Mafic dykes of the East Antarctic shield

345 Pages·2014·27.31 MB·English

MAFIC DYKES OF THE EAST ANTARCTIC SHIELD:
EXPERIMENTAL, =CHEMICAL AND PETROLCGICML STUDIES
FOCUSING ON THE PRaTEROZOIC EVOLUTION
OF THE CRUST AND MANTLE
\kol'
Scott M. Kuehner
B.A. (Minnesota), MSc. (Univ. Western Ontario)
Submitted in partial fulfilment of the requirements
of the degree of Doctor of Philosophy
at the University of Tasmania.
September 1986
This thesis contains no material which has been
accepted for the award of any other degree or
diploma in any University and, to the best of my
knowledge and belief, contains no copy or
paraphrase of material previously published or
written by another person, except where due
reference is made in the text of this thesis.
Scott M. Kuehner
September, 1986.
This thesis is dedicated to the memory of my father,
who passed away during the course of my study.
MILTON LESTER KUMMER
May 3, 1923 - September 21, 1983
For as long as I can remember, he worked six,
and sometimes seven days a week, but still managed to
find time to watch me participate in various
High School athletic programs.
page
List of Figures
List of Tables ix
Acknowledgements xi
Abstract xiii
PART 1
INTRODUCTION 2
REGIONAL GEOLOGICAL HISTORY OF THE EAST ANTARCTIC SHIELD 3
MAFIC DYKE SWARMS 5
PURPOSE OF STUDY 6
Chapter 1 THE EMPLACEMENT DEPTHS OF TWO VESTFOLD HILLS MAFIC
DYKES DETEMAINED BY DUPLICATING NATURAL PHENOCRYST
ASSEMBLAGES THROUGH THE APPLICATION OF HIGH PRESSURE
EXPERIMENTAL PETROLOGY
INTRODUCTION 1:2
1.1 SAMPLE EVALUATION 1:3
1.1.1 Sample descriptions 1:3
1.1.2 Appraisal of liquid compositions 1:4
1.1.3 Determination of emplacement pressures
and temperatures by applying geothermometry
and barometry to natural phase assemblages 1:6
1.2 TECHNICAL CONSIDERATIONS 1:12
1.2.1 Experimental methods 1:12
1.2.2 The iron exchange problem 1:14
1.3 EXPERIMENTAL RESULTS 1:17
1.3.1 Results of the experimental study of sample
060 and comparison with the natural phase
assemblage 1:17
1.3.2 Results of the experimental study of
sample 206 and comparison with the
natural phase assemblage 1:24
1.4 CONCLUSIONS 1:35
1.4.1 Mbthodology 1:35
1.4.2 Emplacement pressure of sample 060 1:36
1.4.3 Emplacement pressure of sample 206 1:36
page
Chapter 2 THE EMPLACEMENT PRESSURES OF SEVERAL EAST ANTARCTIC
DYKE SUITES ESTIMATED FROWTHE EXPERIMENTAL.STUDIES
OF VESTFOLD HILLS DYKE COMPOSITIONS
INTRODUCTION 2:2
2.1 ESTIMATION OF EMPLACEMENT PRESSURES .2:3
2.1.1 High-Mg tholeiites (ca.2420 Ma) 2:3
2.1.2 .Fe-rich tholeiites (ca.1200 2:4
2.1.3 -Fe-rich tholeiites (ca.1800 Ma)
2.2 DISCUSSION OF THE 'IMPORTANCE OF - AL REGIONAL
PRESSURE GRADIENT IN THE NAPIER CCMPLEX 2:9
2.3 CONCLUSIONS 2:11
2.3.1 Napier Complex high-Mg-tholeiites 2:11 -
2.3.2 Napier Complex Fe-riCh tholeiites • 2:11
Chapter 3 GARNET DEVELOPMENT WITHIN MAFIC DYKES OF TEEVESUSCMD
BITTx• EVALUATION AND IMPLICATIONS
