Palaeomagnetism of the Lappajärvi impact structure, western Finland

Pesonen, L. J.; Marcos, Nuria; Pipping, F.

doi:10.1016/0040-1951(92)90160-8

Cited by 30 publications

(26 citation statements)

References 25 publications

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“…4). This means that the remanence is mainly carried by pyrrhotite, similar to what is described for the Lappajärvi impact structure, Finland (Pesonen et al 1992). In samples from the uppermost part of the drill core LB-08A, pyrrhotite is a minor component and the weak magnetization is mainly carried by a magnetite-like phase (Fig.…”

Section: Demagnetization Behaviormentioning

confidence: 48%

“…The higher coercive forces found in our study is in line with a higher amount of smaller magnetic grain sizes, which increase magnetic hardness. Higher coercive forces (26-46 mT) are also described for the Lappajärvi impact structure, where also pyrrhotite is described as magnetic carrier of NRM in the impact lithologies (Pesonen et al 1992).…”

Section: Demagnetization Behaviormentioning

confidence: 99%

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Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana

Kontny

Elbra

Just

et al. 2007

Meteorit & Planetary Scien

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Abstract-Rock magnetic and magnetic mineralogy data are presented from the International Continental Scientific Drilling Program (ICDP) drill cores LB-07A and LB-08A of the Bosumtwi impact structure in order to understand the magnetic behavior of impact and target lithologies and their impact-related remagnetization mechanism. Basic data for the interpretation of the magnetic anomaly patterns and the magnetic borehole measurements as well as for new magnetic modeling are provided. Magnetic susceptibility (150-500 × 10 −6 SI) and natural remanent magnetization (10 −3 -10 −1 A/m) are generally weak, but locally higher values up to 10.6 × 10 −3 SI and 43 A/m occur. Sixty-three percent of the investigated rock specimens show Q values above 1 indicating that remanence clearly dominates over induced magnetization, which is a typical feature of impact structures. Ferrimagnetic pyrrhotite is the main magnetite phase, which occurs besides minor magnetite and a magnetic phase with a Curie temperature between 330 and 350 °C, interpreted as anomalous pyrrhotite. Coercive forces are between 20 and 40 mT. Brecciation and fracturing of pyrrhotite is a common feature confirming its pre-impact origin. Grain sizes of pyrrhotite show a large variation but the numerous stress-induced nanostructures observable by transmission electron microscopy (TEM) are assumed to behave as single-domain grains. We suggest that the drilled rocks lost their pre-shock remanence memory during the shock event and acquired a new, stable remanence during shock-induced grain size reduction. The observed brittle microstructures indicate temperatures not higher than 250 °C, which is below the Curie temperature of ferrimagnetic pyrrhotite (310 °C).

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Section: Demagnetization Behaviormentioning

confidence: 48%

Section: Demagnetization Behaviormentioning

confidence: 99%

Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana

Kontny

Elbra

Just

et al. 2007

Meteorit & Planetary Scien

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“…Paleomagnetic data have long proved useful in the study of impact craters to investigate stratigraphy and age, crater structure, physical property contrasts for magnetic anomaly studies, characterization of impact lithologies, and lateral correlation of ejecta deposits (e.g., Pilkington and Grieve 1992;Pesonen et al 1992;Urrutia-Fucugauchi et al 1994, 1996.…”

Section: Discussionmentioning

confidence: 99%

Paleomagnetic and rock magnetic study of the Yaxcopoil‐1 impact breccia sequence, Chicxulub impact crater (Mexico)

Urrutia‐Fucugauchi

Soler-Arechalde

Rebolledo-Vieyra

et al. 2004

Meteorit & Planetary Scien

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Abstract-Results of a detailed paleomagnetic and rock magnetic study of samples of the impact breccia sequence cored in the Yaxcopoil-1 (Yax-1) borehole between about 800 m and 896 m are presented. The Yax-1 breccia sequence occurs from 794.63 m to 894.94 m and consists of redeposited melt-rich, clast-size sorted, fine-grained suevites; melt-rich, no clast-size sorting, medium-grained suevites; coarse suevitic melt agglomerates; coarse melt-rich heterogeneous suevites; brecciated suevites; and coarse carbonate and silicate melt suevites. The low-field susceptibility ranges from −0.3 to 4018 × 10 −6 SI, and the NRM intensity ranges from 0.02 mA/m up to 37510 mA/m. In general, the NRM intensity and magnetic susceptibility present wide ranges and are positively correlated, pointing to varying magnetic mineral contents and textures of the melt-rich breccia sequence. The vectorial composition and magnetic stability of NRM were investigated by both stepwise alternating field and thermal demagnetization. In most cases, characteristic single component magnetizations are observed. Both upward and downward inclinations are present through the sequence, and we interpret the reverse magnetization as the primary component in the breccias. Both the clasts and matrix forming the breccia appear to have been subjected to a wide range of temperature/pressure conditions and show distinct rock magnetic properties. An extended interval of remanence acquisition and secondary partial or total remagnetization may explain the paleomagnetic results.

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“…Such a weak magnetic relief is often a typical signature of Finnish impact structures as documented, for example, in the cases of Lappajärvi, Karikkoselkä, Paasselkä, and Suvasvesi South. This signature is interpreted by the apparent or proven lack of highly magnetic impact melt rocks in these structures (Pesonen et al 1992.…”

Section: Previous Geophysical Studiesmentioning

confidence: 99%

“…The impact structures have the potential to contain economic resources such as oil, gas, diamonds, metallic ores, building materials, and water reservoirs (e.g., Grieve et al 1994;Pesonen et al 1999). Impactites often carry a stable thermoremanent magnetization (Pesonen et al 1992), which provides a tool to study the apparent polar wander paths (APWP), thus providing new data for paleogeographic reconstructions. Recently, paleointensity during the geological past has been successfully measured using impact melt samples (Nakamura et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Paleomagnetism and petrophysics of the Jänisjärvi impact structure, Russian Karelia

Salminen

Donadini

Pesonen

et al. 2006

Meteoritics &Amp; Planetary Science

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Abstract-Paleomagnetic, rock magnetic, and petrophysical results are presented for impactites and target rocks from the Lake Jänisjärvi impact structure, Russian Karelia. The impactites (tagamites, suevites, and lithic breccias) are characterized by increased porosity and magnetization, which is in agreement with observations performed at other impact structures. Thermomagnetic, hysteresis, and scanning electron microscope (SEM) analysis document the presence of primary multidomain titanomagnetite with additional secondary titanomaghemite and ilmenohematite. The characteristic impact-related remanent magnetization (ChRM) direction (D = 101.5°, I = 73.1°, α 95 = 6.2°) yields a pole (Lat. = 45.0°N, Long. = 76.9°E, dp = 9.9°, dm = 11.0°). Additionally, the same component is observed as an overprint on some rocks located in the vicinity of the structure, which provides proofs of its primary origin. An attempt was made to determine the ancient geomagnetic field intensity. Seven reliable results were obtained, yielding an ancient intensity of 68.7 ± 7.6 μT (corresponding to VDM of 10.3 ± 1

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Palaeomagnetism of the Lappajärvi impact structure, western Finland

Cited by 30 publications

References 25 publications

Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana

Petrography and shock‐related remagnetization of pyrrhotite in drill cores from the Bosumtwi Impact Crater Drilling Project, Ghana

Paleomagnetic and rock magnetic study of the Yaxcopoil‐1 impact breccia sequence, Chicxulub impact crater (Mexico)

Paleomagnetism and petrophysics of the Jänisjärvi impact structure, Russian Karelia

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