Browsing by Subject "Precambrian"

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  • Veikkolainen, Toni H.; Biggin, Andrew John; Pesonen, Lauri J.; Evans, David A.; Jarboe, Nicholas A. (2017)
    State-of-the-art measurements of the direction and intensity of Earth’s ancient magnetic field have made important contributions to our understanding of the geology and palaeogeography of Precambrian Earth. The PALEOMAGIA and PINT(QPI) databases provide thorough public collections of important palaeomagnetic data of this kind. They comprise more than 4,100 observations in total and have been essential in supporting our international collaborative efforts to understand Earth's magnetic history on a timescale far longer than that of the present Phanerozoic Eon. Here, we provide an overview of the technical structure and applications of both databases, paying particular attention to recent improvements and discoveries.
  • Tiira, Timo; Janik, Tomasz; Skrzynic, Tymon; Komminaho, Kari; Heinonen, Aku; Veikkolainen, Toni; Väkevä, Sakari; Korja, Annakaisa (2020)
    The Kokkola–Kymi Deep Seismic Sounding profile crosses the Fennoscandian Shield in northwest-southeast (NW–SE) direction from Bothnian belt to Wiborg rapakivi batholith through Central Finland granitoid complex (CFGC). The 490-km refraction seismic line is perpendicular to the orogenic strike in Central Finland and entirely based on data from quarry blasts and road construction sites in years 2012 and 2013. The campaign resulted in 63 usable seismic record sections. The average perpendicular distance between these and the profile was 14 km. Tomographic velocity models were computed with JIVE3D program. The velocity fields of the tomographic models were used as starting points in the ray tracing modelling. Based on collected seismic sections a layer-cake model was prepared with the ray tracing package SEIS83. Along the profile, upper crust has an average thickness of 22 km average, and P-wave velocities (Vp) of 5.9–6.2 km/s near the surface, increasing downward to 6.25–6.40 km/s. The thickness of middle crust is 14 km below CFGC, 20 km in SE and 25 km in NW, but Vp ranges from 6.6 to 6.9 km/s in all parts. Lower crust has Vp values of 7.35–7.4 km/s and lithospheric mantle 8.2–8.25 km/s. Moho depth is 54 km in NW part, 63 km in the middle and 43 km in SW, yet a 55-km long section in the middle does not reveal an obvious Moho reflection. S-wave velocities vary from 3.4 km/s near the surface to 4.85 km/s in upper mantle, consistently with P-wave velocity variations. Results confirm the previously assumed high-velocity lower crust and depression of Moho in central Finland.
  • Veikkolainen, Toni Henri Kristian; Kukkonen, Ilmo Tapio (2019)
    Radiogenic heat production in Finland has been previously studied using airborne gamma-ray surveys and glacial till measurements alike. For the first time, this paper presents a detailed survey on the spatial variation in radiogenic heat production determined using outcrop samples obtained from all important lithologies of the country. The dataset of 6465 samples represents mostly Mesoarchean (about 2.7 Ga), Paleoproterozoic (ca. 2.2-1.8 Ga) and Mesoproterozoic (ca. 1.6-1.3 Ga) rocks. Nearly all data are from Precambrian Fennoscandian Shield area, but heat production appears to be highly variable, and above global Archean and Proterozoic averages. Spot readings show an arithmetic average of 1.34 +/- 1.19 mu Wm(-3), and a range from 0.02 to 19.4 mu Wm(-3). The interpolated areal average of the whole area is 1.42 +/- 1.41 mu Wm(-3). The high standard deviation of data is related to the geochemical characteristics of uranium (U), thorium (Th) and potassium (K) resulting in a skewed distribution of heat production. Mesoproterozoic anorogenic rapakivi granites, and late Paleoproterozoic Svecofennian granitoids show the highest heat production values in the range of 3-5 mu Wm(-3). The results show no distinct dependencies of heat production with geological age, metamorphic grade nor seismic P-wave velocity, but an increasing trend of heat production with SiO2 content and decreasing trends of heat production with Fe2O3 content and with rock density are evident. Surface heat flow (44 borehole data values) correlates weakly with heat production (r = 0.35). The general heterogeneity of heat production calls for supporting information from other geophysical methods for better understanding of the thermal state of the lithosphere in Finland and beyond.
