Geochronological Boundaries and Geodynamic Interpretation of Alkaline-Mafic Magmatism in Kuznetsk Alatau

摘要

There are numerous small but intricately differentiated alkaline-mafic intrusions that are mainly confined to Caledonian lithostructural complexes in northern Kuznetsk Alatau. The parental alkaline-mafic magma was, presumably, generated from moderately depleted HIMU mantle with ε_(Nd) varying from ～5.0 to 5.7. During their ascent in upper lithospheric horizons, the melts experienced crustal contamination with selective accumulation of radiogenic ~(87)Sr (~(87)Sr/~(86)Sr_0 ～ 0.7024-0.7065) in subsequent differentiates. The crustal contribution is also confirmed by the relatively heavy oxygen isotopic composition in rock-forming clinopyroxene, feldspar, and nepheline (δ~(18)O ～ 7.2-10.7 per thousand ) as compared to primary mantle values.