Pre-Caledonian Metamorphic Complexes Within the Southern Part of the East Greenland Caledonides

Pre-Caledonian metamorphic complexes within the southern part of the East Greenland Caledonides

A. K. HIGGINS

SUMMARY Isotopic dating and recent regional mapping tions of the Scoresby Sund region are extended have led to reappraisal of conventional inter- northwards into the classic areas of the central pretations of the southern part of the East metamorphic complex where the widely accept- Greenland Caledonides. The metamorphic ed concept of a deep-seated Caledonian orogeny complexes of the Scoresby Sund region pre- was developed. A similar development to that serve evidence of Archaean and Proterozoic of the Scoresby Sund region seems probable, orogenic episodes, and high grade metasedi- though statements should be treated with mentary sequences thought to be late Pre- reservation until new field work and isotopic cambrian Caledonian geosynclinal rocks have studies have been completed. Brief mention is yielded middle Proterozoic isotopic ages. The made of parallel developments in the Cale- intensity of the Caledonian orogeny is much donian fold belts of northern Europe. less than formerly imagined. The interpreta-

I. Main elements of the Caledonian fold belt THE CALEDONIAN fold belt of East Greenland extends from latitudes 7°0 to 82°N, occupying most of the wide strip of land between the coast and the inland ice (Fig. i). Metamorphic complexes dominate the fold belt and consist of a variety of gneisses, migmatites, granites and metasediments. In the southern part of the fold belt from latitudes 73° to 74°N the metamorphic complexes are flanked to the east, and locally to the west, by generally non-metamorphic sequences of the late Precambrian Eleonore Bay Group (Figs. I, 3, P1. I). The lower part of the up to 14 ooo m thick Eleonore Bay Group succession consists of arenaceous and argil- laceous sediments, while the upper part includes spectacular limestone and dolo- mite units (P1. i). On the east side of the metamorphic complexes the late Pre- cambrian sequence is succeeded by the Tillite Group (3oo-I 300 m) and a largely carbonate Cambro-Ordovician sequence (c. 3000 m). These sediments exhibit for the most part a simple style of Caledonian folding and faulting. Upper Palaeozoic molasse deposits occupy large areas especially between latitudes 720 and 74°N, and narrower outcrops occur further south; their accumu- lation was disturbed by several minor phases of late Caledonian deformation. Mesozoic marine sediments succeed them, and outcrops are found along parts of the present outer coastal region from latitude 76°N southwards as far as the broad sedimentary basin of Jameson Land (Fig. I). Tertiary basalts conceal the continuation of the Caledonian fold belt south of latitude 7o°N. The western edge of the East Greenland Caledonides follows roughly the line of the innermost nunataks. Foreland windows believed to represent intact parts of the Greenland shield occur beneath eastward dipping major thrusts in western

Jl geol. Soc. Lond. vol. x32 1976, pp. 289-305, 3 figs. Printed in Northern Ireland.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 29 o .4. K. Higgins

-81 ° "" ~i ,

:.... ! 1 . I 0 50 100 km ,

,,.°° ~.°.'* : ~..~:..:.~

-78 ° .., ~ o.... :°' .,a

Caledonian Dronning fold belt Louise La

/ Thrust

Fault -75" I ! Quatemary, ice I Tertiary baselts (& alkali intrusions) Jurassic- Cretaceous

Permian - Trias (mainly marine)

Devonian - Permian (molasse - type sediments)

Cambrian - Ordovician •.~':.".t<.~ .=' (& Silurian in NE Greenland) Charcotf Eleonore Bay Group & Tillite Group Land ~.~ I in central East Greenland. Hagen Fjord Group in North-East Greenland Pre- Carolinidian sediments in NE Greenland Liverpool Metamorphic complexes (fold belt) Land

Metamorphic complexes (foreland) Sund

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphic complexes 291

G~.seland-Paul Stern Land, Charcot Land, Dronning Louise Land and Kronprins Christian Land (Fig. x).

2. History of research

The East Greenland Caledonian fold belt is reasonably well known despite the difficulties of access, due largely to the expeditions led by Lauge Koch between 1926 and I958. The region between latitudes 720 and 76°N is covered by i:25oooo geological maps (Koch &Haller I97t ). The most comprehensive accounts of the fold belt are those of Hailer (t97o , I97t ). The western broad region of crystalline rocks between latitudes 7°0 and 74°N has become known as the central metamorphic complex. This complex has played a significant role in the development of ideas concerning the genesis of the fold belt. It was considered by some early workers to be an essentially Archaean massif (e.g. Parkinson & Whittard I93I , Teichert t933, Odell i944). Others, however, claimed that the stratigraphy of the late Precambrian Eleonore Bay Group could be traced into and throughout the central metamorphic complex and that it must therefore be a manifestation of Caledonian granitization and migmatization (e.g. Backlund I93O, Wegmann I935). Detailed work by members of Koch's expeditions seemed to support the latter interpretation (Hailer I955, i958 , Wenk & Hailer i953) , and the central metamorphic complex was thus widely regarded as the deep-seated mobile infrastructure of the Caledonian fold belt. High grade metasedimentary rocks within the complex have been viewed as transformed parts of the late Precambrian succession. While substantial areas of former Archaean rocks were recognized in southern parts of the central metamorphic complex, they were considered to have undergone petrogenic rejuvenation during the Caledonian orogeny (Hailer & Kulp i962 , HaUer i97i ). In the period 1968-72 the Geological Survey of Greenland undertook systematic mapping in the Scoresby Sund region (7o°-72°N), hitherto one of the least known parts of the fold belt. At first results appeared to conform with the traditional view of Caledonian orogenesis. However, as work progressed and isotopic ages became known in increasing numbers, it became clear that the metamorphic complexes of the Scoresby Sund region retain many characteristics of a complex pre-Cale- donian history. 3. Geology of the Scoresby Sund region Crystalline rocks outcrop in the western half of this region (7o°-72°N) and in the narrow strip of Liverpool Land (Fig. I). The late Palaeozoic and Mesozoic rocks of the Jameson Land basin are described by Birkelund & Perch-Nielsen (in press). The western broad area of crystalline rocks represents the southern half of the

