Petrogenesis of Late Cenozoic Collision Volcanism in Western Anatolia, Turkey

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Durham E-Theses
Petrogenesis of late cenozoic collision volcanism in
western Anatolia, Turkey
Aldanmaz, Ercan
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Aldanmaz, Ercan (1998) Petrogenesis of late cenozoic collision volcanism in western Anatolia, Turkey,
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Petrogenesis of Late Cenozoic Collision Volcanism in
Western Anatolia, Turkey
by
Ercan Aldanmaz
The copyright of this thesis rests
with the author. No quotation
from it should be published
without the written consent of the
author and information derived
from it should be acknowledged.
A thesis submitted in partial fulfilment of
the requirements for the degree of
Doctor of Philosophy
Department of Geological Sciences
University of Durham
September 1998
€1
2^ FEB 1999
Declaration
I declare that this thesis, which I submit for the degree of Doctor of Philosophy
at the University of Durham, is my own work and not substantially the same as any
which has previously been submitted at this or another university.
Ercan Aldanmaz
University of Durham
September 1998
Copyright © Ercan Aldanmaz
The copyright of this thesis rests with the author. No quotation from it should be
published without the written consent of Ercan Aldanmaz and information derived it
should be acknowledged.
ABSTRACT
Petrogenesis of Late Cenozoic Collision Volcanism in Western Anatolia, Turkey
Western Anatolia exhibits a record of almost all stages of a collision event and its related
magmatic processes. Following an Eocene continent-arc collision, Western Anatolia region
experienced a complete cycle of thickening and orogenic collapse. The early stage of collision-
related volcanism, which was most evident during the Early Miocene (<21 Ma), produced a
considerable volume of lavas and pyroclastic deposits covering a broad compositional range
from basaltic andesites to rhyolites. The volcanic activity continued into the Middle Miocene
with a gradual change in eruptive style and rock compositions. The Middle Miocene activity,
formed in relation to localised extensional basins and was dominated by lava flows and dykes of
basalts to andesites composition. Both the Early-Middle Miocene rocks have calc-alkaline and
shoshonitic character. The late stage volcanism, from 11.0 to 8.3 Ma, was marked by alkali
basalts and basanites erupted along the localised extensional zones.
The Early-Middle Miocene volcanic rocks exhibit enrichment in LILE and LREE relative
to the HFSE (characterised by negative Nb and Ta anomalies) and are characterised by high
^^Sr/^^Sr and low '''^Nd/''^Nd (-ENCI) ratios. These characteristics indicate a mantle lithospheric
source region carrying a subduction component inherited from a pre-collision subduction event.
Perturbation of this subduction-metasomatised lithosphere by delamination of the thermal
boundary layer is the likely mechanism for the initiation of the post-collision magmatism.
Trace elements systematics suggest that the Early-Middle Miocene series underwent a
hydrous crystallisation (dominated by pargasitic amphibole) in deep crustal magma chambers.
Subsequent crystallisation in shallower magma chambers follows two different trends: (1)
anhydrous (pyroxene + plagioclase-dominated; and (2) hydrous (edenitic amphibole -t-
plagioclase + pyroxene dominated).
Trace element and isotope modelling shows that the Early-Middle Miocene rocks have
been affected by assimilation combined with fractional crystallisation processes, and that the
effects of assimilation decrease gradually from the Early Miocene into the Middle Miocene.
This indicates a progressive crustal thinning related to the extensional tectonics that prevailed
from the latest Early Miocene onwards.
In contrast to the Early-Middle Miocene rocks, the Late Miocene alkaline rocks are
characterised by low ^^Sr/^^Sr and high ''''Nd/''^Nd (-(-£Nd) ratios and have OIB-type like trace
element patterns characterised by enrichment in LILE, HFSE and L-MREE, and a slight
depletion in HREE, relative to the N-MORB compositions. REE inversion modelling indicates
that these rocks formed by partial melting (with degrees of ~2 to -10%) of a spinel + garnet
Iherzolite source. Trace element and isotopic systematics are consistent with decompression
melting of an enriched mantle asthenospheric source.
Acknowledgements
First, my deepest thanks to my supervisor. Dr. Julian A. Pearce, for his helpful
comments, criticisms and patience. Needles to say, this work would never have been
finished without his constant help and encouragement. He painstakingly went through
each chapter and offered many invaluable suggestions.
I would like to express my gratitude to the University of Kocaeli, Turkey, and to
the Turkish Higher Educational Council for their financial support during the past four
years.
The original idea of this project stems from Prof. Yucel Yilmaz who first
aroused my interest in the magmatic evolution of Western Anatolia. I would like to
express my personal gratitude to him.
I would like to thank Dr. Mehmet Keskin for his invaluable help and advise
during the initial stage of this project.
