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Paper No. 6-42
Presentation Time: 8:30 AM-5:45 PM
A COMPARISON OF A HOT SPOT BASALT FROM KILAUEA, HAWAII AND A CONTINENTAL BASALT FROM GRANTS, NEW MEXICO
Samples were collected from Kilauea, Hawaii and Grants, New Mexico. Previous research shows that the Kilauea basalt is a true picritic, tholeiitic basalt and the El Malpais basalt will be andesitic in nature. Both are high in silica, but the Kilauea basalt should have a higher olivine content. Compositional differences are expected because the Kilauea basalt is derived from an oceanic hotspot while the El Malpais basalt is derived from the mantle and travelled through continental crust to reach the surface. The Hawaiian basalt was collected near the middle of the flow while the El Malpais basalt was collected from the toe of a flow, which also increases the differences between the two. Basalt samples were analyzed using thin section petrology and XRD analysis using a Rigaku Miniflex II. Samples were pulverized and powdered to <125 microns. The XRD scan was then interpreted using the Jade 9.0 program. The Kilauea basalt includes a high silica content, abundance of forsterite, ortho and calcium-poor clinopyroxenes, and possibly hypersthene. Olivine phenocrysts can be seen in thin section, along with a large amount of clinopyroxene and plagioclase feldspars in groundmass. There are many glomerocrysts of plagioclase and olivine present throughout the thin section. The XRD confirmed a high silica content and a high amount of forsterite with a small amount of fayalite. Other minerals present are augite, diopside, enstatite, hedenbergite and sanidine. It is expected that basalts from the El Malpais flow will be more andesitic in nature. This includes a high silica content and a groundmass of mainly plagioclase and pyroxene phenocrysts. A plagioclase-rich groundmass is seen in thin section along with pyroxene phenocrysts is a range of sizes. This composition is further reflected in XRD, where labradorite and augite are shown as constituent minerals. Other minerals present are magnetite, silica, forsterite, fayalite, diopside and bytownite.