Preferred orientation and anisotropy of seismic and magnetic properties in gabbronorites from the Bushveld layered intrusion

Joshua M. Feinberg; Hans Rudolf Wenk; Gary R. Scott; Paul R. Renne

doi:10.1016/j.tecto.2006.03.017

Preferred orientation and anisotropy of seismic and magnetic properties in gabbronorites from the Bushveld layered intrusion

Joshua M. Feinberg, Hans Rudolf Wenk, Gary R. Scott, Paul R. Renne

Earth and Environmental Sciences-Twin Cities

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

37 Scopus citations

Abstract

The preferred orientation of plagioclase and pyroxene in gabbronorites from the Bushveld layered igneous intrusion (South Africa) was investigated using electron backscatter diffraction. In two localities 200 km apart (Belfast and Rustenburg) strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane (defined by (010) planes of plagioclase and (100) planes of pyroxene). The pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure. Primary magmatic oxides are also influenced by the preferred orientation of plagioclase, generating an oblate magnetic susceptibility fabric parallel to the foliation plane. Plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p-waves traveling 4-8% faster in the vertical than in the horizontal direction.

Original language	English (US)
Pages (from-to)	345-356
Number of pages	12
Journal	Tectonophysics
Volume	420
Issue number	3
DOIs	https://doi.org/10.1016/j.tecto.2006.03.017
State	Published - Jul 7 2006

Bibliographical note

Funding Information:
The authors would like to thank R. Merkle for his help in organizing field research in the Bushveld Complex. We are grateful to the Paleomagnetism Laboratory at Scripps Institution of Oceanography (L. Tauxe, J. Gee, and J. Steindorf) for use of their equipment and software for AMS measurements. J. Gilman helped collect EBSD measurements. A. Forrester of Kelgran Ltd. kindly gave us access to the Rustenburg Grey and Belfast Black quarries. L. Maré of the Council for Geoscience, South Africa, is thanked for providing drilling equipment used in sampling. Discussions with M. Gibson and S. Webb about seismic anisotropy in the Bushveld were most helpful. HRW acknowledges hospitality at the GfZ Potsdam, where part of this research was completed. This research was funded by National Science Foundation grants EAR-0236925, EAR-0309686 and EAR-0337006. We also thank O. Bolle and S. Ji for constructive reviews of the manuscript.

Keywords

Anisotropy of magnetic susceptibility
Bushveld
Emplacement mechanisms
Layered intrusions
Plagioclase preferred orientation
Seismic anisotropy

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title = "Preferred orientation and anisotropy of seismic and magnetic properties in gabbronorites from the Bushveld layered intrusion",

abstract = "The preferred orientation of plagioclase and pyroxene in gabbronorites from the Bushveld layered igneous intrusion (South Africa) was investigated using electron backscatter diffraction. In two localities 200 km apart (Belfast and Rustenburg) strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane (defined by (010) planes of plagioclase and (100) planes of pyroxene). The pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure. Primary magmatic oxides are also influenced by the preferred orientation of plagioclase, generating an oblate magnetic susceptibility fabric parallel to the foliation plane. Plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p-waves traveling 4-8% faster in the vertical than in the horizontal direction.",

keywords = "Anisotropy of magnetic susceptibility, Bushveld, Emplacement mechanisms, Layered intrusions, Plagioclase preferred orientation, Seismic anisotropy",

author = "Feinberg, {Joshua M.} and Wenk, {Hans Rudolf} and Scott, {Gary R.} and Renne, {Paul R.}",

note = "Funding Information: The authors would like to thank R. Merkle for his help in organizing field research in the Bushveld Complex. We are grateful to the Paleomagnetism Laboratory at Scripps Institution of Oceanography (L. Tauxe, J. Gee, and J. Steindorf) for use of their equipment and software for AMS measurements. J. Gilman helped collect EBSD measurements. A. Forrester of Kelgran Ltd. kindly gave us access to the Rustenburg Grey and Belfast Black quarries. L. Mar{\'e} of the Council for Geoscience, South Africa, is thanked for providing drilling equipment used in sampling. Discussions with M. Gibson and S. Webb about seismic anisotropy in the Bushveld were most helpful. HRW acknowledges hospitality at the GfZ Potsdam, where part of this research was completed. This research was funded by National Science Foundation grants EAR-0236925, EAR-0309686 and EAR-0337006. We also thank O. Bolle and S. Ji for constructive reviews of the manuscript.",

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AU - Feinberg, Joshua M.

AU - Wenk, Hans Rudolf

AU - Scott, Gary R.

AU - Renne, Paul R.

N1 - Funding Information: The authors would like to thank R. Merkle for his help in organizing field research in the Bushveld Complex. We are grateful to the Paleomagnetism Laboratory at Scripps Institution of Oceanography (L. Tauxe, J. Gee, and J. Steindorf) for use of their equipment and software for AMS measurements. J. Gilman helped collect EBSD measurements. A. Forrester of Kelgran Ltd. kindly gave us access to the Rustenburg Grey and Belfast Black quarries. L. Maré of the Council for Geoscience, South Africa, is thanked for providing drilling equipment used in sampling. Discussions with M. Gibson and S. Webb about seismic anisotropy in the Bushveld were most helpful. HRW acknowledges hospitality at the GfZ Potsdam, where part of this research was completed. This research was funded by National Science Foundation grants EAR-0236925, EAR-0309686 and EAR-0337006. We also thank O. Bolle and S. Ji for constructive reviews of the manuscript.

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N2 - The preferred orientation of plagioclase and pyroxene in gabbronorites from the Bushveld layered igneous intrusion (South Africa) was investigated using electron backscatter diffraction. In two localities 200 km apart (Belfast and Rustenburg) strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane (defined by (010) planes of plagioclase and (100) planes of pyroxene). The pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure. Primary magmatic oxides are also influenced by the preferred orientation of plagioclase, generating an oblate magnetic susceptibility fabric parallel to the foliation plane. Plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p-waves traveling 4-8% faster in the vertical than in the horizontal direction.

AB - The preferred orientation of plagioclase and pyroxene in gabbronorites from the Bushveld layered igneous intrusion (South Africa) was investigated using electron backscatter diffraction. In two localities 200 km apart (Belfast and Rustenburg) strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane (defined by (010) planes of plagioclase and (100) planes of pyroxene). The pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure. Primary magmatic oxides are also influenced by the preferred orientation of plagioclase, generating an oblate magnetic susceptibility fabric parallel to the foliation plane. Plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p-waves traveling 4-8% faster in the vertical than in the horizontal direction.

KW - Anisotropy of magnetic susceptibility

KW - Bushveld

KW - Emplacement mechanisms

KW - Layered intrusions

KW - Plagioclase preferred orientation

KW - Seismic anisotropy

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ER -

Preferred orientation and anisotropy of seismic and magnetic properties in gabbronorites from the Bushveld layered intrusion

Abstract

Bibliographical note

Keywords

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