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

In the Middle Silurian, the Iapetus is rapidly closing, and deformation starts along the Caledonian margin of Baltica. The sketch profile from southern Norway shows where the origin of the main tectonic units is shown. Foreland molasse sedimentation starts in the late Wenlock showing that the topography was growing in the hinterland

INFORMATION FROM SEDIMENTATION AND DEFORMATION IN THE FORELAND NOTICE: FIRST INDICATION OF INCREASED SEDIMENT INFLUX IN THE WENLOCK DEFORMATION STARTS IN THE LATEST SILURIAN VOLCANIC ASH (BENTONITES) FROM LARGE CALC-ALKALINE ERUPTIONS ALONG THE TERMINAL ISLAND-ARCS IN THE CLOSING IAPETUS OCEAN

IN THE EARLY DEVONIAN THE NAPPE STACK IS ESTABLISHED EXTENSION COMMENCES AT HIGH STRUCTURAL LEVELS ACROSS THE BELT THE LOWER CRUST UNDERGOES HIGH-PRESSURE LOW-TEMPERATURE METAMORPHISM

Scandian phase of the Caledonian Orogeny: Closure of ocean; Continental collision and Establishment nappe-stack Top Uppermost Allochthon Exotic rocks (Laurentian?) Upper Allochthon Outboard, oceanic terranes Early-Caledonian def/met complexes Middle Allochthon Basement cored nappes of Baltic origin Early-Caledonian def./met. complexes Lower Allochthon Late-Proterozoic-Silurian cover Base Autochthon-Parauthocthon Baltic cover and basement

Approx pin-line Typical foreland deformation, major decollement on Mid. Camb - Lr Ord black “alun” shales. Most of the foreland strongly eroded, but preserved downfaulted in the Permian Oslo-rift From: Morley 1986 Example of balanced section, Asker, Oslo area

WE HAVE THE BEST EXAMPLES IN THE WORLD OF HIGH- AND ULTRA-HIGH PRESSURE METAMORPHIC ROCKS, STILL WE HAVE MANY PROBLEMS UNDERSTANDING THESE ROCKS!

The high and ultra-high-pressure rocks in Norway HP-UHP rocks in W-Norway: Large area, well exposed, great variety prograde and retrograde relationships T C; P GPa Eclogite w/polycrystalline qtz after coesite, loc. Barmen, Nordfjord 2 cm

Coesite in garnet Coesitt-eclogite Nordfjord Micro-diamond dissolved from garnet-kyanite gneiss at Fjørtoft (Dobrzhinetskaya et al. 1995) Micro-diamond (c) in inclusion within spinel, in turn included in garnet (Van Roermundt et al. 2002) ULTRA-HIGH-PRESSURE IN THE WGC, high-silica garnet (majorite) + 10  m

Southern WGR (HP) Nordfjord Region HP to UHP [Labrousse et al. (in review), 1) staur - gar in KFAMASH (from Hacker et al. 2003, 2) hydrous solidus bio-granite, 3) Hydrous solidus musc-granite, Data from a) Chauvet et al 1992, b) Hacker et al. 2003, c) Engevik et al Outer eclogites, d) Krogh 1980 Inner eclogites e) Cuthbert et al 2000, Moldefjord data from Terry et al. 2000]

Age of coesite eclogite ? (gar, omp, phe, kya, coesite) Unpubl. ages from David Root (2003) PhD, UCSB

AT CA 410 TO 405 Ma ULTRA-HIGH PRESSURE METAMORPHISM AFFECTS THE LOWER CRUST. RAPID EXHUMATION (5-10 mm/yr) OF THE HP-UHP CRUST STARTS BY A COMBINATION OF THRUST - STACKING, VERTICAL SHORTENING AND EXTENSION AT HIGH CRUSTAL LEVELS. DEVONIAN BASINS FORM AT THE SURFACE.

BAFFIN ISL ELLESMERE ISL. RINGNES ISLS. PRC WALES ISL. BOOTHIA UPLIFT INGLEFIELD UPLIFT Latest Silurian to early Devonian deformation far from the suture! AX HEIBERG ISL. Major contractional events, Arctic Canada: Caledonian ≈ Ma Ellesmerian ≈ Ma EureKan ≈ Ma

ANALOGY WITH THE SCANDINAVIAN-GREENLAND CALEDONIDES: pre-collision subduction polarity away from fast-moving plate size collision velocity ≈ 10 cm/yr near orthogonal collision duration (10-s of million years) major continental plates Outline of the N-Atlantic Caledonides in a tight late Silurian/early Devonian fit superimposed on the Himalaya-Tibetan Plateau Region topography

Late - to post-orogenic tectonic processes and exhumation mechanisms (ROCKS APPROACHING THE SURFACE) 1)EROSION (MINOR ON A REGIONAL SCALE) 2)THRUST STACKING + EXTENSION AND/OR EROSION (IMPORTANT FOR BRINGING HP AND UHP ROCKS NEXT TO EACH OTHER? 3)VERTICAL CO-AXIAL SHORTENING/HORISONTAL STRETCHING (IMPORTANT FOR MID AND LOWER CRUST AFTER EXHUMATION TO AMPHIBOLITE FACIES) 4)HINTERLAND EXTENSION FORLAND SHORTENING (IMPORTANT AT AN EARLY STAGE OF COLLISION) 5)TRANS-TENSION (IMPORTANT) 6)WHOLE-SALE EXTENSION BY PLATE-DIVERGENCE (IMPORTANT)