Major‐Element and Isotopic Variations in Mauna Loa Magmas over 600 ka

• Published in: Hawaiian Volcanoes pp. 59 - 78
• Main Author: Rhodes, J. Michael
• Format: Book Chapter
• Language: English
• Published: Hoboken, NJ John Wiley & Sons, Inc 20.03.2015
• Subjects: crustal components; eclogite; garnet trace element; harzburgite; isotopic diversity; Lō'ihi plume; major‐element composition; Mauna Loa magmas; pyroxenite; source lithology
• ISBN: 9781118872048; 1118872045
• DOI: 10.1002/9781118872079.ch4

This chapter covers about 600 ka of Mauna Loa's magmatic history, contrasting the lack of major‐element variability with significant isotopic diversity. There has been little change in the major‐element parental magma compositions over this time period. In contrast, there is considerable variation in isotopic ratios, implying varying contributions of Loa and Lō‘ihi plume components over time. There is, however, no clear age‐related trend. Recent studies have questioned the ubiquity of peridotite as the source of Hawaiian shield‐building tholeiites. They argue, instead, for the presence of recycled crustal components in the discrete form of eclogite/pyroxenite. The lack of a clear correlation between isotopes and major elements, especially SiO 2 , suggests that there is no need for this eclogite/pyroxenite component in the source. A peridotite fertilized by melts from recycled crustal components is sufficient. The uniform but high SiO 2 content of Mauna Loa magmas coupled with varying isotopic compositions and a garnet trace element signature is consistent with the formation of these magmas through the reaction of a low‐SiO 2 parental magma (3–4 GPa) with buoyant, depleted, residual harzburgite at shallow levels in the plume.