Geochemistry & Mineralogy of Fluvial Sediments in the Southern Alps, New Zealand

220 Pages·2017·11.83 MB·English

UUnniivveerrssiittyy ooff WWoolllloonnggoonngg
RReesseeaarrcchh OOnnlliinnee
Faculty of Science, Medicine & Health - Honours
University of Wollongong Thesis Collections
Theses
2012
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ZZeeaallaanndd
Emma Marie Kiekebosch‐Fitt
University of Wollongong
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RReeccoommmmeennddeedd CCiittaattiioonn
Kiekebosch‐Fitt, Emma Marie, Geochemistry & Mineralogy of Fluvial Sediments in the Southern Alps, New
Zealand, Bachelor of Science (Honours), School of Earth & Environmental Science, University of
Wollongong, 2012.
https://ro.uow.edu.au/thsci/32
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contact the UOW Library: [email protected]
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AAbbssttrraacctt
Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand
long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to
investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to
either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being
highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has
been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry
of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate
the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of
chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this
study has been undertaken to improve the understanding of the response of chemical weathering to uplift
and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments.
Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while
geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic
analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is
predominantly occurring within the weathering profile. In contrast, weathering during transport in the
fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining.
Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its
depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High
uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the
weathering profile. The extent of chemical weathering is consequently inhibited, whereby only the most
mobile elements are depleted. Therefore, the Southern Alps are classified as a weathering limited setting,
where the intensity of chemical weathering is largely controlled by the residence time of sediments
(uplift) and rainfall.
DDeeggrreeee TTyyppee
Thesis
DDeeggrreeee NNaammee
Bachelor of Science (Honours)
DDeeppaarrttmmeenntt
School of Earth & Environmental Science
AAddvviissoorr((ss))
Tony Dosseto
KKeeyywwoorrddss
u-series, Sr isotopes, uplift
This thesis is available at Research Online: https://ro.uow.edu.au/thsci/32
UNIVERSITY OF WOLLONGONG 
Geochemistry & 
Mineralogy of Fluvial 
Sediments in the           

Southern Alps, NZ
The Influence of Climate & Tectonics on 
Chemical Weathering   

Emma Marie Kiekebosch‐Fitt 
10th October, 2012 

Submitted in part fulfillment of the requirements of the Honours degree of Bachelor of Science 
(Advanced) in the School of Earth and Environmental Sciences, University of Wollongong 2012
The information in this thesis is entirely the result of investigations conducted by the 
author, unless otherwise acknowledged and has not been submitted in part, or 
otherwise, for any other degree or qualification. 

Emma Kiekebosch‐Fitt 
10/10/2012
i
Acknowledgements 
I would like to extend my thanks to the numerous people who generously assisted 
me throughout the various life stages of my study. Without such assistance I would 
not have been able to undertake this study and for that I am grateful. I would firstly 
like to acknowledge, and give special thanks, to my supervisor Dr. Anthony Dosseto. 
Your guidance, expertise, enthusiasm, patience and feedback have been invaluable 
and I appreciate the time you spent introducing me to the research world. 
Furthermore, I would like to thank Associate Professor Brian Jones and Dr. Samuel 
Marx, for sharing valuable knowledge that aided in the development of my study.   
Thank you to all of the supporting staff at the School of Earth and Environmental 
Sciences, University of Wollongong, particularly José Abrantes and Michael Stevens. 

To all my fellow honours students, whom I shared long days of laughter, tears, 
encouragement, chocolate and tea with, you have been such an amazing support 
network. To my friends and family, thank you for your continual support and 
encouragement, while helping me to keep life in perspective. Lastly to Dave, thank 
you for everything, you finally have the old me back! 

ii
Abstract 
Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In 
order to understand long‐term climate change and the fluctuations in atmospheric 
carbon dioxide, it is paramount to investigate the regulators of chemical weathering. 
The controls of rainfall and uplift have been reported to either enhance or inhibit the 
extent of chemical weathering, and therefore their relationship is still being highly 
debated in literature. Investigation of this relationship in the Southern Alps of New 
Zealand has been modest in comparison to the Himalayas. These studies have either 
focused on solute geochemistry of rivers, and therefore do not integrate weathering 
history of the catchment, or have failed to investigate the interplay between the 
controls of uplift and precipitation.  

