Holmes, Samuel John (2019) the Pre-Depositional History of the Applecross Formation, Northwest Highlands, Scotland
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Holmes, Samuel John (2019) The pre-depositional history of the Applecross Formation, Northwest Highlands, Scotland. MSc(R) thesis. http://theses.gla.ac.uk/41219/ Copyright and moral rights for this work are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This work cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Enlighten: Theses https://theses.gla.ac.uk/ [email protected] The pre-depositional history of the Applecross Formation, Northwest Highlands, Scotland. Samuel John Holmes BSc (Hons) Submitted in fulfilment of the requirements for the Degree of Master of Science School of Geographical and Earth Sciences College of Science and Engineering University of Glasgow November 2018 Abstract The provenance of Applecross Formation sedimentary rocks (Torridon Group, Northwest Scotland) is a topic of significant debate owing to difficulties in clearly correlating various datasets for the region (detrital mineral studies, sedimentology, and palinspastic restorations) to create an accepted palaeogeographic reconstruction. This study aims to elucidate the source area of Applecross sedimentary rocks and modes of deposition and transportation. LA-ICP-MS 206Pb/238U dating of detrital zircon samples from various stratigraphic levels within the Applecross Formation type area is utilised to assess variations in the source over time. Sampling is spread through ~2000m of stratigraphy, along a ~15km outcrop parallel transect between Applecross and Loch Kishorn. Data reduction is undertaken using Iolite data reduction software. U-Pb detrital zircon peaks of Mesoproterozoic (1280-1520Ma) and late Palaeoproterozoic (1680-1980Ma) age are dominant throughout the Applecross Formation. Minor early Palaeoproterozoic (2191-2265Ma) and Archean components up to 3346±43Ma are present. These data are in broad agreement with detrital zircon data from elsewhere in the Applecross Formation presented by Rainbird, Hamilton and Young (2001) and Krabbendam et al. (2017), suggesting a uniform input of well mixed sediment from a single source. Terranes in the foreland basin of the Grenville Orogen are favoured as source areas, with transport in an orogen axial foreland trunk system. Detrital Zircon U- Pb geochronology is combined with sedimentological context to determine depositional style. Deposition is interpreted to occur in a large scale distributive system similar to the Okavango Delta, Botswana, with unconfinement occurring during an extensional phase of the Grenville Orogen associated with rotation of Baltica relative to Laurentia at the time of deposition (see Rivers, 1997; Cawood et al., 2007). This proposal correlates known detrital mineral and sedimentological datasets. Further work is required to support the model; additional detrital zircon datasets are required to confirm the validity of a single sediment input. Further evidence for localised extension in the Applecross region is required to substantiate unconfinement of an established foreland trunk river system. I Chapter 1-Introduction Table of Contents The pre-depositional history of the Applecross Formation, Northwest Highlands, Scotland. ...................................................................................... I Abstract ....................................................................................... I List of Tables and Figures ................................................................. VI Acknowledgements ....................................................................... VIII Author’s Declaration ....................................................................... IX Chapter 1 Introduction .................................................................. 1 1.1 Objectives ......................................................................... 1 1.2 Setting .............................................................................. 2 1.3 Detrital zircon geochronology .................................................. 6 1.4 Previous work ..................................................................... 7 1.5 Rodinia configuration ........................................................... 11 1.6 Grenville configuration and basements ...................................... 14 1.6.1 Rockall Plateau ............................................................. 18 1.7 Palaeocurrents and sedimentology ........................................... 19 1.7.1 Torridon Group setting ..................................................... 19 1.7.2 Diabaig Formation .......................................................... 20 1.7.3 Applecross Formation ...................................................... 20 1.7.4 Aultbea Formation .......................................................... 21 1.7.5 Cailleach Head Formation ................................................. 21 Chapter 2 Methodology ................................................................. 22 2.1 Preliminary fieldwork and sample collection ................................ 22 2.1.1 Study area ................................................................... 22 2.1.2 Sampling regime ............................................................ 22 2.2 Laboratory protocol ............................................................. 23 2.2.1 Mineral separation .......................................................... 23 2.2.1.1 Crushing ................................................................. 23 2.2.1.2 Washing ................................................................. 23 II Chapter 1-Introduction 2.2.1.3 Sieving ................................................................... 23 2.2.1.4 Magnetic separation ................................................... 23 2.2.1.5 Density separation ..................................................... 25 2.2.1.6 Sample assessment, picking, and mounting ....................... 25 2.2.2 Analysis ....................................................................... 27 2.2.2.1 SEM cathodoluminescence and secondary electron imaging .... 27 2.2.2.2 Sample mapping ....................................................... 28 2.2.3 Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA- ICP-MS) 29 2.2.3.1 Laser setup ............................................................. 29 2.2.3.2 ICP-MS setup ............................................................ 30 2.2.3.3 Standards ............................................................... 31 2.2.4 Data reduction .............................................................. 31 2.2.4.1 Kernel density estimates and probability density plots .......... 33 Chapter 3 Results........................................................................ 36 3.1.1 Zircon textures in Cathodoluminescence ............................... 36 3.1.1.1 Zoning ................................................................... 36 3.1.1.2 Metamorphic overgrowths ............................................ 36 3.1.1.3 Metamictization ........................................................ 37 3.1.1.4 Fracturing ............................................................... 37 3.1.1.5 Inclusions ............................................................... 37 3.1.1.6 Ablation pit morphology .............................................. 37 3.1.2 Plesovice Zircon standards ................................................ 38 3.1.2.1 Standards data ......................................................... 38 3.2 LA-ICP-MS ages: Applecross Peninsula ........................................ 39 3.2.1 Kernel Density Estimates (KDE) ........................................... 39 3.2.1.1 SA2 – SA 3.1 ............................................................. 39 3.2.1.2 SA4 - SA7 ................................................................ 40 3.2.1.3 SA5 ....................................................................... 41 III Chapter 1-Introduction 3.2.1.4 SA8 ....................................................................... 42 3.2.1.5 SA10 - SA21C ........................................................... 43 3.2.2 Stratigraphic succession ................................................... 44 3.2.2.1 Age variation through stratigraphy .................................. 48 3.2.2.2 Age variation through stratigraphy summary ...................... 54 3.3 Ablation spots .................................................................... 56 3.3.1 Ablation sites ................................................................ 56 3.3.2 Table of ablated spots ..................................................... 57 3.3.3 Analysis quality ............................................................. 58 Chapter 4 Discussion .................................................................... 61 4.1 Detrital zircon age data ........................................................ 61 4.2 Source areas ...................................................................... 67 4.2.1 Archean-early Palaeoproterozoic ........................................ 69 4.2.2 Palaeoproterozoic .......................................................... 69 4.2.3 Early Mesoproterozoic age gap ..........................................