Particular thanks must go to Ron Hardy for his help and encouragement during
the sample preparation and XRF analyses; and to Dr. Chris Ottley for his help and
advise on ICP-MS analyses.
I would like to thank Drs. Peter Hill, Stuart Keams and Simon Burgess at the
Electron Probe Unit of Edinburg University for their help and advise on Electron Probe
analyses.
I would like to express my appreciation to Prof. John Mitchell at Newcastle
University for carrying out radiometric dating; and to Dr. Matthew Thirlwall, Gery
Ingram and Dr. Robin Gill at Royal HoUoway, University of London, for their help and
advise on radiogenic isotope analyses.
The list of people from the department in Durham, who I would like to thank, is
quite long. It starts with the staff: Prof. Maurice Tucker, Prof. Bob Thompson, Dr. Gill
Foulger, Dr. Grenvile Holland, Dr. Graeme Pearson, D. Stevenson, G. Ruth, Gerry,
Alan, R. Lambert, Julie, Karen, Carol, Claire, D. Asbury, D. Schofield; the fellow
geochemists: Nurdane, Affonso, Teresa, Vicky, Robin, Andy, Gordon, Sarah(s), Kate;
the postgraduate friends: Roberto, Tobby, Alun, Wayne, Jonny, Ziad, Simon, Gail,
Ismail, Caroline, Ian, Matt.
Final thanks go to my parents for their continual moral support during the course
of this study.
CONTENTS
Chapter 1: INTRODUCTION Page
1.1. Geological Setting and Distribution of Volcanism 2
1.1.1. Tectonic Setting 2
1.1.2. Distribution of the Volcanism 6
1.2. Previous Studies of Western Anatolian Volcanism 8
1.3. Objectives of This Thesis 14
1.4. Description of The Thesis 16
Chapter 2: GEOLOGY AND VOLCANO-STRATIGRAPHY
OF WESTERN ANATOLIA
Introduction 18
2.1. The Ezine-Gulpinar-Ayvacik Area (EGA) 20
2.1.1. The Basement Rocks 22
2.1.2. The Ezine-Ayvacik Section 26
2.1.2.1. The Kestanbol Pluton 26
2.1.2.2. The Kiziltepe (Volcanic) Unit 27
2.1.2.3. The Cinarkoy Pyroclastic Deposits 27
2.1.2.4. The Cakmak Tuff 27
2.7.2.5. The Ezine (Volcanic) Unit 28
2.1.2.6. The Dededag (Volcanic) Unit 28
2.1.2.7. The Ultrapotassic Lamproite Dykes 29
2.1.2.8. The Tastepe Volcanics 29
2.1.2.9. The Ezine Volcanics 30
2.1.2.10. The Ayvacik Volcanics 31
2.1.3. The Assos-Babakale-Gulpinar Section 32
2.1.3.1. The Babakale (Volcanic) Unit 32
2.1.3.2. The Bademli (Volcanic) Unit 35
2.1.3.3. The Koyunevi Ignimbrite 36
2.1.3.4. The Suruce Andesite 37
2.1.3.5. The Bergas Ignimbrite 38
2.1.3.6. The Bakacak (Volcanic) Unit 44
2.1.3.7. The Behram Andesite 44
2.1.3.8. The Balabanli Ignimbrite 46
2.1.3.9. The Kovacli Dyke Swarms 54
2.2. The Diklli-Ayvalik-Bergama (DAB) Area 55
2.2.1. The Basement Rocks 55
2.2.2. The Ayvalik-Kozak Section 60
2.2.2.1. The Kozak Pluton 60
2.2.2.2. The Maden Island Pluton 61
2.2.2.3. The Kucukkoy (Volcano-sedimentary) Unit 61
2.2.2.4. The Ballica (Volcanic) Unit 61
2.2.2.5. The Alibey Dyke Swarms 62
2.2.2.6. The Ulubey (Volcanic) Unit 62
2.2.2.7. The Akcapinar (Volcanic) Unit 63
2.2.2.8. The Seytansofrasi Ignimbrite 64
2.2.2.9. The Besiktepe Dacite 65
2.2.2.10. The Odaburnu Dke Swarms 65
2.2.3. The Dikili-Bergama-Foca Section 66
2.2.3.1. The Kiratli (Volcanic) Unit 66
2.2.3.2. The Madra River Dyke Swarms 66
2.2.3.3. The Salihler Volcanics 69
2.2.3.4. The Kabakum Dacite 69
2.2.3.5. The Mt. Seyret (Volcanic) Unit 71
2.2.3.6. The Karagol (Volcanic) Unit 72
2.2.3.7. The Kalarga Andesite 72
2.2.3.8. The Foca (Volcanic) Unit 75
2.2.3.9. The Foca Dyke Swarms 77
2.2.3.10. The Egrigol Andesite 77
