Two major unconformities beneath the Neoproterozoic Murchisonfjorden Supergroup in the Caledonides of central ,

DAVID G. GEE and ALEXANDER M. TEBEN’KOV

Gee D. G. & Teben’kov A. M. 1996: Two major unconformities beneath the Neoproterozoic Murchisonfjorden Supergroup in the Caledonides of central Nordaustlandet, Svalbard. Polar Research lS(I), X1-91. Two unconformities have been found in central Nordaustlandct. New mapping has located a major unconformity at the base of the Neoproteroaoic Murchisonfjorden Supergroup, with quartzites and basal conglomerates of the Djevleflota Formation unconformably overlying dark phyllites of the Helvetestlya Formation and metavolcanic rocks of the Svartrabbane Formation. A second unconformity separates the Helvetesflya from the Svartrabbane formations. These rocks were isoclinally folded, metamorphosed in lower greenschist facies, and, apparently, syntectonically intruded by Grenville-age granites, prior to uplift, erosion and Neoproterozoic deposition. Caledonian tectonothcrmal activity, as recorded in rhe Neoproterozoic srrara, appears to vary very little across Svalbard’s Eastern Terrane from Ny Friesland, in the west, to Murchisonfjorden in western Nordaustlandet and, via Wahlenbergfjorden, to the central Nordaustlandet area, described here. Upright folds with associated high angle, usually E-dipping cleavages. charactcrise the Caledonian deformation over an east-west distance of about 100 km. This evidence allows the possibility that the pre-Devonian basement, to the east of Nordaustlandet, beneath the northern Barents Sea (Barentsia), may be composed of Grenville-age complexes little influenecd by Caledonian tectonothermal activity. Alternatively, Barentsia is dominated by Caledonian hinterland tectonics, with extensive middle Paleozoic tectonothermal reworking of a Precambrian basement. David G. Gee, Department of Geophysics, Uppsala University, Villauagen 16, S-752 36 Uppsala, Sweden; Alexander M. Teben’kou, Polar Marine Geological Expedition, ul. Pobedy 24,189510 Lomonosoo, Russia.

mented Neoproterozoic sandstones, shales and Introduction carbonates of the Murchisonfjorden Supergroup Some of the most inaccessible, exposed areas of (Kulling 1934; Flood et al. 1969; Ohta 1982a, b). the Barents Shelf occur in northeastern Svalbard, A significant unconformity is inferred to also exist where crystalline complexes of granites, augen at the base of the Murchisonfjorden Supergroup, gneisses and migmatites have long been known but the contact, occurring beneath Lady Franklin- (Nordenskiold 1864, 1866) to be overlain by fjorden, is apparently not exposed on land in nearly unmetamorphosed sedimentary rocks (the western areas. Hecla Hoek formations) of Neoproterozoic and Further east, in central Nordaustlandet, a Early Paleozoic age (Kulling 1932, 1934). The similar unconformity (or unconformities) has relationships between these crystalline rocks and been inferred by various authors, but not pre- the fossiliferous successions have been much dis- viously demonstrated. Thus, Sandford (1950, puted, and only recently (Gee et al. 1995) has 1956), on the basis of several expeditions to the clear evidence been presented of a Grenville age area, concluded that a major unconforrnity should for some of the granites. The latter intrude both exist between underlying metamorphic complexes the migmatites and some of the metasedimentary and overlying little-metamorphosed sedimentary rocks (Fig. 1). and volcanic rocks; however, neither he nor Flood In northwestern parts of Nordaustlandet, an et al. (1969) were able to unambiguously demon- unconformity, first documented by Ohta (1982a), strate a regionally significant unconformity. This separates low grade metasedimentary rocks (the paper documents two major breaks in the stra- Brennevinsfjorden Group) intruded by ca. 950 tigraphy; we now know that the problems of their Ma granites (Gee et al. 1995), from an overlying identification relate to the existence of low grade volcanic and volcaniclastic sequence (the Kapp metasedimentary rocks of both Mesoproterozoic Hansteen Group); the latter underlies well-docu- and Neoproterozoic age. 82 D. G. Gee & A. M. Teben’kou

Fig. I. Geological map of Nordaustlandet and Ny Friesland (from Gee et al. 1995), with location of Fig. 2.