FIO. I elements of" the Caledonian fold belt in East Greenland.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 292 A. K. Higgins

central metamorphic complex, and it can be divided into several zones of dis- tinctive character limited by major thrusts or faults (Fig. 2). In the extreme west several windows cut through flat-lying thrust sheets expose outcrops of presumed foreland. The thrust sheets themselves are made up of infracrustal and supracrustal rock units which characterize a zone running from south of Vestfjord to HinEs Land. An east dipping N-S trending thrust separates this zone from a very different zone to the east, dominated by migmatitic and granitic rocks and trace- able from G~sefjord through Milne Land and Renland to the Stauning Alper. Although late Precambrian and Lower Palaeozoic rocks are widespread between latitudes 720 and 74°N, in the Scoresby Sund region they are restricted to an isolated development in Canning Land (Fig. 3). (A) FOR ,LANV WINDOWS Two major windows through the presumed Caledonian thrusts occur, one in extreme western G~seland and Paul Stern Land, and the second around Charcot Land. The rocks exposed in the windows are assumed to represent parts of the Greenland shield. Within the G~seland--Paul Stern Land window a basement of hornblende- biotite gneisses and augen gneisses cut by discordant amphibolite dykes is unconformably overlain by a thin sequence of weakly metamorphosed sediments(Wenk i96i ). Mineral ages of 189o Ma (K-At on biotite) and 2290 Ma (Rb-Sr on micro- cline) were obtained on the basement rocks by HaUer & Kulp (1962). Local psephitic or tillite developments occur at the base of the sedimentary sequence, which mainly comprises cream-coloured marbles (up to 300 m thick). Overlying sericidc quartzites and chloritic schists referred to the sedimentary sequence by Wenk (I96X) have been interpreted as highly tectonised basement gneisses by Phillips ¢t al. (I 973). The age of the sediments is uncertain; Wenk considered that they represented the basal part of the Eleonore Bay Group, whereas Phillips et al. have speculated that the psephitic developments might correlate with the Tillite Group (Eocambrian) and the marble sequence with the Cambro-Ordovician carbonate succession. Most of Charcot Land, a strip of western HinES Land and some nunataEs make up the Charcot Land window, preserved beneath a major arcuate thrust which has a westward displacement of at least 4 ° km. The rock units include an infracrustal complex of banded gneisses, augen gneisses and amphibolites, overlain by at least 2000 m ofsupracrustal rocks including marbles, quartzites, semipelitic and pelitic rocks, and basic intrusives and extrusives (Steck 1971). Two late-post- kinematic intrusions are largely emplaced in the infracrustal complex; one of these, a pegmatitic muscovite granite, has yielded mineral ages of 162o-x 870 Ma as well PLATE I Steep eastward dipping strata of the upper Eleonore Bay Group in the northernmost Stauning Alper, showing a rather simple style of deformation. Dips decrease north of the fjord. Minor N.-S. trending faults are common. The boundary with the metamorphic complex is situated in the fjord just west of the left edge of the photograph. Route 653 G-NV no. o95x6, copyright Geodetic Institute, Copenhagen. Reproduced by permission A/649/72.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Jl. geol. Soc. Lond. x32, I976 HIGGINS

PLATE I 202

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Jl. geol. Lond. x32 , I976 HIGGINS

PLATE 2A

PI~ATE 2B

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphiccomptexes 293

as Caledonian ages (Hansen et al. I973a, b), whilst the second, a quartz diorite body which also veins the supracrustal rocks, has yielded a zircon age of x9oo Ma (Steiger & Henriksen i972 ). A spectacular tillite several hundred metres thick rests unconformably on the quartz diorite intrusion (Henriksen & Higgins I969, Steck I97I ). The Charcot Land supracrustal rocks were considered by the first investigators to represent the basal part of the Eleonore Bay Group and were compared with the supracrustal rocks in the western GAseland-PauI Stern Land window (Wenk 196 t, Vogt t965). The only direct isotopic dates are mineral ages of 632 Ma (K-At on hornblende: Hansen et al. I973b ) and 4 t t Ma (Rb-Sr on biotite: Hansen et al. 1973a), but the veining by the quartz diorite suggests they may be considerably older. There is no clear evidence of the age of the Charcot Land tillite, though it has usually been assumed to be Eocambrian (Steck i97t , Phillips et al. i973). A preliminary search for microfossils has proved negative (G. Vidal, pers. comm).

(B) VESTFJORD--HINK8 LAND ZONE Two main lithostratigraphic units characterize the zone stretching from south of Vestfjord to Hinks Land: the Flyveffjord infracrustal complex and the Krummedal supracrustal sequence. The Flyverfjord infracrustal complex outcrops most extensively around Flyverfjord and inner Nordvestfjord where it comprises a variety of gneisses, amphibolites, ultrabasic lenses and occasional granitic masses. The gneisses exhibit complex fold patterns (P1. 2A), and are cut locally by con- spicuous swarms of folded, discordant amphibolite dykes. Isotopic ages indicate that the genesis of the complex extends well back into the Archaean: Rex & Gledhill (I974) have obtained a Rb-Sr isochron of 3ooo Ma on samples collected from the north coast of Flyverfjord; Hansen et al. (i 973a) record a K-Ar mineral age of 2525 Ma on hornblende from a discordant amphibolite; and Steiger & Henriksen (I972) interpret the age of intrusion or last major reactivation of a foliated biotite granite as 2345 Ma on the basis of zircon analyses. A number of younger mineral ages on rocks from the complex suggest there was significant Caledonian overprinting. Red-brown weathering metasediments of the Krummedal supracrustal sequence form a contrasting cover to the generally leucocratic Flyverfjord complex. They