. INTRODUCTION . 3:2
3.1 FIELD OBSERVATIONS ON THE OCCURRENCE OF GARNET 3:3
3.2 PETROGRAPHIC OBSERVATIONS ON. AMPHIBOLE AND
GARNET FORMING. REACTIONS _3:6
3.3 PETROGENETIC IMPLICATIONS 3:8
3.4 P-T DETERMINATIONS.. 3:12
3.4.1 Gt-Cpx thermometry . 3:13
3.4.2 Gt-Cpx-Plag-Qtz barometry 3:13
3.4.3 Cpx-Plag-Qtz barometry 3:14
3.5 CONCLUSIONS 3:15
Chapter 4 COMEDSIONS: INTEGRATION OF MAFIC: DYKE STUMES WITH
THE PREVIOUSLY DESCRIBED HISTORY OF THE VESTFOID EaLLS
AND ENDERBY LAND - IMPLICATIONS FOR ARCHEAN-PROTEROZOIC
UPLIFT PATHS IN THE EAST ANTARCTIC SHIELD
INTRODUCTION 4:2
4.1 THE UPLIFT PATH OF THE NAPIER COMPLEX 4:3
4.2 THE UPLIFT PATH OF THE VESTFOLD HILLS 4:5
4.3 DISCUSSION 4:6
iii
page
PAFfr 2
INTRODUCTION
Chapter 5 GENESIS OF THE C.2420 NAME SUITES
AL: THE • HIGH4I3 THOLEIITES
INTRODUCTION 5:3
5.1 INITIAL CHEMICAL CHARACTERIZATION OF SUBGROUPS 5:4
5.2 PETROGRAPHY AND CRYSTAL CHENESTRY 5:6
5.2.1 Subgroup I 5:6
5.2.2 Subgroup II • 5:10
5.2.3 Subgroup III 5:11
5.2.4 Discussion of samples with distinctive
characteristics 5:12
5.2.5 Comparison of orthopyroxene phenocryst
characteristics of the subgroups 5:14
5.3 P-T ESTIMATES 5:16
5.4 RELATIVE AGE RELATIONSHIPS OF THE SUBGROUPS 5:17
5.5 MAJOR:AND TRACE ELEMENT GEOCHEMISTRY EMPHASIZING
SOURCE CHARACTERISTICS 5:19
5.5.1 Major element characterization 5:19
5.5.2 Subgroup I 5:20
5.5.3 Subgroup II 5:24
5.5.4 Subgroup III 5:25
5.5.5 Rare earth elements 5:26
5.6 CRYSTAL FRACTIONATION WITHIN THE HIGH-MG DYKE SUITE 5:28
5.6.1 Subgroup I 5:28
5.6.2 Subgroup II 5:28
5.6.3 Subgroup III 5:29
5.7 THE ROLE OF CRUSTAL CONTAMINATION 5:31
5.8 SUNEARY AND DISCUSSION OF SUBGROUP CHARACTERISTICS 5:33
5.9 ESTIMATION OF THE DEPTH OF MELTING 5:37
B: THE FE-THOLF71TES
INTRODUCTION 5:41
5.10 RELATIVE RELATIONSHIPS BETWEEN THE FE-THOLEIITES
AND HIGH-MG THOLEIITE SUITE 5:42
5.11 PETROGRAPHY AND CRYSTAL CHEMISTRY OF THE
FE-THOLEIITES • • 5:43
5.12 WHOLE-ROCK CEOCEENESTRY 5:46
5.12.1 Major elements 5:46
• 5.12.2 Trace elements 5:49
5.12.3 Rare earth elements 5:51
iv
page
5.13 SUMMARY OF THE GEOCHEMICAL CHARACTERISTICS OF THE
FE-RICH THOLEIITE SUITE 5:53
5.14 SUMMARY OF AND INFERENCES FROM THE HIGH-MG,
FE-RICH THOLEIITE ASSOCIATION IN THE VESTFOLD HILLS 5:55
Chapter 6 PETROLOGY AND GECCHEMISTRY CF THE CA. 1360 MATHCLEITIES
INTRODUCTION 6:2
6.1 INTERSECTING RELATIONSHIPS WITHIN THE THOLEIITE
SUITE 6:3
6.2 PETROGRAPHY AND CRYSTAL CHEMISTRY OF THE
THOLEIITE DYKES 6:5
6.2.1 Petrography 6:5
6.2.2 Crystal chemistry 6:7
6.3 WHOLE BOCK GEOCHEMISTRY 6:9
6.3.1 Major elements 6:9
6.3.2 Trace elements 6:12
6.3.3 BEE 6:15
6.4 SUMMARY AND DISCUSSION 6:17
Chapter 7 SUMMARY 7:1
REFERENCES R:1
APPENDIX 1 - Averaged microprobe analyses and CIPW
norms of glass compositions from the
experimental liquidus study of 65060
and 65206 A:1
APPENDIX 2 - Major and trace element analyses and CIPW
norms of dykes from the Vestfold Hills A:5
LIST OF FIGURES