Previous work in central by Sandford (1956), Flood et al. (1969), Hjelle (1978), Ohta (1982~)and Lauritzen and Ohta Nordaustlandet (1984), and several Russian expeditions have pro- The Caledonian bedrock of central Nordaust- vided unpublished reports of the pre-Carbon- landet is exposed between two major ice-caps, iferous geology. Vestfonna and Austfonna, in the vicinity of The regional structural relationships in central Rijpfjorden and inner Wahlenbergfjorden and in Nordaustlandet were established by Sandford the broad open N-trending valley connecting (1956). He showed the approximate distribution these two waterways. South of Wahlenberg- of the rock units, with migmatites and granites fjorden, flat-lying Carboniferous successions (his “metamorphic complex”) occurring in a unconformably overlie the Caledonian rocks. major N-trending antiform extending through Geological maps of the area have been published Rijpdalen, from innermost Wahlenbergfjorden to Two major unconformities beneath the Neoproterozoic Murchisonfjorden Supergroup 83

Rijpfjorden, and flanked to the east and west by that the low grade metamorphosed sedimentary synforms containing Neoproterozoic successions. and volcanic rocks had a more complex structural The Rijpdalen Antiform plunges north in the history than the overlying Murchisonfjorden south and south in the north, and, from the latter lithologies and they therefore preferred the area, the migmatites and granites spread north- hypothesis (Flood et al. 1969 pp. 95-96) that a eastwards to occupy most of northeastern Nor- major unconformity separated these two strati- daustlandet . graphic units. Nevertheless, the exact location Sandford (1956) recognised several of the Neo- and interpretation of the importance of the uncon- proterozoic formations that had been defined formity were disputed, being influenced not only further west by Kulling (1934) in the classical by the field relationships, but also by the first Murchisonfjorden area. Kulling (1934) had shown isotope age-determination studies- Rb/Sr whole that the various pre-Vendian units in that area - rock and mineral ages of ca. 600 Ma ages on dolomites, limestones, shales and sandstones (his schists of the “metamorphic complex” (Hamilton Murchison Bay Formation) - were underlain, on & Sandford 1964). Support for the interpretation Botniahalvoya, by a succession of volcanic and that the Murchisonfjorden Neoproterozoic strata low grade sedimentary rocks that he referred to were underlain by a basement complex of mig- as the Cape Hansteen Formation. In central matites, granites and low grade volcano-sedi- Nordaustlandet, similar lithologies, though with mentary rocks was found locally, for example, only subordinate volcanites, were found by Sand- east of Bengtssonbukta, where a quartzite con- ford to separate the sandstone units (Flora Series) glomerate was recognised (Winsnes in Flood et of the Murchison Bay Formation from the under- al. 1969, p. 37) to discordantly overlie low grade lying “metamorphic complex”. Pink granites were metasediments. recorded to cut both the Cape Hansteen For- In general, the lithologies below the Mur- mation and the underlying rocks. Sandford com- chisonfjorden Supergroup in central and western mented (1956, p. 358), “It is pertinent, then, to Nordaustlandet are similar. However, whereas consider whether the Cape Hansteen Formation in western Nordaustlandet Flood et al. (1969) is stratigraphically unconformable on the meta- recognised that the sub-Murchisonfjorden rocks morphic complex, or is a part of a disharmonic composed two major mappable units, the Bren- mass between the surface of the complex and the nevinsfjorden and Kapp Hansteen formations competent beds of the Flora Series.” He noted (together comprising their Botniahalvoya (1956, p. 357) the presence of “sheets of meta- Group), in central Nordaustlandet they were morphosed sediments” between the granitic rocks unable to distinguish these formations. And in of the “metamorphic complex”, but no evidence the latter area, an independent quartzite and dark of metamorphic transition into the low grade phyllite unit, with subordinate intercalations of Cape Hansteen rocks; he therefore concluded carbonates, was identified - the Austfonna For- that an unconformity must exist between them. mation, overlying the other formations of the The structural complexity of the migmatites and Botniahalvoya Group in the Rijpdalen Antiform. the granites, contrasting with the relatively