Baltica. A synopsis of vendian-permian palaeomagnetic data and their palaeotectonic implications

Torsvlk, T H , Smethurst , M A., Van der Voo, R , Trench, A , Abrahamsen, N and Halvorsen, E , 1992 Baltlca. A synopsis of V e n d l a n P e r m m n palaeomagnetic data and their palaeotectonlc implications Earth-Sci. Rev , 33 133-152. In light of recent additions to the Palaeozoic palaeo-magnetlc data-base, particularly for the Ordovlclan era, a revised apparent polar wander (APW) path for Baltica has been constructed following a rigorous synthesis of all Late Precambr lan-Permlan data The AP W path is characterized by two prominent loops Firstly, a Late Precambr lan-Cambr lan loop probably relating to a rifting event and secondly, a younger loop relating to a Mid-Silurian (Scandlan) colhsion event These features Imply major change In plate-tectonic reconfiguratlon Baltlca probably represented an individual continental unit m Early Palaeozoic times and was positioned m high southerly latitudes in an "'inverted" geographic orientation In such a reconstruction Baltlca was separated from the northern margin of Gondwana by the Tornqulst Sea and from Laurentla by the Iapetus Ocean The Tornqulst Zone is thus interpreted as a passive or dextral transform margin during the early Palaeozoic While undergoing counter-clockwise rotations (up to 1 6°/Ma), Baltica drifted northward through most ol the Palaeozoic, except for a short period of southerly movement in Late Silurian-Early Devonian times after colhslon with Laurentla. Rapid movements in latitude (up to 9 cm/y r ) are noted m Late Precambr lan/ear ly Palaeozoic times and slgmficant decrease in velocities throughout Palaeozoic time probably reflect the progressive amalgamation of a larger continent by Early-Devonian (Euramerlca) and Permian (Pangea) times The Tornqulst Sea had a principal component of palaeo-east-west orientation. Hence it is difficult to be precise in the timing of when micro-continents such as Eastern Avalonla and the European Masslfs ultimately collided along the southwestern margin of Baltica These micro-continents are considered to have been peripheral to Gondwana (m high southerly latitudes) during the Early Ordovlclan. Eastern Avalonla clearly had rifted off Gondwana by Llanvlrn-Llandedo times and may have collided with Baltlca during Late Ordovlclan times, although the present available Sdunan palaeomagnetlc data from Eastern Avalonia may suggest colhslon in Late Silurian t imes Across the lapetus facing margin of Baltica, Laurentla was s~tuated in equatorml to southerly latitudes during most of the Lower Palaeozoic These continents collided in Mid-Silurian times, l e a first collision between southwestern Norway and Green land /Sco t land which gave rise to the early Scandlan Orogeny (425 Ma) in southwestern Norway possible followed by a later, but less dramatic, Scandlan event in northern Norway at around 410 Ma Since Baltlca was geographically reverted m early Palaeozoic times, the colhsional margin could not have been a margin that once rifted off Laurentm as assumed in a number of plate-tectonic models I N T R O D U C T I O N The Palaeozoic palaeocontinent of Baltica is bounded to the west by the Iapetus suture, C o r r e s p o n d e n c e to: T H. Torsv ik , G e o l o g i c a l Su rvey o f Norway , P B 3006 L a d e . N-7002 T r o n d h e l m , Norway . to the north by the Trollfjord-Komagelv Fault Zone (Fig. 1), to the east by the Ural mountains, to the south by the VariscanHercynian suture, and to the southwest by the Tornquist Zone (Pegrum, 1984). As such, Baltica includes parts or all of Norway, Sweden, Finland, Denmark, Poland, Russia, Es0 0 1 2 8 2 5 2 / 9 2 / $ 1 5 00 © 1992 E l sev ie r Sc ience P u b h s h e r s B.V. Al l r igh t s r e s e r v e d 134 T H TORSVIK ET AL Trond H Torsvlk (34) was awarded a Dr. Phdos from the Umversaty of Bergen m 1985 From 1982 to 1988 he was a research fellow at the Umversltles of Bergen and Oxford and later held a visiting sc~entlst stipend at the University of Oxford (1989 and 1090) Dr Torsvlk is now a senior scwntlst at the Norwegmn Geological Survey Current works emphasize the global perspectwes in palaeomagnetlc palaeogeographical reconstructions In 1991 he was awarded the Outstanding Young Scientist Award from the European Umon of Geosclences Allan Trench: Born September 27, 1963 Present position Reserach Fellow m Geophysics, Umv. of Western Austraha Previous position and Degrees' BSc (HONS) Geology, London Umverslty in 1985 Ph D m Geophysics, Glasgow Umverslty m 1988 Research Fellow m Geophysics, Oxford Unwerslty m 1989-91 Geophysicist at the Norwegmn Geological Survey m 1991 Enk Halvorsen, born July 8, •942. Master of Science m Geophysics (Umverslty of Bergen, Norway) 1966 Semor lecturer, Sogn og Fjordane College, Norway. Dr Mark Andrew Smethurst (31) BSc Honours degree m Geology Umverslty of Lwerpool 1979-1982 PhD University of Leeds 1983-1986 Post-Doctoral Research Fellow' University of Oxford 1986-1989 Semor Geophysicist Norwegian Geological Survey 1989 to present. Rob Van der Voo, born August 4, 1940. B Sc, M Sc. and Ph D. degrees m 1961, 1965 and 1969 all from the University of Utrecht, the Netherlands. Chairman and Professor of Geological Sciences at the Umverslty of Michigan, U S A Nlels Abrahamsen, born Aprd 25, 1939 Mag sclent (Aarhus Umvers~ty, Denmark) m Geology 1965 Ph D m Geophysics (Aarhus University, Denmark) 1971. Semor lecturer, Dept of Earth Sciences, Aarhus University, Denmark. BALFICA SYNOPSIS OF VENDIAN PERMIAN PALAEOMAGNETIC DATA 135 tonia, Latvia, Lithuania and Ukraine. During Palaeozoic time, a number of orogenic events occurred along the margins of Baltica, ultimately leading to the incorporation of Baltica into the supercontinent Pangea. In this paper, we quantify the Palaeozoic drift history of Baltica using a rigorous synthesis of presently available palaeomagnetic data. In so doing, we attempt to further constrain the geotectonic history of the continent's margins. A newly-determined apparent polar wander (APW) path for Baltica will be described in detail. The generation of that APW path followed thorough re-evaluation of all published poles for Baltica made during the European Geotraverse Palaeomagnetic workshop in Lulefi, Sweden (Pesonen and Van der Voo, 1991).