RODINIA'S BALTICA: INTERNAL STRUCTURE AND MARGINS

ProtoBaltica (i.e.- the East European Craton) was formed between 2.0 and 1.7 Ga by the gradual amalgamation of its three crustal segments, each having an Archean core and individual Paleoproterozoic tectonic histories. The oldest Paleoproterozoic belts (2.2-2.0 Ga) dominate southeastern ProtoBaltica, while the orogenic belts in the NW have mostly developed between 1.9 and 1.8 Ga. The central 1.8-1.7 Ga collisional belt marks the terminal amalgamation of these crustal segments, defining this craton as a single entity.

After amalgamation, ProtoBaltica's western and eastern margins, and its interior, experienced distinct tectonic events recorded by magmatism, sedimentation, and deformation. These events indicate an active continental margin at ca. 1.7-1.5 Ga in the west and the south, coeval with intracratonic sedimentation, and rifting in the east. A set of transpressional-transtensional deformation zones and associated AMCG magmatism made up the western half of the craton, whereas a system of rifts following the Paleoproterozoic intersegment suture zones appears to have formed in the east and southeast.

A mantle-plume event at ca. 1.27-1.25 Ga obviously affected northern Baltica, where a large province of dolerite and mafic dykes with associated sedimentary grabens exists.

Rodinia amalgamation at ca. 1.0 Ga manifests in ProtoBaltica as the Sveconorwegian collisional orogeny in the west, a new set of intracontinental rifts/aulacogens along the Paleoproterozoic collisional belts, and the development of passive margins along northern, northeastern, eastern, and southeastern ProtoBaltica.

The break-up of Rodinia is recorded by 850 Ma bimodal magmatism in the northwest. The oldest evidence for the complete separation of Baltica is ca. 610 Ma oceanic crust (e.g. Sarek terrane) in western Baltica, but separation likely occurred before this. A passive margin persisted here, whereas the southwestern, southeastern and northeastern margins of Baltica, document collision between the craton and oceanic lithosphere until about 550 Ma. Therefore it can be inferred that almost all ProtoBaltica was ocean-facing at some time in its Neoproterozoic history. The southern Neoproterozoic margin of Baltica remains enigmatic, illustrating the need for future work here.

This is a contribution from the Nordic Work Group.