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Attrition of Mantle Cargo During Kimberlite Ascent: Insights ATTRITION OF MANTLE CARGO DURING KIMBERLITE ASCENT: INSIGHTS FROM ANALOGUE EXPERIMENTS by DAVID SASSE B.Sc., The University of British Columbia, 2016 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Geological Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) December 2019 © David Sasse, 2019 The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis entitled: Attrition of mantle cargo during kimberlite ascent: Insights from analogue experiments submitted by David Sasse in partial fulfillment of the requirements for the degree of Master of Science in Geological Sciences Examining Committee: James Kelly Russell, Geological Sciences Supervisor Thomas Jones, Geological Sciences Supervisory Committee Member Maya Kopylova, Geological Sciences Supervisory Committee Member Lucy Porritt, Geological Sciences Additional Examiner ii Abstract Kimberlite magmas transport mantle cargo in the form of xenoliths and xenocrysts to the surface of the Earth. Due to the lack of recent kimberlite eruptions and unanswered questions concerning melt composition and magma rheology, the mechanisms supporting efficient ascent of these cargo-rich magmas remains enigmatic. Although olivine is the dominant mineral phase in kimberlite, given the polymineralic nature of mantle xenoliths, xenocrysts are transported as a multi-mineral mixture. Within the ascending dyke, high particle concentrations and high velocities resulting in turbulent flow provides an environment for frequent particle-particle interaction. Xenocryst morphologies, textures and size distributions observed in kimberlite deposits are not reflective of how they occur in xenoliths and are therefore modified during ascent to the surface. The degree of modification of each mineral varies and is a function of its chemical and physical properties. Here I present a series of analogue attrition experiments on the mantle minerals: olivine, orthopyroxene, clinopyroxene, garnet and diamond designed to inform on the ascent of kimberlite magmas. Data is collected on particle size distributions, particle morphologies and particle velocities. Natural xenocrysts extracted from coherent kimberlite reveal remarkably similar surface features and morphologies to that of the experiments suggesting that attrition indeed operates during kimberlite ascent. Kimberlite ascent velocities are estimated by using a scaling analysis of the experiment conditions and by investigating impact pits observed on the surfaces of kimberlitic olivine and garnet xenocrysts. Both methods result in calculated ascent velocities of ~ 4 m s-1. In mineral mixtures, cleavage is shown to be a controlling factor in determining attrition rates whereby minerals with cleavage undergo accelerated breakdown. I suggest that the accelerated breakdown of orthopyroxene increases assimilation rates, contributing to the onset of turbulent ascent. iii Lay Summary Anyone who has walked along a beach, or a dry stream bed will have at some point observed the remarkably well rounded and polished pebbles. These shapes and textures are the result of low energy collisions over long periods of time. Kimberlite is a rock type well known for being the major global source of diamonds. The magma that goes on to form the rock, kimberlite, originates deep in the Earth’s interior and picks up mantle rocks and minerals on its way to surface. The mantle material observed in kimberlites is often anomalously well rounded and just like the pebbles in a stream, began as angular fragments. This study aims to better understand the processes that lead to the observed morphologies in kimberlite and to gain insight into the conditions present during the ascent of kimberlite magma towards the surface. iv Preface This thesis was completed under the supervision of Dr. Kelly Russell and Dr. Thomas Jones who collectively designed the project, offered direction and helped with editing. This dissertation is original, unpublished, independent work by the author, Sasse. D. The project was completed as a requirement of the NSERC CREATE program: Diamond Exploration and Research Training School (DERTS). v Table of Contents Abstract ................................................................................................................................... iii Lay Summary ........................................................................................................................... iv Preface ....................................................................................................................................... v Table of Contents ..................................................................................................................... vi List of Tables ............................................................................................................................ ix List of Figures........................................................................................................................... xi List of Symbols ...................................................................................................................... xvii Acknowledgements ................................................................................................................. xix Chapter 1: Introduction ............................................................................................................ 1 Chapter 2: Background on Attrition ........................................................................................ 6 2.1 Particle Attrition Mechanisms and Applications ...........................................................6 2.2 Applications in Engineering .........................................................................................9 2.2.1 Applications in Chemical Engineering .....................................................................9 2.2.2 Applications in Mining .......................................................................................... 11 2.3 Attrition in Geological Environments......................................................................... 13 2.4 Applications in Volcanology ...................................................................................... 14 2.5 Attrition in Kimberlites .............................................................................................. 17 Chapter 3: Attrition Apparatus for Experiments .................................................................. 23 3.1 Modifications to the Attrition Apparatus .................................................................... 25 3.2 Experimental Conditions............................................................................................ 26 3.3 Scaling the Experiments to the Natural System .......................................................... 29 vi 3.4 Data Collection During and After Experiments .......................................................... 30 3.5 Experimental Grid ..................................................................................................... 34 Chapter 4: Sample Characterization...................................................................................... 36 4.1 Sample Characterization ............................................................................................ 36 4.1.1 Density Measurements ........................................................................................... 36 4.1.2 2D Shape Characterization ..................................................................................... 38 4.1.3 Scanning Electron Microscopy ............................................................................... 40 4.1.4 Summary of Experiments Chosen for Analysis ...................................................... 40 4.1.5 Mineral Properties Summary .................................................................................. 42 Chapter 5: Results and Analysis ............................................................................................. 43 5.1 Attrition of Individual Minerals ................................................................................. 43 5.1.1 Fines Production Datasets ...................................................................................... 43 5.1.2 Grain Size Distributions ......................................................................................... 49 5.1.3 Experiment Observations / Videography ................................................................ 52 5.1.4 Grain Shapes and Surfaces ..................................................................................... 58 5.2 Attrition of Mineral Mixtures ..................................................................................... 72 Chapter 6: Discussion ............................................................................................................. 75 6.1 Transport Duration and Velocity of Kimberlite Ascent .............................................. 75 6.2 Morphology and Surface Features of Coherent Kimberlite Xenocrysts....................... 79 6.3 Mineral Physical Properties Related to Attrition Susceptibility and Mechanisms ....... 84 6.4 Attrition Mechanics ................................................................................................... 86 6.4.1 Abrasion Mechanics..............................................................................................
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