MAJOR ELEMENT, TRACE ELEMENT, AND ISOTOPIC COMPOSITION OF EMPEROR SEAMOUNT CHAIN AND ONTONG JAVA PLATEAU BASALTS A Dissertation Submitted to the Graduate School of the University of Notre Dame in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by John T. Shafer, B.S. Clive R. Neal, Director Graduate Program in Civil Engineering and Geological Sciences Notre Dame, Indiana December 2006 This document is in the public domain. MAJOR ELEMENT, TRACE ELEMENT, AND ISOTOPIC COMPOSITION OF EMPEROR SEAMOUNT CHAIN AND ONTONG JAVA PLATEAU BASALTS Abstract by John T. Shafer The Ontong Java Plateau (OJP) and the Hawaiian Ridge-Emperor Seamount Chain (HR-ESC) are two of the largest volcanic structures on Earth. As the OJP covers an area of more than 2 × 106 km2, the plateau represents the largest known magmatic event in Earth’s history. Equally impressive, the HR-ESC stretches for more than 6,000 km through the north-central Pacific Ocean. Despite the magnitude of these events, the chemistry of significant portions of the OJP and the HR-ESC are poorly known to completely unknown. A full understanding of the chemistry of the OJP and the HR-ESC is necessary to make realistic models of their formation. Major element, trace element, platinum group element (PGE), and isotopic ratio analyses have been conducted on samples collected from several locations on both the OJP and the HR-ESC using inductively coupled plasma-optical emis- sion spectroscopy (ICP-OES), ICP-mass spectrometry (ICP-MS), and negative thermal ionization mass spectrometry (NTIMS). Using a combination of the aforementioned analytical techniques, it was dis- covered the OJP has more geochemical variation than previously recognized, es- pecially at the margins of the plateau. The discovery of a previously unknown John T. Shafer lava type from the volcaniclastic succession at Site 1184 on the eastern salient of the OJP and more primitive lava types from basaltic crustal xenoliths suggests that further sampling via deep sea drilling is necessary to better understand the complex origins of the worlds largest igneous province. ESC seamounts have been assumed to undergo similar stages of development as their younger Hawaiian counterparts despite the paucity of non-dredge sam- ples. The investigation of a greater than 300 km thick sequence of basement from Nintoku Seamount confirms that a typical ESC volcano develops in a similar manner to modern Hawaiian volcanoes. PGE and Re/Os isotopic work on three ESC seamounts suggests that both recycled oceanic crust and outer core material contribute to the overall PGE budget in the Hawaiian plume but that it requires unusual melting conditions for both sources to manifest themselves. DEDICATION To my wife and family ii CONTENTS FIGURES.................................... vii TABLES .................................... xi ACRONYMS .................................. xiii ACKNOWLEDGMENTS ........................... xv CHAPTER 1: INTRODUCTION TO LARGE IGNEOUS PROVINCES ANDTHEPROBLEMATHAND .................... 1 1.1 OverviewofProblem ......................... 1 1.1.1 TheOntongJavaPlateau . 1 1.1.2 Hawaiian Ridge-Emperor Seamount Chain . 4 1.2 SolvingtheProblem ......................... 6 CHAPTER 2: THE ONTONG JAVA PLATEAU: GEOLOGICAL SETTING, PETROLOGY, & GEOCHEMISTRY . 7 2.1 Overview................................ 7 2.2 Geological Setting and Physical Geology . 7 2.3 ModelofFormation.......................... 8 2.4 Petrology&Geochemistry . 11 2.5 VolcaniclasticrocksandSite1184 . 15 CHAPTER 3: HAWAIIAN RIDGE-EMPEROR SEAMOUNT CHAIN . 17 3.1 Overview................................ 17 3.2 HistoryofMantlePlumes . 17 3.3 The Hawaiian Ridge-Emperor Seamount Chain . 24 3.3.1 PhysicalGeology ....................... 24 3.3.2 Geochemistry of the Hawaiian Islands . 27 3.3.3 Geochemistry of the Emperor Seamount Chain (ESC) . 34 3.3.4 Movement of the Hawaiian Mantle Plume . 38 3.4 Summary ............................... 39 iii CHAPTER 4: COMPOSITIONAL VARIABILITY IN LAVAS FROM OCEAN DRILLING PROGRAM SITE 1184, ONTONG JAVA PLATEAU . 41 4.1 Samples ................................ 41 4.2 Results................................. 43 4.2.1 Petrography.......................... 43 4.2.2 MajorElements........................ 45 4.2.3 TraceElements ........................ 51 4.2.4 Radiogenicisotoperatios. 58 4.3 Discussion............................... 61 4.3.1 Theinfluenceofalteration . 61 4.3.2 Petrogeneticinterpretations . 69 4.3.3 Sourceregion ......................... 73 4.4 Conclusions .............................. 74 CHAPTER 5: ONTONG JAVA PLATEAU XENOLITHS FROM THE IS- LANDOFMALAITA ........................... 76 5.1 GeologyofMalaitaandtheSolomonIslands . 76 5.2 TheMalaitanAln¨oite. 79 5.3 Previous Work on Aln¨oite Xenoliths . 