Fluvial sediments record conditions of chemical weathering at the catchment scale, 
whilst integrating its weathering history. Therefore, this study has been undertaken 
to improve the understanding of the response of chemical weathering to uplift and 
precipitation in the Southern Alps, utilising the geochemistry and mineralogy of 
fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction 
and optical microscopy, while geochemical techniques included X‐ray fluorescence, 
uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest 
that modern chemical weathering is low to moderate and is predominantly occurring 
within the weathering profile. In contrast, weathering during transport in the fluvial 
system appears to be dominated by physical abrasion, which contributes to 
downstream fining. Furthermore, 238U was shown to be leached with increased 
residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, 
rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the 
western coast, increase erosion and therefore reduce sediment residence time in the 
weathering profile. The extent of chemical weathering is consequently inhibited, 
whereby only the most mobile elements are depleted. Therefore, the Southern Alps 
are classified as a weathering limited setting, where the intensity of chemical 
weathering is largely controlled by the residence time of sediments (uplift) and 
rainfall.  
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Table of Contents 
Acknowledgements ....................................................................................................................ii 
Abstract ........................................................................................................................................ iii 
Table of Contents ....................................................................................................................... iv 
List of Figures ............................................................................................................................ vii 
List of Tables ............................................................................................................................ xix 
Chapter One: Introduction ...................................................................................................... 1 
1.1 Silicate Weathering – A Sink for CO  ....................................................................................... 1 
2
1.2 Main Factors Influencing Silicate Weathering .................................................................... 4 
1.3 Aims and Objectives ....................................................................................................................... 6 
Chapter Two: Literature Review ........................................................................................... 8 
2.1 Sediment Composition & Geomorphology ........................................................................... 8 
2.2 Sediment Composition & Chemical Weathering ................................................................ 9 
2.3 Elemental Ratios & Mobility ..................................................................................................... 10 
2.4 Chemical Weathering Indices ................................................................................................... 12 
2.4.1 Weathering Index of Parker ............................................................................................. 13 
2.4.2 Chemical Index of Alteration ............................................................................................ 14 
2. 5 Isotopic Fractionation & Chemical Weathering .............................................................. 16 
2.5.1 Strontium‐ Isotopes .............................................................................................................. 16 
2.5.2 Uranium‐ Series ..................................................................................................................... 17 
Chapter Three: Regional Settings ...................................................................................... 21 
3.1 Tectonic Setting .............................................................................................................................. 21 
3.2 Geology of the South Island ....................................................................................................... 24 
3.2.1 Torlesse Terrane ................................................................................................................... 25 
3.2.2 Buller Terrane ‐ Haast Schist ........................................................................................... 28 
3.3 Climate ........................................................................................................................................... 28 
3.4 Physical Erosion ............................................................................................................................. 30 
3.5 Hydrology ......................................................................................................................................... 30 
3.6 Vegetation ......................................................................................................................................... 30 
3.7 Catchment Settings ....................................................................................................................... 31 
iv
3.7.1 Catchments Draining Pahau Torlesse Terrane ......................................................... 33 
3.7.2 Catchments Draining Rakaia Torlesse Terrane ....................................................... 37 
3.7.3 Catchments Draining Haast Schist ................................................................................. 41 
Chapter Four: Methods .......................................................................................................... 45 
4.1 Site Selection and Sampling Technique ............................................................................... 45 
4.2 Sample Pre‐Processing ................................................................................................................ 45 
4.3 Grain Size Analysis ........................................................................................................................ 46 
4.4 Petrological Analysis .................................................................................................................... 47 
4.5 Mineralogical Analysis ................................................................................................................ 47 
4.6 Major and Trace Elemental Analysis ..................................................................................... 48 
4.7 Loss on Ignition .............................................................................................................................. 51 
4.8 Isotopic Analysis ............................................................................................................................ 51 
4.9 Geospatial Analysis ....................................................................................................................... 55 
4.9.1 Defining Sample Catchment Areas ................................................................................. 55 
4.9.2 Distance from Headwaters ................................................................................................ 57 
4.9.3 Average Annual Temperature and Rainfall................................................................ 57 
4.9.4 Average Uplift Rates ............................................................................................................. 57 
4.9.4 Simplifying Regional Geological Map ........................................................................... 58 
4.10 Statistical Analysis ...................................................................................................................... 58 
Chapter Five: Results & Discussion ................................................................................... 59 
5.1 Mineralogical and Geochemical Analysis of Grain Size Fractions ............................ 59 