PLATE 2

A. complex fold interference patterns in banded leucocratic and hornblende gneisses of the Archaean Flyverfjord infracrustal complex, Hinks Land. B. Dome-like body of augen granite on the south-east coast of ReMand of the type which has yielded U-Pb zircon ages of 95° Ma. (Steiger & Henriksen I972, Hansen et al. I974). The structure in the enveloping migmatitic paragneisses is deceptively simple in appearance, and in fact isoclinal folds are warped over the arch of the granite. The cliff face is about x6oo m high. The ship 'Perla Dan' can be seen (arrowed) at the left of the photo.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 294 A. K. Higgins

I .." "":: ~-~! .:~

J / -71"30" [ ~ Nordvestfjord

[/ ::5;;'"'": :::'""' Nunatakke¢/I ....,4::!i / RENLAND i-i~, I I

LAND

I I

Peul Stern Land

v v v-~-"~. :"v v v v v'.¢ /.v v': ":. det" '.::, --- ::,~ ~..~ ::v v v v.-: W v v v ::'~ :..~.:, "...... :.~;t-.~ ...,- U':v.v...~ .-"vv..vvv~ -:'.~' .~...~.: .. :9 V..v..~ '.. v v/ ...~.-', , ::""~'"~. V ~ "..v.~...... "!:" 0 2() ~ 40kn' ...... ":::.~ ~. .:o"

end" to late kinematic granite • Tectonic window ~ Syn migmatite granite • Tertiary bemalt

./'~,/Fault, thrust ~ Augen granite I..±~,., q Jur~mic- Cretaceous

/x//Main folds ~ Migmatitic gneiss ~ Carboniferous - Triem

Age data in m.y. • I~. mmedel supracrustal S~luence ~ late and post - kinematic granite

A.N. Alfabet Nunatakker Flyverfjord infmcnis',a, complex ~ Oiodte/monzonito intrusions Kr. Ksummedal ~G letscherland migmalite complex ~ Pyroxenite

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphic complexes 295

comprise a varied sequence of pelitic and psammitic rocks up to 2500 m thick: kyanite-garnet-mica schists are dominant in southern parts of the zone, and con- spicuously banded mica schists and quartzites occur in northern areas (Higgins x974). Marbles, amphibolites and lenticular outcrops ofbreccias and agglomerates locally occur near the base. No formal subdivision of the Krummedal supracrustal sequence has yet been attempted. A 7-point Rb-Sr isochron of i I62 Ma appears to date the main metamorphic event (Hansen et al. i974) , and suggests deposition of the sequence earlier in the Proterozoic. Younger Rb-Sr mineral ages ranging from c. 9oo Ma to c. 45o Ma can be interpreted as a variable response to Caledonian overprinting. The Flyverfjord infracrustal complex and the Krummedal supracrustal sequence have been deformed together, and most intensely in southern parts of the zone. There are at least two generations of tight to isoclinal recumbent folds with E.-W. or NE.-SW. axial trends, and a set of later more open structures with N.-S. or NNW.-trending axes. Linear structures have dominantly E.-W. trends, and gentle plunges eastwards or westwards. Evidence of amphibolite-facies regional metamorphism is seen in the Krum- medal supracrustaI sequence throughout the zone. In pelitic rocks kyanite and garnet are common, occurring mainly as static overprints on the minor structures and schistosity, and staurolite is recorded locally. The metamorphic grade often appears to increase upwards within the Krummedal supracrustal sequence. Pelitic schists become more gneissic due to an increase in feldspar grain size and the development of quartzo-feldspathic layers and lenses, and at a high structural level migmatites locally occur. There is evidence that some of the migmatitic developments are parts of thrust sheets, which may have been derived from the zone of granitic and migmatitic rocks to the east (cf. Homewood I973). Displace- ments on these thrusts may exceed xoo kin. The main thrust movements are clearly younger than the main metamorphic phase, and there is usually a marked contrast in metamorphic grade between the rocks in the foreland windows and those in the overlying thrust sheets. A late retrogressive metamorphic episode has left a widespread but variable impression on the high grade assemblages; chlorite, sericite and prehnite are widespread alteration products, and large muscovite laths and small euhedral garnets sporadically overprint fabrics in the mylonites along the main thrusts. Early workers compared and correlated the supracrustals of the Krummedal sequence with the lower Eleonore Bay Group, and the various tectonic and metamorphic events post-dating its deposition were therefore viewed as Caledonian. Isotopic ages now suggest that the main amphibolite-facies metamorphism and much deformation relate to a c. I2OO Ma orogenic event, and that Caledonian activity in the gneiss and schist zone was mainly responsible for thrust development and the weak retrogressive metamorphic overprint (Phillips et al. x973, Higgins x974).

FIG. 2 The geological divisions of the metamorphic complexes in the western half of the S¢orc~by Sund region.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 296 A. K. Higgins

