Nd and Sr isotopes in ultrapotassic volcanic rocks from the Leucite Hills, Wyoming

摘要: Nd and Sr isotopic compositions Rb, Sr, Sm concentrations are reported for madupites, wyomingites orendites from the Pleistocene volcanic field of Leucite Hills, Wyoming. All Hills rocks have negative eNd signatures, indicating derivation or contribution an old light rare earth element (LREE) enriched source. In this respect they similar to all occurrences high potassium magmas so far investigated. But variations comparatively small 87Sr/ 86Sr ratios unusually low high-K (0.7053–0.7061, one sample excluded). These values suggest that REE enrichment source was not accompanied by a strong increase in Rb/Sr. Wyomingites isotopically indistinguishable which is consistent with chemical petrographic evidence their common magma series depending on emplacement conditions. Basic ultrabasic madupites more silicic wyomingites/orendites distinct (madupites: eNd= −10.5 −12.3; wyomingites/orendites: −13.7 −17.0) despite Sm/Nd complete overlap 87Sr/86Sr. Selective bulk assimilation crustal material unlikely significantly affected magmas. The measured considered reflect values. characteristics madupite wyomingite/orendite preclude fractional crystallization, primary magma, liquid immiscibility partial melting homogeneous Two distinct, LREE slightly heterogeneous sources required. Heterogeneities were most pronounced between each centre (butte mesa). relationship evolution discussed basis two simple alternative sets models: