Karelian Craton transect (Finland, Russia): Greenstone belts, ophiolites and eclogites
Leaders: Petri Peltonen and Pentti Hölttä (Geological Survey of Finland), Alexander I. Slabunov (Institute of Geology, Petrozavodsk, Russia)
Other Guides: Asko Kontinen, Tapio Halkoaho, Asko Käpyaho, Oleg Volodichev, Alexandra Stepanova Alexandra, Alexander Samsonov and Andrey Schipanskiy
Understanding when and why plate tectonics began is one of the most important unresolved problems in understanding Earth. The aim of this field trip is to demonstrate the recent discoveries made in Archean Karelian Craton that are relevant to the operation of modern-like accretion tectonic and seafloor spreading processes in the Meso- and Neoarchean and Palaeoproterozoic times. We will examine in detail the Khizovaara structure, recently described as collage of a part of the Archean Iringora SSZ-ophiolite and an arc complex. Visit to Kostomuksha greenstone belt (interpreted as a remnant of Archean oceanic plateau + major economic BIF mine) and Kuhmo-Tipasjärvi (Ni-Cu, Au showings) greenstone belts allow us to discuss the various geodynamic settings (mantle plume, spreading center, subduction) proposed for Archean volcanic successions. In the Gridino area on the White Sea we will examine spectacular Archean eclogites. They belong to a Neoarchean melange interpreted to have formed in subduction zone and exhumed due to an collisional orogeny. A full day will be devoted to the 1.95 Ga old complete Precambrian ophiolite: the Jormua Ophiolite Complex - recently reinterpreted as transitional passive-margin type ophiolite with truly unique Archean subcontinental mantle outcropping covering tens of square kilometers.
The excursion will take place from 28 July to 4 August 2008.