The oxidation state of deeply subducted, altered oceanic crust

307 Pages·2016·25.03 MB·English

The oxidation state of deeply
subducted, altered oceanic crust:
An experimental study and the
evidence from natural samples

Prokopiy Vasilyev

A thesis submitted for the degree of
Doctor of Philosophy of
The Australian National University

May 2016

© Copyright by Prokopiy Vasilyev, 2016

All Rights Reserved
Declaration

This thesis contains the results of research done in Research School of Earth
Sciences, The Australian National University, between 2012 and 2016. All
material presented in thesis is original and has never been accepted or
submitted for the award of any other higher degree or graduate diploma in any
tertiary institution. To the best of author’s knowledge and belief, the thesis
contains no material previously published or written by another person, expect
where otherwise acknowledged.

Prokopiy Vasilyev

Canberra

May 2016
ACKNOWLEDGEMENTS v

Acknowledgements

Firstly, I want to say that I am very grateful to my supervisor – Greg Yaxley. Apart from
being the best supervisor in the world, he is an amazing human being and a brilliant
scientist. This project had a lot of ups and downs and through his great support and
encouragement I was able to go through all of it. Thank you Greg, for being my
supervisor and giving me the opportunity to research this challenging and interesting
project!

Special thanks go to my supervisory panel: Hugh O’Neill, Andrew Berry, Joerg
Hermann. Their guidance, reviews and comments were always extremely helpful.
Hugh helped me a lot with thermodynamic modeling, experiments and understanding
the value of oxygen fugacity. I am thankful to Andrew for taking me to Australian
Synchrotron and performing XANES experiments despite the puzzling nature of
eclogite garnets.

I am very thankful to Heidi Höfer, for introducing me to her “flank” method and
applying it to experimental and natural samples (this sentence needs to change).
Without precise and accurate measurements of ferric to total iron ratios, I would never
be able to calibrate the oxybarometer reactions. I also want to thank other people in
Goethe University, especially Alan Woodland for his support and for Mössbauer
measurements of eclogite garnet standards. Thanks to Anja Rosenthal for
collaboration in developing those standards; to Richard Arculus for supplying some
African eclogite xenolith samples, to Andrei Korsakov for the unique samples of
kyanite-bearing eclogite xenoliths and to Dmitri Zedgenizov for many eclogite xenoliths
from Udachanya kimberlite pipe.

Many thanks go to my colleagues in the experimental petrology laboratory. I would
never have been able to conduct all my experiments without technical support of
vi ACKNOWLEDGEMENTS

David Clark, Dean Scott and David Cassar. Thank you for helping me with trying out
new experiments, new designs and for teaching me how to be true a experimentalist.
I also want to thank the team from the Centre of Advanced Microscopy at the
Australian National University, especially Frank Brink and Hua Chen for helping me
with measuring and taking beautiful BSE images on SEM. With their guidance and
discussions I was able to process all data and improve my understanding of
quantitative analysis. I want to thank Harri Kokkonen for helping me with make the
impossible possible. Without your help I would never been able to perform ultra-thin
polishing on such a challenging experimental samples. Big hugs to Ulli Troitzsch first of
all for XRD courses and, more importantly, helping me with XRD measurements,
including trying a “guerilla” technique of reflective scanning on experimental samples.
I want to thank David Paterson from XFM beam line of Australian Synchrotron for
being so supportive and helping us with our XANES measurements.

Special thanks go to RSES team of amazing staff. From the first email I sent prior to
enrolment to the last day of my PhD, I received endless support from the best HDR
student coordinator - Maree Coldrick. Many thanks to Josephine Magro for being an
amazing group administrator. Without you I would never be able to solve the
bureaucratic problems that come with being Russian citizen abroad J. Eric Ward,
thank you for hiring me as “delivery boy” of RSES for the last few months of my PhD
and being such a cool man. I want also to thank the IT team of RSES (especially Duncan
Bolt) for bringing my laptop back from the despair of the blue screen of death. And
many thanks to other members of RSES who helped and supported me all these years:
Mary Anne King, Mary Hapel, Joy McDermid and others. I want to specially thank
Penny King and Steve Eggins for giving me the opportunity to demonstrate for the Blue
Planet course so many times.
ACKNOWLEDGEMENTS vii

I am very grateful to Sue Kesson for rewarding me with her travel grant and the kind
words and support I received from her afterwards. I want also to say thank you to
former Vice Chancellor of ANU, Ian Young, for a travel grant that I spent to attend a
conference in Italy.

And special thanks go to Katy Evans, my first “grown up life” boss. Thanks a lot, Katy,
for believing in me and offering post doc position even before I finished my PhD.