simple Subsequent work on Botniahalvoya (Gee et al. more or less cylindrical folding of the Neo- 1995) has demonstrated that the Brennevinsfjor- proterozoic strata, also prompted this inter- den and Kapp Hansteen units are both sub- pretation. divisible into formations and therefore should Flood et al. (1969) carried out an extensive have group status. Because a major unconformity helicopter-supported mapping program of Nord- separates these units on Botniahalvoya (Ohta austlandet in 1965. In central Nordaustlandet, 1982c), the term Botniahalvoya Group was aban- they recognised that there was a metamorphic doned (Gee et al. 1995). transition from the underlying migmatites and The stratigraphy of the Murchisonfjorden foliated augen granites into the so-called Cape Supergroup (Table 1) has also been modified Hansteen Formation, with staurolite, andalusite since its early definition by Kulling in 1934 (the and garnet crystallising syntectonically in the Murchison Bay Formation) and correlation from immediate contact zone. Metamorphic grade the type areas, eastwards into central Nord- decreases rapidly to lower greenschist facies away austlandet is not without problems. In the from the contact. Younger reddish granites cut Murchisonfjorden area, below Vedian tillites, all these rock units. Flood et al. (1969) showed Kulling (1934) distinguished six series (for- Table I. Stratigraphic correlation of the Meso- and Neoproterozoic successions of central and western Nordaustlandet NORDAUSTLANDE-I WESTERN CENTRAL WESTERN I CENTRAL WESTERN CENTRAL WESTERN CENTRAL (Kulling 1934) (Sandford 1956 (Flood et al. 1969) (Otha 1982 a&b) (Ohta 1982c) (Gee et al. 1995 (This paper) NORVIK Series NORVIK Series (shales) NORVIK Fm NORVIK Fm NORVIK Fm NORVIK Fm NORVIK Fm

FLORA Fm FLORA Fm FLORA Fm FLORA Fm FLORA Fm FLORA Series FLORA Series (quartzites) KAPP LORD Fm KAPP LORD Fm KAPP LORD Fm KAPP LORD Fm KAPP LORD Fm (shales) Successions below WESTMAN- WESTMAN- WESTMAN- WESTMAN. WESTMAN- repeated BUKTA Fm BUKTA Fm BUKTA Fm BUKTAFm EOKTA Fm WESTMAN- 1 BUKTA Fm by (shales) recumbent folding. PERSBERGET PERSBERGET PERSBERGET PERSBERGET Frn Frn Fm Fm Frn (quartzites) I AUSTFONNA MEYERBUKTA Group MEYERBUKTA DJEVLEFLOTA Fm (INNVIKHBGDA Fm Formation with st ' DJEVLEFLOTA basal conglom. subord. 1st) and BASAL QZITE W ?uno ormity? JVL formations) igfezre_d - ,.,...*.I AUSTFONNA 8 ---- CAPE KAPP PLATEN KAPP SVART- HANSTEEN formations HANSTEEN HANSTEEN HANSTEEN BRENNEVINS- RABBENE Formation CAPE Formation Group Group Formation (Phyllites, HANSTEEN FJORDEN KAPP qz porphyries Formation (metased.) HANSTEEN 8 700~00~200000~ andesites & BRENNEVINS- KAPP w agglomerates & FJORDEN HELVETES- conglomerates) HANSTEEN Undiff. BRENNEVINS- BRENNEVINS- -BRENNEVINS- FLYA (volcanite) FJORDEN FJORDEN FJORDEN Formation formations (migmitates & Formation Group Formation (Intruded by Metamorphic granites intrude (Intruded by - BOTNIA- ca. 1050 Ma complex ca. 950 Ma granites) (migmatites & HALV0YA granites) granites) Group) Two major unconformities beneath the Neoproterozoic Murchisonfjorden Supergroup 85 mations) grouped into two main units, and inter- “Basal Quartzite” (Ohta 1982c, p. 52), enter- preted the lower part of the succession to be taining the possibility of a regional break beneath repeated by recumbent folding. Flood et al. the Murchisonfjorden Supergroup. However, (1969) placed the upper units (dominated by both granite intrusions and migmatisation were dolomites and limestones) into the Roaldtoppen thought to influence the Austfonna Group, and Group and the lower (shales and quartzites) into these were regarded therefore as Caledonian. the Celsiusberget Group. They rejected Kulling’s (1934) “recumbent fold” interpretation and recognised beneath the Celsiusberget Group a New mapping of central third cycle of shales and quartzites, the Frank- linsundet Group. Subsequently, Ohta (198213) Nordaustlandet showed that the lowermost quartzites of the In 1994, a camp was established on Helvetesflya, Franklinsundet Group (the Persberget in the watershed between Rijpdalen and Flaum- Formation) were underlain by another, somewhat dalen. This allowed a ten day investigation of the different shale-dominated unit, which he named central part of the area between Vestfonna and the Meyerbukta Formation. Austfonna and a closer examination of the In central Nordaustlandet, the general relationships between the Murchisonfjorden Murchisonfjorden Supergroup relationships were Supergroup strata