Interpretation of magnetic fabrics in the early proterozoic diabase dykes of Keuruu, central Finland

We have studied the crustal structures of the Palaeoproterozoic Svecofennian (c. 1.9 Ga) Orogeny with the help of large scale seismic reflection surveys (FIRE 1-3), preliminary structural field work and geological and geophysical databases. The central part of the orogen is occupied by the Central Finland Granitoid Complex, which comprises two suites of granitoid rocks and associated mafic and volcanic rocks. The complex and the surrounding supracrustal belts are cut and deformed by numerous shear zones and faults; here divided into six groups. The most prominent reflections are usually shear zones or faults on outcrops. The granitoid complex is interpreted as a deep, lower-level section of an old core complex, where the younger granitoid intrusions form the basins and older granitoid intrusions and associated volcanic rocks form the horsts. The upper-middle crust detachment zone is exposed at the northeastern edge of the complex and middle crust is exposed in the migmatitic domes at northern and western margins.The seismic reflection sections display a frozen image of orogenic thickening and lateral spreading. The decoupling of the upper, middle and lower crust during spreading resulted in the formation of layered superstructure-infrastructure of the crust.

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“…2; Korsman et al 1997;Puranen et al 1992) that left highly reflective tails behind (Figs 5 & 7b; CMPs 15800 and 18000).…”

Section: Formation Of Layered Svecofennian Crust With Superstructure-mentioning

confidence: 89%

A case study of lateral spreading: the Precambrian Svecofennian Orogen

Korja

Kosunen

Heikkinen

2009

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“…AMS was measured on 109 diabase specimens. Measurements were conducted for both non-demagnetized and alternating-field (AF) demagnetized samples, since AF demagnetization does not cause significant changes in AMS (Puranen et al 1992). For Salla Diabase Dyke the degree of anisotropy is typically below 5%, indicating that the samples have no significant AMS, and the samples are thus suitable for palaeomagnetic study.…”

Section: Anisotropy Of Susceptibilitymentioning

confidence: 99%

Palaeomagnetism of the Salla Diabase Dyke, northeastern Finland, and its implication for the Baltica-Laurentia entity during the Mesoproterozoic

Salminen

Pesonen

Mertanen

et al. 2009

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New palaeomagnetic and rock magnetic results are presented for the 1122 + 7 Ma Salla Diabase Dyke in NE Finland. A positive baked-contact test proves that the dyke has a primary natural remanent magnetization carried by magnetite. The characteristic remanent magnetization direction (D ¼ 42.28, I ¼ 73.98, k ¼ 75.78, a 95 ¼ 4.88) of 13 sites along the large single dyke provides a virtual geomagnetic pole (VGP) position of Plat ¼ 718N, Plon ¼ 1138E (A 95 ¼ 8.18). Although secular variation may not have been fully averaged out, the new VGP provides an important result to define the late Mesoproterozoic position of Baltica. The VGP is not close to any known Proterozoic palaeopoles of Baltica, and therefore the pre-Sveconorwegian apparent polar wander path (APWP) of Baltica must be modified. The pre-Sveconorwegian (c. 1.3-1.0 Ga) APW swathes of Baltica, Laurentia (including the Logan Loop) and Kalahari cratons show similar shape, but new well-dated palaeomagnetic poles for c. 1.25-1.12 Ga interval from these continents are required to test the similarity. The Salla dyke VGP provides hints that the Mesoproterozoic Baltica-Laurentia connection in the Hudsonland supercontinent assembly lasted until 1.12 Ga.

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“…Park et al 1988;Ernst 1990;Cadman et al 1992;Ernst & Baragar 1992;Puranen et al 1992;Staudigel et al 1992;Lanza 1994;Raposo & Ernesto 1995;Raposo 1997;Varga et al 1998;Herrero-Bervera et al 2001;Ferr6 et al 2002) has considered that kma x must be parallel to flow direction without further questioning (Fig. 5) …”

Section: The Ams Of Hawaiian Dykes a General Consensus Seems To Appearmentioning

confidence: 99%

Anisotropy of magnetic susceptibility of lava flows and dykes: A historical account

Cañón‐Tapia¹

2004

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The basic assumptions made in the interpretation of the anisotropy of magnetic susceptibility (AMS) of lava flows, dykes and other tabular intrusive rocks have changed with time. This paper presents a historical account of those changes. Because several aspects of the AMS of these types of rocks are still open to debate, the historical perspective helps us to appreciate better the limitations that had to be faced at different times, therefore providing some clues that can be used to solve such controversies. Also, by benefiting from hindsight it is possible to devise alternative approaches that can be employed to interpret the AMS of these types of rocks. Although some adjustments to current models will be made as new results become available, it seems that at present the main components of the basic model of AMS in lava flows and tabular intrusive rocks have been finally reached, leaving behind most of the apparent contradictions found in earlier works. This progress is undoubtedly an important advance in our understanding of the nature of AMS in general.

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Interpretation of magnetic fabrics in the early proterozoic diabase dykes of Keuruu, central Finland

Cited by 22 publications

References 24 publications

A case study of lateral spreading: the Precambrian Svecofennian Orogen

A case study of lateral spreading: the Precambrian Svecofennian Orogen

Palaeomagnetism of the Salla Diabase Dyke, northeastern Finland, and its implication for the Baltica-Laurentia entity during the Mesoproterozoic

Anisotropy of magnetic susceptibility of lava flows and dykes: A historical account

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