(C) Ok.SEFJORD-STAUNING ALPER ZONE A zone of dominandy migmatitic and granitic rocks can be traced from Ggseland through Milne Land and Renland to the Stauning Alper (Fig. 2). The continuation of this zone can be traced as a narrow wedge north of latitude 7 2 °N where it has an irregular contact with the Eleonore Bay Group which is usually obscured by granite intrusions and faults (Fig. 3). The rocks grouped on Fig. 2 as migmatitic gneiss are extremely variable. They include sequences of rusty brown migmatized paragneisses in which pelitic and psammitic palaeosome alternates with garnet bearing neosome, as well as migma- rites containing a high proportion of granitic neosome with the palaeosome occurring as discontinuous layers, schollen or agmatites. With a further increase in neosome proportion there is a gradation into rock units which have been termed migmatite granites. The palaeosome is largely of sedimentary origin, though no lithostratigraphical divisions can be distinguished within the migmatites except for a discontinuous series of marble lenses. However, thick relatively non-migmatitic metasediments correlated with the Krummedal sequence are found especially at the western edge of the zone around Nordvestfjord and similar sequences occur in eastern Milne Land; apparent thickness of up to 8ooo m have been recorded (Higgins 1974). Areas locally characterized by abundant amphibolite inclusions occur within the migmatites and it is possible that they represent migmatized equivalents of a basement complex (Henriksen & Higgins i973). At an early kinematic stage in the development of the migmatites, massive bodies and extensive sheets of augen granite were emplaced; in some areas they became involved in isoclinal folding of nappe dimensions (Chadwick 197 I, 1975) or formed major domal structures (P1.2B). The so-called migmatite granites often have diffuse and irregular contacts with the gneissic migmatites and some outcrop over areas of up to 5 km by 25 km. Dioritic to monzonitic intrusions occur as both major and minor sheets and dykes; one 5oo m thick hypersthene monzonite sheet in east Renland was emplaced between two phases of migmatization (Chadwick i975). Late-and post-kinematic granite sheets and plutons are prominent in the eastern part of the zone; they are of variable composition and some have cores of hornblende syenite. North of latitude 72°N, post-kinematic biotite and biotite- muscovite granites cut and vein the Eleonore Bay Group. Sillimanite and garnet are common in the migmatites, and also occur in the augen granites and migmatite granites. Cordierite and andalusite are found in eastern parts of the zone. In some areas granulite-facies conditions were reached (Kalsbeek 1969, Chadwick 1971 ). As in the Vestfjord-Hinks Land zone to the west, high grade assemblages in general show slight modification in response to late retrogressive metamorphism. The metasediments, migmatites and augen granite sheets exhibit large scale isoclinal recumbent folding. Later deformation produced less intense ENE.- trending folds in Milne Land and G~seland, and large scale N.-S. trending warps in the Stauning Alper (Fig. 2). The majority of isotopic ages are Rb-Sr and K-Ar mineral ages, and only a few are U-Pb ages on zircon and monazite; ages obtained range from 373 to 165o Ma (Larsen 1969, Hansen & Steiger 1971 , Hansen etal. 1972 , 1973a , b, I974, Steiger

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphic complexes 297

& Henriksen i972 , Oberli & Steiger I973). The zircon ages oft. 95 ° Ma on two augen granites (Hansen et al. 1974) are of particular interest, although in view of the possibility of zircons containing inherited components of an earlier source (Pidgeon & Johnson I974) some reservations are necessary. At present the dates are interpreted as the time of intrusion of the augen granites (P1. 2B), which suggests that the closely related migmatitic and deformation events relate to a middle Proterozoic orogenic episode. Other ages suggest that a number of the late kinematic granites are Caledonian and that there was a significant Caledonian metamorphic overprint. Confirmation of these interpretations awaits further isotopic studies, but on present evidence the composite character of the Gb~sefjord- Stauning Alper zone seems likely to be largely a pre-Caledonian development.

(D) LIVERPOOL LAND The isolatedcrystalline region of Liverpool Land comprises gneissesand migma- titcs, marbles and other metasediments, amphibolites, and a variety of synkine- matic intrusions (Coe & Cheeney I972 ). Koch (i929) and Kranck (i935) have suggested the region represents a deep-seated level of the Caledonian fold belt. However, although only three mineral age dates are so far available, two of them, I I83 Ma and I I24 Ma (K-Ar on hornblende; Hansen et al. i973b), suggest that the crystallization of at least part of the gneisses was a Precambrian event, while the third of 434 Ma (Rb-Sr on biotite: Hansen & Steiger 197 x) suggests that the largest of the granites is Caledonian. There are three main areas of gneisses and supracrustal rocks separated by intrusive complexes, but the relationships between the three areas are uncertain, and there are no obvious correlations with metasedimentary sequences elsewhere. The thickest supracrustal sequence has an apparent thickness of I I km, but duplication and inversion of at least parts of the sequence are likely. Sillimanite is abundant in northern areas, and kyanite and garnet are found further south. The intrusions include granodiorites, monzonites, monzodiorites and granites exhibiting a great variety of textures (Coe & Cheeney 1972 ). (E) CAN INO LAND Canning Land contains the only outcrops of the Eleonore Bay Group between latitudes 7°° and 72°N (B~itler I948 , Caby I972 ). The succession is similar to the classic succession farther north between latitudes 7 =0 and 74°N and the standard nomenclature and numbering has been applied. About 2ooo m of the lower Eleonore Bay Group and 3ooo m of the upper Eleonore Bay Group are preserved, succeeded by the Tillite Group and Cambrian strata (8oo m). The succession is non-metamorphic and characterized by open folding and disruption by minor faults and thrusts. Studies of stromatolites from the upper Eleonore Bay Group suggest a Vendian age (6oo-7oo Ma-Bertrand-Sarfati & Caby I974).

4. Discussion It is an obvious line of speculation to extend the present interpretations of the metamorphic complexes of the Scoresby Sund region northwards into the classic

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 298 A. K. Higgins

areas of the northern half of the central metamorphic complex. The Vesffjord- Hinks Land zone can be extended northwards through Gletscherland, Hagar Bjerg and the Niggli Spids area (Fig. 3). The G~seland-Stauning Alper zone can also be continued northwards, though soon wedging out between the thrust to the west and the Eleonore Bay Group outcrop to the east. However, until new field work and isotopic studies have been completed any statements should be treated with reservation. Only brief mention is made here of some of the major problems, as a fuller more descriptive approach is presented elsewhere (Henriksen & Higgins, in press, Haller 1970, 197 I).

