Parental Sources of High–Alumina Alkaline Melts: Nd, Sr, Pb, and O Isotopic Evidence from the Devonian Kiya–Shaltyr Gabbro–Urtite Intrusion, South Siberia

The isotope geochemistry (ε Nd ( t ) 4.8–5.4, 206 Pb/ 204 Pb in 18.05–18.36, 207 Pb/ 204 Pbin 15.53–15.57, 208 Pb/ 204 Pb in 37.59–37.83, 87 Sr/ 86 Sr( t ) 0.7048–0.7057, δ 18 O SMOW 8–10.5‰) and trace element composition of the Kiya–Shaltyr gabbro–urtite pluton allow us to suggest a heterogeneous source and complex geodynamic settings of the Devonian alkali magmatism in the Kuznetsk Alatau. It is assumed that its evolution took place under conditions of partial mingling of matter of the depleted (PREMA) and enriched (EM) mantle with crustal contamination of the evolving melt. Such an interaction could have been a result of superposition of a mantle plume and an active margin (OIB and IAB components). In fold belts this led to the formation of hybrid high-alumina foidoite magmas.