The Neoproterozoic Timanide Orogen of eastern Baltica: introduction

D. G. GEE 1 & V. PEASE 2

1Uppsala University, Department of Geosciences, Villaviigen 16, 752 36, UppsaIa, Sweden 2Department of Geology and Geochemistry, Stockholm University, SE-106 91, Sweden

This volume was conceived during EUROPROBE' s investigations into the dynamic evolution of the Palaeozoic Uralide Orogen and relationships northwards into the Eurasian high Arctic. During these European Science Foundation studies, the preservation of Neoproterozoic deformation over large regions of northern Europe became increasingly apparent. This mainly Vendian tec- tonic event is referred to as the Timanian Orogeny and became the focus of many recent and on-going investigations. Much pro- gress has been made in understanding Timanian Orogeny and a Memoir synthesizing our current knowledge is not only timely, but also relevant to Neoproterozoic global tectonic reconstructions.

The type area for the Timanide Orogen is located in the Timan Range of northwestern Russia, which separates the East European Craton from the Pechora Basin and Polar Urals. The orogen extends over a distance of at least 3000 km, from the southern Ural Mountains of Kazakhstan to the Varanger Peninsula of north- ernmost Norway, flanking the eastern margin of the older craton (Fig. 1). From the Timan Range, it reaches northeastwards below the thick Phanerozoic successions of the Pechora Basin and Barents Shelf (O'Leary et al. 2004), and reappears in the Polar Ural Mountains and northwards through Pai Khoi to Novaya Zemlya. Timanian orogeny thus influenced a vast region of north- western Russia. The Phanerozoic cover, Arctic shelf areas and, further east, Uralian deformation, obscure the importance of this orogenic event for the geodynamic evolution of Europe.

The Timanide Orogen has been referred to by various other names, most frequently as the 'Baikalides'. The term 'Baikalian Orogeny', with a type area along the southern margin of the Siberian Craton, was introduced by Edelstein (1923) and promoted by Shatsky (1963), and suggested a tectonic event that started in the Late Precambrian and finished in the Early Palaeozoic. Other authors prefer to restrict 'Baikalian' events to those that took place in the Neoproterozoic time interval of 850-650 Ma (e.g. Khomentovsky 2002). The term 'Baikalian' has also been used to designate a late Precambrian stratigraphic system in Siberia, corresponding to the Cryogenian of the IUGS Inter- national Stratigraphic Chart (2000). To avoid ambiguity, we advo- cate the use of the term 'Timanian' Orogeny to describe the late Neoproterozoic tectonic events documented along the eastern margin of the East European Craton, best exemplified in the Timan-Pechora region, and restrict the use of the term Baikalian to tectonic events associated with Siberia.

For much of the last century, the dominating hypothesis for the evolution of northwestern Europe has explained Timanian tectono-thermal activity in terms of rift basin (aulacogen) inver- sion. Thick Neoproterozoic and partly Mesoproterozoic sedimen- tary successions were described and interpreted to separate blocks of older Precambrian crust that previously had been a part of the Archaean and Palaeoproterozoic core of Europe. Thus, Stille (1958) inferred that the Timanides were a result of deformation between the Fennoscandian Craton and an outboard continent, which he called Barentsia. Subsequent geophysical studies, particularly potential field, but also seismic, suggested a more

complex crustal evolution. Deep drilling (up to c. 5 km) of the Pechora Basin provided convincing evidence (Belyakova & Stepanenko 1991) that a broad belt of calc-alkaline igneous rocks flanked terrigenous slope-to-basin deposits of the Timan Range. Late Neoproterozoic granites carry Grenville-age zircon xenocrysts and complexes of this age were shown to exist further towards the hinterland within the Palaeozoic allochthons of the Subarctic Urals. Late Neoproterozoic ophiolites, albeit frag- mented, were described from the Polar Urals (Dushin 1997). Thus, despite powerful resistance (e.g. Ivanov & Rusin 2000), an alternative hypothesis has emerged that favours the existence of a Timanian accretionary orogen, on the eroded roots of which were deposited the early to mid-Palaeozoic rifted and passive margin successions which flanked the Uralian ocean. Continent-ocean collision played an important role in the orogenic process and some authors (e.g. Sengor et al. 1993) have speculated on the possible continuity between the 'Timanian' and Uralian oceans; however, the question remains unresolved.