(A) ARCHAEAN INFRACRUSTAL COMPLEXES It was not surprising that the FIyverfjord infracrustal complex should preserve a complex Archaean history. Wenk (I 96 I) and Vogt (1965) both reported Archaean rocks, and Hailer & Kulp (i962) observed that the basement exposures in the Scoresby Sund region showed less alteration than areas further north, and partly preserved their old foliation. It was, however, not initially realised that the overlying Krummedal supracrustal rocks could be early Proterozoic, and that basement and cover could have been deformed and metamorphosed during a Protero- zoic orogenic event; on the basis of the isotopic data available this seems the most probable interpretation. The central metamorphic complex from latitudes 720 to 74°N was divided by Haller (I955) into three main structural units: (I) the Gletscherland migmatite complex comprising migmatitic banded and veined gneisses, foliated and nebulitic migmatitic granites, marble and amphibolite units, and in a few areas discordant amphibolite dykes; (2) the Niggli Spids dome with a core of homogeneous adamel- litic granite containing bands and schlieren of gneisses, overlain by amphibolite and hornblende gneisses, and augen gneisses; (3) the Hagar migmatite sheet con- sisting of leucocratic banded and veined gneisses, foliated migmatite granites and occasional amphibolite bands. These three infracrustal units have been folded together with the overlying supracrustal rocks; they form dome-like or tongue- shaped cores to major structures and enclose thin synclinal strips or wedges of metasediments. This region has been generally regarded as the central zone of Caledonian rnigmatitic activity (Haller 197 i). It is clear that parts of these infracrustal complexes were regarded by Hailer as originally having been parts of the ancient basement (Hailer & Kulp t 962, Hailer 197 I), but due to their extensive reworking they were assigned to the Caledonian crystalline complex. However, if the northern half of the central metamorphic complex developed in a similar way to the crystalline complexes of the Scoresby Sund region as new field work suggests, then Haller's three structural units are likely to yield isotopic evidence of an Archaean origin and Proterozoic reworldng, and only superficial influence of Caledonian orogenesis.

(B) EARLY PROTEROZOIC SUPRACRUSTAL ROCKS The Krummedal supracrustal sequence which is widely exposed in the Scoresby Sund region and was formerly assumed equivalent to the lower Eleonore Bay Group, is now believed to have been deposited early in the Proterozoic, after the

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphic complexes 299

main events recorded in the Archaean basement (2345-3000 Ma) and before the main metamorphic event dated at 1162 Ma. High grade metasedimentary sequences are also common within the central metamorphic complex between latitudes 72°-74°N (Fig. 3) and the general lithol- ogy, weathering colour and style of deformation of many of the sequences closely resembles those exhibited by the Krummedal supracrustal sequence. Many workers in the region have claimed that all metasedimentary sequences are equivalents of the lower Eleonore Bay Group, and a few K-At Caledonian mineral ages have been obtained by Haller& Kulp (1962). However in the absence of comprehensive isotopic studies the age of at least the high grade sequences is an open question.

(c) PROTEI~OZOIC OROOENESlS The isotopic evidence points to a significant orogenic episode in the Scoresby Sund region corresponding in time with the well-established Grenville-Sveco-Norwegian event of North America and northern Europe (9oo-12oo Ma). The main metamorphic episode in the Krummedal sequence (c. 1162 Ma) seems to have accom- partied much of the folding in the Vestfjord-Hinks Land zone. The emplacement into the migmadtes of the Ggsefjord-Stauning Alper zone of a suite of plutons giving ages of 95o-I 15° Ma associated with migmadte generation and deformation seems likely to relate to the same orogeny. There are currently no published pre-Caledonian isotopic ages for the central metamorphic complex between latitudes 720 and 74°N, but the distribution of infracrustal rocks and high grade metasediments in the region (Fig. 3) is sufficiently similar to the Scoresby Sund region for a parallel development to be suspected. It is possible therefore that the celebrated dome-like and tongue-like migmatitic structures described by Haller (1955, 1958, 197o, 1971) may in part be a con- sequence of Proterozoic orogenesis, though the contribution of Caledonian orogenesis remains uncertain.

(D) L oNoR sAY oRo P The former general correlation of all metasedimentary rocks within the crystalline complexes between latitudes 7°0 and 74°N with the lower Eleonore Bay Group is now suspect. The metasediments within the Scoresby Sund region, for example, appear to represent several middle Proterozoic or older successions. Outcrops of demonstrable Eleonore Bay Group are thus now restricted to two N.-S. belts of non-metamorphic to slightly metamorphic sediments on either side of the central metamorphic complex (Fig. 3); there are also the limited exposures on Canning Land; and fairly extensive outcrops occur around Ardencaple Fjord (c. 75°3o'N). The lower Eleonore Bay Group varies in thickness and has its maxi- mum development in the Alpefjord region, while the upper Eleonore Bay Group has a markedly uniform development throughout its outcrop. The contact of the Eleonore Bay Group with the central metamorphic complex appears to be transitional, though the eastern border of the complex is largely faulted or obscured by granite intrusions. The position of the base of the Eleonore Bay Group was a great problem to many early workers, and the problem is revived with the revised interpretations presented here. Thus, on the west side of the

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 300 A. K. Higgins

Eleonore So ;lavering 0 ~:.;,..~...,-~" F''"

~"Z-:

Petermann B

Chercot Land ' 72 =-

~.~

.~.,. / I !~ RENLAND ..... '~.;~;!¢-- -~,~ ~ ( JAMESON LAND I LAND

'5'C'O'9['~'RysuND /..~." >),>~,,,-~:.~#/," ::,~ ...... ~..,...!- ...... ,

0z , 100i 200I km /" l" Fault J Thrust

X ~ LOW grade metasediments J~ ~ Cambrian- Ordovician ] J Post - Caledonian rocks

~. o,ou0 .. - age stratigraphically°0"-- known

~,~ Gneisses, migmatites j E ~ Eleonore Bay Group Caledonian and older intrusions - slightly metamorphosed ~ in metamorphic complexes