following
page
Figure 11.1 Location map of the Vestfold Hills and Enderby Land 3
1.1 Location of dykes from the Vestfold Hills chosen
• for experimental studies (65060, 65206) 1:3
• 1.2 Photomicrographs of the textural relationships
in the experimentally studied samples • 1:3
• 1.3 Natural phase compositions of the experimentally
studied samples plotted in the pyroxene quadrilateral 1:4
1.4 Lindsley's graphical thermometer applied to the
phenocryst assemblages of 65060 and 65206 1:9
1.5 Comparison of the effects of Fe-exchange between
Pt and Fe capsules on the composition of the
• experimental charge 1:16
1.6 Experimentally determined P-T diagram for sample 65060 1:17
1.7 SEM photomicrographs of run results (65060) 1:17
1.8 1 atmosphere phase composition plotted on the
Ca-Mg-Fe diagram (65060) 1:17
•
1.9 Al203 and TiO2 variations in 1 atmosphere pyroxene
compositions (65060) 1:17
1.10•1 atmosphere pyroxene compositions compared with
temperature estimates from Lindsley's graphical
thermometer (65060) 1:18
1.11 High pressure pyroxene compositions plotted on
the pyroxene quadrilateral .(65060) 1:19
1.12 Variation in the Al203 content of experimental
pyroxenes with pressure, and compared with natural
pyroxenes (65060) 1:19
1.13 Experimentally determined phase diagram for •
sample 65206 1:24
1.14 SEM photomicrographs of run results (65206) 1:24
1.15 Variation in plagioclase composition with
pressure (65206) • 1:24
1.16 Mbtastable pyroxene compositions (Ca-Mg-Fe; Ti02,
Al203.vs WO; 65206) 1:28
1.17 10 kbar,11800C pyroxene compositions after 2 and .
5 hour run times. (Ca-Mg-Fe; Ti02,Al203 vs Wo; 65206) 1:29
1.18 10 kbar,12000C pyroxene compositions after 2 and
5 hour run times (Ca-Mg-Fe; Ti02,Al203 vs Wo; 65206) 1:29
1.19 Experimental Ca-clinopyroxene compositions
• .(Ca-Mg Fe; 65206) . 1:32
-
1.20 Comparison of experimental orthopytoxene and calcic
clinopyroxene compositions with the natural -
phenoctysts (65206) . 1:.33
vi
following
page
Figure 2.1 High-Mg basalt composition projected onto the plane
(Jd+CaTs)-Oliv-Qtz . 2:3
2.2 High-Mg basalt compositions projected onto the
plane Diop-Oliv-Qtz 2:3
2.3 Group 1 Fe-rich tholeiites projected onto the plane
(Jd+CaTs)-Oliv-Qtz 2:5
2.4 Group 1 Fe-rich tholeiites projected onto the plane
Diop-Oliv-Qtz 2:5
2.5 Photomicrograph of sample 3793 2:5
2.6 Photomicrograph of sample 49590 2:5
2.7 Photomicrograph of sample 65206 2:5
• 2.8 Group 2 Fe-rich tholeiites projected onto the plane
(Jd+CaTs)-Oliv-Qtz 2:6
2.9 Group 2 Fe-rich tholeiites projected onto the plane
Diop-Oliv-Qtz 2:6
2.10 1800 ma dyke suite projected onto the plane
• (Jd+CaTs)-Oliv-Qtz 2:7
2.11 1800 Ma dyke suite projected onto the plane
Diop-Oliv-Qtz 2:7
2.12 Location map of Enderby Land dykes 2:9
Figure 3.1 Location map of garnet-bearing samples in the
Vestfold Hills 3:3
3.2 Photographs of three garnet-bearing hand samples 3:3
