SmNd study of Archean alkalic rocks from the Superior Province of the Canadian Shield

摘要: The Abitibi Volcanic Belt in eastern Superior Province of the Canadian Shield is largest continuous greenstone belt world and a key example late Archean crust. This has, general, suffered low intensity metamorphism deformation, and, as result, stratigraphy geology are well established. Tholeiitic calc-alkaline series igneous rocks present this about equal proportions. However, undersaturated potassic leucitic volcanics Timiskaming Group unique feature belt. SmNd systematics were determined for twelve volcanic rocks. These show nepheline, diopside and/or olivine plus leucite norm highly fractionated REE pattern. Sm Nd concentrations range from 25 to 160 45 300 times chondritic abundance, respectively. isotopic data yield an isochron age 2702±105Ma these with initial eNd +1.9±1.6. establishes alkalic rock be one oldest their kind. From stratigraphic relations, 2705 Ma upper limit values +1.8 +2.2 at also limits. Further, small but positive value isochron, when compared other mantle-derived Province, indicates that mantle was heterogeneous beneath lavas derived depleted mantle.