and underlying volcano-sedi- established by the mid 1950s (e.g. Sandford 1956), mentary rocks. with the Vendian tillites exposed on the northern The new mapping (Fig. 2) extended from the side of inner Wahlenbergfjorden, underlain by Murchisonfjorden basal contact along the margin the carbonates of the Roaldtoppen Group and of Vestfonna in the western limb of the Rijpdalen shales and quartzites of the Celsiusberget Group. Antiform, eastwards via the Venesjcben Synform Flood et al. (1969) recognised the formations of to the Kvartsitthaugen Synform, exposed along the Franklinsundet Group, northeast of the edge of Austfonna. The type area for the Vestfonna (north and south of Bengtssonbukta) Austfonna Group was not within the range of the and further south in inner Wahlenbergfjorden 1994 operations, but was examined briefly in 1995. (north of Etonbreen). The basal quartzites of the Similar major Caledonian folds, further west Franklinsundet Group were correlated with the along Wahlenbergfjorden, involve Vendian til- Persberget quartzites and shown to directly over- lites and, in the vicinity of Hinlopenstretet, Cam- lie the Austfonna Formation along the eastern bro-Ordovician strata; in central Nordaustlandet, margin of Vestfonna. Further east, quartzites and these are upright structures, with a cleavage in overlying shales in the Venesjcben Synform were the shales dipping generally at high angles east- shown to be similar to the Persberget and wards. A variety of faults complicate the fold Westmanbukta formations. However, in these geometry of the major N-trending Rijpdalen eastern areas, they rest on the undifferentiated Antiform and flanking synforms. volcano-sedimentary rocks of the “Botniahalv~ya Described below are the lithologies and struc- Group” and unconformable relationships were tures of the Helvetesflya area, with a focus on the therefore inferred. evidence for major unconformities beneath the Ohta’s (1982~)map of central Nordaustlandet Murchisonfjorden Supergroup strata and within revised the stratigraphic relationships between the underlying volcano-sedimentary succession. the Murchisonfjorden Supergroup and underlying rocks. He interpreted the Austfonna Formation lithologies to be equivalent to his newly defined Meyerbukta Formation (from western Lithologies and stratigraphy Nordaustlandet) of the basal Murchisonfjorden The stratigraphy of central Nordaustlandet is succession. He upgraded the Austfonna unit to treated here in two parts: underlying units, group status and included within it three for- equivalent to Flood et al’s (1969) Botniahalvcbya mations, a Basal Quartzite, a middle shale- Group (referred to here as the Helvetesflya and dominated section (the Djevleflota Formation) Svartrabbane formations), and unconformably and an upper sandstone-shale unit (the Innvik- overlying units in the basal part of the hagda Formation). He also documented the local Murchisonfjorden Supergroup. With regard to I development of an unconformity beneath his the latter. one of the formations included bv Ohta FIR 2 Geological map of the area between Vestfonna and Austfonna. central Nordaustlandet.

(1982~)in the Austfonna Group dominates on distribution of the Persberget Formation quartz- Helvetesflya - the Djevleflota Formation. We ites in the eastern and western limbs of the Rijpda- therefore distinguish only the Djevleflota For- len Antiform and their relationship to underlying mation on the new geological map (Fig. 2), with strata. Ohta (1982~) recognised that, in the underlying thin basal quartzites in eastern areas Venesjoen Synform on Djevleflota, these quartz- and basal conglomerates outcropping along the ites were underlain by a varied packet, estimated margin of Vestfonna. to a little over 1000 m in thickness, of shales and subordinate calcareous sandstones, quartzites and minor limestones; he therefore defined a new Djevleflota Formation and basal quartzites and formation in this area. The succession is well conglomerates preserved and primary structures are abundant Flood et al. (1969) and Ohta (1982~)showed the (Fig. 3). Two major unconformities beneath the Neoproterozoic Murchisonfjorden Supergroup 87

Fig. 3. Sedimentary structures in the sandstones of the Djev- Fig. 4. Basal conglomerates of the Murchisonfjorden leRota Formation. A. Ripple marks. B. Mud cracks. Supergroup: Locality close to the eastern margin of Vestfonna (see Fig. 2). Clasts of quartzite, vein-quartz and dark meta- volcanites in both A and B.

