformation in North Greenland 425 Figure 13. (a) Simplified N S cross-section A A (not exaggerated) through the subvertical lower sandstone unit of the Upper Cretaceous clastic succession with a 10 m thick mafic sill 15 km east of the Depot Bugt (for location see Fig. 2). (b) Geological sketch map of the easternmost outcrop of the Harder Fjord Fault Zone with mudstones of the Lower Cambrian Frigg Fjord mudstones (Polkorridoren Group) in the north and the vertical lower sandstone unit of the Upper Cretaceous strata in the south. Lower hemisphere stereographic plots (equal area) of fabric elements (c) and of strike-slip faults and shear planes with slickensides (d) within the deposits of the Upper Cretaceous succession 15 km east of Depot Bugt.

20 426 K. PIEPJOHN & W. VON GOSEN Figure 14. For legend see facing page.

21 Polyphase deformation in North Greenland 427 is very similar to the situation on Svalbard, which was already located north of Greenland during this period of time (Fig. 15a) (e.g. Harland et al. 1984; Heafford & Kelly, 1988; Stemmerik & Håkansson, 1991). There, several asymmetric basins (half-grabens) were formed in Carboniferous time parallel to long, major and linear fault zones and partly filled with red clastic sediments (e.g. Cutbill & Challinor, 1965; Gjelberg & Steel, 1981; Steel & Worsley, 1984; Johannessen & Steel, 1992). Whether the small basins along the ancient Harder Fjord Fault Zone have been related to lateral movements (pull-apart basins) or to pure N S extension, remains unclear. On Svalbard, however, the basin formation was controlled by extensional faulting with a possible subordinate sinistral component (e.g. McCann & Dallmann, 1996). 4.d. Late Permian Large-scale (?about 200 km) dextral displacement along the fault zone was suggested by Håkansson & Pedersen (1982), who argued that several local Late Permian basins in the Harder Fjord Fault Zone have been simultaneously filled with clastic deposits similar to many other syntectonic basins along strike-slip faults. However, there is only a single occurrence of Upper Permian deposits in the fault zone north of Midtkap. This basin was most likely produced by a reactivation of the lineament, but the absence of en échelon folds, oblique thrust faults or lateral slickenside lineations argues against large-scale strike-slip movements during this period of time. 4.e. Late Cretaceous In the Late Cretaceous, two important events dominated the development in North Greenland: a long phase of magmatic activity with the intrusions of mafic sills and dyke swarms began around 103 Ma (Manby et al. 1998) and was terminated by the extrusion of the Kap Washington volcanics at the Cretaceous Tertiary boundary at 64 ± 3 Ma (Larsen, 1982; Estrada, Höhndorf & Henjes-Kunst, 1998). The other event was the sedimentation of clastic deposits in late Santonian time in the study areas along the Harder Fjord Fault Zone (Håkansson, Heinberg & Stemmerik, 1981; Birkelund & Håkansson, 1983) and in the Campanian Maas-trichtian time interval at Kap Washington (Batten et al. 1981; Batten, 1982). Our observations along the Harder Fjord Fault Zone show that the emplacement of mafic sills and dykes into Lower Palaeozoic and Upper Cretaceous strata post-dated the late Santonian sedimentation (Fig. 14c). Their generation indicates a period of post-late Santonian extension in the Harder Fjord Fault Zone area, which probably caused a downfaulting of Cretaceous strata in narrow graben-like structures along the pre-existing Carboniferous faults (Fig. 14c). In the study areas, the Santonian sandstones with conglomerate and chert-pebble layers in the lower sandstone unit suggest fluvial conditions which gave rise to shallow marine sedimentation in the upper siltstone unit with the deposition of dark siltstones containing relics of inoceramids. Given the wellsorted, fine-grained character of the deposits, the comparability of the sediments in the different exposures over long distances along the Harder Fjord Fault Zone, and the thickness of more than 500 m in the Santon Gletscher area, it is reasonable to postulate a wide cover of Upper Cretaceous deposits (Fig. 14b) rather than the development of small, narrow and fault-bounded local basins. There was no field evidence found to indicate