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Significance of AMS analysis in evaluating superposed folds in quartzites

Published online by Cambridge University Press:  25 May 2010

MANISH A. MAMTANI  and
POULOMI SENGUPTA
MANISH A. MAMTANI*
Affiliation:
Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur-721302, India
POULOMI SENGUPTA
Affiliation:
Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur-721302, India
*
*Author for correspondence: mamtani@gg.iitkgp.ernet.in
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Abstract

Quartzites tend to be compositionally homogeneous, and because of this, deformation related fabric elements (foliations and lineations) are poorly developed in them. This makes structural analysis of deformed quartzites challenging. The measurement of anisotropy of magnetic susceptibility (AMS) is useful for recognizing structural imprints in rocks that lack mesoscopic fabrics and the present study is carried out with an aim to demonstrate the robustness of AMS in analysing such deformation imprints in quartzites. AMS data of samples from folded quartzites located in an approximately 10 km2 area around Galudih (eastern India) are presented. Although on a regional scale, superposed deformation and ductile shearing are known from the area, the investigated quartzites do not preserve mesoscopic evidence of these large-scale features and have developed folds that plunge gently towards the SE with a vertical NW–SE-striking axial plane. The magnetic foliation recorded from AMS analysis is parallel to the axial plane, while the orientation of the magnetic lineation varies from SE through vertical to NW. This is similar to the large-scale fold axis variations recorded in various regional domains mapped over an area of about 200 km2. It is concluded that although the imprint of regional superposed deformation is not obvious on the mesoscopic scale in the quartzites around Galudih, this imprint can be detected from the magnetic fabric. The present study thus highlights the usefulness of AMS in analysing superposed folds in quartzites.

Keywords

anisotropy of magnetic susceptibilityfoldsdeformationquartzites
Type
Original Article
Information
Geological Magazine , Volume 147 , Issue 6 , November 2010 , pp. 910 - 918
Copyright
Copyright © Cambridge University Press 2010

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