Major tectonic processes illustrated with examples from the

Major tectonic processes illustrated with examples from the Geology of Norway • • • Intro and overview of the Late Proterozoic to Permian tectonic evolution Baltica becomes a tectonic entity The margins of Baltica Early deformation along the Caledonian margin Ophiolites and island arcs Towards continental collision and the Scandian orogeny Late to post-orogenic tectonic processes Late Palaeozoic continental rifting Start of a new Wilson cycle

OUTBOARD ACTIVITY: From the Ægir Sea to the Iapetus and Tornquist Oceans The oldest supra-subduction zone ophiolites and island-arc complexes in the Scandinavian Caledonides (`Group 1´) formed in this time-span in the Early to Middle Ordovician (495 to 465 Ma) while Baltica started to drift northwards with velocities up to ~10 cm/yr

Plate-tectonic velocities of Baltica quantified by pal-mag. data (Torsvik & coworkers) Timanian From: Torsvik & Rehnström 2002

Nordkapp The Scandian produced a Evidence forcollision Early-Caledonian nappe stackand which can be tracedis deformation metamorphism along theinentire belt: Theterranes Lower, common the outboard Middle, Upper and from Nordkapp to Uppermost Stavanger allochtons Example, Uppermost allochthon, Troms 30 E 70 N Tromsø The outboard terranes: Upper and Uppermost Allochthons 65 N (Upm A): continental margin rocks Trondheim including marbles of Laurentian (? ) origin; composite batholiths; ophiolite/island-arc rocks, para/orthogneisses with Proterozoic (? ) protoliths (Up A): mostly ophiolites primitive Bergen Oslo 60 N Stavanger 10 E island-arcs, mature magmatic arcs, associated metasediments (late Cambrian-early Silurian) Local Proterozoic basement

Early-Caledonian events; where and when? 460 Ma Middle Ordovician Corfu et al. in 2006, in press Tromsdalstind eclogite These events clearly occurred outboard of Baltica, and the rocks containing their record was emplaced ‘piggy-back’ during the Scandian collision Middle Ordovician unconformity over the Lyngen ophiolite (Up Alloch) Eclogite facies metamorphism and deformation in the Tromsø region (Upm Alloch) Corfu et al. 2003

`Group 1´ type ophiolites and island-arc complexes: • Situated within the Upper Allochton between Karmøy in the south and Lyngen in the north • Ages spanning 495 to 465 Ma (within uncertainty) with the Leka, Karmøy ophiolites as the oldest and arc-plutons and volcancs as the youngest • Both spreding axis and arc-magmatism have geochemical subduction zone signatures Lyngen Narvik Leka Gjersvik Trondheim area Otta-Foldal Roberts et al. 2002 Subduction polarity away from Baltica, eventually build-up of mature arcs Bergen Bømlo/Stord Karmøy

Arc-related plutons AGE OF GROUP-1 OPHIOLITES/ISLAND -ARCS From: Pedersen 1992 From: Roberts et al. 2002

A slide with Norwegian ophiolite summary

Nordkapp 70 N Tromsø 30 E Evidence for pre - Scandian deformation and metamorphism is common in the outboard terranes from North-Cape to Stavanger Example, North Cape The outboard terranes: Upper and Uppermost Allochthons 65 N (Upm A): continental margin rocks Trondheim including marbles of Laurentian (? ) origin; composite batholiths; ophiolite/island-arc rocks, para/orthogneisses with Proterozoic (? ) protoliths (Up A): mostly ophiolites primitive Bergen Oslo 60 N Stavanger 10 E island-arcs, mature magmatic arcs, associated metasediments (late Cambrian-early Silurian) Local Proterozoic basement

The North Cape story, when? Sedimentation until Early Silurian (Aeronian-438 Ma); syn-tectonic gabbro and granites (438 -433 Ma); Peak Barrovian metamorphism (~436 Ma) RAPID TECTONIC EVOLUTION! Corfu et al. in 2006, in press Syn-tectonic gabbro Sil North cape Kya Staur Gar Syn-metamorphic granite Andersen 1981