2.2.3.11. The Nebiler Volcanics 79
2.3. Summary 80
Chapter 3: MAJOR AND TRACE ELEMENT
GEOCHEMISTRY
Introduction 82
3.1. Major Element Characteristics of the Volcanic Rocks 82
3.1.1. Classification of the Volcanic Rocks Using Major
Element Geochemistry 82
3.1.2. Harker Diagrams for Major Elements 87
3.2. Trace Element Characteristics of The Volcanic Rocks 90
3.2.1. Trace Element Variations of The Volcanic Rocks 90
3.2.2. Rare Earth Element Patterns 94
3.2.3. Multi-Element Patterns 98
3.2.4. Trace Element Ratios 102
3.3. Chapter 3 Summary 105
Chapter 4: PETROGRAPHY
Introduction 106
4.1. Volcanic Rocks From The Ezine-Gulpinar-Ayvacik (EGA) Area 106
4.1.1. Highly Porphyritic Acid-Intermediate Lavas (Early Miocene) 106
4.1.2. Pyroclastic Rocks (Ignimbrites) (Early Miocene) 112
4.1.3. Weakly to Moderately Porphyritic Dyke Swarms (Early Miocene) 118
4.1.4. Aphyric to Weakly Porphyritic Mafic Alkaline
Lavas (Late Miocene) 121
4.2. Volcanic Rocks From The Dikili-Ayvalik-Bergama (DAB) Area 126
4.2.1. Highly Porphyritic Acid-Intermediate Lavas (Early Miocene) 126
4.2.2. Aphyric to Slightly Porphyritic Intermediate Lavas
(Middle Miocene) 128
4.2.3. Aphyric to Moderately Porphyritic Basaltic Lavas (Middle Miocene) 130
4.3. Interpretation and Sunmiary of the Petrography 134
Chapter 5: MINERAL CHEMISTRY
Introduction 137
5.1. Classification of the Minerals 137
5.1.1. Olivine 137
5.1.2. Pyroxene 140
5.1.3. Plagioclase Feldspar 145
5.1.4. Amphibole 147
5.1.5. Biotite-Phlogopite 147
5.1.6. Oxide Minerals 150
5.2. Estimation of Magmatic Intensive Parameters 152
5.2.1. Temperatures and Oxygen Fugacities 152
5.2.1.1. Pyroxene geothermometer 152
5.2.1.2. Amphibole-Plagioclase geothermometer 155
5.2.1.3. Fe-Ti Oxide geothermometer 157
5.2.2. Pressure Estimates 159
5.2.2.1. Clinopyroxene geobarometer 159
5.2.2.2. Al-in-hornblende geobarometer 161
5.3. Chapter 5 Summary 164
Chapter 6: ISOTOPE SYSTEMATICS AND
PETROGENESIS
Introduction 166
6.1. Nd-Sr Isotope Characteristics of The Volcanic Rocks 166
6.2. Petrogenesis of The Volcanic Rocks 171
6.2.1. Petrogenesis of the Calc-alkaline and Shoshonitic Volcanic Rocks
(Eraly-Middle Miocene) 171
6.2.1.1. Crystallisation history of the volcanic rocks 111
6.2.1.2. Assimilation combined with fractional crystallisation (AFC) 178
6.2.1.2.1. Evidence for assimilation and/or mixing: Overwiev 178
6.2.1.2.2. Estimation of the end-member compositions and bulk
partition coefficients 180
6.2.1.2. AFC Plots 181
6.2.1.3. Model for magma generation 186
6.2.1.4. Mantle melting in response to post-collisional tectonics 191
6.2.1. Petrogenesis of the Alkaline Volcanic Rocks (Late Miocene) 197
6.2.2.1. Fractional crystallisation 197
6.2.2.2. The source mineralogy 200
6.2.2.3. Partial melting processes 202
6.2.2.3.1. Overwiev 202
6.2.2.3.2. Modelling mantle melting 204
6.2.2.4. Constraints on the degree of partial melting and the initial mantle
composition 207
6.2.2.5. The source characteristics 111
6.2.2.6. Mantle melting and magma generation in response to
lithospheric extension 223
6.3. Chapter 6 Summary 224
Chapter 7: CONCLUSIONS
Introduction 227
7.1. Volcano-stratigraphy 227
7.2. Structural Evolution 228
7.3. Magmatic Evolution 229
REFERENCES 232
APPENDIX 261
A. ANALYTICAL GEOCHEMISTRY 261
B. GEOCHEMICAL DATA SET
XRF DATA 265
ICP-MS DATA 279
ELECTRON PROBE DATA 283
C. ACCURACY AND PRECISION OF THE DATA