Petrology and geochemistry of Hawaiite lavas from Crater Flat, Nevada
Journal Article
·
· Contributions to Mineralogy and Petrology
Hawaiite-type lavas were erupted in three cycles (3.7, 1.2, and 0.3 M.y.) at Crater Flat, Nevada. The compositions of all three cycles, considered together, form a "straddling" alkalic series as defined by Miyashiro, in which the less evolved basalts plot near the normative olivine-diopside divide and the more evolved basalts project into hypersthene or nepheline fields. Fractionation modeling based on the oldest cycle allows the removal of olivine, clinopyroxene, and amphibole to arrive at the more evolved hawaiite compositions. In general, fractionation of phlogopite or feldspar is limited by the fractionation modeling and by Eu/REE relations. In detail, all hawaiites within one cycle (3.7 M.y.) need not be derived from a single parent magma. Varied parentage is more evident between cycles although all cycles are consistently of hawaiite composition. Basalts of the youngest two cycles are generally enriched in trace elements. Superimposed on this enrichment is a lack of Rb variation, leading to Rb/Sr ratios far lower than required to generate the high {sup 87}Sr/{sup 86}Sr ratio (0.707) typical of basalts in this region. The very low Rb/Sr ratios limit processes that may lead to trace-element enrichment during magma evolution (cyclic recharge of a fractionating magma chamber). Decreased fractions of mantle melting leaving phlogopite in the residuum or an earlier event of metasomatic transport from phlogopite-bearing mantle rocks into a phlogopite-absent mantle assemblage might explain the observed trace-element enrichment with low Rb/Sr.
- Research Organization:
- Los Alamos National Lab., New Mexico
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 60606
- Journal Information:
- Contributions to Mineralogy and Petrology, Journal Name: Contributions to Mineralogy and Petrology Vol. 80; ISSN 0010-7999; ISSN CMPEAP
- Country of Publication:
- Germany
- Language:
- English
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