80 5.4 The Xenolith Suite Studied for this Work . 82 5.5 AnalyticalMethods.......................... 82 5.6 Results................................. 82 5.6.1 Petrography.......................... 82 5.6.1.1 BM/SI-7........................... 83 5.6.1.2 PHN5802.......................... 83 5.6.1.3 PHN3939.......................... 84 5.6.1.4 PHN5765.......................... 85 5.6.1.5 PHN5792.......................... 86 5.6.1.6 PHN5793.......................... 87 5.6.1.7 PHN5843.......................... 88 5.6.1.8 PHN5853.......................... 89 5.6.1.9 PHN5854.......................... 89 5.6.1.10 ST-7............................. 90 5.6.2 MajorElementData . .. .. 92 5.6.3 TraceElementData . .. .. 96 5.6.4 Sr-andNd-IsotopicData. 103 5.6.5 ElectronMicroprobeData . 105 5.7 Discussion ............................... 111 5.7.1 OriginofREEAnomalies . 111 5.7.2 Thermobarometry. 115 5.7.3 Relationship of the Basalt/Gabbro Samples to the OJP . 120 iv 5.8 Conclusions .............................. 125 CHAPTER 6: HAWAIIAN PLUME SOURCE HYBRIDIZATION: EVI- DENCE FROM NINTOKU SEAMOUNT, EMPEROR SEAMOUNT CHAIN ................................... 127 6.1 NintokuSeamount .......................... 127 6.2 Samples ................................ 129 6.3 Results................................. 132 6.3.1 MajorElements. .. .. 132 6.3.2 TraceElements ........................ 137 6.3.3 SrandNdIsotopes . .. .. 148 6.4 Discussion ............................... 152 6.4.1 Chemical and Isotopic Variations with Depth (Stratigraphic Age)intheSite1205DrillCore . 152 6.4.2 Influence of Alteration of Chemistry . 154 6.4.3 Role of Fractional Crystallization and Crystal Accumulation 157 6.4.4 Role of Melting Processes and Source Heterogeneity in Cre- atingVariationWithinNintoku Lavas . 162 6.4.5 Model for the Formation of the Nintoku Post-Shield Basalts 163 6.4.6 A Physical Model for Nintoku Post-Shield Magmatism . 174 6.4.7 Constraints from Sr Isotope Variations with Time on Pet- rogenesis of Hawaiian-Emperor Post-Shield Lavas . 176 6.5 Conclusions .............................. 179 CHAPTER 7: THE PLATINUM GROUP ELEMENT AND RE–OS ISO- TOPIC COMPOSITION OF THE EMPEROR SEAMOUNT CHAIN . 181 7.1 Introduction.............................. 181 7.1.1 DetroitSeamount, ODP Leg 197,Site 1203. 182 7.1.2 Nintoku Seamount, ODPLeg 197, Site 1205 . 183 7.1.3 KokoSeamount, ODPLeg197,Site1206 . 185 7.1.4 PGEsandtheHawaiianPlume . 186 7.2 AnalyticalTechniques . 189 7.3 Results................................. 189 7.3.1 Petrography.......................... 189 7.3.1.1 DetroitSeamount. 189 7.3.1.2 NintokuSeamount . 190 7.3.1.3 KokoSeamount. 190 7.3.2 MajorandTraceElements . 191 7.3.2.1 Detroit Seamount (∼ 81Ma) ............... 195 7.3.2.2 Nintoku Seamount (∼ 56Ma)............... 197 7.3.2.3 Koko Seamount (∼ 48Ma) ................ 199 7.3.3 Platinum Group Elements and Re–Os Isotopes . 200 v 7.4 Discussion ............................... 204 7.4.1 Significance of Pd and Os Depletions . 205 7.4.2 PGEandRe–OsSystematics . 210 7.4.3 Effect of Sulfide Retention in the Source of the Hawaiian Plume ............................. 220 7.5 Conclusions .............................. 223 CHAPTER8:CONCLUSIONS . 226 8.1 TheOntongJavaPlateau . 226 8.2 Hawaiian Ridge-Emperor Seamount Chain . 228 8.3 Summary ............................... 231 8.4 RelevanceandFutureWork . 232 CHAPTER 9: ANALYTICAL TECHNIQUES . 234 9.1 OverviewofTechniques. 234 9.2 SamplePreparation. 234 9.3 LossonIgnition............................ 235 9.4 MajorElementAnalysis . 237 9.5 TraceElementAnalysis. 240 9.6 Platinum Group Element Analysis . 246 9.7 IsotopeAnalyses ........................... 248 9.7.1 Sr-, Nd-, & Pb-Isotope Analysis as part of Chapter 4 . 249 9.7.2 Sr- & Nd-Isotope Analysis as part of Chapter 6 . 250 9.7.3 OsIsotopeAnalyses . 252 BIBLIOGRAPHY ............................... 253 vi FIGURES 1.1 Map of the Ontong Java Plateau and surrounding area . 2 1.2 Map of the Hawaiian Ridge-Emperor Seamount Chain . 5 2.1 Map of the Ontong Java Plateau, highlighting the island of Malaita 12 87 86 2.2 Graph of Sr/ Sr vs. ǫNd for OJP basalts and MORB basalts . 13 2.3 Primitive mantle normalized profiles of basalts recovered from Site 803................................... 14 2.4 Map of the Ontong Java Plateau, highlighting the eastern salient andSite1184 ............................. 16 3.1 Schematic of a rising mantle plume . 20 3.2 Map of the Hawaiian Ridge-Emperor Seamount Chain . 25 3.3 Map of the Hawaiian Islands showing the Kea and Loa trends .. 28 3.4 208Pb/204Pb vs 176Hf/177Hf, 87Sr/86Sr, and 143Nd/144Nd isotopic ra- tios showing the distinct fields for Kea and Loa trend volcanoes . 29 3.5 MgO vs SiO2 forKilaueatholeiiticbasalts . 30 3.6 Incompatible element diagram of Kilauea shield