Etah meta-igneous complex and the Wulff structure: Proterozoic magmatism and deformation in Inglefield Land, North-West Greenland

A hitherto uninvestigated collection of crystalline rocks from north-eastem Inglefield Land (c. 79°N) allowanew interpretation of the Precambrian geology of the region. The majority of the samples high-grade basic, intermediate and granitoid rocks are referred to the Etah meta-igneous complex, which has been shown to be mid-Proterozoic in age in the type area in south-western Inglefield Land. In areas of high deformation there is a gradation from massive rocks of igneous aspect into folded and variably migmatised gneisses. Thus the magmatic complex provides a gauge of the nature and intensity of Proterozoic (Hudsonian) deformation and metamorphism. In Inglefield Land Proterozoic deformation produced different structural styles; thus in the north-east the Wulff structure a large-scale refolded isoc1inal structure characterises a region that lacks an obvious preferred regional foliation direction, while in the south-west, linear E-W trending belts with steep dips dominate the structural pattem. The Proterozoic evolution is outlined from the formation of the Etah Group, a supracrustal sequence that pre-dates the Etah meta-igneous complex, to uplift, peneplanation, deposition and magmatism in the late Proterozoic. Inglefield Land is not part of the Rinkian mobile belt of West Greenland, and it is stressed that the obvious conti:mation of the Proterozoic geology is into Ellesmere Island.


Introduetion
Inglefield Land (781O'N -79°lO'N, c. 10 000 km 2 ) is underlain by Precambrian crystalline basement overlain by Proterozoic and Cambrian platform strata (figs 1 & 2). The crystalline rocks are truncated by a Precambrian peneplain surface that dips shallowly to the north-west (see fig. 5). The overlying unmetamorphosed and undeformed platform strata form large outliers along the coast producing pronounced coastal cliffs. This basic geology was recognised by Koch (1920).
Few bedrock investigations have been undertaken in Inglefield Land since Lauge Koch's pioneer work between 1917 and 1922. These have been concentrated in the extreme south-west in the region between Foulke Fjord and Rensselaer Bugt (fig. 2;Cowie, 1961;Dawes, 1972Dawes, , 1979. Apart from unpublished commercial work (e.g. by Internationalt Mineselskab A/S in 1973) the only geological visits to the region north-east of Rensselaer Bugt were those in 1976 and 1977 during GGU's mapping programme in Washington Land. The time spent in Inglefield Land was mainly allocated to the study of the platform strata (Peel, 1978;Peel etat., 1982), but in both 1976 and 1977 the opportunitywas taken to sample the basement complex.
Recent isotopic dating of rocks around, and north of, Foulke Fjord (Etah meta-igneous complex, Dawes et al., 1988), as well as field and chemical studies of the northernmost exposures of the Greenland shield at the head of Victoria Fjord (81°30'N, fig. 1) (Henriksen & Jepsen, 1985;Hansen et at., 1987) focus attention on the basement in the relatively unknown intervening area -north-eastern Inglefield Land. For this reason the 1976-77 rock collection has been restudied and is evaluated here. This allows important inferences to be made about the nature and distribution of Proterozoic plutonism and deformation, and a summary of Proterozoic evolution in Inglefield Land is presented.

General geology of south-western Inglefield Land
In south-western Inglefield Land (Kap Alexander to Rensselaer Bugt) the basement is composed of three main rock groups: the Etah Group of metasedimentary supracrustals, the Etah meta-igneous complex and a variable gneiss group (Dawes, 1972(Dawes, , 1976. The Etah Group, where examined along the coast between Foulke Fjord and Kap Hatherton ( fig. 2), is composed of marble, calc-silicate rock, garnet-bearing pelitic schists with units of quartz-rich schist, siliceous gneiss and garnet-biotite (-sillimanite-cordierite) gneisses. The supracrustal rocks form steep, E-W striking belts that are generally light in colour and thus easily seen on aerial photographs.
