The geochemistry and geochronology of Quaternary collision- related volcanism in the southern Lesser Caucasus: from development of the mantle source to magma generation and eruption Patrick James Sugden Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Earth and Environment October, 2019 - ii - The candidate confirms that the work submitted is his own, except where work which has formed part of jointly-authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. The work in Chapter 3 of the thesis has appeared in publication as follows: Sugden, P. J., Savov, I. P., Wilson, M., Meliksetian, K., Navasardyan, G., & Halama, R. (2019). The Thickness of the Mantle Lithosphere and Collision-Related Volcanism in the Lesser Caucasus. Journal of Petrology, 60(2), 199-230. The candidate was responsible for some of the field sampling in September 2015, sample preparation (rock crushing), Sr-Nd isotope analysis and all written text. All ideas presented as new are the candidate’s own. The contribution of the other authors were in: repeated field campaigns between 2004 and 2013; Savov assisted in the preparation of some of these older samples (rock crushing); Savov analysed a small number of the samples for Sr-Nd isotopes; Major and trace element analyses were performed externally at ACME labs, Vancouver, Canada; Navasardyan and co-workers produced the geological map in Figure 4 of the publication. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. The right of Patrick James Sugden to be identified as Author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. © 2019 The University of Leeds and Patrick James Sugden - iii - Acknowledgements This research has been carried out by a team which has included Ivan Savov, Marjorie Wilson, Khachatur Meliksetian, Ralf Halama, Gevorg Navasardyan, Samuele Agostini and Dan Barfod. My own contributions, fully and explicitly indicated in the thesis, have been: (i) taking part in sample collection fieldtrips in 2015 and 2017; (ii) preparing samples from the 2012, 2013, 2015 and 2017 field campaigns for geochemical analysis (rock crushing); (iii) preparing samples for thin sectioning; (iv) strontium and neodymium cation column chemistry; (v) preparing and loading samples onto metal filaments for Sr-Nd isotope analysis; (vi) analysing samples for Sr-Nd isotope ratios on the Triton Thermal Ionisation Mass Spectrometer at University of Leeds; (vii) performing all geochemical calculations and modelling presented in this thesis; (viii) preparing samples for boron isotope analysis at IGG-CNR Pisa using cation and anion exchange columns; (ix) sample preparation for Ar-Ar dating, including rock crushing, magnetic separation, density separation, leaching and hand picking; (x) petrographic imaging of volcanic rocks using both traditional petrographic polarising microscope and the scanning electron microscope at the University of Leeds; (xi) electron probe microanalysis of amphibole and clinopyroxene phenocrysts to measure their major element composition. The other members of the group and their contributions have been as follows: Ivan Savov has worked on all field campaigns from 2004 to 2017, and has prepared samples collected 2004-2010 for geochemical analysis, as well as analysing the Gegham obsidians and Tezhsar alkaline complex samples for B and δ11B in Pisa; Marjorie Wilson has supported Ivan Savov in supervising the candidate’s PhD project and providing comments and advice at every stage of the project; Khachatur Meliksetian has worked on all field campaigns from 2004 to 2017, providing in depth knowledge of the local geology; Ralf Halama provided comments on the Journal of Petrology manuscript which is included here as Chapter 3, as well as providing comments and feedback on Chapter 4; Gevorg Navasardyan worked using GIS software, remote sensing and extensive fieldwork to produce the Geological map of Syunik volcanic highland which was adapted for this thesis in Chapters 2 and 5; Samuele Agostini conducted boron isotope analyses using the Neptune series multi-collector (MC) inductively coupled plasma mass spectrometer (ICP-MS) at IGG-Pisa; Dan Barfod packaged samples for irradiation and then carried out argon isotope analysis at the Scottish Universities Environmental Research centre, before using the in-house software package to calculate the ages presented in Chapter 5. - iv - The 4 years I have spent as a PhD student have been a unique and often rewarding time. While this thesis is the culmination of 4 years of my own struggles and successes, none of it would have been possible without a whole range of people I have tried to thank below. Sincerest apologies if anyone was left off. First of all, I must thank Ivan Savov and Marjorie Wilson for all their help over these past 4 years in the various