The petrology and geochemistry of lavas from the west flank of Mauna Kea Volcano, Hawaii
- Author:
-
Perdue, Elizabeth Ann
- Title:
- The petrology and geochemistry of lavas from the west flank of Mauna Kea Volcano, Hawaii
- Periodical:
- Geological Sciences
- Year:
- 1982
- Volume:
- M.A.
- Pages:
- 171 p.
- Subject:
-
Mauna Kea volcano
Petrology Hawaii Island
Geochemistry
Lava analysis
- Summary:
- The Island of Hawaii is the southeasternmost and youngest island in the Hawaiian Archipelago, a 2600 km volcanic mountain chain in the Pacific Ocean. The island is composed of five volcanoes, Kohala, Hualalai, Mauna Kea, Mauna Loa and Kilauea. Kilauea, Mauna Loa and Hualalai have been active in historic time; Mauna Kea last erupted about 4000 years ago. Lava flows and tephra cones of alkalic basalt, alkali-olivine basalt, ankaramite, plagioclase basalt, porphyritic basalt and hawaiite are exposed on the west flank of Mauna Kea. This volcanic suite contains phenocrysts of olivine, clinopyroxene and plagioclase in an intergranular to trachytic groundmass of clinopyroxene, plagioclase, olivine, titanomagnetite, ilmenite, chromian spinel, apatite and phlogopite. The rocks vary from aphyric to strongly porphyritic with as many as 40% phenocrysts. Microprobe analyses of olivine, clinopyroxene, plagioclase, spinel, and Fe-Ti oxides were obtained in order to characterize the mineral chemistry of this volcanic suite. Olivine ranges in composition from 87% to 44% Fo and is typically normally zoned from Mg-rich cores to Fe-rich rims. The suite contains only one pyroxene, a clinopyroxene, which varies in composition from 35% to 45% Wo, from 30% to 53% En, and from 4% to 28% Fs. Plagioclase phenocrysts and groundmass laths vary in composition from 82% to 28% An and are typically normally zoned. The Fe-Ti oxides vary in composition from 53.4% to 92.5% ulvospinel and from 72.9% to 99.8% ilmenite. Twelve whole rock analyses (eight new analyses and four from the literature) show that the lavas exposed in the study area are alkalic in composition. The analyses form linear trends on MgO-oxide variation diagrams, suggesting that the suite may have been formed by fractional crystallizatlon of olivine, clinopyroxene and/or plagioclase from an alkali-olivine basalt parent magma. Least squares mass balance calculations show that the alkalic basalts can be related to an alkali-olivine basalt parent magma by the removal of clinopyroxene, olivine, and plagioclase from the latter. The plagioclase basalt bulk composition can be reproduced by the addition of plagioclase to an alkali-olivine basalt parent magma, and the ankaramite bulk composition can be formed by the addition of clinopyroxene, olivine, and plagioclase to an alkali-olivine basalt parent magma. However, mass balance calculations show that the hawaiites cannot be related to the remainder of the suite by fractional crystallization of the observed phenocryst phases.
- Date:
- 1982
- Collection:
- Monographs