The Etah Group is invaded on all scales by rocks of the Etah meta-igneaus camplex that is composed of a variety of plutonic rocks characterised mineralogicaIly by the presence of orthopyroxene. The intrusions take the form of large discordant bodies as well as sheets and   fig. 1. The black dots mark the general area or four sample locations; tne fifth, Oll tne Wulff :slruclurc, is shuwn in fig. 6. Struclures shawn in the shield :1way from the coast arc interpreted from aerilll photographs. Inland arcas, particularly in tne eas! and south-east, have il heavy surficial cover. For this reason Ila structural trends afC shawn in the area imrnediatcly south of Septembersøerne. and Ihc Etah Group farlhcr south is shown as hrokcn outcrops. Gcology from Dawcs (1970. fig. 224) wilh fig. 3) and aerial photograph study. veins (figs 3 & 4). Main rock types are hypersthcnc-bcaring quartzofeldspathic granodioritic and dioritic rocks. with gradations lO quartz-puor rocks. These are illtl'uded by granitic rocks varying from teucocratic to re!alivcly mcJanocratic hypcl'sthene-biotite-garnet varieties. and also pegmatites and apJitcs. Thcsc plutonic rock types are generally massive to poorly foliatcd. The melanocratic rocks in particuJ<lf have a lypicaJ grccnish culour and waxy sheen, with green feJdspars and commonJy (~oJouTcd quartz; in Ihe Jeucocratic rocks feldspaTS ean be pink to brownish fed. Other rocks af the compJex are thin basic metadykes, discordant to the foliatian of the othcr rocks. and these are cut by a late generation af reddish granitic vcins. Thcrc is a gradation from rocks af the Etah mcta-igneous complex to well-foliared and banclcd gncisscs uf thc variable gneiss group. This relationship beaTs witness to the complex srfuctural history post-dating the intrusion af tile igneous rocks ( fig. 5).
The variable gneiss group is essentiaIly composed af a concordant series af foliated, banded or migmatitic rocks -granulites, gneisses and schists -that generaJly cOllrain both K-feldspaT and plagioclase in variable ratios. Ouartz-rich gneisses a[so occur; hypersthene and garnet are com mon. This gnciss group probably cOlltains ortho-and paragncisses derived from both the Etah meta-igncous complex and Etah Group supracrustals. However, to what extent the variable gneisses also include older crusta! matcrial, i.e. a basement to the Etah Group, is at present unknown.

North-eastern Inglefield Land
Hitherto publishcd details from the region north-east of Rensselaer Bugt include those of Koch (1933) and the petrographic descriptiolls of the few samples avaihl.blc to Callisen (1929). Of particular note is the presence of hypersthene-bearing igneous rocb at sevcral localities (Koeh's 'Etah Formation') and diverse gneisses (Koch's 'grey gneiss'). From this information, and based on aeria! photograph interpretation, thc Etah Group, the Etah meta-igneous comp!ex and the variable gneiss group have been interpreted as occurring throughout Tnglefield Land (e.g. Dawes, 1976;fig. 2). Earlier map subdivision of the basement by Koch had been limitcd to an area uf 'intrusive rock' around Kap Agassiz (Koch. 1920), a feature ornittcd from his later. larger-seale map (Koch, 1933).
A prominent feature east of Dallas Bugt is a large horscshoc-shaped structurc about la km across ( fig. 6). Tilis refolded isociinal structurc, illustraled earlier by Dawcs (1976, fig. 230), is refcrred lo here as the 'Wulff structure' -named atter Thorild Wulff, Swedish botanist and member of thc 2nd Thule cxpedition, who perished in the district in .1917. Fig. 5. Protcrozoic geology of south-western Inglefield Land. Stccply-dipping, crystallinc rocks of the shield. trullcated by a well-developcd pcncpJain and overl<lin by the Helikian Rensselaer Bay Form(ltion -sediments and cliff-forming basaltic intfusions. Metascdimcnts ol' the Etah Group predominate in the cliffs to the right; more massive rocks to the lefl afe mainl)' meta-igncous rocks af the Etah complex. View is eastwards from eoast south of Kap H<llhcrton, more or less along the regional strike af the cryslal1inc rocks. Height af inland cliff is about 3S0 m.

The sample colieelion
The rock collection forming the basis af (his feport com prises 30 samples from rive areas af north-eaSlern Inglcficld Land: Kap Agassiz, the Wulff structure, Advance Bugt, Dallas Bugt and Kap RusselI ( fig. 2). The samples from Kap Agassiz were collected by H. F. .lepsen in 1976 during a short hclicuptcr refuelling stop en route to the soutb; the bulk af the coHcction was made tlle fullowing summer by J. S. Peel and J. D. Collinson during field work on the platform sediments af the region.
Thin scctions of 26 uf the samples have been studied.

Kap Agassiz
Six samples are available from the Kap Agassiz area (GGU 212658-63). Tlle rocks were collectcd within a stone's throw af cach other an tlle north side af a nunatak 011 the south side uf Humbuldt Gletscher ( fig. 2). Tlle basement here is compuscd uf generally reddish weathering and pourly foliated granitic and intermedillte meta-igneous rocks.
