Evidence for preservation of crustal root beneath the Proterozoic Lapland‐Kola orogen (northern Fennoscandian shield) derived from P and S wave velocity models of POLAR and HUKKA wide‐angle reflection and refraction profiles and FIRE4 reflection transect

Abstract

[1] We present an analysis of the crust and upper mantle in the northern Fennoscandian shield, based on new P and S wave 2-D velocity models of the POLAR and HUKKA wide-angle reflection and refraction profiles and results of a new seismic reflection experiment in Finland (Finnish Reflection Experiment). The profiles are almost collocated and crossed the Proterozoic Lapland-Kola orogen. A substantial difference of the depth of ''the wide-angle Moho'' (40-42 km) and ''the reflection Moho'' (47-50 km) was found. In order to explain this difference, we compared the velocity models to published values of Vp and Vp/Vs for the main types of lower crustal and mantle rocks. We found that the main reason for disagreement is that the wide-angle Moho and the reflection Moho correspond to different petrological boundaries. In the southwest and northeast portions of the profiles, the wide-angle Moho marks contact of either anorthositic or granulitic lower crust with a reflective layer in the upper mantle composed of peridotites and pyroxenites. The reflection Moho represents the bottom of this lower layer. In the center of the profile the wide-angle Moho marks the top of a large eclogitic body in the upper mantle, representing a well-preserved crustal root beneath the Lapland-Kola orogen formed because of the collision of three former Archaean crustal blocks (terranes or microcontinents). Lack of postorogenic tectonic collapse suggests another mechanism for stabilization of the lithosphere in the area. Upper mantle reflectors at depth of 65-75 km may mark the upper boundary of the cold and mechanically strong Archaean upper mantle wedge. Alternatively, these reflectors may represent a top of uplifted asthenosphere that can explain preservation of crustal root.Citation: Janik, T., E. Kozlovskaya, P. Heikkinen, J. Yliniemi, and H. Silvennoinen (2009), Evidence for preservation of crustal root beneath the Proterozoic Lapland-Kola orogen (northern Fennoscandian shield) derived from P and S wave velocity models of POLAR and HUKKA wide-angle reflection and refraction profiles and FIRE4 reflection transect,

Crustal seismic structure and depth distribution of earthquakes in the Archean Kuusamo region, Fennoscandian Shield

“…The upper crustal reflectors are presumably related to Archean greenstones and Paleoproterozoic mafic magmatism (Kukkonen et al, 2006). The reflection Moho is generally rather diffuse, but where observed, it approximately coincides with the corresponding refraction Moho (Kukkonen et al, 2006;Janik et al, 2009). …”

“…The Archean bedrock has been surveyed along FINLAP (Luosto et al, 1983) and POLAR (Luosto et al, 1989;Walther and Flüh, 1993;Janik et al, 2009) refraction seismic profiles in northern Finland as well as along Kem-Uchta (Berzin et al, 2002), Kem-Tulos, and Pechenga-Kostomuksha ) refraction profiles in north-western Russia (Fig. 1b).…”

3d Model of the Deep Structure of the Svecofennian Accretionary Orogen: A Geodynamic Interpretation

“…В то же самое время аналогичные исследования были прове-дены в юго-восточной части Фенноскандинав-ского щита по системе профилей проекта FIRE в Финляндии . Полученные результаты положены в основу моделей глубинного стро-ения и геологической эволюции докембрия Финляндии [Kontinen, Paavola, 2006;Korja et al, 2006a, b;Janik et al, 2009].…”

Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

“…Table 3 presents the starting model and constraints on model parameters we used in inversion. Parameters of the uppermost layer of the model (V p , V s and density) were obtained from results of H/V analysis presented in our study and parameters for the other layers were constrained using the P-and S-wave velocity models from previous study by Janik et al (2009). These models were obtained for seismic controlled-source profiles closest to our study area.…”