The studies of the Timanides included in this Memoir are struc- tured to provide a comprehensive overview of the orogen. The first three contributions treat the pre-Timanian rifted margin of the East European Craton. Roberts et al. describe the Neoproterozoic passive margin sedimentary successions of the Kanin Peninsula, and northern and central parts of the Timan Range. Maslov provides comprehensive descriptions of the Mesoproterozoic and Neoproterozoic (Riphean-Vendian) stratigraphy preserved within the Uralian foreland and western flank of the Ural Moun- tains, making regional correlations to the Timan-Pechora area. Grazhdankin follows with an overview of the late Neoprotero- zoic differential subsidence patterns of the East European Craton in the Mezin Basin SW of the Timan Range, significantly relating this to development of a Timanian foreland basin in the late Vendian.

The magmatic, metamorphic and structural evolution of the Timanide Orogen is described regionally, divided into the Timan Range, the Pechora Basin, and Ural Mountains. Roberts & Olovyanishnikov present the structural and tectonic develop- ment of the Timanide Orogen in the Timan region. Larionov et al. present U-Pb ages on an alkaline igneous suite in northern Timan which provides constraints on the beginning of Timanian Orogeny. Using Neoproterozoic high-grade metamorphic rocks from the Kanin Peninsula, Lorenz et al. document PIT conditions associated with Timanian orogenesis.

In the Pechora Basin region, drillcore samples of pre-Palaeozoic basement provide the foundations for our understanding of the pre-Palaeozoic events. Belyakova & Stepanenko's paper (1991) documenting the different structural and metamorphic zones within the basement to the Pechora Basin, is particularly important. New geochemical evidence from Dovzhikova et al. (2004) suggests that the Precambrian mafic complexes in the Pechora zone represent Neoproterozoic oceanic crust, probably accreted during Timanian orogenesis. Pease et al. provide geochemical evidence for the calc-alkaline affinity of Vendian granitoid rocks which are inter- preted to indicate late-orogenic westward subduction beneath north- eastern Baltica at about 560 Ma.

From: GEE, D. G. & PEASE, V. (eds) 2004. The Neoproterozoic Timanide Orogen of Eastern Baltica. Geological Society, London, Memoirs, 30, 1-3. 0435-4052/04/$15 © The Geological Society of London 2004.

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2 D.G. GEE& V. PEASE

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Fig. 1. Geological map of the eastern margin of Baltica, showing the extent of the Timanides from the southern Urals to Novaya Zemlya and the Varanger Peninsula (VP).

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THE NEOPROTEROZOIC TIMANIDE OROGEN OF EASTERN BALTICA: INTRODUCTION 3

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Late

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Middle

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Mesoproterozoic

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Stenian 1200

Ectasian 1400

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Plumb {1991) Keller & Chumakov [1983) lUGS [2000]

Fig. 2. Comparison of Mesa- and Neoproterozoic timescales used in this volume.

Within the Ural Mountains, the evidence for Timanian orogeny is fragmentary and the contributions are geographically restricted to the Polar and Northern Urals. Glodny et al. report Timanian protolith ages within the eclogitized Marun-Keu complex and discuss their implications for the pre- and early Uralian evolution of the northeastern European continental margin. Remizov & Pease present geochemical and U - P b age data from the Dzela complex which indicate Neoproterozoic island arc magmatism. Beckholmen & Glodny follow with a description of, and age con- straints for, blueschist metamorphism in the pre-Ordovician base- ment to the Kvarkush anticline, also interpreted within a Timanian tectonic framework.

The sections on Timanian Orogeny are followed by descriptions of post-Timanian platform successions, which are important for interpreting the timing of orogeny and the post-Timanian return to a passive margin setting. These include assessment of the regional Early Palaeozoic unconformity across the Timanides (Bogolepova & Gee), as well as Late Cambrian age constraints from acritarchs of Kolguev Island on post-Timanian deposition (Moczydlowska et al.). Finally, regional correlations are explored in which it is concluded that Timanian Orogeny does not extend to Svalbard (Gee & Tebenkov; Johansson et ai.), but is present on Novaya Zemlaya (Korago et aL). Work in progress also suggests it influences Franz Josef land basement (Pease et al. 2001). Comparison is made between the Neoproterozoic passive margin of western Baltica, in the Scandinavian Caledonides, and contemporaneous orogeny in the Timanides (Siedlecka et al.). Similarities in the Neoproterozoic tectonic evolution of Baltica and Siberia are also explored (Vernikovsky et al.).