The snrnplcs are all ol' massive rocks that range from medium-grained melanocratic grcenish quartz diorilc to greenisll grey and pink finc-grained granite. The rocks are characterised by the presence uf orthopyroxcne Ol' mineral replaeemcnts of pyroxene. Tlle Fig. 6. Aerial view af the care af tlle Wulff structure, nonh-eastern lnglefieJd Land; a closed isodinal stfllclUrc whh strep. non herI y dipping sides, refolded by an approximately E-W trending isoc1inal antiform. Distance across view is aboul 9 km. A-B represents the traverse across tile westerly dipping hingc ()f !he antiform, along which samples have bccn collcctcd. Aerial photograph 239 C, no. 80; copyright Geodaetisk Institut (A200/R7). rnajority uf the granitcs contain K-feJdspar, aften perthilic, and plagiodase. Most are fairty leucocratic and only one canfains biotite in addition to orthopyroxclle. Of particlllar note is il sample af paIe weatherillg, hypersthenc quarlz Jioritc containillg biotite that an fresh surfaces shows a greenish greasy lustre, typical af granulite [acies rocks.

Wulff structurc
The samples from the Wulff structure (242136-45, 242175) come from its western flank about 8 km so uth-eas t of the head of Advance Bugt ( fig. 6). There a series of granitic gneiss and schists, granites and basic-ultra basic schists have a steep westward dip foldcu around the main NE-trending axis of !he horseshoe-shapcd structure. The samples eome from a traverse ilbout l km lang across regional strike where all thc rock iayers seem to form a concordant serie:s. Field relatiollships noted on outcrop seale point to the polyphase nature of the rock series; discordant, pink to rust y red, granite vcins (including pegmatites and aplites) are present within the acidic to h'1Sic rocks.
Many af the rocks are rusty weathering and friable; 011 fresh surfaces several show the grecnish colour characteristic af granulitc facics rocks. The rock suite is characterised by the presence of hypersthene, with or without garnet, in both acidic and basic varieties, and by the two feldspars in the granites. K-feldspar is commonly perthitic.
In the foliated and sehistose granitie rocks both hypersthene and biotite show a preferred orientation; in these rocks as well as in the more massive, fine-to medium-grained granites, both minerals show various stages of replacement.
Particularly interesting are samples of paIe greenish yellow and grey, garnet-hypersthene granites in which either K-feldspar or plagioclase may be the dominant feldspar. These rocks vary in grain-size from fine to medium to pegmatitic varieties. One sample is characterised by garnets 'peppered' throughout the rock, many euhedral up to 7-8 mm across.
The only ultramafic rock in the collection is a schist composed of amphibole and orthopyroxene in roughly equal amounts, together with heavily replaced olivine.

Advance Bugt
A prominent feature of the crystalline basement in parts of north-eastern Inglefield Land is the occurrence of rusty yellow gossan weathered areas. Samples were collected from one such area at the head of Advance Bugt, on its south-eastern side ( fig. 2).
The three samples (GGU 242135,242176-7), all taken from the same general area, have a rusty brown to yellow weathering surfaee with gradation to a friable crust. The rocks are paIe cream to yellow on fresh surfaces and deficient in mafic minerals. They range from rather massive, fine-grained rock to quartzitic muscovite schist, being composed essentiaIly of K-feldspar (mainly perthite), plagioclase, quartz and paIe mica, with or without sillimanite and garnet, and opaque minerals. Quartz is commonly in intergrowth with both perthite and plagioclase; garnet ean be pseudomorphed by chlorite.
The primary nature of these leucocratic rocks is unclear; they probably represent psammitic metasediments. The origin of the rusty gossan products is uncertain; no concentrations of iron-rich minerals are present in the available material. The rocks have been fractured and hydrothermally altered. Thin veins rich in epidote and iron oxide (?hematite) cut the quartzofeldspathic matrix of the rock and in severely altered material feldspar is replaced by sillimanite (?contact metamorphic produet) that forms a prominent mineral of the friable crust.

Dallas Bugt
The samples in the collection from Dallas Bugt come from three localities about 4 km south-east of the head of the bay (GGU 242118-22, 242172-4) ( fig. 2). In this area a varied suite of meta-igneous rocks outcrops in which three main intrusion phases are recognised in the fieid. A complex of massive to foliated granitic, quartz dioritic and basic rocks is cut by slightly discordant, thin metabasic dykes and younger pink acidic veins.
The granitic rocks are fine-to medium-grained, generally leucocratic, containing both plagioclase and K-feldspar with or without garnet and biotite. Where present, biotite produces a foliation. In a plagioclase-rich leucocratic variety, feldspar is heavily altered. The quartz dioritic intermediate rocks have hypersthene as the dominant mafie mineral, with or without hornblende and biotite. Fresh surfaces have a greenish grey colour and a waxy sheen. The basic rock in the collection is a black schistose pyribolite composed of horn-blende and orthopyroxene in roughly equal amounts with fresh plagioclase, biotite and opaque minerals.
The metabasic dyke material cutting the rocks above is also a pyribolite, containing both orthopyroxene and hornblende. The late addie veins range from aplitic varieties to pegmatitic; they are commonly pink, contain plagioclase, perthite and quartz and are deficient in mafic minerals.