  • Pesonen, Lauri J.; Korja, Annakaisa; Hjelt, Sven-Erik (Institute of Seismology, University of Helsinki, 2000)
  • Lahtinen, Raimo; Korja, Annakaisa; Arhe, Katriina; Eklund, Olav; Hjelt, Sven-Erik; Pesonen, Lauri J. (Institute of Seismology, University of Helsinki, 2002)
  • Ehlers, Carl; Eklund, Olav; Korja, Annakaisa; Kruuna, Annika; Lahtinen, Raimo (Institute of Seismology, University of Helsinki, 2004)
  • Kukkonen, Ilmo T.; Eklund, Olav; Korja, Annakaisa; Korja, Toivo; Pesonen, Lauri J.; Poutanen, Markku (Institute of Seismology, University of Helsinki, 2006)
  • Korja, Toivo; Arhe, Katriina; Kaikkonen, Pertti; Korja, Annakaisa; Lahtinen, Raimo; Lunkka, Juha Pekka (Institute of Seismology, University of Helsinki, 2008)
  • Heikkinen, Pekka; Arhe, Katriina; Korja, Toivo; Lahtinen, Raimo; Pesonen, Lauri J.; Rämö, Tapani (Institute of Seismology, University of Helsinki, 2010)
  • Kukkonen, Ilmo; Kosonen, Emilia; Oinonen, Kati; Eklund, Olav; Korja, Annakaisa; Korja, Toivo; Lahtinen, Raimo; Lunkka, Juha Pekka; Poutanen, Markku (Institute of Seismology, University of Helsinki, 2012)
  • Eklund, Olav; Kukkonen, Ilmo; Skyttä, Pietari; Sonck-Koota, Pia; Väisänen, Markku; Whipp, David (Institute of Seismology, University of Helsinki, 2014)
  • Kukkonen, Ilmo; Heinonen, Suvi; Oinonen, Kati; Arhe, Katriina; Eklund, Olav; Karell, Fredrik; Kozlovskaya, Elena; Luttinen, Arto; Lahtinen, Raimo; Lunkka, Juha; Nykänen, Vesa; Poutanen, Markku; Tanskanen, Eija; Tiira, Timo (Institute of Seismology, University of Helsinki, 2016)
  • Heinonen, Aku; Aalto, Aleksi; Väkevä, Sakari; Heikkinen, Pekka J.; Korja, Annakaisa (2017)
    The Finnish Reflection Experiment (FIRE) is a reflection seismic experiment that was conducted in collaboration with the Universities of Helsinki and Oulu, Geological Survey of Finland (GTK), and the Russian company Spetsgeofizika in the early 2000’s. The dataset comprises over 2100 kilometers of deep seismic reflection profiles that transect all the major Precambrian geological formations of the Finnish bedrock. Regardless of its extent and high quality, the FIRE dataset has been relatively underused up to date. FIRE-ATT is an open science project conducted as a part of the Ministry of Education and Culture of Finland -funded Open Science and Research Initiative (ATT – Avoin Tiede ja Tutkimus) at the Institute of Seismology, University of Helsinki in collaboration with the AVAA team of the ATT initiative and GTK. The project has produced a revised data archive and a new mobile-responsive intuitive map-based user interface – the OpenFIRE service – for FIRE data sets. The data are available for browsing and download through the AVAA portal maintained by the ATT initiative.
  • Luoto, Toni; Salminen, Johanna; Obst, Karsten (2021)
    Baltica and Laurentia form the core of the hypothesized Mesoproterozoic supercontinent Nuna in most paleogeographical reconstructions. Long gaps still exist in the Mesoproterozoic paleomagnetic record of Baltica, and different relative configurations for Baltica and Laurentia have been presented. This study presents new paleomagnetic data obtained for mafic dykes on Bornholm (Denmark, southwest Baltica). We provide a new 1.326 +/- 0.010 Ga Bornholm Group I paleomagnetic key pole (Plat: 06 degrees N, Plon: 165 degrees E, K: 21, A95: 6 degrees) for Baltica. This pole supports the low-latitude equatorial core of Nuna at 1.33 Ga, where Kola Peninsula and Northern Norway of Baltica were facing northeastern Greenland of Laurentia. Based on statistically different magnetization directions with Group I and differences in Nb-Zr-Y systematics, we propose a separate Bornholm Group II paleomagnetic pole. This undated, poor-quality pole indicates a paleolatitude of ca. 50 degrees, possibly reflecting an age difference compared to Group I, accompanied with the continental drift. On Bornholm, the wide Listed and Kas dykes of uncertain age yield significantly different paleomagnetic results compared to the other studied dykes there. In addition, the virtual geomagnetic poles (VGPs) of these dykes are 45 degrees apart from each other. On the basis of similar Nb-Zr-Y systematics with the dykes of the 0.98-0.94 Ga Blekinge Dalarna Dolerite Group (Sweden) and overlapping paleomagnetic data with the high-quality 0.95-0.94 Ga paleomagnetic poles of Baltica, an early Neoproterozoic age for the magnetization is proposed. The relatively big discrepancy between Listed and Kas VGPs could stem from an unaveraged paleosecular variation or from a small but significant age difference during rapid plate movements.