I really want to thank my friends from RSES. The incredible Kate Holland -
housemate/colleague/friend, I will miss your loud laugh and beautiful smile. Yoga
goddess Ali Kimbrough and her talented fiancé Daniel Becker, thank you for your
friendship and your support for last few difficult months of my PhD. My “French crew”:
Antoine Benard and Marion Louvel, I will see you soon in Yokohama and we need to
finish the paper Antoine J. My officemate and close friends Paolo Sossi and Jason
Doull, it was great few years with you guys and thank you for helping me to adapt to
the Australian reality and guiding me through classic British humor. Patrick Goodarzi,
thanks a lot for your support and help, buddy. Kate Kiseeva, thank you for recruiting
me during an IMA meeting in Budapest, you were my example for persistence and
productivity. My dear Shannon Avalos, the most beautiful creature of the RSES team, I
hope you are enjoying South America. My “big brother” in experimental petrology,
Jeremy Wykes, thank you for all you support and all technical discussions we had. And
I want to thank guys for being my friends for all these years: Piers, Thomas, James,
Tazz, Oliver, Yana, Arina, Swiss Chris, Shayne and others. Special thanks to my climbing
crew for unforgettable moments in Yosemite, Arapiles and all other Australia, Ben
Young, Suzanne Marselies and others.

I want to address my very special thanks to my parents for all their endless support
and love. Finally my greatest thanks to Mitchell Platt, for being with me and being
willing to go with me to new adventures in Perth.
viii ABSTRACT

Abstract

Eclogitic xenoliths from kimberlites are occasionally diamond-bearing, and are often
interpreted as having an origin as subducted oceanic crust. The existence of diamonds
in these rocks constrains equilibrium temperatures and pressures of some eclogites to
the upper mantle. However the additional critical parameter controlling the stability of
diamonds, oxygen fugacity (ƒO ), is poorly constrained in eclogitic assemblages.
2

A series of piston-cylinder experiments were conducted using model carbonate and
kyanite bearing eclogite assemblages to determine the ƒO of the limiting reaction for
2
graphite vs. diamond:
CaMg(CO ) + 2SiO = CaMgSi O + 2C + 2O
3 2 2 2 6 2
as a function of pressure (P=3.5-6 GPa) and temperature (T=900-1300oC).
The oxygen fugacity in the experiments was determined using Fe-Ir alloy ƒO sensors
2
and a newly developed Fe-Pd-based redox sensor for high-pressure experiments. The
experimental data allowed calibration of two redox reactions (involving garnet-
clinopyroxene and garnet-kyanite) as oxybarometers to determine ƒO of eclogitic
2
rocks. Both reactions can be used to evaluate the ƒO2 of UHP metamorphic eclogites
and eclogite xenoliths from kimberlites.

The accuracy of the calculated ƒO is highly dependent on precision of the garnet
2
Fe3+/ΣFe measurements, which were obtained using the flank method and the
synchrotron based Fe K-edge XANES method. Both reactions were calibrated and used
to estimate ƒO of diamond, kyanite and coesite bearing eclogite xenoliths from
2
Udachnaya kimberlite pipe, Yakutia, Russia. The relatively high ƒO2 of diamond stability
in eclogite relative to peridotite at the upper mantle PT conditions may explain the
higher abundance of diamonds in eclogite xenoliths and constrains the mechanism of
transport of carbon to the deep mantle.
DEFINITIONS ix

Definitions

Acronyms

BSE – Back-Scattered Electrons
DCDD/G – Dolomite-Coesite-Diopside-Diamond/Graphite Reaction
EDS – Energy Dispersive X-Ray Spectroscopy
EMFDD/G – Enstatite-Magnesite-Forsterite-Diopside-Diamond/Graphite Reaction
EMOD/G – Enstatite-Magnesite-Olivine- Diamond/Graphite Reaction
FMQ – Fayalite-Magnetite-Quartz Reaction
FsMC – Ferrosilite-Magnetite-Coesite Reaction
IW – Iron-Wüstite Reaction
MORB – Mid-Ocean Ridge Basalts
SE – Secondary Electrons
SEM – Scanning Electron Microscopy
WDS – Wave Dispersive X-ray Spectroscopy
XANES – X-ray Absorption Near Edge Structure
XFM – X-ray Fluorescence Microscopy
XRD – X-ray Diffraction

Selected list of abbreviations and symbols

Carb – carbonate
Coes – coesite
Cpx – clinopyroxene
D – diamond
x DEFINITIONS

Dol – dolomite
G – graphite
Grt – garnet
Ky – kyanite
Mag – magnesite
Ol – olivine
Opx – orthopyroxene
{Hed} – hedenbergite-based oxybarometer reaction
{Ky} – kyanite-based oxybarometer reaction
{sensorHed} – hedenbergite-based redox reaction of noble metal alloys sensor
{sensorKy} - kyanite-based redox reaction of noble metal alloys sensor
a – activity of the component i in a solution
i
G and G – total and molar Gibbs (free) energy of a solution, respectively
m
G – the Gibbs (free) energy of reaction
r
G – partial Gibbs (free) energy of component i
i
R – Universal gas constant
W – Margulis parameter of subregular solution of components i and j
ij
X – mole fraction of a component i
i
ƒO – oxygen fugacity
2
γ – activity coefficient of component i
i
a.p.f.u – atoms per formula unit
mol% - molar percent
σ – standard deviation
wt% - weight percent