that the Upper Cretaceous occurrences at Santon Gletscher and east of Depot Bugt were related to syn-sedimentary tectonic activities or represent pull apart basins as suggested by Håkansson & Pedersen (1982) and Stemmerik & Håkansson (1991). Our observations indicate that the Harder Fjord Fault Zone was not active during the time of deposition of the Upper Cretaceous sediments. The N S-trending dyke swarms in northwestern Johannes V. Jensen Land and northern Nansen Land die out before reaching the Harder Fjord Fault Zone (Higgins, Friderichsen & Soper, 1981; Soper, Dawes & Higgins, 1982; Friderichsen & Bengaard, 1985; Bengaard et al. 1987). In Nansen Land, Soper & Higgins (1987, 1991b) described offsets of Ellesmerian Figure 14. Interpretative cartoons (not to scale) illustrating the possible tectonic evolution of the Harder Fjord Fault Zone in the study areas. (a) Ellesmerian deformation in this area is characterized by large-scale, NNW-vergent F2 folds in the Polkorridoren and Vølvedal Groups. First detectable movements along the fault zone can be assigned to the deposition of the coarse red Depot Bugt conglomerate in small, narrow basins, which can be related to post-ellesmerian uplift, erosion and blockfaulting during (?)Late Carboniferous times. It is possible that the normal faults have been reactivated during the formation of the Late Permain basin north of Midtkap. (b) In Late Cretaceous times, the fluvial lower sandstone unit and marine upper siltstone unit were deposited without significant evidence for tectonic activities along the fault zone during that time. (c) After the late Santonian deposition, numerous intrusions of mafic sills and dykes took place in North Greenland. They indicate an important stage of extension north of the fault zone which presumably was accommodated by dextral movements along the reactivated Harder Fjord Fault Zone. (d) Post-Late Cretaceous Eurekan N S compression is characterized by N-directed steep reverse faults and S-directed thrusts along pre-existing fault lines affecting Lower Cambrian to Ordovician deposits, the (?)Upper Carboniferous Depot Bugt conglomerate, Upper Cretaceous sediments and post-upper Santonian mafic intrusions. In the Frigg Fjord area, the E W-trending block with the 500 m thick Cretaceous succession and the underlying cherts including the Ellesmerian structures is rotated into a vertical position.

22 428 K. PIEPJOHN & W. VON GOSEN DeGeer Fracture Zone West Spitsbergen Fold-and-Trust Kap Cannon Trust Zone Belt Trolle Land Fault Zone Wandel Hav Strike-Slip Mobile Belt Labrador Sea Figure 15. For legend see facing page.

23 Polyphase deformation in North Greenland 429 structures and stratigraphic boundaries along the western segment of the Harder Fjord Fault Zone which indicate 20 km of dextral strike-slip movements. Although we found no clear structural evidence of lateral displacements in the study areas, a post-late Santonian phase of dextral strike-slip along the fault zone, which accommodated crustal extension in the north during the emplacement of the N S dyke swarms (Soper & Higgins, 1991b), seems to be likely (Fig. 15b). Hence, it is possible that strike-slip patterns of this Late Cretaceous tectonic stage have been overprinted or destroyed during subsequent Eurekan compression. 4.f. Tertiary (Eurekan deformation) The Palaeozoic Frigg Fjord mudstones and Vølvedal cherts, the (?)Upper Carboniferous Depot Bugt conglomerate, the Upper Cretaceous deposits and mafic intrusions were affected by the post-late Santonian Eurekan deformation (D3) (Fig. 14d). Along the Harder Fjord Fault Zone it is generally characterized by compressional structures which are dominated by C3 shear planes, S3 fracture cleavage planes, and N- and S-directed reverse and thrust faults. With the exception of some thrust-related small-scale F3 folds, the studied sediments do not exhibit fold structures which could indicate a folding of the entire pile of rocks. The overall geometries of the structural elements indicate major N S compression. The strike of shear planes and cleavage planes (C3, S3) as well as δ3 lineations, changes from a ENE WSW trend in the Nornegæst Dal area, a more or less E W trend in the Santon Gletscher area to a ESE WNW trend east of Depot Bugt in the Frederick E. Hyde