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

Abstract

The isotope geochemistry (ε_Nd(t) 4.8–5.4, ²⁰⁶Pb/²⁰⁴Pb_in 18.05–18.36, ²⁰⁷Pb/²⁰⁴Pbin 15.53–15.57, ²⁰⁸Pb/²⁰⁴Pb_in 37.59–37.83, ⁸⁷Sr/⁸⁶Sr(t) 0.7048–0.7057, δ¹⁸O_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.