Early-Caledonian events; where? The Honningsvåg Igneous Complex has primary magnetization and is well dated (437. 5 -438. 9 Ma)! Flysch sedimentation, deformation, plutonism and metamorphism of early Silurian age near North Cape Kirkland et al. 2005 440 Ma The ‘Finnmarkian’ orogeny as originally proposed by Sturt, Ramsay and co-workers (including me) does not exist. The ‘Finnmarkian’ complexes comprise late-Proterozoic rocks related to the Timanian orogeny and pre-Caledonian rifting (now positioned in the Middle Allochthon) as well as overlying outboard rocks (Magerøy, Hellefjord, Lyngen) that belongs to the Upper Allochthon The HIC palaeomagnetic data from Torsvik et al. 1992, reinterpreted with the new precise U/Pb ages from: Corfu et al. 2006, JGS (in press) THESE DATA SUGGEST THAT THE POSITION OF THE MAGERØY ROCKS IN THE LOWER SILURIAN WAS EQUATORIAL, AND MOST LIKELY CLOSE TO THE LAURENTIAN MARGIN

MATURE ISLAND-ARC VOLCANIC AND COMPOSITE PLUTONIC COMPLEXES BUILD DURING THE MIDDLE TO LATE ORDOVICIAN Bindal-Helgeland Smøla-Hitra Up Hovind Gp. Sunnhordland

First Scandian HP metamorphism ~ 424 ± 5 Ma Outboard activity related to magmatic arcs and back-arc spreading in the Iapetus ocean U/Pb ages of intrusives and some volcanics, compiled by Corfu et al. 2006, in press.

Closure of the Tornquist Ocean “Soft docking” of Avalonia before the Late Ordovician ?

INTRA-ARC INCONFORMITIES BELOW MID-LATE SILURIAN OR DEVONIAN CONGLOMERATES (UCF-3) IN SUNNHORDLAND

1 EARLY-CALEDONIAN (PRE-SCANDIAN) TECTONIC EVENTS ALONG THE CALEDONIAN MARGIN OF BALTICA? 1) W-Finnmark, type area for ‘Finnmarkian’ now discredited. Caledonian deformation and metamorphism Finnmark is Scandian 2) Nordbotn (~500 Ma eclogites, these need 2 3 to be dated again by more precise methods) 3) Seve-Jämtland (~454± 4 Ma eclogites same age as Tromsø! Are these really in rocks of Baltic origin or are they outboard? ) 4) Otta-Foldal-Røros (pre-470 Ma) 5) Atløy, W. Norway (Ar-450 Ma + strat. ) 6) Jæren (eclogites of unknown age in Jotun nappe type rocks, same as Bergen eclogites, ie. early-Scandian or Baltica-Avalonia collision? ) 4 5 7) Stratigraphy in foreland, clastic cromite, most likely from ophiolite in the lower middle Ordovician? 7 6 The telescoped Caledonian margin of Baltica

Stratigraphic (ucf + fossils) and geochronological evidence (Ar) for an early Caledonian event at 450 Ma, Sunnfjord area, W. Norway 443 Ma Silurian fossils older than 450 Ma 1640 Ma 428 Ma 5 km Brekke and Solberg 1987 Andersen et al. 1990, 1998, Eide et al. 2000 Def/met 450 Ma

Early-Caledonian events; the Baltica-Avalonia assembly Tornquist Sea closure by subduction under E-Avalonia in ~455 -440. Geological evidence? Fauna provinciality between Baltica and Avalonia disappears Mid-Ordovician metamorphic ages (Ar) in North-Sea basement Subduction magmatism in England - Wales Kinnekulle K-bentonite a ~455 Ma supervolcano eruption producing ~1000 km 3 ash Deformation/metamorphism in nappes of SW. Norway (Atløy, Jæren)? From Torsvik & Rehnström 2003

IAPETUS IS CLOSING AND CONTINENTAL COLLISION TAKES OVER FROM THE WENLOCK

THE LATE-SILURIAN FULL SCALE COLLISON BETWEEN BALTICA AND LAURENTIA