Kap RusselI
The basement immediately east of Kap RusselI (where it disappears beneath the overlying sedimentary cover, see fig. 2) is dominated by red weathering granitic and more mafic massive rocks in which ill-defined pegmatite patches and pink acidic sweats occur.
The single sample available (GGU 242129) is a pink to purplish weathering, mediumgrained, two-feldspar granite. Brown to green biotite is the main mafic mineral, being partially replaced by chlorite. The plagioclase is heavily saussuritised and the rock is cut by thin veins with epidote and sericite.

Correlation
The majority of the rock samples from Kap Agassiz, the Wulff structure, Dallas Bugt and Kap RusselI ean be referred to the Etah meta-igneous complex. Several of the granites and hypersthene quartz diorites are mineralogicaIly and texturally identieal with the rocks around Foulke Fjord, which were initially recorded by Schei (1903) and described by Bugge (1910) and Holtedahl (1917).
In addition the field information from the sample areas strongly suggests a close similarity in igneous and tectonic chronology with the type area of the Etah meta-igneous complex. Thus a suite of acidic and intermediate rocks with some basic varieties showing evidence of varying intensity of deformation, and in which granitic rocks are intrusive into hypersthene quartz diorites, are cut by metabasite dykes and by later red pegmatitic and aplitic materia!.
It is concluded that the Etah meta-igneous complex has a wide distribution in northeastern Inglefield Land. However, to what extent the metasedimentary Etah Group and the variable gneiss group are present is uncertain. The only possibIe metasediments in the present collection are the quartzofeldspathic micaceous rocks of the gossan zones from Advance Bugt. Other possibie metasediments are the sillimanite-bearing gneisses described by Callisen (1929) from Kap Scott and Septembersøerne ( fig. 2). Several white to paie grey banded zones interpreted as marble-rich sequences occur inland between Marshall Bugt and Septembersøerne. Several of these occurrences, like the Advance Bugt rocks, are characterised by gossan weathering.
No banded gneisses or migmatitie rocks comparable to the variable gneiss group of the Foulke Fjord area occur in the present collection. The granitic gneisses present appear to represent orthogneisses, i.e. derivatives of the Etah meta-igneous complex. However, among the rocks described by Callisen (1929) are several gneisses that Koch (1933) included as part of his 'grey gneiss' terrain which he surmised to be older than the marble-rich metasediments and diorites. The questions as to whether Koch's grey gneisses are synonymous with the variable gneiss group and whether any of the gneisses pre-date the Etah Group must await further study.

Proterozoic magmatism, metamorphism and deformation
Two principal conc1usions drawn from the present rock collection are: (1) that the Etah meta-igneous complex forms a prominent part of the basement outcropping at least as far north as Humboldt Gletscher, and (2) that the complex is affected by strong polyphase deformation that produced large isoc1inal folds like those involved in the Wulff structure.
Results of a Rb-Sr isotope whole rock study of rocks from the type area of the metaigneous complex in south-western Inglefield Land have been interpreted as indicating a strong mid-Proterozoic metamorphic event at around 1800 Ma (Dawes et al., 1988). The low initial 87Sr/86Sr ratio (c. 0.7032) is taken to indicate that the complex has not passed through a long crustal history prior to metamorphism and it is considered extremely unlikely that the rocks represent Archaean material.
This Proterozoic age inference is confirmed by U-Pb age dating work on correlatable meta-intrusive rocks in adjacent Ellesmere Island where certain quartzofeldspathic plutonic rocks cutting gneiss and marble-rich metasediments have been referred to the Etah metaigneous complex (Frisch & Dawes, 1982, see below). For example, zircon from a hypersthene-bearing quartz diorite from Cape Isabella ( fig. 1) has yielded a U-Pb concordia age of 1912 ± 1.6 Ma; an age regarded as recording the time of magmatic emplacement of that particular plutonic body (Frisch & Hunt, 1988).
Field relationships both in Inglefield Land and in Ellesmere Island indicate that the Etah meta-igneous complex is composed of several generations of intrusive material. The absolute ages of the rock phases are as yet unknown and the complex in Inglefield Land may contain magmatic rocks emplaced prior to 1912 Ma. It should be noted that Frisch & Hunt (1988) present evidence for magmatic emplacement of orthopyroxene-bearing granitoid rocks from Ellesmere Island as early as c. 1950 Ma. Whatever the precise intrusion age of the meta-igneous rocks in north-east Inglefield Land, the folding, deformation and metamorphism of the rocks are a measure of the degree of Proterozoic (Hudsonian) plutonism and diastrophism in the region.
