Lihir-Tanga-Feni Arc, Pa

359 Pages·2016·27.67 MB·English

A petrological study of peridotite & pyroxenite
xenoliths from the West Bismarck Arc and the Tabar-
Lihir-Tanga-Feni Arc, Papua New Guinea

Sarlae Ruth Buffett McAlpine

December 2015

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

Declaration of Originality

The work presented in this thesis was carried out at the Research School of Earth Sciences,
Australian National University. I certify that this thesis contains no material that has been
accepted for any degree or diploma at any university. This thesis is a product of my own original
research and the words contained within are my own, except where otherwise acknowledged.

Sarlae R. B. McAlpine

4 December 2015

Acknowledgements

To my primary supervisor, Professor Richard John Arculus, I give a most sincere thank
you. It has been a wonderful journey. I am grateful for your brilliance, your patience, the
travel, our discussions. Thank you for providing me with such a beautiful sample suite, and
the opportunity to dabble in the fantastically complex world of arc petrology.

I am lucky enough to have had an all-star supervisory panel. Thank you to Professor Hugh
St. Clair O’Neill, Professor Jonathan Blundy, Associate Professor Gregory Yaxley, Dr
Frances Jenner and Dr Oliver Nebel. It was very meaningful to take so many of you home
to my beautiful Norfolk Island, and to bring back so much of the basalt on our return.

To Mervyn and the late Katalin Patterson, thank you for your continuing support of RSES
students in the form of your Travel Fellowship, which I was extremely fortunate to be
awarded. With this support I was able to spend an exceptional three months at Bristol
University with Prof. Blundy where I received superb scientific challenges, hospitality at
Blundy Towers, and the loan of the world’s squeakiest pushbike. I would also like to extend
a thank you to Stuart Kearns for microprobe support, and Charly Stamper for her
friendship and shandies. Thank you to Nicola Corkin and Phillip Pogge von Strandmann
for feeding me many a night, and introducing me to Exhibition Cider at the Cori-tap.

A very big thank you to Antoine Bénard for much discussion, and the finessing of many
petrological ideas. You arrived at the perfect time of my studies, and it has been a pleasure
working with you. Thank you to Lynton Jaques for encouraging me in my efforts to
understand one of the world’s most complex regions. And thank you to Kelly Strzepek for
your time and encouragement.

To Maree Coldrick, you are a delight, and make every day of being a student a little bit
brighter. To Kay Provins, Mary, Josephine, and all of the administrative support, thank
you. To Ulli Troitzsch, Nigel Craddy and John Vickers, your scientific and technical
expertise was so gratefully received. I have good memories of weighing powders, cutting,
and epoxying rocks. To Andy Christie, thank you for an invaluable hour on the microscope.

To my dear PhD friends, Iona Stenhouse, Tomas O’Kane, Kate Boston, Clemens Augenstein
and Paul Stenhouse. Hurrah! We made it! To my housemates (Danielle, Meg, Kate, Jenna,
Anna) and officemates (Kate Kiseeva, Claire Krause), thank you for the tea and chocolate.

To the Australian National University, what a wonderful undergraduate, honours and
postgraduate experience. To my Geology lecturers, Richard Arculus, David Ellis, Stephen
Cox, Bear McPhail, Patrick DeDecker, Bradley Opdyke and John Mavrogenes. To my
Chemistry lecturers, Mark Ellison, Geoff Salem, Rob Stranger and Germain Cavaglissio. It
was an honour being taught by you all, thank you, I have had very happy university days.

To those at Geoscience Australia, particularly Dr Clinton Foster, Dr Richard Blewett and
Team Stavely. Thank you for giving me your full support, and time for the completion of
writing. I look forward to a very rewarding scientific career with you.

To my dearest Tarun Whan, you gave me so much time, support, cooked me delicious
dinners, and taught me so very much. You are the best partner a scientist could hope for.

Lastly, and especially, to my darling Mother and Father, who followed me around the
world. Thank you for everything. x

Abstract

Some of the most refractory peridotite samples described in the literature
comprise clasts up to 15 cm in size, hosted in satellite cones of Ritter Volcano in the
West Bismarck Arc, Papua New Guinea. Host lavas are MgO-rich (13.9-16.6 wt%),
mostly non-accumulative picritic tholeiites, representing the most primitive
magma types in the region. The lava can be divided into two distinct geochemical
groups: a low-Ti series (TiO 0.25-0.3 wt%) and a high-TiO series (TiO 0.4-0.45
2 2 2
wt%).

This thesis documents the chemical composition and mineralogy of the
picritic hosts and peridotite suite of Ritter, and compares the latter with a
peridotite suite from the Tubaf Seamount in the Tabar-Lihir-Tanga-Feni Arc of
Papua New Guinea.