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphic complexes 3° I

central metamorphic complex in the Petermann Bjerg region, Wenk &Haller (i953) have described a transition from non-metamorphic Eleonore Bay Group sediments into high grade metasedimentary rocks of the central metamorphic complex. Recent field work indicates that this 'transition' may be a composite phenomenon, and that the contact hetween the base of the Eleonore Bay Group and high grade, presumed early Proterozoic supracrustals is here a complex thrust zone modified by Caledonian overprinting. North of Isfjord there are extensive outcrops of low grade metasediments (Hailer I953) whose present stratigraphical position is uncertain, though in places there are apparent transitions upwards into slightly metamorphosed equivalents of the lower Eleonore Bay Group (Fig. 3)- Low grade metasediments are also found in the nunatak region north-west of Petermann Bjerg, and around Eleonore S~. There is little doubt that some of the low grade sequences are part of the Eleonore Bay Group, but others may prove, like the low grade rocks of Charcot Land and western G~seland-Paul Stern Land in the Scoresby Sund region, to be of widely different ages from those usually assumed.

(E) CALEDONIAN OROGENESIS The Caledonian orogeny influenced the entire East Greenland fold belt to a varying extent. In the metamorphic complexes which comprise a great deal of the fold belt it is difficult to separate the older pre-Caledonian and younger Caledon- ian elements, and even where isotopic ages are available they can be interpreted in different ways. However, substantial new evidence implies that the Caledonian orogeny was much less intense than previously supposed. Deformation, metamorphism and plutonism can only with confidence be attributed to the Caledonian orogeny where the late Precambrian-Ordovician sediments are involved. The style of deformation seen in the late Precambrian rocks generally comprises open N.-S. trending anticlines and synclines, and gentle flexures (P1. I) ; in many places these structures are modified by several episodes of late faulting. Some of the large scale N.-S. open structures within the metamorphic complexes may also be Caledonian. The major thrusts along the west margin of the fold belt are generally considered to be Caledonian, and have dis- placements of at least 4o km, and possibly > I oo km. The highest metamorphic grade reached in safely identifiable Eleonore Bay Group sediments corresponds approximately to the garnet zone. In the Scoresby Sund region a widespread late retrogressive metamorphic phase is regarded as Caledonian, as also are the garnet and muscovite growths which overprint cata- clasfic textures in the mylonites. The numerous Caledonian mineral age dates signify that there was a Caledonian thermal overprint of regional extent. A number of late to post-kinematic plutons in central East Greenland have

Fxo. 3 The Caledonian fold belt between latitudes 7°0 and 74°N. The Eleonore Bay Group is distinguished from metasediments of uncertain and older age, and Caledonian granites are distinguished from intrusions of uncertain and pre-Caledonlan age.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 302 A. K. Higgins

discordant contacts with the Eleonore Bay Group rocks and can be presumed Caledonian (Fig. 3). Similar bodies entirely within the metamorphic complexes may also be Caledonian, but some otherwise similar intrusions have yielded pre- Caledonian ages. On stratigraphical evidence the main phase of the Caledonian orogeny in central East Greenland can be placed between the upper middle Ordovician and the upper middle Devonian. Caledonian radiometric ages show a range of 37 ° to 470 Ma. 5. Comparison with northern Europe Depending upon which of the pre-drift reconstructions of the North Atlantic region is favoured, the west coast of Norway may once have been as close as 2oo km to the east coast of Greenland, whereas the mainland of Scotland was perhaps situated c. 6oo km south of the Scoresby Sund region and in direct continuation with the southern projection of the East Greenland Caledonides. The unification of the circum-Aflantic Caledonian fold belts thus achieved is impressive, but the minimum distances of supposed separation permit no more than general com- parisons. However, isotopic ages in both the Scandinavian and Scottish Caledon- ian fold belts have in recent years also led to reappraisal of traditional viewpoints and it is relevant here to emphasize the similarities with the East Greenland Caledonides.

(A) SCANDINAVIAN CALEDONIDES It is becoming increasingly clear that considerable parts of the core zone of the Scandinavian Caledonides consist of Precambrian crystalline rocks, which have been remobilised to a varying extent by Caledonian processes. Caledonian metamorphism can apparently no longer be considered the dominant metamorphic event throughout the region, although the widespread Caledonian K-Ar mineral ages show that it was significant. The basal gneisses within the southern Caledon- ian fold belt in Norway have now yielded many Sveco-Norwegian Rb-Sr isochron ages (c. 9oo-1200 Ma--Brueckner 1972, Heier et al. 1972, Pidgeon & Rb~heim 1972 ) as well as some greater ages (Andresen et al. 1974). Some of the metasedimentary sequences within the basal gneiss region believed on traditional geological arguments to be metamorphosed Caledonian geosynclinal rocks have also yielded pre- Caledonian ages (Brueckner 1972). There are striking parallels with current interpretations of the Scoresby Sund region. In northern parts of Norway, Sveco-Fennian and older ages have been recorded within the Caledonides (Heier & Compston 1969). As very little isotopic work has been carried out in northern parts of East Greenland comparison of geochronological provinces is premature, but it may be significant that the isochron age of c. 28oo Ma for granulite facies gneisses on Langoy in the Lofoten islands (Heier & Compston 1969) lies in reasonably close proximity, on conventional we-drift reconstructions, to the c. 3ooo Ma date on banded gneisses at Danmarkshavn (76°5o'N.) in East Greenland (unpublished data by R. H. Steiger, pers. comm.).