A common mineral assemblage of the quartzofeldspathic rocks of the Etah meta-igneous complex is plagioc1ase -K-feldspar (perthite) -quartz -hypersthene ± biotite ± hornblende ± garnet. Orthopyroxene ranges from fresh to altered but it appears to be essentiaIly in equilibrium with other mafic minerals. The rocks are interpreted as having been intruded during or slightly prior to a regional granulite facies event. Break-down of orthopyroxene and biotite, and the generation of hornblende, indicate a local retrogression at amphibolite facies conditions.
The Wulff structure indicates that at least two, possibly three, phases of deformation and large-scale folding affected the igneous complex producing major isoc1ines and refolded structures. This has produced a structural pattern characterised by a variable regional foliation trend. This contrasts with the structural style in south-western Inglefield Land where the regional foliation has aregular, roughly E-W strike with linear and sheared belts of steeply inc1ined rocks persistent over tens of kilometres. This linear structure is prominent at the outer coast from north of Kap Alexander to the Kap Inglefield area; inland, definition is less distinct due to heavy cover of surficial deposits, but the straight belt structure appears to persist to the roland lee ( fig. 2).
The Elah meta-igneous complcx pre-datcs tlle developmcnt af the prominent E-W i"oliation pattern which must lherefore alsa be af Proterozoic age. However, an outcrop scale il is evident that the Etah meta-igneous rocks (as well as the Etah Group) in south-western Inglefield Land have a[so passcd through a complex polyphase teclonic history. Thus, in the Mea sDurh Df FouJkc Fjord whcre rocks af igneous aspect grade iota weJl-foJiared and vcincd orthopyroxene gneisses, small-scale fold patterns resemblc the structural style af northcastern Jnglcficld Land ( fig. 7), while in northern Prudhoe Land (solIth of Inglefield Land, fig. I) large-scale recumbent isoc1ines characterise the granulite facies gneisses (fig. 8). Isoc!inal folds are also preserved within the linear bells north af Faulkc Fjord anel are particularly visible causing repetitions of layers in the Etah Group. The pronounced E-W tectollic grain is regardcd as a late stage in the Proterozoic deformational history post~dating the main isoc!inal fa/ding episodes ( Table l).
The gHn'is rclationship between the Etah Group and the Etah meta-igncous complex is unequivocal; in areas of low deformation, igneous bocties are profoundly discarclant to the main structure af the metasediments. 'Ibwards areas of high deformation there is a gradation from such discordaneies to a generaJly coneordant intcrlcaving af the two rock groups.
However, Oll outcrop seale the relationships between meta-igneous rocks and metasediments eao he compicx, and cantaet metamorphie effects and flow deformatiun in marble are widespread phenomena (fjgs 4 & 9). Where most intense the mobilisatioll af the carbonate rock is associ8ted with severe folding and break-up of smaller intrusians -sheets. dykes and veins~so that boudins alld fragments af granite and metabasite are isolatcd in marble (figs 10 & Il). Igneous bodics within marble commonly display contact metamorphic rims. The deformation effects due to magm<ltie injeclion are of more than anc age; early flow folds in marble and deformed mctabasic c1ykes are cut by I<.lter baudinaged granite veins.
The Etah meta-igneous complex represents a syn-kincmatie suite of intrusions; the detailed chronology af magmatic emplacement. deformation and metamorphism must await further field study. an single outcrops it ean bc difficult to differentiate bct\\'ccn folding in tne Etah Group that is duc to flow deformation induced by magmatic emplacement, and deformation effects that may prc-dale t.ile emplacement of the complex, or even late effects due Io the main Hudsonian deformalion (Table l). Tnc lattcr ean be established by the Fig. 7. Srnall-scale elongal cd dom e struclure in pyroxene arthognciss. North af Kap Alexander within the arca af E-W trcnding. stccply dippin/; regional foli.'llion. regional structural disposition of the meta-igneous complex and its occurrence in major folds like the Wulff structure. Evidence of deformation and metamorphism prior to emplacement of the igneous complex (stage 3 in Table 1) is based on the presence of folds affecting the Etah Group that are cut by granite units, for example in the thick supracrustal belt north of Etah (Sunrise Pynt belt of Dawes, 1976). Such granites also post-date the development of a strong planar fabric in the metasediments which, in the pelitic lithologies, is developed as a thoroughly penetrative schistosity involving biotite (± garnet and amphibole). However, the relationship of this regional metamorphic and deformational event to the basic and intermediate rocks of the complex that generally are seen to be the earliest intrusion phases has not been determined.
