Tehostekuvassa fysiikan laitosta etuoven suunnalta

1b. Paleomagnetism of Mesoproterozoic Satakunta sandstone and dolerites

Participating scientists

  • J. Salminen, project leader
  • R. Klein, M.Sc., Ph.D. student
  • S. Mertanen (Geological Survey of Finland)
  • L.J. Pesonen, prof. (emeritus)

Project goals

The goal is to carry out a paleomagnetic and rock magnetic study of the Mesoproterozoic Satakunta sandstone and Subjotnian dyke swarm, Finland, with implications for a Northern Europe - North America (NENA) connection within Nuna supercontinent.

Highlights

For Subjotnian dykes at western coast of Finland we separated a dual-polarity, high-stability remanence component, that is confirmed to be primary by several positive baked-contact tests. The combined mean direction for N-S (1565 Ma; Lehtonen et al., 2003) and NE-SW trending dykes, showing both polarities, is D = 11.5°, I = 3.3° (alpha95 = 8.8°), yielding a key paleomagnetic pole (SK1) for Baltica at 29.3 °N, 188.1 °E (A95 = 6.6°). It fulfills the first six of seven Van der Voo's (1990) reliability criteria for paleomagnetic poles.

The new Satakunta SK1 pole, when compared to the nearly coeval Western Channel Diabase pole (1590 ± 4 Ma) from Laurentia, allows the NENA fit at 1.57-1.59 Ga. Based on geological evidence E-W dykes have been proposed to belong a swarm that is ca. 100 million years older than the N-S dykes. E-W trending dykes show a dual polarity direction of D = 356.9°, I = 8.3° (alpha95 = 15.9°), yielding a paleomagnetic pole (SK2) for Baltica at 32.6 °N, 205.5 °E (A95 = 14.3°). Based on coeval paleomagnetic data and correlations of geochronology and basement geology of Baltica and Laurentia, the NENA fit is validated at 1.77 -1.75 Ga, 1.59-1.57 Ga, 1.46 Ga, and 1.27 Ga, and by comparing single virtual geomagnetic poles at 1.63 Ga. However, the mean 1.63 Ga data from Laurentia (Melville Bugt dykes, Greenland; Halls et al., 2011) and Baltica (Sipoo dykes, Finland) are offset by about 30°. The previous Satakunta sandstone remanence direction (Neuvonen, 1973) is probably contaminated by the Jotnian diabase heatings (Klein et al. 2013).

Validation of NENA for both older and younger times suggests to us that a variety of factors, such as less than highest-quality or not coeval paleomagnetic data, possible unrecognized tilting of the continental blocks, or a non-symmetric geomagnetic field, other than cratonic reconstruction, can explain the minor 1.63 Ga mean pole discordance.

Fig.1: Testing the NENA fit.
Fig.1: Testing the NENA fit. a) High quality poles of Laurentia and Baltica rotated to NENA configuration. Used poles are listed in Table 6, b) Virtual geomagnetic poles for Melville Bugt dykes, Greenland (normal polarity is used; Halls et al., 2011) and for Sipoo dykes, Finland (Mertanen and Pesonen, 1995). Additionally SK2 pole of this study is plotted. Baltica and its poles are rotated to reference frame of Laurentia by Euler pole: Plat = 47°, Plong =1.5°, angle = 49° (Evans and Pisarevsky, 2008). Poles from Greenland are rotated to reference frame of Laurentia by Euler pole: Plat = 67.5°, Plong =241.5°, angle = -13.8° (Roest and Srivastava, 1989).
Fig.2: Reconstruction of Baltica and Laurentia in the NENA fit.
Fig.2. Reconstruction of Baltica and Laurentia between 1.63 Ga and 1.27 Ga forming the core of NENA. Archean cratonic areas: Baltica (Ko - Kola; K - Karelia; V-U - Volgo-Uralia; Sar - Sarmatia); Laurentia: (S - Slave, Sup - Superior, H - Hearne; R - Rae; Wy - Wyoming; Nain in Greenland). Proterozoic: Baltica (SVF - Svecofennian domain; LK - Lapland-Kola; G - Gothian; B-B - Baltic-Belarus; SVN - Sveconorwegian); and Laurentia (Pn - Panokean; Mz - Mazatzal; Ya - Yavapai; TH - Trans-Hudson; Tl - Taltson; Wo - Wopmay; NQ - New Quebeck; T - Tornget, FR - Foxe-Rinklan; Lb - Labradorian; Nag - in Greenland).
Fig.3: Paleomagnetic directions of Satakunta sandstone.
Fig.3: A) Mean paleomagnetic directions for sandstone normal polarity (SSN), sandstone reversed polarity (SSR), sandstone baked component (SSB) and postjotnian diabase (DB) component. Neuv. represents the paleomagnetic direction for sandstone by Neuvonen (1973). B) Paleomagnetic poles with 95% confidence circle (darker grey) plotted with key and other significant paleomagnetic poles (lighter grey) implies a deposition age of 1.42-1.65 Ga. Poles SS, SSB and DB are the primary sandstone pole, the baked sandstone pole and postjotnian diabase pole, respectively. C) Reconstruction of Baltica and Laurentia at 1.6 Ga based on mean poles for Baltica and Laurentia. Euler pole for Baltica is Lat: 0°, Lon:263°, angle -62°, and for Laurentia Lat:11.3°, Lon: 305.8°, angle: -73.7°. Poles for Baltica (B) and Laurentia (L) shown with age (Ma)..
R. Klein and J. Salminen S. Mertanen, F. Karell and S. Raiskila
Fig.4: Sampling done by R. Klein and J. Salminen. Fig.5: Sampling done by S. Mertanen, F. Karell and S. Raiskila.

Recent publications

  • Klein, R., Pesonen, L.J., Salminen, J., Mertanen, S., 2013. Paleomagnetism of Mesoproterozoic Satakunta sandstone, Western Finland. Precambrian Research, in press.
  • Salminen, J., Mertanen, S., Evans, D.A.D., Wang, Z., 2013. Paleomagnetic and geochemical studies of the Mesoproterozoic Satakunta dyke swarms, Finland, with implications for a Northern Europe - North America (NENA) connection within Nuna supercontinent. Precambrian Research, in press.
  • Klein, R., Pesonen, L.J., Mertanen, S., Kujala, H. 2010. Paleomagnetic study on Satakunta sandstone, Finland. In: Abstracts of 6th Symposium on the structure, composition and evolution of the Lithosphere, Finland, October 27-28, 2010, p. 33-35. 3 p.
  • Klein R., Pesonen L.J., Kujala H., Paleomagnetic study on the Proterozoic Satakunta sandstone and associated diabase sheets in Fennoscandia. In: Abstracts of the 12th "Castle Meeting" New Trends in Geomagnetism, Palaeo, Rock and Environmental Magnetism. Castle of Nové Hrady, Czech Republic, August 29 - September 10, 2010. Travaux Géophysiques XXXIX, p. 39.