In the western limb of the Rijpdalen Antiform, In the eastern limb of the Venesjcien Synform, only about 100 m of the Djevleflota Formation is the basal part of the Djevleflota Formation is exposed beneath the Persberget quartzites (thick- poorly exposed; a few quartzite outcrops occur ness probably reduced by normal faulting), and and the base is not seen. Further to the northeast, basal conglomeratic beds are locally preserved. this formation is exposed again beneath the Conglomerates, described by Winsnes, in Flood Persberget quartzites in the Kvartsitthaugen Syn- et al. (1969, p. 37) from west of Rijpfjorden, in form. Here, the succession beneath the quartzites the base of the Persberget Formation, may also contains much green-grey cross-laminated silt and be part of this Murchisonfjorden basal unit. Ohta graded fine sandstone with quartzites at the base. (1982c, p. 47) referred to a “basal breccia” at the However, the contact to the underlying base of the Persberget Formation, west of Brina, Helvetesflya dark phyllites and Svartrabbane in southwestern Rijpdalen and inferred that it andesites is tectonic. marked the base of a separate sedimentary cycle The basal conglomerates of the Murchison- within the Murchisonfjorden Supergroup. This fjorden Supergroup are of particular interest. In unit probably also coincides with our basal the field, a variety of clasts were recorded, includ- Murchisonfjorden conglomerate. ing red quartzites, vein quartz, dark phyllites, Beneath these basal conglomerates, in the west- dark greenish mafic volcanic rocks, and light acid ern limb of the Rijpdalen Antiform, the litho- volcanics (Fig. 4). In thin section, the meta- logies are dominated by dark phyllites of the volcanic rocks in the clasts are similar to those in Helvetesflya Formation. In this area, the new the Svartrabbane Formation. Relic fluidal and mapping does not support the correlation (Ohta porphyritic textures are recognisable; quartz and 1982c) of these metasediments with the feldspar are altered to quartz-sericite aggregates Djevleflota Formation. and the glass in the acid rocks has recrystallised to 88 D. G. Gee & A. M. Teben’kou form a fine-grained matrix. Tourmaline-bearing mation and the former to the Kapp Hansteen clasts are conspicuous in these basal conglom- Formation, noted by previous investigators, sup- erates. ports correlation with Botniahalv~ya.A major unconformity separates these units.

Helvetesflya and Svurtrabbane volcano- Helvetesflya Formation (dark phyllites) .-Mon- Sedimentary rocks otonous dark phyllites, some of them black (1- Two mappable formations occur below the Mur- 2% graphite), dominate this phyllite formation. chisonfjorden Supergroup. The one (Helvetesflya Many of these lithologies have been described Formation) is dominated by dark phyllites, previously as shales or slates, but all that we have locally, with volcanic intercalations; the other mapped have a strong, penetrative, fine-grained, (Svartrabbane Formation) is mainly composed sericitic schistosity and a superimposed crenu- of andesites with subordinate rhyolites. The lation that is usually conspicuous. Thin (a few Helvetesflya metasedimentary rocks are’ often centimetres) sandy intercalations are frequent relatively well preserved and “way-up” has been and usually graded. Thicker quartzites are rare in recorded locally. It may prove possible, with more this formation. Isoclinal folding makes thickness detailed mapping, to beiher control the stra- estimates very uncertain, but the formation is at tigraphy, but the occurrence of tight to isoclinal least a few hundred metres thick; it is interpreted folding and local inversion do not allow this on to be largely of turbidite origin. the present data base. The Svartrabbane volcanic rocks are widespi-ead in the upper structural levels Suartrabbane Formation (uolcunites).-The Svar- of the Rijpdalen Antiform in the eastern limb trabbane volcanic and associated sub-volcanic where they overlie the sedimentary units. Simi- intrusions of central Nordaustlandet have been larity of the latter to the Brennevinsfjorden For- described in some detail by Teben’kov (1983) and Ohta (1985). The fine-grained penetrative schistosity makes it often difficult to be sure whether the massive, volcanic rocks are extrusive or intrusive. However, in many outcrops, good exposures of transitions from volcaniclastic rocks to massive volcanites occur; in addition, the pres- ence of sedimentary clasts in rhyolites and the intercalation of agglomerates with andesites, pro- vide good evidence of extrusion (Fig. 5). The massive mafic rocks have been previously referred to as diabase and basalt, but have been shown by geochemical studies to be andesitic in composition (Teben’kov 1983; Ohta 1985). Interbedded dark phyllites occur locally and sub- ordinate quartzites are also present. Ohta (1982~) reported thin carbonate units in the contact between the Svartrabbane and Helvetesflya for- mations. In 1995, a major unconformity was found to separate Helvetesflya turbidites from Svartrab- bane volcaniclastic rocks. Ohta (1982c, p. 50) referred to the presence of conglomerates sep- arating these volcanic and sedimentary rocks at Kjedevatna and inferred local unconformity. Our 1995 mapping shows that the Helvetesflya metasediments, with well-preserved sedimentary Fig. 5. Svartrabbane Formation volcanic rocks: A. Agglom- structures (e.g. graded bedding and cross-lami- erates cut by granite sheet (bottom left). B. Rhyolites with sedimentary clasts, probably derived from the underlying Hel- nation), are locally inverted and overlain by a thin vetesflya Formation. (up to ca. 5 m) quartzite pebble conglomerate, Two major unconformities beneath the Neoproterozoic Murchisonfjorden Supergroup 89 passing up into rhyolites and andesites of the Svartrabbane Formation.

