Chapter 32 - Paleoarchean Rocks in the Fennoscandian Shield

Abstract

Paleoarchean (3.5–3.2Ga) rocks have been found only in six locations in the Fennoscandian Shield. Three of these are in the western part of the Karelia Province: one is in the Norrbotten Province and two in the Vodlozero subprovince. In addition, two localities are known where the zircon ages of tonalite–trondhjemite–granodiorite gneisses are c.3.1Ga. Apart from Vodlozero, the Paleoarchean areas are small, possibly only a few tens of km2, surrounded by Neoarchean granitoid gneisses. A few Paleoarchean zircon grains have been found in Proterozoic metasedimentary rocks that overlie the Archean basement, suggesting that more Paleoarchean rocks are still to be found. The ancient remnants are interpreted to represent fragments of older crust that accreted with a Neoarchean continent at around 2.7Ga.