A new approach to understanding the origin of Fuerteventura, Canary Islands (Spain): A U-Pb, Hf and O isotope and minor- and trace-element detrital zircon study by Madisen Sagan A thesis submitted in partial fulfillment of the requirements of the degree of Master of Science Department of Earth and Atmospheric Sciences University of Alberta © Madisen Sagan, 2018 ABSTRACT The Canarian Archipelago contains seven islands proximal to the African continent and High Atlas Mountains. The origin and magmatic evolution of these islands has been a contentious issue for several decades. This particular archipelago is unique because three of the islands (Fuerteventura, La Palma, La Gomera) have been reported to contain uplifted portions of the intrusive complex, potentially exposing the earliest phases of the islands growth. There are numerous published K-Ar and Ar/Ar dates for this early magmatic activity on the oldest island, Fuerteventura, ranging from 68 to 25 Ma (Le Bas et al., 1986; Muñoz et al. 2005) but the veracity of these dates is uncertain due to a pervasive greenschist-facies metamorphic overprint. In order to better understand Fuerteventura’s early magmatic history, we have conducted a U-Pb, Hf and O isotope and minor- and trace-element detrital zircon study of sand samples from three locations proximal to the intrusive complex. A U-Pb and geochemical study of detrital zircons is an efficient method to evaluate the early growth history of the island since most of the uplifted complex consists of zircon-bearing rocks (granite, syenite, nepheline syenite, gabbro, anorthosite, carbonatite) and the U-Pb system is largely immune to low-grade metamorphism. The Hf and O isotope study helps to develop an understanding of the magma source of these intrusive rock units and evaluate the role of lithospheric contamination during the magmatic activity. A total of 260 zircon grains were secured in an epoxy mount and analyzed using in-situ U-Pb Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-MC- ICPMS). The U-Pb detrital zircon ages from this study range from the Early Oligocene to Early Pliocene (33.7-3.8 Ma), with mixture modelling results exhibiting four prominent ii age peaks at 4.4, 16.8, 21.1, and 25.5 Ma. There is no evidence for the existence of Cretaceous magmatism on Fuerteventura in this study. A total of 149 single detrital zircon grains were analyzed for their trace-element content using a New Wave UP-213 laser ablation workstation coupled with a Thermo Scientific iCAP-Q Quadrupole Inductively Coupled Plasma Mass Spectrometer (LA- ICPMS) to subdivide the zircons based on probable magma provenance (e.g., syenite, nepheline syenite, carbonatite, anorthosite, kimberlite, granite, and gabbro) to further develop our understanding of the islands magmatic evolution. The main distinguishing geochemical features of the detrital zircons are their Ti and Y concentrations, along with the magnitude of the Eu/Eu* anomaly. Using these geochemical criteria, the detrital zircons analyzed from this study indicate the following provenance: 51% syenite, 36% anorthosite/gabbro, 7% nepheline syenite, and 5% carbonatite. These rock proportions vary between sample populations, with the northern sector containing nepheline-syenite (39%), syenite (35%), carbonatite (26%) and the central sector containing syenite (54%), anorthosite/gabbro (42%), nepheline-syenite (2%), carbonatite (1%), and undefined (1%). A subset of the mounted grains (n=133) were analyzed for their hafnium isotope composition using a Laser Ablation Split Stream (LASS) technique. The new zircon Hf isotopic data can be divided into three distinct groups: a predominant zircon suite with εHfi values ranging from +7.5 to +10.4, a more ‘depleted’ population ranging from +10.6 to +15.2, and a more ‘enriched’ population ranging from -0.2 to +7.0. The zircon εHf values are relatively consistent (+7.5 to +10) in the early part of Fuerteventura’s magmatic history from 34-20 Ma, but an abrupt change occurs at ~20 Ma, where these younger zircons display εHf variation reflecting both depleted and enriched isotopic iii signatures. The depleted signature discontinues after an apparent hiatus from 14.5- 6.5 Ma, while the enriched signature is observed to persist into the Late-Miocene to Pliocene samples. A total of 191 oxygen isotope (18O/16O) spot compositions were measured on 91 detrital zircon grains using a Cameca IMS 1280 multicollector ion microprobe. The oxygen isotope data exhibit two distinct populations. The first group, representing 12% of the sample population, resembles the mantle-like oxygen field (+5.3 ± 0.3‰) with δ18O values ranging from 5.00-5.48‰ with an average of 5.14‰; the second group representing the remaining 88% of the population, records low δ18O values (3.27- 4.99‰, average of 4.31‰) that are below the zircon mantle field, representing 88% of the sample population. Low δ18O values provide evidence for high temperature rock- water alteration in the source region of these magmas, suggesting an origin for some magmas by melting or assimilation of hydrothermally altered oceanic crust. There are several new features of Fuerteventura’s magmatic history revealed from this study: 1) there are four peaks of magmatic activity (25.7, 21.0, 16.7, 4.4 Ma), 2) Oligocene detrital zircons (33.7-24.4 Ma) dominate the northern part of the complex, 3) magmatic activity in general youngs from north to south, 4) a previously unrecognized period of Late Miocene and Early Pliocene intrusive rocks (6.5-3.8 Ma) must exist in the central part of the island, 5) zircon Hf isotope data require at least three mantle source endmembers to explain the generation of Fuerteventura’s magmatic activity, including an enriched, depleted , and HIMU-plume component, and 6) low δ18O values of some detrital zircons suggest the involvement of hydrothermally altered oceanic crust in the origin of many Fuerteventura magmas. iv PREFACE The research presented in this study investigates the origin and evolution of Fuerteventura, Canary Islands. Fieldwork was completed by Dr. Larry Heaman and myself with the assistance of previous published literature to guide selection of regions of interest. U-Pb purification of zircon fractions from sample 2016MJ-14 and 2016MJ-34 was completed by Dr. Larry Heaman and James LeBlanc, with ID-TIMS analysis conducted by James LeBlanc. The ideas presented here are my own, although they have been developed and refined by many discussions with my supervisor, Dr. Larry Heaman. All the writing and figures presented here are my own work. v ACKNOWLEDGEMENTS First and most notably, I would like to thank Dr. Larry Heaman for providing such an incredible opportunity to pursue my passion of geology. His unwavering support and encouragement provided the grounds for large-scale thinking that was accompanied by high-quality science. He taught me to question the unknown, write with precision and clarity, and be transparent with all science that is reported. The understanding established in this thesis predominantly lends to Larry’s influential teaching and mentorship. I could not have had a wiser, kinder, supervisor to study under and I feel forever thankful for the opportunity. This study would not have been possible without all the support I received from several individuals at the University of Alberta. Dr. Graham Pearson and Dr. Chiranjeeb Sarkar are thanked for the U-Pb and Hf isotope laser split stream spectrometry maintenance and data. Dr. Andy DuFrane is thanked for the maintenance and prep of the LA-MC-ICPMS and Q-ICPMS data collection and review. Dr. Richard Stern is thanked for providing an opportunity to use the high-quality SIMS facility and the thought- provoking discussions. I would also like to thank the following people for various training, analysis, and logistics associated with this project: Andrew Locock, James LeBlanc, Nathan Gerein, Mark Labbe, Igor Jakab, and Marilyn Huff. Any personal development that has taken place during this experience can be attributed to a variety of friends and colleagues. I would also like to thank the Heaman geochronology research group for training me on the various sample processing and preparation for U-Pb zircon studies. Ilona for providing such great morale and technical support. Alex Sheen for offering moments of clarity on multiple software programs. Alix vi Osinchuk for providing great geological insight and for always offering a coffee break. Mike Belosevic for the great life discussions and added comical relief to my office days. A huge thank you to my husband, Angus, who has always encouraged me to pursue my passion and for his unwavering support. Thank you to my family for always being there for me and to my dear friends outside of my academic world that have always been understanding and supportive. vii TABLE OF CONTENTS ABSTRACT ................................................................................................................................................ II PREFACE ................................................................................................................................................... V ACKNOWLEDGEMENTS ........................................................................................................................... VI TABLE OF CONTENTS ............................................................................................................................. VIII LIST OF TABLES ........................................................................................................................................