Granites (Rijpdalen-Winsnesbreen) Red granites occur in a main massif in Rijpdalen, developing a conspicuous thermal aureole in the host rocks to a distance of about 100 m from the contact. This Rijpdalen Granite (Hjelle 1966; Flood et al. 1969) occurs in the core of the Rijpda- len Antiform and appears to be connected from the northern outcrop areas of inner Rijpfjorden, southwards to the Winsnesbreen Granite near Wahlenbergfjorden. The mineralogy of the granite is dominated quartz, albite and microcline with subordinate muscovite (up to 10%) and minor biotite. Tourmaline is frequently present, particularly in association with pegmatites. The aureole mineralogy in the metasedimentary rocks is characterised by garnet and biotite, locally with staurolite; tourmaline also occurs commonly in the metasediments near the granite contact. Shear zones and a semi-penetrative foliation with accompanying brittle deformation are generally present. Fig. 6.Folding in central Nordaustlandet. A.Upright S-plunging Caledonian anticline in the DjevleflotaFormation. B. Sideways- closing Precambrian folds in graded Helvetesflya turbidites Augen gneisses (Ringgisdalen) (length of hammer shaft 40 cm). In the northern part of Fig. 2, augen gneisses and augen granites are in contact with the Helvetesflya rocks. The ductile foliation in the these igneous strata; this conclusion is supported by our new rocks is cut by the Rijpdalen granite. Contact work and Ohta’s unpublished data (Y. Ohta pers. relationships between the augen gneisses and the com. 1996). Major N-trending folds, such as the Helvetesflya Group have been observed in the Rijpdalen Antiform and the Venesjoen and area of Fig. 2, north of Svartrabbane and, further Kvartsitthaugen synforms, with their related high north (Flood et al. 1969, pp. 105-112), in Ring- angle E-dipping cleavages, are apparently the gisdalen (Fig. I); in both areas, garnet, straurolite only major structures to deform the Neo- and andalusite crystallise in narrow thermal proterozoic strata; they clearly fold an earlier aureoles. These gneisses have been interpreted generation of tight to isoclinal folds in the Hel- (Flood et al. 1969) to be derived from granites vetesflya and Svartrabbane formations (Fig. 6). that were intruded during deformation; the latter These older folds, as shown by Flood et al. (1969, was probably of Grenville age, based on recently pp. 85-87), have generally transverse axes (ca. presented U/Pb zircon age-determination studies WNW-ESE) and a well-developed axial surface (Johansson pers. com. 1994). cleavage, with associated fine-grained schistosity. Crenulation of the latter is generally due to the refolding by the N-trending Rijpdalen Antiform Deformation of the Helvetesflya and and related structures. Beneath the basal Mur- chisonfjorden Supergroup unconformity of east- Svartrabbane Formations ern Vestfonna, the axial surface schistosity dips Flood et al. (1969) described the deformation nearly concordantly beneath the overlying con- of the Helvetesflya and Svartrabbane formations glomerates, implying that the folds in the older (their Botniahalvoya Group) to be more complex rocks were recumbent prior to Caledonian than that in the Murchisonfjorden Supergroup deformation. 90 D. G. Gee & A. M. Teben’kov

been described by Krasil’SEikov (1967, translated Regional metamorphism by Harland et al. 1993, pp. 48-49) and by Edwards A fine-grained schistosity, well defined by sericite (1976). An attempt was made by Edwards and and chlorite, characterises the Helvetesflya Taylor (1976) to date these granites by the metasedimentary rocks in most of the area of Rb/Sr method. No isochron was obtained, but an Fig. 2. Crenulation of this fabric resulted in partial indication of a Mesoproterozoic age was reorientation of these phyllosilicates, but only suggested; new studies are in progress. These minor recrystallisation. The latter is compatible granite clasts have been said by Hjelle (in with the evidence in the overlying shales of the Edwards & Taylor 1976, p. 256) to be similar to Murchisonfjorden Supergroup of only incipient the Rijpdalen-Winsnesbreen