The chronological stages numbered 3, 4 and 5 in Table 1 clearly represent a long and complex Proterozoic plutonic history, the detaiIs of which have yet to be unravelled. In south-western Inglefield Land the metamorphic peak of the Hudsonian orogeny appears to have been around 1850--1800 Ma agn (Dawes et al., 1988); K-Ar 'cooling ages' on hornblende indicate waning of the metamorphism around 1750--1700 Ma (Larsen & Dawes, 1974). Retrogression of the granulite facies mineral assemblages occurred during slow uplift of the basement complex. As dcscribcd earlier, the Etah mcta-igneous complex in Inglefic!d Land (stage 4) is considered an PCITological evidence to have becn cmplaced during or slightly prior to granulite facies metamorphism. Thus high-grade mctamorphism must have existcd prior to 1850 Ma. This is supported by the gcochronologicalmodel from adjaccnl Ellesmere ISland lhal ;s bascd on U·Pb isotopic 3nalysis of zifcon and monazite. Friscll & Hunt (19R8) suggest thaI carly intrusion at around 1.96 Ga \Vus followcd by granulite faeies mctamorphism and deformation, <Ind subsequent melting and intrusion prior to 1.9 Ga. Ages af around 1.93 Ga an rnonazite (a mineral considered nol lo be capable af surviving granulite metamorphic conJitions) are cOl1sidered as a minimum for tile granulitc facie~event in Ellesmcre Island. llow far this gcochronology is regionally applicablc must <:lwait comparative isotopic \\fork from Inglcficld Land, but the ages from Ellesmere Island are induded in Table l. Anorhcr open question concerns the age range af intrusive rocks induded in the Etah meta-igncous complex. Based an the isotopic age work in Ellesmere Island referred to above, it mighl bc inferred that the complex in Greenland may contain at least lWO main ages af rocks: those cmplaced at around 1.9 Ga (thc age af tlte Cape Isabella quartz diorite. see abovc). and otlter material. possibly as old as 1.96 Ga. Pending renewed field and isotaric wark in Inglefield Land. the Etah meta-igncous complex is used in a broad sense to includc all mera-igneous rocks that post-dale lhe Elah Group.
Many af the mcta-igneous rocks in south-wcstcrn Inglefield Land show a well-developed pattern af joints. Crush zones are assoeiawd with secondary mineral alteration. predominantly cpidote. mica and ehloritc, while feldspars ean be redde ned and heavily saussuritised. Tilis alteration reprcscnts a low temperature regime associated with the end uf the Hudsonian plutonism or the folIowing cratogenic period.
to be a Proterozoic event associated with prominent fractures that, in some cases at least, are associated with colour changes. In north-eastern Inglefield Land a criss-cross pattern of lineaments post-dating the folds is conspicuous on aerial photographs ( fig. 2). The lineaments have a variable orientation with a concentration in north-west and north-east directions. ane such north-west trending lineament which crosses the Wulff structure forms a prominent gully along which lakes are elongated ( fig. 6). While some of these lineaments may contain basic dyke material, many do not and are vertical to steeply-dipping fractures.
The origin of the lineaments is unknown; those crossing the Wulff structure do not seem to be associated with strike-slip displacement. Whatever their origin -faults, shears, joints, crush zones -the main lineament pattern is not visible in the overlying platform cover. the structures are thus of Proterozoic age. The lineaments presumably date from the cratogenic epoch folIowing initial uplift but pre-date the deposition of the Helikian platform cover -the Rensselaer Bay Formation, pre-1200 Ma old . It should be noted that some lineaments (with trends corresponding to fractures in the basement) also affect the overlying cover, suggesting Palaeozoic (or later) reactivation of some of the Proterozoic fractures.
In gross character, however, the platform rocks throughout Inglefield Land are essentiaIly undisturbed as witnessed by the homoclinal coastal cliffs in which individual beds can be traced over large distances. Where examined, the sporadic lineaments affecting the platform strata indicate normal fauIt displacements of up to a few tens of metres. The main directions of fauIts cutting the Proterozoic to Cambrian platform cover are: north-east, north-northwest and east-north-east ( fig. 2). Faults of the last direction in south-western Inglefield Land are parallel to the main linear structure of the basement suggesting they are reactivated structures controlled by the basement geology.
The age of the fauIt movements that affect the platform cover in Inglefield Land is unknown. In southern Washington Land normal fauIts cut platform strata as young as Ordovician (Jepsen & Dueholm, 1978;Jepsen et al., 1983).

Distribution of Proterozoic rocks
North-eastern Inglefield Land represents the northernmost outcrops 1,the Precambrian Shield of western Greenland which is continuously exposed for over 2 00 km along the coast. To the immediate north and east the crystalline basement is cov red by Humboldt Gletscher and the Inland lee; farther north the shield is blanketed by the:sedimentary cover of Proterozoic and Lower Palaeozoic strata. North of Inglefield Land the shield is only visible beneath the sedimentary cover in a relatively small area (c. 1000 km 2 ), viz. at the Inland Ice margin around the head of Victoria Fjord ( fig. 1).
