Effect of magnetic anisotropy on the natural remanent magnetization in the MCU IVe' layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway

A. R. Biedermann; Michael J Jackson; Dario Bilardello; S. A. McEnroe

doi:10.1002/2016JB013506

Effect of magnetic anisotropy on the natural remanent magnetization in the MCU IVe' layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway

A. R. Biedermann, Michael J Jackson, Dario Bilardello, S. A. McEnroe

Earth and Environmental Sciences-Twin Cities

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5 Scopus citations

Abstract

A strong negative magnetic anomaly, caused by an intense natural remanent magnetization (NRM) approximately opposite today's geomagnetic field, is observed above the MCU IVe' unit of the Bjerkreim Sokndal Layered Intrusion. The anomaly is strongest in the east, close to Heskestad, and decreases when following the layer toward the north and west. This study investigates how the NRM changes along the layer and how its direction and intensity are affected by magnetic fabrics in the intrusion. NRM, low-field anisotropy of magnetic susceptibility, and anisotropy of anhysteretic remanence have been measured on 371 specimens from 46 sites. The orientation of both the magnetic fabrics and the NRM changes for different locations along the layer, and it appears that the NRM is tilted away from the mean paleofield and toward the direction of maximum susceptibility and maximum anhysteretic remanence. When NRM directions are corrected for magnetic fabrics, the angle between the NRM and mean paleofield direction generally decreases for specimens with a single-component NRM. No correlation was found between the NRM intensity and the directional relationship between NRM, magnetic fabric, and mean paleofield.

Original language	English (US)
Pages (from-to)	790-807
Number of pages	18
Journal	Journal of Geophysical Research: Solid Earth
Volume	122
Issue number	2
DOIs	https://doi.org/10.1002/2016JB013506
State	Published - Feb 1 2017

Bibliographical note

Funding Information:
Alexander Michels, NTNU, is thanked for help during fieldwork. Bjarne S.G. Almqvist, Uppsala University, kindly provided access to their MFK1 susceptibility bridge for initial AMS measurements, and Morgan Ganerød, Norwegian Geological Survey (NGU), is thanked for access to their JR6 spinner magnetometer. We are grateful to Peat Solheid for assistance during sample preparation and measurements at the Institute for Rock Magnetism (IRM), University of Minnesota. This study was funded by the Swiss National Science Foundation (project P2EZP2-155517 to A. Biedermann), NTNU, Research Council of Norway (grant 222666 to S. McEnroe), and a visiting fellowship at the IRM, which is supported by the Instruments and Facilities program of the U.S. National Science Foundation, Division of Earth Sciences. Fátima Martín-Hernández and Martin Chadima are acknowledged for their constructive reviews which helped to improve the manuscript and Michael Walter for editorial handling of the manuscript. Additional data tables and figures are available in the supporting information.

Publisher Copyright:
©2017. American Geophysical Union. All Rights Reserved.

Keywords

AARM
AMS
NRM deflection
lamellar magnetism
layered intrusion
magnetic fabric

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10.1002/2016JB013506

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Effect of magnetic anisotropy on the natural remanent magnetization in the MCU IVe' layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway. / Biedermann, A. R.; Jackson, Michael J; Bilardello, Dario et al.
In: Journal of Geophysical Research: Solid Earth, Vol. 122, No. 2, 01.02.2017, p. 790-807.

Research output: Contribution to journal › Article › peer-review

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title = "Effect of magnetic anisotropy on the natural remanent magnetization in the MCU IVe' layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway",

abstract = "A strong negative magnetic anomaly, caused by an intense natural remanent magnetization (NRM) approximately opposite today's geomagnetic field, is observed above the MCU IVe' unit of the Bjerkreim Sokndal Layered Intrusion. The anomaly is strongest in the east, close to Heskestad, and decreases when following the layer toward the north and west. This study investigates how the NRM changes along the layer and how its direction and intensity are affected by magnetic fabrics in the intrusion. NRM, low-field anisotropy of magnetic susceptibility, and anisotropy of anhysteretic remanence have been measured on 371 specimens from 46 sites. The orientation of both the magnetic fabrics and the NRM changes for different locations along the layer, and it appears that the NRM is tilted away from the mean paleofield and toward the direction of maximum susceptibility and maximum anhysteretic remanence. When NRM directions are corrected for magnetic fabrics, the angle between the NRM and mean paleofield direction generally decreases for specimens with a single-component NRM. No correlation was found between the NRM intensity and the directional relationship between NRM, magnetic fabric, and mean paleofield.",

keywords = "AARM, AMS, NRM deflection, lamellar magnetism, layered intrusion, magnetic fabric",

