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Table of contents
1. INITIAL PURPOSE OF THIS THESIS xiii
1.1. Problematic
1.2. The choice of the Solomon Islands
1.3. Initial objectives of this study
2. STRUCTURE & SUBJECT OF THIS THESIS
2.1. Structure
2.2. Notes
LIST OF FIGURES AND TABLES
List of Figures
List of Tables
CHAPTER 1: GEOLOGICAL BACKGROUND OF THE SOLOMON ISLANDS
1. REGIONAL SETTING OF THE SOLOMON ISLANDS
2. THE ONTONG JAVA PLATEAU (OJP)
2.1. Large Igneous Provinces (LIPs)
2.2. Characteristics and structure of OJP
2.3. Origin and formation of the OJP
2.4. OJP Tectonic evolution (from 125 to ~ 30 Ma)
3. TECTONIC MODELS OF OJP-SOLOMON ARC COLLISION
3.1. Timing of the OJP-Arc collision
3.2. Accretion models
4. PRESENT-DAY GEOLOGICAL FRAMEWORK OF THE SOLOMON ISLANDS
5. THE GEOLOGY OF CHOISEUL AND SAN JORGE/SANTA ISABEL AND ITS RELEVANCE TO GLOBAL GEOLOGICAL FRAMEWORK OF THE SOLOMON ISLANDS
5.1. Geology of Choiseul
5.2. Geology of Santa Isabel and San Jorge
CHAPTER 2: GEOLOGY AND GEOCHEMISTRY OF THE “SIRUKA ULTRAMAFICS”: EVIDENCE FOR FLUID METASOMATISM IN AN ISLAND ARC SETTING
