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Mesoscopic and magnetic fabrics in arcuate igneous bodies: an example from the Mandi-Karsog pluton, Himachal Lesser Himalaya

Published online by Cambridge University Press:  23 February 2010

R. JAYANGONDAPERUMAL ,
A. K. DUBEY  and
K. SEN
R. JAYANGONDAPERUMAL
Affiliation:
Wadia Institute of Himalayan Geology, 33 GMS Road, Dehradun-248001, India
A. K. DUBEY
Affiliation:
Wadia Institute of Himalayan Geology, 33 GMS Road, Dehradun-248001, India
K. SEN*
Affiliation:
Wadia Institute of Himalayan Geology, 33 GMS Road, Dehradun-248001, India
*
*Author for correspondence: [email protected]
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Abstract

Field, microstructural and anisotropy of magnetic susceptibility (AMS) data from the Palaeozoic Mandi-Karsog pluton in the Lesser Himalayan region reveal a concordant relationship between fabric of the Proterozoic host rock and the granite. The pluton displays a prominent arcuate shape on the geological map. The margin-parallel mesoscopic and magnetic fabrics of the granite and warping of the host rock fabric around the pluton indicate that this regional curvature is either synchronous or pre-dates the emplacement of the granite body. Mesoscopic fabric, magnetic fabric and microstructures indicate that the northern part of the pluton preserves its pre-Himalayan magmatic fabric while the central and southern part shows tectonic fabric related to the Tertiary Himalayan orogeny. The presence of NW–SE-trending aplitic veins within the granite indicates a post-emplacement stretching in the NE–SW direction. Shear-sense indicators in the mylonites along the margin of the pluton suggest top-to-the-SW shearing related to the Himalayan orogeny. Based on these observations, it is envisaged that the extension that gave rise to this rift-related magmatism had a NE–SW trend, that is, normal to the trend of the aplite veins. Subsequently, during the Himalayan orogeny, compression occurred along this same NE–SW orientation. These findings imply that the regional curvature present in the Himachal Lesser Himalaya is in fact a pre-Himalayan feature and the pluton has formed by filling a major pre-Himalayan arcuate extension fracture.

Keywords

HimalayaMandi-Karsog Plutongraniteanisotropy of magnetic susceptibilitydeformationmylonites
Type
Original Article
Information
Geological Magazine , Volume 147 , Issue 5 , September 2010 , pp. 652 - 664
Copyright
Copyright © Cambridge University Press 2010

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