Granite. growth of sericite and chlorite in the cleavages. The presence of granite boulders (up to 1 m in diameter) in the tillites of eastern Wahlen- bergfjorden and their smaller size further west prompted Edwards (1976) to suggest that the Discussion and conclusions source area lay within a few kilometres distance It can be concluded that a major unconformity from the outcrops. Without evidence for major separates the sedimentary rocks of the facies changes in the Murchisonfjorden Helvetesflya Formation from the volcanic Svar- Supergroup, from the type area of western Nord- trabbane Formation. A second unconformity austlandet to inner Wahlenbergfjorden, this occurs at the base of the overlying Neoproterozoic would suggest that latest Proterozoic extensional strata of the Murchisonfjorden Supergroup. Syn- faulting locally defined an eastern margin to the tectonic intrusion of early granites, during recum- Neoproterozoic basin, exposing basement to bent folding of the Helvetesflya and Svartrabbane Vendian erosion. formations was followed by post-tectonic The new work in central Nordaustlandet, intrusion of the Rijpdalen-Winsnesbreen granite. reported here, supports previous conclusions The latter is not seen to cut the Murchisonfjorden (Gee et al. 1995) that Caledonian tectonothermal Supergroup sediments. The possibility exists that activity on Nordaustlandet is of a fundamentally this granite may be Caledonian in age; however, different character than that found in western the presence of tourmaline in the clasts of the Ny Fnesland. Within the Neoproterozoic suc- basal Murchisonfjorden Supergroup conglom- cessions, from eastern Ny Friedand, via erate and the association of this mineral with Murchisonfjorden and Wahlenbergfjorden to the aureole of the Rijpdalen granite favours the Rijpdalen, the folding is upright to westerly interpretation that the Rijpdalen-Winsnesbreen inclined and the recrystallisation in the associated granite is of Grenville age. cleavages is generally lower greenschist facies, The Ringgisdalen augen gneisses, derived from with growth of fine-grained sericite and chlorite. the syntectonic granites intruding the Helvetesflya Only in the immediate contact to the Planetfjella Formation, have not as yet been investigated Group and in the contact aureole to the Chy- isotopically, but their age is probably pre-Neo- deniusbreen Granite massif in southern Ny Fries- proterozoic. Recent work by Johansson (pers. land are higher greenschist facies conditions com. 1994) has shown that a variety of megacrystic recorded in the Neoproterozoic strata. The Cale- augen granite/gneiss, outcropping along the donian lower greenschist facies tectonothermal northwestern margin of Austfonna (Fonndalen, overprint may increase a little in grade towards Fig. 1) is of Grenvillian (ca. 1050 Ma) age; it may the east, as suggested by K/Ar and Rb/Sr mica be related to the syntectonic intrusions referred ages (Ohta 1994) in the underlying migmatites, to above. but the possibility remains that the pre-Devonian Although granite clasts have not been found basement of the northern Barents Sea is essen- amongst the greenschist facies pebbles in the base tially a Grenvillian complex, partially covered by of the Murchisonfjorden Supergroup of central a slightly deformed blanket of Neoproterozoic Nordaustlandet, it is worth noting that they are and early Paleozoic strata. present in the Vendian tillites, higher in the Neo- proterozoic succession (Kulling 1934). A wide Ackttowledgements. -Our field party in eastern Nordaustlandet in 1994 included three students, J. Gustafsson, J. Nilsson and range of low-grade metasedimentary and meta- S. Sandelin and geornorphologist L. Sernenova. In 1995, we volcanic rocks together with granite boulders have were assisted by E. Tagesson. We thank them all for their Two major unconformities beneath the Neoproterozoic Murchisonfjorden Supergroup 91 contribution to the field investigations, at times under difficult till Nordostlandet 1931. Geol. Foren. Fork Bd 54,13b145. wintery conditions. Our work on Nordaustlandet has been Stockholm 1932. supported by the Swedish Polar Research Secretariat in Stock- Kulling, 0. 