Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005. / Includes bibliographical references. / The 6000-km long, age-progressive linear Hawaii-Emperor Chain is one of the best defined hotspot tracks. This hotspot track plays an important role in the plume hypothesis. In this research, geochemical data on the Hawaiian-Emperor lavas are used to evaluate the plume hypothesis. There are important geochemical similarities among lavas from the Hawaii-Emperor Chain, such as high Ba/Th (>100), high ³He/⁴He (>10 R/R-A) and enrichment in incompatible elements. These distinctive geochemical characteristics are not present in mid-ocean ridge basalt (MORB). Consequently, it is inferred that a common mantle source has been contributing to the Hawaiian-Emperor volcanism for over 80 My, which provides the strongest geochemical argument supporting the plume hypothesis. The distinctive geochemical characteristics of Makapuu-stage Koolau lavas, such as high SiO₂ content, ⁸⁷Sr/⁸⁶Sr, ²⁰⁸Pb*/²⁰⁶Pb*, [delta]¹⁸0, ¹⁸⁷Os/¹⁸⁸Os, La/Nb, Sr/Nb and low CaO content, ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, Th/La, require that recycled ancient oceanic crust including sediments is present in the Hawaiian plume. Some of these distinctive geochemical characteristics are also present in other Hawaiian shields. For example, Kahoolawe lavas also range to low ²⁰⁶Pb/²⁰⁴Pb. / (cont.) However, Kahoolawe lavas are not characterized by relatively high SiO₂ content, Sr/Nb and La/Nb and low CaO content that are characteristic of Makapuu-stage Koolau lavas, and they are offset from other Hawaiian shield lavas to high ⁸⁷Sr/⁸⁶Sr at a given ¹⁴³Nd/¹⁴⁴Nd. Since Hawaiian shield lavas have similar Sr/Nd (variation less than a factor of three), I speculate that the ⁸⁷Sr/⁸⁶Sr offset is a result of varying roles of recycled plagioclase-rich gabbro in Hawaiian shield lavas. Modem Hawaiian volcanoes form two offset trends, i.e., the Loa and Kea trends. Lavas from Loa and Kea trends have important geochemical differences. Specifically, Loa trend lavas have relatively higher ²⁰⁸Pb/²⁰⁴Pb at a given ²⁰⁶Pb/²⁰⁴Pb than Kea trend lavas, that is, Loa trend lavas have higher ²⁰⁸Pb*/²⁰⁶Pb than Kea trend lavas. Loa and Kea trend lavas form different trends in plots of ²⁰⁸Pb*/²⁰⁶Pb vs Sr-Nd-Hf-He isotopic ratios, and the Loihi component (high ³He/⁴He) is a common source component for Loa and Kea trend lavas. The Loa-Kea geochemical differences are inferred to reflect source differences; consequently, different models of plume structure have been proposed. However, I propose an alternative model in which Loa and Kea trend volcanoes sample a common geochemically heterogeneous source. / (cont.) The observed Loa-Kea geochemical differences is inferred as a result of temperature difference between Loa and Kea trend volcanoes which reflects their distances from the center of the hot plume core. / by Shichun Huang. / Ph.D.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/33947 |
| Date | January 2005 |
| Creators | Huang, Shichun |
| Contributors | Frederick A. Frey., Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences., Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences. |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 443 p., application/pdf |
| Coverage | n-us-hi |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/33947, http://dspace.mit.edu/handle/1721.1/7582 |
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