The geology of north-eastern Inglefield Land contrasts with that of Victoria Fjord where the basement is essentiaIly granitic to granodioritic gneissic terrain composed of homogeneous, veined and banded biotite orthogneisses with amphibolite bands. The gneisses are all migmatitic to varying degrees. Within the gneisses occasional supracrustal rocks occur as concordant thin bands. All the rocks, except a smalliate kinematic body of quartz diorite, have metamorphic textures and have recrystallised under amphibolite facies conditions (Henriksen & Jepsen, 1985).
The sample collection from north-eastern Inglefield Land described in this report contrasts markedly in lithology and mineralogy with the collections available from the Victoria Fjord arch (Dawes, 1978;Henriksen & Jepsen, 1985). Of particular note is the absence, in the latter, of orthopyroxene rocks comparable to the Etah meta-igneous complex and the lack of anyevidence for a granulite facies metamorphic event, while no migmatitic gneisses like those characteristic of Victoria Fjord are represented in the Inglefield Land collection.
This difference seen in the hand sample collections is suggested to be of meaningful significance (rather than a question of inadequate representation) by the recent isotopic dating work on rocks from the Victoria Fjord exposures. U-Pb zircon and Rb-Sr whole-rock isotopic data show that the orthogneisses and later quartz diorite body represent Archaean material (c. 3000 Ma, Hansen et al., 1987). Thus, assuming that the rocks analysed by Hansen et al. adequately represent the outcrops, it can be concluded that the igneous rocks from which the gneisses of Victoria Fjord have been derived are not correlatives of the Etah meta-igneous complex.
The absolute age of the Etah Group is unknown; it is either Archaean or early Proterozoic. The marble-rich supracrustal sequence forms a distinct belt over 400 km long from Inglefield Land to southern Ellesmere Island (Frisch & Dawes, 1982). In Ellesmere Island the supracrustals are cut by meta-igneous rocks that are as old as 1.96 Ga, but the relationship to isotopicaIly dated Archaean gneiss is unknown (Frisch, 1983). In Table l the Etah Group is provisionally given an early Proterozoic age assignment.
Whether any of the supracrustal rocks at Victoria Fjord represent Proterozoic material must also remain an open question. The metasedimentary units present there -like the Etah Group of Inglefield Land -contain marble, mica schists and siliceous rocks, but the age relationship to the orthogneisses is unknown (Henriksen & Jepsen, 1985).

The Rinkian mobile belt
On the tectonic/geological map of Greenland (Escher, 1970) the whole of the Precambrian Shield of western Greenland including the region between Melville Bugt and Inglefield Land is designated part of the Nagssugtoqidian orogenic complex which yields K-Ar ages between 1790 and 1650 Ma. The Rinkian mobile belt was introduced as a tectonic provinee by Escher & Pulvertatt (1976) to separate Precambrian terrain in northern West Greenland (c. 69°-74°N) having a distinctive structural style dominated by large-scale dorne structures and recumbent isoclines, from the Nagssugtoqidian mobile belt to the south which is characterised by a prominent regional planar fabric with an ENE trend and steep dips . These contrasting structural styles are produets of varying Proterozoic deformation.
Escher & Pulvertatt (1976) did not define a northern boundary to the Rinkian, since at that time it was unclear how far north into Melville Bugt the characteristic structural style persisted.
In recent reviews of the structural framework of the Precambrian Shield of Greenland, the northernmost part of the west coast including Melville Bugt and as far north as southwestern Inglefield Land has been included in the Rinkian mobile belt (e.g. Kalsbeek, 1986). Isotopic dating has demonstrated the presence of the mid-Proterozoic (Hudsonian) metamorphism and deformation in North-West Greenland (Larsen & Dawes, 1974;Kalsbeek & Dawes, 1980;Dawes et al., 1988).
The Rinkian mobile belt as described by Escher & Pulvertaft (1976) is composed of an Archaean basement overlain by thick and widespread supracrustal rocks of probable early Proterozoic age (the Karrat Group) that have been folded together and are now intimately associated. This geological couplet is intruded by Proterozoic intrusive rocks, notably the large Proven charnockitic granite (72°-73°N) which has a Rb-Sr age of 1860 ± 25 Ma (Kalsbeek, 1981). The Etah meta-igneous complex represents the northernmost area in western Greenland of such Proterozoic magmatism.
The variable state of the Etah meta-igneous complex demonstrates that in Inglefield Land Proterozoic (Hudsonian) tectono-metamorphic activity was intense. Isotopic data from Victoria Fjord (Hansen et al., 1987) demonstrate that high-grade metamorphism at about 1850 Ma (presumably associated with much of the structural history described by Henriksen & Jepsen, 1985) also affected the crust much farther to the north. Thus, folIowing recent usage (e.g. Kalsbeek, 1986) the Rinkian mobile belt might also be considered to extend into north-eastern Inglefield Land and even into northernmost Greenland.