Syntheses of Timanian orogenic evolution have been provided by several authors (e.g. Seng6r et al. 1993; Roberts & Siedlecka 2002; Dovzhikova et al. 2004; Gee 2004). The contributions presented in this Memoir will promote further elaboration. In pursuing research on the Timanides, critical aspects related to this orogeny have been identified for future work. The nature of the hinterland beneath the Pechora Basin and as it is exposed in the Ural Mountains needs more investigation. Determining the role and extent of subduction along the orogen and characteriz- ation of the arc-related magmatic rocks remain a critical point. Future collaborative studies with Russian partners which seek to understand Timanian orogenesis better will undoubtedly contrib-

ute significantly to a clearer understanding of its role in the tec- tonic evolution of Baltica.

Several different geological timescales are in routine use within the scientific community at present. Though the use of the IUGS International Stratigraphic Chart (2000) has been encouraged, the older International Stratigraphic Chart of Plumb (1991), as well as the Russian timescale (Keller & Chumakov 1983) in which Riphean and Vendian are used to subdivide parts of the Pre- cambrian, have also been used. For the convenience of the reader, we provide a cross-reference for these three timescales (Fig. 2). Additionally, the International Commission of Stratigraphy has recently revised the Precambrian timescale (Gradstein et al. 2004), but it has not yet received wide usage. Regarding nomen- clature and especially the translation of Russian stratigraphic terms, a few more years are needed to achieve consensus on these matters.

References

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DOVZHIKOVA, E., PEASE, V. & REMIZOV, D. 2004. Neoproterozoic island arc magmatism beneath the Pechora Basin, NW Russia. GFF, 126, 353-362.

DUSHIN, V. A. 1997. Magmatism and Geodynamics of the Palaeoconti- nental Sector of the Northern part of the Urals, Nedra, Moscow, 211 pp [in Russian].

EDELSTEIN, Y. 1923. Tectonics and ore deposits of Siberia. Izv. Geol. Komminee, 42, 23-50 [in Russian].

GEE, D. G. 2004. Timanides of northern Russia. In: Selley, R. C., Cocks, R. & Plimer, I. R. (eds), Encyclopedia of Geology. Elsevier, Amsterdam.

GRADSTEIN, F., OGG, J., SMITH, A., BLEEKER, W. &; LOURENS, L. 2004. A new geologic time scale with special reference to Precambrian and Neogene. Episodes, 27, 83-100.

IUGS International Commission on Stratigraphy, 2000. International stratigraphic chart, REMANE, J., CITA, M. B., DERCOURT, J., BOUYSSE, P., REPETTO, F. L. & Faure-MURET, A. (eds). Division of Earth Sciences, UNESCO.

IVANOV, S. N. & RUSIN, A. I. 2000. Late Vendian tectonic evolution of the Urals. Geotektonika, 3, 21-32 [in Russian].

KELLER, B. M. & CHUMAKOV, N. M. 1983. Stratotype of Riphean Strati- graphy and Geochronology. Nauka, Moscow, 184 pp [in Russian].

KHOMENTOVSKY V. V. 2002. Baikalian of Siberia (850-650Ma). Russian Geology and Geophysics, 43, 313-333.

O'LEARY, N., WHITE, N., TULI, S., BASHILOV, V., KUPRIN, V., NATAPOV, L. & MACDONALD, D. 2004. Evolution of the Timan-Pechora and South Barents Sea basins. Geological Magazine, 141, 141 - 160.

PEASE, V., GEE, D. & LOPATIN, B. 2001. Is Franz Joseph Land affected by Caledonian deformation? European Union of Geosciences Abstracts, 5, 757.

PLUMB, K. A. 1991. New Precambrian time scale. Episodes, 14, 139-140. ROBERTS, D. & SIEDLECKA, A. 2002. Timanian orogenic deformation

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SENGOR, A. M. C., NATAL'IN, B. A. & BURTMAN, V. S. 1993. Evolution of the Altaid tectonic collage and Palaeozoic crustal growth in Eurasia. Nature, 364, 299-307.

SHATSKY, N. S. 1963. On Cambrian-Proterozoic relations and Baikalian orogeny. Izbran. Trudi. M., Izd-vo Acad. Nauk SSSR 1, 581-587 [in Russian].

STILLE, H. 1958. Die assyntische Tektonik im geologischen Erdbild. Beihefte zum Geologischen Jahrbuch, 22, 255 pp.

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