The northern Polar regions are underlain by some of the least known crust on Earth. Their geological evolution can be reconstructed from studies of land areas along the northern margins of North America, Greenland, Europe and Asia, and from fragments of evidence provided by the high Arctic islands, scattered along the shelves of the Amerasian and Eurasian basins. Geophysical surveys (particularly potential field and seismic), combined with bathymetry, outline the regional structure; they allow extrapolation from the land to the shallow-water shelves and out into the deep ocean basins. Nevertheless, knowledge of the geology and resources of the high Arctic remains rudimentary, and the subject of much on-going exploration.

In recent years, SWEDARCTIC lithosphere research (mainly of bedrock geology) has ranged from Svalbard to Severnaya Zemlya. We are studying the tectonics of this part of the Eurasian margin, both to gain a better understanding of the processes of formation of the Eurasian lithosphere in general, and also to establish a platform for new investigations of the Lomonosov Ridge. Current evidence indicates that the latter rifted off the Eurasian high Arctic margin 50-60 million years ago. Thus, the Mesozoic and earlier history of the northern parts of the Barents and Kara shelves should provide essential information on the composition of the Lomonosov Ridge, on how and when it formed, and on its potential mineral resources, including hydrocarbons.

To find out more about the Barents Shelf, our investigations have recently moved to Franz Josef Land to analyse basement rocks in drill cares taken from a depth of a few kilometres below the Mesozoic cover. For the future, permission is being sought from Russian authorities to study northernmost Novaya Zemlya and to return to Severnaya Zemlya and Taymyr.

SWEDARCTIC 2000 Concentrated on the southern coast of the Barents Sea, on rock  outcrops in the northernmost parts of the Timan Range and on the Kanin Peninsula, these being the formations that can be traced, with the help of magnetic and gravity anomaly data, far out beneath the shallow seas of the Barents Shelf. Indeed, the on-land geology, both shallow and deep, of the Timan-Pechora-Polar Urals region, in combination with off-shore geophysical data, provides the essential platform for interpreting the Barents Sea lithosphere.

Field-work

The expedition focused on areas around Cheshkaya Bay, where the deepest structural levels of the Timan Range are exposed. Nowhere else between the Ural mountain front in the east and the Caledonian mountain front in the west are similar lithologies preserved at the surface in the 2500 km-long Timanide Orogen; they provide unique insight in to the Timanian deep structure, metamorphism and tectonic evolution.

The expedition was composed of six geologists from Russian institutes, five from Swedish, one from a Norwegian institute, and an author/journalist from Sweden. Helicopters transported the expedition, split in to two groups, from Arkhangelsk to northernmost Timan on 8 July. On 19 July, both field groups were transferred across Cheshkaya Bay to the Kanin Peninsula, and on 28 July the entire expedition was airlifted back to Arkhangelsk. A zodiac facilitated transport along the coast of northern Timan and southern Kanin Peninsula. The weather was generally excellent, being exceptionally warm and dry. Expedition members were chosen for their expertise in structural geology, stratigraphy, sedimentology, metamorphic and igneous petrology, and isotope-age dating. Gee took responsibility for one of the field camps and Roberts for the other.

Geology of northern Timan and Kanin Peninsula

Previous work on the regional geology of the Timan Range (Getsen 1987), the local structure of the northern Timan-Kanin area (Getsen 1975) and the associated igneous rocks (lvensen 1964; Andreichev 1998) provided the foundation for our new investigations. With the general distributions of the various rock units already established, it was possible to concentrate on their origin, age and correlation. Our Russian colleagues provided a comprehensive summary of existing knowledge (Olovyanishnikov 2000), which comprised a basis for the new work.

The geology of the northern Timan-Kanin Peninsula area is dominated by a major anticline. This structure folds Palaeozoic successions: Silurian limestones and Devonian fluvial sandstones (with basalts) that were deposited unconformably on a late Precambrian (Neoproterozoic) basement. The latter is mainly composed of turbidites and phyllites that vary in metamorphic grade from low greenschist facies in upper structural levels to high amphibolite facies, with local partial melting, in the deepest parts of the anticline. The low grade metamorphosed strata locally contain exceptionally well preserved sedimentary structures, characteristic of deposition from turbidity currents; even the high grade units preserve graded bedding and some other features of turbidites, despite isoclinal folding and thorough recrystallisation. The sedimentary rocks are thought to be of Neoproterozoic age. They are cut by dolerites and by a remarkable 600 million-year-old alkaline complex of gabbros, syenites (some with nepheline) and granites. The entire complex of metamorphosed sediments and igneous rocks are part of an allochthon that was thrust south-westwards in late Precambrian (Vendian) time before the deposition of the Palaeozoic rocks. This thrusting was part of the Timanide mountain building process that influenced the eastern edge of the East European Craton from the southern Urals, via the Timan Range, to northernmost Norway.

Laboratory studies

Based on the summer’s fieldwork and the collection of a wide range of samples for laboratory analysis, we are carrying out complementary studies of the Precambrian rocks, including:

1.  Structure and regional tectonics
2. Stratigraphy and sedimentology of the metasedimentary successions
3. Provenance of the sedimentary rocks, based on studies of the detrital minerals and their ages
4. Petrology and age of the igneous complexes, both the mafic dykes and the alkaline complex, using U/Ph (and Pb/Pb) methods on zircons and Ar/Ar methods on micas and hornblendes
5. Metamorphic alteration of the turbidites, particularly the high grade parageneses, with studies of P and T and age.

In addition, we are investigating the geochronology of the mid Devonian basalts to assess their potential provenance from a mantle plume(s) during the widespread rifting of the East European Craton in the mid Palaeozoic.

These studies of northern Timan and the Kanin Peninsula are complementary to our on-going research on the Precambrian basement beneath the Pechora Basin, where we are analysing drill cores taken from depths of several kilometres below the young basin strata. This metamorphic complex, below the Palaeozoic (Ordovician) unconformity, is also Neoproterozoic in age and part of the Timanide Orogen. Our recent work (Gee et al. 2000, Pease et al. submitted) has shown that metasedimentary and metavolcanic rocks are intruded by 550 million-year-old granites, derived by melting of the lower crust. The geochemistry of these granites and their zircon-inheritance provide information about the age and character of the lower crust that is essential for understanding the Timanide evolution.

Concluding remarks

Understanding orogeny (mountain building processes) is a highly interdisciplinary exercise. Evidence from surface geology must be integrated with deep geophysical data and geochemistry. With most of the Timan Orogen covered by younger (Phanerozoic) sedimentary rocks, our understanding of the Precambrian basement structure of this region is largely based on geophysical data – deep seismic profiling and magnetic and gravity anomalies. The interpretation of these data, reaching from the edge of the East European Craton north-eastwards across the Timan Range and the Pechora Basin to the Polar Urals, depends not only on the expertise of the geophysicists, but also on the geochemical data (including isotope age and provenance studies) obtained from igneous rocks, sourced in the deep crust and mantle. All disciplines have to work very closely together.