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphic complexes 303

(B) SCOTTISH CALEDONIDES The possibility ofa Precambrian event affecting part of the Moinean of the Scottish Caledonides has been regularly debated since the first c. 7oo Ma ages were obtained on pegmatites (Giletti et al. 19 6 I, Long & Lambert 1963). However, recent comprehensive isotopic work appears to confirm that there was a regional Pre- cambrian pegmatite suite c. 73o Ma ago (Pidgeon & Johnson I973, van Breemen et al. x974). These dates support arguments that the early deformation phases and an early metamorphism of the lower part of the Moine sequence could be Pre- cambrian, while subsequent deformation and metamorphism relate to the Cale- donian orogeny (Powell 1974, Winchester x974). The Precambrian ages so far obtained from the Moine sequence are somewhat younger ethan the main metamorphic events dated in the Krummedal supracrustal sequence of East Greenland. While the general lithologies and deformation and metamorphic histories of the two sequences are similar in many respects, in both regions there are still major problems in distinguishing the affects of Gale- donian orogenesis and it is premature to suggest any close correlation.

Acr.NOWUZVO~mm's. Published with the permission of the Director of the Geological Survey of Greenland. Credit is due to the geologists who mapped the Scoresby Sund region, especially to Niels Henriksen who directed the Survey expeditions; and to R. H. Steiger, B. T. Hamen and co-workers in Ztirich, and to workers in age-dating laboratories elsewhere.

6. References AtORmEN, A., HZmR, K. S., JORDE, K. & NATERSTAD,J. 1974. A preliminary Rb/Sr geochronological study of the Hardangervidda-Ryfylke nappe system in the Reldal area, south Norway. Norsk geol. Tidsskr. 54, 35-47. BAer.t.um), H. G. x93 o. Contributions to the geology of Northeast Greenland. Meddr Gronland 74 (Ix), 207-96. B~.RTa.~-SAt~Aa'I, J. & Ca~Y, R. 1974. Prdcisions sur l'~tge pr~cambrien terminal (vendien) de la s~rie carbonat~e ~i stromatolites du groupe d'Eleonore Bay (Groenland oriental). C. R. Acad. S¢. Paris ~78D, 2267-7o. BmXELU~m, T. & I~aCH-NmLSEN, K. (in press). Late Palaeozoic evolution of central East Green- land. In Escher, A. & Watt, W. S. (eds.) Geology of Greenland. Geol. 8urv. Greenland, Copenhagen. BRtmcm~R, H. K. t972. Interpretation of Rb-Sr ages from the Precambrian and Paleozoic rocks of southern Norway. Amer. J. St. 272, 334-58. BfrrL~R, H. x948. Notes on the geological map of Canning Land (East Greenland). Meddr Grerdand x33 (2), 97 PP- C~Y, R. z972. Preliminary results of mapping in the Caledonian rocks of Canning Land and Wegener Halve, East Greenland. Rapp. Gronlands geol. Unders. 48, 2 t-38. CHADWICK, B. x97 I. Preliminary account of the geology of south-east Renland, Scoresby Sund, East Greenland. Rapp. Gronlands geol. Unders. 34, 32 pp. x975. The structure of south Renland, Scoresby Sund, with special reference to the tecto- nometamorphic evolution of a southern internal part of the Caledonides of East Greenland. Bull. Gronlands geol. Unders. xx2, (also Meddr Gronland 2ox (2)) 67 pp. CoE, K. & Ci-m~mY, R. F. x972. Preliminary results of mapping in Liverpool Land, East Green- land. Rapp. Gronlands geol. Unders. 48, 7-2o. Gzuzan't, B. J., MOOR.BATH,S. & LAMBERT,R. ST. J. x96t. A geochronological study of the metamorphic complexes of the Scottish Highlands. Q. Jl geol. Soc. Lond. xx7, 233-72.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 30 4 A. K. Higgins