3.3 Photomicrographs of metamorphic textures 3:7
3.4 Photomicrographs of metamorphic textures 3:7
3.5 Photomicrographs of metamorphic textures 3:7
3.6 Photomicrographs of metamorphic textures 3:7
3.7 Subsolidus phase relations in the system Na-CMAS 3:8
3.8 Diagrammatic view of the metamorphic phase
compositions used in P-T calculations 3:12
3.9 P-T estimates plotted according to sample location
in the Vestfold Hills 3:14
Figure 4.1 Pressure versus time plot depicting the Proterozoic
uplift history of the Napier Complex 4:3
4.2 Pressure versus time plot depicting the Proterozoic
uplift history of the Vestfold Hills 4:5
•
Figure 12.1 Fe0/M00-Ti02 diagram of dyke analyses collected
in this study
12.2 Fe0/1490-Ti02 diagram of dyke analyses collected
during previous studies
vii
following
page
Figure 5.1 Spiderplot of olivine + orthopyroxene phyric samples 5:5
5.2 Spiderplot of olivine-free orthopyroxene samples 5:5
5.3 (Jd+CaTs)-Oliv-Qtz diagram of high-Mg suite 5:5
5.4 Photomicrographs of high-Mg tholeiite samples 5:7
5.5 Pyroxene and olivine compositions from subgroup I
plotted onto the pyroxene quadrilateral 5:7
• 5.6 Pyroxene compositions from sample 069 plotted
onto the pyroxene quadrilateral 5:7
5.7 Chromite compositions from subgroups I and II
compared with other high-Mg rock types 5:9
5.8 Olivine and pyroxene compositions from subgroup II
• plotted onto the pyroxene quadrilateral 5:11
5.9 Pyroxene compositions from subgroup III plotted
onto the pyroxene quadrilateral 5:11
5.10 Photomicrographs of high-Mg tholeiite samples 5:12
5.11 Pyroxene compositions from the norite plotted
onto the pyroxene quadrilateral 5:13
5.12 Comparison of pyroxene compositions between subgroups 5:13
5.13 Histogram of dyke widths 5:17
5.14 Jensen cation diagram of various high-Mg suites 5:19
5.15 Various high-Mg suites compared on Ti02-Si02 and
Mq0-Si02 diagrams • 5:19
5.16 Various high-Mg suites compared on Cr-Fe0/Mg0
and Ni-Fe0/11g0 diagrams 5:19
• 5.17 Chondrite normalized ratios from subgroup I 5:23
• 5.18 Chondrite normalized ratios from subgroup II 5:23
5.19 Chondrite normalized ratios from subgroup III 5:23
• 5.20 BEE patterns of selected high-Mg tholeiites 5:26
5.21 CaO/Ti02 versus TiO2 and Al203/Ti02 versus Zr
variation diagrams of high-Mg suite samples 5:28
5.22 Elemental ratios of subgroup II, normalized to
• sample 214 5:28
5.23 Elemental ratios of subgroup III normalized to
• sample 214 5:28
5.24 Comparison of high-Mg tholeiite compositions and
estimated parental liquid compositions with
oliv-opx cotectics on the (Jd+CaTs)-Oliv-Qtz diagram 5:36
5.25 Intersecting relationships between high-Mg and
Fe-rich tholeiite suites 5:42
•
5.26 Plagioclase and pyroxene compositions from the
•Fe-rich suite plotted onto Ca-Na-E. and Ca-Mg-Fe
diagrams 5:45
•5.27 Pearce molecular ratio diagrams of major element
• variations in the Fe-rich tholeiite suite 5:46