Processes of mantle enrichment and magmatic differentiation in theeastern Snake River plain; Th isotope evidence
Reid, Mary R (1995) Processes of mantle enrichment and magmatic differentiation in theeastern Snake River plain; Th isotope evidence. Earth and Planetary Science Letters, vol.131, no.3-4, pp.239-254, Apr1995
| Authors | Reid, Mary R |
|---|---|
| Year | 1995 |
| Title | Processes of mantle enrichment and magmatic differentiation in theeastern Snake River plain; Th isotope evidence |
| Source | Earth and Planetary Science Letters, vol.131, no.3-4, pp.239-254, Apr1995 |
| ISSN | 0012-821X |
| GeoRef | 1995-038310 |
| Keywords | actinides; assimilation; basalts; Blaine County Idaho; Butte CountyIdaho; continental crust; cooling; Craters of the Moon; crust;enrichment; fractional crystallization; geochemistry; Idaho; igneousrocks; isotope ratios; isotopes; lava; lithogeochemistry; lithosphere;magma contamination; magmas; magmatic differentiation; mantle; mantleplumes; metals; metasomatism; plate tectonics; radioactive isotopes;rift zones; Snake River plain; southern Idaho; Th-232/Th-230; thermalhistory; thorium; United States; volcanic rocks; Yellowstone Plume |
| DOI | 10.1016/0012-821X(95)00025-8 |
Abstract
The approximately 85 km long Great Rift of southern Idaho bisects thevolcanic depression that forms the eastern Snake River Plain. Thoriumisotope systematics of compositionally diverse lavas of the GreatRift, including those of Craters of the Moon, record a spectrum ofcrust and mantle processes. super 230 Th/ super 232 Th ratiosrange from 0.87 to 1.11 and are enriched in super 230 Th withrespect to super 238 U by up to 13%. Covariations in Th isotopesystematics in lavas from Craters of the Moon reflect crustalassimilation accompanied by fractional crystallization involvingaccessory phases. Temperatures based on apatite and zircon saturationconfirm other estimates of magmatic temperatures and, consideredtogether with volcanic histories, suggest cooling in upper crustalmagma chambers at rates of >10 degrees C/ka. Thermal and chemicalevolution of the Great Rift basalts support their differentiation atlower crustal conditions. Although basalts of the eastern Snake RiverPl ain are generally interpreted as having originated in ancientenriched mantle lithosphere beneath southern Idaho, they shareremarkable chemical similarities with oceanic basalts derived fromenriched sources attributed to mantle plumes. Thorium isotopesignatures of the Great Rift basalts are those of depleted mantle,resulting in the most extreme case of disparity between super 232Th/ super 238 U ratios delimited by Th and Pb isotope systematics.It is difficult to account for this decoupling by invokingsubduction-related U enrichment. A more likely explanation ismetasomatism of hybrid lithospheric mantle in the wake of theYellowstone plume.