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How deceptive are microstructures in granitic rocks? Answers from integrated physical theory, phase equilibrium, and direct observations

Published version
Peer-reviewed

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Authors

Holness, MB 
Clemens, John 
Vernon, Ron 

Abstract

In this contribution, we address the vexed question of the extent to which microstructures in granitic rocks reflect their igneous histories or have been masked by later events. Previous works have tended to address the problem either using theoretical or modelling considerations, or by interpretation of observed microstructures. Here we use an approach that integrates the theory of microstructural development and the results of experimental phase-equilibrium studies with direct observation of natural examples on a variety of scales. We show that the predictions of the theoretical and experimental approaches agree perfectly with the mesoscopic and microscopic evidence from granitic rocks themselves. Our conclusion is that although, in many cases, granitic rock microstructures have been modified by near-solidus reactions and crystallisation, in the absence of tectonic deformation the fundamental elements of their igneous heritage remain intact. This means that it is perfectly in order to infer aspects of crystallisation sequences, magmatic reactions and magma flow through careful microstructural observations. Thus, our answer to the question of how deceptive granitic textures are is, in most instances, ‘not very’. However, some undeformed plutons have undergone fluid-driven alteration, and others have been affected by contact metamorphism. Thus, each case should be examined on its own merits.

Description

Keywords

Granitic rocks, Textural development, Microstructure, Textural equilibration, Recrystallisation, Textural modification

Journal Title

Contributions to Mineralogy and Petrology

Conference Name

Journal ISSN

1432-0967
1432-0967

Volume Title

173

Publisher

Springer Nature
Sponsorship
NERC (via University of Manchester) (R118242)
Natural Environment Research Council (NE/N009894/1)