The Deep Structure of the Karelian Craton along Geotraverse 1-EB

摘要

The results of CMP surveying along geotraverse 1-EB (FGUNPP Spetsgeofizika, 1999) crossing the southeastern Fennoscandian Shield are presented. Based on the geological interpretation of seismic data (sections characterizing the distribution of seismic reflections and effective acoustic impendance) and the available geological maps, a model of the deep structure of the Early Precambrian crust and upper mantle down to a depth of 80 km has been elaborated for the Karelian Craton, Belomorian Tectonic Province, and S vecofennian Accretionary Orogen. The Early Precambrian crust of the Karelian Craton with enclosed Paleoproterozoic vol-canosedimentary belts, the Belomorian Province, and Svecofennian Accretionary Orogen is characterized by an inclined delamination as a combination of thrust-nappe and over- and underthrust structural assemblages formed in the Neoarchean and Paleoproterozoic. The Moho discontinuity is interpreted to be a thick zone of tectonic flow and the displacement of large crustal sheets accompanied by plunging (subduction) of particular crustal fragments into the mantle. The lower crust of the Karelian Craton and the underlying uppermost mantle are of mafic composition (garnet granulite and eclogite), probably with the participation of spinel peridotite below a certain depth level. The lower crust of the Svecofennian Orogen is completely or partially made up of the oceanic crust subducted into the mantle by the late Paleoproterozoic. The proposed models of the structure and evolution of the Early Precambrian crust substantially modify the previously developed concept of the crust beneath the southeastern Fennoscandian Shield regarding it as a combination of blocks with nearly vertical lateral boundaries and individualized internal layering.