Fjord area and is always parallel to the Harder Fjord Fault Zone. The Eurekan compression (D3) along the Harder Fjord Fault Zone is suggested to be latest Cretaceous or younger in age because the youngest deformed rocks in the study areas are post-late Santonian dykes which are cleaved, sheared and cut-off by thrust faults together with their upper Santonian country rocks. This is supported by the situation at the north coast of Greenland; there, the intrusion of the Late Cretaceous dyke swarms was followed by the deposition of thick volcanics and sediments of the Kap Washington Group (Batten et al. 1981; Brown, Parsons & Becker, 1987; Soper & Higgins, 1991b) between Late Cretaceous times and the Cretaceous Tertiary boundary (Larsen, Dawes & Soper, 1978; Batten et al. 1981; Batten, 1982; Larsen, 1982; Estrada, Höhndorf & Henjes-Kunst, 1998). Afterwards, the Kap Washington Group was overthrust by Franklinian deposits along the N-directed Kap Cannon Thrust Zone (e.g. Dawes & Soper, 1970; Brown & Parsons, 1981; Soper & Higgins, 1991b; von Gosen & Piepjohn, 1999) suggesting that the convergent Eurekan deformation (D3) in North Greenland was not older than the earliest Tertiary but Palaeocene and/or younger in age (e.g. Soper & Higgins, 1991b; von Gosen & Piepjohn, 1999). Although the more than 300 km long linear trend of the Harder Fjord Fault Zone suggests that it could have been formed by strike-slip displacements or wrench fault mechanisms, our observations indicate that the deformation (D3) was controlled by compression orthogonal to the pre-existing Harder Fjord Fault Zone rather than by major strike-slip displacements. Neither structural evidence for en échelon folds and thrust faults, strike-slip faults and flower-structures nor major lateral offsets of pre-eurekan rock units and structures were found in the segment of the fault zone between Nornegæst Dal and Hans Egede Land. Important offsets in the range of 20 km are only found in Nansen Land, but these movements are interpreted to be related to the phase of extension and intrusion of mafic sills and dykes prior to Eurekan compression (Soper & Higgins, 1987, 1991b). Therefore, we suggest that the concentration of Eurekan compressional structures along the fault zone was caused by reactivation of the pre-existing (?)Late Carboniferous and post-late Santonian normal faults. This is indicated, for example, by the situation in the Depot Bugt area where younger sediments are reverse faulted over older rocks. The reason for the rotation of the at least 500 m thick block of Upper Cretaceous sediments and underlying Palaeozoic cherts at Santon Gletscher into Figure 15. (a) Position of Svalbard with respect to North Greenland at anomaly 24 time (55 Ma; modified after Srivastava & Tapscott, 1986). The simplified map shows the distribution of the Palaeozoic Ellesmerian and Svalbardian fold-and-thrust belts (e.g. Dawes & Soper, 1973; Soper & Higgins, 1987; Piepjohn, 2000) and the Tertiary Eurekan fault lines in North Greenland (e.g. Håkansson & Pedersen, 1982) and West Spitsbergen Fold-and-Thrust Belt (e.g. Dallmann et al. 1993). White arrows estimated tectonic transport directions. (b) Reconstruction during anomaly 31 time (68 Ma) (Tessensohn & Piepjohn, 1998), modified after Srivastava & Tapscott (1986). The plate boundary between Europe and North America is represented by mid-ocean ridges in the North Atlantic and Labrador Sea and rifts in Baffin Bay and in the Eurasian Basin area. Greenland is still part of the Eurasian plate. (c) Reconstruction during anomaly 24 time (55 Ma) (Tessensohn & Piepjohn, 1998), modified after Menzies (1982) and Srivastava & Tapscott (1986). Until anomaly 13 time (36 Ma), Greenland is a separate plate. Sea-floor spreading takes place in the Eurasian Basin, in the Greenland and Norwegian seas, in the North Atlantic Ocean, in Labrador Sea and in Baffin Bay. (d) Reconstruction during anomaly 13 time (36 Ma) (Tessensohn & Piepjohn, 1998), modified after Srivastava & Tapscott (1986). Extinction of sea-floor spreading in Labrador Sea and Baffin Bay. Greenland becomes part of the North American plate, and the new plate boundary between Europe and North America is marked by sea-floor spreading in the Eurasian Basin and in the Greenland and Norwegian seas.