author = "Biedermann, {A. R.} and Jackson, {Michael J} and Dario Bilardello and McEnroe, {S. A.}",

note = "Funding Information: Alexander Michels, NTNU, is thanked for help during fieldwork. Bjarne S.G. Almqvist, Uppsala University, kindly provided access to their MFK1 susceptibility bridge for initial AMS measurements, and Morgan Ganer{\o}d, Norwegian Geological Survey (NGU), is thanked for access to their JR6 spinner magnetometer. We are grateful to Peat Solheid for assistance during sample preparation and measurements at the Institute for Rock Magnetism (IRM), University of Minnesota. This study was funded by the Swiss National Science Foundation (project P2EZP2-155517 to A. Biedermann), NTNU, Research Council of Norway (grant 222666 to S. McEnroe), and a visiting fellowship at the IRM, which is supported by the Instruments and Facilities program of the U.S. National Science Foundation, Division of Earth Sciences. F{\'a}tima Mart{\'i}n-Hern{\'a}ndez and Martin Chadima are acknowledged for their constructive reviews which helped to improve the manuscript and Michael Walter for editorial handling of the manuscript. Additional data tables and figures are available in the supporting information. Publisher Copyright: {\textcopyright}2017. American Geophysical Union. All Rights Reserved.",

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AU - Jackson, Michael J

AU - Bilardello, Dario

AU - McEnroe, S. A.

N1 - Funding Information: Alexander Michels, NTNU, is thanked for help during fieldwork. Bjarne S.G. Almqvist, Uppsala University, kindly provided access to their MFK1 susceptibility bridge for initial AMS measurements, and Morgan Ganerød, Norwegian Geological Survey (NGU), is thanked for access to their JR6 spinner magnetometer. We are grateful to Peat Solheid for assistance during sample preparation and measurements at the Institute for Rock Magnetism (IRM), University of Minnesota. This study was funded by the Swiss National Science Foundation (project P2EZP2-155517 to A. Biedermann), NTNU, Research Council of Norway (grant 222666 to S. McEnroe), and a visiting fellowship at the IRM, which is supported by the Instruments and Facilities program of the U.S. National Science Foundation, Division of Earth Sciences. Fátima Martín-Hernández and Martin Chadima are acknowledged for their constructive reviews which helped to improve the manuscript and Michael Walter for editorial handling of the manuscript. Additional data tables and figures are available in the supporting information. Publisher Copyright: ©2017. American Geophysical Union. All Rights Reserved.

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N2 - A strong negative magnetic anomaly, caused by an intense natural remanent magnetization (NRM) approximately opposite today's geomagnetic field, is observed above the MCU IVe' unit of the Bjerkreim Sokndal Layered Intrusion. The anomaly is strongest in the east, close to Heskestad, and decreases when following the layer toward the north and west. This study investigates how the NRM changes along the layer and how its direction and intensity are affected by magnetic fabrics in the intrusion. NRM, low-field anisotropy of magnetic susceptibility, and anisotropy of anhysteretic remanence have been measured on 371 specimens from 46 sites. The orientation of both the magnetic fabrics and the NRM changes for different locations along the layer, and it appears that the NRM is tilted away from the mean paleofield and toward the direction of maximum susceptibility and maximum anhysteretic remanence. When NRM directions are corrected for magnetic fabrics, the angle between the NRM and mean paleofield direction generally decreases for specimens with a single-component NRM. No correlation was found between the NRM intensity and the directional relationship between NRM, magnetic fabric, and mean paleofield.

AB - A strong negative magnetic anomaly, caused by an intense natural remanent magnetization (NRM) approximately opposite today's geomagnetic field, is observed above the MCU IVe' unit of the Bjerkreim Sokndal Layered Intrusion. The anomaly is strongest in the east, close to Heskestad, and decreases when following the layer toward the north and west. This study investigates how the NRM changes along the layer and how its direction and intensity are affected by magnetic fabrics in the intrusion. NRM, low-field anisotropy of magnetic susceptibility, and anisotropy of anhysteretic remanence have been measured on 371 specimens from 46 sites. The orientation of both the magnetic fabrics and the NRM changes for different locations along the layer, and it appears that the NRM is tilted away from the mean paleofield and toward the direction of maximum susceptibility and maximum anhysteretic remanence. When NRM directions are corrected for magnetic fabrics, the angle between the NRM and mean paleofield direction generally decreases for specimens with a single-component NRM. No correlation was found between the NRM intensity and the directional relationship between NRM, magnetic fabric, and mean paleofield.

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KW - AMS

KW - NRM deflection

KW - lamellar magnetism

KW - layered intrusion

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Effect of magnetic anisotropy on the natural remanent magnetization in the MCU IVe' layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway

Abstract

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Keywords

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