Heterogeneous basement reworking during Paleoproterozoic collisional orogeny within the Belomorian province, Fennoscandian Shield

Resumo

The distribution of cross-cutting and pseudoconcordant contacts of Paleoproterozoic metagabbro and their Archean host rocks were studied in the central part of the Belomorian province of the Fennoscandian Shield. It was shown that the metagabbro intrusions affected by ductile shearing during nappe stacking exhibit pseudoconcordant contact relationships. As a result of these deformations, Paleoproterozoic intrusions were sheared into boudins and tectonic slices, conformable with the nappe boundaries, while all traces of pre-Paleoproterozoic structures in the host rock complexes were obliterated. It was also shown that the original cross-cutting intrusive contacts can be still observed in intrusions unaffected by Paleoproterozoic nappe stacking. Therefore, analysis of preserved pre-Paleoproterozoic host rock structure may be helpful for reconstructing its Archean tectonic evolution. Based on the spatial distribution of localities with different contact relationships between Paleoproterozoic metagabbro and their host structure in the central part of the Belomorian province, several large domains of different tectonic styles were recognized. It was shown that these differences can be explained by heterogeneous reworking of the Archean basement during the Lapland–Kola collisional orogeny.