Mantle Potential Temperatures of 4.5 to 47 Ma Hawaiian Volcanoes Using Olivine Thermometry: Implications for Melt Flux Variations
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2016-12
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University of Hawaii at Manoa
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Abstract
Hawaiian Ridge volcanoes vary in volume by a factor of 50 due to variations in the melt flux of the Hawai‘i mantle plume. One potential cause for these variations is the plume’s temperature. The objective of this study is to evaluate the relationship between melt flux variations and mantle potential temperature (Tp) of the plume during the formation of the Northwest Hawaiian Ridge (NWHR) that extends 2800 km northwest of the main Hawaiian Islands. Using olivine thermometry of 25 lavas from 10 Hawaiian volcanoes ranging from 1 x 103 km3 to 54 x 103 km3 in volume and 4.5 to 47 Ma in age, mantle potential temperatures are calculated. High-precision electron microprobe analysis of olivine compositions revealed that most of these volcanoes shared similar olivine forsterite (Fo) compositions (~80-88% Fo) with the exception of high forsterite olivines in Gardner lavas (91.85 % Fo, the highest measured in Hawaiian lavas). The highest forsteritic olivines from each sample were used to estimate parental magma compositions. A Monte Carlo simulation method was used to calculate the olivine-liquid equilibration temperature (Tol-liq) of these magmas, the Tp, and uncertainties in temperature associated with equilibrium assumptions made for parental magma composition estimates. The minimum Tol-liq and Tp are for Daikakuji lavas from the second smallest examined volcano at northern end of NWHR (1335 ± 26; 1374 ± 48 oC). The maximum Tp is at Gardner, the largest volcano located in the central part of the NWHR (1614 ± 26; 1703 ± 56 oC). These results yield a Tp increase of 329 oC for the ≥ 12.4 Ma section of the NWHR. Southeast of Gardner, Tp decreases at Mokumanamana to 1521 ± 50 oC. The Tp of the NWHR volcanoes between Mokumanamana and West Nīhoa show no systematic change similar to variations in the melt flux. The maximum Tp from the southeastern portion of the NWHR was from Nīhoa (1632 ± 54 oC) and the minimum Tp from West Nīhoa (1517 ± 56 oC). A second increase in Tp was observed from new Tp estimates for Kaua‘i (1567 ± 42 oC) to the current estimate range for volcanoes of the Island of Hawai‘i (1632 oC ≥ Tp ≥ 1690 oC). These variations in Tp along the Hawaiian Ridge follow an equivalent trend that is observed in the melt flux. The maximum Tp from each volcano have significant Spearman’s rank correlations with the distance from Mauna Loa, the melt flux, and volumes of these volcanoes. These correlations suggest that there is a strong coupling between the melt flux and the temperature of the Hawaiian mantle plume. Tp estimates from the Galápagos and Iceland hotspots show an opposite cooling trend over time. The Louisville hotspot track shows a dramatic decrease in the melt flux since 20 Ma. The Tp estimates from this study show that the Hawaiian hotspot is unique. The plume’s thermal history shows two instances of increasing Tp with increasing melt flux.
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Temperature measurements, Planets--Mantles, Earth (Planet), Olivine
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Hawaii
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Theses for the degree of Master of Science (University of Hawaii at Manoa). Geology & Geophysics
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