Baltica From the Svecofennian Until the Ediacaran: a Paleomagnetic Study of Precambrian Formations of Finland
Year: 2016
Type: dissertation
Abstract: This dissertation presents paleomagnetic results from Baltica for three significant time intervals during the evolution of Precambrian supercontinents: i) 1.87 Ga the onset of the supercontinent Nuna; ii) 1.58 1.57 Ga maximum compaction of Nuna; and iii) ca. 0.6 0.57 Ga the break-up between Baltica and Laurentia which marked the final break-up of the supercontinent Rodinia. Paleogeographic reconstructions at 1.25 Ga and 1.05 Ga which marks the transition from Nuna to Rodinia - is briefly discussed based on existing paleomagnetic results; no new data were produced for these two reconstructions. New paleomagnetic results were obtained from samples from the 1.87 Ga Keuruu diabase dyke swarm (Central Finland), 1.58-1.57 Ga Åland intrusives (Åland archipelago, SW Finland) and ca. 0.6-0.57 Ga Hailuoto sedimentary formation (Western Finland). In addition to these, new paleomagnetic results were obtained from the Satakunta sandstone formation (SW Finland), providing a new paleomagnetic age estimate of ca. 1.63 1.45 Ga for the sandstone deposition, older than previously thought (ca. 1.4-1.3 Ga). The 1.87 Ga Keuruu diabase dykes yield a dual polarity intermediate NNW downward or SSE upward characteristic remanent magnetization (ChRM), positioning Baltica at low latitudes in a way that would proceed into the 1.8-1.2 Ga NENA (North Europe North America) configuration. The age of the Keuruu dykes are defined by a U-Pb (zircon) age of 1870 ± 9 Ma and a Pb-Pb (zircon) age of 1869 ± 7 Ma. The primary nature of the Keuruu ChRM is supported by positive baked contact tests. The Åland intrusives and Satakunta sandstone both yield dual polarity shallow (upward and downward) NNE or SSW characteristic remanent magnetizations (ChRM), positioning Baltica on equatorial paleolatitudes and supporting the NENA configuration between Baltica and Laurentia during the Mesoproterozoic. Well determined U-Pb (zircon) ages narrows the occurrence of intrusion to 1570 1580 Ma. The primary nature of the Åland intrusives ChRM is supported by positive baked contact tests. The Hailuoto sedimentary samples were obtained from a 272 m deep fully oriented drill core. The depostional age of the Hailuoto sediments is poorly constrained at 570-600 Ma, based on fossil records. The Hailuoto pole adds to the scattered Ediacaran paleomagnetic data of Baltica and indicates large distances between other late Neoproterozoic and early Cambrian paleomagnetic poles, implying rapid movement of Baltica from high latitudes at 615 Ma, over the polar region, to low latitudes at 550 Ma. In all these cases a secondary component with shallow to intermediate downward inclinations and northeasterly declinations were observed. This secondary component is commonly observed in the Fennoscandian Shield and has previously been interpreted as a result of oxidizing fluids during the Phanerozoic. In the case of Keuruu and Åland, meteorite impact (from Keurusselkä and Lumparn, respectively) cannot be ruled out as a possible cause of the secondary component. This component is mostly observed at low coercivities/blocking temperatures, but sometimes also at higher coercivities/blocking temperatures, causing asymmetry in the dual polarity results of Keuruu diabase dykes and Åland intrusives. In summary, the work presented in this dissertation provides new paleomagnetic results for Baltica, adding two new key poles to the Paleoproterozoic-Mesoproterozoic apparent polar wander path (APWP) of Baltica. Furthermore, the results provide a better understanding of the movement of Baltica during the enigmatic Ediacaran period. Paleogeographic reconstructions are presented at 1.87 Ga, 1.57 Ga, 1.25 Ga, and 1.05 Ga. The 1.87 Ga reconstruction do not support the NENA or SAMBA configurations, but indicates the onset of Nuna. The 1.57 Ga and 1.25 Ga reconstructions indicate similarities in the relative positions between Baltica, Laurentia, Amazonia, and Siberia during this period. The transition between Nuna and Rodinia is marked by a rotation between Laurentia, and Baltica and Amazonia (and possibly West Africa), forming the Grenville collisional belt.
Source: Työväentutkimus Vuosikirja
Author: R. Klein
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2287780135