Trace element abundances and Sr-Nd-Pb isotopic constraints

71 Pages·2015·7.48 MB·English

UC San Diego
UC San Diego Electronic Theses and Dissertations
Title
Trace element abundances and Sr-Nd-Pb isotopic constraints on the petrogenesis of Juan
Fernandez lavas
Permalink
https://escholarship.org/uc/item/0vk39489
Author
Truong, Thi Bich
Publication Date
2015

Peer reviewed|Thesis/dissertation
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University of California
UNIVERSITY OF CALIFORNIA, SAN DIEGO
Trace element abundances and Sr-Nd-Pb isotopic constraints on the
petrogenesis of Juan Fernandez lavas
A thesis submitted in partial satisfaction of the
requirements for the degree
Master of Science
in
Earth Sciences
by
Thi Bich Truong
Committee in charge:
Professor Paterno Castillo, Chair
Professor James Day
Professor David Hilton
2015
Copyright
Thi Bich Truong, 2015
All rights reserved.
The Thesis of Thi Bich Truong is approved, and it is ac-
ceptable in quality and form for publication on microfilm
and electronically:
Chair
University of California, San Diego
2015
iii
DEDICATION
Dedicated to my parents Thuy Nguyen and Hung Truong.
iv
EPIGRAPH
There is no good way to comprehend any one aspect of geology without studying
the wider matrix in which it rests.
John McPhee
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TABLE OF CONTENTS
Signature Page ..................................................... iii
Table of Contents ................................................... vi
List of Figures ...................................................... vii
List of Tables....................................................... viii
Acknowledgements .................................................. ix
Abstract ........................................................... x
1 Introduction..................................................... 1
1.1 Geologic Background......................................... 6
1.2 Samples .................................................... 9
2 Methods and Results ............................................. 13
2.1 Analytical Methods .......................................... 13
2.2 Results..................................................... 19
2.2.1 Trace Elements ....................................... 19
2.2.2 Radiogenic Isotopes ................................... 21
3 Discussion ...................................................... 27
3.1 Major Element Variations .................................... 28
3.2 Incompatible Trace Element Variation.......................... 30
3.3 The Sr-Nd-Pb composition of the Juan Fernandez mantle source ... 34
3.4 The geochemistry of Juan Fernandez Islands compared to some
Pacific island chains.......................................... 38
3.5 The volcanologic evolution of Juan Fernandez islands............. 40
3.6 Implications for the origin of the high-3He/4He signature of Juan
Fernandez lavas ............................................. 43
3.6.1 The MORB-like 3He/4He of group III lavas ............... 45
3.6.2 The difference in 3He/4He between group I and group II lavas 47
3.6.3 The nature of 3He/4He in Juan Fernandez lavas ........... 49
4 Conclusions ..................................................... 52
References ......................................................... 54
vi
LIST OF FIGURES
Figure 1.1: Bathymetric Map and Location of Juan Fernandez Islands..... 5
Figure 1.2: Sample map of Robinson Crusoe and Alexander Selkirk Islands 7
Figure 1.3: 3He/4He (R ) versus Ba/Zr, Zr versus Nb ................... 12
A
Figure 2.1: Chondrite-normalized rare earth element (REE) patterns ...... 22
Figure 2.2: Primitive mantle-normalized incompatible element spidergram . 23
Figure 2.3: 87Sr/86Sr versus 143Nd/144Nd .............................. 24
Figure 2.4: 206Pb/204Pb-207Pb/204Pb, 206Pb/204Pb-208Pb/204Pb ........... 25
Figure 3.1: MgO (wt.%) versus major element oxides ................... 29
Figure 3.2: Na O (wt. %) versus FeO* (wt. % )........................ 31
2
Figure 3.3: Magmatic process identification diagrams ................... 35
Figure 3.4: 3He/4He (R ) versus 87Sr/86Sr ............................. 37
A
Figure 3.5: Proposed stages of the volcanologic evolution of the Juan Fer-
nandez Archipelago ...................................... 41
Figure 3.6: 3He/4He (R ) versus TITAN Anomalies..................... 44
A
vii
LIST OF TABLES
Table 2.1: Trace element abundance data.............................. 15
Table 2.2: Sr-Nd-Pb isotope composition data.......................... 17
Table 3.1: Helium isotope recalculations............................... 48
viii
ACKNOWLEDGEMENTS
Iwouldliketothank,firstandforemost,myadvisorforthisproject,Professor
Paterno Castillo for his constant availability and encouragement through 4 years
of work. Thank you to my committee members, James Day and David Hilton for
offering their expertise time and time again for my own benefit.
Thanks to everyone at SIO who made this research possible: Joshua Reeves
with my degree requirements, and Chris MacIsaac for the guidance in the lab,
and especially for saving my first strontium cut in the TIMS when it grew legs.
Thank you to Lisa Tauxe for the suggestion in programming class that we should
learn LaTeX. I am also grateful for the help of UCSD librarians who were able to
elucidate the nuances of accessing obscure articles.
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