Sciences de la Terre

Président : Prof. Pascal Kindler, Université de Genève

Reconstructing the Permian Upper Crust-to-Mantle cross-section in the Ivrea-Verbano and Laghi zones (N Italy)

• Organisateur(s) : Prof. U. Schaltegger (Université de Genève)
• Enseignant(s) : Prof. U. Schaltegger (Université de Genève), Prof. M. Dungan (Université de Genève), Prof. O. Müntener (Université de Lausanne), Prof. L. Burlini (ETHZ), Prof. P. Ulmer (ETHZ), Prof. S. Sinigoi (Università di Trieste), Dr. J. Quick (USGS, Reston, USA)
• Public visé : diplômés, doctorants, post-doc.
• 6 jours, 48 heures - Valle d’Ossola, Verbana - mai-juin 2008

The easily accessible southern Alpine crustal domain between Lago Maggiore and the area west of the Valle d’Ossola (Val Strona, Val Sesia, Val Sessera) offers the possibility to study a nearly complete crustal profile from the paleo-surface to the crust-mantle transition. This may be the best preserved and best exposed section through the continental crust anywhere in the world, and as such it has been extensively studied during the last 50 years (i.e., a large body of articles and geologic maps has recently been published). One of the most interesting aspects of the Permian magmatism of this region is that units ranging from the ignimbrites of Valle Sessera and the apparently co-magmatic upper crustal Baveno granite are the same age as mafic intrusions and associated granulite-facies restitic metamorphic rocks of the deep crust. This crustal section has been slightly modified by Jurassic crustal thinning and by a minor component of Alpine crustal shortening, but a reconstruction of the crust suggests that the Permian phase of activity was associated with a transtensional tectonic regime and possibly lithosphere-scale strike-slip faulting, leading to decompression-melting in the lower crust. The ascent of these magmas into the upper crust was accompanied by the formation of transtensional pull-apart basins and extensive volcanism.
Our goal is to organize a highly participatory field workshop involving Ph.D. students, postdocs, and senior researchers that will be devoted to an open examination of the data and interpretations which have led to this hypothesis.
The rocks to see
Crystalline rocks of pre-late Permian age are exposed along an up to 30 km wide band south of the Insubric Line. These units include pre-Late Carboniferous basement, Early Permian intrusions, and Upper Carboniferous-Permian sedimentary and volcanic cover. The basement and cover rocks are deformed but show minimal evidence of an Alpine thermal overprint.
The pre-Permian basement of the Southern Alps is affected by Variscan metamorphism that increases in grade from greenschist-facies in the east to amphibolite-facies in the west (e.g. Serie dei Laghi). Variscan accretion is thought to have started in the Early Carboniferous, and a metamorphic thermal maximum was reached at 340 to 320 Ma. Late-orogenic cooling is recorded by Rb-Sr white mica and biotite cooling ages. Extrapolation of the cooling rates suggests that by 305 Ma, some of the currently exposed areas may have reached near-surface temperatures. Unmetamorphosed sediments resting unconformably on the metamorphic basement of the western and eastern Southern Alps indicate that penetrative deformation and metamorphism in the basement ceased during the interval of Middle Westphalian to Late Moscovian time.
The deep crust is exposed along the western border of the Southern Alps in the Ivrea-Verbano Zone. This zone consists of slices of ultramafic rocks (Premosello, Finero, Balmuccia) in contact with high-grade meta-sedimentary lithologies (the so-called kinzigites and stronalites), which are well exposed in the Sesia and Strona valleys. Amphibolite to granulite facies metamorphism is thought to have outlasted the main period of Variscan deformation and metamorphism by more than 10 to 20 m.y., but before the emplacement of the bulk of mafic magmas of the Mafic Complex. There is a long-standing debate about the age of granulite-facies metamorphism, the

Paléontologie, Sédimentologie, Stratigraphie

• Organisateur(s) : Prof. A. Strasser (Université de Fribourg), Dr É. Samankassou (Université de Fribourg), D. Marty (Porrentruy)
• Enseignant(s) : Prof. J.-P. Berger (Université de Fribourg), Prof. C. Meyer (Université de Bâle), Prof. F. Fürsich (Würzburg, Allemagne), Prof. S. Kidwell (Chicago), Dr. W. Hug (Porrentruy), Dr D. Becker (Porrentruy)
• Public visé : diplômés, doctorants, post-doc.
• 4 jours, 32 heures - Fribourg et Porrentruy - mai 2008

Most sedimentary systems are strongly influenced by biological activity, be it that the sediment is produced by organisms, and/or that organisms modify the sedimentary deposits. It is therefore of utmost importance that the palaeoecology and the taphonomic processes be well understood in order to correctly interpret the stratigraphic record.
Case studies from different depositional environments (carbonate ramps, coral reefs, restricted lagoons, tidal flats, lakes) will be presented and discussed during two days at the University of Fribourg. On a two-day fieldtrip to the Swiss Jura Mountains, coral patch reefs, dinosaur trackways, and oyster beds in Oxfordian and Kimmeridgian platform carbonates will be analyzed. Controlling factors such as sea-level fluctuations, climate changes, and trophic levels will be discussed in a narrow time-frame given by high-resolution sequence stratigraphy and cyclostratigraphy.

Norwegian fjords, glaciers and lakes as records of Late Pleistocene and Holocene Glacial History

• Organisateur(s) : Dr D. Ariztegui (Université de Genève)
• Enseignant(s) : Dr D. Ariztegui (Université de Genève), Prof. A. Nesje (University of Bergen, Norvège)
• Public visé : doctorants, post-doc.
• 7 jours, 100 heures - Bergen, Nordfjord and Jostedalsbreen Norway - 27.07.2008-03.08.2008

Understanding the climate of the Late Pleistocene and Holocene may help us better understand modern-day natural climate variability and make climate predictions. The conventional view of the climate development during the last millennium has been that it followed the simple sequence of a ’Mediaeval Warm Period’, a cool ’Little Ice Age’ followed by warming in the later part of the nineteenth century and during the twentieth century. This view was mainly based on evidence from western Europe (e.g., Switzerland) and the North Atlantic region. Recent research in Norway has, however, challenged this rather simple sequence of climate development in the recent past. These new data indicate that the rapid glacier advance in the early eighteenth century in southern Norway was mainly due to increased winter precipitation: mild, wet winters due to prevailing ’positive North Atlantic Oscillation (NAO) weather mode’ in the first half of the eighteenth century; and not only lower summer temperatures. A comparison of recent mass-balance records and ’Little Ice Age’ glacier fluctuations in southern Norway and the European Alps suggests that the asynchronous ’Little Ice Age’ maxima in the two regions may be attributed to multidecadal trends in the north-south dipole NAO pattern.
The proposed field trip includes the visit to the main evidence of these recent changes in glacier activity in the Nordfjord and Jostedalsbreen region. Additional records of older glacial activity in the Lonfjord area during key intervals of climate change such as the Younger Dryas will also be visited.
The fieldtrip will be guided by A. Nesje from the University of Bergen, Norway, who is a specialist on local glacial geology; and D. Ariztegui from the University of Geneva who presently leads a Norwegian-Swiss research initiative in the area that involves a geophysical and sedimentological study of fjords and lakes.

Swiss Geoscience Meeting

• Organisateur(s) : Prof. P. Kindler (Université de Genève)

Site internet: http://geoscience-meeting.scnatweb.ch/