Petrology of the metamorphic rocks

241 Pages·1991·11.88 MB·English

by  Roger Mason (auth.)

Petrology of the
metamorphic rocks
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Petrology of the
metamorphic rocks
Second Edition
Roger Mason
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
© R. Mason, 1990
Originally published by the Academic Division of Unwin Hyman Ltd in 1990
Softcover reprint of the hardcover 2nd edition 1990
First published in 1990
British Library Cataloguing in Publication Data
Mason, Roger 1941-
Petrology of the metamorphic rocks. - 2nd ed.
1. Metamorphic rocks. Petrology
1. Title
552.4
Library of Congress Cata1oging-in-Publication Data
Mason, Roger, 1941-
Petro1ogy of the metamorphic rocks/Roger Mason. - 2nd ed.
p. cm.
lncludes bibliographical references.
ISBN 978-90-481-4001-5 ISBN 978-94-017-2590-3 (eBook)
DOI 10.1007/978-94-017-2590-3
1. Rocks, Metamorphic. 1. Title.
QE475.A2M394 1990
552' .4-<lc20 90--35106
CIP
Typeset in 10 on 12 point Times by Computape (Pickering) Ltd,
North Y orkshire
Preface
There has been a great advance in the understanding of processes of meta
morphism and of metamorphic rocks since the last edition of this book
appeared. Methods for determining temperatures and pressures have
become almost routine, and there is a wide appreciation that there is not a
single temperature and pressure of metamorphism, but that rocks may
preserve, in their minerals, chemistry and textures, traces of their history of
burial, heating, deformation and permeation by fluids. However, this excit
ing new knowledge is still often difficult for non-specialists to understand,
and this book, like the first edition, aims at enlightenment. I have concen
trated on the interpretation of the plate tectonic settings of metamorphism,
rather than following a geochemical approach. Although there is an impress
ive degree of agreement between the two, I believe that attempting to
discover the tectonic conditions accompanying rock recrystallization will
more readily arouse the interest of the beginner.
I have used a series of case histories, as in the first edition, drawing on my
own direct experience as far as possible. This m<f.lns that some subjects are
treated in more detail than others, and many important topics are barely
mentioned at all. It also means that general concepts appear in a rather
haphazard order in the text. To help my readers, I have provided a glossary
of definitions of terms used in the book, which are indicated in bold type in
the text. I discuss thermotectonic models, based on very simple 2-dimensio
nal analyses, in describing the metamorphic history of many of my examples.
Although many problems remain to be solved in this approach (and I do not
claim that my models are sufficiently rigorous to be contributions to research
discussion), its success in accounting for the shape of many P-T- t paths has
convinced me that it is a useful framework to use in learning about meta
morphism. I hope I have provided my readers with an interesting and sound
basis for further exploration of this fascinating branch of the Earth sciences.
The present form of the book arose from a course of lectures and
demonstrations given at Wuhan College of Geology (since renamed the
China University of Geosciences) in the People's Republic of China in 1986.
I thank President Zhao Pengda and Professor You Zhendong for inviting me
to give the course, Mrs Han Yuqing who worked very hard as my inter
preter, and the students of the class who suffered the culture shock of being
introduced to western-style discussion in lectures! I have been encouraged to
PREFACE
emphasize the tectonic theme in a thorough and constructive review of my
manuscript by Dr M. J. Le Bas. In addition to those I thanked for advice in
my first edition, I would like to thank Dr L. Ashwal, Dr A. P. Boyle,
Professor K. Burke, Dr K. W. Burton, Mr A. J. Griffiths, Dr W. L. Kirk,
Dr J. D. A. Piper, Dr G. D. Price, Ms K. V. Wright, Dr J. W. Valley, and
Dr C. Xenophontos. I thank Dr P. W. Edmondson for compiling the index.
I also acknowledge with thanks receipt of a travel grant from the Central
Research Fund of the University of London to visit classic metamorphic
localities in the USA, and also a grant from the Royal Society of London to
the Sulitjelma '83 Ophiolite Expedition.
Contents
Preface page v
List of tables ix
1 Introduction 1
Definition 1
The processes of metamorphism 2
The three field categories of metamorphic rocks 6
Studying thin sections of metamorphic rocks 8
Laboratory study of metamorphic rocks 9
Why study metamorphic rocks? 16
2 Rock and mineral compositions, and their relationship 18
Classification of metamorphic rocks 18
Chemical compositions of metamorphic rocks 26
The Phase Rule 28
Recognition of equilibrium in metamorphic rocks 32
Composition - assemblage diagrams 37
Metamorphic textures 44
Metamorphic facies 49
Thermotectonic modelling 53
3 Metamorphism associated with igneous intrusions 57
The Skiddaw contact aureole, Cumbria, England 64
The Beinn an Dubhaich aureole, Isle of Skye, Scotland 75
Compositions of fluids in contact metamorphism 84
Thermal models of contact metamorphism 86
viii CONTENTS
4 Dynamic metamorphism 94
The Mutki granitic mylonite, Turkey 95
The Lochseiten Mylonite, Switzerland 103
Dynamic metamorphism in relation to depth 105
5 Metamorphism associated with lithospheric extension 107
Metamorphism at spreading oceanic ridges 107
Metamorphism in sedimentary basins 119
6 Metamorphism in subduction zones 129
7 Metamorphism in collision zones 138
Metamorphic evolution of pelitic rocks of Connemara, Ireland 144
The Sulitjelma copper-mining district, Norway and Sweden 149
8 Metamorphism in stable continental crust 169
Metamorphism in Dengfeng County, Henan Province, China 175
Pyroxene gneisses of northwestern Scotland 177
The Adirondack Mountains, New York State, USA 184
Heat flow and thermal gradients in continental crust 189
9 Metamorphic rocks of the mantle 191
10 Extraterrestrial metamorphism 199
Impact metamorphism 199
Shock metamorphism at the Nordlinger Ries crater, Germany 200
Metamorphism in Moon rocks 205
Appendix 208
Glossary 209
References 220
Index 225
List of tables
Table 1.1 Pressure units used in petrology. page 6
Table 2.1 Scheme of classification of metamorphic rocks in the field 25
Table 2.2 Calculation of ACF values for an analysed basic igneous
rock. 40
Table 2.3 Calculation of AFM values for a pelitic rock. 42
Table 2.4 Names of metamorphic facies and typical mineral assem-
blages of basic rocks and pelitic rocks in each. 52
Table 3.1 Analysis of Skiddaw slate compared with an analysis of
andalusite. 69
Table 3.2 Tectonic and metamorphic history of the Skiddaw
contact aureole. 75
Table 3.3 Reactions in the system Ca0-Mg0-Si0r.C0 at a
2
pressure of 101.3 kPa. 79
Table 3.4 Maximum contact temperatures T max computed for intru-
sion of magma at temperature T m into dry country rocks
at temperature T c· 86
Table 4.1 Textural classification of mylonites. 102