1. INTRODUCTION
2. GEOLOGICAL BACKGROUND AND SAMPLING LOCATION
3. ANALYTICAL METHODS
4. PETROLOGY
5. MINERAL COMPOSITION
5.1. Olivine
5.2. Spinel
5.3. Orthopyroxene
5.4. Clinopyroxene
5.5. Amphibole
5.6. Chlorite
6. WHOLE ROCK COMPOSITION
6.1. Major elements
6.2. Trace elements
7. CLINOPYROXENE GEOCHEMISTRY
8. GEOTHERMOBAROMETRY CHARACTERISTICS
8.1. Temperature
8.2. Pressure
9. METAMORPHIC HISTORY
10. OXYGEN FUGACITY
11. DISCUSSION
11.1. Choiseul peridotites as residues of melting
11.2. Partial melting characteristics
11.3. Choiseul peridotites: MORB or SSZ or OJP-related?
11.4. Evidence for mantle interaction with a metasomatic fluid
12. TECTONIC IMPLICATIONS
12.1. Formation of the peridotites
12.2. Exhumation and obduction
13. CONCLUSION
CHAPTER 3: SUPRA-SUBDUCTION ZONE PYROXENITES FROM SAN JORGE AND SANTA ISABEL (SOLOMON ISLANDS): A METASOMATIC ORIGIN
1. INTRODUCTION
2. GEOLOGICAL SETTING
3. SAMPLING AND PERIDOTITE-PYROXENITE FIELD RELATIONS
4. ANALYTICAL METHODS
4.1. Whole rock analysis
4.2. Mineral analysis
5. PETROGRAPHY
5.1. Primary assemblages
5.2. Retrograde assemblages
6. BULK ROCK COMPOSITION
6.1. Major Elements
6.2. Trace elements
6.2.1. Rare Earth Elements
6.2.2. Other trace elements
7. MINERAL COMPOSITION
7.1. Orthopyroxene
7.2. Clinopyroxene
7.2.1. Primary clinopyroxene
7.2.2. Secondary clinopyroxene
7.3. Olivine
7.4. Spinel
7.5. Amphibole
8. CONDITIONS OF FORMATION OF THE PYROXENITES
8.1. Temperature
8.2. Pressure
9. DISCUSSION
9.1. Arc- or plume-related pyroxenites?
9.2. Mantle versus crustal arc pyroxenites
9.3. Metasomatic formation of SSZ mantle pyroxenites
10. TECTONIC MODEL OF PYROXENITES FORMATION AND EXHUMATION
10.1. Genesis of the pyroxenites
10.2. Exhumation of the pyroxenites
11. CONCLUSION
CHAPTER 4: MINERAL TRACE ELEMENT COMPOSITIONS, STUDY OF FLUID INCLUSIONS AND WHOLE ROCK RE/OS SYSTEM: INDICATIONS OF A COMPLEX SLAB-DERIVED METASOMATIC ORIGIN FOR THE SAN JORGE/SANTA ISABEL PYROXENITES (SOLOMON ISLANDS).
1. INTRODUCTION
2. PRINCIPLES AND ANALYTICAL METHODS
2.1. Mineral trace element chemistry
2.1.1. Principles
2.1.2. Analytical methods
2.2. Study of Fluid Inclusions
2.2.1. Principles
2.2.2. Analytical methods
2.2.2.1. Raman Spectroscopy
2.2.2.2. LA ICP-MS
2.3. The Re/Os system
2.3.1. Principles
2.3.2. Analytical methods
3. RESULTS
3.1. Mineral trace element chemistry
3.1.1. Clinopyroxene
3.1.1.1. Rare Earth Elements (REE)
3.1.1.2. Other trace elements
3.1.2. Orthopyroxene
3.1.2.1. Rare Earth Elements (REE)
3.1.2.2. Other trace elements
3.1.3. Amphibole
3.1.3.1. Rare Earth Elements (REE)
3.1.3.2. Other trace elements
3.1.4. Other minerals
3.1.4.1. Olivine
3.1.4.2. Spinel
3.1.4.3. Pectolite
3.2. Study of the fluid inclusions
3.2.1. Petrography
3.2.1.1. Criteria
3.2.1.2. Fluid inclusions occurrence
3.2.2. Geochemical study of the fluid inclusions
3.2.2.1. By the Raman spectroscopy
3.2.2.2. By the LA ICP-MS
3.3. The Re/Os geochemistry
4. INTERPRETATIONS
4.1. Mineral Partition Coefficients
4.1.1. Opx/Cpx
4.1.2. Amphi/Cpx
4.2. Whole rock Elemental Budgets
4.2.1. Mass balance: comparison between whole rock and mineral trace element chemistry
4.2.2. Trace element distribution for the pyroxenites
4.3. Fluid inclusions
4.4. The Re-Os System
4.4.1. Evidence for Metasomatism
4.4.2. Re-Os isochron and possible age model
5. DISCUSSION
5.1. Characteristics of the pyroxenites from the Solomon Islands
5.1.1. Similarities between the three groups of pyroxenites: a common SSZ affinity
5.1.2. Differences between the three groups of pyroxenites
5.1.2.1. G1-orthopyroxenites