1934: Scientific results of the Swedish-Norwegian holm, thc Polar Marine Geological Expedition (PMGE) in St. Arctic Expedition in the summer of 1931, Part XI. The “Hecla Pctersburg and the Swedish Natural Science Research Council. Hoek Formation” round Hinlopenstredet. Geograph. Ann. We also greatly appreciate excellent communication with Norsk 16 (Stockholm), 161-254. Polarinstitutt and PMGE colleagues and, particularly, discus- Lauritzen, 0.& Ohta, Y. 1984: Geological map of Svalbard sion and review of this paper by A. Krasil’SEikov and Y. Ohta. 1:500,000, sheet 4G Nordaustlandet. Norsk Polarinst. Skr. We also thank P. Witt-Nilsson and M. Friberg for help with the Nr. 154-0, 14 pp. final preparation of the diagrams. Nordenskiold, A. E. 1864: Geografisk och geognostisk beskrifn- ing ofver nordostra delarne af Spetsbergen och . K. Soenska Vetensk. Akad. Handl. 4(7), 1-25. References Nordenskiold, A. E. 1866: Utkast till Spitsbergens geologi. K. Suenska Vetensk. Akad. Handl. 6(7), 1-35. Edwards, M. B. 1976: Sedimentology of Late Precambrian Ohta, Y. 1982a: Relation between the Kapp Hansteen For- Sveanor and Kapp Sparre Formations at Aldousbreen, mation and the Brennevinsfjorden Formation in Botnia- Wahlenbergfjorden, Nordaustlandet. Norsk Polarinst. halveya, Nordaustlandet, Svalbard. Norsk Polarinst. Skr. Arbok 1974, 51-61. 178, 5-18. Edwards, M. B. & Taylor, P. M. 1976: A Rb/Sr age for granite- Ohta, Y. 1982b: Murchisonfjorden Supergroup of LBgdya, gneiss clasts from the late Precambrian Sveanor Formation, northwest Nordaustlandet, Svalbard. Norsk Polarinst. Skr. central Nordaustlandet. Norsk Polarinst. Arbok 1974, 255- 178, 19-40. 258. Ohta, Y. 1982~:Lithostratigraphy of the Hecla Hoek rocks in Flood, B., Gee, D. G., Hjelle, A., Siggerud, T. & Winsnes, T. central Nordaustlandet and their relationships to the Cale- S. 1969: The geology of Nordaustlandet, northern and central donian granitic-migmatitic rocks. Norsk Polarinst. Skr. 178, parts. Norsk Polarinst. Skr. 146, 139. 41-60. Gee, D. G., Johansson, A,, Ohta, Y., Teben’kov, A. M., Ohta, Y. 1984: Caledonian and Precambrian history in Krasil’SEikov, A. A,, BalaSov, Y. A., Larionov, A. N., Gan- Svalbard: a review, and an implication of escape tectonics. nibal, L. F. & Ryungenen, G. I. 1995: Grenvillian basement Tectonophysics 231, 183-94. and a major unconformity within the Caledonides of Ohta, Y. 1985: Geochemistry of the late Proterozoic Kapp Nordaustlandet, Svalbard. Precambrian Research 70, 215- Hansteen igneous rocks of Nordaustlandet, Svalbard. Polar 234. Res. 3 n.s., 69-92. Hamilton, E. I & Sandford, K. S. 1964: Rubidium-strontium Ohta, Y. 1994: Caledonian and Precambrian history in ages from some rocks. Nature. 202, 1208-9. Lon- Svalbard: a review, and an implication of escape tectonics. don. Tectonophysics 231, 183-194. Harland, W. B., Hambrey, M. J. & Waddams, P. 1993: Vendian Sandford, K. S. 1950: Observations on the geology of the Geology of Svalbard. Norsk Polarinst. Skr. 193, 1-150. northern part of North-East Land (Spitsbergen). Quart. J. Hjelle, A. 1966: The composition of some granitic rocks from Geol. SOC. Lon. 15,461-93. London. Svalbard. Norsk Polarinst. Arbok 1965, 7-30. Sandford, K. S. 1956: The stratigraphy and structure of the Hjelle, A. 1978: An outline of the Pre-Carboniferous geology Hecla Hoek Formation and its relationship to a subjacent of Nordaustlandet. Potarforsch. 48 (1/2), 62-77. metamorphic complex in North-East Land (Spitsbergen). Krasil’SCikov, A. A. 1967: Tillitopodobnye parody Severo- Quart. J. Geol. SOC. Lon. 112, 339-362. VostoEnoj Zemli (Tillite-like rocks of North East Land). Teben’kov, A. M. 1983: Pozdnedokembrijskie magmatiteskie Pp. 3&62 in Sokolov, V. N. (ed.): Materialy po stratigrajii formacii Severo-Vostotnoj Zemli (Late Precambrian mag- Spicbergena (Data on the Stratigraphy of Spitsbergen), matic formations of Nordaustlandet). Pp. 74-86 in NIIGA , Leningrad. Krasil’S€ikov, A.A. (ed.): Geologija Spicbergena, PGO. Kulling, 0. 1932: NBgra geologiska resultat frhn expeditionen Sevmorgeologija, Leningrad.