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SummaryIn addition to the well-established extension, compression and transcurrent relative movements between plates of the lithosphere, this paper considers intermediate or oblique relative movements, namely, transtension and transpression. Transtension is already well established in oblique zones of ocean spreading which consist of stepped transform faults. Transpression is a more complex process. The tectonic consequences of a transpression model are outlined and it is suggested that the tectonic style in Caledonian Spitsbergen provides evidence for this transpression regime as an intermediate stage between compression and transcurrence. It is also suggested that transpression should occur generally and may relate the development of transcurrent faults in orogenic belts.

SummaryConsideration of the arctic configuration of the Caledonides leads to a distinction between eastern and western geosynclinal belts. The western belt, comprising the East Greenland, East Svalbard and southern Barents Sea Caledonides is postulated to continue northwards into the Lomonosov Ridge, whilst the western Spitsbergen Caledonides are thought to have originated as part of the North Greenland geosyncline which is also thought to continue northwards to form the western part of the Lomonosov Ridge. The eastern Caledonian geosynclinal belt comprising the Scandinavian Caledonides appears to swing eastwards to link with the Timan Chain and possibly the Urals.The already postulated (‘Proto-Atlantic’) ocean concept is reviewed in the light of the Arctic Caledonides and named Iapetus. Faunal provincialism suggests that the ocean was in existence up to early Ordovician but had substantially closed by mid Ordovician times. Possible relics of the suture marking the closure of this ocean suggest that it lay to the west of the Arctic Scandinavian Caledonides trending NE to latitude 70° N and thence veered eastwards separating the southern Barents Sea Caledonides from those of Arctic Scandinavia, possibly connecting with the northern Uralian ocean. A previous branch of the ocean may have separated East Svalbard and East Greenland as an ocean-like trough. A further (pre-Arctic) ocean may have existed to the north of the North Greenland–Lomonosov Ridge geosynclines. This is named Pelagus.The closure of these oceanic areas and the deformation of the bordering geosynclines delineates three principal continental plates, namely, Baltic, Greenland and Barents Plates. Their relative dominantly E–W motion up to Silurian times produced compression between the Greenland and both the Baltic and Barents plates but dextral transpression and transcurrence between the latter plates. In Late Silurian to Devonian times an increasing northward component controlled late Caledonian transpression and sinistral transcurrence between the Greenland plate and the combined Baltic and Barents plates.

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The Caledonides of Ny Friesland comprise the type Hecla Hoek sequence of Svalbard, a succession of late Proterozoic to Ordovician strata greater than 18 km thick. Three supergroups constitute the sequence: the Stubendorffbreen Supergroup (Riphean), the Lomfjorden Supergroup (late Riphean-Sturtian) and the Hinlopenstretet Supergroup (Varanger-mid-Ordovician). Basement elements have recently been identified within the Stubendorffbreen Supergroup, but their extent and significance is yet to be established. The Stubendorffbreen Supergroup records the deposition of sediments and volcanics (both acid and basic) in an unstable marine environment. In contrast, the Lomfjorden and Hinlopenstretet supergroups record sedimentation in a shallow-marine, periodically emergent, stable environment without volcanism. The Ny Friesland Orogen is divided into two subterranes by the Veteranen Line, a zone of attenuation along which sinistral strike-slip displacement has occurred. This line separates the strongly deformed Stubendorffbreen Supergroup rocks in the west from the less-intensely deformed Lomfjorden and Hinlopenstretet supergroup rocks in the east. Despite these contrasts and the obvious displacement, there is no evidence that a significant stratigraphie break occurs across it.All the supergroups were deformed and metamorphosed during the late Ordovician-Silurian Ny Friesland Orogeny. Early compressional deformation produced isoclinal folding and nappes in the Stubendorffbreen Supergroup rocks, accompanied by amphibolite faciès metamorphism; deformation in the Lomfjorden and Hinlopenstretet supergroups was less intense with open, upright folds and greenschist or subgreenschist facies metamorphism. Early compression was followed by a Silurian transpressive deformation that generated a pervasive lineation in the Stubendorffbreen Supergroup rocks. Transpressive deformation and the associated sinistral strike-slip was focused where strata were in a near-vertical attitude conducive to displacement. At a late stage in the orogeny, and probably still under a strike-slip regime, batholiths were emplaced into rocks east of the Veteranen Line.As a result of continued sinistral displacement (transpression, transcurrence and transtension) along the Billefjorden Fault Zone, Ny Friesland (part of the Eastern Province of Svalbard) finally docked against the Central Province during the late Devonian Svalbardian movements. At the same time, the Central Province docked against the Western Province. In total, hundreds of kilometres of Caledonian displacement along the Billefjorden Fault Zone brought the Eastern and Central provinces into their present positions. Pre-Carboniferous Svalbard is thus a composite terrane of at least three provinces, each comprising more than one minor terrane.

SummaryHopen (Hope Island) in the Svalbard archipelago is difficult of access and only recently has reliable geological information become available. Published information is reviewed and combined with new observations.The island, 37 km long and no more than 2.5 km wide or 370 m high is structurally simple with flat-lying arenaceous strata which are described with three measured sections. Three new local stratal units are defined: Iversenfjellet Formation (325 m, base not seen); Flatsalen Shale Formation (55 m); and Lyngefjellet Sandstone Formation (80 m, top not seen).From a few ammonite, bivalve, saurian and plant megafossil occurrences and 30 palynomorph taxa (newly recorded) the marine and fluviatile facies range in age from possibly late Karnian, through Norian, Rhaetian and possibly into early Jurassic. The Rhaetian flora, well established palynologically, is the first clear evidence of rocks of this age in Svalbard. Associated Sirenites extends the range of this ammonite and suggests that Svalbard may yield significant new evidence for this span of Earth history.