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Neon, Helium and Argon Isotope Systematics of the Hawaiian Hotspot

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Neon, Helium and Argon Isotope Systematics of the Hawaiian Hotspot Universität Potsdam Institut für Geowissenschaften Neon, Helium and Argon Isotope Systematics of the Hawaiian Hotspot Dissertation zur Erlangung des akademischen Grades "doctor rerum naturalium" (Dr. rer. nat.) in der Wissenschaftsdisziplin Geowissenschaften eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Potsdam von Tina Mailer, geb. Krüsmann Potsdam, Juni 2009 This work is licensed under a Creative Commons License: Attribution - Noncommercial - Share Alike 3.0 Germany To view a copy of this license visit http://creativecommons.org/licenses/by-nc-sa/3.0/de/deed.en Published online at the Institutional Repository of the University of Potsdam: URL http://opus.kobv.de/ubp/volltexte/2009/3963/ URN urn:nbn:de:kobv:517-opus-39633 http://nbn-resolving.org/urn:nbn:de:kobv:517-opus-39633 Fire and Ice Some say the world will end in fire, Some say in ice. From what I've tasted of desire I hold with those who favor fire. But if it had to perish twice, I think I know enough of hate To say that for destruction ice Is also great And would suffice. Robert Frost, 1923 Table of Contents Abstract ...................................................................................................................................... 1 Zusammmenfassung................................................................................................................... 2 Motivation and goals of this study ............................................................................................. 3 1 Noble Gas Geochemistry ........................................................................................................ 5 1.1 Noble Gases as Geochemical Tracers .............................................................................. 5 1.2 Noble Gas Reservoirs....................................................................................................... 8 1.2.1 Noble Gases in the Solar System .............................................................................. 8 1.2.2 Noble Gas State of the Earth’s mantle ...................................................................... 9 1.2.3 Noble Gas State of the Earth’s Crust and Atmosphere ........................................... 17 2 Analytical Determination of Noble Gas Isotopes with the VG 5400 Mass Spectrometer.... 20 2.1 Introduction .................................................................................................................... 20 2.2 Ion Separation in a Magnetic Field ................................................................................ 20 2.3 Ion Optics ....................................................................................................................... 21 2.4 Detectors and Isobaric Interferences .............................................................................. 22 2.5 Sensitivity and Discrimination....................................................................................... 24 2.6 Gas Extraction, Gas Purification, Gas Measurement..................................................... 25 2.7 Blanks............................................................................................................................. 26 2.8 Data Evaluation.............................................................................................................. 26 2.9 Uncertainties and Error Propagation .............................................................................. 26 3 Origin and Characteristics of the Samples ............................................................................ 28 3.1 Geological Setting.......................................................................................................... 28 3.1.1 The Plume Theory................................................................................................... 29 3.1.2 Island of Hawaii ...................................................................................................... 31 3.1.3 Maui ................................................................................................................................ 35 3.2 Sample Sites ................................................................................................................... 36 3.2.1 Hawaii Scientific Drilling Project........................................................................... 38 3.2.2 NSF Well................................................................................................................. 39 3.2.3 Surface Samples ...................................................................................................... 39 4 Results ................................................................................................................................... 40 4.1 Major and Trace Elements ............................................................................................. 40 4.1.1 Intershield Comparison ........................................................................................... 45 4.1.2 Influence of Postmagmatic Alteration..................................................................... 46 4.2 Rare Earth Elements....................................................................................................... 47 4.3 Sr, Nd, and Pb isotopic compositions ............................................................................ 49 4.4 Electron Microprobe Analysis of Olivine Phenocrysts.................................................. 55 4.5 Results of the Noble Gas Measurements........................................................................ 56 4.5.1 Helium..................................................................................................................... 56 4.5.2 Neon ........................................................................................................................ 59 4.5.3 Argon....................................................................................................................... 60 4.5.4 Krypton and Xenon ................................................................................................. 64 5 Discussion ............................................................................................................................. 65 He-Ne-Ar Systematics.......................................................................................................... 65 He-Sr-Nd-Pb Isotope Systematics of Kohala and Haleakala ............................................... 74 Constraints about the Hawaiian Mantle Plume Source........................................................ 76 6 Conclusions ........................................................................................................................... 79 7 References ............................................................................................................................. 80 8 Appendix ............................................................................................................................... 86 Acknowledgements ................................................................................................................ 105 Eidesstattliche Erklärung........................................................................................................ 106 Abstract This study presents noble gas compositions (He, Ne, Ar, Kr, and Xe) of lavas from several Hawaiian volcanoes. Lavas from the Hawaii Scientific Drilling Project (HSDP) core, surface samples from Mauna Kea, Mauna Loa, Kilauea, Hualalai, Kohala and Haleakala as well as lavas from a deep well on the summit of Kilauea were investigated. Noble gases, especially helium, are used as tracers for mantle reservoirs, based on the 3 4 assumption that high He/ He ratios (>8 RA) represent material from the deep and supposedly less degassed mantle, whereas lower ratios (~ 8 RA) are thought to represent the upper mantle. Shield stage Mauna Kea, Kohala and Kilauea lavas yielded MORB-like to moderately high 3He/4He ratios, while 3He/4He ratios in post-shield stage Haleakala lavas are MORB-like. Few samples show 20Ne/22Ne and 21Ne/22Ne ratios different from the atmospheric values, however, Mauna Kea and Kilauea lavas with excess in mantle Ne agree well with the Loihi- Kilauea line in a neon three-isotope plot, whereas one Kohala sample plots on the MORB correlation line. The values in the 4He/40Ar* (40Ar* denotes radiogenic Ar) versus 4He diagram imply open 4 4 40 * 3 22 system fractionation of He from Ar, with a deficiency in He. Calculated He/ Ar , He/ Nes 22 4 21 ( NeS denotes solar Ne) and He/ Ne ratios for the sample suite are lower than the respective production and primordial ratios, supporting the observation of a fractionation of He from the heavier noble gases, with a depletion of He with respect to Ne and Ar. The depletion of He is interpreted to be partly due to solubility controlled gas loss during magma ascent. However, the preferential He loss suggests that He is more incompatible than Ne and Ar during magmatic processes. In a binary mixing model, the isotopic He and Ne pattern are best explained by a mixture of a MORB-like end-member with a plume like or primordial end- member with a fractionation in 3He/22Ne, represented by a curve parameter r of 15 (r=(³He/²²Ne)MORB/(³He/²²Ne)PLUME or PRIMORDIAL). Whether the high 3He/4He ratios in Hawaiian lavas are indicative of a primitive component within the Hawaiian plume or are rather a product of the crystal-melt- partitioning behavior during partial melting
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