Svecofennian Ore-Forming Environments: Volcanic-Associated Zn-Cu-Au-Ag, Intrusion-Associated Cu-Au, Sediment-Hosted Pb-Zn, and Magnetite-Apatite Deposits in Northern Sweden of Northern Sweden
The Fennoscandian or Baltic Shield (both names occur in the literature) occupies the northern part of Europe. Pre-cambrian areas are exposed in Norway, Sweden, Finland, and Russia and their continuation beneath the platform cover sequences to the east and south have been better understood through studies within the European “Euro-probe” project. The craton of which the exposed Fenno-scandian Shield forms a part is bordered to the west by the Caledonian orogenic belt. Precambrian rocks of the same craton outcrop again in the Ukrainian Shield and the Voronezh Massif (cf. Gee and Zeyen, 1996).
The Fennoscandian Shield is composed of Archean to Neoproterozoic rocks (Fig. 1). It is beyond the scope of this guidebook to describe all the different settings in detail, but adjoining areas that both predate and postdate the Svecofennian rocks that are the main interest of this field trip will be briefly described. The term Svecokarelian is used for the orogeny that occurred between 1900 and 1800 Ma (i.e., emphasizing deformation and metamorphism as defining the orogeny), while the term Svecofennian is used for the supracrustal rocks that were emplaced during c. 1.95 Ga to 1.85 Ga. To the reader unfamiliar with literature on the Fennoscandian Shield it is important to remember that these terms are not used consistently in the literature.
The pre-Svecokarelian crustal growth can be subdivided into Archean and Paleoproterozoic. During the Archean, greenstone belts and tonalite-trondhjemite-granodiorite (TTG) terranes formed, while crustal growth during the Paleoproterozoic involved rifting of the Archean basement with the formation of rift-fill sequences of sedimentary and igneous rocks, and addition of juvenile Paleoproterozoic crust by accretionary processes along the margin of the Archean continent.
The oldest known rocks in the Shield are c. 3.1 Ga in age and were generated during the Saamian Orogeny (3.1—2.9 Ga). Rocks of the age 3.2 to 2.7 Ga are present in the Archean nuclei of the shield and are composed of tonalitic gneisses and migmatites. The oldest documented magmatic and metamorphic event took place at c. 2.84 Ga (Nurmi and Sorjonen-Ward, 1996). Rift-related greenstones, subductiongenerated calc-alkaline volcanic rocks and tonalitictrondhjemitic igneous rocks were formed during the Lopian Orogeny (2.9—2.6 Ga). These greenstone belts form a prominent part of the Finnish and Russian bedrock, but are minor in Sweden. The Hattu schist belt in the southwestern part of the Archean of Finland seems to record a collisional arc setting
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