Structure and metamorphism of the Gran Paradiso massif, western Alps, Italy

212 Pages·2012·13.09 MB·Dutch

GEOLOGICA ULTRAIECTINA
Mededelingen van de
Faculteit Aardwetenschappen
Universiteit Utrecht
No. 199
Thermal evolution of high-pressure
metamorphic rocks in the Alps
Fraukje M. Brouwer
Cover illustration: Spinel-corundum-plagioclase symplectite surrounding kyanite in a
metabasic rock from the Lepontine gneisses near Bellinzona, Switzerland. SEM backscatter
electron image.
Thermal evolution of high-pressure
metamorphic rocks in the Alps
Thermische evolutie van hoge druk
metamorfe gesteenten in de Alpen
(met een samenvatting in het Nederlands)
PROEFSCHRIFT
ter verkrijging van de graad van Doctor aan de Universiteit Utrecht

op gezag van de Rector Magnificus Prof. Dr. H.O. Voorma

ingevolge het besluit van het College voor Promoties in het openbaar te verdedigen

op 20 november 2000, des namiddags te 16.15 uur

door

Fraukje Myriam Brouwer

Geboren op 24 mei 1973, te Uden
Supervisors:
Prof Dr. R.L.M. Vissers
Prof Dr. MJR. Wortel
Members ofthe dissertation committee:
Prof Dr. R. Compagnoni
Dipartimento di Scienze Mineralogiche e Petrologiche
Universita degli Studi di Torino, Italy
Prof Dr. M. Engi
Mineralogisch-Petrographisches Institut
Universitat Bern, Switzerland
Prof Dr. S.M. Schmid
Geologisch-Palaontologisches Institut
Universitat Basel, Switzerland
Prof Dr. ].L.R. Touret
Faculteit Aardwetenschappen
Vrije Universiteit Amsterdam, The Netherlands
ISBN 90-5744-°56-3
Voor mijn ouders
-----.
NWO
The research described in this thesis was conducted at the Faculty of Earth Sciences,
Utrecht University, under the programme of the Vening Meinesz Research School of
Geodynamics (VMSG). The author acknowledges financial support from the Geosciences
Foundation (GOA, currently ALW) of the Netherland~ Organi~ation for Scientific
Research (NWO), project number 750-196-15.
Contents
Samenvatting (Abstract in Dutch) II

Riassunto (Abstract n Italian)
IS

Abstract 19

Chapter I Introduction 21

1.1 Scope of this study 21

1.2 Approach 22

1.3 Outline of this thesis 22

Chapter 2 Introduction to Alpine geology 25

2. I Plate tectonic setting 25

2.2 Geometry of the Alps 25

2·3 Structure of the central and western Alps 28

2.3.1 The central Alps 28

2.3.2 The western Alps 29

2.3.3 The Ligurian Alps 31

Chapter 3 Metamorphic history of the Lepontine gneisses around Alpe

Arami, southern Switzerland 33

3· I Abstract 33

3·2 Introduction 33

3.2.1 Geology of the Lepontine Alps 33

3.2.2 The origin and history of the Alpe Arami peridotite 36

3.2.3 The study area 37

3.3 Structural history of the Lepontine gneisses 38

3.3. I Structures of the gneisses 38

3.3.2 Comparison with regional studies 44

3.4 Lithologies and mineral chemistry 45

3·4· I Petrography 45

3.4.2 Eclogites and eclogite-amphibolites 46

3.4.2. I Petrography of eclogites and eclogite-amphibolites 46

3.4.2.2 Symplectitic transformations 47

3·4· 2. 3 Mineral chemistry of eclogites and eclogite­
amphibolites 49

3.4.3 Cima Lunga metapelitic lens 52

3.4.3.1 Petrography of metapelites 53

3.4.3.2 Mineral chemistry of metapelites 56

3.4.4 Thermobarometry 56

3.4.5 CompllatlOn of the PTt trajectory 63

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Contents
3.5 Geodynamic implications 66
3.5. J Juxtaposition ofthe Cima Lunga nappe and the Arbedo zone 66
3.5.2 Three possible scenarios for Alpe Arami and the
Lepontine gneisses 67
3.5.3 Implications for orogenic processes 68
3.6 Conclusions 70
Chapter 4 Structure and metamorphism of the Gran Paradiso massif,
western Alps, Italy 73
4· I Abstract 73
4.2 Introduction 73
4.2. I Geology of the western Alps 73
4.2.2 Gran Paradiso massif 75
4.3 Structure of the Gran Paradiso basement 77
4· 3· J Pre-Alpine deformation 77
4.3.2 Alpine deformation 77
4.4 Metamorphism of the Gran Paradiso basement 80
4.4. I Petrography 80
4.4.2 Mineral chemistry 85
4.4.3 Thermobarometry 89
4.4.4 Compilation of the PTt trajectory 94
4.5 Geodynamic implications 98
4.6 Conclusions 99
Chapter 5 Metamorphic history of ec10gitic metagabbro blocks from a
tectonic melange in the Voltri massif, Ligurian Alps, Italy JOJ
5. I Abstract IO I
5.2 Introduction 101
5.2. I Geology of the Voltri massif J 0 J
5.2.2 Tectonic melange in the northern Voltri massif I02
5.3 Metagabbros of the Voltri melange 105
5.3.1 Petrography 105
5.3.2 Mineral chemistry 107
5.4 Metamorphic history 109
5·4· I Thermobarometry 109
5.4.2 Compilation of the PTt trajectory II3
5.5 Discussion I 16
5.5. I Comparison with previous studies I 16
5.5.2 Tectonic implications II6
5.6 Conclusions 118
8
Contents
Chapter 6 The thermal evolution of convergent margins: a numerical
modelling study applied to the Alps 119
6. I Abstract II9
6.2 [ntroduction I 19
6.3 Possible causes for heating 122
6.3. I Processes in the upper mantle 122
6.3.2 Radiogenic heating within the deformed crust 124
6.3.3 Selection of possibly viable hypotheses 126
6.4 Numerical investigations 126
6.4. I Slab detachment 126
6.4.2 Tectonically Accreted Radiogenic Material (TARM) 129
6.4.3 Comparison of model results for the two hypotheses 131
6.5 Comparison of model results with observations: a test of the hypotheses 133
6.5. I Geodynamic setting and PTt trajectories of se1ected areas 133
6.5.2 Comparison of model results with observations 136
6.6 Exhumation of high-pressure rocks in the Alps ] 38
6.7 Conclusions 141
Chapter 7 Conclusions and future research 143
References
Appendix I Thermobarometry ]57
AI.I Introduction 157
AI.2 Garnet-omphacite thermobarometry 157
AI.2.I Krogh (1988) 157
AI.2.2 Holland (1983) 157
AI.2.3 Powell (1985) 159
AI.3 Garnet-phengite thermometry 160
AI.4 Phengite barometry 161
AI.5 Garnet-clinopyroxene-phengite barometry 162
AI.6 Garnet-amphibole thermometry 163
AI.7 Garnet-amphibole barometry 164
AI.8 Amphibole-plagioclase thermometry 167
Al.9 GASP barometry [69
AI.IO Garnet-biotite thermometry 17°
AI.IO.I Ferry and Spear (1978) 17°
AI.IO.2 Hodges and Spear (1982) [70
AI.IO.3 Kleemann and Reinhardt (1994) 171
AI. I I Simultaneous solution of GASP and garnet-biotite 171
ALlL1 GASP and Ferry and Spear (1978) 172
ALlL2 GASP and Kleemann and Reinhardt (1994) 172
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