5.1.2.2. G2-websterites
5.1.2.3. G3-clinopyroxenites (except sample 15.07)
5.1.3. Exceptions within the groups
5.1.3.1. In the G1- orthopyroxenites
5.1.3.2. In the G2-websterites
5.1.3.3. In the G3-clinopyroxenites
5.2. Characteristics of the metasomatism: evidence from the G1-orthopyroxenites and the G2-websterites
5.2.1. Types of metasomatism
5.2.2. Composition of the fluid
5.2.3. Provenance and nature of the fluid
5.3. Sediments: source of the metasomatising agents
6. IMPLICATIONS: GENESIS OF THE SAN JORGE AND SANTA ISABEL PYROXENITES
6.1. Formation of the G1-orthopyroxenites and the G2-websterites
6.2. Formation of the G3-clinopyroxenites
7. CONCLUSION
CHAPTER 5: ORIGIN AND NATURE OF THE MAFIC COMPLEXES OF THE SANTA ISABEL, SAN JORGE AND CHOISEUL ISLANDS: EVIDENCE FROM MINERALOGICAL AND GEOCHEMICAL CHARACTERISTICS
1. INTRODUCTION
2. GEOLOGICAL BACKGROUND
2.1. Choiseul Island
2.2. San Jorge and Santa Isabel
3. SAMPLING AND FIELD RELATION
3.1. Choiseul Island
3.2. San Jorge and Santa Isabel
4. TEXTURAL AND PETROLOGICAL CHARACTERISTICS
4.1. The volcanic rocks and schists
4.2. The gabbros
5. WHOLE CHEMISTRY
5.1. Analytical methods
5.2. Volcanic rocks and schists
5.2.1. Major elements
5.2.2. Trace elements
5.2.2.1. Rare Earth Elements (REE)
5.2.2.2. Other trace elements
5.2.3. Tectonic discrimination Nb-Zr diagram
5.3. Gabbros
5.3.1. Major elements
5.3.2. Trace elements
5.3.2.1. Rare Earth Elements (REE)
5.3.2.2. Other trace elements
6. MINERAL CHEMISTRY
6.1. Volcanic rocks and schists
6.1.1. Pyroxene
6.1.1.1. Clinopyroxene
6.1.1.2. Orthopyroxene
6.1.2. Plagioclase
6.1.3. Amphibole
6.2. Gabbros
6.2.1. Pyroxene
6.2.2. Plagioclase
6.2.3. Amphibole
6.3. Mineral trace element compositions
7. SR AND ND ISOTOPIC COMPOSITIONS
7.1. Analytical procedures
7.2. Volcanic rocks and schists
7.3. Gabbros
8. DISCUSSION
8.1. Chemical mobility
8.2. Volcanic rocks and schists: origin and significance
8.2.1. Voza Lavas and Choiseul Schists: one unit with a NMORB/BABB origin
8.2.2. Extrusive rocks from San Jorge: what origin?
8.2.2.1. Is the 16.13-columnar lava a boninite?
8.2.2.2. The 16.14-dyke: a typical MORB-related Fe-Ti basalt
8.2.2.3. Pillow-basalts from Santa Isabel and schist from San Jorge: a OJP origin
8.3. The gabbros from Santa Isabel/San Jorge and Choiseul: origin and significance
8.3.1. Gabbros from Choiseul
8.3.1.1. The coarse-grained to pegmatitic gabbros: an arc-like cumulate
8.3.1.2. The Oaka Metamicrogabbros: frozen melts from BABB environment
8.3.2. The Gabbros from Santa Isabel and San Jorge
8.3.2.1. A cumulate origin
8.3.2.2. Composition of parental melt: evidence for arc origin
8.3.2.3. San Jorge and Santa Isabel gabbros: evidence for highpressure arc-cumulates
9. CONCLUSION
CHAPTER 6: CONSEQUENCES OF THE OJP-ARC COLLISION
1. IMPLICATIONS FOR THE DEHYDRATION PROCESS
1.1. Before OJP-arc collision
1.2. Chocking of the subduction: OJP arrival at the subduction zone
1.2.1. Melting of the sediment: is it possible?
1.2.2. The transition blueschist-eclogite at high depth?
2. IMPLICATIONS FOR THE COMPOSITION OF THE MANTLE WEDGE
2.1. Before OJP-arc collision: metasomatism and melting of the mantle wedge
2.2. Chocking of the subduction: OJP arrival at the subduction zone
2.2.1. Formation of the G1- and G2-pyroxenites
2.2.2. Genesis of boninite
3. HARD OJP-ARC COLLISION: IMPLICATIONS FOR THE EXHUMATION AND OBDUCTION PROCESSES
3.1. Exhumation of portions of mantle wedge along the slab
3.2. Exhumation of SSZ-related terranes
3.3. Obduction of the OJP-related terranes
CONCLUSION
References
Appendices