aspects of work which have culminated in this thesis. Quite simply, none of it would have been possible without their time, patience and engagement in the project. In particular, I would like to thank them for repeatedly prioritising my various manuscripts and always providing punctual and detailed comments, despite their busy and varied schedules. Thank you Ivan for all that energy, enthusiasm and support in the field, in the lab, at conferences and in science generally. Thanks to Marge for passing on some of that far-reaching experience in igneous petrology, scientific publishing and much else besides. Thanks also for those trips to the Fav and Weetwood Hall, they were some of the most pleasant and enjoyable supervision meetings I ever had! A mention has to go out to my Armenian colleagues- Khachatur Meliksetian, Gevorg Navasardyan, Edmond Grigoryan and Davit Manucharyan. Without their help and in-depth knowledge of the local geology it would be impossible to have such successful field trips to their beautiful country. Special thanks must go to Gevorg, for all the work he has done to produce the geological map of the Syunik volcanic highland (adapted for Chapters 2 and 4). I must also thank Edmond for opening up his home to me in 2017, while we prepared to head out into the field. I would like to thank Jason Harvey and Bob Cliff of the University of Leeds for all their help in showing me the ropes of column chemistry and thermal ionisation mass spectrometry. I spent very many long hours in that lab, but Jason and Bob made sure I had some good data to play with at the end of it all. Thank you also to Richard Walshaw for all his help in electron probe micro-analysis. Samuele Agostini and the others at IGG-CNR-Pisa deserve thanks for all the training they provided in boron isotope analysis, and for showing me their beautiful city (and fantastic pizza). Similarly, Dan Barfod provided me with excellent support at SUERC as I found my feet in preparing samples for Ar-Ar dating. I would like to thank the Geochemistry Special Interest Group and the Institute of Geophysics and Tectonics for their financial support which allowed me to attend some of the largest international conferences in geoscience- AGU and EGU. Thank you to all the people who stopped for chats about volcanoes, Armenia, and much else besides at both of these conferences. - v - To the other PhD students I have had the pleasure of knowing and working with these past few years, thank you for being such great colleagues. Special thanks go to Lubka, Eduardo and Autumn for all their advice on labwork, petrology and all things boron! Personal “thank you”s must go to my housemates Beth, Josh and Louise who have helped keep me sane, and made my time at Leeds a happy one which I will look back on with fond memories. Thanks also to Linda for all the pep talks when being a PhD student was not so easy. The final thanks must go to my parents, Sally and Mark, who have always encouraged me to pursue my passion for Earth Science. I also thank them for the delicious food and home comforts which have kept me going through these final few weeks. - vi - Abstract The Arabia-Eurasia continent-continent collision zone is unique on Earth for hosting widespread Quaternary post-collisional volcanism. This thesis explores the geochemistry of understudied volcanic rocks from the southern Lesser Caucasus mountains. It builds a holistic model of post-collisional magmatism: from how the magmatic source evolved before and after collision, the mechanism by which this source partially melted, and how magmas were able to ascend through the crust. The thesis also explores how aspects of this model might have changed over the duration of Quaternary volcanism. Major and trace element concentrations, as well as Sr-Nd isotopes are used to build a petrogenetic model for magmatism. Boron isotopes provide further information on the evolution of the mantle source. Ar-Ar ages show how the processes of magma ascent and eruption may have evolved over time. Amphibole and clinopyroxene geothermobarometry establish the pressure- temperature conditions of crystal fractionation. Southern Lesser Caucasus magmas are not contaminated by assimilation of continental crust. The ubiquitous arc-like geochemistry reflects an inherited subduction component, which is dominated by sediment melts. Metasomatic amphibole stores the component in the lithosphere after collision, and then initiates melting following its heating-induced breakdown. Heating results from small-scale convective removal at the lithosphere-asthenosphere boundary and/or relaxation of non-linear geothermal gradients within the lithosphere. The parental magma produced is a 1% partial melt formed at depths close to the garnet-spinel transition (~80 km).