However, Pulvertaft (1986) has adopted a much more restricted approach in his appraisal of the Rinkian. Hence, because of uncertainties as to the age of both rocks and structures a(ound 69°-70 0 N, the Rinkian is not extended as far south as in the initial description given by Escher & Pulvertaft (1976). This approach is reiterated by Grocott & Pulvertaft (in press) who only extend the Rinkian north to just south of 75°N, the northern limit of areas of supracrustal rocks that are the supposed correlatives of the Proterozoic Karrat Group . farther south. In describing the Rinkian as a mobile belt less than 500 km wide (between 71°a nd 75°N) these authors stress the connection to the Foxe fold belt of eastern Canada. Thus, rather than fostering the idea of a northern continuation in Greenland, the Rinkian is assessed to be the eastern part of a Foxe-Rinkian belt ( fig. 12). In the most recent system of o , Fig. 12. Map of lands around Baffin Bay showing the location of the Ellesmere Island -Inglefield Land belt and Foxe-Rinkian belt, two major belts of Proterozoic stratigraphy, structure and magmatism that span the seaway. All exposures of Precambrian Shield within the area covered by the map, i.e. Greenland, Baffin Island, eastern Devon Island and south-eastern Ellesmere Island, have been affected by the Proterozoic Hudsonian orogeny. Location of Foxe-Rinkian belt is taken from Pulvertaft (1986); the islands west of Baffin Island and areas in Greenland, within this belt, which are shown blank on the map, are composed of younger cover rocks.
Precambrian tectonic units in North America -Archaean province, Proterozoic orogen, Proterozoic fold belt (Hoffman, in press) -the Foxe-Rinkian is a fold belt within an Archaean (Rae) province.
Melville Bugt (75°-76°N) separates the Rinkian terrain, sensu stricto, from the Precambrian complex of North-West Greenland (Dawes, 1976). The few isotopic age determinations available from Melville Bugt indicate the presence of Archaean crust that has been reactivated in Proterozoic time (Kalsbeek & Dawes, 1980;Dawes et al., 1988). However, although there are clear similarities in Precambrian history between the Melville Bugt region and terrain to the south (Dawes & Frisch, 1981), the unifying features of the Rinkian -a characteristic structural style and the presence of early Proterozoic supracrustal rockscannot be substantiated. Indeed, folIowing the initial field study, Dawes & Frisch (1981) argued, on compositional and regional correlation grounds, that the majority of the supracrustal rocks examined along Melville Bugt probably pre-date the Proterozoic supracrustals in the northem part of the Rinkian. Thus, on present evidence the extension of the Rinkian farther north than 75°N is problematic.
Accurate knowledge of the structural frarnework of the Precambrian of Melville Bugt (and also farther north in North-West Greenland) must await further fjeld work and a systematic isotopic dating study. Thus, the relationship between the Proterozoic terrains north and south of Melville Bugt must, for the time being, remain speculative. One model is the presence of two dlstinct Proterozoic fold belts within what is essentiaIly an Archaean provinee (see below and fig. 12).
In any case it is pertinent to stress here that the Proterozoic structures in Inglefield Land and environs do not conform to a particular structural style -the criteria used in West Greenland to differentiate between Proterozoic mobile belts. Thus the large-scale recumbent isoclines present in northem Prudhoe Land and the structural pattern of north-eastern Inglefield Land, characterised by large folds such as the Wulff structure and the lack of a dominant regional strike direction, resemble most the prominent style of the Rinkian. In contrast the intervening area of south-western Inglefield Land, with the regular E-W strike and pronounced steep dips, resembles the linear structural pattern of the Nagssugtoqidian mobile belt. Field evidence, including shear deformation of refolded structures, suggests that the Nagssugtoqidian tectonic style post-dates the Rinkian style in Inglefield Land.
has documented the comparable timing of the main metamorphic events (Dawes et al., 1988;Frisch & Hunt, 1988).
The name Etah meta-igneous complex, with a type area in south-western Inglefield Land, has been extended to cover the corresponding magmatic suite in Ellesmere Island (Frisch & Dawes, 1982). This serves to accentuate the geological unity between the two lands; in both regions gradations from massive igneous rocks to isoclinally folded granulite-facies gneisses attest to the common Proterozoic deformation and metamorphism that affected the two areas. From stratigraphic, structural and metamorphic aspects the presence of a Proterozoic belt stretching for hundreds of kilometres from Inglefield Land through south-eastern Ellesmere Island (Frisch, 1981) is areality.
The Inglefield Land -Ellesmere Island geologicallink is considerably more obvious than the correlation of Inglefield Land to the Rinkian mobile belt. Proterozoic (Hudsonian) plutonism affected a large part of the North American craton ( fig. 12); correlation of belts of stratigraphy and structure like the Ellesmere Island -Inglefield Land and the Foxe-Rinkian belts provides a detailed indication of the primary geological units of the craton.