t-~t.t~R, J. x953. Geologic und Petrographic von West-Andrdes Land und Ost-Fraenkels Land (Nordost-gronland). Meddr Gronland • x3, 5, 196 pp. 1955, I958. Der "Zentrale Metamorphe Komplex" von NE-Gr61and. Teil I, II, Meddr Gronland 73, x (3), I74 Pp.; x54 (3), 153 PP. t97o. Tectonic Map of East Greenland (I :5oo ooo). An account of tectonism, plutonism and volcanism in East Greenland. Meddr Gronland •7• (5), 286 pp. 197 I. Geology of the East Greenland Caledonides. Interscience Publishers, New York, 413 PP. & KULP, J. L. x962. Absolute age determinations in East Greenland. Meddr Grenland x7x (I), 77 PP. HANSON, B. T. & STEIOER, R. H. 197I. The geochronology of the Scoresby Sund area. Progress report I : Rb/Sr mineral ages. Rapp. Gronlands geol. Unders. 37, 55-7. , -- & I~N~IKSEN, N. I972. ibid. Progress report 2: Rb/Sr mineral ages. Rapp. Gronlands geol. Unders. 48, 1o5- 7. OB~RLX, F. & SamlOER, R. H. I973a ibid. Progress report 4: Rb/Sr whole rock and mineral ages. Rapp. Gronlands geol. Unders. 58, 55-8. , FRICK, U. & SamIGER, R. H. x973b, ibid. Progress report 5: K]Ar mineral ages. Rapp. Gronlands geol. Unders. 58, 59-61. , OBERLX, F. & SamIG~R, R. H. 1974. ibid. Progress report 6: Rb-Sr whole rock and U-Pb ages. Rapp. Gronlands geol. Unders. 66, 32-8. HEXER, K. & COm~STON, W. 1969 . Interpretation of Rb-Sr age patterns in high-grade metamorphic rocks, north Norway. Norsk. geol. Tidsskr. 49, 257-83. , NAaXRSa'AD,J. & BRYHNX, I. 1972. A Rb-Sr whole rock isochron date from the Stavanger area, south Norway. Norsk geol. Tidsskr. 5a, 377-83. t-IENRImS~N, N. & HIGOINS, A. K. x969 . Preliminary results of mapping in the crystalline complex around Nordvesffjord, Scoresby Sund, East Greenland, Rapp. Gronlands geol. Unders. 2I, 5-2o...... & -- 1973. Preliminary results of the mapping in the migmatite complex around Font~ord and GAsefjord, Scoresby Sund. Rapp. Gronlands geol. Unders. 58, 7-I5. & ~ (in press). East Greenland Caledonian fold belt. In Escher, A. & Watt, W. S. (eds.) Geology of Greenland. Geol. Surv. Greenland, Copenhagen. HlOOlNS, A. K. 1974. The Krummedal supracrustal sequence around inner Nordvestfjord, Scoresby Sund, East Greenland. Rapp. Gronlands geol. Unders. 67, 34 PP. HomswooD, P. I973. Structural and lithological divisions of the western border of the East Green- land Caledonides in the Scoresby Sund region between 7I°OO' and 71°22'N. Rapp. Gronlands geol. Unders. 57, 27 PP. KALSBE~K, F. 1969. Preliminary report on the geology of Bjorneoer, Scoresby Sund. Rapp. Gron- lands geol. Unders. 26, 33 PP- KOCH, L. i929. The geology of East Greenland. Meddr Gronland 73 II (I) 204 pp. & HALL~R, J. i97i. Geological map of East Greenland 72-76°N. Lat. (1:25o ooo). Meddr Gronland t$3, 26 pp. KapoK, E. H. I935. On the crystalline complex of Liverpool Land. MeddrGrenland95 (7), I22 pp. LARS~N, O. I969. K/Ar determinations. Rapp. Grenlandsgeol. Unders. x9, 62-7. LoNo, L. E. & LAu~RT, R. Sa'. J. 1963. Rb--Sr isotope ages from the Moine series. In Johnson, M. R. W. & Stewart, F. H. (eds) The British Caledonides. Oliver & Boyd, Edinburgh & London. 217-39- OBERLI, R. & SaXlG~R, R. H. 1973, U-Pb age determinations on zircons and monazites from a migmatite area on Bjorneoer, Scoresby Sund, East Greenland. A preliminary report. Rapp. Gronlands geol. Unders. 58, 63-74. OD~LL, N. E. I944. The petrography of the Franz Josef Fjord region, North-East Greenland, in relation to its structures. A study in regional metamorphism. Trans. R. Soc. Edinb. 6•, 221-46. PARg_rNsorq, M. M. L. & WHrrTARD, W. F. I93 I. The geological work of the Cambridge expedition to East Greenland in I929. Q. Jl geol. Soc. Lond. 87, 65o-74. PmLLXPS, W. E. A., STIL~, C. J., FRmERtCa-ISEN,J. D. & J~MXLIN, L. I973. Preliminary results of mapping in the western gneiss and schi.qt zone around Vestl]ord and inner G~efjord, south- west Scoresby Sund. Rapp. Gronlands geol. Unders. 58, 17-32.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021 Pre-Caledonian metamorphic complexes 305

Pmo~on, R. T. & tL~n% A. t972. Geochronological investigations of the gneisses and minor intrusive rocks from Kristiansund, west Norway. Norsk geol. Tidsskr. 52, 24x-56 & JOHNSON, M. R. W. I973. Isotopic evidence for 'early' events in the Moines. In Pidgeon, R. T., MacIntyre, R. M., Sheppard, S. M. F. & van Breemen, O. (eds), Geochronology isotope geology of Scotland. Scottish Univ. Research Reactor Centre. & ~x974. A comparison of zircon U-Pb and whole-rock Rb--Sr systems in three phases of the Cam Chuinneag granite, northern Scotland. Earth Planet. Sci. Lett. 24, xo5-x2. POWELL, D. x974. Stratigraphy and structure of the western Moine and the problem of Moine orogenesis. Jl geol. 8oc. Lond. x3o, 575--93. REx, D. C. & GL~DmLL, A. x974. Reconnaissance geochronology of the infracrustal rocks of Flyvenejord, Scoresby Sund, East Greenland. Bull. geol. Soc. Denmark. 23, 49-54. STECK, A. I97 I. Kaledonische metamorphose der praekambrischen Charcot Land Series, Scoresby Snnd, Ost-Gronland. Bull. Gronlands geol. Unders. 97, (also Meddr Gronland x92 (3), 69 pp. STSXOm% R. H. & I-~NRmSFN, N. x972. The geochronology of the Scoresby Sund area. Progress report 3: zircon ages. Rapp. Gronlands geol. Unders. 48, io9-i 4. TEmrmRT, C. I933. Untersuchungen zum Bau des kaledonischen Gebirges in Ostgr6nland. Meddr Gronland 95 (x), x2 t pp. VAn BREvm~N, O., PInG-ON, R. T. & JOHNSOn, M. R. W. t974. Precambrian and Palaeozoic pegmatites in the Moines of northern Scotland. Jl geol. Soc. Lond. x3o , 493-5o7. VOOT, P. x965. Zur Geologic yon Siidwest-Hinks Land (Ostgr6nland 7t°3o'N). Meddr Gronland x54 (5), 24 pp. W~Gm~'qn, C. E. x935. Preliminary report on the Caledonian orogeny in Christian X's Land (North-East Greenland). Meddr Gronland xo3, (3), 59 PP. W~NK, E. I96I. On the crystalline basement and the basal part of the pre-Cambrian Eleonore Bay Group in the southwestern part of Scoresby Sund. Meddr Gronland x68 (I), 54 PP. -- & HAU.ER, J. x953. Geological explorations in the Petermann region, western part of Fraenkels Land, East Greenland. Meddr Gronland xxx (3), 48 PP. WINCHESTER, J. A. x974" The zonal pattern of regional metamorphism in the Scottish Caledonides. dl geol. Soc. Lond. x3o, 5o9-24 • Received 8 May I975; revised typescript received t 7 September x975.

A. K. HtGGINS, Gronlands Geologiske Undersogelse, Ostervoldgade xo, DK- 135o Copenhagen K, Denmark

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/132/3/289/4896931/gsjgs.132.3.0289.pdf by guest on 02 October 2021