POLYGENETIC QUATERNARY VOLCANISM AT CRATER FLAT, NEVADA

Citation
Tk. Bradshaw et Ei. Smith, POLYGENETIC QUATERNARY VOLCANISM AT CRATER FLAT, NEVADA, Journal of volcanology and geothermal research, 63(3-4), 1994, pp. 165-182
Citations number
40
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geology
ISSN journal
0377-0273
Volume
63
Issue
3-4
Year of publication
1994
Pages
165 - 182
Database
ISI
SICI code
0377-0273(1994)63:3-4<165:PQVACF>2.0.ZU;2-G
Abstract
Alkali basalts erupted during the Quaternary at Crater Flat, Nevada, r ecord a complex history of polycyclic and polygenetic volcanism. Magma s from the two main centers (Black Cone and Red Cone) are petrographic ally and geochemically similar, although field evidence suggests a num ber of separate eruptive events. High incompatible element concentrati ons, low Nb/La and high Zr/Y indicate that the magmas were derived by small degrees of partial melting from the lithospheric mantle. At Red Cone, a significant range of Sr, La, Ce, Ba and Th concentrations is o bserved with time (e.g., Sr range 1308-1848 ppm): the youngest samples having the more elevated values. However, there is only limited varia tion in the compatible trace elements (e.g., Sc and Ni). The array of compositions at Red Cone could not have been produced by changes in th e degree of partial melting, or by fractional crystallization. Rather, a model of magma mixing is proposed between relatively enriched and d epleted end-members. The cluster of Black Cone data falls consistently at the least-enriched end of the Red Cone sample arrays, suggesting t hat the Black Cone magma represents one of the mixing end-members. The modeling indicates that the magmatic plumbing systems of the two cent ers were linked, at least during the early stages of volcanism. Moreov er, volcanic activity may have occurred at a number of sites along the length of the magmatic feeder zone during a single eruptive phase. Th is could have significant implications for volcanic hazard assessment in the region around Yucca Mountain, and the proposed nuclear waste re pository.