5.1.1 Mineralogy ............................................................................................................................... 59 
5.1.2 Geochemistry .......................................................................................................................... 62 
5.2 Grain Size Analysis ........................................................................................................................ 68 
5.3 Mineralogy ........................................................................................................................................ 72 
5.3.1 X‐ray Diffraction Analysis .................................................................................................. 72 
5.3.2 Petrology ‐ Thin Section Analysis ................................................................................... 77 
5.4 Major and Trace Geochemical Analysis ............................................................................... 86 
5.4.1 Source Rock Composition .................................................................................................. 86 
5.4.2 Elemental Ratios .................................................................................................................... 88 
5.4.3 Major Elements ...................................................................................................................... 90 
5.4.4 Trace Elements – Sr, Ba, Rb & U ................................................................................... 101 
5.4.5 Weathering Indicies – CIA & WIP ................................................................................ 107 
5.4.6 Elemental Ternary Diagrams ........................................................................................ 109 
v
5.5 Sr‐Series Isotopes ....................................................................................................................... 114 
5.6 U‐ Series Isotopes ....................................................................................................................... 118 
Chapter Six: Weathering in the South Island and the Role of Climate and 
Tectonics ................................................................................................................................... 123 
6.1 Where is Weathering Occurring? ........................................................................................ 123 
6.1.1 Chemical Weathering Trends ........................................................................................ 123 
6.1.2 Intensity of Chemical Weathering ............................................................................... 132 
6.1.3 Physical Weathering Trends ......................................................................................... 134 
6.2 Climate, Tectonics & Weathering ........................................................................................ 136 
6.2.1 Rainfall & Physical Weathering .................................................................................... 136 
6.2.2 Rainfall & Chemical Weathering .................................................................................. 137 
6.2.3 Uplift & Chemical Weathering ...................................................................................... 144 
Chapter Seven: Conclusions, Limitations & Perspectives ....................................... 146 
7.1 Conclusions ................................................................................................................................... 146 
7.2 Limitations & Perspectives ..................................................................................................... 148 
References ................................................................................................................................ 149 
Appendices .............................................................................................................................. 156 
Appendix A: Grain size Fraction Data ....................................................................................... 157 
Appendix B: Grain Size Data .......................................................................................................... 160 
Appendix C: Mineralogical Data – X‐ray Diffraction ........................................................... 161 
Appendix D: Mineralogical Data – Thin Section Point Count .......................................... 163 
Appendix E: Major and Trace Geochemical Data ................................................................. 165 
Appendix F: Sr Isotopic Data ......................................................................................................... 170 
Appendix G: U‐series Data .............................................................................................................. 171 
Appendix H: Normalised Mobile Elemental Ratios versus Uplift .................................. 172 
Appendix I: Normalised Mobile Elemental Ratios versus Rainfall ............................... 174 
Appendix J: Thin Section Descriptions ..................................................................................... 175 
Appendix K: Petrology Photos ...................................................................................................... 184 
vi
List of Figures 
Figure 1: Diagram of the uranium‐238 decay series in a proton number (Z) versus 
neutron number (N) (Dosseto et al. 2008). .................................................................................... 18 
Figure 2: Schematic diagram of recoil ejection of 234Th from a spherical grain as a 
result of alpha decay of 238U, followed by beta decay of 234Th to 234U (Dosseto et al. 
2008). .............................................................................................................................................................. 20 
Figure 3: Tectonic setting of New Zealand, showing subduction trenches to the north‐
east and south‐west and the transverse Alpine Fault connecting the two trenches 
(Williams, 1991). ....................................................................................................................................... 21 
Figure 4: Late Quaternary annual uplift contour map of New Zealand (Williams, 
1988). .............................................................................................................................................................. 23 
Figure 5: Tectonostratigraphic terranes that have been identified in South Island, 
New Zealand (University of Otago, 2011). ..................................................................................... 24 
Figure 6: Schematic representation of deposition of the Pahau Terrane. The PF 
numbers represent Torlesse petrofacies. Arrows demonstrate erosion and 
subsequent deposition. PF4 is derived from PF1‐PF3. Pahau source includes all 
Rakaia petrofacies, the volcanogenic terranes to the west and the intervening Haast 
Schist terrane.(Roser & Korsch 1999) ............................................................................................. 26 
Figure 7: Map of central and southern New Zealand showing distribution of major 
geologic divisions, Torlesse sub‐terranes and Torlesse petrofacies (Roser & Korsch 
1999). .............................................................................................................................................................. 27 
Figure 8: New Zealand mean annual (A) rainfall and (B) temperature based on the 
period 1971 ‐ 2000 (NIWA, 2003). .................................................................................................... 29 
Figure 9: Prominent land use map of New Zealand (NZMAF, 2006) .................................. 31 
Figure 10: Simplified geological map of the Conway catchment, South Island, New 
Zealand. Drainage boundary is shown by the red line and the sampling location by 
the asterisk. Modified from Nathan (1993). .................................................................................. 34 
Figure 11: Simplified geological map for the north‐east region of the South Island, 
New Zealand. Drainage boundary is shown by the solid lines and the sampling 
locations by the asterisk. Modified from Nathan (1993). ........................................................ 35 
vii