| The Tasse basalts of southeastern British Columbia, Canada, are host to a variety of mantle xenoliths consisting predominantly of spinel lherzolite with minor dunite and pyroxenite. On the basis of REE patterns, the xenoliths are divided into three groups reflecting varying degrees of mantle metasomatism: (1) Group 1; concave-up LREE patterns; (2) Group 2; flat to moderately LREE-enriched patterns; and (3) Group 3; strongly LREE-enriched patterns. The majority of xenolith are enriched in LILE, LREE, U, Th, Pb, and Sr, and depleted in HFSE and HREE. These geochemical characteristics are consistent with a sub-arc mantle source. The Tasse lavas are compositionally alkaline basalts and display OIB-like trace element patterns. They have positive epsilonNd (+3.8 to +5.5) values, with 338--426 Ma depleted mantle model ages, and display OIB-like Nd, Sr and Pb isotopic compositions. The Sr--Nd--Pb isotope and trace element characteristics suggesting that they originated from an upwelling asthenospheric mantle source. |
