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This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Ituarte, Lia S Title: Exploring differential erosion patterns using volcanic edifices as a proxy in South America General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. Exploring differential erosion patterns using volcanic edifices as a proxy in South America Lia S. Ituarte A dissertation submitted to the University of Bristol in accordance with the requirements for award of the degree of Master by Research in the Faculty of Science, School of Earth Sciences, October 2020. 61425 words Abstract Porphyry Copper Deposit (PCD) exploration faces a challenging future, since promising areas for exploration are buried. PCDs form at kilometres depth, while volcanoes are the surface expression of extensive magmatic systems. Although not all volcanoes generate PCDs, it may be that all PCDs formed under a volcanic centre. As there are no complete magmatic-volcanic profiles available, I study the distribution of the exposed magmatic-volcanic portions. In this study, I compile eruption, volcano and PCD data for the Andes and then develop a tool to identify favourable areas for finding porphyries close to the surface. This methodology, however, does not distinguish enriched from barren porphyries, nor detect the intensity of the mineralization. My results show when exploring for PCDs, high prospectivity areas are the eroded and remaining edifices of inactive stratovolcanoes. They also show that volcano erosion and PCD exposure in the Andes depend strongly on climate. There is a negative correlation between height and more humid climate for Pre- Quaternary edifices and, as the number of volcanoes drops with wetter conditions, the numbers of mineralised deposits rise. This trend of reduced number and height of edifices continues towards extreme latitudes, as well as close to the current Chilean coastline, the Intermediate depression and Precordillera. This suggests a strong erosion gradient increasing towards the south and west of the Andes. The Arica Bend region and the Precordillera are areas of great importance, since they reflect the greatest exhumation in the Andes by exposing mineralised intrusions, therefore it becomes enormously relevant distinguishing these regions of high-erosion (South Peruvian Cordillera) from low-erosion (Altiplano plateau). Geomorphology is a promising tool for finding PCDs, since paleosurfaces could protect and preserve mineralised intrusions, while coupled mechanisms (tectonic uplift and climate) may facilitate the exposure of PCDs by river incision or rotational landslides. 2 Dedication To my family, without whom none of my achievements would have been possible. 3 Acknowledgements I want to thank BHP for the financial support and the information provided during the database creation stage, also to Thiago Oliveira (BHP) and Cam McCuaig (BHP) for their collaboration, constant feedback and enthusiasm on my results. I would also like to thank Laura Evenstar and Anne Mather for plenty of discussions and for showing me how to fall in love of Geomorphology. Especial thanks to Laura, who reviewed some chapters of my thesis. Finally, I am profoundly grateful to my supervisor, Alison Rust, who went far and beyond her responsibilities, motivated me with her extensive knowledge in volcanology during these years and encouraged me to finish this work. 4 Author’s declaration I declare that the work in this dissertation was carried out in accordance with the requirements of the University's Regulations and Code of Practice for Research Degree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate's own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. 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DATE: .......................... 5 Table of Contents Exploring differential erosion patterns using volcanic edifices as a proxy in South America .... 1 Abstract ...................................................................................................................................... 2 Dedication .................................................................................................................................. 3 Acknowledgements .................................................................................................................... 4 Author’s declaration .................................................................................................................. 5 1 Chapter 1: Introduction .................................................................................................... 13 1.1 Comparing PCDs against modern volcanoes ....................................................................... 14 1.1.1 Eruptive and fertile periods versus dormancy and barren epochs ............................................... 22 1.1.2 Timing: PCD development and volcanic activity ........................................................................... 24 1.1.3 Distribution of volcanoes and PCDs .............................................................................................. 26 1.2 The Andes ............................................................................................................................ 26 1.2.1 Evolution of the Andes: tectonics, climate, erosion and magmatism .......................................... 26 1.2.2 Magmatism ................................................................................................................................... 28 1.2.3 Tectonics ....................................................................................................................................... 30 1.2.3.1 Uplift during Eocene to Oligocene ............................................................................................ 31 1.2.3.2 Uplift during Oligocene to present day .................................................................................... 32 1.2.3.3 The Bolivian Orocline................................................................................................................ 33 1.2.3.4 Precordillera region .................................................................................................................. 34 1.2.3.5 Tectonic Segments ................................................................................................................... 35 1.2.3.6 Sediment control on subduction plate speeds .......................................................................... 35 1.2.3.7 Crust Destruction and Mass Wasting ....................................................................................... 39 1.2.4 Climate .......................................................................................................................................... 39 1.2.4.1 Summary of the climate control in the Andes .......................................................................... 39 1.2.4.2 Summary of the climate in the western Andes ........................................................................ 40 1.2.4.3 Summary of the climate in the eastern Andes ......................................................................... 41 1.2.5 Erosion .......................................................................................................................................... 42 1.2.6 Surface evolution of volcano edifices ........................................................................................... 49 1.2.6.1 Stratovolcanoes morphometric model ..................................................................................... 49 1.2.6.2 Evolution model for the degradation for Central Andean volcanoes ....................................... 50 1.2.7 Porphyry deposits in the Andes .................................................................................................... 52 1.2.7.1 PCDs exhumation ..................................................................................................................... 52 1.2.7.2 PCDs types and relation to depth of formation ........................................................................ 53 1.3 Summary .............................................................................................................................