The Ritter and Tubaf peridotite suites have experienced minimal alteration
through serpentinisation or chloritisation. Petrologic study reveals however, that
they have experienced various degrees of melt depletion, host magma infiltration,
metasomatism, dissolution/re-precipitation and replacement. The sample suite can
be divided into three broad groups: residues from partial melting, re-equilibrated
samples and a third category comprising samples from both the ‘residual’ and ‘re-
equilibrated’ categories that have been ‘contaminated’ by secondary melt
infiltration processes.

Olivine-spinel exchange geothermometric calculations give temperatures of
~670 to 1140 °C for Ritter, and 755 to 840 °C for Tubaf, consistent with
entrainment in host lavas from the sub-arc lithosphere. However, the bulk
compositions, crystalline phase major element compositions coupled with trace
element geochemical characteristics of these suites reflects a complex petrogenetic
history, likely established in regions of magma generation in a supra-subduction
zone, mantle wedge setting. Olivine is highly forsteritic (Fo# 86.8-95.7 for Ritter,
and Fo# 87-91 for Tubaf), spinel is extremely Cr-rich (Cr# 40.4-89.3 for Ritter, and
Cr# 45.0-69.1 for Tubaf), CaO in olivine, and Al O in orthopyroxene are
2 3
consistently very low (<0.05 wt% and <2 wt% respectively), and primary
clinopyroxene is absent. The trace element abundance patterns of primary
orthopyroxene and secondary clinopyroxene display depletions relative to rare
earth elements in high field strength elements, consistent with equilibration with
arc-type magmas.

Olivine-spinel oxygen barometry shows a range from reduced to oxidised
conditions relative to the fayalite-magnetite-quartz buffer for both Ritter (-1.43 to
+1.84 log units fO ) and Tubaf (-1.26 to +0.86). Evidence from Zn/Fe, V/Sc and
10 2
Mn/Fe systematics suggests that independent of tectono-magmatic setting, the
source of arc magmas, evidenced by these peridotites, may be indistinguishable in
terms of oxidation state to that of mid ocean ridge basalts. This study gives a rare
insight into the nature of the sub-arc mantle and the generation of arc magmas.

Key Words: sub-arc mantle, peridotite, mantle xenolith, lithosphere, redox state,
petrology, metasomatism, picrite, arc magmatism
Definitions

Acronyms:

AFM Al-Fe-Mg
CI Carbonaceous Chondrite
EMP Electron Microprobe
EMPA Electron Microprobe Analysis
HFSE High Field Strength Elements
HREE Heavy Rare Earth Elements
HTS High Ti Suite
IAB Island Arc Basalt
ICP-MS Inductively Coupled Plasma Mass Spectrometry
LILE Large Ion Lithophile Elements
LOD Limit Of Detection
LOI Loss On Ignition
LREE Light Rare Earth Elements
LTS Low Ti Suite
MORB Mid Ocean Ridge Basalt
NB New Britain
OIB Ocean Island Basalt
OJP Ontong-Java Plateau
OSMA Olivine Spinel Mantle Array
PM Primitive Mantle
PNG Papua New Guinea
QFM Quartz-Fayalite-Magnetite
REE Rare Earth Element
RV Research Vessel
SEM Scanning Electron Microscope
SHAARC Submarine, Hydrothermally Active Arc
SHDR Dredge
SS Southern Surveyor
TAS Total Alkali and Silica
TLTF Tabar-Lihir-Tanga-Feni
WeBIVE West Bismarck Vents Expedition
WB West Bismarck
WBD West Bismarck Dredge
WDS Wavelength-dispersive
WR Whole-rock
XRF X-Ray Fluorescence

Variables & Parameters:

D Partition coefficient
fO Oxygen fugacity
2
P Pressure
T Temperature
t Time or duration
X Molar fraction
Σ Sum
Abbreviations:

amph Amphibole
cat Cation
cpx Clinopyroxene
Di Diopside
En Enstatite
Fa Fayalite
Fig Figure
Fo Forsterite
minc Melt inclusion
ol Olivine
opx Orthopyroxene
plag Plagioclase
phlog Phlogopite
pyx Pyroxene
spi Spinel

Conventions:

Cr# molar Cr3+/(Cr3++Al3+)*100
Fe# molar Fe3+/(Fe3++Cr3++Al3+)*100
FeO* ‘total Fe’, with all Fe measured in the 2+ cation state
Fe O * ‘total Fe’, with all Fe measured in the 3+ cation state
2 3
Fo# molar Mg2+/(Mg2++Fe2+)*100 in olivine
Mg# molar Mg2+/(Mg2++Fe2+)*100
°C degrees Celsius
GPa gigapascal
Hz Hertz
kV kilovolts
mJ millijoule
mL millilitre
µm micrometre or micron
mm millimetre
nA nanoampere
nm nanometre
ppm concentration in parts per million
s second
wt% concentration in weight percent